944S head on 951 engine
02-23-2004, 04:53 PM
#46
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posted prev. by Scott Gomes
>>>Either the 8V or 16V head can be used to make significant horsepower, but depending where and how you need the engine to work will ultimately determine which head is better for "your" application. <<<
My application? The track, PCA GT newbie. Would you suggest a 4v head as a sensible way to extract some good "average hp" out of a 2.6 liter?
>>>Either the 8V or 16V head can be used to make significant horsepower, but depending where and how you need the engine to work will ultimately determine which head is better for "your" application. <<<
My application? The track, PCA GT newbie. Would you suggest a 4v head as a sensible way to extract some good "average hp" out of a 2.6 liter?
02-23-2004, 11:43 PM
#47
Drifting
Originally posted by Under Pressure Performance
Just wanted to demonstrate that peak numbers are great for bragging rights, but "average" numbers is what wins races.
Just wanted to demonstrate that peak numbers are great for bragging rights, but "average" numbers is what wins races.
Amen brother!
02-24-2004, 01:59 AM
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Johne, Russ, and other Fellow Rennlisters,
Thanks for your inquiries - Here's some additional information for the both of you...
Johne - You asked how the cam profile, turbo, valves specs, and lifter configuration affect performance, well, let's dive right in...
The cam, turbo, and head (valvetrain) all work together. Get one wrong, and you basically throw away much of the gains from the other two. You can have a turbo that "should" flow enough CFM to support 600 crank HP, BUT if the head will not get the CFM in the cylinders, well, then the turbo and cam become a "bit" irrelevant. Sure you will see "some" gain, but unless the cam and head work together with the turbo you simply do not get the full advantage of running such a turbo.
So, how does each effect the other, and how do you know what will work best in your application? Well, the very first thing you need to know is how you plan to use the car. Don't get all caught up in specific "power" and "torque" figures just yet. Once you know how you plan to use the car, this will dictate whether or not you will be giving something up to make your goals a reality.
In all but the most basic applications, there's always something to give up, some sort of compromise. If you are looking for a real strong track car, then more likely than not you will be giving up some low end power and torque, but if you have a daily driver and want a real fast street car, then perhaps you will compromise the top end performance for better low end performance. Then there are the combination track/street cars which are best built to have great mid range with a some low end, and some top end performance compromise.
Once you know how you need the car to work, the problem becomes getting it to work within that window - So, let's take a look at how we can accomplish this...
Let's begin where everyone else ends, the head. In most cases, everyone starts with the turbo. They buy the biggest turbo they can get to fit under the intake, stick it on their engine, then question the disappointing results.
We start with the head because this is the point of entry/exit from the cylinders, and that, coupled with the engine displacement, will ultimately dictate how much CFM we can stuff into the engine.
There are some very important head parameters that need careful attention to assure better than average performance. It is these parameters that we can play with to make the head flow what we want, and where we want it.
Such things like; port velocity, port shape, swirl, valve design, back cut, valve seat/valve mating, seat angles, and a host of other requisites are all things we can play with to make the head flow the numbers we need, and to get the port velocity to be what we need, where we need it.
A head that flow big numbers is not necessarily a better head than one that flows less CFM. What makes a good head is not the question, who can develop a good head is the question to ask.
Once we know how much CFM the head will flow at several valve lifts, we can then determine a cam profile based on the head's characteristics.
The cam is the key player in timing the breathing pattern for the engine. It determines when the valves should open and close, and how long they should stay open, but it also determines how fast the valves open and close as well. This is VERY important in a performance engine.
A cam NEEDS to be custom ground for a specific application to do its job effectively. Generic off the shelf cam are just that, generic, they will yield less than stellar results as they are designed to work in a host of applications and use very basic profiles to accomplish this goal.
A true custom cam will cost several times the cost of an off the shelf cam, but you will get several times the result from that part alone. The camshaft should NEVER be overlooked. It is an essential part of a high output engine.
Valve overlap, lift, duration, and several other factors determine where the cam will make power, but remember, all this is irrelevant if the cam and head do not work together - Which is why we do the head first, then the cam.
Now, let's look at the turbo...
Yes, the final of the three amigos, the place where most people start, is where we go last, the turbo. Now that we know what the head will flow, and we have designed a cam to work "with" the head, we can now "develop" a turbo to work with this application. Yes, I said develop - Nothing off the shelf.
It is very unlikely that you will find a turbo that will be the perfect marriage for any given application, so most find the best bolt-on compromise and order it - WRONG! - For the best results you will likely need a truly custom turbo configured specifically for your application.
Instead of wondering if you should buy a K26/8, K27, K29, 60-1, T60, or any other off the shelf turbo, you really need to consider a custom configuration designed specifically for "your" application.
The compressor and turbine housings are usually chosen to fit a particular packaging criteria (where will the turbo go, and how much room is there for it to fit) while the compressor and turbine wheels define the boosting characteristics of the turbo.
Both the housings, and the wheels generally dictate the "amount" of CFM available, and the A/R ratio generally defines "where" the CFM is available and at what efficiency. Many people sell turbochargers, few "truly" understand the science behind them, even fewer can apply this knowledge to develop a turbo for a specific application, which is why you see so many people running similar turbos on a very wide range of engines.
Most buy what is readily available, and we have all known one person or another that has bought and sold several turbochargers before he/she found one that is the lesser of the evils. Right out of the gate, a true custom turbo will cost a bit more than something off the shelf, but in the end it is money in the bank.
In short, extraordinary performance requires extraordinary parts. Generic parts yield generic results, not sure how to say it any simpler.
Man, I didn't even get into the differences and pros and cons of the 8V versus the 16V heads, but all the above still applies to either head. For a quick comparison of the 8V versus the 16V, read on...
Doing nothing to either head, the 16V will outflow the 8V head hands down. The 16V head has better low lift flow. You can modify an 8V head for a lot less than you can modify a 16V head. The 8V head is a lot more plentiful should you need a replacement. The 16V head has a more efficient combustion chamber design. The 8V head does not carry the cams (which is good and bad) The 16V head has O-Ringed exhaust seals, and the list goes on and on...
Basically, the 8V and 16V heads are two different animals that can be used in a variety of applications. Each works differently in stock form, but the 8V is better suited on a stock turbocharged 2.5L running less than 6,800 RPM. The cams in the 16V have a bit too much overlap for low RPM turbo operations and really make the turbocharged 2.5L suffer in the bottom end - BUT, go back and read everything I have said above, and consider a modified 16V head, with custom cams - Now, that is a different story indeed!
Well, my fingers are beginning to get warm from all this two finger typing, so I will let all the above absorb for a while - If anyone has any questions, please feel free to ask - After all, that is what I am here for.
Thanks for reading!
Oh, by the way - Russ, based on everything you mention regarding your application I think we should schedule a telephone conversation as I am not sure my fingers can endure the response I have for you.
Feel free to give me a call, or send me you phone number and a best time to call and we can go from there.
Thanks for your inquiries - Here's some additional information for the both of you...
Johne - You asked how the cam profile, turbo, valves specs, and lifter configuration affect performance, well, let's dive right in...
The cam, turbo, and head (valvetrain) all work together. Get one wrong, and you basically throw away much of the gains from the other two. You can have a turbo that "should" flow enough CFM to support 600 crank HP, BUT if the head will not get the CFM in the cylinders, well, then the turbo and cam become a "bit" irrelevant. Sure you will see "some" gain, but unless the cam and head work together with the turbo you simply do not get the full advantage of running such a turbo.
So, how does each effect the other, and how do you know what will work best in your application? Well, the very first thing you need to know is how you plan to use the car. Don't get all caught up in specific "power" and "torque" figures just yet. Once you know how you plan to use the car, this will dictate whether or not you will be giving something up to make your goals a reality.
In all but the most basic applications, there's always something to give up, some sort of compromise. If you are looking for a real strong track car, then more likely than not you will be giving up some low end power and torque, but if you have a daily driver and want a real fast street car, then perhaps you will compromise the top end performance for better low end performance. Then there are the combination track/street cars which are best built to have great mid range with a some low end, and some top end performance compromise.
Once you know how you need the car to work, the problem becomes getting it to work within that window - So, let's take a look at how we can accomplish this...
Let's begin where everyone else ends, the head. In most cases, everyone starts with the turbo. They buy the biggest turbo they can get to fit under the intake, stick it on their engine, then question the disappointing results.
We start with the head because this is the point of entry/exit from the cylinders, and that, coupled with the engine displacement, will ultimately dictate how much CFM we can stuff into the engine.
There are some very important head parameters that need careful attention to assure better than average performance. It is these parameters that we can play with to make the head flow what we want, and where we want it.
Such things like; port velocity, port shape, swirl, valve design, back cut, valve seat/valve mating, seat angles, and a host of other requisites are all things we can play with to make the head flow the numbers we need, and to get the port velocity to be what we need, where we need it.
A head that flow big numbers is not necessarily a better head than one that flows less CFM. What makes a good head is not the question, who can develop a good head is the question to ask.
Once we know how much CFM the head will flow at several valve lifts, we can then determine a cam profile based on the head's characteristics.
The cam is the key player in timing the breathing pattern for the engine. It determines when the valves should open and close, and how long they should stay open, but it also determines how fast the valves open and close as well. This is VERY important in a performance engine.
A cam NEEDS to be custom ground for a specific application to do its job effectively. Generic off the shelf cam are just that, generic, they will yield less than stellar results as they are designed to work in a host of applications and use very basic profiles to accomplish this goal.
A true custom cam will cost several times the cost of an off the shelf cam, but you will get several times the result from that part alone. The camshaft should NEVER be overlooked. It is an essential part of a high output engine.
Valve overlap, lift, duration, and several other factors determine where the cam will make power, but remember, all this is irrelevant if the cam and head do not work together - Which is why we do the head first, then the cam.
Now, let's look at the turbo...
Yes, the final of the three amigos, the place where most people start, is where we go last, the turbo. Now that we know what the head will flow, and we have designed a cam to work "with" the head, we can now "develop" a turbo to work with this application. Yes, I said develop - Nothing off the shelf.
It is very unlikely that you will find a turbo that will be the perfect marriage for any given application, so most find the best bolt-on compromise and order it - WRONG! - For the best results you will likely need a truly custom turbo configured specifically for your application.
Instead of wondering if you should buy a K26/8, K27, K29, 60-1, T60, or any other off the shelf turbo, you really need to consider a custom configuration designed specifically for "your" application.
The compressor and turbine housings are usually chosen to fit a particular packaging criteria (where will the turbo go, and how much room is there for it to fit) while the compressor and turbine wheels define the boosting characteristics of the turbo.
Both the housings, and the wheels generally dictate the "amount" of CFM available, and the A/R ratio generally defines "where" the CFM is available and at what efficiency. Many people sell turbochargers, few "truly" understand the science behind them, even fewer can apply this knowledge to develop a turbo for a specific application, which is why you see so many people running similar turbos on a very wide range of engines.
Most buy what is readily available, and we have all known one person or another that has bought and sold several turbochargers before he/she found one that is the lesser of the evils. Right out of the gate, a true custom turbo will cost a bit more than something off the shelf, but in the end it is money in the bank.
In short, extraordinary performance requires extraordinary parts. Generic parts yield generic results, not sure how to say it any simpler.
Man, I didn't even get into the differences and pros and cons of the 8V versus the 16V heads, but all the above still applies to either head. For a quick comparison of the 8V versus the 16V, read on...
Doing nothing to either head, the 16V will outflow the 8V head hands down. The 16V head has better low lift flow. You can modify an 8V head for a lot less than you can modify a 16V head. The 8V head is a lot more plentiful should you need a replacement. The 16V head has a more efficient combustion chamber design. The 8V head does not carry the cams (which is good and bad) The 16V head has O-Ringed exhaust seals, and the list goes on and on...
Basically, the 8V and 16V heads are two different animals that can be used in a variety of applications. Each works differently in stock form, but the 8V is better suited on a stock turbocharged 2.5L running less than 6,800 RPM. The cams in the 16V have a bit too much overlap for low RPM turbo operations and really make the turbocharged 2.5L suffer in the bottom end - BUT, go back and read everything I have said above, and consider a modified 16V head, with custom cams - Now, that is a different story indeed!
Well, my fingers are beginning to get warm from all this two finger typing, so I will let all the above absorb for a while - If anyone has any questions, please feel free to ask - After all, that is what I am here for.
Thanks for reading!
Oh, by the way - Russ, based on everything you mention regarding your application I think we should schedule a telephone conversation as I am not sure my fingers can endure the response I have for you.
Feel free to give me a call, or send me you phone number and a best time to call and we can go from there.
02-24-2004, 02:41 AM
#49
Race Car
Scott, I take it from the length and time of your reply that you truthfully don't sleep many hours per night.....
I'm interested in this thread as evidenced by the post I've made here.
I'm currently building a 3.0 liter from a 968 engine assembly and I'd like to discuss the head/cam combo options, both 8V and 16V on my dime.
I'm up late usually too and wouldn't mind calling after hours as to not interupt your every day shop time, your call.
As I told you a month or so ago during the emails we traded when I purchased those door handles, I'm heading to the Canadian F1GP and I'll have several days from Sunday to reach Indianapolis for the week's following USGP. I'd like to make plans to stop by UPP and meet up with you for a short visit and depending on your recommendations possibly dropping off head/cams.
Terry S.
944t@bellsouth.net
I'm interested in this thread as evidenced by the post I've made here.
I'm currently building a 3.0 liter from a 968 engine assembly and I'd like to discuss the head/cam combo options, both 8V and 16V on my dime.
I'm up late usually too and wouldn't mind calling after hours as to not interupt your every day shop time, your call.
As I told you a month or so ago during the emails we traded when I purchased those door handles, I'm heading to the Canadian F1GP and I'll have several days from Sunday to reach Indianapolis for the week's following USGP. I'd like to make plans to stop by UPP and meet up with you for a short visit and depending on your recommendations possibly dropping off head/cams.
Terry S.
944t@bellsouth.net
02-24-2004, 03:02 AM
#50
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Terry,
As long as I get five hours sleep I feel good the following day. If I get too much more than five hours sleep, I get a headache and feel quite useless the following day.
That said, I would welcome your call anytime it is convenient for you. While I appreciate you consideration for not wanting to take me away from my work, you should also understand that your concerns are part of my work. Truthfully, I can give you as much time as required to answer any questions you may have, regardless of the time of day, or night.
If evenings work better for you, then that is not a problem whatsoever. Please feel free to let me know what works best for you and we can talk shop. Feel free to use the number below anytime till 11:00 PM EST - I will happily take calls right up to that time, then if we talk till 3 AM, so be it - If it were not for others in the house, I would take calls later - While I will talk till the wee hours of the morning, I prefer that the phone not ring much later than 11:00 PM
In the most sincere way, please do not hesitate to pick up the phone and call right up to 11:00 - It is not a problem.
Look forward to your call!
As long as I get five hours sleep I feel good the following day. If I get too much more than five hours sleep, I get a headache and feel quite useless the following day.
That said, I would welcome your call anytime it is convenient for you. While I appreciate you consideration for not wanting to take me away from my work, you should also understand that your concerns are part of my work. Truthfully, I can give you as much time as required to answer any questions you may have, regardless of the time of day, or night.
If evenings work better for you, then that is not a problem whatsoever. Please feel free to let me know what works best for you and we can talk shop. Feel free to use the number below anytime till 11:00 PM EST - I will happily take calls right up to that time, then if we talk till 3 AM, so be it - If it were not for others in the house, I would take calls later - While I will talk till the wee hours of the morning, I prefer that the phone not ring much later than 11:00 PM
In the most sincere way, please do not hesitate to pick up the phone and call right up to 11:00 - It is not a problem.
Look forward to your call!
02-24-2004, 04:35 AM
#51
Drifting
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Hi Scott,
Yes very enlightening. In context
to the turbo you mentioned. How
custom can one get when every
tuner is basing their turbos on the
replica #8 or 10 housing with either
a stage III or V turbine wheel ?
One thing I can't figure out is why
Turbonetics did not improve on the
design hot housing.
Yes very enlightening. In context
to the turbo you mentioned. How
custom can one get when every
tuner is basing their turbos on the
replica #8 or 10 housing with either
a stage III or V turbine wheel ?
One thing I can't figure out is why
Turbonetics did not improve on the
design hot housing.
02-25-2004, 12:57 AM
#53
Drifting
Scott, I agree with everything that you have posted here but....
Going the route that you have listed, while the "correct" way, is also the $$$$ way as well. Most customers do not want to spend the money necessary to obtain that kind of info. Every so often one comes along and wants to go that route. We are in the process of doing that right now for a guy with a GT3RS motor that we are twin turbocharging.
It's hard to convince someone to spend that kind of money vs. buying a kit from Vitesse(sp?). It usually boils down to economics and bang for the buck.
The second thing is even with matched mechanicals, if you do not have the proper engine management it's not worth squat. It can flow to the moon but if you cannot control fuel and timing it will quickly be a pile of scrap. This is worth mentioning with the detail of your response. It can't be overlooked.
Good info though.
Going the route that you have listed, while the "correct" way, is also the $$$$ way as well. Most customers do not want to spend the money necessary to obtain that kind of info. Every so often one comes along and wants to go that route. We are in the process of doing that right now for a guy with a GT3RS motor that we are twin turbocharging.
It's hard to convince someone to spend that kind of money vs. buying a kit from Vitesse(sp?). It usually boils down to economics and bang for the buck.
The second thing is even with matched mechanicals, if you do not have the proper engine management it's not worth squat. It can flow to the moon but if you cannot control fuel and timing it will quickly be a pile of scrap. This is worth mentioning with the detail of your response. It can't be overlooked.
Good info though.
02-25-2004, 01:57 AM
#54
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Chris,
You are absolutely correct! - Doing it right does cost money, but you do it once when you do it right - Hence my motto, Built it once - Build it right!
True there are many folks just looking for some instant gratification and a relatively decent bang for the buck, but most that come my way are looking for something a bit extraordinary.
In regard to controlling the engine, yes, full engine control is a prerequisite. I have stated in another post that engine tuning is critical, and the devices used for tuning cannot be simple band-aids.
I believe it was several posts ago that I expressed the importance of engine management.
There will always be a strong larger market for bolt-on upgrades, but there will also always be the smaller group of hardcore enthusiasts, racers, speed freaks, and pure performance junkies that I enjoy catering to. They push me to be innovative. They fuel my passion for pushing the envelope. They allow me to push my abilities as an engine builder and tuner.
Sure there are a lot less people willing to spend the money it takes to build the "all-out" projects, but that is what I enjoy, and that is what I live for.
There are plenty of parts pushers out there already supplying the bolt-on market, and I tip my hat to them. The parts they supply put smiles on many faces, and make most people happy with the expected results - However, lurking in the shadows are those that desire something different - Something that can't be found everywhere - Something only others like themselves are able to relate to and justify.
Cult-like is the passion which inevitably drives one to crossover and make their way to the dark side. Here, they are greeted with open arms. Let the power and torque fill your senses. Succumb to science of the inner workings. Come to the forbidden playground. Be one with the Engine... Luke I am your fath.... uh, ummm... Sorry, I got a little carried away - Happens every time!
Thanks for reading.
You are absolutely correct! - Doing it right does cost money, but you do it once when you do it right - Hence my motto, Built it once - Build it right!
True there are many folks just looking for some instant gratification and a relatively decent bang for the buck, but most that come my way are looking for something a bit extraordinary.
In regard to controlling the engine, yes, full engine control is a prerequisite. I have stated in another post that engine tuning is critical, and the devices used for tuning cannot be simple band-aids.
I believe it was several posts ago that I expressed the importance of engine management.
There will always be a strong larger market for bolt-on upgrades, but there will also always be the smaller group of hardcore enthusiasts, racers, speed freaks, and pure performance junkies that I enjoy catering to. They push me to be innovative. They fuel my passion for pushing the envelope. They allow me to push my abilities as an engine builder and tuner.
Sure there are a lot less people willing to spend the money it takes to build the "all-out" projects, but that is what I enjoy, and that is what I live for.
There are plenty of parts pushers out there already supplying the bolt-on market, and I tip my hat to them. The parts they supply put smiles on many faces, and make most people happy with the expected results - However, lurking in the shadows are those that desire something different - Something that can't be found everywhere - Something only others like themselves are able to relate to and justify.
Cult-like is the passion which inevitably drives one to crossover and make their way to the dark side. Here, they are greeted with open arms. Let the power and torque fill your senses. Succumb to science of the inner workings. Come to the forbidden playground. Be one with the Engine... Luke I am your fath.... uh, ummm... Sorry, I got a little carried away - Happens every time!
Thanks for reading.
02-25-2004, 03:00 AM
#55
Great info! I've sat back and enjoyed the info and reading. Its very timely as the development on the 2V head is almost finished for my engine project. While I agree with everything stated so far, I would like to add a few small extra's.
Given all things been equal, a 4V Head will out perfrom a 2V head, period! But things are never equal. As it has been stated, cost becomes a real factor ( by 2 ) when doing a 4 V head. More Porting, more parts, more labor. I asked for the 2V head to be done as I was sure more would want to go this route. The 4V head way is for the more serious racers.
That all been said, I have a few small things to add. Port velocity is very important, but on NA engines, not Turbocharged engines. The velocity of the Inlet port is a function of Compressor speed and backpressure. In a Turbo engine, the exhaust gas cannot be used to scavange the Inlet port. What needs to be addressed is the backpressure and exhaust flow. Increasing the exhaust flow allows the head to exchange the air from the intake side to the exhaust side at higher efficiency. This is the % that is always talked about. The exhaust flow at a certain % of the Intake. This stops the head/engine from the typical constipated action most street engine are. By increasing the exhaust flow, the trim on the Turbine can be changed to "open" up the exhaust, lowering the backpressure allowing the head to exchange at a better rate, while still having the same turbine efficiency. Less boost, but higher CFM flow or a lower presure ratio on the comp wheel, shorter Cam profiles, faster ramp speeds etc., all makes for a better tuned engine. Now thats the theory. Heres the pudding. I managed to get Neil to give up the Flow numbers of the Heads they have been working on. In the end, anyone can buy one and flow it. That was my argument.
So here are the numbers, all measured at 25 inHg with same inlet and exhaust bells, at 0.050in lift intervals to 0.550.
Stock 944 Head. Stock 951 Head
Intake Exhaust Intake Exhaust
27.5 21.9 31.4 22.1
55.5 47.4 56.1 51.5
88.5 70.7 87.0 72.1
120.9 98.2 116.4 96.6
144.3 118.4 142.5 116.1
157.3 134.3 158.8 130.8
167.6 147.0 173.5 140.6
174.9 162.0 186.7 154.0
180.8 171.6 197.0 160.4
189.6 178.0 204.3 165.2
196.9 181.2 208.7 170.0
As can be seen the 951 Intake flows more than a 944 Intake, but the 944 Exhaust flows more and can be reworked with no ceramic liner. Now with porting and different Valve sizes, which cannot be released yet, these are the new numbers for the 944 Head.
Intake Exhaust
38.6 28.8
68.4 66.6
99.6 94.5
128.0 113.6
154.5 141.2
171.2 154.9
185.7 173.8
199.4 181.9
210.1 196.9
219.4 204.5
227.5 209.3
These are the base numbers, but I'm told there is more with Chamber work, (de shrouding) which would not be done on a stock Piston, as this would lower the Comp ratio. These numbers are what the "stock" reworked heads will flow, unless it is found on the dyno/in car that the btm end goes away. These numbers are hoped to allow the Cam design to be suited and give a better overall flatter torque curve. This will also allow the Turbo to be matched better, with a different Trim on Turbine side and a closer match on the Comp side.
At least here are some numbers to see, not the normal voo doo data that typically gets told. I'm sure there will be heads that flow better etc, but for those who wish to get something out of the 2 Valve Heads , this is a start. To go with these heads is the new 4 butterfly Intake. as soon as it is finished, it will be added to the head and flowed a one piece. This should lower the the numbers some, but hopefully not by much.
Given all things been equal, a 4V Head will out perfrom a 2V head, period! But things are never equal. As it has been stated, cost becomes a real factor ( by 2 ) when doing a 4 V head. More Porting, more parts, more labor. I asked for the 2V head to be done as I was sure more would want to go this route. The 4V head way is for the more serious racers.
That all been said, I have a few small things to add. Port velocity is very important, but on NA engines, not Turbocharged engines. The velocity of the Inlet port is a function of Compressor speed and backpressure. In a Turbo engine, the exhaust gas cannot be used to scavange the Inlet port. What needs to be addressed is the backpressure and exhaust flow. Increasing the exhaust flow allows the head to exchange the air from the intake side to the exhaust side at higher efficiency. This is the % that is always talked about. The exhaust flow at a certain % of the Intake. This stops the head/engine from the typical constipated action most street engine are. By increasing the exhaust flow, the trim on the Turbine can be changed to "open" up the exhaust, lowering the backpressure allowing the head to exchange at a better rate, while still having the same turbine efficiency. Less boost, but higher CFM flow or a lower presure ratio on the comp wheel, shorter Cam profiles, faster ramp speeds etc., all makes for a better tuned engine. Now thats the theory. Heres the pudding. I managed to get Neil to give up the Flow numbers of the Heads they have been working on. In the end, anyone can buy one and flow it. That was my argument.
So here are the numbers, all measured at 25 inHg with same inlet and exhaust bells, at 0.050in lift intervals to 0.550.
Stock 944 Head. Stock 951 Head
Intake Exhaust Intake Exhaust
27.5 21.9 31.4 22.1
55.5 47.4 56.1 51.5
88.5 70.7 87.0 72.1
120.9 98.2 116.4 96.6
144.3 118.4 142.5 116.1
157.3 134.3 158.8 130.8
167.6 147.0 173.5 140.6
174.9 162.0 186.7 154.0
180.8 171.6 197.0 160.4
189.6 178.0 204.3 165.2
196.9 181.2 208.7 170.0
As can be seen the 951 Intake flows more than a 944 Intake, but the 944 Exhaust flows more and can be reworked with no ceramic liner. Now with porting and different Valve sizes, which cannot be released yet, these are the new numbers for the 944 Head.
Intake Exhaust
38.6 28.8
68.4 66.6
99.6 94.5
128.0 113.6
154.5 141.2
171.2 154.9
185.7 173.8
199.4 181.9
210.1 196.9
219.4 204.5
227.5 209.3
These are the base numbers, but I'm told there is more with Chamber work, (de shrouding) which would not be done on a stock Piston, as this would lower the Comp ratio. These numbers are what the "stock" reworked heads will flow, unless it is found on the dyno/in car that the btm end goes away. These numbers are hoped to allow the Cam design to be suited and give a better overall flatter torque curve. This will also allow the Turbo to be matched better, with a different Trim on Turbine side and a closer match on the Comp side.
At least here are some numbers to see, not the normal voo doo data that typically gets told. I'm sure there will be heads that flow better etc, but for those who wish to get something out of the 2 Valve Heads , this is a start. To go with these heads is the new 4 butterfly Intake. as soon as it is finished, it will be added to the head and flowed a one piece. This should lower the the numbers some, but hopefully not by much.
02-25-2004, 12:53 PM
#56
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M42Racer, you wrote...
>>Port velocity is very important, but on NA engines, not Turbocharged engines. The velocity of the Inlet port is a function of Compressor speed and backpressure. In a Turbo engine, the exhaust gas cannot be used to scavange the Inlet port.<<
Where did you get that information from? - Your source is a little misguided. He is not flat out wrong, he is not correct either. To state that port velocity is not important on a turbocharged engine is to subscribe to the "general" belief that (in a turbo car) intake and exhaust port velocity, port shape, valve size, runner length, plenum size, and throttle body size are somewhat irrelevant as the air is being compressed and forced into the engine. This mindset has been the basis for many since the dawn of turbocharging, but it is not necessarily true, read on...
It IS true that port velocity is "critical" in a N/A engine, but that does not mean that it is not "important" in a turbocharged engine. Port velocity in a turbocharged engine affects several things like; the engine's volumetric efficiency, the BSFC, the rate of flow in and out of the head. All of which has a great affect on the engines output.
Also, in my last post, the assumption that has been made is that I refer only to the exhaust port velocity, but I am not referring exclusively to the exhaust ports. The intake AND exhaust pot velocity are VERY important, even in turbocharged engines.
You don't have to take my word for it, but I know a little something about this subject. Years back when I started this business, my claim to fame (so to speak) was my headwork - Thats is where I started it all. I know from personal experience, as an absolute certainty, that port velocity (intake and exhaust) has a great affect on the operational performance of a turbocharged engine. That said, there is not a person on the planet that can convince me that port velocity is not important on a turbocharged head. Not as "critical" as in a N/A engine, sure, but not important? - My experience dictates otherwise.
The KEY is NOT getting the head to flow big numbers, but getting the head to flow the biggest numbers without sacrificing the port velocity. Again, port velocity contributes to moving the volumetric around the RPM
band, it affect many things that many do not take into consideration - Again, you don't have to take my word for it.
You also wrote...
>>What needs to be addressed is the backpressure and exhaust flow. Increasing the exhaust flow allows the head to exchange the air from the intake side to the exhaust side at higher efficiency.<<
Absolutely - I completely agree. There are many other things that need to be addressed also, but I was just trying to stay within the scope of the thread - However, you are correct, the exhaust path is also critical - As is the intake plumbing, intercooler, throttle body, plenum design and size, runner length, runner shape, manifold temperatures, and so on... We could go on and on, and on...
Chris, Thanks for your response.
All, Thanks for reading.
>>Port velocity is very important, but on NA engines, not Turbocharged engines. The velocity of the Inlet port is a function of Compressor speed and backpressure. In a Turbo engine, the exhaust gas cannot be used to scavange the Inlet port.<<
Where did you get that information from? - Your source is a little misguided. He is not flat out wrong, he is not correct either. To state that port velocity is not important on a turbocharged engine is to subscribe to the "general" belief that (in a turbo car) intake and exhaust port velocity, port shape, valve size, runner length, plenum size, and throttle body size are somewhat irrelevant as the air is being compressed and forced into the engine. This mindset has been the basis for many since the dawn of turbocharging, but it is not necessarily true, read on...
It IS true that port velocity is "critical" in a N/A engine, but that does not mean that it is not "important" in a turbocharged engine. Port velocity in a turbocharged engine affects several things like; the engine's volumetric efficiency, the BSFC, the rate of flow in and out of the head. All of which has a great affect on the engines output.
Also, in my last post, the assumption that has been made is that I refer only to the exhaust port velocity, but I am not referring exclusively to the exhaust ports. The intake AND exhaust pot velocity are VERY important, even in turbocharged engines.
You don't have to take my word for it, but I know a little something about this subject. Years back when I started this business, my claim to fame (so to speak) was my headwork - Thats is where I started it all. I know from personal experience, as an absolute certainty, that port velocity (intake and exhaust) has a great affect on the operational performance of a turbocharged engine. That said, there is not a person on the planet that can convince me that port velocity is not important on a turbocharged head. Not as "critical" as in a N/A engine, sure, but not important? - My experience dictates otherwise.
The KEY is NOT getting the head to flow big numbers, but getting the head to flow the biggest numbers without sacrificing the port velocity. Again, port velocity contributes to moving the volumetric around the RPM
band, it affect many things that many do not take into consideration - Again, you don't have to take my word for it.
You also wrote...
>>What needs to be addressed is the backpressure and exhaust flow. Increasing the exhaust flow allows the head to exchange the air from the intake side to the exhaust side at higher efficiency.<<
Absolutely - I completely agree. There are many other things that need to be addressed also, but I was just trying to stay within the scope of the thread - However, you are correct, the exhaust path is also critical - As is the intake plumbing, intercooler, throttle body, plenum design and size, runner length, runner shape, manifold temperatures, and so on... We could go on and on, and on...
Chris, Thanks for your response.
All, Thanks for reading.
02-25-2004, 01:47 PM
#57
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One English race engineer once told
me. To build a super turbo head you
must apply the same technic that you
would use in building N.A race head.
After the head is done, you can start
adjusting the parameters to optimise
performance.
Is this through Scott ?
me. To build a super turbo head you
must apply the same technic that you
would use in building N.A race head.
After the head is done, you can start
adjusting the parameters to optimise
performance.
Is this through Scott ?
02-25-2004, 01:59 PM
#58
Rennlist Junkie Forever
Port velocity is very important in a turbo charged engine.
And there's one point that was not made...
If you have poor port velocity, your power off boost will suffer which, all thing being equal (which they are not), effectively reduces the amount of exhaust gas available to drive the turbine at lower rpms, which translates to more lag.
It's definitely a balancing act.
TonyG
And there's one point that was not made...
If you have poor port velocity, your power off boost will suffer which, all thing being equal (which they are not), effectively reduces the amount of exhaust gas available to drive the turbine at lower rpms, which translates to more lag.
It's definitely a balancing act.
TonyG
02-25-2004, 07:58 PM
#59
Rennlist Member
Thanks for the unselfishness of your posts, Scott. I'm guessing you might be done with this thread, but in case you're (Scott) still responding, I also have a question. Or, anybody else, if they know for sure:
It was rightfully stated that there needs to be an air exchange from the intake to the exhaust. Does this imply that there needs to be some valve overlap at around TDC to achieve this? If not, can this exchange still be somewhat achieved? Does it even matter if the turbo hotside is restrictive when there is absolutely no overlap? Is there some small amount of valve overlap in stock form? Is this part of your (Scott) goal with your heads; to increase valve overlap?
Thanks again.
It was rightfully stated that there needs to be an air exchange from the intake to the exhaust. Does this imply that there needs to be some valve overlap at around TDC to achieve this? If not, can this exchange still be somewhat achieved? Does it even matter if the turbo hotside is restrictive when there is absolutely no overlap? Is there some small amount of valve overlap in stock form? Is this part of your (Scott) goal with your heads; to increase valve overlap?
Thanks again.
02-25-2004, 10:34 PM
#60
Maybe I mis spoke here. what I have been told, is in a Turbo engine/head, the velocity of the air is affected by many other factors not found in a NA head. You can wish for the fastest velocity and see it on a Flow bench, but when all other parts are bolted up, everything changes. Porting or any re shaping of the Intake or exhaust ports for low lift will help here, but as soon as the backpressure rises, the shape will have little effect over volume. Yes, we can have smaller ports in a Turbo head, which will help the velocity, but you pay for it at higher boost. It is a trade off as stated. My point was poorly made, but the point I was trying to get across was that when the backpressure is up, and the Intake mmanifold pressure is up, it is all down to Comp air speed. any additional speed gained from the port shape will be very small if any at all. In a NA engine, typically the Cam centers are closer together to help with exhaust scavanging, exhaust pulses matched at the same time as the Inlet reversion wave, stuff. In a turbo engine the lobe centers are way further apart, negating and exhaust help. We cannot run the sort of overlap in a Turbo engine we do in a NA engine, or all the HP goes down the exhaust. It is really this scavanging that is added by port velocities. I think we are talking about the same thing here, but in theory we all want what we usually cannot have, or we think are getting it, when in fact we are never. I think this is a case of the same. I have seen on the Flow bench my head is tested on, the tubes fitted to measure the air speed, and they use some sort of dye to show just where the air is going. It is unfortunate that a turbo and running Exhaust system cannot be fitted to the Flow bench. I was told that on their Dyno they fit some sort of encoding wheel to the crankshaft which measures the rotational speed and the amount it jerks when the cylinders are charged. This way they can tell which cylinders are better charged, exhausted etc, and the best VE. I know that my 930 engine was fitted with a pressure tranducer in a special spark plug which showed the cylinder pressures, so I am sure that between the 2 measuring devices, we should be able to get the most out of these old heads. I hope so.