928 Intake tubes
07-13-2001, 12:02 AM
#31
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my take....or should i say my intake : )
i have an indoor/outdoor temp sensor on my engine. One sensor over the radiator, directly inside the inake of a tube. The other is on the pre-filter side of the of the airbox over the MAF.
The insulated tubes do help. They help most when the car is at a stop and help keep the engine heat invading the volume of air that makes up the inside of the tube...or the airbox(which is why i insulated the bottom of mine) THAT HOT AIR IS THE AIR YOUR ENGINE WILL SUCK IN IMMEDIATLY UPON "STOMPING" on it. A few seconds after the car is acclerating and moving, the air temp will be very close to ambient (usually a few degrees above it) both at the intake above the radiator and above the airbox. the time that the moving air spends in the tube and the airbox while the car is moving/engine sucking air is not long at all.....not long enough to induce a significant heat transfer.
when you STOP..engine at idle...or shut down..then the tubes will defintiley help!
i have an indoor/outdoor temp sensor on my engine. One sensor over the radiator, directly inside the inake of a tube. The other is on the pre-filter side of the of the airbox over the MAF.
The insulated tubes do help. They help most when the car is at a stop and help keep the engine heat invading the volume of air that makes up the inside of the tube...or the airbox(which is why i insulated the bottom of mine) THAT HOT AIR IS THE AIR YOUR ENGINE WILL SUCK IN IMMEDIATLY UPON "STOMPING" on it. A few seconds after the car is acclerating and moving, the air temp will be very close to ambient (usually a few degrees above it) both at the intake above the radiator and above the airbox. the time that the moving air spends in the tube and the airbox while the car is moving/engine sucking air is not long at all.....not long enough to induce a significant heat transfer.
when you STOP..engine at idle...or shut down..then the tubes will defintiley help!
06-09-2002, 10:46 PM
#32
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OK, anyone heard of the MAF screen removal for a performance modification? I'm from around Seattle and we have a group of 928 owners who like to get together for track time and dyno runs.
There's a car which did pretty well on its numbers and it says that the airbox was modified with the MAF screen removed. The link for the graph is: <a href="http://www.pacnw928.com/events/2002/0406-Dyno-V.html<a href="http://www.pacnw928.com/events/2002/0406-Dyno-V.html" target="_blank">web" target="_blank">http://www.pacnw928.com/events/2002/0406-Dyno-V.html[URL=http://www.pacnw928.com/events/2002/0406-Dyno-V.html]web</a> page</a>
Comments?
Andrew
There's a car which did pretty well on its numbers and it says that the airbox was modified with the MAF screen removed. The link for the graph is: <a href="http://www.pacnw928.com/events/2002/0406-Dyno-V.html<a href="http://www.pacnw928.com/events/2002/0406-Dyno-V.html" target="_blank">web" target="_blank">http://www.pacnw928.com/events/2002/0406-Dyno-V.html[URL=http://www.pacnw928.com/events/2002/0406-Dyno-V.html]web</a> page</a>
Comments?
Andrew
06-10-2002, 04:32 AM
#34
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I would like to just add one idea.
Attack the major source of the heat!
"Header Wraping" your headers or stock exhaust manifolds!
I have used this stuff on several of my project cars and can say from experience IT WORKS. By reducing heat you will also prolongs the life of anything rubber under a tight hoods and on the 928 I think it may be able to lower the intake air to ambient at idle.
JMO
Max
Attack the major source of the heat!
"Header Wraping" your headers or stock exhaust manifolds!
I have used this stuff on several of my project cars and can say from experience IT WORKS. By reducing heat you will also prolongs the life of anything rubber under a tight hoods and on the 928 I think it may be able to lower the intake air to ambient at idle.
JMO
Max
06-10-2002, 04:55 AM
#35
Yes, removing the screens will reduce the restriction to air flow. It was my airbox that was tested, but the modifications were more than just the removal of the screens. I don't have the actual numbers here, but I think that the gain that they got from the modified airbox was 7 hp and 10ft/lbs of torque or so. That was with the stock POrsche filter in the airbox. Using a K&N filter resulted in less power than the Porsche filter.
06-10-2002, 05:08 AM
#36
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Shock waves?
-I've seen them on the wings of 727's before, but I'd have a hard time believing that our intake tubes have enough flow speed to even reach 0.10M!
If I had to guess, the venturi section is there to increase air flow over the timing belt. A venturi can induce flow several inches ahead of itself- this is probably why it is there.
The quandry about the whole subject is that unless you own one of the later cars with knock sensors, you really only benefit a small amount from the cool air intake.
(Not that I'm about to take it off of my '85 S2)
From the S4 onward, knock sensors will maximize power with cooler intake air by advancing the timing, thus some sort of good cold air system will make a big difference.
Here's a question: on the later cars, did the insulated tubes provide for timing belt cooling?
-As to removing the intake screen, I did this on a previous car (Corrado) and it made a difference at high rpm- but obviously doing this alone won' t do much for you. You have to do other things to help air flow as well (you know- its like making sure all the doors are WIDE open). You run the risk of damaging the MAF sensor though.
Normy!
'85 S2
-I've seen them on the wings of 727's before, but I'd have a hard time believing that our intake tubes have enough flow speed to even reach 0.10M!
If I had to guess, the venturi section is there to increase air flow over the timing belt. A venturi can induce flow several inches ahead of itself- this is probably why it is there.
The quandry about the whole subject is that unless you own one of the later cars with knock sensors, you really only benefit a small amount from the cool air intake.
(Not that I'm about to take it off of my '85 S2)
From the S4 onward, knock sensors will maximize power with cooler intake air by advancing the timing, thus some sort of good cold air system will make a big difference.
Here's a question: on the later cars, did the insulated tubes provide for timing belt cooling?
-As to removing the intake screen, I did this on a previous car (Corrado) and it made a difference at high rpm- but obviously doing this alone won' t do much for you. You have to do other things to help air flow as well (you know- its like making sure all the doors are WIDE open). You run the risk of damaging the MAF sensor though.
Normy!
'85 S2
06-10-2002, 09:28 AM
#37
Man!
Haven't seen the MASTERS all clumped together in quite a while.
Topic of some interest, no doubt!
From where I started - Battle of the K&N's -
I was, personally, looking for a less restrictive flow. The topic of the tubes was pretty well covered then, though some new stuff has been brouht up on this thread. Kudo's to all.
I tend to agree with the cooler/denser air theory.
Just take a ride on a cool damp night - no other changes -. If all I am getting is single digit performance jumps then I must, truly, have a calibrated butt.
Tony didn't come right out and say it but, anyone who lives in the extremely hot, dry, climes knows of what he speaks. Insulation simply has to make a difference. I've seen dry and bagged ice used for fuel and intake cooling purposes at the drag's. There is a reason. As to the technical brief on dead air , parabolic to square wave form,
smooth wall vs rippled, it read like a textbook and is valid ... up to a point.
The point being the volumetric efficiency of our respective engines. Without modification to the heads -cam change ( lift duration ), porting, valve size changing, perhaps a little milling,
plus headers, and timing event changes our engines in stock form - no SC or Turbo - can only flow so much air at a given rpm/mph range. The jury is still out on smooth vs rough port work.
I've seen both and heard from proponents of each of these opinions. Sometimes pure math works sometimes not. Was it Abby from the soverign state of Louisiana that had a smooth 'knife edge' port job on the wide body, SC project? even there things will be hard to quantify. 6.4L, SC'd, serious porting,cam, oversized valves. Same CC?
For a real HP increase, not over stock, but just to get close to spec. it's the new cap, rotor, coil, wires route. Increase your octane and advancing timing a tad will give you a few more,
free flowing exhaust(s) might add some more-we really need to document and Dyno here- but, can also take away some torque, particularly, at the bottom end.
If I had $800.00 that Euro motor up in Nova Scotia would be on it's way to Texas, thats a 70 -100 HP gain over my 210 HP or so and as far as I can see that's a much better deal than SC'or Turbo addition by about $2000.
Again My Little 82'Weissach is a kick-*** machine, especially when you consider she is 20 years old and tangling with some bonafide production street-apes.
I do know futility when I see it though...it looks like late model LS 1's in any of the GM bodies, Stang's, Vette's...All pushing in excess of 350 HP stock. Good 0-60, 0-100, 1/4 mile times.
Don't fool yourself about the top end ... fender to fender on a surface street covering the mile at 16-19 seconds is not where you want to be!
These engines will cost you a bundle to improve upon, period! why don't you just have yours detailed every month, clean yourself up a little, polish some of those untapped social skills and go babe hunting.. much better return
John S, and Pattycakes
Haven't seen the MASTERS all clumped together in quite a while.
Topic of some interest, no doubt!
From where I started - Battle of the K&N's -
I was, personally, looking for a less restrictive flow. The topic of the tubes was pretty well covered then, though some new stuff has been brouht up on this thread. Kudo's to all.
I tend to agree with the cooler/denser air theory.
Just take a ride on a cool damp night - no other changes -. If all I am getting is single digit performance jumps then I must, truly, have a calibrated butt.
Tony didn't come right out and say it but, anyone who lives in the extremely hot, dry, climes knows of what he speaks. Insulation simply has to make a difference. I've seen dry and bagged ice used for fuel and intake cooling purposes at the drag's. There is a reason. As to the technical brief on dead air , parabolic to square wave form,
smooth wall vs rippled, it read like a textbook and is valid ... up to a point.
The point being the volumetric efficiency of our respective engines. Without modification to the heads -cam change ( lift duration ), porting, valve size changing, perhaps a little milling,
plus headers, and timing event changes our engines in stock form - no SC or Turbo - can only flow so much air at a given rpm/mph range. The jury is still out on smooth vs rough port work.
I've seen both and heard from proponents of each of these opinions. Sometimes pure math works sometimes not. Was it Abby from the soverign state of Louisiana that had a smooth 'knife edge' port job on the wide body, SC project? even there things will be hard to quantify. 6.4L, SC'd, serious porting,cam, oversized valves. Same CC?
For a real HP increase, not over stock, but just to get close to spec. it's the new cap, rotor, coil, wires route. Increase your octane and advancing timing a tad will give you a few more,
free flowing exhaust(s) might add some more-we really need to document and Dyno here- but, can also take away some torque, particularly, at the bottom end.
If I had $800.00 that Euro motor up in Nova Scotia would be on it's way to Texas, thats a 70 -100 HP gain over my 210 HP or so and as far as I can see that's a much better deal than SC'or Turbo addition by about $2000.
Again My Little 82'Weissach is a kick-*** machine, especially when you consider she is 20 years old and tangling with some bonafide production street-apes.
I do know futility when I see it though...it looks like late model LS 1's in any of the GM bodies, Stang's, Vette's...All pushing in excess of 350 HP stock. Good 0-60, 0-100, 1/4 mile times.
Don't fool yourself about the top end ... fender to fender on a surface street covering the mile at 16-19 seconds is not where you want to be!
These engines will cost you a bundle to improve upon, period! why don't you just have yours detailed every month, clean yourself up a little, polish some of those untapped social skills and go babe hunting.. much better return
John S, and Pattycakes
06-10-2002, 02:44 PM
#38
The venturis are in the intake tubes for noise reduction, and the accordian-like ribbing is just to make the tubes easier to install and remove. Both of those things will reduce airflow. Yes, I know that there's some literature from Porsche that says the venturis do not cause any loss. Look at the date that information was written. That was from the years of the early cars, when even the Euro cars were making only 229hp. If you're making 229 crank horsepower, you can be assured that the venturis do not restrict you power any. With the GTS, Porsche did away with the venturi, and used straight insulated tubes instead. There's no venturi in them. The GTS tubes do have the timing belt cooling holes, and can be used on earlier cars. At around $140 each, I think I'll pass on the genuine Porsche version though.
The generally accepted rule of thumb is a 1% increase in power for every 10 degree drop in intake air temperature. That's the intake temperature as measured at the air inlet to the engine.
The knock sensors do not increase timing. They only retard it. In other words, they will not advance timing any further than what it normally is, no matter how high your fuel's octane is, or how low the intake air temperature is. The sensors are only responsible for reducing ignition timing from the normal timing advance if knocking is detected.
The insulation on the intake tubes helps, but only at very low speeds. The dry and bagged ice on drag cars is an attempt to reduce temperatures as much as possible, maybe even below what the ambient temperature is.
From everything I've read on it, the rough port finishing is to create turbulence to reduce fuel settling out of the air/fuel mixture. It goes back to the days of carburators when the air/fuel mixture had to travel a long way before it got into the cylinders. With modern fuel injection, there really isn't even any air/fuel mixture that travels any distance. The fuel injectors basicly just spray right at the back of the intake valves.
The generally accepted rule of thumb is a 1% increase in power for every 10 degree drop in intake air temperature. That's the intake temperature as measured at the air inlet to the engine.
The knock sensors do not increase timing. They only retard it. In other words, they will not advance timing any further than what it normally is, no matter how high your fuel's octane is, or how low the intake air temperature is. The sensors are only responsible for reducing ignition timing from the normal timing advance if knocking is detected.
The insulation on the intake tubes helps, but only at very low speeds. The dry and bagged ice on drag cars is an attempt to reduce temperatures as much as possible, maybe even below what the ambient temperature is.
From everything I've read on it, the rough port finishing is to create turbulence to reduce fuel settling out of the air/fuel mixture. It goes back to the days of carburators when the air/fuel mixture had to travel a long way before it got into the cylinders. With modern fuel injection, there really isn't even any air/fuel mixture that travels any distance. The fuel injectors basicly just spray right at the back of the intake valves.
06-10-2002, 03:27 PM
#39
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Just to throw more stuff into the discussion--
Take a look at the top half of the airbox, where the ribbed hoses attach. Notice how the cross-sectional area there is reduced where it squeezes down to less than an inch high by about four inches across.
And another comment just in passing--
For all but the high-RPM, full throttle periods, the biggest restriction is the throttle. If there was more flow 'available' due to other restictions being reduced, you'd compensate by pressing a little less on the loud pedal.
I know that there are more than a few folks who are willing to sacrifice a lot of time, effort and $$ to get that last bit from the engine, but for most of us street drivers, the throttle is virtually always the flow limiter.
Take a look at the top half of the airbox, where the ribbed hoses attach. Notice how the cross-sectional area there is reduced where it squeezes down to less than an inch high by about four inches across.
And another comment just in passing--
For all but the high-RPM, full throttle periods, the biggest restriction is the throttle. If there was more flow 'available' due to other restictions being reduced, you'd compensate by pressing a little less on the loud pedal.
I know that there are more than a few folks who are willing to sacrifice a lot of time, effort and $$ to get that last bit from the engine, but for most of us street drivers, the throttle is virtually always the flow limiter.
06-10-2002, 03:58 PM
#40
Three Wheelin'
[quote]but for most of us street drivers, the throttle is virtually always the flow limiter.<hr></blockquote>
Don't forget being stuck behind blue-haired little old ladies in full-size american boats driving 20 below limit with their turn signal on!
Don't forget being stuck behind blue-haired little old ladies in full-size american boats driving 20 below limit with their turn signal on!
06-10-2002, 10:51 PM
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This is a question for Mike Schmidt and to anyone with possible explanations.
Mike, you say that the K&N resulted in less horsepower during your modified airbox dyno session. Are you saying the good ol' Porsche OE filters are better or is it just because of your certain setup worked better with the OE filter?
Just wondering if I should slap this brand new Mahle air filter in place of the current K&N....
Andrew
'84 928S
<img src="graemlins/yltype.gif" border="0" alt="[typing]" />
Mike, you say that the K&N resulted in less horsepower during your modified airbox dyno session. Are you saying the good ol' Porsche OE filters are better or is it just because of your certain setup worked better with the OE filter?
Just wondering if I should slap this brand new Mahle air filter in place of the current K&N....
Andrew
'84 928S
<img src="graemlins/yltype.gif" border="0" alt="[typing]" />
06-10-2002, 11:29 PM
#42
I don't think that the modified airbox would have really been a factor in the difference between the Porsche filter and the K&N one. That modified airbox testing wasn't the first time that the stock filter made more power on a dyno than the K&N one when comparing the two. I don't know why, but that's what happened. Smoother, less turbulent air flow with the stock filter maybe? The K&N filter supposedly lets more dirt through it than the stock filter does too, but I don't know if any real tests have been done to confirm that. I use a stock filter in my car, and have a K&N that I'll probably put on Ebay if I ever get around to it.
06-11-2002, 02:49 PM
#43
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Thats an odd one. I was over at the Dyno Shop over here and some guy brought in a '90 928 GT with a K&N and the car dynoed about 1 hp higher than having the stock. Was there anything obstructing the air flow? or were there any factors regarding the air/fuel ratio that were modified other than the airbox mod?
I've never actually heard of a K&N resulting in less horsepower before... <img src="confused.gif" border="0">
I've never actually heard of a K&N resulting in less horsepower before... <img src="confused.gif" border="0">
06-11-2002, 03:12 PM
#44
There were absolutely no other changes except for switching the air filters, and the runs were done right after one another. Several runs with each configuration were done to make sure that the runs were consistent. Is it possible that the comparison you saw was with a dirty stock filter? Were several runs done with each filter?
Below is a dyno chart showing the representative runs between the stock and K&N filters during the airbox test. Both runs were done with the modified airbox and no MAF screen. The only change made to the car was in the air filters. Several runs were done with each configuration, and these two runs were picked as the best typical representation for their group of runs. The red lines are with the stock filter, and the blue ones are with the K&N filter. The actual peak horsepower numbers are the same. At anything less than about 5100 RPM the stock filter is making more power though.
Below is a dyno chart showing the representative runs between the stock and K&N filters during the airbox test. Both runs were done with the modified airbox and no MAF screen. The only change made to the car was in the air filters. Several runs were done with each configuration, and these two runs were picked as the best typical representation for their group of runs. The red lines are with the stock filter, and the blue ones are with the K&N filter. The actual peak horsepower numbers are the same. At anything less than about 5100 RPM the stock filter is making more power though.
06-12-2002, 03:01 PM
#45
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woah Mike, thats really weird. My 944 made power when i put a K&N on it. I would have expected an increase on that dyno sheet. It looks like it actually lost torque and power below 5000 rpm! 
I think I'll stick to stock paper filter then. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />
I think I'll stick to stock paper filter then. <img src="graemlins/cussing.gif" border="0" alt="[grrrrrrr]" />