Reducing compress ratio with shorter con.rods!
11-30-2006, 12:18 PM
#16
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Originally Posted by 968TurboS
Chris, I respect you a lot and appreciate you sharing your years of knowledge with us. I know we have spoken to the phone in the past. My question is, if the thicker gasket yields a 9:1 compression and we are working with a 16 valve head, with its better pent roof design, I don't think detonation at 9:1 should be such a concern even if you run 1 bar. I personally think 1 bar should be max for street cars anyway running on pump gas, so I might be on the conservative side.
Maybe just because no one has done it before, people have their reservations, but I do believe this setup would remain intact for upto atleast 1 bar. People do this all the time, this is not trying to reinvent the wheel. People also question shorter rods/dished pistons but my setup has run since 1996 when it was initially done by Heimrath.
Hopefully I will be able to back it up in the near future with a conversion of my own.
Regards.
Raj
Maybe just because no one has done it before, people have their reservations, but I do believe this setup would remain intact for upto atleast 1 bar. People do this all the time, this is not trying to reinvent the wheel. People also question shorter rods/dished pistons but my setup has run since 1996 when it was initially done by Heimrath.
Hopefully I will be able to back it up in the near future with a conversion of my own.
Regards.
Raj
I think 9:1 for a street motor is a good idea. A little better low end response is a good thing and keeping it to 1 bar will give you good longevity and help to keep the intake temps down.
You are right about the 4v heads – they are a lot less particular about the quench area.
If I were not using custom pistons on my usually stuff I would be tempted to experiment with the thicker head gaskets (Cometic can make just about anything you want). If you use an adjustable cam timing gear than the change in cam timing is not an issue.
The thicker head gasket allows you to use a lot of stock type parts to keep the budget down and availably up. Once you get into custom parts and mods you start down that slippery slope that ends up in many custom parts in order to get it just right.
11-30-2006, 12:37 PM
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The car will be used as a daily driver and sometimes on track weekends. Dont hate me, paintjob and all the other mods have cost me little too much to abuse it on the tacks every day..
I am planning to use GT35R with 0,82 AR wit maximum boost around 1.4 bar. The allmost stock setup should take this power with fully balanced bottom end and H-profile conrods..
But now to the calculations.. I corrected myself by chirs formula and now how it looks
Stock 88mm stroke
Displacement 747,17
“Burn Chamber” 74
Total volume 814,17
1mm of extra volume 8,490
Compression ratio 814.17/74.00 11,0022973:1
1 mm sorter rod
Displacement 747,17
“Burn Chamber” 74.00 + 8,49 extra volume 82,49
Total volume 829,66
Compression ratio 814.17/82.49 10,05770396:1
2 mm sorter rod
Displacement 747.17 747,17
“Burn Chamber” 74.00 + 8,49*2 extra volume 90,98
Total volume 814.17 838,15
Compression ratio 814.17/90,98 9,212464278:1
3 mm sorter rod
Displacement 747,17
“Burn Chamber” 99,47
Total volume 846,64
Compression ratio 814.17/99,47 8,511511008:1 (this is the best solutin
I am planning to use GT35R with 0,82 AR wit maximum boost around 1.4 bar. The allmost stock setup should take this power with fully balanced bottom end and H-profile conrods..
But now to the calculations.. I corrected myself by chirs formula and now how it looks
Stock 88mm stroke
Displacement 747,17
“Burn Chamber” 74
Total volume 814,17
1mm of extra volume 8,490
Compression ratio 814.17/74.00 11,0022973:1
1 mm sorter rod
Displacement 747,17
“Burn Chamber” 74.00 + 8,49 extra volume 82,49
Total volume 829,66
Compression ratio 814.17/82.49 10,05770396:1
2 mm sorter rod
Displacement 747.17 747,17
“Burn Chamber” 74.00 + 8,49*2 extra volume 90,98
Total volume 814.17 838,15
Compression ratio 814.17/90,98 9,212464278:1
3 mm sorter rod
Displacement 747,17
“Burn Chamber” 99,47
Total volume 846,64
Compression ratio 814.17/99,47 8,511511008:1 (this is the best solutin
11-30-2006, 12:42 PM
#18
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There's a truth to what Chris says - the end goal needs to be clearly defined. The point I was trying to make was that your creative thinking is commendable - just because Porsche decided to come up with a particular solution for the Turbo 968 doesn't necessarily mean it's the correct one for you. As with everything else in design or engineering - the solution one eventually reaches is a compromise of all factors. . .
That said, the 968 turbo pistons are one way to do it - if you've got money trees growing in your back yard. The thicker head gasket idea is a possibility, as is the shorter con. rods solution. All have their advantages and disadvantages. All I'm saying is there's nothing magical about 7:1, 7.5:1, 8:1 or any other c/r - you can run whatever c/r you want, you just have to consider what the implications are for your boost and end goals. There are some very low c/r cars (7:1-ish) that make sick power, but they're very dependent on the turbo or supercharger in order to do so. Careful matching, tuning and upkeep of the forced-induction system becomes key. Alternatively, you can most certainly run higher c/rs (the 9.5:1, 10:1, 10.5:1 types) with lower boost and very careful tuning and very high-octane fuels. The advantage to this type of setup is you'll have better "off boost" performance but the downside is that you will be putting yourself at risk of preignition and you better pay very careful attention to the tuning, timing and monitor closely for knock.
Good luck with your project - should be interesting to see what direction you choose and how it comes out.
That said, the 968 turbo pistons are one way to do it - if you've got money trees growing in your back yard. The thicker head gasket idea is a possibility, as is the shorter con. rods solution. All have their advantages and disadvantages. All I'm saying is there's nothing magical about 7:1, 7.5:1, 8:1 or any other c/r - you can run whatever c/r you want, you just have to consider what the implications are for your boost and end goals. There are some very low c/r cars (7:1-ish) that make sick power, but they're very dependent on the turbo or supercharger in order to do so. Careful matching, tuning and upkeep of the forced-induction system becomes key. Alternatively, you can most certainly run higher c/rs (the 9.5:1, 10:1, 10.5:1 types) with lower boost and very careful tuning and very high-octane fuels. The advantage to this type of setup is you'll have better "off boost" performance but the downside is that you will be putting yourself at risk of preignition and you better pay very careful attention to the tuning, timing and monitor closely for knock.
Good luck with your project - should be interesting to see what direction you choose and how it comes out.
11-30-2006, 12:59 PM
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There is one more thing what I would concider when choosing the compress ratio is the turbine compressro map. You don't want to have a compresor what gets into midrange in 1.4 to 1.9 bar when you have 9ish comp.ratio. So I think you should concider this as well.. Id like to make somewhat 550 reliable crank hp. with pumpgas I thing GT35R should get me there with 1.3-1.4 bar..
Markus
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11-30-2006, 07:03 PM
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I don't know if anyone has notices, but there is somethig wrong in the calculations.
displacement 747.17
"burn chamber" 74.00
total volume is 821.17 not 814.17 for a correct CR of 11.09689
Their is nothing wrong with running 9+CR. Porsche and others had race engines with high CRs with great deal of success. Just a couple of examples are 956/962 family. Although the engine started in 1982 with 2.6L and a 7:1 CR to make 620 Bhp and some 460 lbft at 17 psi, in the later years the same engine was racing with a 9.5:1 at 17psi. Now at 3.0L it produce a nice 720 Bhp and a healthy 590 lbft from 4,500 to 5,500 rpm. Also the 997 and 996 turbo run a 9:1 and 9.4:1 CR.
another non porsche is Mazda and Mercedes-Benz. Mazda runs on the Mazdaspeed 6 a 9.5:1 at 17-19 psi and Mercedes 9.5:1 at 19 psi on their V12 engines.
Regards,
AL,
displacement 747.17
"burn chamber" 74.00
total volume is 821.17 not 814.17 for a correct CR of 11.09689
Their is nothing wrong with running 9+CR. Porsche and others had race engines with high CRs with great deal of success. Just a couple of examples are 956/962 family. Although the engine started in 1982 with 2.6L and a 7:1 CR to make 620 Bhp and some 460 lbft at 17 psi, in the later years the same engine was racing with a 9.5:1 at 17psi. Now at 3.0L it produce a nice 720 Bhp and a healthy 590 lbft from 4,500 to 5,500 rpm. Also the 997 and 996 turbo run a 9:1 and 9.4:1 CR.
another non porsche is Mazda and Mercedes-Benz. Mazda runs on the Mazdaspeed 6 a 9.5:1 at 17-19 psi and Mercedes 9.5:1 at 19 psi on their V12 engines.
Regards,
AL,
Last edited by AL951; 11-30-2006 at 09:05 PM.
11-30-2006, 09:08 PM
#21
One note that hasn't been taken into consideration with shorter rods, and is also why I have never really thought to go that route is that it changes a lot of the windage characteristics of the bottom end. I am not engine builder nor a mechanical engineer, but I have done a fair bit of research on it. I've never played with numbers on the bottom of a 968, but on other cars it really effects a lot.
We have chosen to work with a stock compression ratio engine, 6-8psi system. 11:1 is high, but most people that will be interested in following my footsteps with the low boost setup won't be tracking the car. The setup will be designed for increased power for around town driving. I've come to the realization from talking about nearly 30 different 968 owners that most do not track there cars more than once or twice a year. There is a lot that goes into tuning and especially a turbo kit that effects how an engine takes it. As to people referring to 11:1 Honda motors, I have been around many S2000's running stock C/R with up to 14psi with no ill effects. The problem that I have seen in nearly all the turbo kits I have surveyed for 968's and 951's is the tuning is half ***. A little knock is not considered normal (I have actually been told that some knock is the norm, just not a lot). Anyone without their glasses on can see what the differences are when you put a decent chip in a 951 vs. and over the counter chip. Even my 968 chip had flaws in it...it really amazed me.
In the end, when running a high compression ratio and boost, your not going to bend rods or burn pistons. With the stock headgasket in place, its going to go well before you bend a rod. With spikes all over the tuning charts you might, but in general headgaskets are the weakest spot in nearly all turbo kits. Thats where Stg. 2 comes in (insert evil smiley face). I still don't understand why there is a general feeling that the 968 engine and transmission is weak? Porsche doesn't underbuild anything.
Wes
We have chosen to work with a stock compression ratio engine, 6-8psi system. 11:1 is high, but most people that will be interested in following my footsteps with the low boost setup won't be tracking the car. The setup will be designed for increased power for around town driving. I've come to the realization from talking about nearly 30 different 968 owners that most do not track there cars more than once or twice a year. There is a lot that goes into tuning and especially a turbo kit that effects how an engine takes it. As to people referring to 11:1 Honda motors, I have been around many S2000's running stock C/R with up to 14psi with no ill effects. The problem that I have seen in nearly all the turbo kits I have surveyed for 968's and 951's is the tuning is half ***. A little knock is not considered normal (I have actually been told that some knock is the norm, just not a lot). Anyone without their glasses on can see what the differences are when you put a decent chip in a 951 vs. and over the counter chip. Even my 968 chip had flaws in it...it really amazed me.
In the end, when running a high compression ratio and boost, your not going to bend rods or burn pistons. With the stock headgasket in place, its going to go well before you bend a rod. With spikes all over the tuning charts you might, but in general headgaskets are the weakest spot in nearly all turbo kits. Thats where Stg. 2 comes in (insert evil smiley face). I still don't understand why there is a general feeling that the 968 engine and transmission is weak? Porsche doesn't underbuild anything.
Wes
11-30-2006, 10:59 PM
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Originally Posted by AL951
Mazda runs on the Mazdaspeed 6 a 9.5:1 at 17-19 psi and Mercedes 9.5:1 at 19 psi on their V12 engines.
Regards,
AL,
Regards,
AL,
12-01-2006, 12:49 AM
#23
Hally,
Direct injection has been used for many years in higher forms of racing and in Lamborghini's. It takes a very sophisticated ECU to time everything perfectly, but rather than mixing the air and fuel before it enters the combusion chamber, the ECU specifically calculates when the spray fuel directly into the combustion chamber. This makes a much cleaner, more precise burn. It removes a lot of the ifs and whens out of the intake manifold. This isn't something that could be easily put into cars as an upgrade.
Wes
Direct injection has been used for many years in higher forms of racing and in Lamborghini's. It takes a very sophisticated ECU to time everything perfectly, but rather than mixing the air and fuel before it enters the combusion chamber, the ECU specifically calculates when the spray fuel directly into the combustion chamber. This makes a much cleaner, more precise burn. It removes a lot of the ifs and whens out of the intake manifold. This isn't something that could be easily put into cars as an upgrade.
Wes
12-01-2006, 01:07 AM
#24
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Also to add a bit to it, you need to run some ridiculous amount of fuel pressure for this setup, something in the range of 26000psi plus. Piezo (sp) is the injector setup most of these gasoline injection systems are using.
Its similar in setup to diesels.
Raj
Its similar in setup to diesels.
Raj
12-01-2006, 02:11 AM
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AL951 you are right here. calcuation mistake was only on the firs total volume calculation.
Well Using shorter rods in stroker kits have proven to be a working soultion.. And they have done it with 4.5mm units for years! Rod angle on stroker kits should be even worse because they are shorter that the ones I planned to use. They are alos aircraft material etc...
944 CARRILLO ROD SET OF 4 FOR 2.8L STROKER 4.55MM SHORTER THAN STOCK LENGTH RODS. (allow 6-7 weeks)
One of the most susceptible points of failure in conventionally designed connecting rods is the fastener system. At Carrillo, we have exerted a great deal of effort into developing rod bolts for specific applications. This effort has led to the utilization of four different bolt designs. The largest bolt available is a 7/16 inch diameter thread, fabricated either from AISI H11 tool steel or Multiphase® material. Many questions are directed to us regarding proper bolt selection. Briefly, the H11 bolt (WMC7 and WMC6) is a high quality, aircraft standard fastener, applicable to most high performance uses. Under racing conditions, we suggest that the H11 bolts be changed periodically. In comparison, the Multiphase® bolt (SPS-CARR) is designed to be a non-replacement type fastener.
THe third option is to dish the stock pistons! Does anyone have any picture material how stock 968 pistons would look. Is there enough material on the top so some material can be removed?
I don't know if anyone has notices, but there is somethig wrong in the calculations.
displacement 747.17
"burn chamber" 74.00
total volume is 821.17 not 814.17 for a correct CR of 11.09689
displacement 747.17
"burn chamber" 74.00
total volume is 821.17 not 814.17 for a correct CR of 11.09689
944 CARRILLO ROD SET OF 4 FOR 2.8L STROKER 4.55MM SHORTER THAN STOCK LENGTH RODS. (allow 6-7 weeks)
One of the most susceptible points of failure in conventionally designed connecting rods is the fastener system. At Carrillo, we have exerted a great deal of effort into developing rod bolts for specific applications. This effort has led to the utilization of four different bolt designs. The largest bolt available is a 7/16 inch diameter thread, fabricated either from AISI H11 tool steel or Multiphase® material. Many questions are directed to us regarding proper bolt selection. Briefly, the H11 bolt (WMC7 and WMC6) is a high quality, aircraft standard fastener, applicable to most high performance uses. Under racing conditions, we suggest that the H11 bolts be changed periodically. In comparison, the Multiphase® bolt (SPS-CARR) is designed to be a non-replacement type fastener.
One note that hasn't been taken into consideration with shorter rods, and is also why I have never really thought to go that route is that it changes a lot of the windage characteristics of the bottom end. I am not engine builder nor a mechanical engineer, but I have done a fair bit of research on it. I've never played with numbers on the bottom of a 968, but on other cars it really effects a lot.
We have chosen to work with a stock compression ratio engine, 6-8psi system. 11:1 is high, but most people that will be interested in following my footsteps with the low boost setup won't be tracking the car. The setup will be designed for increased power for around town driving. I've come to the realization from talking about nearly 30 different 968 owners that most do not track there cars more than once or twice a year. There is a lot that goes into tuning and especially a turbo kit that effects how an engine takes it. As to people referring to 11:1 Honda motors, I have been around many S2000's running stock C/R with up to 14psi with no ill effects. The problem that I have seen in nearly all the turbo kits I have surveyed for 968's and 951's is the tuning is half ***. A little knock is not considered normal (I have actually been told that some knock is the norm, just not a lot). Anyone without their glasses on can see what the differences are when you put a decent chip in a 951 vs. and over the counter chip. Even my 968 chip had flaws in it...it really amazed me.
In the end, when running a high compression ratio and boost, your not going to bend rods or burn pistons. With the stock headgasket in place, its going to go well before you bend a rod. With spikes all over the tuning charts you might, but in general headgaskets are the weakest spot in nearly all turbo kits. Thats where Stg. 2 comes in (insert evil smiley face). I still don't understand why there is a general feeling that the 968 engine and transmission is weak? Porsche doesn't underbuild anything.
Wes
We have chosen to work with a stock compression ratio engine, 6-8psi system. 11:1 is high, but most people that will be interested in following my footsteps with the low boost setup won't be tracking the car. The setup will be designed for increased power for around town driving. I've come to the realization from talking about nearly 30 different 968 owners that most do not track there cars more than once or twice a year. There is a lot that goes into tuning and especially a turbo kit that effects how an engine takes it. As to people referring to 11:1 Honda motors, I have been around many S2000's running stock C/R with up to 14psi with no ill effects. The problem that I have seen in nearly all the turbo kits I have surveyed for 968's and 951's is the tuning is half ***. A little knock is not considered normal (I have actually been told that some knock is the norm, just not a lot). Anyone without their glasses on can see what the differences are when you put a decent chip in a 951 vs. and over the counter chip. Even my 968 chip had flaws in it...it really amazed me.
In the end, when running a high compression ratio and boost, your not going to bend rods or burn pistons. With the stock headgasket in place, its going to go well before you bend a rod. With spikes all over the tuning charts you might, but in general headgaskets are the weakest spot in nearly all turbo kits. Thats where Stg. 2 comes in (insert evil smiley face). I still don't understand why there is a general feeling that the 968 engine and transmission is weak? Porsche doesn't underbuild anything.
Wes
12-01-2006, 02:23 AM
#27
Markus -
From previous conversations I thought you were starting with a 3.0L? Are you doing a 2.8 from you 2.5 8V? My concern was rod angle with 104mm pistons and 88mm stroke? If your doing 100mm bore then it may be a non-issue. I know guys have done the shorter rod solution many times before, but I was just curious as to its effect with windage and if anyone had ever taken the time to do measurements. Since its a shorter rod it should have better characteristics, but not always from my understanding. As to the 968 pistons, there appears to be plenty of room to pull 2-3mm off. The only concern I have with that is your taking the risk that the machine shop does a good job and also that the structural integrity of the piston isn't altered. You were talking about some pretty good power, so I was/am unsure of the durability when you start removing surface area. My piston builder can build custom pistons to fit alusil blocks. You can get anything done that you want with them for a reasonable price. I can't remember if we spoke about this before. Takes about 6-weeks.
Wes
From previous conversations I thought you were starting with a 3.0L? Are you doing a 2.8 from you 2.5 8V? My concern was rod angle with 104mm pistons and 88mm stroke? If your doing 100mm bore then it may be a non-issue. I know guys have done the shorter rod solution many times before, but I was just curious as to its effect with windage and if anyone had ever taken the time to do measurements. Since its a shorter rod it should have better characteristics, but not always from my understanding. As to the 968 pistons, there appears to be plenty of room to pull 2-3mm off. The only concern I have with that is your taking the risk that the machine shop does a good job and also that the structural integrity of the piston isn't altered. You were talking about some pretty good power, so I was/am unsure of the durability when you start removing surface area. My piston builder can build custom pistons to fit alusil blocks. You can get anything done that you want with them for a reasonable price. I can't remember if we spoke about this before. Takes about 6-weeks.
Wes
12-01-2006, 03:56 AM
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I am going with full 3.0 liter. I was just reffering that 2.5 liter blocks are running 3.0 liter crank with shorter rods sucsessfully. It is not hard to push that engine into the limits of 550 hp as it is really efficent and the head flows ridiculos amount of air!
Removing material from piston will affect their reliability! because Im after big power.. I think it would be ok to run somwhat 400-450hp with it..
Installing thicker headgasket will affect squisch area!
Rod combo still seems to be the best and most affordable option because rods needs to be changed anyway. (althoguht this will affect rod angle and squish area) it is proven to work...
I was thinking to do soemthing like this
Installing shorter billet H-profile rods.
New rod bearings (Porsche OEM)
Balancing the bottom end (pistons rods and crank with flywheel and clutch assemble and front pulley installed)
ARP had studs
Cometic multilayer headgasket
GT35R with 0,82AR
Stock exhaust manny welded to 951 crossover pipe
3" stainless steel downpipe with catback exhaust
Tial 40mm wastegate
Bosh 044 pump with 10mm fuel lines and adjustabe FPR
720cc injectors
Custom intake manifold by using stock runners full radius velocity stacks and dual plenum (also called diffuser desing)
68 mm thorrle body
Custom Intercooler 600*300*100mm
2.5" SS intercooler pipes
Lightned flywheel with GT2 pressure plate and 968 clutch disk
Tatech pro engine management with wasted spark ignition and variocam control
Removing material from piston will affect their reliability! because Im after big power.. I think it would be ok to run somwhat 400-450hp with it..
Installing thicker headgasket will affect squisch area!
Rod combo still seems to be the best and most affordable option because rods needs to be changed anyway. (althoguht this will affect rod angle and squish area) it is proven to work...
I was thinking to do soemthing like this
Installing shorter billet H-profile rods.
New rod bearings (Porsche OEM)
Balancing the bottom end (pistons rods and crank with flywheel and clutch assemble and front pulley installed)
ARP had studs
Cometic multilayer headgasket
GT35R with 0,82AR
Stock exhaust manny welded to 951 crossover pipe
3" stainless steel downpipe with catback exhaust
Tial 40mm wastegate
Bosh 044 pump with 10mm fuel lines and adjustabe FPR
720cc injectors
Custom intake manifold by using stock runners full radius velocity stacks and dual plenum (also called diffuser desing)
68 mm thorrle body
Custom Intercooler 600*300*100mm
2.5" SS intercooler pipes
Lightned flywheel with GT2 pressure plate and 968 clutch disk
Tatech pro engine management with wasted spark ignition and variocam control
12-01-2006, 10:03 AM
#29
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Originally Posted by whakiewes
As to the 968 pistons, there appears to be plenty of room to pull 2-3mm off. The only concern I have with that is your taking the risk that the machine shop does a good job and also that the structural integrity of the piston isn't altered. You were talking about some pretty good power, so I was/am unsure of the durability when you start removing surface area.
Raj
12-01-2006, 10:10 AM
#30
Raj,
What amount of boost and what tuning? Did a local shop do this or did you send them off? I guess my biggest concern with that option is finding a machine shop that I trust enough, as stock 968 pistons are expensive enough.
Wes
What amount of boost and what tuning? Did a local shop do this or did you send them off? I guess my biggest concern with that option is finding a machine shop that I trust enough, as stock 968 pistons are expensive enough.
Wes