Current Peak Cylinder Pressures on Turbo S-I engines
Current Peak Cylinder Pressures on Turbo S-I engines
(OP)
I have read a number of threads here regarding PCP on turbocharged engines, mostly in regard to Diesel or other experimental or developing engine tech. The minimal info. on turbo S-I PCPs however left me wanting for more info. Since virtually all major pass car companies are downsizing to turbo 4 & 6 cyl. engines for EPA mandated mpg requirements in the U.S., I thought this might be a good time to revisit this subject as the prior threads were circa 2008 and a lot of changes have occurred in pass car turbo engine development since then.
My personal interest is for a turbo 3.2L VR6 engine project where I want to be certain that the head gasket is capable of managing the PCP under maximum boost even though this would only be encountered for short duration at WOT. I've reviewed many SAE and other tech papers on theoretical / modeling techniques to estimate PCP but the best real world measured hard data I have found was on the Honda turbo 1.6L F1 racing engine circa 2000. The PCP on this engine was 16.7 MPA, i.e. ~2422 PSI @ 2.5 bar absolute(A), boost @ 12,000 RPM. I will be running a max of 2.38 bar (A) (on rare occasion), at a more modest 6,500 rpm. The PCP is likely to be some what limited by the 92 R+M/2 premium pump octane fuel used based on my past experience. Honda's 1.6L turbo F1 engine like other F1 engines of the day used 84% Toluene with higher energy content but more importantly the ability to use 37 degrees total advance at ~12,000 rpm while only measuring 101.7 RON. (The F1 rules limited the fuel octane to 102 RON). I have dyno developed numerous turbo S-I engines with <2 bar (A) boost on Indolene (simulated 92 R+M/2 premium fuel), that limited max ignition advance to ~20 deg. total @ WOT in the RPM range from ~4500-6500 rpm.
On a four cyl. turbo S-I pass car engine circa 1990 that I worked on we were seeing ~1250 PSI measured PCP in this engine with ~2 bar (A) boost. Based on that engine I'm estimating the 3.2L VR6 engine to have ~1724 PSI PCP at the increased 2.38 bar (A) boost. I know GM, Ford, VW and many more companies are currently running some significant boost in small turbo S-I pass car engines so I'm hoping that those with firsthand knowledge can offer up some current PCPs on production pass car engines along with the associated boost pressure as this obviously alters the PCP considerably. I will not be running an over-boost system so I'm primarily interested in steady state WOT PCPs to see how close my estimated 1724 PSI PCP relates to other real world measured data at similar boost pressures. I am aware that there are many variables in PCPs not the least of which is fuel type, octane, IAT, static compression ratio, total ignition timing, etc.
I appreciate any input. I'm sure those working in advanced engine development have moved on considerably from the currently available turbo S-I engines, which in themselves have come a long ways from yesteryear turbo S-I engines in performance, drivability, fuel economy and reliability. My goal is 100% reliability in this 3.2L VR6 turbo conversion engine. I'm not looking for extreme performance in this application.
My personal interest is for a turbo 3.2L VR6 engine project where I want to be certain that the head gasket is capable of managing the PCP under maximum boost even though this would only be encountered for short duration at WOT. I've reviewed many SAE and other tech papers on theoretical / modeling techniques to estimate PCP but the best real world measured hard data I have found was on the Honda turbo 1.6L F1 racing engine circa 2000. The PCP on this engine was 16.7 MPA, i.e. ~2422 PSI @ 2.5 bar absolute(A), boost @ 12,000 RPM. I will be running a max of 2.38 bar (A) (on rare occasion), at a more modest 6,500 rpm. The PCP is likely to be some what limited by the 92 R+M/2 premium pump octane fuel used based on my past experience. Honda's 1.6L turbo F1 engine like other F1 engines of the day used 84% Toluene with higher energy content but more importantly the ability to use 37 degrees total advance at ~12,000 rpm while only measuring 101.7 RON. (The F1 rules limited the fuel octane to 102 RON). I have dyno developed numerous turbo S-I engines with <2 bar (A) boost on Indolene (simulated 92 R+M/2 premium fuel), that limited max ignition advance to ~20 deg. total @ WOT in the RPM range from ~4500-6500 rpm.
On a four cyl. turbo S-I pass car engine circa 1990 that I worked on we were seeing ~1250 PSI measured PCP in this engine with ~2 bar (A) boost. Based on that engine I'm estimating the 3.2L VR6 engine to have ~1724 PSI PCP at the increased 2.38 bar (A) boost. I know GM, Ford, VW and many more companies are currently running some significant boost in small turbo S-I pass car engines so I'm hoping that those with firsthand knowledge can offer up some current PCPs on production pass car engines along with the associated boost pressure as this obviously alters the PCP considerably. I will not be running an over-boost system so I'm primarily interested in steady state WOT PCPs to see how close my estimated 1724 PSI PCP relates to other real world measured data at similar boost pressures. I am aware that there are many variables in PCPs not the least of which is fuel type, octane, IAT, static compression ratio, total ignition timing, etc.
I appreciate any input. I'm sure those working in advanced engine development have moved on considerably from the currently available turbo S-I engines, which in themselves have come a long ways from yesteryear turbo S-I engines in performance, drivability, fuel economy and reliability. My goal is 100% reliability in this 3.2L VR6 turbo conversion engine. I'm not looking for extreme performance in this application.





RE: Current Peak Cylinder Pressures on Turbo S-I engines
I'd say, if you can keep your PCP under 2000 psi, you're probably OK. As an indicator, do a stress calculation on your connecting rods in compression, and see what they're good for.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Current Peak Cylinder Pressures on Turbo S-I engines
By design the engine PCP is being kept below 1800 PSI to eliminate head gasket leaks. I'm curious what PCPs the current pass car turbo S-I engines are seeing as the boost pressures continue to increase.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
1. Very short duration of PCP plus piston mass vs elasticity of load path below the piston mean that rod stress resulting from PCP does not approach the value obtained from a steady state calculation.
2. PCP occurs very close to TDC when inertial load on the rod is at its greatest (tension)
Link Mercedes claim puts PCP in the region of 400 bar (6000 psi)
Link Gasketless interface for boosted FSAE engine.
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
These engines can handle a lot of boost but the known weak links of the stock configuration are the headgasket and connecting rods (in compression). The weak links only get exposed under extremely high boost and/or poor tune conditions, i.e. high peak pressures.
Naturally, there are several robust, aftermarket solutions for both weak links.
If you doubt the assertions about bent connecting rods, go ahead and sign up, and challenge them.
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Current Peak Cylinder Pressures on Turbo S-I engines
This VR6 engine is actually quite robust as the engine is reported to have been originally intended to be a Diesel engine. The OEM forged steel rods and crank as well as the beefy block are far stronger than a typical hi-perf S-I engine. With the stock rods these engines are known to run completely reliable with 8.5:1 and 2 bar (A) pressure. That being said, this engine will use Crower's strongest forged steel I-Beam style con rods, with Mahle forged 9:1 turbo pistons, pins, rings. Special stainless valves and bronze guides are replacing the OEM components to address the increase thermal load. This engine is being upgraded for the loads it is expected to experience.
So far I have not found any reliable source that indicates that the head gasket leaks on the VR6 engines even at 2.6 bar (A) boost, which I find amazing based on other engine development work that I have conducted in the past. The OEM gasket is a multi-laminate stainless steel (MLS), design that is reported to be totally reliable.
I'm looking for real world measured PCPs on similar boost pass car S-I turbo engines to see how they compare to my past experience with in-cylinder pressure traces and projected PCP for this engine.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Current Peak Cylinder Pressures on Turbo S-I engines
"Maximum combustion pressure has been increased from 200 to 210 bar (3046 psi)" (Latest BMW 750D.) Diesel I know, but getting up there for a production car.
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Pass car Diesel engines are starting to approach PCPs typical of HD Diesel designs for increased efficiency and power. As the PCP increases attention needs to be given to everything else for structural integrity, engine vibration, etc. It's really cool to see the high torque and fun drivability of the newer HP Diesel engines and still obtain excellent fuel economy.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Current Peak Cylinder Pressures on Turbo S-I engines
And just for S&Gs, imagine the BRM V16 turbocharged with today's EMC capabilities.
jack vines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Any number of auto companies can confirm in their testing that the DI gas vaporization process in the cyl. produced such a significant drop in induced charge chamber temp that they were able to increase the static compression ratio by as much as a full point, i.e. going from 11:1 to 12:1 in numerous engines with no other changes than going from PFI to GDI. There are likely SAE papers on this if you're interested.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Just thought you might be able to cite a paper. I am interested in this because thermodynamically, the total charge cooling from the vaporization of liquid fuel should be the same between the two cases. I do expect that the cooling of hot spots can be dramatically different and that this can be a big advantage wrt octane requirement and permissible CR. Thanks.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
PFI typically injects some or all of the fuel into the port with a closed valve for better vaporization, depending on the EFI strategy being employed. I know that VW is one company who raised the static compression on their 3.2L VR6 engines from ~11:1 up to ~12:1 when they changed from PFI to GDI. They were quite public about the cooling effect and compression bump so that's why I suspect an SAE paper may exist from them or other car makers who bumped the compression ratio based on the in cylinder cooling effect.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Yes GDI is achieved at much higher injection pressures than conventional PFI and the "entire process" for the most part lends itself to cooling the intake charge and piston crown to deter detonation and allow more static compression and or more ignition timing on NA as well as boosted applications. It turned out to be an important discovery for gas engine advancement including reduced exhaust emissions and lower fuel consumption. One negative associated with GDI is that many engines tend to build up carbon deposits on the intake valves. PFI washed much of the oil vapor/carbon build-up off the intake valves that GDI engines are unable to do unless you use both PFI and GDI on the same engine as at least one auto maker has done to address the carbon build-up issue with GDI.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Anyone else have firsthand knowledge of PCPs on current S-I pass car engines running boost in the 2.5 bar range?
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
These expedients work for just about everybody else. It seems VW is leaving something (a lot!) on the table.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
http://www.eng-tips.com/viewthread.cfm?qid=412274
RE: Current Peak Cylinder Pressures on Turbo S-I engines
RE: Current Peak Cylinder Pressures on Turbo S-I engines
My comment on GDI charge cooling was in response to durablack2's post on PCPs in GTDI engines even though the original thread requested info. specifically on PCPs in PFI S-I engines. My comment was not intended to start a discussion on GDI combustion process and/or charge cooling, it was to note that GDI engines may have higher PCPs based on increased static compression and the ability to run higher boost than a PFI boosted engine due to the charge cooling documented in GDI engines.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
I read that and thought that you were asking about Stratified Ignition engines, my mistake - my job typically refers to S-I as stratified ignition (lean burn) since I work with just gasoline, no one feels the need to call out SI as a spark ignited engine... So I just realized that my comment about lean burn does not answer the question you're asking.. Although the PCP's for those stratified ignition that I mentioned are accurate...
RE: Current Peak Cylinder Pressures on Turbo S-I engines
Correctly managed, lean-burn results in reduced combustion/exhaust/valve temperatures.
je suis charlie
RE: Current Peak Cylinder Pressures on Turbo S-I engines
There was no issue for me with your comment. I understood that you were referring to GTDI engines and that is why I noted they could have higher PCPs than conventional PFI S-I engines due to the additional charge cooling.
RE: Current Peak Cylinder Pressures on Turbo S-I engines
"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz
RE: Current Peak Cylinder Pressures on Turbo S-I engines
http://www.eng-tips.com/viewthread.cfm?qid=412274
RE: Current Peak Cylinder Pressures on Turbo S-I engines
More reliably, 115 bar peak
RE: Current Peak Cylinder Pressures on Turbo S-I engines