John Speake

I think you are incorrect about John Kuhn's turbo kits. The standard kit is used with a stock engine to about 550RWHP (as does Tim Murphy's Stage 3 kit). The combustion shape of the 32v head is very good, as it was derived from one of the Porsche racing cars.

John Kuhn does offer a lower compression option for those wanting to go even higher boost.

Darklands

My mistake .I saw the option small block with different compression.
Do you think it´s ok to run the engines under boost with stock compression a long time under full load?

John Speake

If the head gaskets are in good shape, then yes. I understand that there are high mileage cars running at that level of boost for considerable mileages. I am sure some people will contribute their experiences to this thread.

The volumetric efficiency of the 928 is very poor at higher engine rpm, boosting overcomes that deficiency but the resulting combustion pressures aren't excessive. But I'm not an expert....

dprantl

https://rennlist.com/forums/8284860-post94.html

Dan
'91 928GT S/C 475hp/460lb.ft

AO

There are no kits on the market today that require any internal engine modifications. I'm running 9.5 psi (soon to be 11 psi) on my GT and I think it's a bit less than ideal @ 10.5 CR.

I've got a set of 951 pistons ready to go in my next motor. On a stock S4, that would lower the compression ratio to about 7.5 to 1 I think. Todd from Green Bay did this on his red SC'd car that's running near 30psi of boost at 670+ RWHP!

hacker-pschorr

A well known 928 PCA racer Jean-Louis and his wife Agnes have been racing a 10.4:1 compression EuroS with a Murf928 supercharger system for 3-4 years now with about 8-9 psi manifold pressure

Another example where a focus on the tuning trumps the idea of "how much boost" is capable.

Anyone from the racing circle can attest to how hard Jean-Louis drives. I'm hoping to setup his car for some HD video this spring during the Memorial Day event.

928mac

I know most factory engines with boost (turbo or SC) have lower compression.

Maybe it is to correct for people that use reg fuel.

I have never played with boosted engines that much just GM factory stuff
(2.2 turbo, 3.8 Grand national turbo, Buick 3.8 SC Regal and others)
All of these had no more then 9:1cr

I guess if you don't have any detonation then you don't worry about it

Brad

hacker-pschorr

9:1 is still very common with production vehicles. I've read the Veyron is 9:1 or 9.3:1. Some of the 1.8T Audi/VW engines are 9.5:1

I'm not saying 10.4 is the way to go or a good idea, just an example of pushing the limits a bit. He does run 25% 100 octane mixed with 92. That detail slipped my mind before.

Within reason I suppose. I wouldn't toss a huge amount of boost into my 10.9:1 944S engine. I wouldn't be afraid of 10-12psi either.

trialattorney

I insdtalled Carl's s/c kit for my 84 928 (picture is my avitar); it was not exactly a seemless installation but no serious or major problems. The big problem was the crap powerdyne s/c that kept breaking belts. Carl stood behind his kit and rebuilt my s/c at least 3 times until finally he installed his new bits and pieces and a new superduty belt and it has not done probably 30 hours at various racetracks (willow springs, Auto-club speedway, buttonwillow primarily) without issue. I have had the car at Marks' Sharktoberfest the last couple of years and I even took people out for drives who were considering s/c'ing their cars. Carl had me lower the boost to keep the belt from breaking, so I'm not pushing 10psi anymore, but the car pulls from 0 up to its power curve with no lag. The biggest problem is the oil blow-by that we have never been able to solve. Each 15 minute session on the track costs me 1 qt of oil. I had to fabricate a much larger tank to catch the oil that would otherwise blow all over my engine when the smaller catch can filled up. Also, the larger injectors Carl supplied with his kit didn't work for me, so I used, and am still using, the stock injectors. I recently broke the cam gear so that engine is torn down at the moment. I also just recently purchased a euro 4.7 motor and that is just back from the machine shop - it is now a 5.0 liter balanced engine that is being rebuilt and to which Carl's s/c kit will be installed. I will probably change out the belt drive with a Scorpion gear drive (they now own the rights to the Powerdyne gear drive and mfg their clone versions of same), and that will require oil in and out lines. I moved the air intake from where Carl's kit had it (just behind radiator) to inside the driver's side wheel well; it gets cooler air at that location. Other than the oil blow by Carl has stood behind his product; answered questions and made suggestions. When he was last down at Sharktoberfest, he drove my car and made additional suggestions. I'm sure Tim is equally responsive with the Murf kits. I don't know how many 4.7 s/c kits Carl has sold, but my car is certainly one of them. Once the "new" engine is rebuild, I will rebuild the cam gear broken motor as a spare. I have invited 928 owners to the track to sit in the car as I drive it around to experience the s/c feel but only 1 turned out to take advantage. Once we're up and running again, I'll make the same offer. You will be able to see the car at this year's Sharktoberfest assuming (1) Mark is going to sponsor it again this year; (2) that I ever get the engine done; and (3) it will have Carl's engine management kit installed on it as well, so it will be a "showcase" for Carl's design. I like the Murf kit, as well and what I like best about it is it comes already with a gear drive (again, Carl's last fix has lasted for a long time and I have no reason to think it would not still work if I didn't decide to go with a gear drive powerdyne clone once the motor is done. So, either way, you will be blown away with the diference if you have a 16v engine. Since I have not s/c'd either of my 32v cars, I cannot speak for them, but I would make my 32v a 6.4 liter before I s/c'd it. Just my thoughts.

trialattorney

Sorry - it should read, "now done 30 hours"; I did not break the cam gear racing the car; my car was (and will still be, I hope) street legal, and I was pulling into a gas station, slowly, when it gave away. Just its time.

andy-gts

Les,
Greg Brown is in the process of fixing the "oiling issues" we are all plagued with at high boost and rpm. He will unveil after full dyno testing and has a thread on the monster engine build he is doing on rennlist.

928mac

Carl, Greg, Members, would a extra gal container of oil mounted at the oil cooler keep oil in the pan longer? or does that oil empty into the pan?
An oil scavenging assist may be the only way, if not.

I sure like the baffle system that Sterling uses and I feel that it must be a major windage improvement.

To polish the return tubes to increase flow will help.

I don't believe opening/porting the return cavities (at the bottom) will help without controlling the windage issue first.

Good Rings to reduce blow by, windage and deflectors, pressure equalization between pan and cam covers.

IMHO

Iwanna928

Can't wait to see what Greg has up his sleeve. I plan on building a 4.5L this summer that will have high compression and a cam that wants to rev!

This will be awesome to see and just in time for my build!

Tony

When you CC the heads and pistons they tend to come out less that the stock/book amount also....every little bit helps.

Carl Fausett

Thanks for the update, Les. 30 hours of racing without a problem is a real achievement for any SC kit.

I hope readers understand that street driving a SC kit is a walk in the park compared to racing. Every SC kit I have seen, regardless of brand/maker, has had their fair share of issues whn racing.