924Board.org

[chris79]

Anyone know if in this forum there are some post related to modification of head of 924 aspirated for restore 150cv as in origin ?

[Rasta Monsta]

I think CV is Italian for HP.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[v8carreragts]

CV = cavalo velocidade or horse speeds basically horse power. The same in Portuguese and Spanish
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84 944--924 Carrera GTS clone w/520HP Chevy 302 V8--RUNNING!
2015 AUDI Q7
2013 Dodge Charger R/T AWD HEMI
2013 Chevy Cruze

[fiat22turbo]

NA cylinder head has no combustion chamber, it is flat on the bottom.

The combustion chamber is on the piston face. To gain power you need different pistons (custom made) or a supercharger or turbocharger to force more air in the cylinders.

Some minor gains can be made with the cylinder head with careful work on the intake and exhaust ports, but not likely 25hp worth.

In both of the above cases you'd need higher octane gas and the ability to carefully monitor and tune the fuel and ignition system to ensure you don't damage the engine internally.

Please read the following thread:

http://www.924board.org/viewtopic.php?t=25795
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[!tom]

There have been discussions regarding head modifications to increase power, specifically in reworking the ports.

Apparently there is someone who did significant research and had sorted out a method for substantial flow gains, but after suggestions that someone would copy his work without permission he clammed up.
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78 924 NA
5-lug

[leadfoot]

Two posts up sticky
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[chris79]

as I read on forum www.porschemania.it the 924 engine has some limits in head that reduce power to 125hp. If this limits are removed from aspiration the power of engine is 150cv without any changes.
It's possible ?

[snakoil]

there was discussion of thinnger head gasket that would increase CR
http://www.924board.org/viewtopic.php?t=36554&highlight=decking

but since you already have the ROW pistons I assume this might make your engine an interference engine

Otherwise I would look on the trhread from ideola about high comp pistons for cheap
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1979 924 NA

[chris79]

Not. Limits in the head of 924 aspirated are in intake ducts and forum said that sending head in UK engineers can remove this limits and power of engine is 150cv.

[morghen]

For 150 hp you need to port and match the head, cut away some mm from the block(or use different pistons) run 100oct gas, use alot of ignition advance and use an improved valve cam.

You can get @10 cv from cutting the block(increase compression ratio) easly
you can get @5 cv from porting and port matching the intake/exhaust
you can get @10 cv from using high octane gas, more advance and a hot cam.

I think 150 cv/hp is fairly easy and cheap...maybe one could even pull 150hp without a new cam.
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Supercharger and EFI kits
https://www.the924.com

[ideola]

Some perspective.

The hottest NA setup documented that I am aware of are the D-Prod cars which were running 13:1 CR, 931 head, kugelfischer CIS (and later sidedraft carbs after the kugelfischer was outlawed by SCCA). Those cars were in the 180BHP vicinity, many of them on the ragged edge, requiring rebuilds after every race.

There are ITB cars that are getting somewhere in the area of 130-140 BHP with a highly restrictive set of rules, most of the bump over stock power probably coming from increased CR (~9.8:1 more or less, as .5 increase over stock Euro spec of 9.3 is the max allowed by rules).

U.S. spec 9.0:1 CR got 120BHP, and that's with all the emissions crap. Euro sepc 9.3:1 CR got 125 BHP.

So if you can get ~5 BHP, or roughly 4% increase from .3 points of compression, and ~20 BHP (at best), or roughly 16% from .8 points of compression, you can get an idea of approximate increases available through conventional methods.

It's arguable how much increase can be gotten due to the head alone. All of my research indicates not much using the port limited / valve limited / cam limited NA head. Bang for the buck, the best approach is to increase CR by using a thinner Cometic gasket, *minor* shaving of the *block* (NOT the head!!!!), or different pistons.

US Spec S1 931 pistons with NA head will yield 9.6:1
US Spec S2 931 pistons with NA head will yield about 10:1
Euro Spec S2 931 pistons with NA head will yield about 10.5:1

There are many other variables that will impact the final CR and HP, but bang for the buck, I've come to the conclusion that on a limited budget, $$$ are best spent on increasing CR rather than expensive head modifications that yield questionable gains.

My next budget build will be stock NA head with stock valves, basic porting, and stock cam, using S1 or S2 pistons. And maybe I'll throw that Windblown turbo on it just for fun.
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erstwhile owner of just about every 924 variant ever made

[nickthompson]

I'm kind of partial to my method of getting 150hp. LoL

[Rasta Monsta]

[nickthompson]

Yes Rasta it is but it lacks thw WTF factor that I love so much.

[leadfoot]

Either turbo/supercharge is the only cost effective method of extracting power from an N/A vs time and results...
Cost approx $1000 and net 150hp+
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...