Lizard928

Quotes from Ian928

I also think I remember reading that putting the S3 heads on a S4 block would lower the compression substantially. Is this correct? Have anyone calculated the resulting compression? if this is correct then putting S4 heads on a S3 engine, would raise the compression, anyone know how much, would it take it up a full point, or does it not make any difference, imo I doubt it would make a difference as the S4 waas the same head just larger valves installed in it.

S4 valves in ported S3 head = S4 flowing heads with S3 cams (more aggressive cams than original S4) I though the S3 cams were exactly the Same as the S4, anyone??

Old & New

Just an aside... If you put a later intake on an earlier car, then what would need to be done to get the flappy working? Also, the idle stabilizer valves are different. It is starting to sound like it might be just as easy to drop in an S4 engine & deal with the wiring / brain / etc. You would pick up all the advantages of the S4 engine that way.

Just heresay, but I understand that S3 heads on an S4 yield about an 8.7:1 compression ratio.

Another nice question is - can anyone comment on S3/GT/hotter cams in an S4? How far can you go before it needs to be rechipped or piggybacked?

Lizard928

that would mean installing S4 heads onto an S3 engine would result in a CR of 11.3:1, can someone plz confirm this

Ian928

Well, this sure sounds promising! 8,7:1 should be nice for boosting!

Gbyron:
I would use everything from the S4 except heads from the S3. I am not worried about machining the S4 intake to the manifold, I have a friend that does a lot of nice work on Ford Cosworth engines. He suggests to make a new intake, but I like the idea of keeping the flappy.

The block I am talking about did get a smack in the crash, one engine mount would have to be rewelded. The Crank is 0,01mm on the first cylinders, 0,001mm on the next, according to the owner. I could have the engine almost for free. I'm thinking that a reputable shop maybe could check the block for trueness?

On the side, I have aquired the books "Supercharged!" and "Maximum Boost" by Corky Bell and also "4-stroke performance tuning" by A Graham Bell. These are great reading for the novice!!

Jim bailey - 928 International

Lizard ....Yes S-4 heads on an 85-86 32 valve short block makes an engine which will not run on pump gas ..too much compression , detonation . Customer in Australia proved that several years ago . The 85-86 valves are smaller BUT with boost that is not important might make better torque at lower engine speed off boost .

Lagavulin

Since you seem like you're interested in forced induction, I would also recommend acquiring A. Graham Bell's 'Forced Induction Performance Tuning' too.

If I were you, I'd suggest first reading the applicable Corky Bell book dependant upon which route you think you're heading: supercharger or turbo.

Lizard928

what is the difference between the 2 head designs? less compression chamber on the S4 heads?

Jim bailey - 928 International

piston dish is different , head dome is different .

Lizard928

Thanx Jim

Lizard928

well if the cr #s are correct you would be running at around an 11:1 cr, which would mean you would have to run 94 octane

Ian928

OK, so it is the dome of the pistons and the shape of the combustion chamber that differs between S3 32V and S4 and make it possible to either raise or lower the compression by switching parts around.

What about the squish? Will the squish effect be compromized if you put S3 heads on a S4 engine? If you just put shorter rods in the engine, I assume squish would be affected, and as someone mentioned (Lagavulin?) disturbing the squish effect will probably give more detonation.

Maybe this is a cheap(er) way to reduce CR for boosting S4 engines? At least in the US, where you have a lot of S3 engines around.

Maybe even, the S3 head is better for use in conjunction with a centrifugal supercharger than the S4, (according to Jim B) it might provide better performance on lower RPMS where it is needed without compromizing too much at boost.

Ian928

Lagavulin,

Maybe you could be kind enough to make some calcultions for this proposed engine setup?

Lagavulin

I'm not sure what the proposed engine setup is, so if you could provide those parameters, I'd be more than happy to help out.

Ian928

Lagavulin,

This is the setup I am thinking about:

S4 engine with S3 heads =
5.0 liter
~300chp(?)
CR 8,7:1
IC

Well, I am thinking what the power output will be and how much boost is necessary to bring the chamber temp to 1075°C. Based on available information I think that aiming for this number should create a robust setup for the 928. Thanks!

Lagavulin

According to Tim, the 85-86 heads have quite a bit larger combustion chamber to the tune that if bolted onto a stock S4 block, the new compression ratio will be somewhere in the vicinity of 8.2:1.

Assuming a 4% loss of hp per point of compression we figure the new NA crank hp:

New NA Crank hp = 316 hp x [1.0 – (.04 x 1.8)] = 316 hp x .928 = 293.2 hp

Using 293.2 crank hp, centrifugal thermal efficiency of 75% and IC efficiency of 85%:

Boost = 37 psi
CC Temp = 1075.05
Crank HP = 972.52

That’s quite a bit of horsepower. However, it wouldn’t be realistic using the stock cast pistons at this boost/hp level and expect any type of longevity.

Here are more hp predictions using the same configuration, but lowered boost:

Boost = 30 psi
CC Temp = 1063.79
Crank HP = 849.74

Boost = 25 psi
CC Temp = 1054.95
Crank HP = 761.02

Boost = 20 psi
CC Temp = 1045.26
Crank HP = 671.34

Boost = 15 psi
CC Temp = 1034.51
Crank HP = 580.57

All the above scenarios will require fuel system mods. And the question remains regarding the stock cast pistons, how much can they endure? They do have nice thick ring lands, a plus; but can they quickly wick away enough heat from their crown so as to not deform and fail while under high boost?

So that is the real question, the stock cast piston strength under high boost. And then, what is considered ‘high boost’; anything over 14.7 psi?

I’m willing to bet that the stock crank and rods are more than up to the task, just as it is with the stock bottom end 800-900 rwhp Supra guys.