S3 vs S4 Engine

928 S3 Engine vs S4 - what is the difference between a 1986.5 5.0l 32V and the S4 engine of the same description. Specifically, I understand the HP difference of 288 vs 316 with the S4, but is it the same block? Is it a bore/stroke difference? Can the earlier 288hp S3 be machined/built up to the later spec?...I lot of questions from a very curious member.

While there are quite a few detail changes, the most obvious major change is the intake manifold system, with the Heimholtz Resonator (flappy valve). The earlier cams are actually better for power than the later ones.

While you could use the later intake on the earlier block, you would also need to swap the LH ECU and harnesses to control the flappy valve.

Wally Plumley
928 Specialists
www.928gt.com

Hi Wally

Can I chime in with a question about this. I've read on Rennlist comments that the S3 inlet manifold is 'better' than the S4. Can you enlighten me please? Is the S4 manifold more of a compromise to give a broader range of performance?

Cheers

Richard

Thanks for the input...this is exactly what I have been trying to understand. I have found a few data sources that suggest the S3 and especially the euro S2 and S3 as being a bit quicker in the 0-60 and 1/4-mile times. I was not sure if that was just due to weight increases with the later S4's but is sounds like despite the lesser HP - 288 vs 312, the performance characteristics on the rev band and power range have a noticeable impact.

Wally mentioned the intake manifold difference. The engine control system system are quite different too. The 1985 - 1986 US models use the first generation of LH and EZF spark system (25 pin modules), the 1987 and newer 928s have the second generation system (35 pin modules). The 1985 - 1986 LH & Spark less sophisticated, use lower computational capable microcontrollers (8039 vs. 8031 in the newer). The 1987 and newer 928s have the EZK spark system, which has knock control so the spark timing can be much more advanced without danger of spark knock.

will the newer EZK spark system work with the S3 engine?