S3 vs S4 Engine

  • Giovanni22265
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25 Nov 2014 12:35 - 28 Nov 2014 06:53 #17777 by Giovanni22265
S3 vs S4 Engine was created by Giovanni22265
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.
Last edit: 28 Nov 2014 06:53 by Giovanni22265.

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05 Jan 2015 11:09 #17909 by wallyp
Replied by wallyp on topic S3 vs S4 Engine
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

Wally Plumley
928 Specialists
www.928gt.com

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06 Jan 2015 04:10 #17912 by Ranfurly
Replied by Ranfurly on topic S3 vs S4 Engine
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

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06 Jan 2015 07:25 #17913 by Giovanni22265
Replied by Giovanni22265 on topic S3 vs S4 Engine
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.

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12 Jan 2015 00:20 #17919 by Rich928
Replied by Rich928 on topic S3 vs S4 Engine
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.

Rich
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1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast

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12 Jan 2015 13:20 #17923 by Giovanni22265
Replied by Giovanni22265 on topic S3 vs S4 Engine
will the newer EZK spark system work with the S3 engine?

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12 Jan 2015 19:48 #17925 by Rich928
Replied by Rich928 on topic S3 vs S4 Engine
The 928 S4 EZK module will not work with the 1985 - 1986 Porsche 928. The 1985 - 1986 engines do not have the provisions for spark knock sensors and the cam position sensor that the EZK requires. The wiring harnesses are different, the 1985 - 1986 use a 25 pin connector to the module, the 1987 and newer use a 35 pin connector.

Rich
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1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast

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15 Jan 2015 09:55 #17935 by wallyp
Replied by wallyp on topic S3 vs S4 Engine
Remember that the Rest of the World (i.e., non-USA) market could choose the 16-valve or 32-valve engines in '85, and perhaps '86. Those last 16-valve engines are neat pieces, and very desirable.

Wally Plumley
928 Specialists
www.928gt.com

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15 Jan 2015 10:44 #17936 by Rich928
Replied by Rich928 on topic S3 vs S4 Engine
To add a bit more detail on Wally's comment, the 5-liter 32 Valve 928 motor for ROW was an option in markets that gave incentives for running lead free gas that was just coming on the market in some areas of Europe/world at the time. Those 928 ROW cars fitted with the 32 Valve motor had CATs .... it was the same engine as used for the US market.

The ROW 928s for 1984 - 1986 were 16 valve 4.7 liter motors fitted with LH and EZF spark control but no CATs.

Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast

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23 Jan 2015 08:06 #17955 by wallyp
Replied by wallyp on topic S3 vs S4 Engine
BTW - On the '85 and '86 models only, there is an "octane loop" on the cable from the EZF ECU connector. This is a single wire loop, with a connector in the middle. This wire should NOT be connected! When the wire is connected, it retards the timing three degrees to allow for poor grade gasoline. Connecting the wire will cost a few hp and mpg...

Wally Plumley
928 Specialists
www.928gt.com

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