kccampro

Ok, so I currently have an S3 and an S4 32v motor in the garage. My plan is to have the S3 cams modified and put them in the S4 motor. From what I’ve read about the S3 motor it is less powerful mainly due to the ECU parameters and the intake design. I’m going to be using an MSIIv3.57 and an EDIS-8 ignition no matter which motor I use so stock fuel mapping is not a factor in either case.

So here’s my question, if the S3 cams are closer to GT cam specs, is the S3 motor the better one to go with assuming I can use the S4 stock intake? Or is there another reason to stay with the S4 motor and have the S3 cams modified to work? There is another part to this which is the S4 motor has less miles than the S3 but lets assume all things are equal for this question (comparable compression, etc).

atb

The S4 heads and intake flow better than the S3. The S3 cams are more agressive.
I'd say you're on the right track for the best combo of parts.

ptuomov

* S3 lobes are the same as GT lobes, but the lobe separation angle is different. LSA is 110 for GT, 114 for S3 (from memory). S4 has "smaller" cams, and 106 LSA.
* S3 has no knock sensors if remember correctly.
* S4 has bigger valves and a smaller combustion chamber than S3. S3 has a bigger piston dish.
* For a normally aspirated engine, someone should roll the dice and put S4 heads on a S3 short block. For a turbo engine, someone should roll the dice and put S3 heads on a S4 short block. I think the latter has been done.
* Neither intake manifold is going to shine at high rpm.

I guess for an univentful build, I would start with the S4 engine. Then, I would get the S3 cams modified and reground and the head shaved a bit to give a higher effective compression. Search for Dennis Kao's 5.0 screamer motor to see what can be done.

kccampro

The thought occured to me to use the S4 heads on the S3 shortblock but I've read other posts that would put the CR way above what I can handle on pump gas.

Thanks!

ptuomov

I am exercising my powers of reading minds and see that here's what you want to do:

https://rennlist.com/forums/928-foru...and-video.html

When I first saw the results and the minimal invasive surgery needed, I though "holy **** this is the best 928 engine build ever."

Email / pm DK and Jim Morton, they'd probably be willing to tell you a lot more about the build.

Lizard928

The dish on the S3 piston is smaller than S4 pistons.

If you want NA then you can use the S3 shortblock with S4 heads and get a little over 11:1 CR which is not too high.
I personally prefer the S3 heads to the S4 for a few reasons. But you could always use the S3 head and just put bigger valves in it.
Keep in mind that from what I have heard from Louie and Porken is that the S3 motor is far less prone to knock. I believe this is due to a much higher port velocity.

Either way you will have fun. If you do put the S4 heads on the S3 bottom make sure to check valve clearance as you may have to notch the pistons a little.

kccampro

Yes, I've been reading and re-reading Dennis's threads and I already reached out to Jim about my desire to run the S3 cams in my S4 heads. Great info.

Thanks... yet again!

danglerb

Why limit yourself to any of the fairly mild stock cam grinds?

mark kibort

If its NA, that 11:1 looks attractive. Im near that right now with my stroker, with stock S4 heads and I still use pump gas with no issues. I think we went through the calculations,and I seemed to remember the CR to be more like 11.5:1.

GlenL

That's on the edge for pump gas but with the ECU and knock sensors from the S4 it'll be safe.

ptuomov

Doesn't that critically depend on the cams, specifically on the intake closing event timing?

123quattro

With knock control and the ability to tune the spark curve, I wouldn't be afraid to run 11.5:1 on 93 octane. I wouldn't if only 91 was available.

Rick Carter

AFAIK no one has dynoed S4 vs S3 intake. A tuned S3 motor seems to have more power than a tuned S4 motor but not a tuned GT motor.

James Bailey

Wonder why some GTS engines have had issues with detonation on California "premium" pump gas ??

Tom. M

Colin had converted his old S3 engine to MS and was able to eek out about 310 or 315 on Louie's dyno. We then put that MS system on my track car (91S4 engine0 and it put down 320 ish..and with some minor tuning it got 330 rwhp. I still have some more tuning to go, and need to free up the exhaust too..so I expect even more out of it.

I also think Ken (Porken) has gotten about 315 out of one of his...(but as with Ken..there are a bunch of asterisks and notes about the runs..which I have forgotten what they mean )

And if you add in GT cams (or modified S3 cams) to the mix....the numbers go up from there...