V2Rocket

I see a lot of research here for S4+ stuff but haven't yet found flow figures for the S3 heads.

While the ports are radically different shapes, the cross-sectional area is very similar from S3 to S4 (when imagined as a circle of equivalent area to the actual port, the "port diameter" for both heads is about 47mm).

The S3 of course also has 35mm intake valves vs the S4+ 37mm.
The S4's port is wider which should lend itself to feeding the valves better.

PorKen's chips show that an S3 engine with chips and exhaust puts out very similar power to an S4 with chips and exhaust. So there is good flow in the S3 head, but when do they run out vs the S4?

Carl's flow figures for an S4 are ~260cfm @ 28" at 0.400" lift. I don't need to know flow figures above 0.400".

I would expect the S4 to outflow the S3, but by how much?

SMTCapeCod

Here's a little commentary.
https://rennlist.com/forums/928-foru...s-pistons.html

Can't recall whether any of "Slate Blue" build threads got into S3 flow.

V2Rocket

I've gone through the threads and didn't see much, maybe I missed over what might be there.

Even if the S3 flows 10% less than the S4 I will be content...I know "flowbenches are like dynos" and they can vary and not be a perfect predictor of running-engine performance but they are a useful yardstick nonetheless.

I am sticking an S3 head onto a 944 Turbo bottom end (after cutting valve notches of course) and will be boosting it...just curious.

Stock 944 8v head is 190cfm or so around peak lift, stock 944 16v head is 280-300cfm depending who you ask and what lift they run.

S3 being at 240+ would be good enough for my uses, but the more the merrier

ptuomov

Why?

V2Rocket

To get 4-v head flow while keeping the same combustion chamber volume as the 2-v head, keeping the CR roughly the same (8:1) to boost safely on CA's finest 91AKI pump gas. (944S/928S4 head puts the CR with 951 pistons at over 9:1).

944 2-v (turbo) exhaust manifolds bolt up to the S3 heads which means no expensive 4-v headers have to be fabricated.

S3 heads themselves are inexpensive.

There are 2 other folks trying this experiment as well but I don't know how far they've gotten yet. "Just to see if we can."

ptuomov

What cams will fit to the S3 heads that work with a four cylinder turbo motor?

V2Rocket

944S camshafts fit.
I had to have the lift on the cams cut down to 10mm though because the stock 11mm intake lift looked like it was touching the casting.

My engine will be supercharged so the requirements are a little different from the turbo stuff...but you can play with the cam timing enough to make it work. Not optimal, but neither is the budget.

That said, 4v 944 turbo guys use the stock cams and get 400-500-600hp with good spool.

BC

I'm sad you cut the cams. Someone here made a tool. To cut the casting for more lift.

ptuomov

Strosek Ultra

V2Rocket

the cams had heavy pitting on the tips so they needed service.
I would rather cut the cams than the head.

I am not convinced that 1mm of lift by itself (without touching duration) makes all that much difference, based on 2 data points...

1) the 944 2v engine got a revised cam with 8 degrees more exhaust duration and 1mm more exhaust lift after 1985, and along with a revised DME the net power gain was 4hp.
2) the old "rule of thumb" that not much more airflow is gained once you lift a valve more than 25% of its diameter, due to curtain area equaling valve head area. in this case 10mm (new cam lift) is still 28.5% of the S3 valve diameter (35mm) and that's what Porsche chose as max lift on the production S3 cars anyways.

Plus...it's 1 less mm I need to cut into my pistons, my goal is 0-interference. And it will keep my springs happy...

Imo000

How much material will be left after the flycutting?

Strosek Ultra

How did you cut down the lift? The cams need to be regrind with a different profile having one less mm lift to achieve what you want. For high lift cams I have made a special tool for further cutting of the cam lobe cutouts at the lifter bores.
See post #286.
https://rennlist.com/forums/928-foru...ughout-20.html
Åke

ptuomov

Wouldn't you get the desired compression from simply using the 944 16v head and dishing the 951 pistons? From memory, the 951 piston squish pads are asymmetric and too large for any of the 16v heads. If modify the piston and/or the 16v 944 head combustion chamber instead of fitting 928 S3 heads. That said, I understand if it's just a question about whether one can do it. This is a hobby after all.

V2Rocket

The 951 pistons are plenty thick but I have a junk one I'm going to cut up to measure thickness so I know what's left, will put that info here when done.

I had Web cams do the work, maybe they changed the profile but I don't know off hand. I'll see the cams in a few hours and post specs.
I have a low miles assembled 951 short block and will be cutting reliefs "in situ" with an in-head fly cutter courtesy of lindy tools.

Removing pistons for face milling is more than I want to do- if I were going that far I'd get custom pistons whipped up.

Strosek Ultra

If you have had the lift reduced by one mm WEB Cam they for sure has put on another profile. One other solution is to regrind the lobes with the same profile reducing the base circle diameter so the top of the lobe will clear the edge at the lifter bores. The maximum valve lift will be the same (not reduced) but you will end up with another problem of the valves being too short which can be corrected by lash caps. Also the valve spring installed height has to be corrected by skims under the spring base in order to keep the valve spring pressure unchanged.
Åke