ptuomov

Maybe it's the cams. I think it'll depend a lot on the intake valve closing event timing and the velocity of the charge entering the chamber. Later closing, less knock. Higher velocity, less knock. Both are influenced a lot by the cams.

FBIII

My GT engine is complete except for one 3R head. I have a good S3 shortblock and a pair of good 2R heads . I have been seriously considering the S3 bottom end with the S4 heads and GT cams. Do I just need to take a GT or S4 piston to the machine shop with my S3 pistons and have them mimic the cuts? I figure going this route will save me the immediate difficulty of finding the 3R head and once found I would have the original GT engine as a spare.

GlenL

Not exactly but to some extent. What makes the charge pop is absolute pressure. If you've got cam timing that keeps volumetric efficiency down then the pressure on the compression stroke will be lower.

ptuomov

It's kind of complicated. I don't understand it, really. Temperature matters, charge turbulence matters, etc.

These guys claim to be using all the tricks in the book to run very, very high static compression ratios without detonation: http://theoldone.com/

Lizard928

Tom,

just to expand on your info. My car put down 310rwhp and 320 lbs ft
that was with a dual 2.25" crush bent exhaust system with a really bad H in it.
The other thing to note is that the motor in question had some serious gouging on the number 6 cylinder. It had around 80% leakdown on that bore...
And my tune was fairly concervative as I did not have any knock sensors for tuning.
I believe the damage to the bore happened prior to the install, and was caused by the piston coating failing.

Who knows what a properly tuned S3 motor could put out, but I would bet with a good exhaust 330-340. With a different intake there is loads more to be had, add cams etc and it keeps going up.

928SS

iirc, the US S3 put out 288chp. not sure how you'd get nearly 50 rwhp out of exhaust alone, but Kragen might have something that'll claim to get you there, lol.

it's a slippery slope when you start messing around like this. as you increase airflow, other stuff needs
to change - exhaust, intake, fuel delivery, tuning, etc...

I put GT heads on my S3 block in my 85S stroker. it's not a trivial conversion, but worked out well for me, after I changed everything else.

intake manifolds are NOT interchangable

I believe the Flappy in the later intakes can actually help produce a fatter torque and HP band by tuning the plenum length to 2 different RPMS. F1 cars take that idea and have fully adjustable TB's that allow the length change to an infinate variation of RPMS, and seem to pull a lot of HP out a small displacement as a result (along w/a few other tweaks). the S3 intake is fixed, so the best you can do is tune for a single specific RPM.

electronics need to be upgraded if you plan to implement the flappy in an older car. it wasn't too bad on mine, once we figured out which wires went where, lol

cams are NOT simply swapable - the S3 cams are longer, need to be cut down to fit properly, and there is an issue w/one of the journals that needs a bit of modification.

if you have an S3 block -it's great for boring out because the cyl walls are cast a bit thicker, so it's easy to get 104 or so mm out of them vs the 100mm bores

a lot of the HW is NOT swapable either - covers, tbelt stuff, intake linkage, etc... imo, the later cover HW is MUCH better than those stinking shoulder bolts the S3 uses.

the S4/GT heads can take a larger valve than the S3 heads with less work, although I believe doc Brown managed to get 968 sized valves into an S3 head with a lot of coaxing. power was about the same at the end of the day, IIRC. (could be wrong on that though, doc Brown would know details)

using the later heads w/968 valves, regrinding GT cams or regrinding/modifiying S3 cams, punching out the cyls, slapping in a longer stroke crank and using GTS stuff is really about the best you can do for a NA 928 motor, sharktuning, maybe a 928SP blackbird intake, headers, more or less, imho.

Greg Brown at Precision Motorwerks in Anaheim does this type of work, and builds some mean NA motors after he throws in a few of his goodies and magic sauce. there are a few threads about his stuff here.

bout all I can remember off the top of my head, hope this helps

BC

Of the two, my vision for a new motor is the S3 bottom end (rebuild, drilled, coated, etc) and S4 heads. 11:1 or higher compression, and ethanol. And then boost. The cams would be S3 or higher, like Simard's Cams or Colins. Custom intake, or a heavily massaged Stock S4 intake. With that you would need to have the ECU deal with variations in flow. MASSIVE variations. I don't see why we can't surpass 400 rwhp with no boost. Add boost and the sky is the limit.

Yes - I said 11:1 compression AND boost. You can do that with ethanol. With no detonation, you simply do not have to worry about blowing it all up as much.

Hilton

Aussie rennlister "john gill" has done the former I believe - although he used an Aussie S3 bottom end, which is slightly lower static compression than US S3, as its the smog motor version originally sold in Australia, Switzerland and as an option in Germany.

Lizard928

I am doing the S3 heads with S4 pistons for my twin turbo motor.
Also the S4 manifold can be used on an S3 block but you need to cut off 2 tabs off the block. The S3 manifold will bolt up to the S4 heads but there are no bosses on the block to hold the TB. This can be fairly easily bypassed though.

That said however the S4 and S3 intake ports are of different shapes and it would take some work to get them to mate perfectly.

Also Rob, what you are talking about is a stroker motor which if the OP had the $40K+ to spend on a motor I imagine that he would have already have called and talked to Greg.

SQLGuy

I actually installed an S4 manifold on my '85 S3. I didn't do any before and after dynos... sorry. I also think that the car always ran too lean, and that was not solved before I sold it, but the manifold DID bolt on just fine and the car seemed to me to run better with it than with the stock manifold.

The S3 intake ports are about 2mm smaller than the S4 ports, but the centers and bolt holes all line up. Porting might not have been a bad idea, but Lucky, over at Devek suggested that I might actually have some benefit with the port edge stripping off the dead air near the walls of the manifold.

For the flap, I rigged up a schmidt trigger circuit based on applying a high pass filter to the CPS signal, and also tying in the load signal from the EZF MAP sensor. The tricky thing was that the CPS amplitude also changed with temperature, so, IIRC, I had to buffer, rectify, and filter the all pass signal and compare that to the buffered, rectified, and filtered high pass signal to get a consistent analog >3000 RPM indication.

(BTW, I'm pretty sure I still have all the pipe organ pieces around in a box somewhere,...)

Hilton

One trick they don't mention (which is somewhat contentious) is Singh Grooves cut into the quench area?

Some of the reading on their use from hotrod builders, and places like the volvo turbobricks forums, makes for some interesting and thought-provoking information, if a little anecdotal at present; lots of people seem hung up on whether it directly makes more power.. a very few experienced builders say it enables a very non-traditional style of tune vs. AFR's which can increase power, reduce fuel consumption, and make a difficult engine much more tractable.

It has occurred to me that S4 heads, S3 bottom, bigger-than-S3 cams, and some swirl-enhancing, detonation-reducing modifications like grooves, higher port speed, staggered-event cams, and more, could make a high compression pump-gas engine very driveable for street usage.

But I know even less than Tuomo, and am too easily swayed by innovation over tried and tested, so chances are if I tried to build an engine it would explode on first start. However, if I could persuade someone else to do it and give me their build notes should it succeed, I'd be happy to try it

ptuomov

This I believe is not the conventional wisdom. I think the conventional wisdom is to have the head port, gasket, and runner be flush or the port slightly larger. I have no idea whether the conventional wisdom is correct.

Mike Frye

True, but the exhaust is not the only thing holding the S3 back. The stock tuning was WAY conservative. The intake may also be limiting it some.

Ken has dyno-ed over 300rwhp with his new chip/FPR and I think some exhaust mods.

My car dynoed at 292 at the wheels with the following mods:

Autothority chips (they don't increase HP, just give a huge fuel dump during the cruise map, no change at WOT AFAIK)

Air pump delete

Lomas X-pipe

Intake refurb and smoothed out the casting marks inside as far as I could reach with a dremel.

Cams advanced 2 deg (which probably lowered the top-end, but moved the torque hump down a bit in the RPM range, where I like it).

Stock cat-back, stock air filter setup, stock FPR.
********
Since then I've added Porken's chips, 55psi FPR and my snorkel CAI filter setup. Once I get the transmission fixed and back in I plan to dyno again. I'll post results.

SQLGuy

If you're talking about the intake ports here, then this is also not conventional wisdom. Believe it or not, you actually want a rough surface on the walls of the intake ports to help break up fuel puddling.

Mike Frye

Sorry, meant intake runners: I'm pretty sure they're supposed to be round on the inside.

I think Ken went one step further and matched the intake ports with the intake runners so there was no 'lip' at the transition. I didn't do that.

I was very disappointed in the quality of the casting on the intake runners and the cam covers when I got them stripped down to bare metal. I would have expected better from the 'flagship of the line' in the 'big 80s'.


BTW- to the OP: That 292-300 rwhp is comparable to stock GT numbers. Obviously with some exhaust mods you would be able to go above that for an S4/GT, but it's much closer than the reported stock numbers would lead you to believe, and much of it is available from just tuning/fuel delivery as Ken has shown.