Porschefile

That's cause it's just too cost prohibitive for most people unfortunately. I wish there was a more cost effective solution sometimes, to the point where I feel like doing a non-Porsche motor swap out of pure anger for the convoluted 944 motors. The 8v heads definitely suck, efficiency wise, though it's not such a big deal. Just beat the head to submission with copious amounts of boost!

Fishey

I don't see why its so cost prohibitive to run a 16v head. It really doesn't take to much in terms of $$ to change to the 16V head other then the cost of the head itself.

hot-J

Actually, he sees full boost just before 4k at 38-3900

Porschefile

Because the 16v conversion, that comes with the attached 3.0L is pretty expensive! Seriously, doing a turbo conversion on an S2 or 968 motor is pretty expensive as a good condition motor is generally going to be around ~$4k alone, then factor in a turbo, manifolds, etc, etc. Or there is the 944S route. Supposedly the S head will bolt to the 951 block, though I've heard the water jackets don't line up and if that's the case it will require some custom work. The few times I've seen those heads for sale they seemed to be around $1-2k. Then you have to have custom cams made if you really want to do it right. Then there is the issue of tuning, custom manifolds, etc.

Porschefile

You sure it's a Greddy T78? He must have switched to a smaller hotside as all of the dynos and numbers I've ever seen are around 4.5k.

hot-J

It says t-78 on it, and the hotside is bigger than my 60-1 #10 by far. We do have a sneaking suspition the internals were reworked, just because of the responsiveness, but cant justify cracking it open to check.

hot-J

Oh and yes the 16v is an insane amount more $$ to do it RIGHT.

toddk911

Didn't Porsche use a 2 valve head on the 993TT and single cams?

I know a lot of people said that was a mistake, but Porsche said they gto better results their way.

?????

toddk911

So save the 1-2K on the 16V head approach and put that towards a REAL nice, highly effecient turbo instead.

AL951

Toddk911,

You are correct. The 993TT is 2 valves head and a single cam.And not only that, it is the same basic engine Porsche use for their all magthy turbocharged 934, 935 and the US version of the 962. They do differ on the design part to our engines though. The 911 engine has hemipherical chambers, that are more turbo frendly.Ours look more like a Ford 5.0 or Chevys 350 or Ls1.

The main reason Porsche didn't use a 16v head on our cars was that of cost versus benefit. You have to remenber that back in the 80's The japonese car were not that powerful. Nissan could only get 200 Bhp form a 3L V6. Misubishi 178 Bhp from 2.6L. and Toyota with a 24v 3L inline 6 could do no better that 227 Bhp ( somebody correct me if number are not right).All were turbocharged, So to Porsche didn't make sence to install 16v head. Even with 217 Bhp the power-to-weght ratio was in favor of the 951.


Regards,
AL

toddk911

Great Info Al!

Also, I saw the comparrison of those Asian cars with the 944T and it proved to be #1 in almost all categories, proving Prosche did not need the 16V head I guess

I rememebr reading the broshure on the 993TT and seeing "hemispherical head" and saying "hey, the 911 has a Hemi head!!

So ours is more of a flat head design?

hot-J

Can anyone that is currently running a GT turbo post thier mods, and dyno graphs? A few people have responded they have them, lets see how benificial they are on our cars. Eventhough we ran alitttle off topic here, this has proven to be an interesting thread.

AL951

Yes, our heads looks very simular to an American V8 engine, with the major diffrences of the cam location. But I dont see that as a major problem, after all their are plenty of Twin turbocharged Ford and Chevy V8, making insane amonts of power. Also ST has demostrated that big power can be had with the "inferior" head design of our cars.

Regards,
Al

Porschefile

Yep, they're 2v SOHC. Though ultimately Porsche stuck with a 2v design due to cooling issues. They've experimented with 4v DOHC heads for decades. I believe one version of the 935, as well as some variants of the 956's and 962's (and heck, the 936 for that matter) use aircooled blocks and special watercooled 4v heads. The production 959 used an aircooled block and DOHC 4v water cooled heads as well (at least I'm pretty sure the block was aircooled) In aircooled only form they just don't have the proper cooling capacity for 4v heads. Ultimately a 4v head is more superior as the spark plug is generally placed in the most efficient spot, the center of the combustion chamber. This provides a faster and more efficient burn and helps resist detonation.

toddk911

I agree. It has been, and continues to be proven, that hot spots and pre det. are issues of poor tuning annd not motor/head designs.