Turbo S2?
03-18-2002, 02:22 AM
#16
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[quote]Originally posted by Danno:
<strong>Or even better, is to use both the 3.0l block with the 3.0l head. Since you're going to be making head modifications anyway, might as well do it on the better head. The 4v head flows about twice as much air as 2v head at high-RPM</strong><hr></blockquote>That may be true, but I think one of the main reasons the factory used the 8V head on the 968 Turbo S was cooling. I had a conversation with the owner of the very rare 924 GTP car at Laguna Seca during the Porsche bash in 1998 (see current Excellence for article about this car) and he said the production 16V head does not provide adequate water cooling of the head when used in a turbo installation.
<strong>Or even better, is to use both the 3.0l block with the 3.0l head. Since you're going to be making head modifications anyway, might as well do it on the better head. The 4v head flows about twice as much air as 2v head at high-RPM</strong><hr></blockquote>That may be true, but I think one of the main reasons the factory used the 8V head on the 968 Turbo S was cooling. I had a conversation with the owner of the very rare 924 GTP car at Laguna Seca during the Porsche bash in 1998 (see current Excellence for article about this car) and he said the production 16V head does not provide adequate water cooling of the head when used in a turbo installation.
03-18-2002, 10:24 PM
#17
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It's not too hard to fix though, you just need to do a little porting of the passages for better flow, and add a higher volume pump.
Why go to all the trouble of modifying a 2V head, and adding low compression pistons and cylinder sleeves and many thousand of dollars, when a 951 motor can be had for $2500, and a stroker kit for another $1500 or so, and you get to sell the 3l for $4000 or so?
I think I could turbocharge a 3L if I could find low compression pistons. They have to be specially coated however, because of the block compound. Hence the cylinder sleeves and different pistons.
Why go to all the trouble of modifying a 2V head, and adding low compression pistons and cylinder sleeves and many thousand of dollars, when a 951 motor can be had for $2500, and a stroker kit for another $1500 or so, and you get to sell the 3l for $4000 or so?
I think I could turbocharge a 3L if I could find low compression pistons. They have to be specially coated however, because of the block compound. Hence the cylinder sleeves and different pistons.
03-19-2002, 02:57 PM
#19
Race Director
"I think I could turbocharge a 3L if I could find low compression pistons. They have to be specially coated however, because of the block compound. Hence the cylinder sleeves and different pistons.
People have used the the 968 pistons milled down a bit for lower compression:
Then you can get 1.0mm shorter H-beam rods (much, much stronger and lighter than stock I-beam rod):
Finally, top it off with a thicker headgasket and you're set at about 9.0:1 compression (Audi uses 9.5:1 on their turbo, Porsche GT1 has 9.5:1, Porsche 996 has 9.x:1?).
The reason you want to go with a 3.0L 4-valve head is the higher power potential. Larger capacity than 2.8L with stoked 951. Better combustion-chamber shape with higher-flowing heads. You can get equivalent power with a wider non-dropping torque curve at lower boost than a modified 951 engine. This is old news really since David Chen (San Jose) built a 968-Turbo sleeper over 6 years ago. Dwain @ Vision had his 968-Turbo featured in the Oct-2001 issue of European car. Both used modest boost levels compared to a 951 and had much better throttle response with less lag. Dwain's car at 18psi of boost got 500hp!!! That's about 200hp more than a 951 at the same boost...
People have used the the 968 pistons milled down a bit for lower compression:
Then you can get 1.0mm shorter H-beam rods (much, much stronger and lighter than stock I-beam rod):
Finally, top it off with a thicker headgasket and you're set at about 9.0:1 compression (Audi uses 9.5:1 on their turbo, Porsche GT1 has 9.5:1, Porsche 996 has 9.x:1?).
The reason you want to go with a 3.0L 4-valve head is the higher power potential. Larger capacity than 2.8L with stoked 951. Better combustion-chamber shape with higher-flowing heads. You can get equivalent power with a wider non-dropping torque curve at lower boost than a modified 951 engine. This is old news really since David Chen (San Jose) built a 968-Turbo sleeper over 6 years ago. Dwain @ Vision had his 968-Turbo featured in the Oct-2001 issue of European car. Both used modest boost levels compared to a 951 and had much better throttle response with less lag. Dwain's car at 18psi of boost got 500hp!!! That's about 200hp more than a 951 at the same boost...
03-20-2002, 03:40 AM
#21
Race Director
Well, the 'special' characteristics of the pistons pretty much requires you to use the stock S2/968 pistons for compatibility. If you go with aftermarket pistons, you want hypereutectic pistons for low-expansion (block doesn't expand much). Or else you're going to get rattling pistons until they're warmed up. Also an iron-coating on the sides for abrasion resistance.
You can get those 4340 chromoly rods from just about anyone; they're pretty much household commodity items in the performance market place. It looks like a Manley rod in that photo. Unless you know all the engineering specs and dimensions, I would go with a 'tuner' who has experience with these Porsche engines.
Check out Garrity Repta <garrity928@mindspring.com> at <a href="http://63.69.86.102/garrity/Performance.htm" target="_blank">Performance Auto Works</a>
or Scott Gomes <BodyWrksIn@aol.com> of Under Pressure Performance. Scott's the only one who've built a 500rwhp+ 951 that has a dyno chart he can send me. A 968-based 4-valve engine has gotten over 600rwhp. So these guys knows what they're doing. You won't get much info out of them though, so you just have to tell them what you want like, "set of 1.0mm shorter S2/968 4340 H-beam rods for a turbo project."
You can get those 4340 chromoly rods from just about anyone; they're pretty much household commodity items in the performance market place. It looks like a Manley rod in that photo. Unless you know all the engineering specs and dimensions, I would go with a 'tuner' who has experience with these Porsche engines.
Check out Garrity Repta <garrity928@mindspring.com> at <a href="http://63.69.86.102/garrity/Performance.htm" target="_blank">Performance Auto Works</a>
or Scott Gomes <BodyWrksIn@aol.com> of Under Pressure Performance. Scott's the only one who've built a 500rwhp+ 951 that has a dyno chart he can send me. A 968-based 4-valve engine has gotten over 600rwhp. So these guys knows what they're doing. You won't get much info out of them though, so you just have to tell them what you want like, "set of 1.0mm shorter S2/968 4340 H-beam rods for a turbo project."
