16 valve turbo

[ds475]

easy question for you gurus, but was there a year when the turbo came stock with 16 valves? which 944's came with 16 valves?

[Britwrench]

No, all the 944 Turbos (86-92 ROW, 86-90 2.5L US) cam with 8 valves.
The 994S (87-88 2.5L) and 944S2 (89-92 ROW, 89-91 3.0L US) were 16 valves. All street production 968 (92-95) are 16 valve. Limited production (and never available in the US) 968Turbo was 8 valve.

[ds475]

wouldn't a 944s/s2 turbo converted be able to have a LOT more hp in relation to a regular 944 turbo running the same specs?

[Ebs]

I have never seen a 16 valve turbo 944. I believe even the Turbo 968 RS was only 8 valves.

[ds475]

why is the 16 valve turbo not pursued more often?

[Britwrench]

Simply because there's no point. The 8V Turbo can be modified to as much power as anyone can use, reliably. The 16v offers no advantage.

[ds475]

couldn't the 16v wind up quicker? breath easier and in return have more power?

(i'm not a mechanic, so bear with me...)

[Britwrench]

In theory, you are probably right. In practice there has been so much development of the 8V both by the factory and by independent tuners that the 16V is now out of the picture in the aftermarket.

[350HP951]

16V offer a lot of advantages to 8V depends on what you are trying to accomplish. The reason no one is using the 16V head is that they are hard to come by and are not cheap. That being said in response to your question about an S2/S being able to make massive HP the answer is not really. The CR is too high on the S/S2/968 to run a lot of boost and have a motor that still runs. There are pistons available (came from PMNA) to run lower CR in the 3.0L engine and run 15 maybe even 18 psi.

The converted 968s tend to make a ton of torque and are probably a blast to drive even at only 6 psi.

[ds475]

thanks guys, for sharing your knowledge.

[DannoXYZ]

THe main advantage of 16V over 8V is high-RPM flow. The 16v heads easily flow twice as much as the 8V ones. If you've seen dyno-charts of 8V upgraded 951, you'll see that the torque-curve drops like 25-30% from its peak at redline. That's why it's so hard to get an 8V car over 450rwhp. You have to do extensive head-porting, cams, valves, 4-1 headers, custom intake-manifold with shorter runners, etc. To get 450rwhp from an 8V car, you're looking at 25-26psi.

With a 16V head, you can flow a lot more in the upper-RPMs. Due to the lower restrictions, you'll need less boost to flow the same CFM of air. Problem is Porsche never made a 16V 944 Turbo aside from the 924GTP prototype that had 420bhp. So you have to fabricate all your own parts like an intake-manifold and exhaust-headers. Check out the Oct. '01 issue of European Car. Vision had a 16V 944 Turbo conversion. It made 525rwhp @ 18psi boost.

[Wolf1]

This dyno chart shows the difference between an 8v and 16v engine at the same boost levels.

[swilliams]

Careful, too - the first 16V heads were interference types; you goof the belt, you lose the motor - big time. Stick with the S2 head!

[DannoXYZ]

Uhh.... ALL of the 8V and 16V heads are interference designs...

[Shawn Goodwin]

in 1981 le mans, porsche ran a 924 GTP, which was a tubo charged 16v prototype of what later became the 944s motor.
see "excellence" magazine, may 2002 for more info.

[swilliams]

Caught me talkin outta school, Danno! The 924 2.0 liter was not an interference type, the rest of the breed are. I have always been told, though, to avoid the expensive, and fragile 16V head like the plauge - I guess I merged some information. I hope no one reports me to Zuffenhausen!

[tab tanner]

swilliams, If a 924 2.0 is not an interference engine the tell me why I have repaired three non turbos and two turbos, they all had broken belts and bent valves?? Maybe you know somthing I don't

[swilliams]

"The timing belt in a 924 is reported to be far less finicky than the 944 or 924S. Since the 2.0 engine does not have an interference design where the pistons and valves share space, a failure of the timing belt does not produce the kind of expensive collataral damage as in the case of the 944 or the 924S, viz. a piston hitting the open valves, necessitating an expensive engine rebuild. While the maintenance interval for the 924 timing belt is the same, the expensive tensioning tool is not needed."

5.6.1 Timing Belts

http://www.rennlist.com/944values/9685.htm

[tab tanner]

swilliams
I'm not argueing, I just though I missed somthing. Since the 924s that I worked on where interference engines. I'll look at the tread Thanks

[Wolf1]

The 924 2.0 liters that I have torn down look like non-interference type to me. The piston remains about 1/4-3/8" below the block at tdc.
However, some of these old relics are using different pistons to increase compression ratio, these could easily cause interference in the case of a slipped or broken belt.