interesting work on the throttle body flange...

 

its a S2 throttle body with 951 turbo throttle spindle & cam machined to fit and aftermarket TPS fitted....

 

Do these larger displacement engines require a different intake manifold, in any way other than fitment? Do they require a corresponding increase in intake air volume through the intake, or does a stock 951 intake flow well enough?

 

I cant say whether they do, however there are a lot of high horsepower 951's using the stock TB and manifold, I would have expected the air flow to match horsepower more than engine size.
I used part of the 951 manifold log and runners matched to 968 runners to the head, then all port matched and cleaned internally, also used the 944S2/968 flange and TB.
However the plenum volume is too small if you calculate based on engine capacity, what impact I will never know.

I actually wasnt looking for absolute power but wanted something that looked factory stock best I could.

 

While arguably de-tuned, the original 968 Turbo RS used a similar setup (stock 951 intake/TB). The Intake may not be the limiting orifice in the system.

 

based on some flow numbers thrown around these parts (RL), the dohc head ports flow more than the 951 intake.

so ideally you'd have a fatter-runner intake to maximize the flow...but boost can make up for lots of shortcomings.

that said, i think it's worth exploring a larger TB for these engines. at least big enough to match the hole on the manifold (~60mm)...the 968 uses the same size as the 944NA/944S/S2/951, a 55mm blade...but the larger displacement "should" call for a larger tb.

i know its apples to oranges, but the ford 4.6 2v puts out 260hp (not a whole lot more than the stock 968, but with much smaller cylinders) and ford saw fit to use a 65mm tb there. and mustang guys find a few horses here and there (5-7whp) by going up to 70 or 75mm tb.

 

Actually the S2/968 TB is larger than the turbo thats why I used the S2 throttle body and it does need the original manifold to be opened up had to do exactly that process to fit the S2/968 flange, so its does what you point out V2Rocket

 

how much larger??

 

Cool. Thanks for the replies.

 

Is the bolt pattern the same as a 951 TB?

 

I cant remember exactly it was a while back about 3-4mm larger in diameter of the throttle plate, when you put them up against each other its quite noticeable.

Tom, the flange hole centers are much bigger 70mm vs 62mm so not the same