911 head flows

[jluetjen]

Does this information match your predictions concerning flow and gas speed for 32mm vs. 36mm ports?

Predictions???

The only predictions* that I've made have to do with the empirical observation that 32 mm intake ports are good for 160-180 HP, 36 mm intake ports are good for 210 -220 HP and you could most likely straight-line in between those two points for a ROM estimate. I acknowledge that Jack and others may disagree with that observation and I'm certainly not looking to reopen that whole bruhaha right now. Since HP is really only a function of air-flow at the peak torque engine speed and how fast it drops off from there, I don't see any thing here that would disagree with that observation. The other observation which I'd make is that this represents the HP at one point on the rev range. How you manage the performance across the rest of the rev range is where the real art is, and this is a function of all of the variables in the engine and head design.

* The other predicition that I've made recently is 172 RWHP for TonyG's car -- and the jury is still out on that one!

Was that suitably evasive???

[snowman]

Looking at the graph I would say that my measurement at 0.1" is in error. Its possible its not but not likely to be correct. If you move the data up to match the line above it, it agrees pretty well with everything else. So I would say to do so if you use the data to sim the engine perf.

[jluetjen]

Jack;
Before you return the head, here's a way to determine if the 76 mm VW cylinder really was the factor in the low valve lift data point. Do you have any porsche cylinders for a larger engine -- say 2.4 or 2.7? If you can retest it with an oversize cylinder (since you don't have an 80 mm cylinder available), you'll get another data point. If the data point is still low, that will suggest that the cylinder is not the problem. If the data point goes back up, then it suggests that it might. Then go back to the original set-up with the VW cylinder and do a retest to confirm that there wasn't anything in the original set-up that would skew the data. Other options: A Baked Bean can is a little larger then 80 mm's and would most likely be suitable for the situation assuming that you could get it to seal OK.

[Tom F2]

I'm reviving this thread, because it seems to be the most extensive discussion of converting 2.4 T heads to 2.4 S, something that I would like to do.

Has anyone sliced a specimen of each kind of head, to see exactly how the port profiles compare? It's not just a matter of dimensions, it's all kinds of little details of how the turn in the port is shaped. Take a look at Smokey Yunick's book, he has some great illustrations of this, albeit in Chevrolet motors.

It LOOKS like a 2.4 T head will become the same as a 2.4 S head, if one opens the intake manifold side to 36 mm and the exhaust side to 35, and blends it in around the guide bosses, but that blending is critical.

So, tell me, can it be done and, if so, who knows how to do this?