Jack; Is that the TK head that I sent in??? You might also want to measure the ID of the ports every 1/2 inch or so to see if there is any point where the port dimensions are the same. I suspect that the answer will be that they are not the same until the bowl.

Thanks again for offering to flow the heads!

Yes, its your heads, cleaned up a bit. I will try to measure everything possible. Should be doing it early next week.

What I got from Snowman was that it's not necessary to increase the flow of the heads. So, suppose I have a 2.7, and say I want to run an early S cam. It doesn't matter whether I have 32 or 36 mm ports, because either one will provide more flow than the engine can utilize?

Now, if I assume that 36 mm is the optimum size for the ports on a 2.7 engine with S cams, am I better off opening up 32 mm heads to 36 mm, or should I leave the ports at 32 mm, since I would probably do more harm than good to the heads by porting them to 36 mm, by myself?

I don't recommend any serious porting on ANY heads without the aid of a flowbench and a littte experience. Incorrectly ported or uneven flowing heads will often produce less HP than a stock head. It's OK to port match them to the intake and exhaust as long as the bare minimum of material is removed and it's the same on all the heads. If you had a 36mm head to compare against I suppose you could open up the 32mm heads using the 36mm as a reference but even that is risky. The best and most usable power will come from heads ported by a professional will experience and testing on you type of heads and motor.

!!!!
 

I agree. Port match your heads, ie match them to the gaskets, nothing more. I noted the 2.2 heads did not need changing, I have not analyzed the 2.7 heads.

I do not agree that a "professional" must port the heads. All you need is a little knowledge, available from a number of sources. You MUST flow test the heads however, to KNOW that you have made an improvement. To flow test only takes a homemade flow bench. Whats needed? Just a shop vac and a couple of feet of plastic tubing, and a couple of books, available from most librarys.

What else is needed??? Something like DYNO 2000, an engine simulator program. This will enable you to know if you have gone far enough in your porting.

I have seen several 2.2 T heads and S heads now. The S heads seem to be T heads with the opening at the intake port, opened up to match the rest of the intake port size. Looks to me that Porsche designed the S head, had it cast, a bit smaller than necessary, probably so they could accurately control the port size. Then for the T head, they left it alone, for the S head they machined it out to 36mm. Again most of the diffence is AT the opening, the rest of the port seems to be almost at size already. OR was it really this way, Porsche had a good design, and marketing had them close it up, to make a lower performance engine. I really think it looks as though thats what they did.

Why do I say this? Well running the engine dyno program I can get numbers that agree with Porsches numbers for HP. But playing with the numbers, it looks like Porsche had a 180 Plus HP engine, and did everything they could to tone it down, almost without success!!! Even the T cam, if retarded 10 degrees, yields 150 plus HP!!!

Its been long enough, long enough for Porsche engineers to have retired, and , be willing to tell the way it REALLY was. Any takers???

911s; That's the point of this thread. Snowman says "Yes -- leave them at 32 mm", I say "No -- open them up to 36 mm or better yet 38 mm". Snowman has based his conclusions on his analysis and the results from the modelling program that he describes. I've based my conclusions on a fairly wide ranging analysis based on published data on 45 different 911 models. I've also tried to validate my model based on blind predictions of the results for at least another 10 engines. While not perfect, I did tend to be "in the ball park".

Snowman has an S head of mine (36 mm ports) and a TK head (30 mm ports) of mine to measure on the flow bench that he has access to. Hopefully someone will also share a T or E head with 32 mm ports as well as an SC or Carrera head to complete the analysis. Once he's done we should hopefully have some hard data about head flows.

As far as making any changes, once again there is a difference of opinion. Some say leave to the pros. I don't buy in to the whole "black magic" thing myself. I agree that the best way is to have a model like a real "S" had to copy and then use a flow bench to confirm the results. But if you are careful, just doing a good copy of the stock "S" ports will most likely net you most of the results in 95% of the situations. Worst case is you can have someone plunge a mill into the ports to open them up to the nominal desired diameter and then you smooth the transitions yourself. A number of guys have done this on this BBS and are not complaining of the results, even when raced competitively. Finally, I would also agree that if you are going to race your car competitively and want the last 2% from your heads, your best bet is to have a pro do it since there are still details of the bowl and seat area which I am just about clueless about. But then you are into the question of which "pro"?


Ultimately the right thing to do to your engine is up to you.

I have a set of 69' 2.0E heads and a set of 73' 2.4E heads laying around.
Would either of these help in the analysis?

Snowman,
I also use the Dyno 2000 program and have learned alot from it. In 1969 when alot of the cams etc were developed we didn't have these powerful tools to work with. Additionally, at the time, large overlap cams were seen to produce the most peak horsepower. Today we concern ourselves with the "area under the curve". Modern engines are much more efficient today then in 1969. The Porsche six is still a good motor and can benefit from the learning of the past 40 years. Looking backwards for performance will insure your place at the rear of the field.

Ed (69911e);
Sure they would. I'll send you Snowman's address via PM.

I am posting the results of the head flows as a new thread. See "911 head flow"