Cylinder head porting
 

How beneficial is having 3.0-3.2 heads professionally ported. Considering the short length of each runner, how much can you achieve. I understand that shape plays a big part in flow, but how much? Flow bench results along with back to back dyno numbers would be great info if any of you have gone through this. Thanks, Bob

According to Bruce Anderson's 911 performance book, there's little to be gained by porting. Speaking from a little experience, I know it's easier to hurt flow than to improve it. If you are not building a race engine, clean them up with some sandpaper and rotary sanding tool, and leave the rest alone. If you don't have the larger 39mm intake port heads, then get those.

I think you can gain a lot with porting especially for a high performance track car. Shaping of ports can be important, too. I would consult with Bill at Xtreme Heads in FL. It may take time but it’s usually worth the wait. There was a build here where a good set of SC heads were sent to Xtreme and installed on a SC engine case with GT3 crank and 100mm pistons and engine made north of 380 Hp on 50 PMO carbs. Bill ports to give good power around the range.

R Lane if this is for one of your track cars with a big cam, I would highly recommend sending heads to Xtreme or someone other that has proven track record with porting.

Yes, if you are building a race car, then go to one of the (few) builders who have a successful record of building winning race engines. Bring lots of money.

The most important part would be the valve job. If you have a good valve job, you are 90% there. Having the MCSA for your engine size and operating rpm will determine port size. That pretty much is it for 911 heads. The valves are so big in comparison to the port sizes, there is not much that can be improved upon with porting. On most conventional heads the port will reduce in diameter to the valve throat (except for the turn into the bowl) and the valve seat throat being the absolutely smallest part of the port. On a standard 911 port it is the exact opposite with the valve seat throat being between 43.5-44mm and the actual port being anywhere from 32mm to 41mm. Hard to accelerate the air from a small area to a larger one.

There is a lot to be gained by porting heads....quite a bit more than a good valve job alone provides. The rest of the engine needs to be optimized though. That would include headers, the intake system, cams, etc.

You want the best you can get with Factory heads? Go to Dick Evilrude or Bill at Xtreme. The best way to go by a huge margin is to get Xtreme heads which do not have some of the limitations of the Factory castings.

I experimented on some 911/930 heads over 20 years ago and collected the results. If anybody cares and or likes numbers, I attached my results below.


http://forums.pelicanparts.com/uploa...1730513771.jpg

Another set of data. This is from a long ago post.



http://forums.pelicanparts.com/uploa...1730519913.jpg


I had Xtreme do a set of 3.0L heads for me. They needed everything so I had the full work done with bigger valves (53mm & 42.5) with 8mm stems and new seats, twin plug, etc. Had them flow the heads when done. My numbers are very close to the 3.2 XTR numbers. My intake ports are 42MM and exhaust are 36mm. I have yet to build the engine but am expecting good power.

This will be a fun build for me, 3.5L . 74.4 crank turned down to use Pankl 130mm Titanium rod. Custom pistons 10.5 to 1. GT3 oil pump. 100MM Nickies with Custom CP pistons. EFI with ITB's 46mm.
Still waiting on parts and machining so I can assemble, but am expecting good power.

john