yo2001

Well, I got P79 head fully ported and polished. My dilema is the exhaust ports came out little bit larger than intake ports. (Intake is 1 1/2 in and exhaust 1 5/8 in) Is that bad. The car used to be real slow in lower rpm. but I think the cam was too small (274). I'm thinking that I'm going to built into turbo motor with this head and L28 crank, L24 rods, with 89mm custom pistons. Any suggestion?

tyco1983

I'm not too familiar with the P-series heads. How did the head come out with larger exhaust valves? So you're running 35mm intake and 43mm exhaust? That's real screwed up. You're killing yourself with the size of your intake. Did you do the port work? Did you buy it with the work done? Did you have someone do the work for you? On my E31 head I had the seats cut out and the larger 44mm intake valves with 35mm exhaust dropped in. The flow into the head is much more important than the flow out of the head, that is why factory makes intake larger. I wouldn't use that head if I was you-in addition, if you plan on going turbo, there are port and polish jobs that are specifically suited to give you optimal performance with forced induction. Tell me about the head work done.

yo2001

I done it with my buddy from a head shop. I pulled the tin sleeves from the exhaust ports out and the ports was smoothed out. I don't think there are actually 8mm difference more like 2-3mm. It's matched ported with the gasket. (sorry, I don't have the exact measurement with me) bowl areas were smooth out and ported too. chamber was smoothed polished. Cut some the exhaust side of the head chamber for a detonation proof. Also, new guides, shaved seats, SS valves. I'm worried that the large exhaust ports will cause some lag since there will be slower velocity of air. I'm thinking using the manifold instead of header so the air can packed in good before the turbo. How about I port out the intake some more? to least the same size as exhaust ports?

tyco1983

Oh-I thought you were talking about the exhaust and intake INSIDE the combustion chamber. I'm not real sure on the size of the external ports-every shop has their own theories and tricks with their size. Exhaust being a little too big isn't a worry as long as it isn't larger than the gasket you're working with. Then you would run into some back up flow problems. I suggest you run a pair of the nice thick flange MSA headers. I bought a pair and had them jet hot coated. Whatever you do, make sure that you have ports that exactly match your manifold gasket. If you have a Fel-Pro gasket, you could even use an exacto blade to enlarge each port equally. When I had my headwork done, they set the head on a bench flow which measure CFM across each port. They would then take it off and correct accordingly. Finding almost equal flow across your cylinders is pretty important so be careful when you are opening them up.