ported gt40p heads need advice on exhaust and intake runners - Ford Mustang Forums

dandeman · #1 (**permalink**) 12-06-2008, 07:48 PM

I have gt40p heads been opened up for 1.9intake and 1.55 exhaust valve. Only bowl work has been done to them. The intake runner and the exhaust runner havent been touched at all.

INTAKE VALVE TEST DATA----EXHAUST TEST DATA
.50-------33.92----------------25.97
.100------64.55-----------------58.816
.150------96.77-----------------82.362
.200------124.2-----------------107.38
.250-----152--------------------130
.300-----171.19-----------------143..31
.350-----190.0-------------------147.76
.400-----200.34------------------147.76
.450-----203---------------------147.76
.500-----206.3-------------------147.76
.550------203.25-----------------147.76

I was wondering if i should open up the intake runner to a 1250 gasket, and smooth out the exhaust runner if that would help the flow any, or would it hurt the flow? I really dont understand this flow sheet at all but that was the raw test flow data that i put up above. What does the Corr. Flow range mean? The flowbench chart at .200 on the Corr. flow range it shows 197, and i dont know what that means.

jthorn9 · #2 (**permalink**) 12-07-2008, 05:16 PM

Don't know flow sheets myself too well, however the key to the heads is going to be in the exhaust port more than the intake port. I'd port match both as best as you can. Just keep in mind that you want to port match the port almost directly even with the gasket, a little small is OK, but don't go larger than the gasket, by even a hair, it will not properly seal. The intake ports are going to be a little harder to port as they're fairly straight, but the exhaust ports will be a little easier as they have a small bump on one side of the port, which is where most of the porting will come from.

dandeman · #3 (**permalink**) 12-07-2008, 07:30 PM

Ya i planed to open them up a little more. I was thinkin of tryin to open the exhaust to a 1415 exhaust gasket. But i have heard to be careful cause the water jacket is very close. Im new to porting, i gasket matched my explorer intake with the stock gasket and didnt have a problem. But i never ported anything that is iron. Im goin to try to port the intake side to a 1250 gasket since it so close it wont take much.

jthorn9 · #4 (**permalink**) 12-08-2008, 09:18 PM

Yea, I'm porting my GT-40 X-303 exhaust ports now, but I'm porting them to a stock gasket, so I'm not really taking out all that much, biggest part is that bump I was telling you about along the top of the port, but I do know that the wide port gaskets will run you close to the water lines.

dandeman · #5 (**permalink**) 12-09-2008, 08:45 PM

yea i think i know what your talking about. In the exhaust runners at the top of the runner there is a little dimple in the runner. Is that what your talking about? If i smooth that out will it help it flow better? I was planing on opening the exhaust to a 1416 gasket but i dont wanna mess up my heads cause i have to much money in them. IF i only spent 200 on them it would be a different story. I just cant really find any information on porting these heads, and how easy it is mess them up.

jthorn9 · #6 (**permalink**) 12-10-2008, 10:22 PM

It's just after the dimple, it's a lump of aluminum that flows like this:

top, lump, excuse the dots, I had to use them to space the slash out that simulates the lump
______
...........\-

_______
bottom

The gasket matches perfect except for that lump, now this is on GT-40 X303 heads that have larger runners than the regular GT-40s.