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I bought a mustang that already had a 331 stroker in it. The original owner said that he had gone above and beyond to get the heads and intake to flow better than they appear on the surface. The 331 is topped with GT40 cast iron heads and a Cobra intake manifold. He said the heads were hand ported completely and then extrude honed plus had 2.02/1.60 valves, and that the same port job was true of the intake. The compression ratio with SRP pistons and heads milled to 56cc should be about 11.1 in my best guesstimate. Yes, he spent way too much money on stock parts. I have personally removed the intake and yes, it was very nicely ported in my opinion and limited experience, so maybe he was telling the truth. Ok, on to my cam
ISKY Camshaft Specs# 371275/284
[email protected] 228/238
LSA 112º
Lift 520/544
Valve Overlap 9º
shaft question. It has an Isky cam.
Is this amount of overap correct for a 331 with 11.1? It would seem that even with all the porting and larger valves, the heads would be restricitive. Would it benefit more with a camshaft that has less overlap? I'm completely clueless. This car has always pulled like a freight train to 6000rpm. Thanks for the input.
 

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Imho that is not what I would put in it for a cam. First thing it is more likey closer to 10.5 to1 comp and installing that size intake valve usually hurts the airflow because the bowl is not really designed for that sized valve so the head loses airspeed and makes the port a little lazy. But that head is small so with the right cam they can run pretty good. How hard are you trying to turn this engine? And what are you expecting it to do performance wise? In LIberty Dan
 

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I bought a mustang that already had a 331 stroker in it. The original owner said that he had gone above and beyond to get the heads and intake to flow better than they appear on the surface. The 331 is topped with GT40 cast iron heads and a Cobra intake manifold. He said the heads were hand ported completely and then extrude honed plus had 2.02/1.60 valves, and that the same port job was true of the intake. The compression ratio with SRP pistons and heads milled to 56cc should be about 11.1 in my best guesstimate. Yes, he spent way too much money on stock parts. I have personally removed the intake and yes, it was very nicely ported in my opinion and limited experience, so maybe he was telling the truth. Ok, on to my cam
ISKY Camshaft Specs# 371275/284
[email protected] 228/238
LSA 112º
Lift 520/544
Valve Overlap 9º
shaft question. It has an Isky cam.
Is this amount of overap correct for a 331 with 11.1? It would seem that even with all the porting and larger valves, the heads would be restricitive. Would it benefit more with a camshaft that has less overlap? I'm completely clueless. This car has always pulled like a freight train to 6000rpm. Thanks for the input.
Where did you get that overlap number that doesn`t seem right a cam like that should be over 50 deg of overlap. In Liberty Dan
 

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Where did you get that overlap number that doesn`t seem right a cam like that should be over 50 deg of overlap. In Liberty Dan
Sorry looked that number up it is 9deg hate those wide lobe seps on these engines. In Liberty Dan
 

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Discussion Starter #5
It's my daily driver and sees about 400-700 miles a week. Sucks that I can only run 21 degrees total timing w/o detonation so I'm looking into Meth injection or swapping over the AFR 165's that are currently on my truck over to the car. I'm not really looking for anymore performance, but one can never have enough I suppose. It pulls down 26mpg on the hwy with 3.73 rear gears, but only about 11-12mpg in town. I took it to the track but toasted the clutch before I could make a good 1/8th mile pass. I had to let off the gas and let it catch between shifts. I ran an [email protected] with a 2.2 or 2.4 60' time. I really can't recall. I think the 2.4 resulted in a 87mph trap speed. I think it will go 7's now that the clutch is new and with the addition of drag radials.

So I guess 9º of overlap really isn't all that much???
 

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Is this a Gt40 or Gt40p head? In Liberty Dan
 

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2.02/1.6 valves will not go into iron GT-40 heads without hitting water, plus the ports will never be able to support the valve size. I have 1.900 with a 50 deg valve job and 90%percent throat in my GT-40P heads. The intake port flows 242-246 cfm, damn good for that head. Trust me a 1.940 would never work if done properly. Sure you can grind the seat to fit the 1.940 valve and leave a huge radius under the seat, but what good is that?.
 

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2.02/1.6 valves will not go into iron GT-40 heads without hitting water, plus the ports will never be able to support the valve size. I have 1.900 with a 50 deg valve job and 90%percent throat in my GT-40P heads. The intake port flows 242-246 cfm, damn good for that head. Trust me a 1.940 would never work if done properly. Sure you can grind the seat to fit the 1.940 valve and leave a huge radius under the seat, but what good is that?.
I have seen some one put a 2.02 valve in a iron gt40 head with a 45deg seat but the head didn`t flow well and the port sounded poor and was unstable. I have never seen that tryed with a p head though,and that is a very good cfm number for that p head that you have @ what valve lift did you get that airflow number. And what are you running them on?In Liberty Dan
 

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I have seen some one put a 2.02 valve in a iron gt40 head with a 45deg seat but the head didn`t flow well and the port sounded poor and was unstable. I have never seen that tryed with a p head though,and that is a very good cfm number for that p head that you have @ what valve lift did you get that airflow number. And what are you running them on?In Liberty Dan
Its was toward .700 lift. The port was clean all the way up. It hit 230 around .600 and just kept going. I have the sheet at home somewhere. I used a 1.90 intake valve with a 50deg seat with a 90% throat, exhaust valve was 1.50 or 1.52. I have some photos I can dig out also. They still on the shelf for future use. Married with 2 kids does not leave much time.
 

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Here, I copied a post I made on a different website. I have more hours in the heads than a care to think about.


Well I tried a 55 deg seat and came up with these numbers, the valve size is still 1.900. The port is fully opened up along with a pushrod tube.

.200 - 114
.300 - 176
.400 - 219
.450 - 223
.500 - 226
.550 - 230
.600 - 234
.650 - 236
.700 - 238
.750 - 240
.800 - 240
.850 - 242
.900 - 242
.950 - 243

I'm not totally happy, but encouraged enough to finish all the other ports and then go back and try some other ideas. I also tried a aftermarket undercut stem valve, made no difference. I feel that .400-.700 is lacking 5 cfm or so from where it should be, it maybe in the short turn. I also may fill some areas with putty to try a few ideas.

I just use copper/brass tubes from the hardware store. I would love to press in some thicker steel tubes and open the pinch up more, but the lifters would need to be offset. With a 45 deg seat the .200 and .300 #'s were better(does not mean anything), but were down after .300 compared to the 55 deg seat. Plus the larger throat of the 55 deg seat should pick up power anyway.

.200 - 130
.300 - 186

55 deg seat
.200 - 114
.300 - 176

Every time I made the valve larger, the flow picked up everywhere.
 

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Bill those are good numbers for a gtp head,I looked back and we have never flowed a P head that went go in the 240s. Most of the ones I have seen were around 220cfm and flattened out about 570/600 lift. I did flow a set of gt40s nonps that went mid 250s at around 650 lift and the one thing I remember was someone had made the floor of the port were it turned over the short side very wide and they also had a lot of work in them. Well good luck all this talk of cast iron makes me glad I don`t port much cast iron anymore LOL. In Liberty Dan
 

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The short turn needs to be very wide, the roof needs to be raised. Everyplace that is a problem, you need to worry about hitting water. If I had time to try some things, I think 250cfm is possible.
 

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Bill that looks pretty good,what is the mcsa? InLiberty Dan
 
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