GT-40 head porting, a compilation with a bunch of pics and measurements

[Guest]

[David Claflin]

I was putting springs on the heads that are the most heavily ported and run into a rather odd issue, which I should be accustomed to by now
I'm setting up the comp bee hive springs to work with  comp lobes that have .570 and .563 on the intake and exhaust with 1.6 scorpion rockers. I got one head done using a .050 spring cup and a .060 shim under the intake and a .015 shim under the exhaust. I started to do the other head and just thought I'd check the height to make sure they were the same as the first head.  Turns out I only needed a .050 spring cup under the intake and no shim at all under the exhaust.
I put a level across the valve cover rail and measured to the spring seat and it was actually different. The heights to the valve seal machine was the same, but the spring seat was deeper on one head.
One head of this pair is a replacement I got somewhere as managed to put a hole in the exhaust port roof initially, the replacement head does not have the hole drilled for the air port. They both have the same marking otherwise. Just thought I'd share, it never hurts to double check, especially if you're  using third hand junk. 

[David Claflin]

Just to provide some more info on this. I had picked up another set of heads at the junkyard, I opened up the bowls like the others, but not as aggressively, did the exhaust ports, and opened up the intake port height to match the ported explorer intake. I put these on the 94 cobra, 75MM TB, genuine fox cobra upper with some work done, ported lower,  stock HO cam, with 1.7s, heads were milled .020, longtube mac 1 5/8 headers, 3" VRS X-pipe, 3" mac cat back with pypes race pro mufflers. We put this on the dyno last Friday, it made 319/340.

My LX with a ported holley SMII intake, 80MM-R TB, more heavily ported GT40 heads, milled heads, B cam , with 1.7s, accufab longtubes, VRS 3"X, 3 catback with ultraflows made 321/308. I had my street tires on the back which consist of 275/60-15 tires on a 15x10 steel wheel which might have affected it some.

[Outlaw Bill]

Your results are not surprising since the B cam is only 10hp or so better over the stock camshaft but gives up some torque many times.

[David Claflin]

Your results are not surprising since the B cam is only 10hp or so better over the stock camshaft but gives up some torque many times.

I wasn't expecting a whole lot of difference, but I intend to go back maybe next month and run it again with the smaller tires (225/60-15s) just to see. I had ran this engine with a ported GT40 lower, and a box upper, with the stock cam and 1.7s, and smaller tires and dumps on it last year and it made something like 316/318. The engine that is in the cobra is fresher, I just put new rings and bearings in it last year. I have to correct the cobra numbers also, looking at my notes it made 311/339, not what I wrote above.

[bill88stang]

Great info

[David Claflin]

I wasn't expecting a whole lot of difference, but I intend to go back maybe next month and run it again with the smaller tires (225/60-15s) just to see. I had ran this engine with a ported GT40 lower, and a box upper, with the stock cam and 1.7s, and smaller tires and dumps on it last year and it made something like 316/318. The engine that is in the cobra is fresher, I just put new rings and bearings in it last year. I have to correct the cobra numbers also, looking at my notes it made 311/339, not what I wrote above.

Just as a follow up to this I did run the car on the dyno again with the smaller tire/wheel and it made virtually no difference.
Also, wanted to see if anyone had experience in putting larger intake valves in these heads. I've got a set of 1.90 valves from my son's AFR165s, and wondered if it would be a worthwhile addition to these more heavily ported heads.

[Outlaw Bill]

1.900 is largest you want to go, its what I have in my GT-40 experiments. Some have used 1.940 but you better use a standard 45 deg valve job and not get crazy with 90-92% throats. You may see 250 cfm with the 1.900 but it depends on the flow bench. Seems 250 cfm is the wall for iron GT-40's.

[David Claflin]

1.900 is largest you want to go, its what I have in my GT-40 experiments. Some have used 1.940 but you better use a standard 45 deg valve job and not get crazy with 90-92% throats. You may see 250 cfm with the 1.900 but it depends on the flow bench. Seems 250 cfm is the wall for iron GT-40's.

Is it the bowl, throat or chamber size that really limits the valve size?

[Outlaw Bill]

1.900 is largest you want to go, its what I have in my GT-40 experiments. Some have used 1.940 but you better use a standard 45 deg valve job and not get crazy with 90-92% throats. You may see 250 cfm with the 1.900 but it depends on the flow bench. Seems 250 cfm is the wall for iron GT-40's.

Is it the bowl, throat or chamber size that really limits the valve size?

Throat and bowl, gets thin and water is all round that area.

[David Claflin]

OK, thanks, I'll leave them alone and run the stock valves. These are going on an 86 short block I got from The Chad anyway, so the smaller valve might be more ideal in this application anyway.

[David Claflin]

Just to follow up some with this buffoonery, I got a junkyard explorer shortblock, ported explorer heads and intakes, 80MM TB, 1 3/4 longtubes, 3" X-pipe, 3" bullets, little weenie cam, cobra rockers, 4.30 gears, T5, 3,000 pound turd with me in it. Made 336/331 on the dyno, ran 7.49@ 91.1 with a 1.58 60ft when it was 81 degrees, 56% humidity, 29.9 BP. First time running this combo so hoping to squeeze more out of it. Also had 2" removed from this upper, next time going to try a full length runner upper to see what it does. On the dyno this upper I ran made 8HP more, but lost some torque in the midrange. The full length runner upper helps on the shift recovery, I think.
I was fighting clutch issues for awhile, either the spec stage II was too grabby, so put a FMS king cobra in it, and that wouldn't hold it, so finally used a centerforce pressure plate, that the clutch disc was bad, along with a FMS clutch disc, that the pressure plate had failed, that odd combination is the best one I've had in it...LOL!!

[jtmustang]

Sounds like it’s working for the pile of parts listed. What little weenie cam?

My son has been driving his 90 for a year now and has been buzzing me about putting a cam and some heads on it..

For what we have the gt40 heads are what I’m thinking,I’ve played around a lot with the regular and P heads back in the day, porting, valves etc..

So gonna read back thru here , and been trying to find some heads locally.. not nearly as plentiful as they use to be

[David Claflin]

Its the intake from the comp xe-270, and an exhaust lobe that has more duration than what the XE-270 comes with, but lift is the same. I was skeptical of getting more aggressive with the lift seeings as I had these cobra rockers laying here and wanted to use them. A crane engineer said they were never meant for anything over .500 lift, and these are .544.

[David Claflin]

Hey Guys!!!

So, I found that if I preview the post first, then click submit, it will load it. If I try to go to submit right away it'll time out.