Would it be a good idea to put '93-'95 Cobra gt40 iron heads on my original '72 short block? How do they compare to the '72 heads? I know the combustion chambers are 2-4cc's bigger, so how much of a compression drop will that be, and is it significant? These heads I'm looking at have 1.94 and 1.54 valves, is that good? will they clear my pistons? thanks, Jon
I have those heads & they are pretty good for a stock head. It depends on how much power you want. I don't think they stack up well with the aftermarket heads. That year mustang didn't make alot of power but the torque was there. Pistons clearing I think but I could be wrong depends on the lift & duration of your cam(I think). When I change my heads, I also change alot of things at the same time so the outcome was great. I couldn't tell you about the cc's with the stock pistons though. The exhuast side could use some porting. They dont flow well there.
That would be a GREAT idea Even without porting the exhaust, they will flow much better than any iron heads you can buy, except for the GT40P (which I use) Best thing is, pull your head off, put this one on. No adjustments, nothing. They are a direct fit, keep the GT40 rockers and everything. Use your stock pushrods. I bought mine for $300 a pair, cleaned them up to get the loose grease and dirt off of them, ground out the "thermactic" smog bump and lightly polished the outer half of the exhaust port as deep in as I could reach with my Dremel tool. Easily a 50 HP improvement (that is 50 "seat-of-pants" HP, not dyno-tested HP, so it could be more or less than that).
Hey thanks The heads I'm looking at already have the exhaust ported. How much will my compression ratio drop with these heads?
You won't know the difference...You will pick up so much extra horsepower that the .1-.3 loss of compression won't even bother you.
72 stock heads vs those heads modded as described... I'd agree with the 50 hp at the flywheel. No doubt. The things are ported and have decent valves. Makes a big difference. The 72 rockers won't work. Someone on the board had some Cobra rocker arms. They posted on a recent thread that got into rocker ratio. I'd do a search on that. The member said that they had no use for them, however they didn't say they were for sale either, but it's worth a quick PM. The combustion chambers could lose as much as a whole compression point. I don't know the numbers off top of my head, except to say that the 72 short block can't afford to lose ANY amount of chamber. Check the heads, someone may have milled them while all the other work was going on. If not, you can have them milled quick before you put them on the car. Good luck Dave
Just for giggles, I ran it through the engine analyzer... Stock short block, 4v Performer, 600cfm, 1 5/8" headers, and stock heads... 240 fwhp. Same, but add ported GT40 iron heads with 1.94 valves... 315 fwhp. 75 fwhp!!! That's over 50 rwhp... I know it's not a real dyno, but it's a sure sign of the difference between the heads. Btw: When the engine was modeled totally stock... down to the 2v and single exhaust, the head swap only added 33 fwhp. But with all the restrictions on everything, it's still a wonder. Dave
I THOUGHT it felt like a good kick. What is the compression on your sample "dyno" program? I have the 74 with 8:1, and I would be interested to know if I am near 300 HP...Also, can you put in a torker 289 with heavy porting and my cam...or even better, where do I get the program and I will do it myself
have .030 shaved off them it should put the comp back pretty close to what you have now around here its $30 a head to have it done. Did it a couple times and so far had no intake sealing problems or bolt alignment problems.
When the heads are milled, shorter push rods are needed correct? What size would be needed for a .030 mill?
.030" shouldn't sweat the pushrods IMO. No worries at all if you have adjustable rockers... Edit: However, when milling beyond a certain point, they say you should have your intake milled to prevent misalignment. I know .020" is safe, but forgot if .030" or .040" is the point where the intake will need milling. I am pretty sure it is .040" max before intake mill. If I am wrong, someone will chime in. How many CCs do stock GT40 heads have?
