Hey guys, I picked up a pair of GT40 heads at the AutoFair in Charlotte a few months ago. I want to get them milled to both bump up the CR and also to ensure they are not warped or anything. I do not know how much to get milled off of them though. Should I do .010"? .020"? Also, how do I know if they need a valve job or not? The machinist can do a three angle valve job for $125 but money is rather tight right now so I want to know if it is necessary or not. Thanks.
"I want to know if it is necessary or not." NOT!!! on a stock engine, used heads, I would resurface the heads and lap the valves...
You can mill up to .040 before getting into intake fit issues. As for a valve job, that depends on how long and where they were stored and how well the valves and seats were lubricated prior to being stored. It would be best to at least relap the valves before using the heads.
I have a set of these that have been cleaned up. I was also thinking about some minor porting at home, like intake gasket matching. Any thoughts on the benefits of this?
i tried MINOR porting at home and ruined a set. The water jackets are not very far in there. I took out the thermactor bumps with no problem, and opened the ports a little. Not enough to gasket-match them, but maybe halfway there. Milled .015 (I think that was what we finally ended up with) just to clean it up and square it. As for the water jacket, I hit it after taking maybe .125" of material off. Not much. This was just inside the thermactor bump area. So, long story short, these heads are already really good flowing heads, and they didn't leave a whole lot of extra material to remove. So be very careful how much you try to take off. Unless you are an expert porter and know these heads inside and out (literally).
Just a thought here but taking more than .060" out of a thin-wall casting is asking for trouble unless you check to see that there was no core shift in the casting process. On a port, if you take .060" of both sides you open the port by nearly 1/8" overall. probably requiring larger gaskets to prevent restriction. where ports are concerned - bigger is not always better. Cleaning the sharp edges, smoothing transitions in the bowl and repairing areas that cause unwanted turbulance will be enough in most stock engines with stock heads. When you begin raising the rpm with more duration, larger intake, bigger carb and larger exhaust then you start thinking about larger valves and runners. There is a science and an art in porting cylinder heads. Many factors come into play when it comes to enlarging the ports and in most cases it is unnecessary.
I just take the thermactor bump out, polish the intake & exhaust then gasket match the intake. I've done it to a few sets of heads now. I don't know if it really makes that much difference... The 93 Cobra heads were milled from the factory compared to the stock GT40 heads, the specs are all over online
Check them with a straight edge and feeler gauges if available. As far as the valves visually inspect them for pitting and wear at the seat area. Lapping valves is controversial. It destroys the interference angle?? So they say. I've done it many times though. Any valve job is a 3 angle anyhow. Thats just lingo. Give them a quick lap if you like to check sealing.
Ummm, no they're not all 3 angle. I've heard of 5 angle jobs and the set of E7 heads I ported for my V8 Ranger were done using a Serdi machine to contour the valve seats. Lapping shouldn't destoy the seat angles at all, it's purpose is to create a better seal between the seat and valve by hand lapping them together using a lapping (similar to a rubbing compound) compound.
I meant any base machine shop valve job. Meaning no less than 3 angles would be cut anyhow. Should have been more clear. Didnt bother since he certainly doesnt need anything more than 3 angle. No need to complicate things for the fellow.
And clean any casting marks out of the valve pockets, put a little taper on the valve guides. http://mustangforums.com/forum/5-0l...-how-to-port-and-polish-gt-40-heads-pics.html
I cleaned up the sharp edges under the valve seats, removed the exhaust humps, 5 angle valve job an dshaved them 40 thou. Big diffence over the E7's.
If you notice in the mustangforum link, he didn't do much. Just knocked off the thermactor bump and opened the ports a little, then polished what he could reach. These heads are designed so well that there isn't much you need to do to them. This is all that I did to my current set, and I took a little off the valve guide.
Actually, those heads are designed to be so cheap to produce that you cannot do much to them period. Very thin-wall design and are prone to a lot of core shift from one batch to the next.
