Machine shops typically charge by the job for standard stuff like boring, etc. Hourly rates are usually reserved for unusual projects. I can't say what the going rates are in your area, but around here there is usually about a $150 charge for a block service (clean, check for cracks, replace all core & galley plugs, and hone), and then its like $25/hole to bore the block.
On the GT40 heads, the ports are only big by stock port standards. Those heads were installed on 5.0 engines mostly (302), and the 351 in the first gen Lightning (that engine had a tiny cam in it though, otherwise the heads would have been too small for a 351 with more RPM potential).
The GT40s are a bit of a mixed bag though. First, make sure they are GT40s and not GT40Ps. GT40s have three vertical ribs cast into the front of the head. GT40Ps have four. The P head is actually better performance wise, but header fitment can be more difficult, and likely whatever you have now is not going to work.
Second, as for compression, most of the GT40 heads check in right around 64ccs, which is going to yield about 9:1 compression on a standard bore 302. Boring the engine will increase the compression ratio, because the swept area increases in volume, but its minor, maybe 0.10, so from 9:1 to 9.1:1 with a 0.030" overbore. You can adjust the compression several ways (head gasket thickness, decking the block or heads, piston dish or dome volume), but I like to set the squish distance at 0.040" and then make changes to chamber or piston volumes to get to where I want to be. In truth though it makes very little difference on a stock or mild performance build, but the engine builder in me just does things a certain way.
Third, the issue with the GT40P heads is that the stock springs won't take much cam, in fact a stock HO cam from a 5.0 is too much, and that cam is considered tiny. So to use the P heads for performance you need to change the springs. In theory the GT40 springs will take more lift, but the ones from stock vehicles (even the Cobras, Lighting, etc.) don't have very good springs. The Ford Racing GT40s had better springs in them, but there's probably no way to tell, so I would swap the springs as cheap insurance.
Now we start to get into the problem with the GT40 heads. How many miles are on them? You're already changing the springs, which means the valves are coming out, so you might as well get a valvejob. If you're going to spend penny one on them you need to make sure they aren't cracked or warped. Now you're getting them hot tanked, Magnafluxed, a valve job, new springs (might as well install new locks, keepers, and seals too), and those cheap or even free heads are starting to get kind of expensive. Once you get close to the $1,000 mark in them you are in entry level aluminum head territory, and you can almost certainly find a set of used aluminum heads on Craigslist for less. The big difference there is that aftermarket heads flow better and make more power, plus they are lighter and will tolerate about a full point more compression without detonation (10:1 vs. 9:1 for iron). The GT40s were a good stock head, but they were still a stock head, designed with emissions requirements in mind as well as cost. Ultimately you have to make the call, but I live by the adage that the wrong part at the right price is still the wrong part. Your first order of business is to lay out your goals for the engine and then you need to see what's going to fit that goal, as well as budget. Give me some guidelines and I'll gladly help get you there.
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Ozblitz wrote:
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