or you can look for early 351w heads (almost the same as the GT40)

 

Dang, GT40 are the only cheap/still good performance heads around?

Edit - just read the post above this one

351 heads will fit a 289? and even older 351 heads from the 70s or 80s will be good?

 

The problem with 351W heads is that unless you get a set of older small-chamber heads, they're going to have massive combustion chambers that will drop your compression ratio well below what you'd want. Generally people who have a set of the old heads know what they have and won't sell them for cheap.

GT40 heads use port castings very similar to the 351W heads, hence the flow/power increase. But again, hard to find a set of non-P heads for cheap, unless you get lucky at a junkyard.

If your heads don't need to be rebuilt, I'd do an exhaust port-match job in your garage and save money for a set of aftermarket heads in the future. The port-match makes a big difference in the stock heads and will allow your engine to take advantage of any exhaust mods you've done (headers, dual exhaust, etc).

 

Care to explain what an exhaust port-match is?
If it's something I can easily research and find an article or something that i'll be able to understand, just tell me

Thanks!

 

If you can't afford to get good heads now, then run what you have and save up until you CAN afford good heads. Unless you can find a good deal on some GT40 or early 351 heads I wouldn't waste my time. If you have 2 fully built 302's, the difference between GT40 heads and a good aftermarket head can be as much as 50-100hp depending on the build, possibly more

 

With an exhaust port match, basically what you're doing is openening up the exhaust port up to match the exhaust gasket. Pre-87 289/302 heads have horrible exhaust port castings. Opening them up will result in a significant increase in flow.

Basically what you need to do is mark the exhaust mating surfaces with machinist's blue (or red/blue sharpe, which is cheaper and easier), scribe thegasket porton the surface,and open the exhaust port to within 1/16" of the mark. Then you can remove the thermactor hump (the biggest restriction in the port) and smooth the rest of the port to make a nice transition to the gasket area.

I did this to my built 68 heads and compared it to my original 67 heads; there's a huge difference between the two. They won't flow as well as 351W or GT40 heads, let alone aftermarket heads, but i'll buy you some breathing room until you can afford an aftermarket set.

 

Sounds pretty easy, thanks for explaining it


I saw some GT40's on ebay for like $100

I saw a lot more but they were GT40P's or whatever the P's are

 

It is really simple and only takes a couple hours. You do need a die grinder (not just a dremel)and carbide bit though, which are good things to have aroundanyway.

 

I have all that I'm pretty sure.
Thanks for the info![8D]

67mustang302
What would be the hp gain between stock heads and GT40s? Or between stock heads and stock w/ exhaust port matching?

 

General rule of thumb dave: $=hp
Kinda sucks for us younger guys....
Did you ever figure out that fiberglass hood?