Only the intake ports are different from 289/302/5.0 heads, and they're only about 10-15% better flowing anyway, probably 15hp difference. Stock for stock, its not worth it. Why not a set of ported 302 heads from Thumper? $500 shipped completely assembled with high performance parts and probably a good 30hp

 

We need to write a head FAQ. There are about 4 threads going on right now in the last week about this topic.

 

It depends on the exact heads that you are comparing..The early 351 heads had the bigger valves so they will breath much better than the 1977 and later junk 351 heads that were the same as the 302s....With porting the 351 heads can flow significantly better than the stock 302 heads...Of course you can always install bigger valves in the 302 heads and port them as well to acheive basically the same thing.

 

New GT-40 heads have the same size valves as the old 351w heads and flow slightly better. Combustion chamber size is different though, so it depends on your pistons to ensure you don't end up with too low/high of compression ratio with a head swap. Not as easy as just randomly picking a head and putting it on the motor.

 

Check out this web site...it gives a lot of different flow numbers on heads. Stan Weiss' Flow Numbers

 

Only the intake ports are different from 289/302/5.0 heads, and they're only about 10-15% better flowing anyway, probably 15hp difference. Stock for stock, its not worth it. Why not a set of ported 302 heads from Thumper? $500 shipped completely assembled with high performance parts and probably a good 30hp

got website?

 

Only the intake ports are different from 289/302/5.0 heads, and they're only about 10-15% better flowing anyway, probably 15hp difference. Stock for stock, its not worth it. Why not a set of ported 302 heads from Thumper? $500 shipped completely assembled with high performance parts and probably a good 30hp

got website?

www.thumperoforangepark.com

 

Only the intake ports are different from 289/302/5.0 heads, and they're only about 10-15% better flowing anyway, probably 15hp difference.

Are you kidding?...Have you looked at various exhaust ports over the years?..Non of them are very big but at least some are wide open..Others have big thermactor bumps and pipes stuck in them..I have a set of 68 J-code heads that came with a smog pump and you can't even stick your pinky finger through the exhaust port its so congested..

 

New GT-40 heads have the same size valves as the old 351w heads and flow slightly better. Combustion chamber size is different though, so it depends on your pistons to ensure you don't end up with too low/high of compression ratio with a head swap. Not as easy as just randomly picking a head and putting it on the motor.

I have a set of 69 351W heads I was planning to use on a 289 build but after talking to my engine builder he explained that if I use those heads I'll have to go with higher compression pistons to make up for the compression loss with the larger chamber size in the 351 heads. Unless I have to replace the pistons anyhow for an overbore I'm just going to stick with the 289 heads and do a basic rebuild.

 

that all depends on what compression you had with the 289 heads. In todays sorry gas the most compression I would run would be 9.5 to 10. The usefulness of the swap also depends on how much your machinest would charge to machine a set of 302 heads for bigger valves and the cost of the new valves..........and as for thermactor bumps, just get a dremmel tool and grind them down.......He said he is on a buget, which is just like a friend of mine who is building a 351w every penny counts. While aluminum heads are very superior to the stock heads the price is high also heads can be changed later on to aluminum without much difficulty........Mike U.

 

Yeah the 289 heads have a cc of 54.5 while the 351w heads have 60.4 You'd get a definite drop in compression going to the windsor heads unless you do a piston change.

 

I have a set of 69 351W heads I was planning to use on a 289 build but after talking to my engine builder he explained that if I use those heads I'll have to go with higher compression pistons to make up for the compression loss with the larger chamber size in the 351 heads. Unless I have to replace the pistons anyhow for an overbore I'm just going to stick with the 289 heads and do a basic rebuild.

Mill those heads about .030 and you'll get your compression back. Piston to valve clearance will be less if that is a concern, but you can check that easy enough. Intake manifold will have to be milled too.

 

Tracy's right. Also what I ment was that you might have too much compression with the 289 heads...
I have a compression calculator so I did a comp check with the early 351w heads at 60cc
Bore..............4.0
stroke............3.0
head vol..........60cc
gasket bore ......4.09
deck clear........0
piston vol........0 {flattop}
gasket thickness..040 {felpro}
and the compression ratio was 10.00 with the 60cc 351w heads.........
Also if you wanted you wouldnt even have to mill the heads, just use a thinner head gasket......Mike U.

 

Yeah the 289 heads have a cc of 54.5 while the 351w heads have 60.4 You'd get a definite drop in compression going to the windsor heads unless you do a piston change.

You're still not necessarily comparing apples to apples, though. The '68 289 heads and all but the J code 302 heads have 60.4 or larger combustion chambers.

General rule of thumb (excluding Boss 302, '68 289's and 302 J codes), compression is raised by swapping to the early 351w heads on a 302 (or '68 289), but dropped by adding them to a 289.

The base '68/later 289 and 302's only had about 8.5:1 compression or less.

You will see an increase in performance on any stock 302 (again excluding Boss and J code) by swapping the heads for early 351w heads. You may or may not see an performance gain, because of compression drop on a '67/earlier 289.

I have unported '69 351w heads on my 289, in my '66. I knew, when I built the 289, though, that I was going to run these heads, so went with 10:1 compression pistons. With a mild cam and headers, the car runs consistent 14.3's @ 100mph in the 1/4.

 

Good point John, the combustion chamber did change in 68 on the 289 heads. I could have sworn he had a 67, but alas his car is a 68. Then again that assumes his 289 is original. My reply was supposed to be directed towards Doug's comment on his 289.