289 heads on 302 bad?

[Tyman]

Started upgrading my stock 2bbl intake to Edelbrock performer + qjet and noticed my 302 block has 289 heads! Are these the same as the 302's or is it hurting my performance with smaller valves or something?

 

[Skuzzlebutt]

The 289 heads probably have a smaller combustion chamber, boosting your compression. If the valves are smaller it wouldn't be by very much and not have any affect until you get up high in the rpm range.

I don't the specs on either of these two points, it's just supposition.

 

[kwspony]

the original 289 in mine was a 302 block and 289 heads. I think it is normal and not a problem.

 

[6677ebman]

I've done it several times and it seemed to make a big difference with the difference in compression, I'd strongly recommend doing that, IMO 289 heads are much better than any '73-79 302 heads (the earlier '68-'72 302 heads are pretty much the same as 289 heads)

 

[Mikey]

The combustion chamber volumes varied greatly between the various years of the Ford smallblock. Grab a copy of "How to Rebuild Your Smallblock Ford" for the details. If you want me to look up a year for you when I get home, let me know. The 68 head has one of the largest volumes with the 73 having a smaller volume. I know this because I put on 73 heads on my 68 Cougar rather than the original due to this difference. Why, you ask? Different piston dish designs.

Good luck,
Mikey