Khaled Ghraizi

Hello everyone. I own two pontiac firebirds, one being a 75 formula and the other 79 trans am with 403 oldsmobile engine. I've been doing alot of research on how to increase horsepower of my 1979 trans am. Im not looking for any thing over the top, just for a descent 350 to 400 hp would be great. All the other forums suggested changing the heads to a 350 to increase compression. I would like to keep the original heads. Any suggestions (pistons and cam would be great). including part numbers would be amazing. Thank you.

svnt442

The factory heads on the 403 are pretty bad. To swap to some early 350 heads is an easy way to raise the compression without spending a ton of cash. Other than a cleanup and probably a valve job, you would need to open up the bolt holes on the early heads to accept ½" head bolts as they are 7/16" from the factory.
I'm assuming you have a shaker on the 79 so swapping the intake can be problematic, otherwise I would suggest going to BBO heads. To do that would require the use of a performer RPM intake and that would kill the functionality of the shaker without heavily modifying it.

Khaled Ghraizi

Thank you for the reply. I think I am in luck since I just dismantled the engine only to find that the heads turned out to be 350 heads (3a) to be exact. I read that they have 77cc as oppose to the 83cc the 403 heads have. How good are they.

Khaled Ghraizi

oddball

Is that with a capital A - 3A? Those are later year smog heads that are not particularly good either. The problem is the exhaust ports just got worse and worse, and they never were very good. I don't believe the 3A's give you much opportunity.You can do some porting work on them and help a little.

There's two major approaches with a 403 - flat top pistons with big chamber heads (4A/3A or big block heads or Edelbrock heads), or the stock dished pistons with early 350 small chamber heads (e.g., 5, 6, 7 or 7a (little a)). The early small block heads run under 70cc.

All depends on how much you want to spend and what you want to get out of it.

To can limp by with the later heads but doing whatever you can to the exhaust ports, having a bit spread between the intake and exhaust duration, and good headers.

Doug Blake

The original 403 4A heads has large combustion chamber, and 1.995" / 1.562" or 1.500" exhaust and 350 sized ports. Switching to a 350 #5-#7 head, and then installing W-31 valves will wake up the motor. Toss the "3A" emission heads. They have huge chamber size and small valves.

Better to run set of BBO “C” heads. Run 2.072" intakes and 1.710" exhausts. Shave the heads .040", Fill heat riser passages, braze the center divider on the exhaust port.

oddball

Right, all depends on how much you want to spend and what, specifically, you want at the end of it. A set of correctly finished Procomp heads are an extreme bargain, especially compared to all the work required on original iron heads. Just don't run Procomp heads straight out of the box. Edelbrocks are better in that regard, but still need to be checked.