I drive an all original 79 trans am and I was wondering why people always say swap the olds 403 for the pontiac 400?  In a recent issue I came across the 1979 Pontiac Trans Am - Old School article and noticed that the guy was making over 500 hp on a 403 setup for the street.  Why do so many people go for the 400?  

Jon, alot of people look at the 403 cars (or the 305 chevy motors) as mutts because they aren't pure Pontiac powered. I agree to a certain extent, but if Pontiac offered it and built it then it should be ok. If you want to build the 403, go for it, check with Mondello for the best Olds related info and parts. They can be fast, but because they were originally a smog design, most guys don't give it a second thought. Of course a really easy swap is an Olds 455! Just bolt it in and go. As for the 400, well it is generaly considered Pontiac's workhorse with an excellent mix of horsepower and torque, and it is pure Pontiac!
Steve  

I am in the market for a late Gen 2 Trans Am.

I am trying to decide if I care if it is a stick shift or not.

In general it seams that the manual trans cars come with the pontiac 400, and the automatics come with the Olds 403.

The autos are of course far more common.

I have also read a couple articles on Olds 403 making  500+ hp.

Is there actually any advantage of one engine over the other?

Is one more reliable, or easier/cheaper to increase power on?

It sounds like swapping in an early set of 350 chevy heads, or big block heads onto the 403 to increase compression and improve air flow, along with a cam will make a huge difference.  The torque curve of the 403 is very appealing too.  

The 403 was only available with the th350 automatic, the 400 was available with either the th350 auto (th400 prior to '75) or the Borg Warner super t-10 four speed manual. The 400 has a longer stroke than the 403 and therefore more low end torque and it's a true Pontiac mill. The 403 can be improved with earlier Olds 350/400 heads or small chamber 455 heads, or Edelbrocks aluminum jobs if your budget can handle them. The 350 Chevy heads do NOT bolt on to either the 400 Pontiac or Olds 403. Remember when increasing compression ratio, these are large bore engines and 9.5:1 is about max on pump gas with iron heads.
Steve  

Hey, barneyformula is right! just to add to what he said,  you can build a 400 true pontiac, or the 403 olds, as i have done both, and i would highly recommend sticking with the pontiac mill. I think the reason most stay with the 403 is either originality or cost savings. but what I have discovered is that there are a ton more parts available for the pontiac engines, and that translates to a more flexible budget. parts for a 403 are a lot harder to come by, and unless youre paying top dollar for aftermarket parts, the factory ones werent meant to hold up to much more than stock power levels, that is, reliably. I have owned both the 403 powered cars and 400 pontiac, and have been much happier with even stock performance with the pontiac. i dont remember whether dollar amounts were mentioned, but it probably cost that guy who built that 403 with over 500 hp a ton more than it would have with a pontiac. and as a sidenote, it's easier to sell a pontiac with a true pontiac engine, then it is with a 403 (i am currently trying to sell a 403 powered 78 *** and it's definitely harder. hope this helps.