Hi Everyone,
I’m in deep in a restoration of my 67 Firebird Convertible and would like some opinions. The car originally came with a 326 with a power glide transmission. The motor ran before I started the restoration. The only issue with the original 326 is it has bad compression in 2 cylinders, nothing a good rebuild wouldn’t fix. However, the machine shop I was talking to has a 400 short block (casting #481998) that he could build for me however I wanted for $1000 less than anyone has quoted me for rebuilding the 326. So would I be better off going with the 400 and storing the original 326 & power glide or do I just get the 326 rebuilt. I want a cruiser, but my foot does get heavy a lot. If I do go with the 400 a friend has a Muncie M21 transmission he would sell to me ridiculously cheap. Is that a good transmission for these cars?
Thank you for any input you can give.
-Chuck Elliott

I would say go with the 400, but PLEASE do not continue with a "400 Sport Option" conversion.

Firebird 400's are going the way of '69 Z-28's where there are more on the road now then Pontiac ever built. It's getting to the point where a Firebird with a "normal" flat (non-scooped) hood is becoming pretty rare.

Thanks for the reply. If I go with the 400 my plan is to try and keep it looking as much as possible like it would if it had a 326. This way if I ever want to put the original motor back into it I don't have to change a lot. I might even keep the 326 emblems on the hood just to see who can tell the 326 from a 400.

Good choice. Remember all Pontiac V8 blocks are pretty much identical on the exterior, so nobody will ever know. PS, the pins on the back of the 400 emblems will not match your 326 hood anyway.

PPS: also refrain from the totally inaccurate practice of putting engine size decals on your air cleaner. Some enterprising smarty decided while reproducing Buick engine decals to change the Buick symbol to a Pontiac arrowhead and thus the uninformed Pontiac owners now all think they belong on their cars.

I have to admit that I put a "400" hood on my 350 firebird. I did however put the 350 emblems on the new hood. I'm not trying to fool anyone, I just love the look of that hood. I also used the improper decal on my air cleaner but it is an aftermarket chrome open element item so I don't see a problem.

I was kidding a bit. Just trying to keep a new member from straying too far too early until they are up on all the wives tales and bad info out there.

Myself, while I DO have a real 400 coupe - I will be putting 455 emblems as they will be the truth in my case.

my car was born 350, PO put a 400 in...and as I love the 400 hood and the old 350 hood had a burn on it, 400 hood came on...emblems also...but no arrowhead on bumper, to not try to fool anyone....my car IS a 400, just wasnt born it....lol

My car was born as a 6cyl automatic. Had a 350, 4 speed and flat hood when I got it. Well we all now how this story ends!

Chuck, does the 400 short block for $1000 less include heads? Water pump? Alternator (with brackets)? exhuast manifolds? Starter? Transmission? Etc. These are all items that may have to be bought so the $1000 savings will be long gone.
If all are included, what heads are they? Low compression smog heads? If so you may see a HP drop from your 326. See http://www.wallaceracing.com/head1.htm

The M21 is an excellent trans.

Wow, Thank you all the replies. Sounds like I wouldn't be alone in changing motors. And I thought it was just all the drag racing guys I work with trying to push to a bigger motor.
I was real surprised when I started looking at getting the 326 rebuilt. The shops around me were quoting $3500 to $5000 for a normal rebuild ($5000 was dyno'd and painted).
The $1000 less includes heads, manifold, and carb. He has quite a few in his shop and will allow me to pick which set I want to use. Which heads should I look for over other heads? The other stuff I figure I could hopefully use from the 326 or look for at some car shows. I figure I'm about a year away from even needing the motor, but I saw this motor and thought it would be a nice motor for my car.

I know a few years back when I had my 326 re-built, all of the parts were very scarce and much more expensive than 400 parts. But my 326 was numbers matching, so I put my head down and bit the bullet!

One of my 68's was an OHC6 3 spd column shift originally, now a RA-V block, #48 heads, dual AFB 4's, 4" crank, 428 hood emblems on a 400 hood with hood tach and open scopes, no bumper emblem, M-22 and 12 bolt.
Don't care if I confuse anyone or not.

Build it any way you want.
If it was a 326 HO I'd leave it original, but a std w/PG, I'd go with the 400 4 spd. Go with what ever hood you want. Flat hoods with hood Tachs look a little weird though, but to each their own.

The M21 would be a great tranny for your car so long as the rear gear is matched for it. Make sure the tranny tailshaft is correct for a Firebird though. It can get tight on the Speedo cable if it's on the shifter side. The tail housing is fairly easy to have swapped out if need be.

My thought process was since it was no longer a numbers matching car I had lots of freedom. I tried to build it like a car guy would have in the late 60's or early 70's. Long story short - build it to please you if your not planning on selling right away.

You need an app 75-85 cc Chamber for decent pump gas compression with Iron heads on a 400. Preferably with screw in rocker studs and big valves. 2.11 int, 1.77 exh.
Small valve heads can be reworked to add bigger valves if you have to replace everything anyway.
Head chart: head chart

A lot depends on how much valve relief cc is in the pistons and how deep in the hole they are at TDC.
A decent machine shop can check all this for you. Shoot for 9.5:1 but a little +- either way is not a big deal.
Compression calculator

If you need new pistons for a re-bore you can get forged dished pistons to match about any head 75 cc and under.