Pontiac 400

[GU O]

Hey there guys,

I have a 1979 pontiac trans am with a 403. Before you laugh at the fact that the motor in the car is different than my thread title, hear me out.

The current 403 has been rebuilt a few times already and I keep having issues. I have put type 7 heads off a 350 rocket with 455 valves on it. the compression should be around 10:1. I am blowing out my main berring like crazy this is the 3rd time its craping out on me! Im now looking to build a new motor to just "drop" in.

I have been tempted to play with a pontiac 400... is this a decent idea? I have not taken one appart so im not sure what it looks like. I know the 403 has webbed mains, and thus the crank flexes when the compression is pushed any.
Back on topic... is the 400 a good motor? i have head that the ports in the head are total crap. Is this true? Has anyone here put a stroker kit and supercharger on one yet? I live in colorado so the supercharger is a huge bonus.

Any help is greatly appreciated. websites, locations ect of parts and information is greatly appreciated.

[Dyno247365]

Originally Posted by GU O

Hey there guys,

I have a 1979 pontiac trans am with a 403. Before you laugh at the fact that the motor in the car is different than my thread title, hear me out.

The current 403 has been rebuilt a few times already and I keep having issues. I have put type 7 heads off a 350 rocket with 455 valves on it. the compression should be around 10:1. I am blowing out my main berring like crazy this is the 3rd time its craping out on me! Im now looking to build a new motor to just "drop" in.

I have been tempted to play with a pontiac 400... is this a decent idea? I have not taken one appart so im not sure what it looks like. I know the 403 has webbed mains, and thus the crank flexes when the compression is pushed any.
Back on topic... is the 400 a good motor? i have head that the ports in the head are total crap. Is this true? Has anyone here put a stroker kit and supercharger on one yet? I live in colorado so the supercharger is a huge bonus.

Any help is greatly appreciated. websites, locations ect of parts and information is greatly appreciated.

If I was a mod, I'd move every offtopic forum to its rightful place, that's why I'm not one and can't answer this question either. I know about newer motors in firebirds and that the 400 is outdated but it came in the bandit didn't it? Then it's a good engine. Ask 79Bandit, you can find him on the firebird forums and he has a 400ci TA.

[curtis73]

The Olds 403 is not a bad motor. I would look to anything but the compression as the cause of that main giving you fits: egged journal, scratched journal, cracked crank, improper endplay, improper seating of the main cap, stretched main bolt... but compression won't do it.

You'll hear a lot of folks complain about the windowed mains on Olds, but just because a solid web is stronger doesn't mean the windowed ones are weak. Joe Mondello used to run 403s all the way to 750 hp before adding a main girdle, so don't jump to that conclusion.

Either engine is great. If you're going to change engine families, though, I wouldn't go with the ho-hum 400. Its a fine engine, but if you're going to take the weight penalty of the Poncho block, at least make it a 455. They can be made from 30-over 400 blocks since 455 blocks are getting scarce and expensive.

I personally love the 403. Huge bore, short stroke. Stock Olds heads suck, and aftermarket ones are expensive, but if you find the right porter they can really fly. They are also nice cubes in a small package.

Caddy 500s are a light engine (just a little more than an SBC) but they are physically a tight fit.

Buick engines are great if you solve the oiling problems with a new front cover and better pump, and the 455 buick is a great performer.

[curtis73]

Originally Posted by Dyno247365

If I was a mod, I'd move every offtopic forum to its rightful place, that's why I'm not one and can't answer this question either. .

Nah... he's asking about an engine swap. That sounds technical to me

[Dyno247365]

Originally Posted by curtis73

Nah... he's asking about an engine swap. That sounds technical to me

oops I meant thread...ah well, it's getting late

or earlier. My cousin just bought a 76 firebird with the 350, can't wait to see it.

[GU O]

thanks curtis, I will have to take a good look into it I guess. the issue is that this firebird is my only car so to put it on hold for any long period of time is difficult.

I am not mechanically inclined enough to rebuild the motor on my own. But i can assemble assemble certain parts of the motor. I put together the heads on the current motor. I agree that the 403 has potential but it also has a fair few flaws... At least thats what i have found during the last 4 builds gone wrong. Maybe i need to find a better builder or something.

The heads are no issue I found though cause the 350 rockets type 7's fit (you need to enlarge the head bolts to fit the 403 block though) And the 455 sized valves fit in with a bit of work.

Still this altitude drives me nuts I cannot make the thing ping for the life of me. I was able to get it to ping once in texas...

Well then i wont do anything for awhile, have been able to find flatops for this motor? christ they are nowhere.

well its the middle of the night and im tired ill write back soon thanks again for all your help

[Dyno247365]

call up a junkyard and try to special order them.

[MagicRat]

Originally Posted by curtis73

Either engine is great. If you're going to change engine families, though, I wouldn't go with the ho-hum 400. Its a fine engine, but if you're going to take the weight penalty of the Poncho block, at least make it a 455. They can be made from 30-over 400 blocks since 455 blocks are getting scarce and expensive.

Just a suggestion, don't sell the 400 so short just yet....... The Pontiac engines are already somewhat slow to build revs, and the 455 is generally a 400 with almost one half inch stroke added.
This makes the engine even slower to build revs. IMO the 455 is better in a heavy car, (old Grand Prix, full size, etc) In something somewhat lighter,(if a 3500 lb F-bird is light....) a 400 may be a better bet, especially with a manual trans.

[GU O]

I have not been sold on either motor just yet. I like my current 403 but it definatly has issues. I might look into a gurdle or something. Anything to strenghten the bottom end. Also has anyone ever found a blower manifold for a 403? or how about some flattop pistons? sheesh you would think its a mystery motor.

Edit for spelling....cause yeah i cannot type

[UncleBob]

not sure what your problem with the crank/journals is, but I can only speak with my personal experience with helping my friend that built a pontiac 455 for his drag race car. He had a couple teething crank issues, and they were either due to NOS "malfunctions" or bad machining.

If you are having repeated crank issues on a low output engine, I'd look at the shop doing the rebuilding, personally. Assuming you've verified the obvious stuff such as oil pressure, oil pan and pickup design, etc.

Even a stroked 455 can be made to rev faster than you can believe with the right head and cams. My buddies race car (I don't remember the exact numbers, but its been bored and stroked to roughly a 468) is rev'd to 7K RPM's and definitely ain't slow about it! Running 10.7's without NOS. Its a fairly mild build with stock ported heads, he's thinking about going with some of the spendy aftermarket aluminum heads....but I'm always trying to talk him into letting me turbo it