Bozang1

Is there much difference between the 455 and the 403 olds motors? Someone said the blocks are the same so in theory you could use the 455 heads on a 403. Anyone know for sure? I found a complete 403 for an ok price. Late 70's motor. 77/78 I think is what the guy said. I would think if the blocks were the same it would be stamped the same ( 455 is stamped 396021, right?)

Bozang1

Never mind, I guess I should have done a little reading first. Larger bore, smaller stroke and at least 100 hp less. And it's a small block. Comparable to the Chevy 400 which was a fantastic motor!! Generally speaking, it sounds like a great motor but I also read that there's other stuff that needs to go with the motor if chosen to use. I'd still really like to find a 455 but a 403 don't sound bad. It's a step in between the 350 and 455. I saw an ad in a paper magazine for a 455 but no details. I'll call tomorrow

BangScreech4-4-2

If you're going to build it for high horsepower, hold out for a 455. They're a lot sturdier.


IIRC, the Chevy 400 was prone to overheating -- I don't think the original SBC block was intended to displace 400 cubic inches. I haven't heard of this being a congenital problem with 403s, though.

Allan R

I think you mean high torque? Both engines can be built for high HP

BangScreech4-4-2

Well, a 455 makes high torque by default, but I would also think that it would have a better chance of staying together at high RPM than a 403, undersquare bore/stroke relationship notwithstanding.

Vandy

While I have agreed with the "no replacement for displacement" theory. I've seen some HUGE numbers from small blocks. All depends on how deep your pockets are and how "new school" you want to be

CutlassDad

Be wary of siamesed bores. The bow tie crowd has a procedure to drill holes in the heads and block on 400's for venting. You get steam if there is air
between the bores that cannot be vented. I spent a lot of years finding ways to vent air from coolant on engines up to 2500 HP.

joe_padavano

I'm not a Chevy guy, and this is a little off-topic, but if the Chevy 400 is such a good motor, why does everyone steal the cranks out of them, drop them into 350 blocks, and make a 383?

Bozang1

Wow! The more I read, people are either far right or far left about the 403. Some love them and some hate them. I found one locally cheap but not so sure that it's much better than my 350 at all.
Has anyone ever heard of putting the 403 crank in the 350 or is it not possible? (Basically the same thing as mentioned above for the Chevys)

I don't plan on running down the track. Just want a nice reliable cruiser that I can occasionally get on to embarrass someone or make them wonder.

joe_padavano

The stroke of a 403 Olds is 3.385" - bore is 4.351"
The stroke of a 350 Olds is 3.385" - bore is 4.057"

Chevy used a variety of strokes and cranks in their SBC family, which is why people mix and match.

Every small block Olds ever built uses a 3.385" stroke, so swap all you want, displacement won't change. Of course, the good news is that this means that a forged 330 crank will drop into a 403.

And since I KNOW someone will say something... yes, of COURSE you can offset grind any SBO crank to change the stroke. That's not the same as taking a 400 SBC crank and dropping it into a 350 SBC block.

People are down on the 403 because they think that every engine must be able to make 7,000 RPM drag strip passes. Obviously the 403 has some structural design flaws that make that difficult, but for a street cruiser it's a great motor.

Bozang1

But is it really worth it? Is it really any better than a 350? Is there really any gain? That minimal displacement coupled with the feared windowed crank journals or whatever makes it sound like it's really not worth it. What do you guys think?
Maybe I should just stick with my 350 for now and worry about the motor last (unless I can grab a 455 for a good price.)

drop top olds

What are your goals? If you don't mention what you are trying to achieve; you may only get general responses. If you are looking for a high rpm motor the 403 is not for you. If you think a 403 can not be a good performer you are dead wrong. If you stay within the limitations of the 403 (around 5000 rpm, look for reducing reciprocating mass).
350's can be good performers too.

What are you trying to accomplish?

Bozang1

Want a nice street performer. I won't be running down the track. I like a nice cruiser but when my foot hits the floorboard, I want to be put back in my seat. My cousin has a worked 400 sbc that put me back in that seat with authority. I liked that feeling. Good news is I just found a complete running 455 for a decent price. Bad news it's a whole day affair for me to get it and I don't have access to an economical pickup so I may be taking the back seats out of my van. She ain't gonna be happy...lol

BangScreech4-4-2

I think this is the way to go. You can certainly build a 350 that'll put you back in your seat. Ask anybody who's driven a W31.


Get the car the way you want it before you go swapping engines.