403 vs. 455

[bdub]

Would comparing these two engines be like comparing the Chevy 454 big block
and the small block 400?
Certainly no parts are interchangable on the chevy's. Everything about the
454 is more massive. Is it not so with the 455 compared to the 403?

Sorry for all the questions but I've little experience with oldsmobile
engines except for the Aurora my wife now drives. (I'm not even sure
there's an engine under all that plastic)!

 

[patrick flowers]

>
> I gotta speak up for my 403. It is not a small block engine. In fact, unless
> you are an expert and saw a 455 and a 403 side by side, JUDGING BY SIZE, you
> probably couldn't tell one from the other.

Justin, I'm not putting down your 403, but it is in the same line of
castings as the olds 305 and 350. These are referred to generically as
the "small block" olds engines. Dick Patterson used this terminology
several times during his tech session on engine building.
Dimensionally, they are very similar and many parts are
interchangeable. The 403 is a fine engine as demonstrated by the many
77 and 78 GMC owners that are very pleased with their coaches as are
you.

Patrick
- --
Patrick Flowers
Mailtoatri63

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[thomas g. warner]

There is absolutely no mistaking a 403 from a 455 at even a casual glance
and especially when it sits in the GMC engine compartment. The 403 is
noticably narrower from valve cover to valve cover, the distributer is in
the front instead of the back, air conditioning compressor is mounted on the
intake manifold, and it is a small block casting. And lastly the engine
castings are of a different composition of metal. From everything that I
have been able to find out the 455 contains a percentage of nickel depending
on casting #. The 403 is indeed a fine engine but not in the same class as
the 455. But than in my eyes there is not another engine available to us
that outclasses the 455 for what it was intended for, long life, torque
(lots of it at low RPM), reliability.

>>
>> I gotta speak up for my 403. It is not a small block engine. In fact, unless
>> you are an expert and saw a 455 and a 403 side by side, JUDGING BY SIZE, you
>> probably couldn't tell one from the other.
>
>Justin, I'm not putting down your 403, but it is in the same line of
>castings as the olds 305 and 350. These are referred to generically as
>the "small block" olds engines. Dick Patterson used this terminology
>several times during his tech session on engine building.
>Dimensionally, they are very similar and many parts are
>interchangeable. The 403 is a fine engine as demonstrated by the many
>77 and 78 GMC owners that are very pleased with their coaches as are
>you.
>
>Patrick
>--
>Patrick Flowers
>Mailtoatri63
>
>The GMC Motorhome Page
>http://www.gmcmotorhome.com
>
>

 

[bdub]

>
>> Would comparing these two engines be like comparing the Chevy 454 big block
>> and the small block 400?
>> Certainly no parts are interchangable on the chevy's. Everything about the
>> 454 is more massive. Is it not so with the 455 compared to the 403?
>
>Bill,
> No, it's not really so. Calling one of these Olds/GMC engines a "big
>block" and the other a "small block" is really innacurate. As far as I know,
>they are both basically the same block. That is to say, the critical
>dimensions (bore spacing especially, cam-to-crank distance, main bearing web
>positions, camshaft, cylinder head bolt patterns, bell housing bolt pattern,
>front cover , timing chain and sprockets, distributor mounting, fuel pump, oil
>pump, motor mounts, etc. etc.) are all identical. They were machined on the
>same production line using essentially the same tooling. They are different
>versions of the same engine
> To my knowledge, the only significant difference between them (and it's an
>important one) is the stroke, with the 455 having a substantially longer
>stroke. Olds did it right, and accomodated the longer stroke with higher
>(~3/8" greater distance from the crank centerline IIRC) block decks. This
>means a 455 is about 1/2" taller and wider than a 403, and a few pounds
>heavier. The intake manifolds differ as the 455's must bridge a greater
>distance between heads. The longer stroke gives the 455 a bit more torque,
>something we all crave.
> I'm sure there are other differences, but they are more on the order of
>year-to-year refinements than major changes. For more complete info, check
>out Mondello's web site and/or the Oldsmobile/Toronado sites.
>
>Hope this helps,
>Rick Staples
>'75 Eleganza (455)


This is the info I've been looking for. I knew it had to be something like
this if an exhaust manifold would be interchangable. I went back and read
several posts from last June also about the subject.

Ok, my take on it now is that the 455 would be the engine of choice but
there's not anything wrong with the 403 either. I'm thinking around a $500
dollor bonus factor for a coach with a 455 in it versus a 403. That's what
I'll keep in mind when we check out this coach today.

Thanks to everyone for the informative responses.

bdub