Home » Public Forums » GMCnet » Differences between 403 and 455
| Re: [GMCnet] Differences between 403 and 455 [message #279098 is a reply to message #279072] |
Fri, 05 June 2015 00:27   |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma:
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USAussie wrote on Thu, 04 June 2015 16:08Domink,
Google is your friend:
http://en.wikipedia.org/wiki/Oldsmobile_V8_engine
http://www.442.com/oldsfaq/ofe403.htm
http://www.442.com/oldsfaq/ofe455.htm
Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Dominik Hertle
Sent: Friday, June 05, 2015 7:21 AM
To: gmclist@temp.gmcnet.org
Subject: [GMCnet] Differences between 403 and 455
Hello all,
Can anyone sum up the differences between both available engines ?
As I know during the model 1976 model year they changed from the 455 to the 403 engine.
What is the difference in power, economy, reliability, maintenance ?
Should I choose my GMC by the engine in it, or are they about equal in general ?
Thank you all,
Dominik
The links provide all the details and statistics. I have some gut feeling comments.
I have run 3 455s. (2 coaches and the current on its second engine. (I dump oil in it every 300 miles.) My friend Randy, who got me started in this madness, has the 403. He tows and I usually don't. He has a 3.70 final drive. I have a 3.21. Even with him towing, I have never had to wait for him. We both have converted to fuel injection. He is a sharp tuner but I am not a total slouch. He consistently gets better mileage than I do. I have a hard time getting the same mileage when he is towing and I am not towing. When he doesn't tow he gets way up into the 10.n.
We live at 2400 feet and there are a couple of fair grades to get here. I rode up once in Randy's coach and that thing came up the hills like a champ. He never shifted and it never hesitated. We were flying. I come up in my coach often, obviously. I don't shift down every time... it is one of those do I, don't I things. I am pushing taller gears but the 403 doesn't mind RPMs because of the shorter stroke. It seems like a tidy, tight engine but small blocks are like that.
Last fall when they were in CA we had to pull a head off the 403. Sure was nice having more room to work in the hatch.
One oddity about the 403 is that it has siamese cylinders, meaning there are no water jackets between 2&4, and 6&8. (other side as well) Apparently this is not a problem. I forget the mileage he has on the coach... I am guessing 78K or something like that. We could feel no ridge at the top of the cylinders. Cylinders looked perfect.
If I ran on to a nice 403, I might just consider swapping. (hate to think about finding all the brackets.)
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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