403 or 455 pros and cons please help

john87442

Apprentice
Supporting Member
Mar 9, 2021
76
18
Ok so I searched the forum on this topic 403vs455. I know a lot would say duh 455 but with the obvious fault of the windowed mains beefed up with a girdle ( see Joe mondello article). What are the pros and cons now, I’m at a decision point after I found out my 403 build really wasn’t built yet (long story) so I could switch it up, and after seeing what hutch has done… we’ll I might have cubic inch envy. Please dump your knowledge on me either way. As always thanks.. looking forward to seeing the replies.
 

rogue_ryder

Master Mechanic
Oct 27, 2017
266
93
Colorado
Based on my experience I'd sell your 403 to a someone looking to restore a 77-79 T/A.

The windowed mains aren't a HUGE deal, I spun my 403 up to 6,000 RPM and I didn't have any spun bearings or cranks puked out. I ran the 4 main girdle with ARP studs and used a 330 crank. The biggest hurdle is finding a machine shop that can correctly torque plate hone the cylinders and finding GOOD pistons. I've been waiting a year for Race Tec to send me a replacement (machine shop only honed a piston to wall clearance of.003 per racetec's specs and I had one cylinder seize when my water temp got sort of hot 230-240) One of the big time NY Olds engine builders told me "that close of a piston to wall was f'ing stupid and 403s are junk" and he said he'd never go less than double that Piston to wall clearance in a 403 using the Forged RaceTec pistons. Another downside to the 403 is that it's not the same metallurgy as the older SBOs, The 403 crank is no better than the 307, if you go for upping the compression you need to toss that noodle in the garbage can and get either a "N" 350 crank or ideally a Forged 330 crank. 403 Heads are Junk too, they have huge combustion chambers and tiny exhaust valves. So you're looking at tossing basically everything but the block and then buying studs, girdle, heads, pistons/rods and then praying it'll hold up to abuse.

Going with a 350 is the better bet based on my experience (and what I have in my car now), there's far more pistons readily available (and at a lower cost) and you don't have to worry about windowed mains (just avoid 77+ 350s). The extra benefit is 350s are cheaper and easier to come by than 403s! For the 350 there's super cheap SpeedPro Forged Pistons, Middle of the Road Mahle Power Pack and even Diamond Racing pistons. You don't HAVE to buy heads, like you would with the 403 depending on your power goals, 7a (not to be confused with 7A) heads and earlier aren't horrible.

The drawback to a 455 in Gbody is that it's one heavy beast at 620# it's anywhere from 60-80lbs heavier than the 307 and there's only expensive ARH headers that'll fit with a BBO in a Gbody (if you want long tubes), If you're going to spend the money to build a 455 you probably don't want manifolds or shorty headers. The 455 would be my 2nd choice after a built 350.
 
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john87442

Apprentice
Supporting Member
Thread starter
Mar 9, 2021
76
18
Thanks for all of that good advice. I really liked my 72 cutlass with the 350, had a lot of fun with it. I really didn’t put much thought into going in that direction but I’m going to check it out.
 
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Oct 14, 2008
8,310
113
Melville,Saskatchewan
As said, the 4A heads need major port work on the exhaust side and the lightweight 403 crank beyond 400 HP is a time bomb, especially with a manual trans, as one member showed by breaking one in 3 pieces. You can add Cutlassefi's 4" stroke crank for around a 480 CI motor 403 based stroker as well. The new BBO Edelbrock heads give decent compression thanks to 403's huge bore. The 455's big mains also seem to give grief in high performance builds, way too many bottom end failures. Then there is fitting the air cleaner with a performance manifold in a G body.
 
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