[Tom Pugh]

I need to make a decision about which block to use for my build, a 400 or a 455. I will be going with a 0.030 over .250 stroker build on the 400, perhaps just .030 if a 455 is used. Early 400 blocks are still readily available, not so much with 455s. I looking for something in the 400 hp level with iron heads, factory. crank. Nothing crazy. I have a set of 6X-8s which could be used for this. Will likely upgrade the rods and pistons to quality forged pieces. I will be using a custom builder for the machine work and assembly of the long block. This will be going into a '67 GTO, Turbo 400 with factory ac. What considerations should I be taking into account before getting serious with this build.?

[Gach]

I would go with 400 block only because of the 3” mains and get a stroker crank.

[mgarblik]

Because of your stated goals, I really don't think it matters. Both are fine. A stroked 400 might make a little nicer engine if a forged crank is used because of the small mains. 400 may cost less as well.

[John Milner]

Really, if 400 horsepower is the goal, a good running 400 with a set of 67-70 72cc big valve heads and something like a Crower 60916 or 60243 cam would likely get the job done.

[steve25]

A 67 GTO with factory air had 3.23 rear gears and just because of that fact a lone I would run the bigger cid build of the two.

For your usage it darn well doesn't matter if you start off with the 3.00" main or the 3.250" main, so go with the one that's easier on your wallet and put that savings else where in the motor build.

[Tim Corcoran]

Either one will get you where you want to be I would say flip a coin. It sounds like you have a good plan for a very nice combo. A Butler Stroker kit is a great way to go, you can have your choice of rods, Ross flat top or custom dished pistons, forged crank, bearings, rings a complete balanced assembly for a decent price.

[Tom Pugh]

Originally Posted by John Milner

Really, if 400 horsepower is the goal, a good running 400 with a set of 67-70 72cc big valve heads and something like a Crower 60916 or 60243 cam would likely get the job done.

what would the static compression ratio be with the 72cc heads? I've seen several sets of 670s and of course the edlebrock and Kaufman heads but I was under the impression these would not be pump gas friendly on a 400.

[steve25]

A 72 cc head on a stock 4.120 Bore 400 would give you about 9.5 to1.

[b-man]

1967 GTO with A/C and auto trans had a 2.93 rear end.

I’d be looking at replacing the 8.2 10-bolt rear with something more robust anyway if you’re planning to actually use all 400 horsepower rather than baby it. Don’t make the same mistake that most guys do by adding horsepower and neglecting to consider the strength of the rest of the drivetrain. The 8.2 10-bolts that came in all the 389 and 400 GTOs are notoriously weak, plenty were broken and replaced under warranty when these cars were new.

Either way additional cubic inches are your friend when tugging a 2-series rear gear.

[steve25]

Even more of a reason to build the stroker!

[android 211]

We can't run the high compression ratios of the 60s on todays gas so we compensate with more cubic inches. I'd perscribe a repro HO open element air cleaner with drop base. A Rochester. A '72 cast iron intake (contact Pontiacman) to go with the 6X-8 heads and headers or RARE manifolds. The 455 with stock crank and rods will be good enough for an automatic AC car that doesn't exceed 5000 rpm. I'd use the Summit 2802 cam. It'll make 400 hp on pump premium and won't break the bank. If you're willing to splurge then have the heads ported, stroker 4.25 crank, forged rods and pistons and hydraulic roller cam. It'll make well over 450 hp.

[hurryinhoosier62]

400 cores are a lot easier to locate than useable 455 cores. In this area, 455s simply do not exist anymore while 481988 400 blocks are still fairly common. If it were me, a 400 block bored to standard 455 bore size with a 4.25 stroke 3” main stroke crank from Molnar would make an excellent starting point for a 500hp street engine.

[Tom Pugh]

point taken. I will running a Turbo 400 which help rear survival, but still. I assume guys are using '66/67 Chevelle 12 bolts. or maybe 68/69s. Whats the hot ticket on a 12 bolt?

[b-man]

Originally Posted by Tom Pugh

point taken. I will running a Turbo 400 which help rear survival, but still. I assume guys are using '66/67 Chevelle 12 bolts. or maybe 68/69s. Whats the hot ticket on a 12 bolt?

100% aftermarket 12-bolt.

All the Chevelle cores are highly sought after by restorers and way overpriced, usually bent and not worth messing with honestly.

[i82much]

Originally Posted by b-man

100% aftermarket 12-bolt.

All the Chevelle cores are highly sought after by restorers and way overpriced, usually bent and not worth messing with honestly.

Does a 12 bolt have any advantages over a 9 inch or a dana 60?

[AG]

Less parasitic loss compared to a 9" and it's lighter, not sure about a Dana 60.

[b-man]

The 12-bolt is lighter and keeps the car all GM.

I actually went with the 8.5 10-bolt because it’s lighter than the 12 and has less parasitic loss than a 12-bolt simply because of the 8.5” ring gear versus 8.875”. I chose the ‘good’ Buick/Olds ‘71-‘72 8.5 that doesn’t use C-clips and comes with bolt-in axles and tapered roller axle bearings that withstand side loads generated during hard cornering.

Of course a 9” or a Dana 60 could be installed but they’re overkill for a 400 horsepower car. Sure the 9” is easier to swap gears with but seriously how many people really need that? Most people are going to have their rear end built with the rear gear they want and never change it. How may guys have multiple different pumpkins or even just one extra sitting around to change the gearing on their 9”, not many I’d say.

One advantage of going aftermarket 12-bolt is you can choose the Ford housing ends and corresponding axles and eliminate those lame C-clips for axle retention or the use of leaky C-clip eliminators like you’d use on a factory 12-bolt. Also it’s a brand new housing that’s not only straight it has thicker axle tubes that are fully welded along with relocated upper trailing arm mounts for improved suspension geometry.

[i82much]

Good info on 12 bolts, thanks. I went Strange S60 years ago. Don't love that a 3.54 gear is the tallest you can get, would probably do a 9" if I had i to do over again.

[sdbob]

The torque down low in rpm with the 455 will get the car moving.Somewhat less expensive than stroked 400. If you original looking stroke the 400.

[HWYSTR455]

Yes, use the Moser 7900FM housing ends, it's a game-changer. Especially if you plan to use disc brakes. I suggest having it narrowed 1" on each side to accommodate the offset of discs.

A new rear like that will last a long time without worry.

Might initially be a little painful in the wallet territory, but you will thank yourself more each year you run it. Just rip the bandage off quickly and don't look back.


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