1967 400 REBUILD for 1972 GTO - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 07-31-2019, 03:27 PM Thread Starter
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1967 400 REBUILD for 1972 GTO

Be gentle, I am new...
My son has acquired a 1972 basket case. Old 455 was trashed from pervious owner.

Here are the Basics:
Have a good set of 6X heads from the 455.
Car came with a TH350 Trans.
Manual brakes
Aftermarket Cooking (Aluminum Radiator and electric fan)
Fairly solid car over all.
3" exhaust all the way out the back
Edlebrock carb and manifold
Been sitting for a couple years. I have not gone thru the gas tank yet.
Have not looked at Rear end gearing.

Looking to make:
A strong but reliable car to play with the Family. (no A/c)
Higher compression motor, I want to run Pump Gas
Fair performance cam, good sound

motor mounts from the 1967 motor, will there be an issue with hooking it up in the new/older mounting
Harmonic balancer and stock fan belt setup. Can I replace this balancer to a newer style and not affect alignment?
Are the flex plates the same between all 350/400 motors and starters?

Motor Specifics: pics of casting numbers and such to follow.
Motor has yet to be pulled apart. More details to follow.
1967 XU 400:
Casting 9786133
From my research it seems to show a 10.5 CR motor.
I will use the 6X heads, should lower the compression some. Hopefully enough to run pump gas
Machine work wise (depending on breakdown findings), Plan on stock as possible, but if it needs to be bored, then suggestions.
I have not selected a Cam, I am use to Hydraulic over solid, but given oil issues, suggestion appreciated.
Will use the edlebrock and aluminum intake

Thanks in advance. I have tried to by thuro...
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post #2 of 7 (permalink) Old 08-01-2019, 06:12 PM
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First thing you want to do is post your question in the correct forum unless you are installing this engine in a 2004-2006 GTO? Then my apologies. If you don't post in the appropriate forum, your post may or may not get answered and I guarantee it will get lost and never answered.

So re-post your question in the "Real GTO Section" of this website to get your answer.
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post #3 of 7 (permalink) Old 08-02-2019, 04:03 PM
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Welcome to the GTO forum !

You aren't the 1st to post in the late model section, & won't be the last.

(1) You can use the early block as long as you use 2-bolt engine & frame mounts. I've read that, at least some, '70-'72 455 GTO's came with 3-bolt engine mounts, which required matching frame mounts.(I suppose some call the parts that bolt to the block, engine or motor mounts, & the parts that bolt to the frame, either engine stands or brackets. I suppose everybody can call 'em whatever they choose.)

(2) IF the 6X heads actually CAME on a 455 engine, from the factory, the chambers are much too big for a 400 cube build. You could make 'em work on a stroker, especially a 4.5" stroker. Now 6x-4 heads, which came on either 350 or W72 400 engines, work great on low compression 400 builds. These and 6x-8 heads are very popular on 400 block stroker builds, with a 4.21 or longer stroke. Look for a small stamped number on the vertical pad, which is to the left of center, looking at the exhaust port side of the head. Maybe the number on yours will be either a 4 or an 8.

(3) Wouldn't even consider an Edelbrock carb, UNLESS it is a Q-jet, made by Weber, & sold for several years as an Edelbrock. I have a 1904 E-Q-jet on my 455 bracket engine.

(4) I'd swap the balancer, timing cover & all pulleys & brackets over to the early '70's type. The later model stuff is easier to find. I'd buy a new balancer. A Powerbond PB1056N is said to be a good quality replacement. That's what I have.

(5) Will most likely need to be bored at least .030". If you stay with the stock stroke, I'd go with Speed Pro L2262F forged pistons, in the bore size you need. You can either have the stock cast rods resized, using ARP brand bolts, or buy new forged rods. I recommend forged. If you decide on a stroker assembly, they come with aftermarket forged pistons, either flat top or dished, as well as forged rods.

(6) Cam choice will depend on lots of factors, including compression, cubic inch, & several other things. The most basic & still popular small 400 cam is an 068 Clone. Melling SPC-7 is probably the most popular of these. The Summit 2801 is also very popular. It is similar to an 068, but has more lift. If you go with more stroke, a Summit 2802 might be more like what you want. I chose this cam for my 455 bracket engine, because I'm on a VERY low budget.

(7) Most '67-'74 350, 400, 428, & 455 engines used the same or very similar flexplates. BUT, some were dual-pattern, and some were single pattern. Some factory torque converters required the smaller bolt circle, and some required the large bolt circle. Some aftermarket converters are dual pattern, so that they'll work with any flexplate.

(8) Well, there's obviously LOTS more that can be said. But, I'd let a GOOD machine shop check out the block/crank & let you know if it's rebuildable. AND, check the heads out. You need to know chamber size, to know if you can use 'em or not. If you can, then the shop will need to check 'em for cracks & see if they are usable. Make SURE that the shop you choose has experience rebuilding Pontiac engines. MANY Chevy shops do NOT.


If your block cannot be rebuilt, here are some options.

400 Long Block

455 Long Block

400 Short Block

455 Short Block


Good Luck !
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post #4 of 7 (permalink) Old 08-03-2019, 07:05 AM Thread Starter
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THx for the Help, I will try and get this moved soon.
I will start looking into the suggestions BigD, and let you know what I find.

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post #5 of 7 (permalink) Old 08-04-2019, 12:26 AM
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Absolutely agree with what bigd said. I'm in the middle of process similar to yours. I could not find anyone local who knew Pontiac and had necessary equipment to do work for me so ended up going with butler performance. So far, they are meeting my high expectations and they are nice to work with. It does however take a bit of time and money. I've had some experiences with budget machine shops that just ended up costing more in the long run to repair what the other guys messed up. Be careful!
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post #6 of 7 (permalink) Old 08-07-2019, 11:17 PM
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bigD pretty much hit it on the head .
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post #7 of 7 (permalink) Old 08-12-2019, 07:17 AM Thread Starter
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Block at Machine shop for clean and magnaflux.
Block was all standard, will need to be bored due to water in 1 cyl.
Crank was all standard. Light rust stains on journals, will polish and make decision if it needs to be turned.
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