New G block build
December 5th, 2018, 08:24 PM
#1
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Join Date: Aug 2015
Location: Houston, TX
Posts: 60
New G block build
In the final stretch of having the original motor for my ‘68 442 redone, and ready for break-in. This has been quite a saga, and thought some of you that haven’t written off the second generation 400, would be interested. Here’s the rundown:
- Matching numbers 83K original mile Texas car. Ran well, but had a couple annoying exhaust leaks at the manifolds.
- Leaks were due to two broken upper exhaust manifold bolts. P.O. tried multiple gaskets, but didn’t solve the issue.
- Also noticed 3 replaced freeze plugs with tension style plugs in the block, all had minor leaks — big surprise as well.
- Decided if heads had to come off anyway to remove the broken exhaust manifold bolts, just bite the bullet and yank the whole motor to know what I have.
- Scroggins Machine in Houston tore the motor down, had a virgin bore block, with both heads seriously cracked... How this thing ran so good is beyond me.
- Local Olds guy had two good C heads, block and new heads now mag checked ok.
- Decided to go with filled exhaust crossovers, removed A.I.R. humps, mild porting, beehive springs, roller tip rockers, push rod guide plates.
- Seriously considerd 4.0 inch pistons, but ultimately went with smaller .040 overbore, Diamond Racing forged pistons, with modern ring pack and quench area designs. Rest of short block is stock, using ARP bolts throughout. All balanced well, no heavy metal needed.
- Custom ground cam, to maximize low end torque, good idle, mild lope.
- Stock intake, carb, distributor and exhaust manifolds will be used.
- Mag check of intake showed more cracks... Strange given Olds reputation for metallurgy in their early motors. Assume this motor led a hot life in the past. Cracks are minor where I can still use it, but will look for a replacement. Jeez....
- Re-install and break-in looking like next week. Can’t hardly wait to see how this dude will run.
- A few work in progress photos included.
December 6th, 2018, 04:33 AM
#3
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,911
Nice build, the 400G isn't the most popular but it beats the 260 or 307 in desirability big time. Honestly, I only other thing I would have done is aftermarket rods, just don't go nuts with RPM's and I am sure it will live a long life. Probably the coolant had straight water in it and rusted. How did the cooling system look, original rad?
December 6th, 2018, 05:52 AM
#4
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Join Date: Nov 2008
Location: Central Fl
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[QUOTE=olds 307 and 403;1140517]Nice build, the 400G isn't the most popular but it beats the 260 or 307 in desirability big time. Honestly, I only other thing I would have done is aftermarket rods,/QUOTE]
X2.
Are the pistons 2618 or 4032? Excessively large quench pad given the bore size but they’re certainly better than most other aftermarket slugs.
X2.
Are the pistons 2618 or 4032? Excessively large quench pad given the bore size but they’re certainly better than most other aftermarket slugs.
December 6th, 2018, 06:36 PM
#5
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Join Date: Jul 2012
Location: Vancouver BC
Posts: 2,788
The 400 G is not as bad as most claim back in the Golden era of NHRA drag racing JR stock the 400 G ran a PR of 12:20 in 1969 on 7" slicks.
Headers and a free flowing exhaust would make a big difference to your build.
Are you using aftermarket rods?
Headers and a free flowing exhaust would make a big difference to your build.
Are you using aftermarket rods?
December 6th, 2018, 07:26 PM
#6
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Join Date: Aug 2015
Location: Houston, TX
Posts: 60
Thanks guys for the comments. I totally agree after becoming a recent convert to the ‘68-‘69 models, they’re really great, and even before the rebuild, it was a strong running car. The G Blocks are dissed way more than they deserve. I ignored these for years, still love the ‘70 and ‘66, but this ‘68 is really growing on me, despite being a PITA during the rebuild. I use the car as a cruise night toy, rarely, if ever expect it to be above 5K, so stuck with the stock rods and ARP bolts. It’s an AC car and I use it during Houston summers, and with the traffic here, will resist going with headers, but running W/Z manifolds with a 2.25 through exhaust with Magnaflows. When I retire to a better climate with less traffic, may revisit that decision, but will probably switch to an aftermarket intake and carb when/if I do that as well to wake this baby up. Will post an update pending break in, and first trip out with the new motor.
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