[wooftfd]

Hi folks, going to start a 64 GTO build, have a couple of questions for the experts...
I'm going to put a 64 HO 421 in the car, is the weight difference between it and a 389 require any suspension upgrades? Springs?

2, I'm planning to do a stock build on the motor, lower compression, better exhaust, and have a convertible frame... will the stock frame take the 421, or should I use the convert? No slicks, or serious launches!!!

Best, Trent

[padgett]

The magazine test cars in '64 had 421s. Bolt right in.

[b-man]

The difference in weight between the various displacement V8 engines is negligible, I would doubt there’s much more than a 25 pound difference if that. The 421 did have a more substantial block casting with more material in certain areas and a slightly heavier crankshaft but none of that would warrant the use of different front springs.

Thread comparing a 1964 389 block to a 1964 421 block:https://forums.maxperformanceinc.com...d.php?t=772999

No need to use the convertible frame but having one is nice if frame replacement is necessary due to corrosion or accident damage. Had a 455 in my daily driver ‘64 Tempest for a number of years and bracket raced with a 455 in a ‘64 GTO with no issues, both cars had the standard frame.

[JSchmitz]

Regular frame and springs will be fine.

[hobbygto65]

421 428 455 weigh 60 lbs more than 389.

[b-man]

Originally Posted by hobbygto65

421 428 455 weigh 60 lbs more than 389.

The cranks are within 5 or 10 pounds of each other if that.

The blocks within 20 or 25 pounds.

Heads essentially the same.

I’m not seeing a 60 pound difference.

Either way no issues with the frame or front springs when swapping a 389 for a 421.

[wooftfd]

Thanks guys!!!
I havent torn down the car yet, frame looks good from underneath... The convertible frame is perfect, even powder coated, but I also have a Tempest convertible custom waiting in the cue if its not needed in the GTO...

[JSchmitz]

Originally Posted by wooftfd

Thanks guys!!!
I havent torn down the car yet, frame looks good from underneath... The convertible frame is perfect, even powder coated, but I also have a Tempest convertible custom waiting in the cue if its not needed in the GTO...

I'm no expert on the convertible frame vs. post/hardtop. But I assume the convertible frame is reinforced quite a bit. Stiffer frame is a good thing regardless if you don't mind the extra weight. I guess it depends on your goals for the car.

[G.T.O.boy]

Think about stroking a 389? Better oiling and revving than a 421 more displacement (450+ CID), factory crank and rods are not as strong (even the factory forged crank and rods) as cast replacements. 389 can have 4 bolt splayed caps added if you are going big power. To get a set of factory rods reworked from a good machine shop it is 300-400 dollars a new set of forged rods is 500-600 dollars. To recon a crank is about the same and a new cast one is 500-600 dollars, and places like Butler can get you a fully balanced set up for around $1,700 with forged pistons forged rods, and cast crank good for at least 600 HP (hard to get in one of these old girls even with ported factory heads). It is all internal so no one knows unless you tell them. If you run the 716 heads that will be the real power limiter, as Pontiac heads are not very good unless you run the newer 400 (ported) style or aftermarket aluminum. You could run the 1963 980 SD heads if you have a large budget and can find them. 1964 389 blocks are 10 pounds lighter than 65 and newer 389 blocks.

[b-man]

Sometimes it’s all about having a real 421 HO that matches the year of your car.

Nostalgia.

That cool factor that a bunch of perhaps better components can’t match.

[MIAGIMAN]

My 64 runs a 421 HO for years & years, " no worries" go for it, It's been a track and street car second all its life with no frame issues with plenty of first gear launches! Like B Man said it's nice knowing you have a 421 onboard.

[padgett]

It was the aluminum headers that would drip on the track.

[wooftfd]

Yup!!!

[wooftfd]

I was more aiming for a period set up, mild 421, stock M20, 323 posi... cruiser with a little grunt, but all '64...

[padgett]

Should look for a later (large shaft) M20 Muncie, 64s were pretty weak.

[Dick Boneske]

My '64 Muncie held up to many 12 second quarter mile runs. It was rear ends that failed multiple times--the original 3.90 Safe-T-Track, '67 8.2 with 4.56 gears, and a '70 Chevelle 12 bolt with 5.86 gears. Many axle failures, spider gear failures, and ring & pinion teeth breakage.

[Tim john]

My friend has a complete 64 GTO engine that could probably be bought if there is interest. Non running, been sitting for years (indoors).

Tim john---