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Old 07-10-2020, 11:35 PM
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Default '64 rebuild

Rebuilding a '64 389, 78XW, 9773155 block, 9770716 heads. 4bbl from the factory but now fitted with tripower. This engine has sat for 40 yrs. and I have never heard it run. Had the machine shop clean and mag the short block. Everything is good. They honed the cylinders to mic them. They are .004 over. They put the ball in my court whether to bore or leave as is. I was told .010 is usually the breaking point for most piston manufacturers. One of the original pistons has a broken skirt, thankfully no damage, the set will be replaced.

To bore or not to bore.....that is the question.

2nd question is compresion ratio on a pump gas, daily driver. The machine shop is comfortable with 10:1 but most everything I read say around 9:1. I'm thinking a mild 068 cam/1.5 rockers, 4spd, RA exh. manifolds, 323 rear end.

For what it's worth, this is a numbers matching engine.

Thoughts, comments, questions? THANKS!

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Old 07-11-2020, 04:08 AM
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I have a 1964 GP with a rebuilt 421 with 9.6 to 1 compression, AT, 2.69 rear and 067 cam. Most of the time it is pretty good but accelerating up hills it will ping. It is other wise stock with the original 4bbl carb. With a wide ratio 4 spd you might get away with 10 to 1 but it would be safer to go with a little less.

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Old 07-11-2020, 04:49 AM
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I would go with the 9:1. If you were using e85 the 10:1 would work. But not with pump gas 93 octane its going to ping if you want correct timing..

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Old 07-11-2020, 05:21 AM
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I would go with a over Bore and the new Pistons .

This will allow you to get the proper ring gap and minimum leakage / blow by!

Blowby / oil getting into the chamber will lower any fuels octane level really fast and make even a 8.5 to 1 motor ping and knock!

The new Pistons will make it easier to hit a target compression of 9.2 to 9.5, also your closed chamber heads are less likely to ping then the later open chamber heads so I would shoot for a 9.5 compression with your pick of the 068 Cam.

Also keep in mind that fordged pistion run 100 on average degrees cooler then cast ones or even hyper types, so in regards to the fuels octane level needed for the motor a fordged piston goes a long way in helping out with ping and knock.

Polishing / rolling over off the the sharp edges of each chamber ( rolled over by .015" ) that hang out passed the head gasket fire ring goes a long way towards keeping at bay ping and knock issues in these motors, in fact all motors, even those with Aluminum heads!

Sink all the money you can into the short block to get it it right as you can always up grade / swap over the heads in a afternoons worth of work.

Good fitting valve guides and good non Telfon Viton type valve seals are also a big part of not getting oil into the chamber for ping control.

Power wise with stock heads, the overbore, tripower ( jetted right!) and the 068 Cam you should have 330 hp under your right foot.

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Last edited by steve25; 07-11-2020 at 05:32 AM.
  #5  
Old 07-11-2020, 12:07 PM
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And cc your heads so you know for sure what you are working with to hit the compression you choose.

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Old 07-11-2020, 04:24 PM
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Here’s a thread detailing a 1964 421 HO build which is quite similar to what you’re building:

In a nutshell I went with dished pistons and ended up at 8.82:1 compression running the 068 cam. My heavy fully optioned Le Mans convertible has factory air conditioning, a TH350 trans and tall highway gearing (2.56:1). I kept the compression somewhat conservative so as not to have any issues running our substandard ethanol-laced 91 octane premium on hot summer days when running the A/C.

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Old 07-11-2020, 07:51 PM
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Quote:
Originally Posted by b-man View Post
Here’s a thread detailing a 1964 421 HO build which is quite similar to what you’re building:

In a nutshell I went with dished pistons and ended up at 8.82:1 compression running the 068 cam. My heavy fully optioned Le Mans convertible has factory air conditioning, a TH350 trans and tall highway gearing (2.56:1). I kept the compression somewhat conservative so as not to have any issues running our substandard ethanol-laced 91 octane premium on hot summer days when running the A/C.
Whats the state of the car now? You did a great job on the build . Nice engine . Should last a real long time...

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Old 07-11-2020, 11:07 PM
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Got back into my air cooled VWs after a 25 year break so I’ve been sidetracked the last few years.

Getting installed this coming fall along with a fresh TH350 and 13” Continental Converter I had refreshed just before Kris closed up shop.
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1964 Tempest Coupe LS3/4L70E/3.42
1964 Le Mans Convertible 421 HO/TH350/2.56
2002 WS6 Convertible LS1/4L60E/3.23
  #9  
Old 07-12-2020, 06:14 AM
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Both are cool projects. Hope to see you get back going on one . That long thread you got going on needs finishing

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Old 07-12-2020, 07:05 PM
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What Steve25 said. I would go .020 or .030 over and get new dished pistons and be done with it. I am running later heads on my '67 GTO with an 068 cam, TH400, and 2.56 rear gear. With my 87cc heads, I am at about 9.3 compression. My car runs premium 91 octane, and will still ping a little with stock timing map on a long grade if the ambient air temp outside is over 100 degrees. I built the engine over 30 years ago, before dished pistons were readily available. If I were to do a build today, I would put the $$$ in the short block and some good dished pistons and run the stock heads on pump gas and be done with it. Do it once and do it right. Start with a fresh bottom end.

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