66 389 rebuild questions? - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 01-05-2014, 01:17 PM Thread Starter
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66 389 rebuild questions?

Hi everyone! Although ive been signed up for a number of years i have not visited the site really at all. This is due to life getting in the way of me and my car, due to lack of funds and time. The old girl got back burnered as im sure many of you can relate too. LOL..Well ive had enough of my poor car sitting covered up in the garage and am gonna get her going again!

The car has great body and paint but the engine is in need of a rebuild I beleive. She burns a bit of oil and as far as I know she has never been apart.

Its a 389 four barrell car that i may swap over to 3X2's.

My first question is where is the best place to buy all items that may relate to my rebuild? Things such as gaskets , bearings, pistons etc.? What sort of things can I expect to come across when rebuilding the engine? Also what is a decent header for these cars? And where to purchase?

Im currently searching for a place to have the engine done but dont know who to trust. Im very concerned with making sure it is done right by someone who appreciates that it is a numbers matching car, preferably a "pontiac guy".

If anyone knows of a good pontiac builder in the southern ontario/upstate new york area, that would be great!

Thanks!
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post #2 of 7 (permalink) Old 01-06-2014, 12:15 PM Thread Starter
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Anyone?
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post #3 of 7 (permalink) Old 01-06-2014, 02:39 PM
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You bet. You're not too far away from someone I happen to think is the best in the business. Jim Lehart, at Central Virginia Machine Service - Home of the Injun Engine!. Look him up and give him a call.

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post #4 of 7 (permalink) Old 01-07-2014, 12:29 PM Thread Starter
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Thanks!
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post #5 of 7 (permalink) Old 01-09-2014, 11:26 AM Thread Starter
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I checked out Central Virginia Machine...and they are pretty impressive! I just have a question . They talk about the need to lower compression to be able to run pump gas.

Im concerned with this for originality reasons and for HP loss. They say you will hurt your engine running even 94 oct? Thats all we ever ran in cars for years and everything was fine. What has changed? Have i been damaging my engine all this time?

I d would really like to just rebuild it back to factory compression but should I? What is everyone else doing? lowering orkeeping the same?

Any input would be great!

Thanks ...Tyler
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post #6 of 7 (permalink) Old 01-09-2014, 11:36 AM
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Do what Jim says. He knows his stuff.

Just because an engine is knocking audibly, doesn't mean it isn't detonating. There is such a thing as 'silent detonation'. If you can find shiny metallic specks on the ends of your spark plugs using a good magnifying glass, the engine is detonating. What you're seeing are melted fragments of piston tops.

Also, understand this: on that otherwise stock 389, a full 10 points of compression (the difference between 9.0:1 and 10.0:1) will make only about 5 or 6 HP difference, if that. Which would you rather have, an engine that you can confidently drive anywhere, any time, any distance and not have to worry about it eating itself, or one that makes maybe 5-6 HP more but you have to constantly watch, work on, tune, worry about, and that still might come apart when it burns holes in the tops of the pistons?

It's your choice.

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post #7 of 7 (permalink) Old 01-10-2014, 10:23 AM
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I can offer a personal example: My '65 GTO has a 389 that I overhauled back in the early '80's and it's got true 10.75 compression: heads cleaned up, chambers are 64cc, flat top forged pistons, big cam, etc. It's backed by a 4 speed and currently, a 3.36 rear gear. This engine was 'on the edge' with 94 octane leaded when it was available, but ran ok. For the past 20 years, with only 91 octane unleaded available, It needs race gas to run. I have driven it only 6,000 miles since 1991 because of this. My '67 GTO with the stock 400 was the same way...until I installed a set of lower compression heads. After lowering the compression to 9.3:1 or so, I was able to drive the car on pump gas. This is the car I drive all the time these days. I helped a friend with his '65 GTO, and he went with a set of custom dished pistons for 9:1 compression. Chose an XE268 cam, ram air exhaust manifolds, otherwise stock. Big surprise? It runs just as hard as my high compression 389 and does it on 89 octane gas. A 9:1 389 will not only run very well on pump gas, but it will also live a long time, too. I destroyed a 428 Pontiac back in the '80's when I pinged it to death on poor quality gas...and I never heard a thing. Broke several pistons. Lower compression is a reality these days, and a great idea.
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