# Rebuilding '65 389 3x2's motor (Suggestions)



## sbutler (Nov 4, 2009)

I just pulled my motor and I am ready to rebuild. Car is '65 GTO Convert 3x2 with 3.55 rear and M-21 trans. I do no want to rebuild stock. Would like to end up with about 400 - 420 HP. I plan to drive it about 1 - 2 K miles/yr. so I do not want something that will not idle and behave in traffic. Ideas?? I am debating on headers since they are hard to fit on a 65 or they hang too low. Should I keep stock manifolds? thanks -Sam


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## Rukee (Feb 8, 2007)

Stock HP were very conservative, rebuild to stock and you will be very happy.


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## Too Many Projects (Nov 15, 2008)

If headers aren't a good option, look into the aftermarket HO manifolds that support 2.5" exhaust. The stock manifolds are rather restrictive.
The engine will also respond nicely to a little more cam too. Don't get carried away with lift or over lap. There are cams out there with more lift and duration but keep the lobe center line (overlap) to a minimum to minimize the choppy idle that makes cruising a challenge. I suggest contacting a reputable Pontiac engine builder, such as your namesake, Butler Performance, or others that come up on a search for Pontiac engines for recommendations for a healthy, streetable cam...:cool

Oh yeah, welcome to the site......:cheers


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## geeteeohguy (Feb 2, 2008)

I agree on the exhaust. A set of the HO manifolds will help it breathe, and will not leak or warp. A really clean install. I would recommend going for as little overbore as possible to clean it up. It's the original block, and it adds about 8 to 10k to the value of your car. If you hog it out with a .060 overbore, you won't be able to rebuild it again. I would also recommend contacting Ross Pistons or Rock&Roll engineering about some slightly dished pistons for your 389. Running the stock pistons will result in near 11 to 1 compression, which is not compatible with today's fuels. I would try to get a set of .010 oversized pistons for it if it'll clean up in .010". Butler performance can build your engine, and they have a really great reputation. If I had a number's matching '65 ragtop, I know I wouldn't want to risk the original block with rookie builders. I have run into a LOT of machine shops over the years that were NOT familiar with the idiosynchrasies of Pontiacs, and have done much harm. Go slow, do the math, and find a compentent machinist!


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## 66tempestGT (Nov 28, 2009)

definitely do some research on your machinist regardless of the engine. lots of headaches can be created. as far as the overbore i wouldnt worry if it had to go more. heck if it adds 8 grand to the value i wouldnt mind 8 sleeves. unless it didnt need building in the first place its probably gonna take more than .0010 to clean and true it up.


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## freethinker (Nov 14, 2009)

sbutler said:


> I just pulled my motor and I am ready to rebuild. Car is '65 GTO Convert 3x2 with 3.55 rear and M-21 trans. I do no want to rebuild stock. Would like to end up with about 400 - 420 HP. I plan to drive it about 1 - 2 K miles/yr. so I do not want something that will not idle and behave in traffic. Ideas?? I am debating on headers since they are hard to fit on a 65 or they hang too low. Should I keep stock manifolds? thanks -Sam


if the car is stock now dont mess it up. its too hard to go back. what i would do is rebuild it stock and then install a nos system. that will give you your performance plus if you ever want to return to stock its a matter of just removing a tank and a few hoses.


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## geeteeohguy (Feb 2, 2008)

Back in the day, overbores on these engines went .030, .040, and .060. I think with a set of custom pistons, a .020 overbore is a possibility. I admit that .010 is probably a pipe dream!! The less material removed, the better.


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## 66tempestGT (Nov 28, 2009)

66tempestGT said:


> definitely do some research on your machinist regardless of the engine. lots of headaches can be created. as far as the overbore i wouldnt worry if it had to go more. heck if it adds 8 grand to the value i wouldnt mind 8 sleeves. unless it didnt need building in the first place its probably gonna take more than .0010 to clean and true it up.


LOL i guess .001 would really be tough! sorry, should proofread


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