what pistons for a 289? - Vintage Mustang Forums

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post #1 of 7 (permalink) Old 11-15-2012, 12:23 AM Thread Starter
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what pistons for a 289?

Just wondering your guys opinions on pistons to get for a 289

right now the motor has GT40 heads,550 carb,rpm intake mani, headers, dual exhaust.

I have a XE268H cam i'm hoping to put in soon so i was just wondering which pistons do you think would be best? i know i lost compression with these heads.

and anything else i should replace on the motor? its a daily driver but i'd like for it to have some spunk as well!

thank you!
- just a young fella trying to learn.

'65 coupe
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post #2 of 7 (permalink) Old 11-15-2012, 06:01 AM
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Might be best to wait until the engine is stripped and have the builder measure the cylinder walls to determine how much wear you have and then he'll determine the particular bore required. Imo you should only go with the next minimum bore required to remove any ridge in the cylinder walls. I think in most 289's, people end up with a .020 or .030 over piston but again wait to get the exact measurement before you order anything. A good source for parts is Summit Racing.
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post #3 of 7 (permalink) Old 11-15-2012, 06:44 AM
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I have TRW forged flat-tops in my 289HP. The originals were cast, so I've overdone it. You could get pop-ups for even more compression, but the price of super-premium gas will kill you, not worth the few hp you'll gain.

Amateur restorer. Well, sometimes I have been paid for it. But not right now.
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post #4 of 7 (permalink) Old 11-15-2012, 07:03 AM
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Little information you MAY already know. Every time a piston approaches the bottom, it's like you standing up on your bicycle pedals with all your weight. The downward force is astronomical.

The piston tries to "rock" about the wrist-pin. This wears the cylinder wall into an egg-shape at the lower end. The FIRST thing a machinist has to do is make the cylinder round again. This is easy to see when boring because when the cutting tool makes a complete 360 without any skipped areas, all egging has been cut away.

Then and only then can he measure to see how much oversize your pistons need to be.
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post #5 of 7 (permalink) Old 11-19-2012, 06:46 AM Thread Starter
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Sorry guys my post never went through and i just noticed!

Caper50 - Well the motor only has about 75k miles on it, does that mean i'd have to take the motor out and bring it to a shop? (might be a dumb question, i apologize)

22GT - Yeah im in college and live in south florida so i definitely cant afford premium prices!what size do you think?

bryan - I was not aware of the egg shape result, thank you for informing me! that leaves me to ask you what i asked caper...This all sounds pricey

'65 coupe
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post #6 of 7 (permalink) Old 11-19-2012, 07:16 AM
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My advice is to drive it while you are still funding college, treat with TLC and unless something comes up in the meantime that prevents you from driving it and it needs immediate repair, look at it then. Like others have stated there are many unknowns until the engine is actually stripped down. With the price of the parts and a shops labour it won't take long before you are over the $3000 mark and that's a very very conservative estimate without a whole lot of machine work. I just went through it.
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post #7 of 7 (permalink) Old 11-19-2012, 07:36 AM
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Caper is right. I live here in fla and the good machine shops are expensive. Owever if you had some failure that you had to fix. There are a few less expensive options around that will get you back on the road.
But yes you need to take out the engine and get it machined in order for you rings to seal properly. Remember your rings wear with you cylinder walls therefore your old rings will seal better than new rings on your motor. What you want to check if your compression and a leak down if you believe you might be having issues.

Good luck.
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