jtettenb

I am building a 289 following edlebrocks proformer rpm power package. Im pretty sure im going to go with a set of hypernemetic pistons but besides that I am lost. Is there any brand you could recommend and any thing specific about the piston that would work well with this package. I am really lost with the differences that manufactures claim such as compression ratio of the piston, flat topped or domed, ring size ect. I just need someone with more experience than me to lead me in the right direction. Thanks alot as always.

67mustang302

Flat top, dish or dome is what the surface of the piston that faces the chamber looks like. Dish is lowest compression, domed is highest, all things being equal. On a street 289 flat tops are usually what you want, since it's a short stroke the compression will be fine for pump fuel. Hypereutectics are ok, but will NOT tolerate detonation, so if you use them you better have your tune right, cuz if you detonate they may crack. I prefer a lightweight forged piston, lighter and stronger, but also more expensive. I like Mahle pistons myself, but there are others that are good as well. It really depends on what you want out of the engine and how much money you have to put in.

jtettenb

Ok I found a set of Mahle forged pistons for 600 bucks. They have a compression ratio of 9.6 to one. This is the same as the edlebrock package says it is intended for. this piston is slightly dished. Mahle also makes a totally flat piston that raises the compression ratio to 10.8 to 1 this package is only 500 bucks. how might this effect my performace? will this require higher grade gas or work as well with my edlebrock package? Also when I replace the pistons I assume I will need new connecting rods. Is this true? Im on a budget and every little bit helps. Thanks a lot.

67mustang302

You need to get your rods checked to make sure they're straight. You shouldn't need new ones, but if the budget allows you can pick up a set of forged Scat/Eagle I-beams for like $200. If you use the stock rods then make sure you upgrade the rod bolts to some good ARP ones. The stock SBF rod bolts are pathetic(shame on Ford for that one). As far as compression, higher compression means more engine efficiency, but higher octane fuel is needed. Cam profile and timing play a role as well, but with that cam you'd be safer at the 9.6ish:1 ratio. I prefer to have a safety margin myself, a little lost power for the security of knowing some bad gas isn't going to destroy my engine. Also, compression ratio is going to depend on your chamber size as well, larger chamber = less compression. And with the Mahles, keep in mind that their ring packs are usually file-to-fit, so you'll have to file them, or take them to someone who can.

jtettenb

Thanks alot for all the help; you have certainly given me direction. Im jumping into this project with less knowledge than is needed but the only way for me to learn is to jump right in. As long as I can keep getting help from you guys I think this just might turn out to be a great running car when its done. Thanks again.

jtettenb

I thought of one more question. isnt the only real difference between a 289 and 302 the stroke? what Im getting at is can I put 302 pistons in a 289? for some reason the 302 pistons are cheaper. Thanks

67mustang302

Yes, the difference in displacement comes from the stroke. But a 302 uses different rods, crankshaft and pistons. If you're not afraid to follow instructions and do some grinding on the block for rod clearancing, you could take a 302 block and put a 347 kit in it. Since you're on a budget and it's your first build, I'd advise you keep the stock rods/crank and build a mild street 289. Start off simple. Remember this is as much a learning experience as it is an investment in performance. You don't want to learn at too high an expense.