Hi, I have a 86 f250 with a efi 302. It has hollowed cats and 2 1/4 dual pipes. What is the highest rpm i can rev it to without damageing it, i'd guess 4 or 5k?

 

5000 should be a safe limit.

 

Thanks, i'll try and shift under that

 

I ran a 1974 302 with a cam, intake, carb, and open exhaust. And regularly reved this stock engine to 6500 RPM + for several years. I went though many transmissions but I never had any trouble with that great little motor. I think these engines are capible of much more than most people think.

Clayton

 

But not all engines are that strong. Some are weaker then others. Plus over the years, mechanicals have changed slightly. I'm sure someday somebody who revs to 5k to shift will miss and go to 5600 and it will survive quite nicely...thier model will just take it better then.

My truck lacks a tach...so I don't know what I'm spinning up to exactly...just LOUD

 

ClatonK, it's the modifications you've made that allowed you to run that high of RPM...your bottom end was probably on the brink of failure if it wasn't assembled to run those RPMs...

My stock 302 wouldn't enjoy anything much past 5000 because of the cam, and other components. RPM redlines depend on many factors, a stock mustang 302 doesn't rev past 6200.

 

Trust me, my stock bottom end was not on the brink of failure even though I was shifting at 6500 rpm. Infact I once tore the engine down to put new rings and bearings in it and other than normal wear it looked great. I ran this engine hard for a long time - no trouble. I even had 2 other 302s since then and shifted beween 5500 and 6000 with them, again it worked fine. I also know 3 other guys with stock 302 bottom ends that rev the snot out of them and no one here has damaged an engine.

Clayton

 

Most 302's are very capable of high RPM running, with no problem. The reciprocating weight is comparitively low, and the relatively short 3.00-inch stroke means that max piston speed per RPM is also relatively low. Piston speed per RPM is a direct function of the amount of stroke. More stroke means greater piston speed. The stress placed on the big end of the rod, the piston pin ect.. can be aproximated by multipling the piston speed squared, by the reciprocating weight. Moreover because the 302 has an excellent rod length/stroke ratio, the reciprocating geometry is also good for high rpm durablity. 4 bolt mains ect.. really are not needed on these engines. Shear stress put on the rod bolts is significantly less than on say a 350 chevy. The lubricating areas of the rod and mains bearings is also optimized for high rpm running.

Ford set the rev limiter on the EFI mustang 5.0's at 6250 RPM. You can bet that Ford set this limit at a very consevative point for a large margin of safty.

 

Mmm yeah it depends on many factors, my old 73 bronco would run out of power at 5200 or there about, but I built that 302 for low end running. My 78 F-150 (which came with a 302 that was cammed for a higher powerband) will run to 6000+ and still have power, tho I don't want to rev higher. A rev limiter is good cheap insurance if you are worried about missing a gear or just overreving.