390 strokers: 431 vs 445

[Cobra #3170]

Originally Posted by scottj

I think he's building a 440 cid... 3.75" stroke, small journal, lightweight stuff.

Correct, going down to a 3.75" stroke and small journal light weight crank and rods to be able to turn 9300 reliably. My main goal was rpm because torque has never been an issue the 498" engine made 632@ 5750. I need to run a 4.88 gear and still be able to get 68 mph in first gear. This is just for Goodguys autox because the turns are so slow the engine was down to 1900 rpm with a 4.27 gear and had no port velocity. A very specialized case because we don't shift (it wastes time).
The long stroke engine was great everywhere else so I would not argue about power or torque. I will be giving up both in search of rpm, and the damn thing might be slower, it is a gamble but we need to pick up some time. I will share dyno numbers and in car performance when we get it done probably in April. I have acceleration data with this particular tire size and compound so can share actual in car data from both engines. We are using the same intake lobe and valve spring so the only limit I was worried about was piston speed. I like a safety factor so we never went over 8200. The new engine should be good to 9300. Rods are lighter, pistons are lighter and the crank is much lighter. Smaller Journals, smaller wrist pins and smaller rod sections.
The old one reved very quickly, don't know how the new one will be but we will see. On a street engine I would definitely go big free torque and HP!