390 strokers: 431 vs 445

[scottj]

Originally Posted by DanEC

Think about Bruce's CSX3170 that I think he has been running a 482 in recently, and he turns it to 8200 rpm. Apparently he hasn't had any problems with a 4.25 inch crank. I think he is building a +500 FE now shooting for 9000 rpm

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

[wkooiman]

I've spun 428s past 6,000 lots of times, and I wasn't worried about blowing them up. They didn't feel lazy either - even with stock/heavy pistons In fact, they revved faster than many of the 302s that I've had in the past.

That's with a 3.98 stroke vs. 3.00 for the 302.

I just bought a 4.25" for my 427, because it was easier to get a decent compression ratio with flat top pistons. I was going to buy a stock 3.78" stroke because I don't need more HP in a Cobra. It's a custom order, though, and as mentioned, I'd have to run pop-up pistons to get over 10:1 CR.

We each buy parts for different reasons. But it does get old hearing the myth that strokers don't rev.

Btw, I also have a 4" crank in a 351C. I'm more worried about the stock block than I am that it won't rev.

[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!

[DanEC]

[quote=Cobra #3170;1417970]Correct, going down to a 3.75" stroke and small journal light weight crank and rods to be able to turn 9300 reliably. /[quote]

Sorry for the mis-quote on engine size. Stupid head crap I've had for the last week has me hallucinating I guess.