STROKEXD said:
Forced induction set-ups do not need to rev as much to produce their power.
5000 for a stocker clevo
9000+ for a mega dollar pro-stocker
6000-7000 for most well built street motors
As an note about the mega dollar Pro Stock engines, they were typically destroked to around 3.25-3.30" to fit the weight breaks based on CID that are now a part of Comp Eliminator.
It is interesting to see what that .20" does to piston speed, which is the real critical factor in determining maximum engine speed (assuming everything is built to take it) because of the material limitations are quickly exceeded by about 6000 FPM, give or take, depending on budget...a lot less for stock parts!
FPM = ( stroke * rpm ) / 6
FPM = ( 3.50 * 9000 ) / 6
FPM = 31500 / 6
FPM = 5250
FPM = ( 3.30 * 9000 ) / 6
FPM = ( 29700 ) / 6
FPM = 4950
4950 is a good point for a factory rod with all the best work done to it. I would never consider running a factory rod that hard these days when you can buy stronger, lighter rods for about what it costs to do all the work to a set of factory rods. A good set of Oliver rods at $1750 will run up to about 6000 FPM with everything else in the super-ultra lightweight category.
My 393 stroker:
FPM = ( 3.85 * 7600 ) / 6
FPM = ( 29260 ) / 6
FPM = 4877
Anytime you can run below 5000 FPM with good strong, lightweight parts, your engine will live "forever."
As a segue on the topic of calculating FPM, an instructor at an automotive school (of all things) was stupid (who said there are no stupid questions, an instructor?) enough to say:
"I do however question some of the formulas. For example I have always wondered how the piston speed formula was arrived at.
(stroke X RPM)/ 6 = fpm ???
I know its been an industry standard for eons but does that constant really make any sense or is it just me, maybe me???"
...that "industry standard" is an example of his stupidity. (Can anyone tell that I don't like this guy?)
The point is that stroke is only 1/2 of the distance that the piston travels, you see, it goes up 3.5" and then back down 3.5" on every revolution and "6" just happens to be half the number of inches in one foot!
stroke * 2 * RPM / 12 = FPM
stroke * RPM / 6 = FPM
...if you figure piston speed for a stocker with hydro lifters:
FPM = ( 3.50 * 6200 ) / 6
FPM = ( 21700 ) / 6
FPM = 3617
This is fairly safe for the material strength of factory parts, even cast pistons (though I don't recommend using them over 3500 FPM, which is exactly 6000 RPM with a 3.5" stroke Clevo)...assuming good rod bolts!
FPM @ 7000 RPM = 4083
That is a very good number for factory rods with good ARP bolts, shot peened, resized, pressed pins OK (prefer floaters) with good quality forged pistons and everything else matching. 4375FPM = 7500 RPM. This is pushing the limits of what I'd consider safe for pressed pins, though I know guys have run them even higher and longer. I just get prickly hairs when I think about it. For brief little shots using synthetics, it will probably live fine. I'd still use a 6800 RPM limiter because there isn't anywhere but the racetrack where there is a difference between 6800 and 7500 unless you happen to be motoring down the road with a 5.46:1 rear gear in first and want to see how much fuel you can burn per km. I can tell you one thing...if you do happen to pull second, it is going to really FLY.
Just so everyone's clear about my point on "unsafe" on the street at any RPM approaching 7000...with a 5.46:1 gear using a 26" tall tire at 7000 RPM it is ~159 Km/h (at 1:1 "high gear") and we all know that 5.46 isn't exactly a street gear ratio. A 3.90 would be ~224 Km/h. Multiply those numbers by the inverse of the gear ratio of the selected gear. EG: 2.46 first gear (inv=.407) .407 * 224 Km/h = 91 Km/h. Not too many places around town to run it up to 91 are there?
Anywhere on the street in any gear there is no place for 7000 RPM using any rear gear. A few young'uns would argue that you can run it up to high RPM using a mountain gear and a transmission with a really low first gear, but my reply is that (assuming not spinning the tires, which is a no-no on the street) there would be too much acceleration rate for it to be safe as other drivers wouldn't be prepared for a car accelerating at such a high rate and could change lanes, pull out from parking lots or even pedestrians step into the street because, well, you were so far away a second ago. Just not safe. Fun and exhilarating maybe...but not very safe.
:davis: