redline

[cwhubb]

does the max rpm of an engine change if its stroked, and if so does the redline move higher or lower than stock?

 

[1967coronet440]

More dependent on your cam and valve train than anything else

 

[cwhubb]

thanks for your answer, but I'm not talking about peak performance rpm, I'm asking about catastrophic failure rpm, using stock type valve train, nothing exotic, just a plain old factory 383 thats stroked

 

[Jerry Hall]

Same answer as @1967coronet440 answered first.

 

[cwhubb]

camshaft stock mopar 268° / 284° advertised, (cant find conversion formula for @ 50 specs) 1:5:1 stamped rocker ratio, hydraulic flat lifters

 

[1967coronet440]

I wouldn’t spin it past 5500, stroke doesn’t determine rpm range

 

[Jerry Hall]

If you want a number, I would say 6000 red line. It will probably blow about 8000 if the springs and lifters will let it get to there.

 

[66 Sat]

It depends in how strong your bottom end is - cast or forged crank, properly balanced, what conrods etc. The valve train and cam will stop it revving too high, but the bottom end will determine when it blows up. Around 5,500 to 6,000 rpm should be safe.

 

[Jerry Hall]

When I have the opportunity to put cars on a dyno, I start with an easy pull to about 4500 rpm. Then look at the HP & torque numbers. I increase in 500 rpm increments until I find max HP & torque. I determine that redline is about 500 rpm above peak HP.

 

[cwhubb]

Thanks everyone, I'm thinking of going stroker and I needed a baseline for component upgrades

 

[cwhubb]

When I have the opportunity to put cars on a dyno, I start with an easy pull to about 4500 rpm. Then look at the HP & torque numbers. I increase in 500 rpm increments until I find max HP & torque. I determine that redline is about 500 rpm above peak HP.

thats what I was looking for, I want to crunch numbers and hit the safest max rpm vs peak performance, and get the two as close as I can with a safety cushion. I can only afford to do a stroker once and I'd be mad if I short changed myself

 

[Cranky]

Gotta know what's in the engine.....ie, rods, crank, pistons and weight of it all and on and on and on. The main thing is knowing what you have for the bottom end of the engine.

 

[cwhubb]

Gotta know what's in the engine.....ie, rods, crank, pistons and weight of it all and on and on and on. The main thing is knowing what you have for the bottom end of the engine.

the kit I really like is the 496 from 440 source, I'm trying to research on my own if 496 is fussier than a smaller ci kit. it looks like their bottom end stuff is bullet proof, but that could just be slick marketing, been suckered before and I've become cynical in my old age lol

 

[Jerry Hall]

Stock bottom end of the 383's are pretty stout. I built a stock bottom end 67 383 in 69 that reached peak HP at 6800 rpm. I shifted at 7000 at the track. I usually had to petal about 60 feet from the line to stay at 7000. One night the car in the other lane was even if not ahead of me at 60 foot out so I held it on the floor. Tachometer said 8500 when I crossed the line. It didn't blow. Bottom end although stock was balanced and blue printed. Maybe that was why it stuck together .

 

[cwhubb]

Stock bottom end of the 383's are pretty stout. I built a stock bottom end 67 383 in 69 that reached peak HP at 6800 rpm. I shifted at 7000 at the track. I usually had to petal about 60 feet from the line to stay at 7000. One night the car in the other lane was even if not ahead of me at 60 foot out so I held it on the floor. Tachometer said 8500 when I crossed the line. It didn't blow. Bottom end although stock was balanced and blue printed. Maybe that was why it stuck together .

nice! I had a 383 in a challenger that I used to abuse as a kid, I was smoking the tires, revving the crap out of it, motor didn't blow but the 7 blade fan sure did!

 

[biomedtechguy]

Bottom end although stock was balanced and blue printed. Maybe that was why it stuck together .

I'm sure that was a significant safety improvement.
CHANGING THE STROKE MAKES FOR A POTENTIAL BIG DIFFERENCE IN REDLINE
Valve train, if stock, and the degree of wear/strength of the valve springs is a major factor in my experience. When I got my 70 V-code Roadrunner (it has a 1971 440, "heavy" rods and forged steel crank from the factory, 6bbl intake and carbs) it used to pull hard, but approaching and beyond 5k fell off sharply. Now this was an odd sensation, because it felt as though the power was really "coming on" before it would fizzle. My intuition was right on that-I thought the valve springs were weak and floating.
It has a wicked sounding cam in it, it's definitely a Purple Stripe flat tappet hydraulic cam. Others and myself are as sure as we can be without measuring the lift and/or duration that it's the 292°/.509 cam, which was the hottest hydraulic cam Direct Connection offered "back in the day". I had already had a lifter collapse when I missed a shift, but it pumped back up after a minute or so. The next time a lifter collapsed from another missed shift (the Hurst shifter was the wrong one, mismatched parts, wrong shifter mounting bolts, etc) the lifter was gone for good. I replaced all of the springs and lifters, locks and retainers with Comp Cams 911-16 springs, 822-16 lifters,
748-16 retainers, and 10° 627-16 locks.
My 440 after those changes, with stock 1978 452 heads and TTi 1 7/8" headers, pulls HARD all the way to 6,000 RPMs and has been to 6,200 countless times. I have my shift light set at 5,800 and my rev limiter set at 6,100.
Now I believe that the peak horsepower comes in below 6k RPMs just from seeing dyno sheets from engines with a good bit more work than mine, but the butt dyno says it's a freight train all the way to 6k!
I assume my connecting rod bolts are stock, and I don't know what the improvements in strength on a steel crank, "heavy" rods motor are, but con rod hardware is a commonly mentioned weak spot.
I used a piston speed calculator to guide me in setting the rev limiter on my 440 and my wife's Pontiac 4 bolt main, cast crank, H-beam forged steel rods, forged aluminum pistons equipped 421 Tripower. It has roller tipped rocker arms, and a CompCams hydraulic roller cam and lifters. Still, the bore/stroke on the 421 is not as conducive to high revs as my 440!
Here are a few piston speed/max RPM calculators: http://thefirstgensite.com/code/maxrpm.htm
http://pontiac-power.com/maxrpm-calc.php
A good video:

Here's a great site with numerous automotive related calculators:
http://www.wallaceracing.com/techarticles.htm

 

[PurpleBeeper]

does the max rpm of an engine change if its stroked, and if so does the redline move higher or lower than stock?

Short answer...yes, it does....sort of.

Long answer...IF the stroker combo has the same piston weight and the rods are heavier because they're longer, you'd have more stress on the bottom end (theoretically lower redline for stroker). In reality, stroker kits usually have lighter pistons & lighter rods, so even with the longer stroke you probably have less stress (higher redline with stroker). It's something about "reciprocating mass" and the length of the lever (connecting rod length and crank "throw") that I can't exactly remember if you're talking "theoretical stuff". Theoretically (ultra high end racing) a shorter stroke has a higher redline.

In real world (even racing) terms, I think your valve gear is the main "redline limiting factor" assuming a reasonably decent built bottom end. Guestimate of 6000 rpm for a hydraulic cam motor and maybe 8000 rpm for a roller cam motor? ballpark?

 

[biomedtechguy]

PISTON SPEED is a critical factor, and in a stroker motor, the piston speed increases, all other things being equal.
Think about it.
If a piston travels 3.75" in one stroke, x 2 (3.75" BDC to TDC, and then TDC to BDC) versus 4", that's a half inch farther per revolution, per piston. In one revolution, that piston has to travel faster than before because it has farther to go.
In the calculator I used, material quality, piston weight (also related to bore) were taken into consideration, so there were 3 "levels" of max RPM to choose from based on those factors. The primary calculation was based on stroke though.

 

[dvw]

Piston speed, bob weight, valve train weight, quality of components. My 572 sees 7200 rpm regularly. Bob weight 2222 grams. Molnar rods/crank, Diamond pistons.
Doug

 

[BSB67]

does the max rpm of an engine change if its stroked, and if so does the redline move higher or lower than stock?

What DVW said.

But, based on the things you have said, you'll have nothing to worry about. Any 383 stroker kit bottom end will go 7000 with correct machining. Your valve train won't let you get there.

Decent build stock stroke 383 bottom ends can go more than 7000. Again, all moot in your case.