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Old 02-10-2011, 02:14 AM
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what would safe rpm be on a 350 chevy with these parts

cast stock crank, eagle i beam rods, cast 9 1/2 to 1 pistons
my valve terrain is pretty solid all roller.
this is my first engine build and i dont want to over rev it.

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Old 02-10-2011, 02:53 AM
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No more than 5,500-6k with cast pistons IMO. If your pistons are hypers (which are still a cast piston), you could goto 6,500rpm. If you're running a hydraulic roller, 6,500rpm would be about the limit anyway and the valvetrain becomes the limiting factor.
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Old 02-10-2011, 05:16 AM
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Here's a simple chart that is fairly accurate, as many racers regularly turn these rpm's, Circle track & Drags.> http://www.chevytech.info/2c26o1.html
Assuming properly built, clearances, torques, detail.
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Old 02-10-2011, 05:21 AM
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Quote:
Originally Posted by SSedan64
Here's a simple chart that is fairly accurate, as many racers regularly turn these rpm's, Circle track & Drags.> http://www.chevytech.info/2c26o1.html
Assuming properly built, clearances, torques, detail.
That's an extremely simplified chart. It gives zero consideration to the parts and fasteners used. Also, as a point of interest, the max RPM it suggests for a 2-bolt 383 (3.75" stroke) is very low considering it suggests a max RPM of 7800 for a 4-bolt 350! Try that with a stock motor and it'll turn into a grenade.
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Old 02-10-2011, 05:39 AM
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V8hed these rpm's & Piston speeds are for a Balanced & Blueprinted engine with quality fasteners. These rpm's are turned most every weekend on tracks all over, but on engines that see regular maintenance.
Blueprint spec etc..> http://www.chevytech.info/1c1.html
http://www.chevytech.info/
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Old 02-10-2011, 05:47 AM
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Quote:
Originally Posted by SSedan64
V8hed these rpm's & Piston speeds are for a Balanced & Blueprinted engine with quality fasteners. These rpm's are turned most every weekend on tracks all over, but on engines that see regular maintenance.
Blueprint spec etc..> http://www.chevytech.info/1c1.html
http://www.chevytech.info/
My problem with that chart is that it doesn't even mention valvetrain parts and that's the part of the engine that often limits RPM. If the chart is targetted mainly at racers, then maybe it assume an all-solid set-up with springs to match, but the OP is likely running a mild-ish hydraulic roller, which would make a big difference. Also, stock cast pistons would not survive at 7800rpm... 4-bolt or no 4-bolt. Neither would the Eagle I-beam rods he's using.
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Old 02-10-2011, 05:58 AM
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How high it`ll rev is controlled with a iron fist by the valve train. The bottom end comes secondary as you can install a valve train that will let it rev to 7500, but you have to have a bottom end that will survive to that. In your case the pistons are going to be the limiting factor as cast pistons don`t like high revs. We use to rev cast pistons to 6000 RPM in a mild 350 that we used in mud racing. In time it broke two piston skirts. You didn`t mention what size engine your running but I`m guessing your running a stock lenth 5.703 rod. The shorter stroke small blocks such as the 327, the 283 and etc will rev higher with cast pistons before they`ll break due to less thrust angle from the shorter stroke and higher rod to stroke ratio.
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Old 02-10-2011, 06:35 AM
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It's all about calculating the piston speed. Use mean piston speed x 6 divided by the stroke.

In your case 3,750 x 6 x 3.48 or just under 6500rpms

Factory cast cranks 3,750 ft/min
Aftermarket cast cranks 4,500 ft/min
Factory forged cranks 4,600 ft/min
Low end aftermarket forged cranks 4,800 ft/min
Race aftermarket cranks 5,500 ft/min
Custom endurance race cranks 6,000 ft/min
ProStock/Mountain Motors 7,500 ft/min
F1 7,500+ ft/min

Your mileage might vary. If you're using something with high miles and your valvetrain has weak springs or other issues then you'll probably never get it to turn any kind of RPMS. This is more of a general engineering calculation.
Now saying the motor will turn 6500 and saying it will make power to 6500 are two different statements.
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Old 02-10-2011, 06:56 AM
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Quote:
Originally Posted by engineczar
It's all about calculating the piston speed. Use mean piston speed x 6 divided by the stroke.

In your case 3,750 x 6 x 3.48 or just under 6500rpms

Factory cast cranks 3,750 ft/min
Aftermarket cast cranks 4,500 ft/min
Factory forged cranks 4,600 ft/min
Low end aftermarket forged cranks 4,800 ft/min
Race aftermarket cranks 5,500 ft/min
Custom endurance race cranks 6,000 ft/min
ProStock/Mountain Motors 7,500 ft/min
F1 7,500+ ft/min

Your mileage might vary. If you're using something with high miles and your valvetrain has weak springs or other issues then you'll probably never get it to turn any kind of RPMS. This is more of a general engineering calculation.
Now saying the motor will turn 6500 and saying it will make power to 6500 are two different statements.

Using your formula of mean piston speed x 6 divided by the stroke, my Scat 9000 cast crank should only be good for 6,000rpm in my 383, which is way off since Scat rate it to 7,500rpm!

These tables are all good for theory, but in the real world, things are often different and, as I've already said, it's the valvetrain that usually limits RPM before the bottom end (although, with the OP's cast pistons, his pistons may actually limit safe max RPM before the valvetrain limits it).
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Old 02-10-2011, 06:59 AM
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Quote:
Originally Posted by v8hed
Using your formula of mean piston speed x 6 divided by the stroke, my Scat 9000 cast crank should only be good for 6,000rpm in my 383, which is way off since Scat rate it to 7,500rpm!
4500 x 6 x 3.75 is 7200 not 6000
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Old 02-10-2011, 07:01 AM
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Quote:
Originally Posted by engineczar
4500 x 6 x 3.75 is 7200 not 6000
My bad, I was using the figure for a stock cast crank.

What I said over and above that still applies, however.
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Old 02-10-2011, 07:09 AM
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No argument here. It's one of those "rule of thumb" things. We shouldn't be able to turn our Stock Eliminator engine as high as we do with the parts that are in it either. But do so all the time.
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Old 02-10-2011, 07:54 AM
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revving an engine at 7000 rpms for extending periods of time is much different then quick snaps up to 7000 rpm.

I have a mild 350 that floats the valves at 7200 rpm. nothing special in the block. stock rods, hyper pistons, arp rod bolts, 4 bolt block, cast crank, balanced.

It has over 100 passes down the 1/4 mile over a 10 year period. Plus countless taco and beer runs. Every time I get in it, I float the valves.
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Old 02-10-2011, 08:23 AM
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Getting back to the OP's valve train...what is "pretty solid"?
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Old 02-10-2011, 08:30 AM
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Quote:
Originally Posted by 68NovaSS
Getting back to the OP's valve train...what is "pretty solid"?
That's valve terrain.
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