Safe rpm

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Yote

Yote

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Re : 72 340 with a step up in cam. ( po didn't know what) . Probably a dumb question but what is a safe rpm to run at shift points without asking for problems? I realize that something can happen at any speed. Just asking for opinions that would not put undue stress on my engine. I am getting older but not beyond hot dogging a little at times.
Yote
 
I always tell people the one RPM before it blows up is the safe RPM.
 
Yote said:
Re : 72 340 with a step up in cam. ( po didn't know what) . Probably a dumb question but what is a safe rpm to run at shift points without asking for problems? I realize that something can happen at any speed. Just asking for opinions that would not put undue stress on my engine. I am getting older but not beyond hot dogging a little at times.
Yote
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My 70 starts to get valve float around 6700 rpm, shift sometime before that- have fun!
 
If you have a smart phone, most have an accelerometer chip in them, download a g-meter app.
Use that to find what rpm your acceleration starts to fade, a hundred under that is optimum shift point.
 
Wrong question.
Should be something like;
I have a street340 with a 727, and peak hp at 5400 rpm. What would be a good shift rpm, to strip it at?
That is answerable in one line.
The 1-2 is about6500, the 2-3 is about6300, trap is about5700.
Yes you can short shift second.
I would short them all and then what YellowRose said;shift loops

Each gear will be different. Why? cuz the splits are different. The 727 ratios are 2.45-1.45-1.00, and the splits are 59%, and 69%. To center your HP peak, such that the outgoing hp is equal to the in-coming hp, the above shift points are sorta guessed at. Most times the power drops off faster, after the peak than it rises up, to the peak. I arbitrarly chopped 300 off the 1-2(6800), and 100 off the 2-3(6500). and YR likes 300 over the peak to trap.

But really what is the safe rpm?
Buy a good tranny blanket and find out!
Ok that's bad. I have been shifting my 3.58 stroke 360 at up to 7200 for 15 or more years and over 100,000 miles, cast crank,stock 340 rods, KB 107s, A-833
Your 3.31 stroke forged crank? same rods, LIGHTWEIGHT pistons, should go higher.
There is a formula based on piston speed.I don't have it.Anybody know it?
 
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I think it's piston speed(feet per minute) = (stroke*rpm) ÷ 6

And for cast pistons it should stay below 3500fpm and forged should stay below 5500 for rule of thumb. I guess this assumes your valve train is up to the chore as well.
 
Except hypers.No rules for Hypers. Hypers rule!
Ok, I'm kidding.
When I built my combo.in 98, I worked the formula backwards.Using the 3500 spec; (3500 x 6)/3.58 =5866. Well that sucks. There was no way I was gonna limit my 367 to that rpm.I couldn't find spec on hypers,so I arbitrarily went up the middle and started from 4500fps.
So (4500 x 6)3.58 = 7542 rpm.Can you imagine camming your street sbm to spin up there?Me either.I thought that was plenty of room
If you have hypers in your stock stroke SBM, it I think it's really hard to get to their limit.I guess that's why my 367 is still hanging in there.
With my current 230* cam, she probably peaks around 5500, maybe a little less. Adding 1200 for an auto powerband; that would then be; 6700 x 3.58)/6=3998fps..... I called it good. And it seems to have worked out for me.
But a Hypered stroker? (6700 x 4)/6 = 4467, is getting up there..............
 
Do what yellow rose suggested and you'll be golden. I always thought it was funny listening to guys brag about turning their stock or near stock engines high rpms. Will they turn up? Sure. Will they make any power there? Not much.

I out ran a bunch of high winding small blocks by only turning mine 6000 or so.
 
Hypers in a 340? 7200 rpm worked for me...but 6800rpm was more frequent.
Rev it till power drops off a hair...note...then shift just below that point and you'll be fine, because something tells me you don't have enough cam to take into rpm's that would hurt it anyways.
 
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