Safe RPM for a 451" range????

[747mopar]

I've been playing a bit to much with my Charger and get into the rev limiter way to often so what's a safe RPM range to twist it up to? It's a 456", cam rpm range of 1,800-5,800 rpm, forged crank, rods have been resized and floated, KB Hyp pistons, all ARP fasteners and the rotating assembly has been balanced. I had it set at 6,000 rpm but it screams right past that easily and often so I bumped it up to 6,750 rpm....... I think that should be plenty safe??????

 

[451Mopar]

I had my old 451 up to 7,000 RPM many times, but it had Ross Forged pistons and a solid roller cam. I'm not sure how much stress the cast pistons will take, or what cam and valve springs you are using?
If you float the valves at too high a RPM, you could bend a valve if it hits the piston? Back in the last 1980's when 451 strokers were using cut down stock cast pistons, the piston pin boss would break at high RPM levels (according to the old Chrysler Power Magazine articles?)

 

[Kern Dog]

I understand the question, but to accurately answer it....
When does it start to drop off in power? If you've had a dyno run you'd know where the peak Hp is. With that info, you'd have a useful guideline to work with. No need to spin it to 6800 if the power has peaked at 6000 and is dropping off.
My 440/493 feels strong through 6500 but I never spin it that high, only a few times when it got away from me. Logic, other documented builds and my own dyno time tell me that my combo peaks before 6000 so I see no reason to spin it any faster than that.

 

[PurpleBeeper]

I'm not an expert, but I've always thought a "rule of thumb" was 5500-6000 for stock, 6000-6500 balanced & 6500-7000 balanced with non-hydraulic tappets & double valve springs. Kern Dog's point is a good one....higher rpm is not necessarily a faster 1/4-mile time. As far as how high you can rev the engine without blowing it up? IMO you are pushing it a little bit. I guess it depends on piston/reciprocating weight, how perfectly the engine was put together, how many runs on the motor, etc. and unfortunately, the only rpm that is "safe" is 0 rpm and that's not much fun

 

[747mopar]

It pulls hard all the way to 6,000 but because I'm now running a 6 speed and 4:30 gears I'm just getting into the rev limiter more often. I'm not asking because I want to shift at a higher rpm I just want to bump it up enough to where I won't get into it as often and wasn't sure what these motors will handle. I always shifted at 6,000 with the automatic in it and it felt perfect so that's not changing....... just my ability to shift quick enough haha so I'll put it down to 6,200 and see if that's enough.

BTW........ solid lift cam and dual springs

 

[mopar 3 B]

What did your cam manufacture recommend?

 

[Cranky]

What rods are in the motor? Stock prepped LY rods will handle 6k and more but I don't like to take them up much higher than that unless the pistons are a good bit lighter than stock.

 

[747mopar]

Stock 1970 440 rods, resized and floated with ARP bolts.

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What did your cam manufacture recommend?

Cam specs say 5,800 rpm but it's still pulling hard right on past that. I'm only wanting to know what the rotating assembly will handle so I can set the rev limiter at a safe rpm.

 

[Kern Dog]

I've read that it isn't the rods that fail, it is the rod bolts. ARPs are a smart move.

 

[Cranky]

I've read that it isn't the rods that fail, it is the rod bolts. ARPs are a smart move.

Put enough stress on a rod, and it'll fail....even with good bolts. Strengthen a weak link and you move it somewhere else.

 

[mmissile]

It pulls hard all the way to 6,000 but because I'm now running a 6 speed and 4:30 gears I'm just getting into the rev limiter more often. I'm not asking because I want to shift at a higher rpm I just want to bump it up enough to where I won't get into it as often and wasn't sure what these motors will handle. I always shifted at 6,000 with the automatic in it and it felt perfect so that's not changing....... just my ability to shift quick enough haha so I'll put it down to 6,200 and see if that's enough.

BTW........ solid lift cam and dual springs

I think you'll keep raising the RPM's, as long as the car is pulling hard. Not that the motor will hold up...but will rev higher. Kind of a natural thing. I tend to use things to their potential, and it costs me money. LOL

 

[Garys1969RR]

It's interesting that these 451s rev so well. Mine does the same thing with a 509 Hyd cam. It likes to rev, but I set the auto trans to shift at 5500 RPM, and that works well. I wouldn't think you would want to go past 6800 RPM, although I'm fairly sure it would take 7000. Seems that IQ 52 has taken some of his 451 builds well past 7000.

 

[Lionized]

... I had it set at 6,000 rpm but it screams right past that easily and often so I bumped it up to 6,750 rpm...

Is your rev limiter working?

Have you had this beast dyno'd? At 6k you should be making max power.
Set your shift points where max power is made and forget it.

 

[Challenger340]

Stock 1970 440 rods, resized and floated with ARP bolts.

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Cam specs say 5,800 rpm but it's still pulling hard right on past that. I'm only wanting to know what the rotating assembly will handle so I can set the rev limiter at a safe rpm.

Why in the world would you be revíng past 5,800 rpm,(the Cams rated max rpm), because of "seat of the pants" feel ?
I can guarantee 2 things.
1.) That if the Cam manufacturer says 5,800 rpm... even THAT would be generous, and more likely you are already on the downside past peak power by 5,500 rpm.... so going slower no matter what your "feeling" is !
2.) You are adding internal stress in the Engine by going past peak power.

You see.... it is NOT a "set" rpm that is the limit for a given set of parts.... it is as long as the set of parts can PULL against a load and still make power which is what determines longevity.
If the Engine can still PULL against a load, and make power... a product of Camshaft and "breathing"even shiatty parts will hang in there.
But conversely,
allow the engine to start "freewheeling" past where it makes power... THAT... will shiatcan even the best parts ! which is exactly what you are doing with a Cam rated for 5,800 rpm.
just sayín....
just because it zips right past 6,000.... that doesn't mean it ain't WELL PAST peak power and is starting to freewheel !
Shift at 5,500 rpm and I guarantee you will go faster !