What could be the max safe rpm?

[SwedCharger67]

Greetings,
I've built a 512 stroker based on the B-block. Since I have fully computerized engine management I can freely set ignition and/or injection cut out rpms. The question is where to set it???

The rotating assembly is very light and the bottom is very solid, I don't think the limitation is here.

The heads are Stealths, with supplied double springs (claimed pressure approx. 330 pounds @ 1.275" .600" lift, approx. 130 pounds @ 1.875" installed height). Retainers and locks are replaced with beefier stuff.
Valve lift is .527 at intake and .547 at exhaust. Cam is hydraulic Lunati xxx703 (https://www.lunatipower.com/Product.aspx?id=1579&gid=362).
From Hughes I have pushrods that are thicker and lighter than original, alu 1.6 roller rockers with studs and billet steel shaft hold downs.

It may well be that the heads run out of steam before reaching the rpm limit but it would anyway be interesting to hear if anybody knows approximately where the valve float could start to appear?

 

[IQ52]

It will probably make it's maximum horsepower before 5,500 RPM, maybe as low as 5,300. There would be no need to redline above 6,000 RPM. My guess is the valve train will become unstable around 5,700 RPM.

 

[bm02tj]

After reading IQ52's posts and tests he has listed I do not think you will get a more accurate answer than his

 

[SwedCharger67]

Thanks for your feedback.
I had hoped for some higher redline but I guess that will require some serious investments in parts and labor.

 

[451Mopar]

Ditto IQ52. That's a small cam for a 512" stroker.

 

[Badvert65]

On a related note....anything over 600 HP on these blocks will need a stud girdle or the main caps will eventually crack and fail.
Play safe...

 

[Dennis H]

Mine runs out of pull at 4850 per the chassis dyno. Thus the chip. Dyno it.

 

[Meep-Meep]

He does have the 1.6:1 rockers so maybe will alter the cam power band a little.

For safe RPM limit with a new stronger crank, lightweight forged 2618 alloy pistons, overall light weight rotating assembly and better than stock valve train I would say 6K easy. 4000 series alloy pistons are typically more brittle due to higher silicon content, but may not affect safe limit RPM that much due to light weight. That does not mean it will make power at or past 6K. I'm thinking on a missed shift or some other accident it should stay together.

 

[Herr_Poopschitz]

Valvetrain weight...ramp acceleration w/ the hydraulic lifters will be the limiting factor...1.6s will provide more grunt lower, but will probably exacerbate issues higher up.

That said, small heads and what's a small cam for a 440...it may rev to 5700 before instability, but power will drop like a rock way before that.

 

[Gpuller]

Thanks for your feedback.
I had hoped for some higher redline but I guess that will require some serious investments in parts and labor.

Go ride your Ducati if you want something that is high winding! ha ha ha

 

[rev.ronnie]

130/330# of spring pressure is going to limit you. You have a .904" lifter, don't be afraid of a little spring pressure.

I'd run it at 160/400# with good quality lifters, after break in, of course. You want to avoid lofting at Max lift and seat bounce.

 

[Supershafts]

It will probably make it's maximum horsepower before 5,500 RPM, maybe as low as 5,300. There would be no need to redline above 6,000 RPM. My guess is the valve train will become unstable around 5,700 RPM.

I agree

 

[bigmanjbmopar]

6500 all day push it baby!

 

[Coyoteduster]

There's really only one sure way to find out ... :laughing4:

 

[SwedCharger67]

There's really only one sure way to find out ... :laughing4:

Hahaha...I have thought about it...! ccasion14:

 

[Meep-Meep]

130/330# of spring pressure is going to limit you. You have a .904" lifter, don't be afraid of a little spring pressure.

I'd run it at 160/400# with good quality lifters, after break in, of course. You want to avoid lofting at Max lift and seat bounce.

400 lbs with hydraulic is OK? I had Lunati say 350 max with a flat tappet hydraulic.

 

[rev.ronnie]

400 lbs with hydraulic is OK? I had Lunati say 350 max with a flat tappet hydraulic.

400 is no problem with a hi-performance lifter. You can do a lot more damage to a cam and valve train parts having the system slack up with a spring that is low on pressure.
Remember, it's a .904” diameter. They are not very aggressive.

 

[Meep-Meep]

Makes sense. I suppose if it's called a cam follower it better do just that.

 

[rev.ronnie]

Makes sense. I suppose if it's called a cam follower it better do just that.

350 pounds on a .842" lifter and a small lobe is probably more stressful because of the aggressive angularity than a .904 lifter on a larger base circle with considerably more pressure.

Mopars really have it good when it comes to the cam and lifters.

 

[SwedCharger67]

spring pressure

Thanks for all the interesting inputs.
Increasing the spring pressure to 400 lbs...how much could that rise the rpm limit assuming all other parts are up to the task?