What RPM Will a stroker Crank hold?

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Cudafever

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I ask this becouse every thing on the internet rates cranks by HP. aka cast= 500 HP, steel 750+, billet 1500++

Obviously the weight of the rotating assemble will have a big factor in this....

Let's say performance H beam rod's(steel) and a standard weight 4" steel crank.

Properly balanced, what is the safe rpm level?
 
More important the RPM capability, where does the power fall off?
 
Cudafever said:
I ask this becouse every thing on the internet rates cranks by HP. aka cast= 500 HP, steel 750+, billet 1500++

Obviously the weight of the rotating assemble will have a big factor in this....

Let's say performance H beam rod's(steel) and a standard weight 4" steel crank.

Properly balanced, what is the safe rpm level?
Click to expand...

It depends alot on the cranks counterweight shapes and their design.
 
So there could be a big differance between, say a engle, and a k1 steel crank, in rpm?

More important the RPM capability, where does the power fall off?
Click to expand...

That would relate more to head flow and camshaft selction.....Right?
 
Yes, as well as spring selection and carb size. Also as Brian started to point out, there's also total weight, pistons being an issue as well. Heavy things do not like to change directions and change of direction quickly becomes more of an issue with higher RPM's. But! If power falls off at 6700, the point of spinning it to 9000 is ......?

I can not answer the question, there are to many variables. Even if it was a all out engine, I could not answer this.
 
Cudafever said:
I ask this becouse every thing on the internet rates cranks by HP. aka cast= 500 HP, steel 750+, billet 1500++

Obviously the weight of the rotating assemble will have a big factor in this....

Let's say performance H beam rod's(steel) and a standard weight 4" steel crank.

Properly balanced, what is the safe rpm level?
Click to expand...

I don't know how much they'll take as has been stated there are a lot of variables. I can tell you that I plan to spin mine to about 7200.
 
If power falls off at 6700, the point of spinning it to 9000 is ......?
Click to expand...



.....I'd like to build a BRICK **** house......too Peee in? LOL :burnout:


No, your Right, if I ever get my truck sold, so i can start this project! It will be a 6500 rpm motor........but if i decide to go with big heads and cam/carb exc, I won't have to fix the bottom end to do it.

So, in my pee brain, I'm looking for a 9000 rpm(more like 8000 rpm) bottom end that will be stress free at 6500.

Yes i realize that my 6500 rpm goal would only reqire a Cast 4" arm but i want room to grow.
 
Cudafever said:
.....I'd like to build a BRICK **** house......too Peee in? LOL :burnout:


No, your Right, if I ever get my truck sold, so i can start this project! It will be a 6500 rpm motor........but if i decide to go with big heads and cam/carb exc, I won't have to fix the bottom end to do it.

So, in my pee brain, I'm looking for a 9000 rpm(more like 8000 rpm) bottom end that will be stress free at 6500.

Yes i realize that my 6500 rpm goal would only reqire a Cast 4" arm but i want room to grow.
Click to expand...

K1's 3.79 crank is a great piece for that! If you want a 4" crank, Scat is what I would use. They do all the roughing AND finishing now so they have complete control over the final product. Plus they look really great. Counterweights are where they should be too.
 
dodge freak said:
I find that hard to believe--if true it must have the best parts and every trick thrown at it................or the tach is off
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Then you don't get out much...

Go look at BB Chevies that turn that much RPM and more. I had them back in the 80's. Takes decent valvetrain.

Brian has built a couple of SBM 4" arm 7000+ rpm deals. I wouldn't call the rotating assembly in any of them anything trick.

More than a 340 can turn 7K+. Cast crank 360's have been turning 7000+, again, ask Brian...
 
Rpm isn't just based on the crank. You have to have very good machining quality too. Bearing clearance is critical. If you're looking for rpm, get better I beam rods, not H beam... Run top quality lightweight pistons. Make sure the assembly is balanced to the limit of modern technology (tenth of a gram is what mine are done to). Use the best racing balancer (ATI, IMO). Crank flex and harmonics is what breaks them. Most mid level (Scat, Eagle, etc) forged 4" cranks, properly prepared, using the right parts, will go much higher than 7K.
 
Ok her i go changing the direction of my own thread but,......the factory stock rods are H....Right? and i thought the "I" was the stronger rod.......Or do i have this bacwards........................?
 
Stock rods are I beams and h beams are a lot stronger (supports higher HP).
 
I try not to spin my race 417cu 360based more than 7000. It reaches peak tq around 5800 so I shift there.
 
scat 4340 I beam rods weight in at 595 grams.....H beams generally come in around 680 ...although i have seen sets weight in at 630 grams..

scat I beams would be strong enough ...plus no grinding is needed....

so pick your rod and stroke it...
 
Cudafever said:
.....I'd like to build a BRICK **** house......too Peee in? LOL :burnout:


No, your Right, if I ever get my truck sold, so i can start this project! It will be a 6500 rpm motor........but if i decide to go with big heads and cam/carb exc, I won't have to fix the bottom end to do it.

So, in my pee brain, I'm looking for a 9000 rpm(more like 8000 rpm) bottom end that will be stress free at 6500.

Yes i realize that my 6500 rpm goal would only reqire a Cast 4" arm but i want room to grow.
Click to expand...

H beams are inheritly stronger than most I beams. So if your building a race engine with a race block, I would use an H beam rod and spin it up. You'll need a good cylinder head but that's not hard to do anymore.
If you use a stock block, then a cast crank/I beam rod works great because it is lighter and is easier on the stock block. The block is the weak link most of the time, so building a killer rotating assembly in a stock block is kinda like lipstick on a PIG!
Brian
 
I disagree that H beams are stronger than I beams. In my experiense, the best rods out there for strength vs weight is an I beam style. Im not a big fan of the H beam design for various reasons, but they do work well.
 
.....I'd like to build a BRICK **** house......too Peee in? LOL :burnout:
Click to expand...
The block is the weak link most of the time, so building a killer rotating assembly in a stock block is kinda like lipstick on a PIG!
Click to expand...

:cheers: LOL Thanks for that.

Thanks to every one, for your thoughts and appinions :cheers:
 
MRL Performance said:
I disagree that H beams are stronger than I beams. In my experiense, the best rods out there for strength vs weight is an I beam style. Im not a big fan of the H beam design for various reasons, but they do work well.
Click to expand...


I agree. My reasoning for saying get good I beams is predominantly weight. H beams are stronger, but with the caveat that they weigh a ton. More weight at high rpm is harder on the crank and block and will rev slower. I'm not saying H beams wont work. Just that if the choice was H or I, and the rpm points were known to be high from the get go, I'd spend some extra coin for lighter, high quality I beams. The less weight you have to control and accelerate and decelerate, the more power can be made safely.
 
Well OK, how about i shake one more angry cat out the bag............

What would be the life expectance of a ALU Rod.

I have never concidered them as they are change out so often with the big boys..............was told, with a 6500 rpm machine they would last for ever.......Yes ......no
 
Cudafever said:
Well OK, how about i shake one more angry cat out the bag............

What would be the life expectance of a ALU Rod.

I have never concidered them as they are change out so often with the big boys..............was told, with a 6500 rpm machine they would last for ever.......Yes ......no
Click to expand...

But they stretch--grow and might hit a valve or the head. My understanding of them.

ALU rods are not for street engines I always heard. Each year the rods will be a little bit longer and one hot sunny day at 6,500, kaboom, a piston hit something cause the rod was too long

Yes lighter is always better just with ALU rods they need to be replace every ????
 
Yeah the stretch i would have to compensate for and valve releaves may have to be inlarged.

and i agree with all you have said, or altleast that would have been the spill i would have told, a year a go.

Not saying that it is in my budget.........but have been told that they are VARY Streetable at a street rpm.
 
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