I was flipping through the newest summit "mini-catalog" I received and came up with a question about these products.

On page 32 they have Summit forged crankshafts.
Quote "Made from high strength 4340 stell, the cranks have been nitrided and micro-polished for added strength and come with large radius journals. For engines up to 650 hp and 7000 rpm."
350 main, 3.48" stroke, 5.7" rod: price is $589.95

However, on page 6 they have this product:
CAT (Cal Auto Transpeed) 5140 Steel Crankshaft
Quote "These tough 5140 chromemoly cranks are built for engines that make 800 + horsepower and 8000 rpm. They have computer designed counterweights to reduce main bearing load, large 0.125" journal radii to disperse stress, and hardened journal surfaces for wear resistance. Each crank is CNC-machined to exact tolerances, magnafluxed, and ultrasonic tested before they're pronounced ready to race."
350 mains, 3.48" stroke: price is $399.95

I don't really understand everything written about these, so I don't know how much is advertising mumbo-jumbo and how much is fact. However, it seems to me that if the horsepower and rpm ratings are correct than the CAT crank would be a much better deal than the forged crank unless there is something I'm overlooking about the differnt metals or ***-knows what else. So someone enlighten me, which of these two cranks would be better and why? Is the CAT crank hyped-up junk, or is the Summit crank an overpriced ripoff?

Note: I'm using the Summit forged crank in comparison to the CAT crank, because I do not have a full catalog available to campare the CAT crank's price with other forged cranks, so I don't know how the Summit forged crankl compares to other cranks on the market.

 

I would say the Summit forged crank would be the strongest of the two, but I'm not sure who makes the Summit cranks or where they come from. The CAT crank didn't say anything about being forged so it would be a steel casting which is a lot stronger than a cast-iron crank is, but keep in mind the CAT crank is made in CHINA and some of the Chinese made stuff I have seen isn't all that good, but some if it is just as good as USA made stuff. Here is a link to the CAT home page:http://www.catpep.com/company.htm

 

Does anyone know if this CAT crankshaft with .125 radii needs the more expensive chamfered bearings? What is considered large enough to need those bearings?

 

Listen to the other guy ! Don't buy Chinese junk. From what I've seen,the best deal on forged cranks is by COLA Cranks. Around $7-800 for good USA forgings.

 

5140 is not as strong as 4340...you can get by with a 5140 crank up to 550-600 NA horsepower...

The claim of 5140 being good to 800 HP is suspect...if you are making that much HP, you can afford a 4340 rotating assembly.

Good luck...

 

the 4340 is the stronger.. it's a very hard forging.
I thin k you may be right about it being cast steel

for what it's worth
I got a 4130 eagle crank for 400 bucks.

when you get into the wider radii cranks you need to run different bearings.... they aren't "street" type bearings, they aer meant to run wider tolerances, and arent' designed to hold oil pressure like street bearings are.

 

Actually, what you with the wider radii crank bearings surfaces and holding oil pressure is that at lower RPM's (around 3K) they don't...there is a reason for this...because it is a RACE part. I am sure it performs well at 4000 and above.

4130 is just below 4340 for strength and 4130 is above 5140 for strength...I thought there was one other common steel in there somewhere...

Frankly, there are quite a few people using 4340 import steel for the same price as lesser grade domestic with good results.

www.dallasexportsales.com

I have looked here and I can get a 4340 crank for a very reasonable price...

Just my $.02

 

I can't remember what the old GM forged crank is.. maybe like a 5150 or something like that.

the reason why people can run those 4340 cranks without them adverse results.. is they are genrally a HUGE overkill for the type of power put through them