If they want me to work quality control for them they need to send me a weekly check. A few of the problems with thier work that I have seen is things that should not even get out the door ever. Sending stuff back and giving them a second shot at it with more than one crank is not acceptable imo.

 

Heck I've had issues with LA Enterprises billet cranks, it is your job to double check somebody elses work if your building an engine. I've disassembled countless oil pumps with machining shavings in them, MSD distributors with loose parts floating around inside.

A good friend of mine bought a race engine from somebody in this board, it had a 9/16 socket under the valve cover, rust on two of the connecting rods and sand packed under the oilpan baffle. When questioned about it they claimed these were his issues. On top of that the clearancing on the block appeared to be performed with a stump grinder and it leaked water.

You shouldn't have to but you should check everything.

 

Anybody who builds engines knows all that. When I check and its off and they have to try again, and they send me a replacement and its off as bad or worse than the last one and this repeats several times with different makes and models. I reserve the right to not do business with them anymore and give them a poor review. The list of companies I buy parts from is pretty short. The list of companies that have imo high quality parts is even shorter.

 

Just for comparison, the stock crank is like 62lbs on an admittedly cheap bathroom scale, so something like a Comet is 20lbs lighter. What lenghts have some of you gone to to remove 20lbs of dead weight much less rotating? How much did you spend on fancy light drg wheels and front skinnies. Granted wheels and tires are on a larger radius so the weight has more impact but you get the idea.

I thin Injuneer is right that it will only showup as acceleration HP gain, don't think it would register in a steady rpm test, but then again acceleration is what all this is about.

 

I got a good deal on a SCAT Ultra Light crankshaft. On my bathroom scale it comes in at 43.6 lbs. So if my stocker weighs close to the 62 pounds that Dwayne found then there is a 18.4 pound savings. That is a lot of rotating mass saved.

 

A lighter rotating assembly is always better if the strength is there. But for some uses it is not going to make a big difference. Most drag cars operate in a fairly narrow rpm band. Example: my bracket car operates between 5,500 and 7,100rpm so there would not be much point in going to any great lengths making the crank light. Light pistons will lower stress on the rods, that's where taking weight off the RA is going to the most good in that sort of application. A street car or a road race car or even a manny tranny drag car is going to benefit a lot more than a drag car with an automatic. Not knocking the light crank idea, just trying to give some perspective. I have an expensive crank with lightening in the Camaro, the race car has a fairly heavy crank. Sounds backwards, but it's not.

Rich

 

Just look up angular momentum, and then apply conservation of energy to it. That will be the end of the story and end all speculation.

Lets ignore bearing drag or any frictional losses they will be roughly the same. You spin up a disc that wieghs 62lbs, and you spin up a disc that wieghs 48lbs. Both of them are giong the same speed, its harder to slow down or speed up the 62lb disc because it can store more momentum. It takes the same amount of energy to slow it down 2000rpm as it does to speed it up 2000rpm.

That is what happens in an engine when you go down the racetrack. Yes the crank/disc will store more hp while its accelerating instead of sending it to the wheels, it will also give it all back to you when you shift right throught he wheels. The only place you're going to get ripped off on the energy is in high gear and you dont get to absorb that energy back (no shift).

Sure sending more to the back wheels is a good thing as you run through the gears. Imo its not worth losing sleep over because the gains will be very marginal.

The moment of inertia is more important in regaurds to how a crank will act rather than its overall weight.

 

Amen!

It pisses me off, and it pisses off the customers when they're told that time is money, and them trying to save a few bucks on the cheapo crank is costing them because I have to measure multiple cranks before they find a decent one. We just went through this with an "RPM International" crank for a 383 mopar - 2 "hand selected" cranks with over .002" bend and journals up to .001" over spec and .002" variance across the width, so bad actually that the connecting rod would not slide up against the radius. Then on top of that the 2nd crank had counterweights that were not cam cut enough and they actually hit the block before the journals laid on the bearings.

After 2 bad cranks, he finally let us supply a good one.

 

Yeah thats kind of another thing why I don't go through that. Average Joe hot rodder doesnt check taper runout straightness or verify fillet radius and wont have it checked for cracks after all its NEW aint it? Hell only a few shops I know of check surface finish. Add to that the average person doesnt know what a stress riser even is how we apply it to mechanical design or the effect it can have on a part or what to look for in that regaurd.

I do my best to make sure companies supplying crap parts don't get any money from me or people I help out. Because everyday people will end up getting screwed when they buy a half *** part and dont have the smarts to verify everything.

 

On the track we see a pretty consistant .01-.015 improvement in ET with lightweight cranks in BBC dragsters but they don't live nearly as long. Not a huge gain. I prefer to use std weight cranks unless it is a heads up kind of deal and then it would be torn down on a regular basis for inspection.

 

Amen.

Rich

 

its more of a butt dyno thing you dont get that much hp from it but you accelerate faster due to quicker revs

 

Not according to post #25.

 

A whole .015! Where do I sign up .

Thats probably a 700hp+ engine to boot.

 

Here is an interesting thread for those interested in the subject. Some of the top engine builders in the country are commenting in the thread.

http://www.speedtalk.com/forum/viewt...ght+crankshaft