Rotational Weight Question
 

Lets say you have C/SA 69 Camaro 375/396, If you ran a conventional 12 bolt with a steel spool non gun drilled axels and ran 10.50 with 1.36 60 foots, if you built a 12 bolt with 35 pounds less rotational weight and ceramic bearings, how much would you pick up?

Re: Rotational Weight Question
 

I think if you picked up .01 in 60 that would be a lot.

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I put an aluminum spool and lightened gear set in mine, and found nothing. I don't waste my money there anymore.

Re: Rotational Weight Question
 

My thoughts are, you could pick up more by having your rear end square in the car and all moving parts on it move smoothly with no binding. The right lube and how much is also important along with having the gears properly set up. I also don't think you could get 35# out of a 12 bolt and if you could all that it would help would be sprung unsprung weight. Tom

Re: Rotational Weight Question
 

What lube do you run?

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Do you think a foot brake combination might have different results? I appreciate all opinions, just trying to learn.

Re: Rotational Weight Question
 

I remember a saying that was attributed to Colin Chapman

A gram of reciprocating weight is worth an ounce of rotating weight

an ounce of rotating weight is worth a pound of chassis weight

Take that with a grain of salt. ---Trevor

Re: Rotational Weight Question
 

I was always told that rotational weight is equal to 4 times the actual weight---- that means that for every pound the effective weight that the engine is trying to overcome would be 4 pounds--- now this may depend on how great the diameter of the object is--- in other words if you have an item that is 2 inches in diameter the rotational weight difference will not be as significant as say an item that is 12 inches in diameter where it should be greater--FED 387

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I asked this before. I was told to spend my money under the hood. All that crap isn't worth .05

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I think if you have the car flogged out, tuned out and drive it perfectly every time, buy that stuff. I do think it can help over time,but it is never one thing, it is all of the things. If there is no more HP to be had, start there. If you can't make minimum weight and you can save unsprung weight why not?( expensive though) You need the good stuff though. I have heard of guys trying some aluminum spools and the deflection hurt more than any weight savings. If you are not hampered by any pesky performance rules, just hop up the bullet. I agree, very small gains for big money. Walk the Comp pits.mthose guys know.

Re: Rotational Weight Question
 

You buy the lightweight stuff when you are building to begin with, or you need new parts. Then it is worth the money. If you're replacing perfectly good reasonably light stuff that is working now, with high dollar trick lightweight stuff, most often it is a waste of money better spent elsewhere.

The lower the power of the engine, the more it has to gain from light parts, as it has no "surplus" power.

Too many people go spend meg dollars on trick stuff long before they've mastered the basics, and maximized the rest of their combination. These are the people who have rarely if ever rented a track or spent days at test and tune sessions.

To the original question, the only way to know what it is worth is to test back to back on a given combination, with serious A-B-A testing. Most people who spend the time and money to do that are understandably quite reluctant to share that hard learned data with anyone, save a few people that share with them.

Some of the very fastest cars have none of the trick stuff in them, not even in the engine. One engine builder responsible for the legendary performance of a certain Stock Eliminator car once told me, while we were discussing dyno parts, that his "shop was filled with camshafts and headers the engine and car did not like", and "the secret to it being fast was not so much knowing what the car liked, but more a matter of learning everything it didn't like".

Re: Rotational Weight Question
 

to answer your question look for a book by Herb Adams on chassis--- he explains in great detail the difference between rotational and static weights and the ET/MPH/HP advantages in going to lighter weight items versus a heavier weight item ---performance wise he breaks it down into static weight-- rotational engine weight-- and rear axle rotational weight ---and the performance gains that can be achieved by using lighter weight components ---This should answer any questions you might have--- educational reading--FED 387

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They may not have the same effect. Also, is the rotational weight wheels or axles? Brakes or spool? Rotational weight isn't all the same. All the weight can be quantified if you know the moment of inertia.

Re: Rotational Weight Question
 

Very good replies and in my experience
there is more between the fenders than
You will ever find in the diff!! My.02$$

Re: Rotational Weight Question
 

Unfortunately, there's not a hard fast rule for the question you ask.

You need to look at the rotational weight AND the effective gear ratio to truly determine the gain you might see.

Translated, rotational weight removed between the tail shaft of the transmission and the tires is not very effective.

Rotational weight removed in the transmission is very effective. Ask the guys Pro Trans or Scott McClay if reducing transmission rotational weight is effective. You won't see the gain in mile per hour, but the lighter transmission will ET better.

Rotational weight of the engine is even better than the transmission. Ask the quick stick guys if they like a light or heavy flywheel.

Reciprocating weight of the engine is beyond my understanding to say how much better it is. I tried to figure it out once but it was beyond my ability to comprehend. But lighter is better.

Re: Rotational Weight Question
 

The laws of physics says any reduction in rotating weight has to be beneficial. But the variables associated with the comparison runs themselves can vary more than the benefits.