I'm back again with the second installment of weight testing. Unfortunately, there were issues (delays) at the track and not enough time to get the accuracy I wanted. Although I believe the results confirm last week's tests.

I removed the passenger seat (51.4# for a LT2 powered) and 10.2# of other junk. I made my first warmup pass at 11.56 and then ran 3 more at 11.51, 11.49, and 11.50.

When compared to last week (without the extra 109#) of 11.64, 11.62, and 11.59, it looks like a big gain. The DA held fairly steady around 2200' and when adjusted they all were 11.22 runs. That's .07-.08 for 61.6# which again translates to .12 per 100#.

That pretty much convinces me that the .10 per 100# is slightly on the conservative side. I don't think I'll have many opportunities for testing until fall. I'll want to get some rotating weight tests then.

 

Hello,

You have to take into account the skinnies have less wind resistance as well as lower weight.

Douglas in Green Bay

 

Hello,

The aerodynamics of the car changes as the weight is placed in different locations (nose pitched up slightly or down slightly) and traction may have improved with the weight in the back.

Douglas in Green Bay

 

Great thread! Love all the data and testing.

I'm not arguing with any previous statements in which I find all of them valid, some more than others LOL. But I want to merely add my experiences to add to this thread.

I believe % of weight change and horsepower can effect ET change as well as where the weight is being changed (front axle vs. rear axle wgt). In the 90s drag racing my 2450lbs 250hp Acura Integra it only took 60-65lbs to make up .10ET difference (wgt location dependant). On my much heavier Pontiac G8 it took 100-110lbs (location dependant) to make up .10ET. Last year on the G8 chasing the US/Aus record I was rewarded significantly by removing weight forward of the front axle (22lbs bumper and 11lbs windshield washer tank/motor) by .05-.065ET consistently compared to previous weekend after computing for DA differences. I did however achieve .02 better 60fts, which I believe was from noticeably higher front end lift on the launch, allowing more weight transfer. Same can be said for rearward of rear axle. Last year when I was attempting to go from the #1 6.0L record (11.303) to #1 all-motor record (11.09) to beat all the strokers and the one LS7 motor, I removed my OEM 46.5lbs battery and 6lbs of battery brackets (that sit behind the rear axle) for a 5lbs shorai lithium battery, and only improved .032ET (DA corrected), not the .045-.05ET I was hoping for. I needed to find more ET so started to look elsewhere (rotational weight and lower DA). As many of you have mentioned before too many variables to consider here but that is my assessment, so take it for what its worth.

I will also add where you change tire/wheel weight also makes a difference as well due to leverage and stored energy into mass (i.e. flywheel principal). Removing 1lbs of weight at 26" should have the same ft lb leverage effect as 2lbs of weight at 13". Therefore tire weight is almost twice as important as rim weight. Last year trying to be creative to get the G8 into the 10s, I changed out the 16.5lbs GTO spare tires to M&H 11.8lbs bias ply tires and I picked up .03-.04ET (DA corrected), which was 40% improved over my 36lbs rule of thumb I had previously discovered. All that weight improvement was on the far end of the tire. I can't speak for the vette yet as I haven't tested anything in my short 5 months of ownership and 5 times to the track....but in my 5 year old G8 with over 1000 drag runs I've determined the following "rules of thumb" averages for a .10ET change (yes there are many scientific reasons why) but an ET change is an ET change and here are "my" results:

Static weight: 106lbs between axles (25-50lbs forward of front axle, 110-125lbs rearward of rear axle)
Rotational weight: 36lbs (24lbs for tires, 36-44lbs for rim).

So far I have been applying all these lessons learned into my new vette and have seen what appears to be similar but not exact effects. I haven't paid close attention to recorded differences, nor have I done 1 change at a time. I am very impressed with how much I improved just adding skinnies and a racey 4000 stall (.8ET improved, with the help of 700ft better DA and 5 less gallons of gas). My goal is to copy my G8 build and see how fast I can take an all-motor Grand Sport. I bought myself a cam swap kit for Christmas, and then headwork will have to wait until spring. I am learning there are way less improvements to make to the C6 versus the G8.

I love this hobby. Keep this useful thread going and I hope to meet all of you at the track sometime!

Chris
Navarre, FL

 

I have found a consistent 1.5 to .2 from using skinnies and taking the passenger seat out.

 

I would definitely like to see more data on the effects of rotational weight. Tires, wheels, brakes, and even clutch/flywheel. Although consistency with a manual is a lot more difficult.

I'd also be interested in seeing how the gains from rotational weight differs when it's removed from the front or rear.

 

Design and do the testing, then share the results. There is no absolute formula that works in all cases, so what you do and share will be added to the total knowledge database.
A couple of the important things to remember is that it takes more than one result doing the test to provide real value. All tests should be run under the same conditions as possible and adjusted for DA differences. You can plug in values in the DragTimes calculator, since the difference between tests are the important numbers.

 

HOXXOH,

I led to this site and this thread by reading through your 1/4 mile tests. Thank you for logging and reporting this data. It is really helpful. Have you did the weight test for rotational mass again (Wheels/Tires)? I have been looking but have not been lucky in finding the thread if it exists. Thanks and sorry for 'reviving' an old thread. I don't like to start new ones on the same topic.

I wouldn't even mind PMing for more details on other weight loss items you found to be significant to affect your 1/4 mile times.