ET vs weight

[DOTracer]

Has anyone here had experiences where their car's combination was insensitive to weight being added or removed?

For example. I have a 100 lb ballast bar that bolts inside the rear bumper. Numerous occassions I've run with and without and seen no measurable difference on the time slip.

Another example. This past winter I put disc brakes on the car front & rear removing 40 lbs of unsprung & rotating weight off. Also switched front wheels & tires which took another 12 lbs of unsprung/rotating weight off. Lastly I took the 12 gallon cell out and replaced it with a 5 gallon cell which removed 45 lbs. Total weight loss was right near 100 lbs, yet again, no performance difference on the ET slip...does stop much better though.

I'm wondering if there's something with the combination that is keeping the car from seeing benefits of weight reduction?

Only other change this past winter was to change from Torco Mach 110 gas to VP C-12.

Just trying to see if there's an inefficiency in my combination that I'm totally missing.

Any thoughts?

[HemiChallenger]

I'm no expert but i'll almost guarntee converter and engine combination come into play a lot. Kind of like how the turbo car's in racing classes require more weight, yet they still run great, and some even run better with more weight. If you have a BBC with a loose converter the extra or less 100 or 200 lbs. the car might not notice, but I'll bet if you had a tight converter the car would definatley notice it.

My truck has a 12in. 3000 stall converter, which actually stalls closer to 2300rpms and any weight added to my vehicle I notice a difference by seat-of-the pants runs. Mustangs with 302's and stick's i also notice a big difference.

Anyways my point being the car set up, converter, gear, tire size and drag coefficient I think play a big role in what you see e/t wise as opposed to vehicle weight by a 100 or 200 lbs.

[Jeff Chandler]

Do you have front travel limiters? What type of shocks front and back? Do you have someone video you on the starting line? You can certainly learn from a piece of video what your car is doing. YOu pulled all that weight of the front end you may not need as much travel so adjust accordingly. What tire are you running? Another thing you can do those Malibus is build an air pan from the grille to the carb if rules permit. With that big of an opening you will see a gain, more than you will from a rear grabbing air pan.

[DOTracer]

I'm no expert but i'll almost guarntee converter and engine combination come into play a lot. Kind of like how the turbo car's in racing classes require more weight, yet they still run great, and some even run better with more weight. If you have a BBC with a loose converter the extra or less 100 or 200 lbs. the car might not notice, but I'll bet if you had a tight converter the car would definatley notice it.

My truck has a 12in. 3000 stall converter, which actually stalls closer to 2300rpms and any weight added to my vehicle I notice a difference by seat-of-the pants runs. Mustangs with 302's and stick's i also notice a big difference.

Anyways my point being the car set up, converter, gear, tire size and drag coefficient I think play a big role in what you see e/t wise as opposed to vehicle weight by a 100 or 200 lbs.

Don't know if there's anything to it or not, but it is a N/A 461 bbc with a 6000 stall 8" converter.

[DOTracer]

Do you have front travel limiters? What type of shocks front and back? Do you have someone video you on the starting line? You can certainly learn from a piece of video what your car is doing. YOu pulled all that weight of the front end you may not need as much travel so adjust accordingly. What tire are you running? Another thing you can do those Malibus is build an air pan from the grille to the carb if rules permit. With that big of an opening you will see a gain, more than you will from a rear grabbing air pan.

Yes, I do have travel limiters but due to the design, can only take 2" of travel out. Max travel is 6", and I have taken 1" out at one time due to the car trying to go on the rear bumper. I leave all the travel in for most runs in average air on average tracks. It's only when the air is real good AND the track is fast that the car will try going so high, otherwise in average conditions it carries the front tires approx 12-16".

Shocks on all four corners are QA1 double adjustable Stocker Stars.

I purchased a digital camcorder, but can never seem to get anyone to use it for me. Car seems to be working quite well off the line the majority of the time.

Rear tires are 325/50-15 M/T ET Street Radial DOT tires, 18-20 psi.


Best run in 2006 at MIR:

1.327 60'
3.840 330'
5.990 @ 113.87 mph
7.871 1000'
9.476 @ 140.08 mph

49.9 degrees
29.2% humidity
19.8 dew point
30.38 barometer
-980' D/A


Best pass in 2007 at Cecil:

1.297 60' (with travel limited 1" from full)
3.838 330'
5.995 @ 113.33 mph
7.878 1000'
9.490 @ 139.56 mph

54.8 degrees
32.7% humidity
26.8 dew point
29.88 barometer
-100' D/A


I've experimented with an air pan off the cowl/windshield two different times and neither time did it yield any gains. If anything, it made the A/F ratio non-linear being lean off the line getting progressively richer as it went down the track. Tried for almost 6+ months last time to solve that A/F issue and simply gave up.

Several years ago I ran one of Dustin White's USM Ram Air systems which way back didn't do anything for the car either.

To bring air in out of the grill opening, I'd have to replace the radiator with one MUCH smaller to have any room for duct work to feed over the carb. The current rad is 19" x 31" and fills the whole opening. I'd also have to butcher the rad support top to give room for the duct work as well. Not really looking to go that route. Simply trying to find out why the car doesn't respond to weight changes.

I've spoken to some who have combinations that can see changes with as little as 20 to 40 lbs.

BTW, the brake weight loss was 25 lbs off the front and 15 lbs off the rear. The front wheels & tires were 12 lbs off the front. Fuel cell loss of 45 lbs was off the rear of course.

[Jeff Chandler]

Darn good numbers for just a 461. You certainly have the engine combo figured out. With the front opening air pan on my Chevelle it picked the car up 0.05-7. I never thought it could work with the stock core support and a full size radiator but we figured it out, regardless of the air pan I really think you should see if you can come up with another system for your limiters. I've always considered front end travel to be free ET, maybe not huge gains but it will help.
Good luck, your car runs great and it's obvious you know what your doing, keep it up.

[HemiChallenger]

6000 stall 8" converter.

Like I said I'm definatley not an expert but I'll amost guarntee thats why you havent seen the e/t. I'd also be willing to bet a tighter converter (4000-4500) would make that car e/t and mph better.

How much does this car weigh with fuel and driver? and what kind of gears are you running?

[mcracecars]

Hi Dotracer,
That formula of 100lbs=.10 sec is more like a guide line that a hard fast rule. If you have some kind of power/speed calculator you will see the faster you try to go the less it becomes. I figured on my trusty moroso speed calculator, if your car weights 3000 lbls with an et of 9.5, take the car down to 2900 lbs it should only pick up .08 sec. Not a lot really and some things that can keep you from reaching it could be things like, chassis flex, converter, tires, even things like weather, and headwinds. Malibus have a large front area, that has to push a lot of air out of the way. This may cause you from not seeing much improvement.
Taking weight out is always a good idea anyway, as is easier on the car as a whole.
good luck with this

[DOTracer]

Car weighs between 3350 and 3400 lbs. Haven't scaled the car in two years, but have been meaning to do so here soon.

Rear gears are 4.10's, rear tires are 325/50 M/T ET radials which measure 27.5" tall.

[Gary Kubisch]

I believe there is enough difference in the weather records you show to somewhat cancel out your changes,I know my car really reacts more to change in barometer.
You also have to consider that it's two different tracks.

The faster you go,the harder to pick up ET but with the changes you made,You've made the car "better" overall which will show up later in the season.

Not to mention,Lighter cars are easier on parts too.

[HemiChallenger]

I'm still not understanding a 6000 stal converter, the thing probably makes peak torque below that. I dont see what the point for a convertter that loose behind a motor that probably only spins to 7250, but i dont know ur engine combination either.

[DOTracer]

I'm still not understanding a 6000 stal converter, the thing probably makes peak torque below that. I dont see what the point for a convertter that loose behind a motor that probably only spins to 7250, but i dont know ur engine combination either.

I tried to ask ATI last week to see if they felt a converter tweak was in order. I couldn't reach my salesman. I then called and spoke with Kenny Ford at PTC. After hearing about the combination he really felt there was not much he could do for me. He also said the flash stall of 6000 is within 200-300 rpm of where he would like it. He also said there's no way of truly knowing the required stall without dyno data to show the torque peak.

I was always told the flash stall should be 1500 rpm less than the shift point. On all out runs I shift at 7400-7500 rpm. It also see's 7400-7500 rpm at the finish line so lockup is quite good at 5.5 to 6%.

[HemiChallenger]

That sounds good and all, but to me realistically I would never have a converter that loose. Even in a drag car with a glide. Any vehicle I've ever driven with a converter looser than a 4000stal isnt even driveable and even if you dont street drive it you cant even drive the thing onto a trailer or up a small hill.

If you feel that is the way you want your combo, good for you. I'm sure this is mostly a track only car.

[DOTracer]

Any vehicle I've ever driven with a converter looser than a 4000stal isnt even driveable and even if you dont street drive it you cant even drive the thing onto a trailer or up a small hill.

WHAT???

I drive the car up on my open trailer with no effort at all. The car will begin to move on level ground from a dead stop with less than 2000 rpm. I footbrake the launch at only 2500 rpm.

Sounds like you may not quite understand torque converters, and the ones you have driven were slipping terribly.

[Shawn Morrell]

That sounds good and all, but to me realistically I would never have a converter that loose. Even in a drag car with a glide. Any vehicle I've ever driven with a converter looser than a 4000stal isnt even driveable and even if you dont street drive it you cant even drive the thing onto a trailer or up a small hill.

If you feel that is the way you want your combo, good for you. I'm sure this is mostly a track only car.

We use a 6000 stall also, with 565 BBC and glide. Works awesome, shift at 7400 go thru the traps at 7400. It is very driveable, don't need hardly any throttle to get it rolling.

[HemiChallenger]

WHAT???

I drive the car up on my open trailer with no effort at all. The car will begin to move on level ground from a dead stop with less than 2000 rpm. I footbrake the launch at only 2500 rpm.

Sounds like you may not quite understand torque converters, and the ones you have driven were slipping terribly.

I'm sure I've driven mostly junk. Dont know. Anything with that kind of stall I had to rev to 2500ish to even get the car to move, and on an incline it was a joke.

[hsutton]

Hi Todd, I'm sure most of the slippage is very accurate with your data logger. I am curious to know what the driveshaft RPM is just before the lights, at the line and after the line. We broke down this info. off of John Heard's car in quarter second increments and were able to determine exact tire growth figures on one of his runs at Tulsa. It was interesting to say the least. The 10.5" M/T E.T. Drag grows from 28.1" to 28.62" at 156 MPH. That car is a nitrous car and was still picking up speed past the line, just before he lifted and is posted over on his site (Dragstuff). Your still running a 400 Turbo and a twelve bolt, aren't you? The lightweight Superglide in my son's Chevelle seems to be more efficient than the 400 Turbo and is 26.5 lbs. lighter. Much more room around trans. tunnel too and has a built in shield.