ET difference - swap to lightweight wheels - Chevy Nova Forum
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Old 8th-March-2017, 08:48 PM   #1
cdahl383
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ET difference - swap to lightweight wheels

Got some new Racestars for my other car and overall shaved about 80lbs off compared to the stock OEM wheels/tires that were on the car previously (55lbs off the front, 25lbs off the rear). Went with some wide drag radials and front skinnies (radials all around).

Car ran high 11's last year in good air. What kind of ET difference would I see from this if any?
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Old 8th-March-2017, 09:49 PM   #2
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I guess the "old" thing is -100 = .1
So you could be close.
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Old 8th-March-2017, 10:04 PM   #3
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Yeah, hoping for at least .1 off the ET.

I mounted the rims/tires on the car last weekend and went for a spin. I can say for sure the weight transfer is way better. The front end shoots way up now when I get on it with that setup.

Hoping it picks up from better weight transfer, less rolling resistance (front skinnies are 4.5" wide vs stock rims that were 9" wide), and less overall weight.
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Old 8th-March-2017, 10:08 PM   #4
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Rotating mass is the best place to lose weight. You should definitely pick up a tenth or two.
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Old 9th-March-2017, 05:06 PM   #5
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I say make it wheelie first then go ahead and make it fast... throw the old tires in the trunk!


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Old 19th-March-2017, 09:34 AM   #6
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Well Carl?
Any news yet?
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Old 20th-March-2017, 10:52 AM   #7
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Quote:
Originally Posted by wht73 View Post
Well Carl?
Any news yet?
There isn't any racing in Michigan yet lol...........a few tracks there are hoping to open in 2-3 weeks
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Old 20th-March-2017, 06:20 PM   #8
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Track doesn't open until April 8th. Still got a few weeks to wait unfortunately.

Hoping for 11.40-11.50's in good air this year! We'll see! I'll update this thread once I get some passes in. Hopefully at some point in April.
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Old 12th-April-2017, 11:14 AM   #9
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Did you go last weekend?
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Old 16th-April-2017, 03:14 AM   #10
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11.76 @ 115mph today

Nope, didn't make it out there last weekend, was up north with my buddy. But I did go down there today. It was really crowded so I only got in one pass, but I went faster than my old PB and the air was way crummier.

Ran 11.76 @ 115mph w/ 1.66 60ft time in 2215ft DA compared to last year running 11.77 @ 116mph w/ 1.73 60ft time in -500ft DA. The car seems to slow up about .1 for every 750ft of DA increase. I did the math and it looks like the car dropped about .4 off the ET and picked up about 3-4mph over last year. Mods this year are tune and lightweight wheels.

Should run 11.40's in really good air, at a minimum 11.50's which is what I was aiming for. Just wanted to hit mid 11's with bolt ons and stuff I could easily reverse (no major engine work, etc.).





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Old 16th-April-2017, 10:42 AM   #11
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Carl, It looks great with those wheels!

Was this just the wheels or the tune also?

So your saying in the same conditions -500DA it should/could run 11.40's
DA gets confusing to me. Is this the same as pressure?

A certain engine builder calls a high pressure (anything over normal 28) free supercharging.
We call it goood air! lol!
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Old 16th-April-2017, 12:09 PM   #12
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Hey Carl, looks like you weren't able to get your coffee back in the cup holder before the tree went green...😴😴



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Old 16th-April-2017, 10:43 PM   #13
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Quote:
Originally Posted by wht73 View Post
Carl, It looks great with those wheels!

Was this just the wheels or the tune also?

So your saying in the same conditions -500DA it should/could run 11.40's
DA gets confusing to me. Is this the same as pressure?

A certain engine builder calls a high pressure (anything over normal 28) free supercharging.
We call it goood air! lol!
Thanks man! I think it looks pretty cool too!

The new mods this year are the wheels and the tune. The tune was supposed to give me around 25-30rwhp, so probably .25-.30 off my ET from that. I'm guessing the lightweight wheels were good for .1-.15 or so in that range. Worth it if you race frequently, but probably not worth the bother for someone who just goes occasionally.

DA stands for density altitude. It takes into consideration air temperature, barometric pressure, and humidity. It affects N/A cars much more than forced induction cars.

Cooler air temp = better DA
Higher pressure = better DA
Lower humidity = better DA

Cooler temps mean cooler intake air temps which makes more power. Higher pressure means more oxygen molecules in the cylinder which results in more power, etc. From what I've seen air temp and pressure make the biggest difference with humidity making a slight difference but not that huge.

-500ft DA is basically like super awesome mineshaft air. Technically you would want to correct your ET/MPH from that to 0ft DA, but no one likes to do that because it results in a slower ET/MPH. Most people like to correct their times from higher DA's though as it gives them a lower ET/MPH.

All it really does is provide you with a way to fairly compare your timeslips from one day to another without the weather throwing things off.

So I ran 11.77 last year and 11.76 this year. Without DA correction, someone would likely think, wow that guy is an idiot, he spent all that money on wheels/tires and a tune/PCM just to go .01 faster? What a moron! But when you look at the reality of things, I ran that 11.77 last year in -500ft DA and ran the 11.76 this year in 2200ft DA. Huge difference in DA and the car still went slightly faster anyway.

Here's some boring math stuff for you...

My car slows up about .1 for every 750ft of DA increase based on averaging all my passes from last year (about 45 or so in different DA's).

-500ft - 2200ft = 2700ft difference between last fall and this spring.

2700ft / 750ft = 3.6. So basically the car should be 3.5 tenths slower between -500ft and 2200ft DA.

I ran 11.76 in 2200ft DA. 11.76 - .35 = 11.41 in -500ft DA. So my car should technically run 11.4X in really good air and 11.5X in decent air based on the math here. But reality is usually not that easy to estimate.

But yeah that's what most people say at the track. Man we've got some really good air tonight! Or man today's DA sucks. Hopefully that makes some sense.

But overall it looks like the car dropped about .4 off the ET and picked up 3-4mph with the tune/wheels, so it was well worth it!
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Old 16th-April-2017, 10:44 PM   #14
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Quote:
Originally Posted by epfatboy View Post
Hey Carl, looks like you weren't able to get your coffee back in the cup holder before the tree went green...😴😴



Sent while texting and drag racing
I was trying to catch a quick nap before I made my pass so I'd be rested up haha!

Yeah .51 is pretty sad, but I don't focus too much on R/T since I'm just testing things out. It was also my first pass of the year, so I was a bit rusty. My burnout wasn't all that great either, but luckily the track prep was good and those big M/T's bit hard off the line.

If I ever got serious into bracket racing I'd definitely have to step it up there haha!
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Old 25th-April-2017, 01:33 PM   #15
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11.62 at 117.12mph w/ 1.61 60ft

Got a new best on Sunday. Ran 11.62 at 117.12mph w/ 1.61 60ft. My car's timer said I did 0-60 in 3.3 seconds on that pass! It was a little cooler than last time I ran, dropped about .15 from last time.

Hoping for 11.50's in cooler air (like 50 degrees or so). Almost there with 11.62 in 67 degree weather.

Transmission tuning just came out for the A8 recently so once that gets ironed out and everything it should be worth another .15-.2 there. Might get into the 11.30's then in good air.




^ 11.62 pass in car with GoPro


^11.70 pass on iPhone from burnout box (good launch shot)
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