Originally Posted by wht73
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!