Bitemark46

I've been told by many different people that a ET Drag on a stock stalled LS1 will lower the mph. But why? I wanted to put a girdle on and run 26's on my wifes car. Thanks. -Mark

EDIT: I guess it would apply to all stock stalled autos? Ford or Chevy for that matter. I'm a stick guy and don't know too much about autos.

Undecided

iTrader: (1)

For starters a 26" slick is 2" taller than the factory tire, so you're losing quite a bit of gearing. The factory tire is pleanty for a stock stalled F-body @ a decent track, I cut low 1.9 high 1.8 every time out. That's about as good as it gets for a fairly stock auto car. Also keep in mind, usually the better the 60' the lower the mph because you're getting there faster. You probaby know that from racing a stick car, the same math applies.

Bitemark46

A nitto drag radial (275/40/17) has a diameter of 25.63" and a stock 245/45/17 has a diameter of 25.68" so I doubt 3/8 of an inch is going to affect gearing that much.

Its gotta have something to do with the stall speed or that it is locked well before it enters the motors powerband. -Mark

9sec93

iTrader: (67)

tire spin will increase your trap speed but not your e.t. so with slicks and better traction you will get a better e.t. but a lower trap speed.

gator's 99TA

iTrader: (2)

teh more a converter slips, the more heat is generated, the less efficient it will ever be. the converer never locks up (unless you make it). just like a slipping clutch disc makes for a lower trapping car. that is the general rule of big converter cars. you are in your powerband longer but at the expense of heat and loss of power at the rear wheels. besides, it shouldnt be too much loss of mph.

jimmyblue

iTrader: (11)

Under-aired fat tires have a lot more rolling resistance
and this steals power away from the trap speed.

Bitemark46

Gator- I understand that the better 60' lowers mph but you said that the converter never locks up?? Factory stall is what 1800? So I thought with converters after that rpm is reached it comes "locked"?

So in my wife's cars case.... traps 109 on regular radials with a 2.0 60ft. With some 26" on it lets say the 60' goes down to 1.8-1.7. So the mph will go down to 107ish. Would that be a fair statment? If so, then it really doesn't lower it cause its an auto. It lowers it because of traction. Not arguing just trying to understand. -Mark

FASTFATBOY

iTrader: (23)

An auto car vs a stick car.....stick car has more rwhp and less rwtq(less mulitplication) the standard trans is more effecient(less moving parts) but is harder to 60 ft..because it makes more rwhp vs the auto car it will mph more.

The auto car will hook and 60 ft better, better 1st half the track because of less shock load, more torque mulitplication(through the converter) but because it is less effecient it will mph less, but often will et better than the stick car.


I see no reason to run slicks, a drag radial is the best of both worlds, you get to keep your gear and drives MUCH better down track.


David

junior28570

iTrader: (22)

Not hear to argue but I'm having a hard time reasoning with this.

Wheel spin will result in a LOSS of power and I would think, net a lower mph AND et. Lower 60ft's represent better use of the power.

Comparing my own time slips .. the higher my 60ft, the lower my et AND mph.

I would GUESS all 1.4000 60ft mph are the same (or VERY near) the same mph. This being because of the short distance and not much room to utilize hp. I'm curious if anyone has any 60ft mph data ... (??)

SPEEDYws6

iTrader: (9)

Bingo, slicks eat up power on the big end.

TS6

iTrader: (41)

Generally speaking, the worse the traction, the better the MPH (within reason).

Slicks to have more rolling resistance but I doubt it would show much difference on the slip.

I'd get some MT drag radials for it and call it good.

9sec93

iTrader: (67)

example: 2005 season, my car ran consistent 9.40's @ 144 mph w/ 1.30-1.33 60', when i would get tire spin on the launch, it would run (depending on how bad the tire spin was, if it wasnt too bad to abort the run) 9.60's @ est. 145 w/ a high 1.3 to a mid 1.4 60'

Magnet

iTrader: (36)

there is no loss of power from spinning...you are jsut not getting the power to the ground. Your et suffers because of this, however your trap speed can actually increase from ssome tire spin because you have MORE TIME to get to the end of the track and you are also higher in your RPM band...

EDIT: obviously this is only within reason...if you spin half the track you are obviously not going to gain mph

junior28570

iTrader: (22)

I should have phrased that differently .. wheel spin is a result of wasted power (and time /et/).

You have data that supports your input ... can't dispute that. It just has always made the most sense (to me) that within the 1/4 (or 1/8) the better your car performs at every instant (the first 60 ft being the most cruical), the better the results. In the end, there is one contant .. the distance. The clock will adjust and is but 1 of 2 means of measuring performance.

I've always looked @ higher trap speeds with lower et's as a result of poor 60ft's ... all else being equal. If that same car would 60ft better, so would the mph increase. Of course, I'm assuming the mph @ the 60ft would be faster.

I do think you're right in keeping within the higher RPM band and it is equally as important as traction in lowering et's. with that being said, I'm inclined to think along the same lines as Bitemark46, the stickier tires are not allowing the car to operate within the cars power band. It's essentially bogging down with slicks, forcing the car to operate too much within the lower rpm range. Not enough power to better utilize that amount of traction. I would think a higher stall converter would help this car a lot.

GEARHED

iTrader: (5)

I'm going through the same thing the last year - always a manual but bought an auto so I can run anything. That being said and on the same learning curve, I think what you mean by "lock up" is from the time you spool up to the time it "grabs" on the converter and solid traction.
Manuals do not have that sort of 'wait' time to lockup, we control that with the clutch.
So with an auto and stock stall, you are better suited to put a higher stall (3000-3200 so you aren't losing anything) to get that traction in the traps you are looking for. You should hit the powerband in your 60' and increase your trap time, I've seen plenty that are a bit slow out of the hole and 60'/80' then pull it out on the trap on this kind of set up. Mine does the same thing but the stall is too high for it and need to come down from the 3600 in there - it won't lockup *until* I hit the traps at which point I've lost all my 60' times.

Daym, have no idea if that helped.....

Bitemark46

I would but aren't DR's harder on the rear than a slick? Atleast that what I thought. Harder sidewall was my thinking..... less give. -Mark

slick1851

You know what, AWD drive guys also say that DRs are harder on parts.....


"Less give"

AL SS590 M6

iTrader: (1)

That's exactly it. The longer that you keep a car out of it's power band the lower the MPH will be even though the ET & 60' could improve due to more traction.

Wnts2Go10O

iTrader: (12)

depends on more than the tire i would think

Vintage Iron55

You are both right. You are speaking of two independent variables that produce similar results. I am sure you can both agree however that the coeficient for horsepower is far larger than that for controlled wheelspin.

It is interesting to note current theory suggests very sticky tires and higher stall speed (or very low starting ratio with a light variable pressure plate and sintered iron slippable clutches for standards) where Guys with manual transissions used to want the tires to turn about one to one and a half revolutions on the launch. That is back in the days of racing with muncies and numerically lower gear ratios like 4.11 or 4.56. Something has to slip for the first 40 or so feet to get the car out smoothly and keep it in the powerband. You guys with automatics have a torque converter do this for you.