Kiwi-85IROC

G'day can someone explain a few things to me.

Why is it that E/T time was very average---> 14.4 (slippery track,rained) yet my top speed was 104mph. I was wheel spinning trying to get the power down for like 1/3 (seemed like it) of the track.

If I reduce my wheel spin by either a hot day and dry track, or slick type tyres, will my mph go up due to me getting traction and therefore acceleration sooner?

A mate said it might go down?? Sounds weird to me, can someone explain the relationship between speed/ET etc etc etc

Kiwi-85IROC

BTW I realise my E/T will go down with traction...its the mph issue thats got me buggered.

BADDEST305

spinning your tires will cause you to get a higher mph
with a good set of tires that hook your mph usally will be a little less but your et will be quicker. gday mate

Kiwi-85IROC

G'day Mate...Yeah I hear ya.....But why?

If I'm wheels spinning for the first 60 feet (Just a figure) surely both my ET and mph will be slower?

AlkyIROC

ET yes, MPH not very much. I was able to race my truck at the last race because I don't have an engine back in my car yet.

First test and tune pass 15.284 @ 89.49. Second pass got some wheel spin and I ran 15.936 @ 87.73. Everything went wrong on that pass. Third test and tune ran 15.285 @ 89.07. Identical ET and slightly lower MPH as everything was warming up.

First round of eliminations I had terrible wheel spin. It was so bad that I lifted to try and get traction. I knew I lost before I hit the 60' mark. ET was 16.429 but the MPH was still up there at 88.41. There was close to a 4 hour difference between the first and last run. I went from a good 2.23 60' time (4600 pound truck) to a wheel spinning 2.747.

Kiwi-85IROC

Roger that....so how do you explain the near MPH? Just doesn't make sense. Surely if the wheels are spinning then terminal acceration & velocity are slower and seeing as how the distance travelled is always 1/4 mile why would a slow ET and a fast ET have the same MPH?

89gta383

iTrader: (5)

My $.02.

A spinning tire resulting in a higher mph says that the gearing isn't correct. I see you have 2.73's. I bet some 3.73 gears would make your mph more consistent assuming you have traction.

Only way to tell is to get some tires and do the experiment.

Kiwi-85IROC

Fair enough.

The question is: Why does a spinning tired give an increased MPH vs a tire with traction.

AlkyIROC

The engine gets into it's powerband quicker because of the higher rpms. It makes more HP at a higher rpm so the mph will be higher.

A higher stall converter and no tire spin will have the same results.

SLP IROC-Z

iTrader: (1)

i think people are getting u confused. i see whats confusin ya, people sayin the mph literally goes up when u spin, nooo. the mph is a measure of the cars power. the mph doesnt literally increase with spin, the E/T increases because of the extra time it takes to accelerate off the starting line. so what u end up with is a slow ET for the MPH. the 102mph is good for a low 13 pass with a 1.8-1.9 60ft time. get some traction with some stickies, the mph might go down but it should stay the same, the chance of it going down is because of the amount of sidewall flex that slicks have, it robs a little power. hope this helps u out.

oh yeah

a good rule of thumb is for every tenth u gain or take off at the 60ft mark it is equal to 2 tenths at the end of the track

example:

2.2 60ft 14.4 ET
2.1 60ft 14.2 ET
2.0 60ft 14.0 ET

Kiwi-85IROC

Thanx for replys...interesting subject, I asked a few people here in NZ and they couldn't really give me a definative answer.

rob231

okay i'm gonna have a try at this. i have heard when you hook you can lose some my per hour. i was told since your e/t is faster you have less time to get up to speed. so if you did 14.4 @104 spinning and say13.7@ 102 hooking that is because you wasted sitting there smoking the tyres. also when you hook you put more load on the drivetrain and is harder to accelerate thru the rpm's.

Kiwi-85IROC

I've been thinkin about this:

I think it all has to do with the non linear acceration/velocity curve that the car faces each time it goes from 0 mph to whatever.

Example: It may take 5 secs once traction is achieved to hit say 70mph and then it takes a further 9 secs to go from 70mph to 104. (example only)

Whether traction is achieved straight away or after 2 sec, its still going to take the same 5 secs or there abouts once you get bite.

The 70-104 mph figure is pretty much a constantly achievable given there is traction.

Hence, this is why you can do a 13.2 @104 or a 14.4@104, its the 0-70 mph time that dictates overall E/T within reason.
The car will probably do 104mph with traction or with little traction within reason as there is about 1-1.5 sec difference between grip or no grip in the first 0-70mph. But the cars power output vs weight over a 1/4 mile distance dictates the speed.

But what about the same car running 14.4 @94 mph with 100 less HP?

In the 14.4@94 situation, the car is getting good traction.
In the 13.2@104 situation, the car is getting good traction with an improved 70+ acceleration figure ie increased HP, say Nitrous.