terminal speed and wheelspin

[Stav]

Just wondering what effect does wheelspin have on terminal mph.When I ran the 14.7 terminal speed it was 92.71mph with a little wheelspin. Is this the culprit?

[Des Flurane]

Can I thread steal as I had something similar today.
First run, unprepped track btw, 14.79 @ 107.69. Then the times came down with the speed.
Last run 14.16 @ 101.16 which was the quickest ET and the slowest terminal.
No 60fts as it was a sponsors invite day. A H*lden sponsor at that. Nice to watch a blown LS1 run a 11.9 though.
So I'm guessing that launch conditions are the key. No wheelspin being best.

[jonbays]

I am nver really sure how the TS and ET relate to each other. there are lots of factors at work.

I have run two times almost identical ET's but with big TS differences and its hard to see why!

60' 330' 660' MPH 1000' ET MPH
2.3440 6.5700 10.0090 71.4500 12.9630 15.4640 90.2400
2.3340 6.5680 9.9900 72.1600 12.9610 15.4740 91.8400

[northey]

Generally speaking if you wheelspin substantially through 1st & and 2nd gear for example, your mph should drop a fair bit. But it doesn't always work like that.

With the drag cars that I ran they were well set up after much experimenting.
If the et was slower than previous it dropped mph. But that is in cars with each bit of gear designed to complement each other. Good traction at the start; correct gearing, little wheelspin, etc.

In street cars most things are a compromise; either tyres, gearing, exhaust, cams, or all of the above.
If you wheelspin (through those 2 gears again) when the engine gets into 3rd and pulls down into it's torque range (at lower revs than you might normally use) they can still accelerate very well and pull the car up to the same speed as a normal start, good traction and heaps of revs will do.

I'm not having a go at anyone here either. Just stating a fact. Street cars are a compromise; race cars should not be.

If the car has good grip, the correct engine size for the cars weight, right cam, carb, etc and gearing and it spins the tyres off the line it will normally lose mph.

For instance, a driver think he's shifting 1st-2nd on every run at 6300 rpm but because he's too busy controlling the car it may do a little more than that. Maybe 6600 rpm. But maybe on one run during the night he does get it right at 6300 and it pulls the engine down a little further in 2nd and into a better rev range. and then 2nd gear pulls a bit harder than it normally does because the engine likes it.

There can be a huge difference between what the driver thinks is a good rev range and what the engine thinks is a good one.
And the engine knows best. The good drivers are those who recognise that and use it to their advantage.

I had a lightweight race car with a crook (internal damage) convertor and a good 292 single 4 bbl engine. That night it ran mid 11's but at 140 mph.
The engine ran in a torque band it liked after it dawdled away from the start line.

cheers

[Stav]

Hmm interesting stuff here. I kind of theorised in my mind but am probably wrong. the fact that we wheelspin actually means we are going slower and so we have a slower mph. With a perfect launch with traction I thought that both et and mph should be higher because we are going faster...I am not sure but anyone who does know better?Please do ....

[protd]

wheelspin does not always result in lower terminal speed it can actualy work the other way and often does.. as the car with a bit of spin can keep the engine in its torque range instead of bogging of the line resulting in more mph at the end.. this is street cars more so as northy has said, i,m not saying that this is always the case however just that it is possible for your mph to increase in some circumstances..

[northey]

Originally Posted by protd

wheelspin does not always result in lower terminal speed it can actualy work the other way and often does.. as the car with a bit of spin can keep the engine in its torque range instead of bogging of the line resulting in more mph at the end.. this is street cars more so as northy has said, i,m not saying that this is always the case however just that it is possible for your mph to increase in some circumstances..

That is very true also and it can bring a higher mph; wheel spin can be an advantage. But the car shouldn't be bogging in the 1st place; it just means that it's not set up correctly and wheel spin helps it out. It would need a change of gearing, exhaust or cam just to name a few things.

There are THOUSANDS of things that change a car's time or mph on the track. The best thing to do is keep asking people who are doing well at the track. Listen to all the advice and then use what you think will work for your car.
Just because it works on your neighbours car doesn't mean it'll work on yours.

The best thing to do when you start racing is KNOW your car. Drive it for at least 1 meeting without changing anything. Keep the shift points the same, same start line procedure, burnout, etc.

When you know how the car feels and reacts make some changes to shift points, etc.
Later when you want to change the car itself ALWAYS do it ONE thing at a time. That way if you have a negative result you can often straight away point to the last change.

If you've changed 6 things since the last run and it goes slower which one caused the problem?

[Stav]

Youre right northey. I have a big power curve and have had the back lowered.Since then it has settled up a bit.Maybe the weight distribution is out a bit. ? I am going to the suspension place for them to look at this.

[Work Horse]

Originally Posted by northey

The best thing to do when you start racing is KNOW your car. Drive it for at least 1 meeting without changing anything. Keep the shift points the same, same start line procedure, burnout, etc.

When you know how the car feels and reacts make some changes to shift points, etc.
Later when you want to change the car itself ALWAYS do it ONE thing at a time. That way if you have a negative result you can often straight away point to the last change.

If you've changed 6 things since the last run and it goes slower which one caused the problem?

Great advice northey! This means lots of trips to the track useless, but it's all good fun.

Generally speaking the first half of the track has the most effect on ET, and the last half the most effect on TS.

If you think your Mph is a little slower than you expected useless, a few more passes down the quarter may show a different pattern. But you need to be running consistent ET's and TS's over many runs to draw any conclusions IMHO

[Stav]

Gtech run testing on several runs show the car with traction exactly the same but real life would be different slightly. 92.71 with spin. For someone to run a 14.7 it would need between 94-96 mph I think with traction.

[Walkinshaw]

Originally Posted by useless

Gtech run testing on several runs show the car with traction exactly the same but real life would be different slightly. 92.71 with spin. For someone to run a 14.7 it would need between 94-96 mph I think with traction.

14.7 @ 93mph (like what you ran) shows pretty much close to a perfect run for the MPH. 96mph should be capable of cutting 14.4's easy.

[FS5]

Originally Posted by useless

Gtech run testing on several runs show the car with traction exactly the same but real life would be different slightly. 92.71 with spin. For someone to run a 14.7 it would need between 94-96 mph I think with traction.

my last few runs i done at willowbank, ranged from 14.72 to 14.9 with mph between 92.5 and 93.2

[SpoolMan]

Change of gearing and tyre height will change your Mph also, here a piece that explains that part of it very well.
http://www.thirdgen.org/gears

Different tyre pressure will also play with your MPH.

[FS5]

i'd agree with northey ,changing gears at the right rpm makes a difference to your trap speed .i have found with mine that changing right on the limiter yeilds the best mph and et.
stav were you manualy changing the gears in your auto or did you have it in drive?
going by your dyno graph ,the way your power curve flattens out up top and dosen't drop off,you'd be best off changing right on the limmiter too ,to keep it in its power band for the next gear.

so dose this mean you'l be going back to the track again

[OED666]

well, this wednesday, i am giong to have as many runs as possible. changing my shift points each run.

i have run a 14.56@ 98.28, and then a 14.268 @ 98.18... 60ft's make a big difference.

[Work Horse]

There is no direct correlation between TS and ET IMHO, way too many variables.

The only way to really know what a car is capable of is a to keep taking it to the track :

[brenx]

Guy's the poor old XB's ran 13.0@97mph traction is the key and so is weight. The XB @ the time weighed 1610kg's pretty sure that was without me in it.

[SprintMe]

i have run a 14.1@97 mph is that a good ts for that time?

[brenx]

Originally Posted by SprintMe

i have run a 14.1@97 mph is that a good ts for that time?

Depends on the weight of the car. My guess is it is. Generally a car setup for the street is 100% compromise, so it doesn't work that well on the strip.

[Des Flurane]

Originally Posted by SprintMe

i have run a 14.1@97 mph is that a good ts for that time?

Try 14.79 @ 107.69, that is a good terminal :sm_headba

[SprintMe]

Originally Posted by Des Flurane

Try 14.79 @ 107.69, that is a good terminal :sm_headba

your et should be better than that what car and power you got

[Quadcams]

Originally Posted by Des Flurane

Try 14.79 @ 107.69, that is a good terminal :sm_headba

Is that the mph you did just recently?

[Des Flurane]

Yup. Lots of wheelspin but when I got going she never bogged down. All the other runs after the start she seems to bog down/ come off the power then picks up.
TS came down as the ET came down.
Second run 14.24 @ 103.28
Was a very strange day.

[Stav]

with massive wheelspin nearly all the way down the 1/4 I got a 16.295 AND 91.82MPH??i dont understand.Maybe mph is not the be all and end all.

The 14.7 92.7 mph did spin at the start for a split second.

[northey]

Originally Posted by useless

Maybe mph is not the be all and end all.

Give yourself a pat on the back!

Mph MEANS NOTHING.

The man who gets to the other end of the track first wins (provided it's inside dial-in if it's that style of racing).

That's Drag Racing in a nutshell!

Get the car to leave the line hard and efficiently and make it work to 660 mark and the rest will come.

If a car has a fantastic mph compared to it's ET, it only means it's too slow to 1/8 mile. It occasionally happens that you can topend cars and win races but first the car has to sixty foot properly.

[Stav]

i have analysed power from slips actually by seeing timeslips then breaking them down 60 foot first then time take between 60 foot to 330,330 to 660 660 to 1000 ft the 100ft to 1/4 mile.This is the best dyno.For my last run I have managed to improve all of these segments. The 660 to 1000 and 1000 to 1/4 really indicate power inbetween them.

[jcxr]

An old equation for the PERFECT run is divide the length of the strip [1320 ft] by your mph. Mind you this is for an absolute PERFECT run

[Stav]

1320/92.71= 14.237946.

No theres a goal!!

[MIEF9640]

OK you all need to rework your thinking last friday night track cold , vht nice and sticky , helped daughters freind vn 5.0lt . reaction of 7.133-15.1@91.50 so here you go breaking 1st beam on finish line is et , beams 1 thru 3 are recording mph do not back off until past final beam and then see the difference . also try to also compare reaction time and then work from there.

[ratter]

Originally Posted by MIZJ8141

also try to also compare reaction time and then work from there.

Reaction time does not affect et, et does not start until the beam has been broken to start the timer