How much speed are you gaining after the 1/8 mile?

I've been trying to find out if or why I've been losing mph on the second half of the track. After reviewing some of my previous timeslips, I found that typically I was picking up between 23-24 mps in the second half . Normally when I ran 88-89 in the 1/8 th, I would run 112-113 in the quarter. About a month back, I found that my mph had fallen off quite a bit. A short time after that, my transmission failed. I figured that maybe the tranny had been slipping in high gear causing me to lose mph. I recently had a new tranny installed but I'm still having the same problem. I ran a best of 12.09 yesterday but only at 109.4. Before these problems, I was running between 112.5 and 113.7 in this type weather. I did notice that my valvetrain was getting very loud in the upper rpm range so I'm now wondering if I might have weak valvesprings. What do you guys think? I cant understand what hold the car back so much. I thought it might have beena lean condition but my o2s were reading .890 mv. What do you guys think?

I only pick up 21 mph in the last 1/4 mile but I'm also topped right out at the finish line.

Even top fuel dragsters running 330 mph only gain another 60-70 mph in the last 1/4 mile.

I gain about 30mph :)

I gain 27mph. ;)

Back in the fall of '99 I was gaining 27mph (81-108), but now I am only gaining 23 (88-111). I think my clutch is slipping so I will have a street twin going in next spring along with a new fuel pump.

26mph 86.5-112.5

i pick up ~24~ mph with my LT1. my big block pontiac picks up ~22~ mph. both cars are NA...the LT1 is a 6 speed, poncho is an auto.

I gain 21-22 typically

20MPH from the 1/8th to the end of the 1/4.

~ 24 mph

I only gain 20 mph. I go from 85mph 1/8 to 105mph 1/4.
I need some more top-end.:( (maybe it's time for a cam :D)

generally, 80% of cars run 79.441 % and 79.818 % of their 1/4 mi. speed in the 8th. or an average of about 79.63%.
10% run slightly faster, 10% slightly slower.

Exa.
80.5 mph in 8th
then
average = 101.1 mph in 1/4
80% run between 100.85 and 101.33

It's not just a typical "20" or "22" mph on the second half. There's more math involved than you might think. If your % is about the same now as before, then you either lost some power throughout the band (which I doubt) or it was just a bad night to run. If your % is skewed with a high 1/8th but lower than usual 1/4 then it's PROBABLY top end loss of some sort.
A more accurate gauge of how your car ran is how the other cars there ran.

Sometimes if you run a faster 60-foot, and a better ET your MPH will come down some. I still have never hear a convincing explanation exactly why but I've found it to be true in many cases.

Also, if you're running quicker than ever but you end up getting near a gear change as you're going through the lights I've had experience where my MPH doesn't change at all, even though I run a quicker ET.

On my traction limited cars that don't 60-foot worth a damn I'll usually run about 22-23 MPH more, if I'm running a car that's near a 13.0 kinda time. But the faster you go, the bigger the difference will be.

Racing into a head wind or on a track that's a slight uphill can make some pretty differences in MPH. If you're running at a different track than usual then don't even bother comparing numbers from some other track- there will always be differences.

There's a lot that affects it.

I usually pick up around 22 mph. Stock motor w/bolt ons, 3560 raceweight.

I usually pick up 26 mph. 91mph 1/8 117mph 1/4 or 90mph 1/8 116mph 1/4. I hope to change that with the th400 install.
Matt

You have to also look into how much you are gaining per second averaged. That is a big indication of how your car is pulling.

Take my combo right now, the difference between the 1/4 to the 1/8 is ET wise 4.251 seconds, MPH is 24.49. This gives me a per second gain of 5.76 MPH on average.

When my car was stock, the difference between the 1/4 to the 1/8 based off of these numbers of 1/8 -9.097@77.99 MPH, 1/4-14.085@99.16 MPH, the car was gaining 21.17 MPH. This gives me a per second gain of 4.244 MPH on average.

One could say your only gaining 3 MPH the second 1/8 more than my stock combo, but I am not only gaining more MPH now, I do it in much less time also.

My old Charger used to gain 27 MPH in 4.0-4.1 seconds. That was a good pulling top end car.

Both those cars combo are in the upper 10%. The 1/8 compared to your 1/4 mi in stock form is 78.65% vs. 78.88% now. Basically, if you trap a certain MPH in the 8th, your MPH in the 1/4 is very predictable most of the time, regardless of combo, gearing, car, etc. If you have a high MPH in the 8th then you will have a proportionately higher 1/4 mph. Simple.

By looking at that stock time my guess on your 60' time would be about the 2.00 range, +-.05 or so.

that 79% thing is pretty good....i was even doing it on a few of my friend's cars that gain a lot in the last 1/8

one of my friends gained about 31mph

118 to 149.....

79% of 149 is 117.71

pretty damn close

I agree with you Dave, you've probably given those springs a healthy workout...lol
My typical gain is around 21-22 MPH
Again, those are some sweet times your running...:bow:

On radials I pick up 30mph (96 to 126)

On et streets I pick up 28mph (100 to 128)

Well today I was able to figure why I've lost so much mph. I was able to put the car on the dyno...results...peak of 319.8. Before, I was pulling 345 on a conservative dyno. For some reason the rpms fall off around 5400 rpms and never really recover til around 6k. With my 3.73 gears, I usually come through the traps around 5800 rpms so I can now see why my 1/8 the mph was normal but my final trap speeds were off. I wish I had a means of posting my dyno graph but I don't. There are quite a few peaks and valleys after 5400 but according to the wide band o2 sensor, air/fuel ratio stayed right around 13.1 so I think that rules out fuel. The graph wasn't real jagged like a bad ignition would normally appear to look. I have no idea where to start. Help guys...

33mph (102 to 135). 102/135 = 76%, so I guess the 79% "rule" isn't too far off even for a blower car.

Rich Krause

Well I was able to test a few valvesprings and found 1 out of the 5 I tested was bad. Spring pressure on 4 was 120 but on the last 1 was 85. Well I guess my next project will be to change all the springs. Hopefully this is the only problem. I'll post results after the springs are replaced and track tested:D

between 28-29 mph from 1/8 to 1/4

My impy only picked up 19.82mph (78.63/98.42), but I have yet to pull the valve covers and my car pushes a lot more air than those dang F-bodies. :D Yup, time for a cam :cool:

The times that I went to the track. I was picking up 31-32mph N/A

On street tires, went 88 in the 1/8th, 120 in 1/4.

Setup is just a 383, with CC306, LT's, 4.11's, and AFR 195 CC heads.

I never was able to see how much it would pick up on ET streets, but it did go an average of 96-97.XX with them in the 1/8th.


Jose

I picked up 27 mph from 1/8-1/4 .