inconsistent 60ft

[slwryde]

I have varying 60' times on my 67 camaro. Each weekend the 60' starts out great with the first pass being the quickest and the last past the slowest.
1st pass 1.43
2nd pass 1.50
3rd pass 1.56
4th pass 1.61

This is the typical scenario. The amazing thing is it starts all over the next weekend.

The car weighs 2800 lb with me in it. 1550lb on the front.
The car runs 10.60s @ 125-126mph.
horsepower is 575@6800
I run a powerglide with 1.76 low.
I have a 4 link with single adjustable strange shocks.
Front suspension is stock.
I leave on the 2 step at 5000rpm
I currently run hoosier qtp 18.5 x 31.


I have had the transmission and converter checked out. Nothing unusual.

My blame is centering around the tires. Maybe the grooves are holding some water and carry it to the starting line.

Any thoughts??

[1320racer]

post up the time slips from the 60 foots you listed and I've got a few questions...

how experienced of are driver are you and how many passes have you made in this car?

[d1hitter]

are u staging the same? and try leaving @ 4000 or 4200

[L78 Nova]

Transmission temperature ??

[slwryde]

Thanks for the help...here are the answers to the questions so far.

I am not an experienced racer. I have been racing on and off since the late nineties. I usually make it to the track around 10 times per year.
I will admit that on the starting line i am usually nervous however I try to pay attention to how I stage and feel as if I do stage fairly consistent.

This car is a new setup for me and last fall was the first time I raced it.
I have very few passes in the car; fewer than 20.
I have no idea of what the transmission temperature is or the line pressure.
I have a Be Cool aluminum radiator in it with the built in transmission cooler.
I never have had a problem with the car over heating and honestly did not think the transmission would be.

Here are the days time slips for the second time I had the car out 1/8 mile

PASS 60ft MPH ET air pressure time slip notes

1 1.454 102.04 6.674 7 psi
2 1.500 103.45 6.684 7 psi
3 1.550 100.90 6.815 8 psi pressure change
4 1.532 103.21 6.776 7 psi
5 1.544 103.21 6.785 7 psi longer burnout
6 1.586 102.04 6.859 6.5 psi try psi change

[rallye bob]

My first observation......... That's way too much tire for that combination...... Let's start there.
What rear gears?

[68camaroSS]

A couple of things pop out. I think you are right that it is the tires. First, why are you running the D.O.T. compound tires? Second, the other post was correct, why are you trying to leave at 5000 rpm on those tires? I would suggest put a set of 14 x 32's on it and go racing, leave between 3500 and 4200 RPM and let us know what happens.

[slwryde]

It is a big tire. My thinking was that the big tire would help with consistent 60ft times on a variety of track conditions. I choose the DOT tires because the car is street legal and I like to drive it on the street once in a while. I had no idea traction would still be a problem.

Rear gears are 5.13
I have changed instant center from 48" out and 10" up
to 59" forward and 9" up with no noticeable difference in results.

I have had the bottom 4 link bars "nose up" trying to achieve as high an
instant center as possible. I am starting to think maybe trying to adjust
the bottom 4 link bars so they point down slightly in the front to see if that will help.

Also I have ordered a set of slicks. When I took the DOT tires off I noticed 3 perfect muddy water stripes inside the wheel tubs!! directly above the grooves in those DOT tires.

I really appreciate every ones advice.

[trikbag406]

I'm with 'L78 Nova',Im thinking transmission temp.Im no powerglide expert,but I know the 400 turbo in my Vega was built without enough clutch stack clearance (I admit,my own doing),and as the day went on,I saw slower 60 ft times,as well as slower ET's. It turns out I was dragging the forward clutches in my trans after it got hot,and the hotter it got,the worse it was.Just my experience.-Lew.

[Bill Baer]

Originally Posted by slwryde

It is a big tire. My thinking was that the big tire would help with consistent 60ft times on a variety of track conditions. I choose the DOT tires because the car is street legal and I like to drive it on the street once in a while. I had no idea traction would still be a problem.

Rear gears are 5.13
I have changed instant center from 48" out and 10" up
to 59" forward and 9" up with no noticeable difference in results.

I have had the bottom 4 link bars "nose up" trying to achieve as high an
instant center as possible. I am starting to think maybe trying to adjust
the bottom 4 link bars so they point down slightly in the front to see if that will help.

Also I have ordered a set of slicks. When I took the DOT tires off I noticed 3 perfect muddy water stripes inside the wheel tubs!! directly above the grooves in those DOT tires.

I really appreciate every ones advice.

I think you will find that the slicks will fix 90% of the problem in my experience big street tires aren't as good as even little drag slicks.
One other thing to keep in mind is engine coolant temperature you need it to be consistent if you want the 60' & ET's consistent.
You might also want to get someone to video record your launches, paint a white stripe on the side wall and pay attention to the inital hit, if you can see the line going around it's hooking, it the line is a blurr then it's not! If the tires spin on the inital hit your 60' and in some cases your reaction times will be inconsistent.