New gears, cut a coil, now terrible 60's.

[oh5gt]

Car always runs 60 foots of 1.74 to 1.76 with occassional dipps up or down.
I've always ran 4:10 gears. Late last year the track changed from 1/4 to 1/8 mile so this season I switched to 4:56 gears. 60 foots today were all 1.9's. Other than cutting half a coil out of the rears all suspension gemotery is the same as last year. 28" tall tires, all of BMR's suspension stuff, QA1's on front, cobra jets and vikings on rear. Using the calculator on the instant center thread, last year I was around 107%.

Anyone have any ideas whats happening here. I wonder did the half coil screw up my suspension setup. Tommoww I'll start reajusting all the suspension. But if anyone has any ideas that might speed up my work, it'll sure help.

Were 4:56's a bad idea.

 

[Marble]

Are your tires old or worn?

 

[skwerl]

I suspect the fucked up springs as the culprit. Springs are a lot more important than you think, and cutting a half coil will have a lot more negative impact than you think as well.

 

[rcm90]

Op, how old are your tires? How was track prep? With the 4.56's your starting line ratio is almost 14.7:1!! That's steep as shit! Without good tires and decent prep, it going to be difficult to get it to stick. IMO

Re-plot the rear to see what the a/s and I/c is.

I suspect the fucked up springs as the culprit. Springs are a lot more important than you think, and cutting a half coil will have a lot more negative impact than you think as well.

Not necessarily. Lots of people run cut 4cyl springs in fox platforms with great results.

 

[W3bb3r04]

Cutting the springs will increase your spring rate. Id say they aren't allowing the rear of the car to squat enough. Id say Kelly will come in and help though. Either that or the tires/track weren't working.

 

[rcm90]

Cutting the springs will increase your spring rate. Id say they aren't allowing the rear of the car to squat enough. Id say Kelly will come in and help though. Either that or the tires/track weren't working.

You don't really want the car to squat. If anything increasing the spring rate out back will hit the tires with more force. That can be adjusted with a/s.

Ideally a car should look like it's leaving for a Sunday stroll (no wasted momentum)

 

[mach828]

Just have to learn to drive it differently so you can cut some good 60s.

 

[lindertw]

cutting the rear springs changed things; check pinion angle along with UCA/LCA geometry. additionally, I saw this post that may be of interest:

I can't figure out what the problem is. The only things I changed as far as geometry goes was my pinion angle and rear gears (went from 3:55 LS to 3:73 spool). I was cutting 1.53-1.55 60' times before. Now I can't get below 1.7 anymore. My pinion was set to -1.5 before but the chassis shop set the pinion angle "more aggressive". It's the only thing I can't figure out.

I'm swapping to 4.56's soon (no other suspension changes). I figure I'll have to make minor adjustments to shock settings/tire pressure, but I expect to be able to launch off the limiter as I did with 4.10's. we'll see

 

[oh5gt]

Thanks everyone. All great suggestions. Yes, the tire are on their last two weekends. Still though, I am not getting any wheel spin. I expect some improvement with new tires.

Now the big thing. Just spent a hour or so checking the measurments. Turns out the UCA is flat. Both front and rear bolts are 18.75" high. So my antisquat is 82.47%. Of course this makes sense, i cut a coil and didn't change anything else.
So looks like I have to move the front UCA to the bottom hole. Playing with the antisquat caculator and Leaving all else the same, changing the UCA number would give me an antisquat of 109%. Better. Will change it tommorrow, check at track in two weeks.

Seems strange to me though that something so simple can effect so much.