01350ss

iTrader: (18)

Last year 12.1 at 120mph. Over the winter added
6pt cage
12 bolt rear
spohn ta
lower control arms
rear sway bar
thunder racing throttle body
switched from td's to a catted y-pipe and gmmg
15x4 skinnies
15x8 with 28" slicks (mt et drag)
4.30 gears
This year 12.8 at 108mph!!
WTF! Please any help is appreciated

transam1998

iTrader: (5)

Well, you weigh a lot more now, the 12 bolt costs some rwhp (I've heard 20), You added cats (another 10hp? maybe more, maybe less). I haven't seen inside GMMG's mufflers, but typically, chambered mufflers don't flow the best, the throttle body wouldn't give you enough to make up those differences. I added a lot of the same stuff you did, except for the cage. My car is now 180 lbs heavier than it used to be.

01350ss

iTrader: (18)

True, but I also lost weight with getting rid of 18" y2k's, and the slicks! Gmmg is straight through also

Villain281H

iTrader: (5)

I can't comment on the total swap, but the rear end is heavier and costs more hp to run than a 10 bolt, the 6-point roll bar can add 45-85 pounds, and going to a full exhaust system over true duals can also add some weight. Also, remember summer air will also slow the car down 2-4 tenths and 1-3 mph over a good winter/spring air pass.

Hope this helps, and you get her back to form!

Derek

Nate_Taufer

iTrader: (1)

what were your 60's? Post up full slips for both runs and maybe we can get a better idea of what is going on.

Nate

smokeum99ta

iTrader: (15)

Your problem is easy. You added alot of weight and lost some power by choking up your exhaust. Not only that but 28" tire is harder to turn than something smaller in height even though you got some 4.30 gears. Then like villian said summer and winter weather effects et's and mph also.

Fade2blk500

iTrader: (18)

nothing he added explains a 12mph loss...

black_z

iTrader: (4)

I would throw it on the dyno and see where the tune is at. Run a compression/leakdown test. Maybe you had some bad gas?