Drag Racing Results - New rear, new suspension, 28" ET street = slower! Help

Car is M6 with S60, Strac & 4.10. 28x11.5-16 ET Street on snowflake wheels with abt 12lbs of air. I just did the S60 swap and also added SFCs, PHB, LCAs, relocated full length TA, and Strano springs. Stock shocks still. Best pass of the night was 8.26 with a 2.0 60'! Wtf? With my old 4.10 10 bolt and complete stock suspension it went 7.96 with a 1.7 60'. The tires for that pass were ET streets but I borrowed them off a friend, and I think they were 26". Yesterday the air was super hot and humid and I was running in the middle of the afternoon, the 7.96 pass was in October after dark with much cooler air. My old 10 bolt also had a 4.10. Surely the difference in tire/air could not have made that much difference for the worst. I was launching at anywhere from 3 to 5k, trying all different rpms. It seemed to hook fine, not a lot of spinning, but couldnt get a 60' worth a shit to save my life. What is the problem?

I would say the heat was a good bit of the problem. I have never ran a dana 60 but doesn't it take a good bit more power to turn than a 10 bolt

Sounds like weather was worse, try to compare the DA and humidity.

They say you get a 5%-7% loss with S60 over a 10 bolt, but rifing in the car I cant tell any loss of power, FWIW the seat of the pants feels the same with the S60. I know the weather hurt but I was hoping for maybe 7.70s with all the suspension and a taller tire since it was able to do 7.90s with all stock stuff and a 26" tire. Ive also gotten a tune, UDP, and chrs 1313 since the 7.90s pass

Those 28" tall tires effectively turned your 4.10s into 3.73s. Use the DA calculator at Dragtimes.com to convert your various times to standard sea level so you're comparing apples to apples.
http://www.dragtimes.com/da-density-altitude-calculator.php

^^this and the added weight of that S60 v. ur 10 bolt..fwiw with the summer heat, u prolly could of ran at least 17lbs of air.

I started out with around 17-18lbs air but it would blow them off, to get it to hook with that much air I would have to launch at a rpm so low that it would bog terribly. The best pass came on abt 12lbs

When i had 28s on my car it would bog and 60ft terrible. Put 26s on it and fixed the problem. You really need 4.30 or 4.56 gears on a 28 tire to get it to work with a 6 speed.

^ I'll believe that in a heartbeat... Considering my results with a 28 vs a 26 that makes perfect sense. I know the air had some to do with it but Im thinking there is more in play than just bad air.

AS all said, these are cumulative variables, Bad DA, sounds like poor track prep since u couldnt hook on a hot day, taller tire, the newly added SFC's=weight, weight of the S60 v. the 10 bolt, and the % power loss with more rotational mass, all together can be the reason for the bad E.T.

I know the added weight is not helping. The SFCs cant weight more than 25lbs combined.. I was hoping the stiffer more efficient suspension setup combined with being able to leave at 5k due to the S60 would be able to offest the losses from the added weight of everything? Is that plausable or did I take a pretty big step backwards?

Also since you changed so much with the suspension did you reset pinion angle? Re-center rear end side to side and front to back? A combination of bad weather, extra weight, a power robbing rear and taller tires all can add up to cause those results.

Taller tire is killing ur gear and the added weight from rear..also could yve slot to do with torque arm setup and how u have the shocks set

Yes I attempted to set the pinion angle but I pretty much just guessed. I am going to mess with it some more because I am getting some minor vibrations at certain speeds when its not under a load. The rear is centered pretty good front to back and side to side. My shocks are stock which I know isnt helping a bit. Im ordering QA1s soon and going to try again when theres better air and hopefully get my hands on a 26" tire to try.

Ive got some 26x8.5x15 hoosier slicks for sale. Pm me if your interested.

No need to guess at pinion angles, angle finders are cheap!

Also u have afterarket springs u need adjustable shocks so u Match it to ur setup

You had a 26 inch tire with a 4.10, now you ran a 28 inch tire wth a 4.10, that's like going to a 3.73, on a car that probably would have been happied going in the other direction (4.30). That, along with the weather being alot worse I'm sure, and add into the fact that you probably just added 150 lbs to the car between the rear and the frame connectors... I'm not entirely surprised to hear it went slower.

You can now however, make runs and figure out how to get it to run better without the rear end falling out of the car so that's a good thing. If you're not planning on alot of power in the future I would go back to a 26 inch tire, if you're planning on leaving the 28's on it, I woudl at least put a 4.30, maybe a 4.56 rear end gear in the car.

Shocks and whatnot as others have suggested will do wonders for getting the car to leave better as well, certainly a worth while place to spend money.

thanks guys for all the insight.. Im trying to pick up a set of 26's now and sell the 28's. Also gonna pick up some QA1s I think. Gonna get a cool night and go again, will post results whenever it happens!

Best of luck, if you can get a video of the car, looking up the drivers side from the back, that will help us see what the car is doing and where improvements can be made.