07 GT not making power?

Jake Schmale · Sep 26, 2020

Hey guys I’ve got an 07 GT 5 speed I’ve had for a couple years and I’ve started racing it at the drag strip. It’s got a Lito tune E85, JLT 3, 3.73 gears, Full exhaust(offroad), CMDP, steeda underdrive Pullies, Race Star wheels, Mickey Thompson tires, gutted trunk, BMR front sway bar delete and radiator support, CJ springs. I’ve been cutting back to back 1.72 60 foot times and can’t get this thing to go faster than 12.9 at 104-105 mph. I’m launching at 4,000rpm with 14 psi. I’m stumped because it doesn’t seem like it’s pulling at the big end. Density altitude was about 2,500 the night I ran it. I’m 500 feet above sea level. Are these normal times or am I missing something? Just seems it should be doing over 106 mph imo.

View attachment 74489

mustanger · Sep 26, 2020

That's actually probably about right with your mods and a DA that high. When I was N/A I had similar mods consisting of a tune, CAI, L/T headers, UDP's, 4:10 gears, M/T drag radials and front runners. The best I ran was 12.4 at 110mph with a D/A that was probably around 0. I think my 60 ft was around a 1.6 or 1.7. Looking at some of the 1/4 mile calculators online, a car that weighs around 3600lbs, and dyno's around 330hp should be around 12.9 at 106. When you say full exhaust do you mean headers as well? You could try datalogging it to see if maybe it's pulling some timing.

JEWC_Motorsports · Sep 26, 2020

Start with a datalog during a pass. 2500 da is terrible. Thats not helping you.

Joe combs · Sep 26, 2020

i agree, that DA is horrible and is what is currently hurting you. Once it starts cooling off I think your times will start dropping.

Dino Dino Bambino · Sep 27, 2020

You definitely should be doing better 'cause your car has roughly the same weight and power as mine. The 2500ft DA is the main reason why your times seem slow. Your DA corrected (to sea level) would otherwise be roughly 12.5 @ 108. As Joe said, just wait for cooler weather.

Jake Schmale · Sep 27, 2020

mustanger said:
That's actually probably about right with your mods and a DA that high. When I was N/A I had similar mods consisting of a tune, CAI, L/T headers, UDP's, 4:10 gears, M/T drag radials and front runners. The best I ran was 12.4 at 110mph with a D/A that was probably around 0. I think my 60 ft was around a 1.6 or 1.7. Looking at some of the 1/4 mile calculators online, a car that weighs around 3600lbs, and dyno's around 330hp should be around 12.9 at 106. When you say full exhaust do you mean headers as well? You could try datalogging it to see if maybe it's pulling some timing.

Yes, it’s got lt’s(offroad). I was wondering the same thing about the timing, but I figured the E85 would help keep things cooler. I’ll definitely look into it.

Jake Schmale · Sep 27, 2020

Dino Dino Bambino said:
You definitely should be doing better 'cause your car has roughly the same weight and power as mine. The 2500ft DA is the main reason why your times seem slow. Your DA corrected (to sea level) would otherwise be roughly 12.5 @ 108. As Joe said, just wait for cooler weather.

The weirdest thing is it went 13.18 in July at 107 mph with a bama 93 tune and 3.31 gears.

Jake Schmale · Sep 27, 2020

I wonder if it could be getting a false knock? Both mufflers are touching the metal exhaust mount under the car where they are dumped.

Jake Schmale · Sep 27, 2020

Here is a picture of the time slips, I’m 8351. The right ticket was with 3.31 gears, and a bama 93 tune in august weather(I wasn’t even getting into 4th gear with those gears in the 1/4). The left ticket is with 3.73 gears, lito E85 tune.

Dino Dino Bambino · Sep 27, 2020

The 3.73 gears are forcing you to shift into 4th gear before the 1/4 mile trap and you're thus losing trap speed. With the 3.31 you could hang on to 3rd gear and gain more speed.
Your 60' of 1.727 does point to you having very good traction off the line. As I see it, you just need better air.
Have you run your car on the dyno? What's your rev limiter set at? 6500rpm maybe?

stkjock · Sep 27, 2020

What rpm are you shifting and crossing the line?

What size rear tire?

Jake Schmale · Sep 27, 2020

stkjock said:
What rpm are you shifting and crossing the line?

What size rear tire?

I’m shifting at about 6,000 and I’m crossing the line at about 5,500-5,600. The rear tire size is 28x11.50x15. The car has 4.11 gears in the rear but with that tire size the overall ratio is 3.73.

Jake Schmale · Sep 27, 2020

Dino Dino Bambino said:
The 3.73 gears are forcing you to shift into 4th gear before the 1/4 mile trap and you're thus losing trap speed. With the 3.31 you could hang on to 3rd gear and gain more speed.
Your 60' of 1.727 does point to you having very good traction off the line. As I see it, you just need better air.
Have you run your car on the dyno? What's your rev limiter set at? 6500rpm maybe?

I have not had it on a dyno yet but the rev limiter is set at 6,600

stkjock · Sep 27, 2020

Jake Schmale said:
I’m shifting at about 6,000 and I’m crossing the line at about 5,500-5,600. The rear tire size is 28x11.50x15. The car has 4.11 gears in the rear but with that tire size the overall ratio is 3.73.

Post the real rear in the future, not the effective ratio, better for people to comment. Are u sure they are 4.11 and not 4.10?

You’re shifting too low IMO and not using the RPM to your advantage

I’d think a shorter tire would help or a taller tire so u can avoid 4th gear, though I don’t have my spread sheet to calculate what size would make sense

this might help
https://www.s197forum.com/threads/m...drop-complete-calcualtor.118353/#post-2132497

Jake Schmale · Sep 27, 2020

stkjock said:
Post the real rear in the future, not the effective ratio, better for people to comment. Are u sure they are 4.11 and not 4.10?
I will do that in the future, I’m positive they are 4.11 I counted the teeth before I had them installed. What rpm would you recommend shifting and launching at? Not trying to blow the motor yet

You’re shifting too low IMO and not using the RPM to your advantage

I’d think a shorter tire would help or a taller tire so u can avoid 4th gear, though I don’t have my spread sheet to calculate what size would make sense

this might help
https://www.s197forum.com/threads/m...drop-complete-calcualtor.118353/#post-2132497

stkjock · Sep 27, 2020

I will do that in the future, I’m positive they are 4.11 I counted the teeth before I had them installed. What rpm would you recommend shifting and launching at? Not trying to blow the motor yet

odd, didn’t realize anyone made 4.11s for the 8.8

I’d shift at 6500

your launch is fine at 4000, but there’s at least a tenth in your 60’

Dino Dino Bambino · Sep 28, 2020

Jake Schmale said:
I’m shifting at about 6,000 and I’m crossing the line at about 5,500-5,600. The rear tire size is 28x11.50x15. The car has 4.11 gears in the rear but with that tire size the overall ratio is 3.73.

1. You're shifting way too early. Try shifting at 6500rpm instead.

2. You have 4.10 gears and with 28" tires, your gearing in 3rd is 15.4mph/1000rpm (6600rpm = 101mph), which means you'd need to shift into 4th to complete the 1/4 mile no matter what.

3. You might be better off using 26" tires instead. If you have enough traction, your 60' time will be quicker, and you can go much deeper into 4th gear by the end of the 1/4 mile. Fourth would be geared at 18.9mph/1000rpm and you could hit the trap at 5700-5800rpm.

Jake Schmale · Sep 28, 2020

Dino Dino Bambino said:
1. You're shifting way too early. Try shifting at 6500rpm instead.

2. You have 4.10 gears and with 28" tires, your gearing in 3rd is 15.4mph/1000rpm (6600rpm = 101mph), which means you'd need to shift into 4th to complete the 1/4 mile no matter what.

3. You might be better off using 26" tires instead. If you have enough traction, your 60' time will be quicker, and you can go much deeper into 4th gear by the end of the 1/4 mile. Fourth would be geared at 18.9mph/1000rpm and you could hit the trap at 5700-5800rpm.

I’ll try shifting at 6,500 and see what happens, I’ll also probably give some 26 inch tires a try once these wear out. I should probably install a crossover pipe to help with the lower rpm torque lol

46addict · Sep 28, 2020

Water is already under the bridge now but you may have been better off crossing the line in 3rd with 3.31s or going with 4.30 gears if you wanted to use 4th. 3.73s are an awkward gear for a 110mph car. And it should all be done with 26" tires.

Dino Dino Bambino · Sep 28, 2020

Are your downpipes separate all the way to the mufflers? An X-pipe crossover would definitely help scavenge exhaust gases at medium/higher rpm and equalize gas flow between the two cylinder banks.

46addict said:
3.73s are an awkward gear for a 110mph car. And it should all be done with 26" tires.

Agree. Same goes for 3.55s to a lesser extent.

07 GT not making power?

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