Looking for help/opinions on gear choices

jas2234

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So long story short. Car is an 07 gt procharged 10 psi. (492/448). To start with I had stock 3650 with 3.73 gears and ran a pretty consistent 11.8-9 at 121 with 2.1 60". Last year switched over to a magnum XL with 2.66 1st gear. Was advised to switch to 4.10's. With that setup I was running consistent 12.0-1 at 117 with 2.1-2 60". Ended up blowing the rear and based off calculations 4.30's put the XL pretty close to the 3650 with 3.73's final drive ratio.

Well the last 2 or 3 times I have been at the track I have been running consistent 12.3-4 at 113-114. With 1.7-8 60". Obviously 4.30's are the wrong gear. I'm wondering what you guys think would be my next best choice. Go back to 4.10s and work on my 60 or try 3.90 or 3.73. And still work on my 60.
 

redfirepearlgt

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JC - Are you making comparisons to passes made in similar DA conditions or are you running 4000DA on the 12.3 pass and negative DA on the 11.8 pass? And what diameter tire?
 

jas2234

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I pulled tickets that were similar DA. There is always the good and bad days. And I was trying to pull tickets that were very close. And I knew I forgot something. Tire is MT ET street R (bias) 28x11.5r15
 
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46addict

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4.30 is the right gear for your setup. If you're blowing the rear you should play with different tire pressures, launching technique, or do suspension work.
 

RocketcarX

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The reduction in your 60' says the 4.30 gears were the right move. Did you also change tires/size. Also the reduced MPH would indicated a loss of horsepower, are you seeing a reduction in boost or RPM on your runs? Maybe shifting too soon.
 

redfirepearlgt

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Have you datalogged to see if you are pulling timing on the big end? The 1.8 60ft improvement should have you theoretically and conservatively closer to 11.7x (or better) on identical passes/DA compared to the 12.0 on a 2.0 60ft.

A friend of mine at work has a procharger setup and he has struggled with it pulling timing due to high IAT temps on the big end. He's put the largest air-air upgrade in, added water injection to no avail, and is now pullying up (he's at 21psi on an F1 as I recall) to try running at a lower boost level to bring down the temps on his monster 3V forged setup. He's running a 4.10 on a bias ply 28 and cuts 1.4x 60's but then it goes to crap on the big end in third as the IAT temps climb out of range. Relocation of the IAT sensor, MAF sensor, improving the flow path, etc have all helped but he still hits that wall in third just past the eighth.

Datalog to see what is going on. It may be that you are running well and can add some timing at WOT. Who knows until you datalog?
 

jas2234

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4.30 is the right gear for your setup. If you're blowing the rear you should play with different tire pressures, launching technique, or do suspension work.
Based off figures I felt the 4.30 were the right choice. When I said I blew the rear I ment I grenaded the factory diff and went with a trutrack this time. I do have full bmr suspension and have airlift. Been the same suspension the whole time.
 

jas2234

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The reduction in your 60' says the 4.30 gears were the right move. Did you also change tires/size. Also the reduced MPH would indicated a loss of horsepower, are you seeing a reduction in boost or RPM on your runs? Maybe shifting too soon.
I did change tires from mt ET street 325/50r15 to mt ET street r (bias) 28x11.5r15. Both are 28" have tried 14-18 psi no changes on the top end. Boost and rpm seem to be the same as always. 1/8th is 3-5 mph (95-97 mph)quicker but then it seems it goes to shit. I shift at 64-6500 I was thinking maybe I was shifting to late and going past my power band. I cant find my dyno sheet, I need to get ahold of JPC and have it sent to me so I can see where my drop off is.
 
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jas2234

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Have you datalogged to see if you are pulling timing on the big end? The 1.8 60ft improvement should have you theoretically and conservatively closer to 11.7x (or better) on identical passes/DA compared to the 12.0 on a 2.0 60ft.
A friend of mine at work has a procharger setup and he has struggled with it pulling timing due to high IAT temps on the big end. He's put the largest air-air upgrade in, added water injection to no avail, and is now pullying up (he's at 21psi on an F1 as I recall) to try running at a lower boost level to bring down the temps on his monster 3V forged setup. He's running a 4.10 on a bias ply 28 and cuts 1.4x 60's but then it goes to crap on the big end in third as the IAT temps climb out of range. Relocation of the IAT sensor, MAF sensor, improving the flow path, etc have all helped but he still hits that wall in third just past the eighth.

Datalog to see what is going on. It may be that you are running well and can add some timing at WOT. Who knows until you datalog?

I'm definitely gonna have to datalog as it seems like your buddy was/is having similar symptoms
And I agree with your math. I was thinking with my current 60' I should be in the 11.7 range.
 

jas2234

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Sorry for multiple posts but for some reason my phone won't let me do multiple quotes. Thanks for the info guys. Any and all help is greatly appreciated.
 

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