Would 2.73's throw a wrench in a supercharged, stalled 6r80's 60' time

skaarlaj

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Another member here was talking about getting 2.73 gears for his Coyote Mustang for 1/2 mile purposes, now it has me thinking about those gears for me in the eighth.

Right now the highest I've trapped so far has been 98mph, and I'm still using the stock 3.15's and I'm into third a bit through the traps. There's a pretty damn large rpm drop on the 2-3 upshift, especially if the converter's locked, and on a centrifugal car it surely feels sluggish when the rpm's drop that much, so I was thinking about 2.73's.

According to my favorite gear calculator, I should be good for nearly 99mph at 7500 in 2nd on 28.3 tall radial pros, but would my 60's suffer from the additional gearing in your opinion? It almost feels a little too short now with a blower and the 5c stall, so I'm thinking this would be a good change for 1/8th mile times. If I ever decide to up the power I'd try the 29.9" tall radial pros and mathematically could carry me up to nearly 105mph without needing third gear at the same 7500rpm
 
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07 Boss

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Rear gears are a torque multiplier. Why would you want to pull torque from your wheels? I would go the other way. Put a gear in so you can get deeper into 3rd.
 

skaarlaj

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The 6r80's 4.17 1st gear is pretty deep, and when you have well over 500rwhp, I can tell you that 3.15's are very short in 1st gear even with 28" tall tires. what trans is in your car, or 1st gear ratio?

If your trans is a 5r55, you'd need 4.10's to have equivalent gearing to a 6R80 with 3.15's in 1st gear same tire, same engine rpm on each.

If you had a 4r70, you'd need 4.56's to be at a similar final ratio in 1st gear as a 6r80 car using 3.15's along with same tire height, same engine rpm.

I'm guessing you don't have a manual trans as a stall converter is mentioned in your sig, but do you feel your car needs more gear with your 4.10's?

I totally understand gearing / torque multiplacation, but harnessing what I have now with the 3.15's has proved to be challenging already. 4.10's would actually put me at a very similar / desirable rpm in 3rd through the traps, but I really hate the huge rpm drop going into 3rd with a centri blower, and I'm afraid I'd have even less control upon launch than I already have. Currently getting a decent 1.62x 60' time without stalling up very high at all, maybe 3K. I'm sure I could foot brake over 4K if I thought I wouldn't spin like a banshee
 
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RED09GT

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With the converter that you have and for 1/8 mile times, it would probably work.
Anyone you can borrow a slightly taller set of rear tires from for a couple of passes? It would be worth a try before swapping gears.
 

skaarlaj

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With the converter that you have and for 1/8 mile times, it would probably work.
Anyone you can borrow a slightly taller set of rear tires from for a couple of passes? It would be worth a try before swapping gears.
Not around here hahaha, but even a 30" tall tire would only get me to barely over 90 with my current gears at 7500 anyways. I'm going to start messing with my suspension and tune-up, and get to where I can run a very low 7 nearly every run, then maybe next year I might try the taller tires / taller gear set-up. Right now my highest trap is 98mph, and if that doesn't go up much or any, the gear swap should make sense, and put me at just shy of 99 mph on a 28.3" tire @ 7500rpms. If I go to the larger radial pro that is 29.9" tall, 7500rpms should take me to over 104mph, But I doubt I'll be finding the power to trap over 100mph any time soon lol.
 
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bunits19714

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i will be at the track this wed and let you know my impression with the car only making only 2 shifts(finishing in 3rd gear)
 

skaarlaj

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i will be at the track this wed and let you know my impression with the car only making only 2 shifts(finishing in 3rd gear)
Right on man! If you make any 1/4 mile hits this summer, let me in on your 60' and 1/8th mile et's and how you like the ratio over-all please.
 

skaarlaj

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Some interesting calculations comparing transmissions in 1st gear

6R80 with 3.15's in the rear = T56 with > 4.88's
 

RocketcarX

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You want the tallest tire with the shortest gear, do not put a taller tire AND a taller gear, that's a problem for a 1500HP car.

Shorten the 1-2 shift if you have too and get down the track in 2nd and 3rd.

I have 4.56 gears in my 08 GT manual trans car on a 28 inch tall tire and would never go back (I also have an N/A 3v)
the 1/8th mile needs gear, tire, and suspension to work. The eighth is all in the 60', if you don't want to make those kind of changed, then 1/4 mile racing is probably a better option as it's less traction dependent.
 

skaarlaj

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You want the tallest tire with the shortest gear, do not put a taller tire AND a taller gear, that's a problem for a 1500HP car.

Shorten the 1-2 shift if you have too and get down the track in 2nd and 3rd.

I have 4.56 gears in my 08 GT manual trans car on a 28 inch tall tire and would never go back (I also have an N/A 3v)
the 1/8th mile needs gear, tire, and suspension to work. The eighth is all in the 60', if you don't want to make those kind of changed, then 1/4 mile racing is probably a better option as it's less traction dependent.
I actually plan on running the 2.73's and will carry me to where I can trap now at the top of second with the converter locked. If I ever add a s550 block that can handle more boost and make more power, I'll then swap to the larger radial pros that are 29.9" tall that should carry me close to 105, and would be perfect.

Also, if you have the 3650 trans in your car and run 4.56's that would be the equivilent to a 6r80 car with 3.73's for final ratio in first if both ran the same heigt tire, and that's already alot deeper than I already run. And no way in hell would I go deeper than I already am. 4.17 1st gear is already tough to make a clean launch with with the 3.15's out back. Spend some time with an online gear calculator and realize that 4.17:1 is pretty friggin deep. And I too would never run anything under a 28" tall tire in an S197 car.
 
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T400Mustang

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I am wondering what your results have been? I have an 07 GT Coyote Swap I am doing now. I am using a 6R80, 30 inch tall Hoosier drag radials, 3:08 gear and a Circle D 6F converter with a Pro-Charger. I am still in the putting it all together now and I am building it for bracket racing 1/8th mile. I am wondering if the Converter will be to loose and if I need to change to a 4C? Then again, maybe I need the loose converter to get the car rolling? If you have any information please share and also what ever calculator your using.
 

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