3.15's MT82 Paxton

[higdominator]

So I visited Mexico last night and ran a buddy of mine with a Paxton/3.33/E85 6R80/3.15/28" tire, no other mods VS my Paxton/3.48/E85 MT82/3.73/27" tire and he pulled me and kept a solid 1-1.5 cars which I couldn't catch from a 60.

I had been thinking about a gear swap before this but it really makes more sense now and since I have a spare loaded rear differential laying around I'm thinking of just doing to see if it's worth it.

However, I'd like to get some input from those who may have done it. Primary uses for the car are trips down south (rolls), some moderate road course action here an there, and I'd like to look at some runway events.

I already have a 3.33 pulley on the way.

So, is 3.15 going to be a total dog without the help of a converter?


EDIT: I have looked at the math and with our different size tires the final ratios would be Very close if I swapped to 3.15's

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[whatsup62]

Tire size does play a big part in it.
Most MT82 FI guys go with 3.31's in rear while the auto guys like the 3.15's.

 

[higdominator]

The numbers suggest I would be in good shape, relatively similar to an auto car's gearing if they are running a 28" tire. I like how that gearing looks MPH/RPM wise.

I won't be running this car from a dig likely ever, so I'm curious how 3.15's would do. I also like the fact that I would be able to stretch the car to 180 or so in 5th without having to worry about hitting the limiter to get there.

Decisions decisions

 

[3beeps]

I don't think I've seen an MT82 car running 3.15 gears. I've heard 3.31 is the sweet spot if you're making a lot of power but my 3.55 gears paired with my 28.4" tire worked VERY well on the street from a roll.

Now I have an auto car with 3.15s and a 27.7" tire so we'll see how that does.

 

[TexasGT]

I have a 2016 Roush car making 741whp and MT82. Swapped the entire pumpkin to 3.15's and love it! 3rd and 4th are crazy strong. I did it to run the Texas Mile. Want to stay in 5th through the end. Don't plan on dragging it, so aluminum housing should be good. Had it for 4-5 months now with no problems.

 

[Ponderthis]

I have 3.15s and just ordered some 25.8" Drag Radials on 17s, Im hoping it will help a lot compared to the 28s I run now!

 

[dubster99]

I have my 3.31 diff in the garage waiting to go in after I install the return system and dial the new tune. 3.15 is too long for the mt82 imo.

 

[TexasGT]

I have my 3.31 diff in the garage waiting to go in after I install the return system and dial the new tune. 3.15 is too long for the mt82 imo.

Curious why you say that? At 700+ at the wheels, tire spin is ridiculous with lower gearing. I had 3.73's and it was worthless. Once I get new tires, I may have a different opinion though.

 

[higdominator]

I have a 2016 Roush car making 741whp and MT82. Swapped the entire pumpkin to 3.15's and love it! 3rd and 4th are crazy strong. I did it to run the Texas Mile. Want to stay in 5th through the end. Don't plan on dragging it, so aluminum housing should be good. Had it for 4-5 months now with no problems.

Curious why you say that? At 700+ at the wheels, tire spin is ridiculous with lower gearing. I had 3.73's and it was worthless. Once I get new tires, I may have a different opinion though.

That's exactly what I was looking for. I'm going to be on a 3.33 & E85. The car is basically undriveable on a street tire and still spins a warm nitto NT01 from a 60 roll. If I leave ANY nannies on it pulls 4* of timing as advance trac reels it in. I won't be doing drag from a dig but will be doing Roll racing and want to try some airstrip events.

I'm just going to swap the rear cover from my diff (16 PP has temp sensor) and toss the whole aluminum housing in as well.


How does it drive around town?

 

[TexasGT]

Way better than the 3.73's, that's for sure! Longer shift points. Gas mileage still sucks, but who cares!!

 

[dubster99]

The 3.15 won't provide a ton more traction than the 3.31, and it'll feel like a dog off the line. If you like to race from a dig, don't go 3.15. You won't need longer than 3.31.

 

[SVT-DADDY]

I think it's the auto trans that's getting you, not the gears.

 

[SolarFlare]

I agree, that auto with smaller pulley got you. If anything I'd say that extremely long gearing wasn't helping him.

 

[higdominator]

The 3.15 won't provide a ton more traction than the 3.31, and it'll feel like a dog off the line. If you like to race from a dig, don't go 3.15. You won't need longer than 3.31.

Actually if you look at 3.31 v 3.15's you have to consider tire height. I have two tires I run depending on what I'm doing. One is a 26", the other is a 27". My tire sizes give me a similar total gear to a 3.31 setup with a 27" or 28" respectively.

I think it's the auto trans that's getting you, not the gears.

No, it's the gears. A simple evaluation of dyno charts and gearing shows the ratios I'm looking at are golden for what I want to do.

 

[SVT-DADDY]

Actually if you look at 3.31 v 3.15's you have to consider tire height. I have two tires I run depending on what I'm doing. One is a 26", the other is a 27". My tire sizes give me a similar total gear to a 3.31 setup with a 27" or 28" respectively.

No, it's the gears. A simple evaluation of dyno charts and gearing shows the ratios I'm looking at are golden for what I want to do.

Then start from a 40 roll. Gears don't make a ton of difference when your roll racing.

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