3.91 and a LSA SC, how do you guys like that combo?

[Joe.G]

I am currently NA and running 3.91, I was going to go to 4.10 but I am glad I did not as I think the 3.45 probably would have been better suited to an SC but just wondering what you guys think of the 3.91 and SC combo.


Thanks

[Ashen 6.2]

Depends on what your goal is or how you plan to drive it. If it’s mostly a fun car and not at the track much, should be good.

I had the 3.91/6l80 when I first got the Maggie. Was a blast on the street, but first gear, most of second and some of third would spin to no end when really getting into it with normal street tires. Drag radials helped a little bit. Broke one axle with that combo as well (at the strip). Was lowered 1” and had offset diff bushings.

Bring lowered will add a bit of stress to the axles when launching. Might want to consider offset diff bushings at some point.

[Jeff_SS]

I love my 3.91's with my LSA. Makes a huge difference because the stock 3.45's made 4th and 5th gear kinda fall on its face a bit.
Now it pulls hard as hell in 4th and 5th.


Can't wait to do more of this racing with a proper hard launch now that I'm not on the stock clutch.

[Joe.G]

I have offset bushings sitting on the shelf, I'll install them at some point, I will do some track days, maybe a drag day here or there but I am more into road course racing.

[bstromback2002]

I have 3.91 gears, Lsa around 600 whp and Manual trans and I’m happy with them. Went from stock to 4.10 now the 3.91. I don’t drag my car or anything and it just seems the 3.91 put the rpm more in a sweet spot for cruising compared to the 4.10. The 4.10 were kind of a mistake. I bought a used low mileage diff from a shop that pulled it out of a customer’s car that was told it was 3.91. I found out it wasn’t when I got it and figured I would try it anyway.


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[Joe.G]

Good to know, I was gou to go 4.10 before I even thought about SC, but I went 3.91 glad I did as I think the 4.10 would be a bit much for my goals.

[1JEWLDSSRS]

Back when I had my 2004 V6 Mustang I had 4.10's in it and it was a quick little pony! Years later I was able to install an Eaton M112 SC off of my friends 03 Terminator Cobra, thanks to supersix motorsports via their "manifold adaptor" plenum, and after the tune and all the 4.10's were absolutely useless with street tires, had to get a good set of drag radials and still had an issue with traction unless I heated them up, which you can't do on the street. It was a 3 speed auto with OD, stock converter, and would just burn them up in all 3 gears. But it was fun!! So the way I see it with a PD blower where you have instant boost right off the hit, 391's and 4.10's will be kinda tricky..

[almimono]

Originally Posted by Joe.G

I am currently NA and running 3.91, I was going to go to 4.10 but I am glad I did not as I think the 3.45 probably would have been better suited to an SC but just wondering what you guys think of the 3.91 and SC combo.


Thanks

3.91s with an SC will work, but they’re pretty aggressive. You may run through gears fast and lose traction. Most boosted setups prefer 3.45 for better drivability and power delivery.

[Joe.G]

Yeah, I would have left the 3.45 but at the time boost wasn't on my mind.

[Z NASTY]

Go with a 3.73, its the best of both worlds. I have a Z/28 with a 3.91 and a ZL1 with a 3.73. The 3.73 is absolutely perfect for the street/track (road course). With 3.73s a stock TR6060 in first will run to 60 which is awesome for digs. I make around 575 wheel on the ZL1 and if I want it blow the tires off and spin clear thru second, I can. If I want it too hook all the way, I can. Its also perfect for street highway. You'll cruise 70mph at 2k rpm. The 3.91 is slightly better at the racetrack, but the Z/28 is down about 100 hp on the ZL1.

[Joe.G]

At this point I don't want to replace anything in the rear, there isn't aotnof gear choices either for these rears. When I built mybolder Camaro there was a ton of choices and 3.73 typically was the go to. I ran 2.73, 3.42, 3.73 and 4.10, when I switched rears to a 9 Bolt I once again was limited and ran a 3.45.

[acammer]

3.91s will be good with an appropriate tire. If this was a drag specific setup even a 4.10 would not be too aggressive for the relative power level, given good traction.

It's important to remember there is a vast difference in transmission gearing between the A6 and M6 cars - so a 3.91 in a TR6060 car is MUCH different than it is behind a 6L80 with a converter. 3.91s with boost in the auto car would be too aggressive, and would necessitate an undesirable 4-5 shift in the quarter mile.