Need help with gear decision on Turbo car that will eventually be a 4R70W car

[nstag8r]

I need help deciding on the gear choice in my car. I am just finishing the turbo build with the IRS out of the car for the delrin bushing upgrade. I have the stock 3.55 in the rear now but have a 3.27 that I bought to put in the car. It is going to be a little wheil before I put the auto in the car so I want some opinions as to which gear I should go with. I know the car will probably like the 3.27 with the 6 speed but will the
4R70W like that gear also. Looking for guys with turbo/auto cars and what gears they are running. I have to pull the diff becasue the pinion seal is leaking really bad so I bought a solid pinion spacer and shim kit to get rid of the crush sleeve and hopefully fix this issue permanately.

 

[Oiljunkie]

What's your set up? I think the 3.55 will work a little better with the auto depending on your turbo set up, but regardless it's a marginal difference

 

[nstag8r]

It is a Hellion 76 using a Precision Billet wheel ball bearing turbo. The cold side is custom made blow thru from the intercooler to the throttle body. I am just wanting to get the most out of the car when I get the auto swap done.

 

[smashedheadcat]

I run 3.55's with my 4r70w. Seems to do just fine, but finding traction has proven difficult. You may see a marginal improvement with 3.27's, but I would imagine the difference would negligible traction wise.

 

[Ponyracer1]

All depends on if your going to be on the street or strip more? Honestly with bigger power number cars, gear seems less and less important because you don't need the mechanical advantage the gearing provides.

If it were me I'd figure out if I what I want to use the car for, (drags/texas mile etc) and figure out the rpm that your going to cross the stripe at. Then use the gearing tables to put your car at the top of it's powerband at that point. Nothing worse than running out of gear and having to shift 100 foot before the stripe.

Why go auto? Most people do for drag racing. But the IRS is garbage if your going in a straight smooth line.

When I go TH400 in my car the IRS will be coming out at the same time.

 

[nstag8r]

I am building the IRS and keeping it as long as it will take the beating. My car is mostly a street car but will go to the track a little. I really enjoy the way the car rides and handles with the IRS in it. I am sticking with the 6 speed for a while to see how I like the turbo with the 6 speed and it may never come out. I have the IRS out of the car right now and thinking I am going to go with the 3.27 and a locker. We will see how it holds up. I know we rear a lot about the IRS being junk but there are also a lot of guys running 9's and 10's all day long with them. I think the IRS gets the bad rap becsaue of the cost to do the upgrades on it. It seems like that most of the guys that have spent the money and done the proper upgrades on them seem to love the IRS. If you think about it the stock 8.8 solid axle is garbage until you dump money into it also. You just gotta decide which one is right for you.

 

[Crusher9008]

I am building the IRS and keeping it as long as it will take the beating. My car is mostly a street car but will go to the track a little. I really enjoy the way the car rides and handles with the IRS in it. I am sticking with the 6 speed for a while to see how I like the turbo with the 6 speed and it may never come out. I have the IRS out of the car right now and thinking I am going to go with the 3.27 and a locker. We will see how it holds up. I know we rear a lot about the IRS being junk but there are also a lot of guys running 9's and 10's all day long with them. I think the IRS gets the bad rap becsaue of the cost to do the upgrades on it. It seems like that most of the guys that have spent the money and done the proper upgrades on them seem to love the IRS. If you think about it the stock 8.8 solid axle is garbage until you dump money into it also. You just gotta decide which one is right for you.

Just so you know i've put every upgrade into my IRS and wouldn't change it for a solid if you paid me. I also recently put a 4R75 fully built into my Cobra and it has 3.55 gears. Baumannator is the best controler and a must.
http://www.baumannengineering.com/tcs.htm

I'm making 676rwhp through my trans and the thing rips like no other.