Automatic Transmission - 4.56 with TH400 too much?

Looks like there is a good chance I'm going to get a TH400 RMVB with transbrake to put into my 2000 Z28. Currently I have a T56 and a 12 bolt with 4.56 gears. I'm starting to put together a list of everything I need to do the swap. My major concern right now is the gears.

At the track I run 28" QTP's so based off the f-body gear calculator I get a top speed of around 121 with my 6800 rpm limit, which should be more then enough with my current setup which has run a best of 12.56@109. Though I'm not sure if I will pick up any mileage just from the tranny swap and how to calculate convertor slip. The TH400 currently has a 4000 stall with it but I'm very tempted to get something with a higher stall of 5000+ and was thinking I get it built with a lower STR to deal well with the gears.

This car isn't a daily driver and my main goal for at least the next couple of years is all out NA 347 track times so I'm not really concerned with turning 4000-5000 rpms on the highway. As long as I can do the ~30 mile drive to Bandimere and swap tires I'll be happy.

So for those with A3's am I going to handicap myself if I leae the 4.56's in or can it be made to work?

Bigger/taller tires out back will help.

all i know is i have a 27" QTP putting a th350 in and 4.11's and i will make it in the 1/4 without a problem but i would think a 4.56 should just make it with a 3spd because if you went 121 with a 6spd i assume that was an automatic will ET better but loose a little mph

just my .02

We were running 4.33s behind a TH400 and used 28" tires. Depending on your setup, your currently running 12s, I would stay the way you are and see what the outcome is. With Jen's Z28 and a H/C combo, we had to go to 29.5" tires. She crossed the traps at 6800 rpms while doing 127 mph.

We were running 4.33s behind a TH400 and used 28" tires. Depending on your setup, your currently running 12s, I would stay the way you are and see what the outcome is. With Jen's Z28 and a H/C combo, we had to go to 29.5" tires. She crossed the traps at 6800 rpms while doing 127 mph. Thanks this is exactly what I was looking for, so one less thing to deal with.

I've got 4.10's in my 12 bolt, th400 setup, 27 inch QTP and at 124 mph I was just over 6800, where I had the shift light set to.. it was coming on right as I was going thru the traps. With a 28 inch tire, you'd be good to a similar mph I'd think.

On the highway, with the stock tires on my car it's at 3500 going 65. If I keep it at about 55 it's at 3000, which I can live with. You'll be probbaly at about 3600 at 55 mph with stock sized tires I'd guess, if you drive to the track on your race tires, I'd think you'd be around 3200 at 55.... not that terrible. Just get used to the idea of cruising at a highway speed that has every car passing you, and you'll be o.k. You'll never have to worry about a ticket going to and from the track if you keep to that mentality that's one plus :)