ordering rear need tire/gear selection help - Third Generation F-Body Message Boards

WheelsUp84z · 02-27-2007, 08:23 AM

after i get paid on the 1st im going to be ordering my rear end, im gonna go with a moser 12 bolt. Im running 15x10" draglites with 5.5" backspace and a th-400 transw/ 4400 stall. motor is a 385 with AFR 210 race heads, 10.5:1 CR and 200 shot of nitrous redline is 6500 rpms. This is a street car that will see a lot of track time (weekend cruiser) I was just wondering what gear/tire size combo would best suit my setup, i was thinking 3.90 gears and 26x11.5x15 et streets. What do you guys think?

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DIGGLER · 02-27-2007, 08:59 AM

your going to destroy those little tires. run a 28x10.5x15 et drag or something like that. maybe a 28x12.5x15 et street i guess?

also, whats up with the 6500 rpm limit with those heads? what kinda cam are you running?
spraying it with a 200 shot and that stall you would be going to 2nd dang near immediately off the line.

WheelsUp84z · 02-27-2007, 09:33 AM

i have the heads because i plan on going more cubes in the future, the cam is 241/249 @.050 .525/.546 110 lsa, nitrous is going to be set up on a progressive controller and i thought about stepping down to a 4k or so stall as well but i have a 4400 already. so you think 28x12.5's? i was skeptical about them fitting and not rubbing.. think i'll be ok?

DIGGLER · 02-27-2007, 02:04 PM

Quote:

Originally Posted by WheelsUp84z

i have the heads because i plan on going more cubes in the future, the cam is 241/249 @.050 .525/.546 110 lsa, nitrous is going to be set up on a progressive controller and i thought about stepping down to a 4k or so stall as well but i have a 4400 already. so you think 28x12.5's? i was skeptical about them fitting and not rubbing.. think i'll be ok?

dot tires like et streets are sized differently than an et drag. et drags are sized off the tread width while dot tires are sized off the section width (buldge)so, an et drag measuring 28x10.5x15 is about the same as a 28x12.5x15 et street. having said that, this size tire on a 10" rim with 5.5" bs will require a decent amount of clearancing on the inner fenders.
cam- i would think that cam would be alright spinning to 7k at least with those heads... progressive controller is cool, i would like one on my car. right now im spraying a 125 shot and shifting to 2nd while the front is still in the air. (shifting at ~6700) 28" tire, 3600 stall, 4.56 gear. engine is a mostly stock LT1 with a 230/236 cam. im hoping once i get some of the gear out of it i can hold 1st gear a little further out....

xpndbl3 · 02-27-2007, 02:41 PM

i'd go 4.10s and 28" tires or even 4.30s. I'd go 9" with tru-trac over a 12 bolt though, which is what i'm ordering up. An aluminum center section will make it lighter than a 12 bolt as well.

ross · 02-27-2007, 09:55 PM

For the spray run a 3.90 or 3.73 and a 28'' tall tire. If you mainly run on the motor do a 4.30 or a 4.10 gear and the 28'' tire again also these gears I selected are for 1/4 mile track.

Stephen 87 IROC · 02-28-2007, 12:18 AM

4.30 - 4.10 and 28" tall tires would be much better. That cam should be good for about 7000 rpm. What's the valve float spec for the cam?

WheelsUp84z · 02-28-2007, 12:38 AM

im not sure on the valve float off hand, its the biggest hyd. flat tappet "voodoo" series cam lunati has. 60105 i believe the part number is. I think im going to go with 3.90's and 28" tires. this car is still going to be driven on the street and i think 4.10's are a bit much. im also going to try and get a 4k stall. diggler, how much does you're car weigh and what are you running for suspension? that thing doesnt have much motor and its sounds like it gets it out of the hole.

DIGGLER · 02-28-2007, 09:05 AM

its somewhere around 3,000lbs im guessing.
s&w torque arm
adjustable lca's w/rod ends
stock '99 camaro ss springs in rear, moroso trick springs in front
koni spa-1's all around
chromoly k member/a-arms
relocation brackets
wolfe drag swaybar

thats the main stuff. engine is a stock LT1 with a mild port job done by myself and 230/236 cam. 8" 3600 converter, th400, 9" spool/4.56's
1.32 60' so far with a 125 shot. still running a mail order tune and im waiting to get it on the dyno with wideband before upping the shot to a 200. i have no idea where the overall tune is right now.... i'll also be putting my frontend limiters on so i hope to pickup a good bit between this stuff.

caribbean 85 · 02-28-2007, 05:01 PM

Recently I went with 28 x 10.5 x 15 with a TH350 tranny and 4.30 gears 9 inch and I found that the larger tires are manhandling my 355 and 4.30 gears
It may be a marginal power issue (this is normally aspirated) but my best et so far has been 12.6 and 1st and 2nd gears run quite long during the pass

I use to get 12.0 easily off the bottle when I had my old combo of 4.10 10 bolt, 700R4 and 26 x 8.5 x 15

So I am stepping up to 4.56 gears as I feel the loss of the 700R4 low first gear by installing a TH350 plus larger tires and the heavier 9 inch rear have changed the dynamics under which my 355 engine works which cannot be compensated by a 4.30 gear

If you go with 28 size tires - and you have the TH400 gear set - I would try 4.30 at a minimum or 4.56 for a good get up and go car

WheelsUp84z · 03-01-2007, 12:53 AM

but my stall speed is much higher than yours is probably and i make peak tq around 4200rpms so if it stalls up to that ill be leaving the line at peak tq and im gonna want taller tires, plus i want to drive the car around on the street so i need something a little shorter

5678TA · 03-01-2007, 03:44 AM

200shot!?!? jeez.. that thing is gonna be in the 9's!! i dont know how high of a trap speed that is but you will definitely want 28 tall tires.. you will run out of gear with a 26".. a 4.30 would be pretty good too..

WheelsUp84z · 03-01-2007, 07:14 AM

Quote:

Originally Posted by 5678TA

200shot!?!? jeez.. that thing is gonna be in the 9's!! i dont know how high of a trap speed that is but you will definitely want 28 tall tires.. you will run out of gear with a 26".. a 4.30 would be pretty good too..

im hoping for 10.5's at 130+ or so..only weight reduction would be lightweight carpet, remove emissions, a/c and heater systems, no rear seats, lightweight racing front seats, no tire and jack, and draglites but with addition of SFC's, 8 pt cage, and 2 10# nitrous bottles. i think the car will be around 3250-3300 race weight (minus driver) to start, later on im going to do tubular k member and fiberglass hood, lexan window, but thats probably not for a while

caribbean 85 · 03-01-2007, 10:59 AM

Wheels up - I am running a Pro torque 8 inch - but I do foot brake - it is rated to flash @ 5200 if I run nitrous - it gets up to about 4000 or a little bit over on flash on foot brake

But I cant physically hold the car on foot brake the car past 2000 rpm - so thats where I think I am losing somethin

I agree with most here - 4.30 should be a good compromise for the taller 28 inch tires and street use

DIGGLER · 03-01-2007, 02:06 PM

im having to footbrake my stuff too. i'll probably be getting the trans freshened up in 2 months and will get a transbrake.

83 Crossfire TA · 03-07-2007, 04:55 AM

Do the math… this is basically the same question as I just answered here:
http://www.thirdgen.org/techboard/or...ml#post3254029 (new tranny/rear combo - lost e/t - need help!!!)

I’m actually a bit lost why this is such a difficult/common question. You want to run X fast, your redline/you want to cross the finish at Y rpm with a specific height tire, just calculate what gear ratio will get you there and leave a slight amount of room so you don’t run out of gear. If you don't have the information to do that, then I would guess that you're asking the wrong question.

FWIW, I’m with some of the others… you’ll have a MUCH easier time with this (traction, gearing, drag…) with a taller, like a 28” tall, tire.