stroked1990RS

what would be the best rear gear to use ? my motor i am building is a 6500 to 7k max would a 4.56 gear red line this sum bitch in the trapps?

84firebird383

Depends on your tire diameter.4.56 is alot of gear tho.

Trevor86TA

Depends on tire diamater and trap speed.

What is the tire size, approximate hp/weight of the car or the estimated trap speed?

IHI

iTrader: (1)

Are you running 1/8th mi. or 1/4 mi.?
what are your cam specs (actual)?
what convertor are your running, stall speed and how effeicent is it
What size rear tire are you running
Whats the weight of your car
what transmission

All those things play into trap rpm, but a off the hip hp guesstimate, tire size, 2 speed/3-4 speed will lend into a better "guess"

For example, I trap at 6600 with my set-up, specs in sig

The truck i drive for a guy is running 4.30 gears and 31" tires and also crosses at 6500. 383cid/2900lbs/4800 stall/glide

AlkyIROC

Last year my 29" tires and 4.56 gears had me crossing the line around 7000 rpm but that's also with a 2 speed powerglide.

stroked1990RS

well the tire is 28'' and the weight ..i don't know that yet i have not had the car weighed ? i gutted it out though i mean gutted it! i am hoping to run 11.50 s with it if that helps any? also i think i am going to run a super street fighter 3500 to 3800 rpm converter
my cam specs are 250/260d 532/555L comp cams solid . the 383 i hope will make atleast 500 hp .. and last i am running a th350 trans. i am kinda new to drag racing ..but i have had fast street cars my whole life . i just want a half way good bracket car .

84firebird383

I stand corrected

IHI

iTrader: (1)

I personally would opt for the 4.11's with that combination and tire size, 4.30's would be max. 4.56's plus 28" tires are going to cause some traction headaches until you can figure them out, and if you want this to be a good bracket car traction is a must.

Hardest thing for anybody to accept is slowing a car down intentionally/knowingly is sometimes a good thing if you want to go rounds and actually make money/place in an event. There is a big difference between fast car and consistent car....

Trevor86TA

6500 and 7000 are pretty far apart. If you are shooting for 11.50s, that's about 117 mph. You should gear the car for 120mph (great air day, running at a different track, small change to setup).

Without factoring in slipage, you would be at:

4.56s, 28" tire and 6500 rpm = 118mph
4.56s, 28" tire and 7000 rpm = 128mph

Again, without slipage, at 120mph, you'd go through the traps at:
4.10s = 5904rpm
4.30s = 6192rpm
4.56s = 6566rpm

IHI

iTrader: (1)

Good point stating without slippage, but with that cam he has convertor selection will put him into a higher slippage range than a standard daily driver convertor-especially if he goes with an 8", which if it's track only is the optimum choice unless he's footbraking-then they might be able to tighten it up some, otherwise a looser 10" might be the ticket, so naturally rpm will be higher due to that fact.

Also one must also consider long term engine life also, spinning a motor to only 6K vs 7K there is a huge durability issue at stake, I've been around racing long enough to know this as fact with 100% certainty. Should he be one of "those" that likes to freshen up motors every year from beating them to death all season then no problem, but trying to make money in bracket racing is tough enough,(anybody saying it's just for fun is either new to the sport or a guy I'd like to line up with since mentally they're not on kill) and when factoring in rebuild's and or repairs every/all year that eats into your profits, time, etc...when I started out years ago I always wanted to go faster, as I matured as a racer and tired of swapping parts/working on cars it quickly became apparent that going fast is cool, but going rounds making money is even better yet....my yearly routine maitenance-chaning oil and checking valve lash. I much rather race a 13.99 second car that stay on the number than a 8 second car that moves throughout the day...but that's the ultimate goal of bracket racing anyways. So using a 4.56 with a 28" tire might be pushing his luck in the heat of the summer even on a national event prepped track as hot tracks, big gears, and small tires do not mix.

I've seen more high revving blocks have issues with either the lower end or valvetrain than motors spinning in a "normal" rpm band..hence mine gets shifted at 6K every pass, I do pick up a little going to 7K, but I save that extra push if I knowingly spin outta the box or knowingly cut a bad light, I use that extra power to "catch up" and get back in the game.

Sorry for the rant, just trying to help make a better educated decsion based off expereince (my own mistakes over the years .

Edit: also wanted to add with "typical" gear changes it adds about 500 rpm.

so if your were running 3.42's and went to 3.73 you'd go from crossing the stripe at say 5000rpm to 5500 rpm.

3.90's to 4.11's is also about 500 rpm

4.11 to 4.30 about 500 rpm

as well as 4.30's to 4.56

so if running a 4.11 trapping at 6K, jumping to 4.56 would put you close to 7K at the stripe. These are generalized, but ypical to what guys at the track have commented after swapping up or down 1 gear size regardless of car's make or motor's hp level.

stroked1990RS

thanks for all the helpful info ...i don't want to start off on the wrong leg...so to speak. i think i will go to the 4.11 gear and hit the trapps at about 6 grand. my cam makes power to my cam is a 3500 to 6500 and the victor is 3500 to 8 k ...now that you know what a am running for a motor and gear. What would be the best conveter to use am i making a bad choice with the 10'' super street fighter .. i was thinking it was going to put my motor in its power band ..at lanch?

thanks guys for all the great help !

IHI

iTrader: (1)

Stall range needs to be in the 4500-5000 range for that cam to hit the power band just right. Use a 2" open spacer on that intake as well to help keep velocity up, just dont use aluminum. Either a plastic or wood spacer, aluminum will heat soak and can change the signal playing goofy tricks on the motor. If it's a serious race car stay away from B&M convertors, cant say I've ever heard of a winning bracket car running one. The 2 most popular are ATI & BTE, in a nutshell-they work...period. I'm running a TCI unit because it was left over from the truck I also run, but we had it gone through so I knew it was fresh, compared to other convertors it is cheap at $700, but it's paid for itself in consistent R/T, ET's, and mph. Just be prepared to spend some money and know the convertor is a very important/critical factor in a winning combination, install a transmission gauge also. Tranney temp is one of the biggest factors of swinging ET's.

It's always hard to justify spending alot on a convertor, but they play big time into how well your car runs out. Call and talk with the techs at the convertor companies, they will ask alot of questions to better nail down what you need, stay away from talking to Summit/Jegs (or other speed shop) tech's since they just sell the stuff, you need to talk directly to the guys building these things to maximize you stuff.

I assume your foot braking so it's a good bet they're gonna recommend a 10" unit to keep the car tight on the hit.