526 SS 96

Hi, I have a Moser 12 bolt W/3:73's, but I want to run a steep gear for the track. I want a ratio for the quickest possible E.T. I have a hot cam, Hooker LT's, 6/gear, & NX kit. I also have a BMR track pack, PH rod, LCA's, Boxed SFC's, and air bags. As for H.P. I have a peak of 435@6200 rpm & 491 TQ @ 3700 RPM. on a 100 shot pulling 4 degrees of timing. I am upping th shot to a 150 when I get the new fuel pump ( a few weeks) so I don't know where the new power band will be, but I want to run steep azz gears. I will be running slicks (ET street/drag) so what's the deal should I run 4:56 or higher?
Aleks

Stephen 87 IROC

You only need enough gear so that you cross the finish line at or around the red line in high gear (not in OD). It all depends on your max rpm and the size of the tires.

Making peak hp at only 6200 rpm doesn't need such a deep gear unless you have something like 33" tall tires.

Many of the cars I see with 5.13 gears also use 30" tall tires and shift around 7200 rpm.

I shift at 6700, have 29" tall tires and only use 4.56 gears. At lower elevation tracks I use 4.30 gears.

526 SS 96

What's wrong with using 5th gear (od)? I see the mustang guys do it all the time and they run 4:56 or higher gears.

RacinLT1

i know about 30 mustang racers,and none have EVER used 5th on the track. OD is geared so out of reach it isnt feasable to consider using it.

1:1 is the last gear you want/need/should ever use on the drag strip,.68-.74:1 simply isnt meant for acceleration.

Stephen 87 IROC

The OD gears are small and weak. They're not designed for high HP drag racing.

taner

it is just as the guys up above have stated. pick how fast you wnat to run and consider what rpm you will be turning optimally for your motor, and then you can decide quite easily. i am guessing with a 26" et street a 4:11 gear will work just fine depending how far up you can rev the motor on the big end.

526 SS 96

Ok, well it probably isn't worth the trouble then. I am about 2-300 rpm from redline at the line anyway. Just curious though, how do some of you guys run 130+? Do you turn 7K+ rpm?

RacinLT1

the guy's that run 130+ usually have 600+hp at the tires.

526 SS 96

You could have 1000 HP at the rear tires, but if your max RPM is 62-6500 RPM & you run 3:73's your Max MPH in 4th gear is abour 118-(Aprox.) 125 MPH. But thanks for your opinion . Whatever though F-it I got the money, so I will try a few diffrent rear end gear combinations and just post my results

Stephen 87 IROC

As a comparison my combination last year typically ran low to mid 11's at 118 mph.

Back when I had a 383 stroker shifting at 6800 rpm. I also used 26" tall tires and 3.27 gears in the diff. I was running 12.0's at 117 mph. The trouble was that I ran out of track before getting close to the red line at the finish line. I think I crossed the finish line at around 5500 rpm. The car would start to pull at about the 1000 foot mark. I was slow off the line but came on really strong at the finish showing that I had good top end HP but because of the poor gearing, the ET was slow.

Typical 12.0 car usually run around 108 mph. By changing gearing, the ET will change if you can use more of the engine's powerband but the mph should stay roughly the same.

Top Fuel dragsters use 3.20 gears only and run 330+ mph. They also have a direct drive tranny (no gears). Only the multi stage clutch controls how fast the power is transfered to the tires.

Another thing to consider is the weight of the car. A 3700 pound car needs a lot more torque to get it moving than a stripped down 2800 pound car. The lighter car doesn't need as much gear since it doesn't have to move as much weight. 600 hp moving 3700 pounds with 3.73 gears would be like 300 hp using 5.13 gears. They'd both accellerate about the same speed but the high hp would eventually pull away.

Joe Brodman

What is with the freaking attitude?? These guys are doing nothing but try to help you.

Against my normal judgement on such things, I guess I'll help.

At 6200 RPM, stock tires (about 25.66"), 3.73 gears, in 4th (6-speed) or 3rd (4L60E) aka your 1:1 tranny ratio, your speed would be: 126.94

What formula did I use. The following:

MPH = (RPM x Tire diameter (in inches)) / (tranny ratio x rear end ratio x 336)

Now remember, that formula does NOT take into account a couple factors, such as any driveline slippage, which you should hope you don't have), and tire growth.

Sadly, I'm finding that maybe I should have went with 4.10 gears on my car. When I got my 12-bolt, I did a couple things wrong calculating it. At the time I was internally stock, and figured I wouldn't be reving the car as high as I am (opps). Secondly, I calculated 26x11.5x16 ET Streets to be 26", when in fact they are 26.2". 4.10's would have ruined me on my ET Streets when I was internally stock, but would probably be the better combo now.....of course my gas mileage would suffer even more.

Now for your car: We won't even talk anything above 4.10's, because you'll see in a second it is senseless. Assuming you shift at 6400 (appropriate for a Hot Cam), and let's say you run the same tires I do, since your combo is basically a little milder than mine. That = 121.72MPH. Put simply, you will run out of gear...since your car should trap higher than that.

Now if you ran let's say a 28x11.5.15 ET Street, which is 27.5", with a 4.10 gear, you'd be at 127.75MPH, which would work out very well.

With your 3.73's and a 26.2" tire, you'll be at 133.8, which is not enough....the problem I'm seeing. As you can see, THIS is what is killing me N/A; 3rd gear is 1.3:1, and I either have to rev **** out of her out in 3rd (around 6900-7000), or hit too steep of a 4th gear.

OTHER option; they do make 3.90 gears for a 12-bolt. With those and 26.2" tires, it will put you around 127.96, the same area as the 4.10's with the 27.5" tires.

You can play with the calculations some more. Of course, if you start going into taller tires, like a 30" tire, you could move up to a 4.56 gear (you'd be around the 125MPH range, which would be close), but we are talking about a pretty large tire, some significant fender trimming to make it fit, etc....and isn't feasible for anyone but the big dogs.

My suggestion; if you really want to mess with the gear ratio, go 4.10 and a 27.5-28" tall tire. There is a good tire selection in that tire diameter range, which will allow you to pick an ET Street, QTP, or full drag tire without worry.

RacinLT1

I didnt limit my reply to a certain gear or rpm range did i?
As a whole,if the car has 600-1khp,it will be geared and tired accordingly.
Friends 87 firebird made 731 rwhp on the dyno,has a 28" tall tire,3.70 gears,and he runs it up to around 6800-7k and it trapped 149 on a shakedown pass.

Relax on the attitude,seems like you got upset cause noone agree'd with your idea.

I go through the lights at 58-6k and with a 27" tire and 3.70's i have trapped 119.

CANTONRACER

Well....you run n2o which as you know generates a load of tq...so why would you over gear your car? Make the tq that you have work for you.

A lot of guys that put a lot of gear in their cars do it for a couple of reasons....you run NA and make your power up high(and they leave @ higher rpms)....you don't make much power and want a better ET....your an unlucky person and only have an 1/8 mile track vs the lucky ones with a 1/4 mile track so who cares about the big end....

Take my combo...I make 360/450 at the wheels NA...going from 3.23's to 3.73's gained me a whole...... .05 maybe, if that. I leave @ 2200 rpm and make all my tq down low...so i didn't need the gears....

Now my new combo I am hoping to make 430/460 at the wheels, but higher in the rpm range so the gearing should benefit much more than before.

Grover

Very good advice Joe. My car is very similar to yours and I have 4.10's in my Moser. When I ran at the track at the end of last year with 28" ET Drags shifting at 6800, I would cross the line at the very top of 3rd or barely into 4th if I shifted early. That netted me the 12.48 run that is in my signature. So basically I didn't have enough power for the tire size and gear that I was running. This year I will be using a 26" ET Street.

taner

on motor i run a 26" et street, when i spray i run a 28" et drag, so that is how i do it. i have the best of both worlds, the 28" tire on motor was a bit much last year, with less weight and a different cam we shall see how it reacts, i hope to run the big tire all year at the track, on motor and spray. on motr i imagine i will be dropping the clutch at 5500rpm.... if not higher.