Ok, Ive been reading alot of posts regarding peoples choice on what rear end gear to install. And Im still not sure what to do. I would like to hear from the street/strip racers out there on what you would choose, given a 1st gear ratio of 2.56 and a 540 cu in. street motor with 600ftlbs, this is a clutch car as well and 28" tires. The car weighs about 3700 lbs with driver.

The last transmission had the 2.2 first and 4.11s, at high rpm launches above 3500 rpm the tires just blow off and lots of spin. At 3000 rpm the spin is not as bad. The top end is 119mph but the 540 runs through the trap at 6000 to 6200. Im not sure if this is to much since I figured I shouldnt be turning this thing more than 5800. With the lower first now is the 4.11s gonna be too much. And is it possible that with lower numerical gears It could pick up more MPH. What is the perfect gear?

Thanks Rich

Http://community.webshots.com/user/67ragtp

I play around with my copy of DRAG drag sim. program just for kicks..

And I know it is a sim. program but at least I can see the trends in part changing.

I bet with your motor, 3.31's, 3.42's or maybe even 3.55's would be fine if you can get her to hook without breaking anything.

DRAG say's my First Gen. car, M-20 and 3.31's and about 26 to 26.5" tall tires if it hooks and doesn't break anything should go 130mph at 10.5 seconds!!

Imputting my 551hp at 5500 rpm and 579t at 4500 rpm 496 motor..

THEORETICALLY!!!!!!!!!!!!!!!Theoretically!!!!!!!

pdq67

PS., heck, I will be happy with an 11.0!!!!

I was under the impression that while difficult to hook at first per se, it was easier to get a ratio like 3.73-4.11 gear ratio to stop spinning and get going than a ratio around 3.08-3.42 ? I have no idea why this would be, but ? Sorry for my rampant topic heists lately, its just I am immersed in chevelle world cus of my cam swap..
I know I took a wrong turn from streetability with the roller, but for the sanity of my head, I have been eyeballing ditching the 3.90s (they whine anyway, the guy told me they would before he installed them, he said that particular brand whines alot) for something like a 3.42, or maybe even the 3.31's I have, although I'd feel bad if they ended up snapping (original to my car ringset).
I am pretty sure I'll be illegal if I put my 26" ET streets on anyway (at the track), so there is no real benefit to me having the 3.90's (sorry to jack the thread here, I just realized I did that) because I will be running on my radials anyway when I go to get a mph #? I mean, lets just say-- what is a 3.90 worth over a 3.42, with the idea that 3.90 is perfectly matched to our hypothetical drag car, then the owner puts in 3.42s, which are not the perfect match for our hypothetical drag car? What loss in performance will he see?

thanks everyone..
My head is just spinning because tomorrow I'm going to know if I like lots of duration or not :D

matt

Originally posted by MadMarv:
I was under the impression that while difficult to hook at first per se, it was easier to get a ratio like 3.73-4.11 gear ratio to stop spinning and get going than a ratio around 3.08-3.42 ? I have no idea why this would be, but ? I think the theory is that with a steep gear, the lower number gear will make your tires spin at a faster speed than higher number gears. For example, if you break the tires loose and the engine revs to 6 grand in first. With 4.11 or 4.56 gears, the tires will be turning at say 40 mph. If you had 2.73's your tires would be going like 75 mph! It should be easier to get the tires to hook up from 40 mph speed difference rather than hauling them back down from 75mph.

Just a theory, but I can believe it.... buddies low 3's geared camaro has big trouble hooking after breaking them loose. But my car hooks relatively easily after breaking them loose with 4.66 gears, and my car is 3 tenths and 3-4 mph faster than his, so it's not that he has more power than me or anything. He's even got wider tires!

chris

You might want to check this site out....it's actually really accurate, and I believe should help you.

http://www.dalesplace.com/htm/information/rpm_calculator.htm

It is true that larger gears (numerically) will spin easier off the line, and then stop spinning easier than smaller gears (numerically). A good example is a mountain bike. When you have it in the smallest gear (literally) it is easiest to spin your tire, but becomes exceedingly difficult to keep it spinning as you move forward. Bulb122 gave a good example with the speed differences. The speed the tires are spinning at, and the speed the car is actually going begins to equalize...therefore eventually hooking. Although it's harder to turn a smaller gear (numerically), you can turn it much faster and keep it going if you have the power to do so. I can vouch for the smaller gears (numerically) spinning (for what seems like)forever if you keep the throttle down after they start spinning. I used to be able to burn out for at least 100ft just mashing the gas off the line with my 3.08's.....ridiculous. graemlins/sad.gif

Naturally if you use smaller gears (numerically), be it transmission or rear end, you will pick up more top end. I personally think 3.55's or 3.73's are great gears.....not only do you get a good launch with them, but you still have potential for decent top end. With a 540 i'm sure you have plenty of torque.....given that, personally I would go with a smaller gear (numerically).

Just my .02 but that doesn't buy much these days. ;) :D

Low gears like 4.56's are easier to initially get the tires spinning than say a 3.31 gear would . But the say 4.56's would rpm so much faster that the engine gets through it's torque range much faster than say a 3.55 would.So once you get past the torque range the tires are much more likely to hook up.A 3.42 set will keep an engine around it's torque peak for a longer amount of time there for spinning the tires for a longer time... Its' torque that spins tires.... once past that killer torque range HP takes over.

The theory holds true about the speed of the tire with the different gears, but for me once it (tires) spins it is all over anyway whether it be 30 mph or 130 mph

The "perfect" gear ratio for a street/strip ride is the gear that gives you the "perfect compromise" to what you want to put up with or can be successful with at the track.

Rich,

I have done this before when in an overgeared situation..... If you feel like trying an expiriment try starting out in 2nd or 3rd gear.That could possibly get you into a range where you might get the tires to hold.....Big inch engines dont need lots of gearing...IF the tires can hook then just let the massive torque do all the work.

Im thinking of going with a set of 3.42s. I hope this turns out to be a good decision. Thanks for the advise.

Rich

I'm most likely going with 3.73s, according to the people I've been talking to 3.73s will work great with my combo, although this post kinda says the opposite. I have a "big" cubic inch engine (505") that won't be reving past 5600 rpms and has TONS of low end torque, behind the 505 is a new Hughes th-400. My '71 MC is alot like Toms other than it makes about 100 less horses and is a few cubes smaller and won't be reving quite as high, and look at his results with 3.42s. With 28"-29" tires I'm hoping to be able to get away with the 3.73s for everyday street driving but if it's not gonna benifit me when racing I see no point in them. Basically what I'm asking (just realized I, too, have hi-jacked the post :rolleyes: ) would 3.73s be "overgearing" my setup?