hey

im workin on the rear of my car and i just aquired a 3.42 rear. now, i was initially gonna get a 3.23 rear and swap in 3.73's.

is there that much of a difference between 3.42's and 3.73s? should i still plan to swap gears?

also, i now have a 2.73 posi.
the car will be a vortec headed 355 with a 750 carb, and a 700r4 trans and im thinking of a 2400 staul

mike

It is worth a couple tenths.

Jim

is there that much of a difference between 3.42's and 3.73s? should i still plan to swap gears?IMO, I say NO! I went from 3.08 gears to 3.42 in my old '70 Nova that ran 14.2's @ 97-98 mph, and I saw NO improvement after the swap. Car still ran within .05 sec of it's previous times, even after 10-20 passes. Actually the best time ever (14.19 @ 98.2) was recorded with 3.08s.

Of course, your results may vary depending on the rest of your combo.

You are looking at a 9% change in gear ratio. Not likely worth the money, unless you are really into getting the absolute most out of the car. A quality torque converter would do FAR more than a gear swap. Put the Money twords a precision industries 9.5" Vigilante converter. I gaurantee you will NOT be disappointed!! smile.gif

I totally agree that the money could be better spent. Assuming that both ratios(3.73 and 3.42) are pretty well in the ballpark for your particular motor and tranny combo, in most cases the difference would not be noticeable enough to justify the cost. Especially with the low first gear that the 700 tranny has, you will already have plenty of gear reduction for a good holeshot with 3.42 gears. As a matter of fact, the total gear reduction in first gear with the 700 tranny and 3.42's is basically identical to using a turbo 350 tranny but with 4.11 gears. If you have ever been in a car with a 350 turbo and 4.11 gears, than you know that thats setup capable of some tire smokin holeshots. You get these numbers by multiplying the transmission gear ratio by the rear gear ratio. So, the 700 has a 3.06 first gear, multiply by 3.42 and you get 10.46. The 2.52 low in a 350 multiplied by 4.11 gives you 10.35 total gear reduction. Very very close as you can see. When you look at it that way, it sounds much nicer. Of course you dont have quite as much gear reduction in other gears compared to what you would have with a 350 4.11 combo, but its nothing to worry about and you should be plenty happy as long as you use the proper camshaft and converter to take advantage of it.

My personal experience in my Nova with a 700R4 and 3.50, 3.70 and 4.11 gears is that the 3.70's were 2 tenths quicker than the 3.50's and the 4.11's were another 2 tenths quicker.
The Vigilante converter is definitely a good investment. On top of the 3-4 tenths you gain over the stock converter, the ability to lock the converter in third gear is worth another 2 tenths and 3 mph.

I guess just to double check everything, aside from the specs you listed so far, what car are we talkin about here. Also, what is the compression and camshaft specs and your intentions for the car(regular driver, weekend car......). Even if you got a full two tenths out of a gear swap as well(maybe, maybe not) is that worth the price of a gear swap to you?

your still gonna go with the 750 brute???
shane

I would spend the money elsewhere. I went from 3.23 to 3.73 and picked up 3 tenths. But that's a bigger jump. If you were hanging on that 13.0edge and wanted that 12 second run, and not eating dinner before the race didn't get you there, then consider the swap.

I agree, leave it alone. The difference between those 2 is pretty slight. I'm sure there's something else about your car that could use all that money amd labor, that would provide much more benefit than that gear swap. Cost/benefit ratio. Now if your car is utterly and altogether PERFECT and optimized in every way other than that, and you discover that your trap RPMs are below your peak HP RPM, and you've got $400 or whatever just burning a hole in your pocket to fix that, then go for it; otherwise, spend your money on a better quality torque converter, which will make the gears make less of a difference.

I wouldn't bother swapping the 3.42's to 3.73's either..spend some time dialing your combo in.
Going from 2.73's to 3.42's will make a noticeable improvement.Go buy some sticky tires instead smile.gif

ovelle-
Jason from BIGS emailed me and really gave me some great advise, he seemed to be a great guy to deal with and he gave me some great advise for the 750 VS carb. i wish i could buy a carb from him, i just dont have that kinda money right now.

as for money for this issue, i can rebuild a rear end myself, and i have 3.73s in my garage set up for the series carrier that i have. however i dont have a rebuild kit yet. i suppose ill just hold on to the gears until i rebuild the trans and get most of the motor finished. then i guess ill just have to make it one of those 'ill do it once everything else is done' things.

my goal is low 12s with the car, gas milage matters....but it doesnt. id drive the car in the summer abit, on weekends abit, and to the track. i suppose if i can drive the car to the track race it, and drive it home, then im satisfied. i figure i should push a 10:1 compression on my motor to make that happen

mike

I went from a 2.77 to a 3.27 Gear in a Camaro and the ET was EXACTLY the same with only a 1 to 2 MPH gain. Not worth it at all. You would think 1/2 a turn would make a good difference, but it doesn't.

Originally posted by caru68:
I went from a 2.77 to a 3.27 Gear in a Camaro and the ET was EXACTLY the same with only a 1 to 2 MPH gain. Not worth it at all. You would think 1/2 a turn would make a good difference, but it doesn't. every combo is going to react differently.....i went from 3.08's to 3.55's in my 71 Chevelle with a stock 400sb and it picked the car up 4 tenths. if you already have the gear and can install it yourself, you know more about it than most of the guys who are giving you advice. ;)

If you make great torque off the line a gear won't help much. The stock type (RV Cams) work good with 2.41-3.08 gearing. Put a 4.10 behind one of those cams and your past your power range.

A cam that is lopey needs a bigger gear because the torque is not available to get it going. There are bigger gains to be had when you have a combo with lower gears like 3.55 thru 5.13's if you have a high performance camshaft and converter.