I know, I know.......... I'm beating a dead horse here....

But I was wondering if the swap from a stock 10b w/ 3.42's to a 12b w/ 3.73's would be that much of a change? M6 btw...

I know it's stronger, but I don't want to have a ridiculously short first gear and I don't want it effecting my HW mileage that much.. I do a lot of HW driving here.. It's the only way to get anywhere, is a 2+ hr trip thru the middle of nowhere (desert) pushing 110 cruising speed.

Any 3.73 owners have opinions?

 

Yes it is, I did just this back in 2002 with my Z28. But, since you have a 6 speed I would go with a nine inch.

Put a 12 bolt into a early Chevelle, Nova, Camaro, etc and you can beat the crap out of it, and not hurt anything. Put one into one of our cars with a torque arm, make a couple 4000 to 5000 dragstrip launches, and I can just about guarantee you'll pick up gear noise. If it is a drag only car, you'll never know or care about the gear noise. Drive your car home from the track, and the noise will drive you nuts. I feel the torque arm stresses the 12 bolt housing, causing distortion. We have never seen this happen with the 9 inch housing.

Exotic Performance Plus strongly recommends the Moser nine inch. This rear is even tougher than the Moser 12 bolt, and the horsepower of the late model F Body cars keeps escalating every year, which requires a very strong rear. With the recent introduction of the 6.2L GM aluminum block and the excellent flowing 6.2 litre heads, the horsepower of these cars is going to just keep climbing at a very fast pace.The nine inch will handle the power, plus we prefer the way the torque arm is bolted to the nine inch in the same way the oem rear-end is attached. (This is the only good thing about the stock 10 bolt...) The Moser 12 bolt uses four short bolts to attach the torque arm, and they have a habit of loosening up, even when loc-tite is used. Why the nine inch is stronger than the 12 bolt. The 9-inch has an internal rear-pinion support that also supports the gear end of the pinion to limit gear deflection under high torque loads. This seems to be the major reason why the 9 inch doesn't start whining after high rpm clutch dumps, when the 12 bolt will pick up noise.The 9-inch locates its pinion gear lower on the ring gear to improve tooth contact, than the 12 bolt does.The 9-inch has a 0.125-inch larger ring-gear diameter and internal pinion support than the 12 bolt does. This is not much of a difference, but it is worth noting. Bob

 

remember too you can change the final ration by tire height choice. go with a 3.73 or 3.90 with a M6 and you wont notice with two overdrives. when you go to the track you can run a smaller tire to up the ratio or a taller tire and bring the ratio down.

 

I don't need a 9" rear.. I'm not a drag racer, and I don't like putting those "F" car parts into a Bowtie...

And FWIW: I'm running a BMR TQ Arm w/ their mount. I still need to get the relo bracket. I'm a street guy who see's little strip and little auto X... It's just a street car, and I want gears with out having to worry about the rear. I'm going w/ the Strange 12b. If I were to go bigger, I'd do a 60.

 

QUOTE=bayer-z28;10348222]I know, I know.......... I'm beating a dead horse here....

But I was wondering if the swap from a stock 10b w/ 3.42's to a 12b w/ 3.73's would be that much of a change? M6 btw...

I know it's stronger, but I don't want to have a ridiculously short first gear and I don't want it effecting my HW mileage that much.. I do a lot of HW driving here.. It's the only way to get anywhere, is a 2+ hr trip thru the middle of nowhere (desert) pushing 110 cruising speed.

Any 3.73 owners have opinions?[/QUOTE]

no it wouldn't be that much of a change.... you need 410's to feel a difference

 

The step from 3.42 to 3.73 is what, about 9% You probably won't even notice a difference. I went (on a Caprice) from 3.08 to 3.42, again about 10%- just made it feel like it was running strong, nothing dramatic- Then I went to 4.10's really woke it up- of course, this is a 4300 lb car- you need gears to move the weight.

The poster that mentioned tires is correct, too- you can vary your final drive ratio by several percent by changing the height of your tires-

 

I'm just afraid of basically LOSING 1st gear due to 4.10's on the street and also losing my HW mileage..

I've seen it before, but does anyone have a vid of driving on the street w/ 4.10's?? It wouldn't be that hard of a change back to say, 3.73's after the strong housing is already in there..

 

i thought i was going to loose alot and you really dont especialy with 6th gear . what do you usualy cruise at on the highway? think of it this way it ur worried about gasmilage your less likely to speed
also you dont lose 1st gear i can still get up to about 42 mph in 1st which is not bad at all most import cars only get to about 35 mph in 1st gear

 

^ Cruise speed on the HW? **** do0d, it's all open desert here for 70+ miles.. SO I cruise at no slower than 90.. No faster than 140 for CRUISING. (depends if I'm in a hurry) I can make it to El Paso in 45 minutes, and that's normally a 1.5 hr drive through the middle of fk'n nowhere!!! Damned the speed limit! 80 miles of STRAIGHT EMPTY desert HW... You'd do it too..

42 in 1st? ****, I tach out @ 45 in first @ WOT from a stop w/ stock 3.42's. I saw a youtube vid of a guy launching from a stop w/ 4.11's and he tached @ around 25 in first.. I could be wrong too.

This is mostly a street car and I don't want it to suck.

 

Bayer Z-28, here is a somewhat different perspective on changing gear ratios from your 3.42.

This is based on your comments of open highway driving in the west, which I can relate to.

I am running a 3.90 gear. It is unarguable that changing to a numerically higher gear ratio will dramatically improve your acceleration from Point A to Point B. You will cover the same distance faster. However, living out west where stoplight to stoplight can be miles apart, a few things to ponder.

Obviously you will be shifting faster which is just a matter of personal preference. Also, your speed range in each gear will be less. With your 3.42's perhaps in 3rd gear you can roll it from 40mph-110pm before shifting. With a 4.10 3rd gear tops out at ~92mph, a 3.73 ~101mph.

And your engine is revving higher in each gear at the same speed than the 3.42's.

I am only giving you this perspective to apply it to your particular application. Undoubtedly a higher numerical gear increases acceleration. But, if your driving is more rural you may not really gain an appreciable difference, and shifting more frequently with higher engine revs is something to consider.

Since I assume you are at higher elevation, the strain on your 10-bolt (uncorrected HP/TQ) may not be as dramatic as it is at sea level. A 3.42 or 3.73 is very highway friendly. If your budget allows you can always experiment with a different gear ratio. That way you can decide before finally investing in a new 9 or 12 Bolt.

Lengthy answer, but I hope it helps.

Good luck.

..WeathermanShawn..

 

Go here and play with ratios : www.f-body.org/gears/ .

I've played with it quite a few times and I think 3.90's/3.89's are going to be the best bet, at least for me.

 

I have the moser rear when I first got it it sounded like a subway train.. I redid the gears checked there work... and they had it 6 thousands to far out of the mesh. I set a new set up nice and quiet. got 20k on it. and did maybe 10 4000 rpm dumps on the track and it is quiet still.. and as far as them 4 torque arm bolts I just use grade 8 bolts and lock washers red lock tight and torque them to 120 ft lbs they haven't moved yet

 

A 9" Moser is not a Ford part, its a Moser part. I went from stock 3.42's all the way to 4.11's and now I just use 6th a little more with NO loss in mileage (25+ on the highway).The difference in performance and WOW factor is hard to describe. It went from a fast street car to a hard launching race car that is still fairly docile around town. I went back and forth on ratios, and in retrospect, 4.11's worked great for my mixed use car. 3.73's wont be too much of a leap, and maybe not enough.