Re: Gear ratio choice
 

Ricky,

I have the same setup. 3.73s w 19s in back. I use 6th most of the time at cruise beginning at about 65. I waffled between 4.10 or 3.73. Probably the 3.90 gear would be sweet spot but the torque band on my motor makes the 3.73 eminently driveable.

Re: Gear ratio choice
 

I dont see me changing tire size any time in the near future , 17's will be it for a while. I'd rather put $$ into my engine and gains some ponies first . so I guess 3:73 might be the best for me? Not getting spanked by a turbo Miata is important to me ! also as well as longevity and fuel mileage

Re: Gear ratio choice
 

Marc installed 4.10's in my '91. It's stock other than the gear change.
The change in driveability is great, and the mileage was still over 21 mpg on the drive home. I have no experience with 3.73 or 3.91 so I can't offer a comparison. It is a great first mod. I just figured with the LT5 power band, I' go all in. No regrets. I doubt that I'll see 173 plus very often.

Re: Gear ratio choice
 

The 3.73 is certainly the economical choice, if your staying with the 315 tire the speedometer correction required is a single 45 tooth driven with no need to change the drive as is required for all of the rest of the choices. I'd just get the 45 tooth from Marc H and be done with it. The 3.73 gear set you have choices and none of the choices are with a "shimmed" outer pinion. All of them are crush collar fits now I believe. When ordering the parts kit and gear kit do yourself a favor and buy 2 collars and two pinion nuts, actually when you buy an install kit from most you'll have the second nut, there are various collars available depending on the gear kit of choice. I've a Dana brand 226mm ring gear 3.73 that has the conventional 2 3/4' collar but I've heard there are some out there that uses a 5/8" (or close) similar to the Nissan builds. My 226mm 4.10 uses that style collar.

Re: Gear ratio choice
 

Started with 345s in my 1st Z and sold it that way. My current Z came with 4.10s and I loved them ! To bad they broke one day. Came back with 4.33s and it was to much gear and a spin on demand situation in 1st and 2nd a little to often. Got set up for ORR work with 3.07s and they worked well for that application. Never got around to changing them and the clutch wear increased a bit for from getting underway with additional slippage under certain conditions. Fuel milage could probably increase if I slowed it down enough with these tall gears. 24 mpg was the best with 3.07 through the western states at 75 to 85 average. After 45 mph with 307 it still accelerates decently imho. Going back to 4.10s asap as all the stuff is here and ready for the bench. Have not run any other gears than those mentioned. The 4.10s were perfect and not much to be gained in MPG in 6th gear no matter what your running except perhaps 4.56. In that case you would be lucky to get 20 mpg... however... most of us here didn't buy into the economy factor when we got the disease. :-D

Here is a great site for looking at gear ratios and tire sizes with our ZF-6

http://www.angelfire.com/fl/procrastination/rear.html

Re: Gear ratio choice
 

I'm getting cross eyed reading this at this time of night....Subscribed to for future read!

Re: Gear ratio choice
 

Guess I am a minority. I love the 345's. however I never track my car, but it does see an occasional 7000 rpm. Most miles are on 70 mph freeways. I just love the history and the smooth massive power. Anything over 60 seems happy in sixth gear.

Re: Gear ratio choice
 

i have 410s in both my cars ,2000 rpms is 70mph . i cruize on the highway @70-75 and get between 23.5- 25mph .6th gear is really better than with the 3.45s 2000rpms with them is 87 mph . great if you live in texas next to the 10 .and its 80 mph speed .

Re: Gear ratio choice
 

Lets say an LT5 makes 370 lb/ft torque. In 4th gear and with 3.45:1 rear gears, your tires have the ability of seeing approx. 1277 lb/ft of torque.

Install some lower gears like a 4.10:1 ratio, ring & pinion, that 370 lb/ft at the engine in 4th gear becomes approx 1517 lb/ft torque.

So by the math swapping from a 3.45:1 ratio down to a 4.10:1 ratio allows a "free" extra 240 lb/ft of rearwheel torque for accelerating your car.

In 1st gear AFTER the clutch has been 100% engaged, that 370 lb/ft or engine torque with the 3.45:1 ratio nets approx. 3396 lb/ft of torque at the rear tire.
Same scenario but with 4.10 gears nets 4035 lb/ft torque at the rear tires for an extra 639 lb/ft of torque at the rear wheels.

Not bad from a simple final drive gear ratio swap.

peace
Hog