Nonni

I have an 86 TA with:

GM Performance ZZ383 (425hp/460 lb ft) , SMI Rochester Quatrajet, dual plane intake, long tube headers
TH700R4 (aftermarket Raptor). 2500 stall, lockup
Tires: 275/40ZR17
Suspension: Stock + subframe connectors, wonderbar, bilstein struts and shocks. I am not going to change the suspension.

Currently my TA has 10 bolt with 2.7x and limited slip (that is not working any more). Needless to say, if I punch it the only tire that is spinning will spin like crazy. I have bought a Quickperformance 9 inch rear end. I did not buy a center section from them because I already have one. It is stored far from where I live and I always though it had 3.50 gearing. A friend of mine (who has been storing it) told me yesterday that its probably 3.00:1

I am not drag racing this car (might go to the dragstrip just to see how quick it is) but its not a daily driver (unless some of the other cars has broken down). I just take it out when its good weather to car clubs meetings and we drive around downtown. Sometimes I take if for a highway drives.

So, since I have an engine with lot of torgue, could I get a way with 3.00 or do you think I will be happier with 3.50? Do you think it would change much in 0-60 or the Quarter mile?

big gear head

Since you have an overdrive transmission you will probably like the 3.50 better. I would recommend putting a Eaton Truetrac in it too.

Nonni

That is what I have always planned. I have already bought the Truetrac

Pro Built Automatics

The difference between the two will not be more than a tenth in the quarter mile in the vast majority of cases.

sofakingdom

iTrader: (1)

I would suggest, rather than either of those 2 ratios, get one that has at least one prime number in its tooth count. Not 3.00 (10 & 30); not 3.50 (10 & 35). Get something like 3.36 (11 & 37... both prime), 3.55 (11 & 39), etc.

TORN

iTrader: (17)

Curious what would prime vs not make a difference of?

Nonni

Then its totally worth it to start with what I have (3.00:1) because I will have lower cruising speed and am not giving up that much of on performance , thanks!

QwkTrip

iTrader: (22)

It is so that the same gear teeth touch less often. It helps promote uniform wear over time.

TORN

iTrader: (17)

Just on a 7.5 ring gear? I selected 3.50 for my ford 9 inch. That's why I was curious.

QwkTrip

iTrader: (22)

It should be taken into account regardless of the type of rear axle.

According to the Richmond Gear website, a Ford 9" 3.50 gear set has a 10 tooth pinion and 35 tooth ring gear. If you took a pen and marked every gear with a number and turned the gears round and round, then you would discover that none of the same gear teeth touch each other until after the 7th full turn of the pinion gear.

Likewise, a Ford 9" 3.55 gear set has a 11 tooth pinion and 39 tooth ring gear. If you did the same exercise as above, then you would find that none of the same gear teeth touch each other until after the 39th full turn of the pinion gear. This distributes gear wear more evenly and the gears will last longer.

TORN

iTrader: (17)

Is it enough wear that one would return a 3.50 gear to change to 3.55 or 3.45 ratio?

QwkTrip

iTrader: (22)

I don't know how that transfers to real miles traveled on the road. You'd have to talk to an engineer that has closely studied the matter. Maybe call a couple different gear manufactures and compare their answers.

big gear head

The 3.50 was a factory for ratio in the 9 inch and there were millions of them made. They lasted for hundreds of thousands of miles in F100s F150s and Ford cars. Most of them never got the oil changed. Use the 3.50 without a second thought.