are the stock 3.23 gears good enough for my Z? :

86 Z28
new 350 (carbed)
performer intake
crane cam
edelbrock cat back
t-5 5-speed

 

I ran high 11's with 3.27 gears and 26" tall tires.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
454 Big Block buildup now in progress for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car
91 454SS daily driver
95 Homebuilt Harley

 

I'd go with 355-373 for a 350 myself. GUess it depends on if you care a lot about highway (not city) mileage. Have fun!

 

I have 3.23s and I have a spare 3.73 rear axle that I plan to swap (one day). Believe it or not, it is because I do a lot of highway driving that I want the 3.73s.

I expect to lose a little gas mileage, but it is for passing that I want to have 3.73s. With 3.23s at 55 mph, the tranny will not kick down into 2nd and if it does, only briefly. For passing, the 3.73s will give me that extra umph I am seeking when passing since I am stuck in 3rd.

But, as others have said and will say, it really depends on your objective (and your setup). For drags with an automatic, you'd find a higher stall convertor will probably give you better results. The stall convertor will get you out the hole fast, while not forcing you to upshift into 4th before you reach the end of the 1/4.

[This message has been edited by Glenn91L98GTA (edited November 17, 2000).]

 

i have a t-5 trans, so what would that do for me on the highway, also how much mileage loss are we talking about here, i do go to New York now and then

 

Changing from 3.23s to 3.73s will reduce your max speed by 14% in every gear or increase your rpms by 14% for a given speed.

You will have to change your speedo gears, but I cannot tell you the combo to install to correct it. I could if it was an automatic. I also cannot tell you IF GM makes a combo of speedo drive/driven gears that will properly adjust it. You can with the automatic because even though GM did not over 3.73s in 1991, there is a combination of drive/driven gears that they made for the automatic that will work.

As for how much your gas mileage will be affected depends on your mix of driving and how hard you drive. I expect to lose upto 10% on the highway, but gain on city driving. This is because with the automatic, you will shift into 4th and lockup the TC within legal speeds within the city. Currently, I have to exceed 40 mph before my tranny will upshif into 4th and lock the TC.

On other vehicles (cars and motorcycles) I have actually noticed an increase in gas mileage when changing to lower gears (larger numerically). This is because the vehicle was so heavily overdriven in top gear that the engine was not in its optimum operating range and the engine actually bogged due to overcoming wind resistance at certain speeds where the engine was not turning enough rpm.

One friend had a motorcycle identical to mine. Because he weighed more than me, he changed the gears to compensate for his extra weight so he could keep up or beat me when we accelerated. After the gear change he was slighlty quicker than me and got slightly better gas mileage. Guess what I did after that?