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[Screaming mad]

Ok yer I know yet another tire question! My question is real simple and hope fully a real simple answer! im running 55 profile at moment (255 55 16) but I want more aceleration outta by baby 3.4l..... If I drop to say 255 40 16 this should give me theoretically better aceleration? or will it be unnoticable? I realise it will mess up my speedo, but will it mess with my auto gear changes? Basically Im looking for a cheap mod, I cant find any one to reprogramme a 3.4l chip, only thing I can think of is ratio's, cheapest way been tyres!

[Dave M]

The difference in acceleration would have to be almost immesurable, and certainly nothing you'll feel SOTP.

[97LT1Z28]

What about gears for the differential? Or, you could look at superchargers too. There's another member named Jessica from South Florida and she has a supercharger on her V6 and she seems to be quite satisfied with the performance.

[Rob B (shoebox)]

One of the parameters the computer uses to control shift timing is MPH. So, anything you do that throws the speedometer off, will also affect the shifts.

[Injuneer]

If you are really running 255/55-16 tires (I don't think you are) and you went to 255/40-16 tires (I don't think you would want to) - you would feel a real seat-of-the-pants increase in acceleration..... about 12.5% more rear wheel torque.

BUT!
I don't think you are really running 255/55-16 tires. That is a truck tire. And, its 27.0" diameter will already have screwed up your speedo and your shift points, and bogged the car down by reducing rear wheel torque compared to the factory tire size. I suspect you are actually running a 255/50-16 tire, which is a popular size for the 4th Gen F-Body.

Might want to check your sidewalls again.

Then there are the issues with the 255/40-16 size:

-I've never heard of that size, and Tire Rack does not list any tires in that size.

-If it did exist, its a 24.0" diameter tire..... nearly 2" smaller in diameter than the tire that came stock on your V6. That is wayyyy too small a tire for a 4th Gen..... it would lower the car 1" closer to the ground, and make the already too large gap between the tire and the fender 1" larger..... and if you really are running the 27" truck tire, the visual gap would grow by 1.5".

You need to A) find out what size tires you really have and B) use the rear axle ratio to improve acceleration..... not fiddling with tires. When you get over 500-600HP, then you can use slicks and be concerned with the better traction of a soft sidewall 28" slick....... but for now, your best choice is "gears".

[Joe 1320]

The easiest way to do a gear swap would be to purchase a complete rear assembly from a V8 car at a wrecking yard. They would come with 3.42s and rear disk brakes too. My 94 3.4 has a 96 Z28 rear with 3.42s and disks. The speedometer is off, I need to purchase a little black box electonic speedo corrector but the accleration is better than a garden variety 3.4

[Screaming mad]

If you are really running 255/55-16 tires (I don't think you are) and you went to 255/40-16 tires (I don't think you would want to) - you would feel a real seat-of-the-pants increase in acceleration..... about 12.5% more rear wheel torque.

BUT!
I don't think you are really running 255/55-16 tires. That is a truck tire. And, its 27.0" diameter will already have screwed up your speedo and your shift points, and bogged the car down by reducing rear wheel torque compared to the factory tire size. I suspect you are actually running a 255/50-16 tire, which is a popular size for the 4th Gen F-Body.

Might want to check your sidewalls again.

Then there are the issues with the 255/40-16 size:

-I've never heard of that size, and Tire Rack does not list any tires in that size.

-If it did exist, its a 24.0" diameter tire..... nearly 2" smaller in diameter than the tire that came stock on your V6. That is wayyyy too small a tire for a 4th Gen..... it would lower the car 1" closer to the ground, and make the already too large gap between the tire and the fender 1" larger..... and if you really are running the 27" truck tire, the visual gap would grow by 1.5".

You need to A) find out what size tires you really have and B) use the rear axle ratio to improve acceleration..... not fiddling with tires. When you get over 500-600HP, then you can use slicks and be concerned with the better traction of a soft sidewall 28" slick....... but for now, your best choice is "gears".

Yer you were right! Had a look today whilst I was out, 255 50 16! sorry! So going to have a look at buying a z28 rear, maybe even the suspension as well as that is better than the 3.4, only problem is there are very few yards in the uk that have us cars, but there are some! if I change my ratio, how much top speed will I loose? Super charger is not an option as they only made one for 3.8 and never for the 3.4l... cheers guys

[thenuge876]

if you check on e-bay or someplace (maybe even the sale and trade section here) you might be able to find a Z28 rear-end to use so it doesnt necessarily have to come from a yard as long as you don't mind the shipping, which i don't know what that would run you. And I'm sure some of the other guys will chime in as I dont quite know for sure, but I do not think youll lose a large amount of top speed, maybe a little but probably nothing significant.

[Joe 1320]

Super charger is not an option as they only made one for 3.8 and never for the 3.4l... cheers guys

there are a handful that make turbos though.