Ok i have an 89 iroc z it has a 350 with a 700 r4 tranny, i have been debating on what type of gears to buy i have it narrowed down to three 3:23, 3:42, or 3:73 now i want a gear that will knock a couple 10th's of a second of my quarter mile time, but i also still want to get descent gas mileage any suggestions? I have been leaning on 3:23's since i read a post that some guy made said he was running about 2700rpm's with a 3:42 that a little high for me. so if anybody could help me out here i would appreciate it. By the way i have 2:77's right now. One more thing i heard if you go higher than a 3:23 you have to get a new carrier is this true???

 

I'm not sure about the carrier thing but I'm running 3.73's no problem!

I'll run about 115 kmph (~65 mph) @ ~2600 rpm. Launching is great. The car jsut bites and takes off! That is if you lauch properly. Too much gas and you'll just roast the tires.

 

The Carriers are separated by 3.08 and lower and 3.23 and higher I believe.I have 3.73's in my Camaro.They are nice at the track but I probably should have went the 3.42 route.I don't know how fast I am going cause my speedometer still has the 2.73 gear in it,but when on the freeway going with Michigan traffic(85 to 90 mph) I am turning about 32-3300. That is a little more than I wanted but no looking back now I guess.The way you get around the carrier issue is Richmond gear sells Thicker gears for the 3.08 and lower carriers. I used my 2.73 carrier when I installed the 3.73's.They sell 3.23's,3.42's,3.73's,4.10's and 4.56 ratios for the 3.08 and lower carrier.Check out a Summit or Jegs and you will see the difference in the prices.They tend to run $10-$20 more.FYI.


James

 

i am running 3.42s in my car and @ 70-75 MPH i am at about 2350 RPM i would say... maybe a little higher... but nothing that bad... my gas milage is still pretty good too

 

With TPI 3.42's are really the best all around gears.

 

irocz8957
You will NOT be using any of those gear ratio's. Reason they are 10-bolt gears and will not work with what you say is in the car now. The rear axle in your 350 car "2:77" is a BW 9-bolt. Just can't go to JEGS or Summit and order gears, tough luck. Also 9-bolt parts are available but are expensive. But look on the bright side of things, you have one hell of a strong rear axle with the best rear disc brakes( PBR 11.655 calipers&rotors) even if it is a 2:77.

 

I'm assuming you have a TPI engine, therefore your best choice is a 3.45 gear set because the TPI 350 is not a high revving engine. People regret using 3.70 gears with them because the engine runs out of breath before the end of the quarter.

This guys sells the right parts for you: http://www.9bolt.com/

 

Either way you are going to have to change the carrier it seems, so if you want to knock off time get 3.73's. If you want gas milage get 3.42's it won't make that much difference. Unless you have a SERIOUS motor your not going to run out of breath in a quarter

 

You can buy a "Ring Gear Spacer" to use 3.23 and higher number gears on a 2.73 carrier. Go with 3.42's for your desired results.(edit:Excuse me, 3.45's

 

Remenber when you Post replies this is a BW 9-bolt we are talking about. 10-bolt axle gears WILL NOT WORK. Now I hope everyone knows the difference between the two.

 

Go to www.9bolt.com and buy a set of 3.45's. They're gonna cost you $300 but you'll get much better pickup without much loss of gas mileage and you'll never have to worry about blowing up the rear.

 

Hi 87LS,

What you say sounds logical but the people who have 3.7x series gears with TPI engines have found, almost overwhelmingly, that it is too much gear. By a lot of experiment they have found that the 3.4x series works best with TPI, due to considerations of torque and the engine's low rpm barrier (4500 or so).

 

I have used 3.73 gears for years and like them. I had 4.10 and didn't like them. I could cruise and get 300 miles on a tank of gas with 3.73 gears. On 4.10, I got 200 miles on a tank.

 

I do have to say I have no experience with a tpi and 3.73 gears. I still can't see how it would hinder the car. All it does is multiply torque and get you to your hp quicker. I do have to say I have never been in one before. Its your car man.

 

87LS...the problem with "getting to your hp quicker" with TPI is that it isn't a horsepower intensive setup. The glory of TPI comes in the down low torque, and 3.70 or 3.73 gears will shoot you straight past that torque before you get the chance to shift. If the peak power came at a higher rpm (as with a single plane carb intake or a Miniram) then 3.73's would be ideal, but TPI is all bottom end...it runs out of air too quickly not to be.