hey guys i have 2.73 gears and i'm going to be instlaling 3.42's this winter, i do quite a bit of highway driving.. how much is this going to effect the speed? i usually run at 80 at about 2500rpm and 100 at about 3000rpm... if i put the 3.42's in am i going to be like 80 at 3000rpm or more or just a little bit more rpm? thanks

by the way i have a 350 bored .030 over, lt1 cam, tpi heads, edelbrock performer tbi intake.. blah balh blah what i'm getting at is it's not the 305 that was in the car and i was told if you have a 305 you shouldn't do the 3.42 swap unless you go as far as to get a cam and intake and a couple other things

 

Use the calculator section on the main page to figure out your RPM difference at speed.

 

uh, here is what i put:

Tire Radius RPM Rear End Ratio Transmission Gear Ratio =MPH

15 / 3000rpm / 3.42 / 1.00 (3rd gear?) / it came up with 78mph??

if it's that much off what do you think a top speed would be?

 

with 3.73s i run at about 3000rpms @ 80mph in overdrive. Not too bad, im used to it by now and i still get about 23mph on the freeway with mods in sig.

 

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You will need to change your speedo gears in order for your spedomoter to read correctly. If not your limiter will now be reached much lower.

 

alright... where can i get the speeo gears? my speedometer is aleady off but i'd hate to make it worse. got a site?

 

A few searches should give you your answer.

 

www.700r4.com sells all the speedo gears.

I calculated that with the 2.73s @ 80mph you're at 2000rpm. With the 3.42s it goes up to 2500rpm. I wouldn't be trusting your stock tach. Mine over reads by about 500rpm.

Robert

 

dont get your speedo gears from 700r4.com, get the part numbers from the FAQ section of the boards and go to your local dealer, they are so much cheaper. Remember too that your actual RPMs will be alittle lower than what you get from the calculator due to the torque converter lockup.