hey everybody right now i have a 91 camaro TBI 305 with a 3.08 gear ratio. i burning major gas on the freeway riding at 4000 rm around 75 mph and have decided to change it but want to know how am i suppose to go about it. how am i suppose to change the ratio? is there like a gear box that i have to replace or can the old one be taken out and tuned the the ratio i want? all answers and opinions are welcomed cause ive very clueless on this and want to learn more about it


thank you ahead of time

 

Assuming your car has a stock V8 T5... If you have the .74 fifth gear and a 3.08 rear axle, you should be turning ~2300 at 70mph with stock height tires. Less if it's the .63 fifth gear. So your 4000rpm at 75mph means something is wrong or unaccounted for somewhere.

Do 10 miles on the freeway. Does the odometer roll over 10 miles give or take a tenth?

Drive by a friend with a new, never-modified car. Do they both read 75 at the same roadspeed?

Pop the VSS out of the driver's side of the trans. tailhousing. What colour is the gear inside the trans? How many teeth are on the gear on the VSS?

Do the wheels turn once when the driveshaft is spun three times?

Maybe you're going 95. Maybe the engine needs attention / tuneup. Maybe it's not really 3.08 or a V8 T5 or correct speedo gears. You should be pulling 25mpg or so, driving reasonably.

 

wait i might have got my gear rstio mixed up but i know my speedometer is accurate cause when i was crusing about 70 on the freeway CHP drove by me to see how fast i was goin n just told me to slow it down since i wasnt going to fast over the limit (lol funny way of knowing) but everything on my car is bone stock.

 

You should borrow or buy a book on rear differentials to get an understanding on them. It's hard to explain in detail all that needs to be done. Quite complicated. This info is from the main page as to what cars were built with what rear ends.;https://www.thirdgen.org/1991-chevy-camaro

 

Well, the highest gear ratio in a third gen was 3.73 and the 5th gear in a V8 T5 with the least amount of overdrive was .74 which would also not put you anywhere near 4000rpm. So you need to figure out what's off (your tach perhaps)...

And a 3.08 is about as low as I'd go with a T5 also... Figure it out.

 

If it's the original T5, then it should be the 0.63:1 fifth.
Now, 3.08 x 1.34 does give 4000 at 75, with 26" tires. So the OP would be driving in third, not fifth. The question is why? Shifter problem? Bent forks?

 

OP: Does it sound like its revved to 4k or does the tach just say it is? The tach's in these cars are almost always off... by a lot.