I have a 88 iroc with a L98 and a T5. Mods so far are, 3" Cat Back, Ram air intake, K&N Filters, and soon to get headers and y pipe.

It's a street only car that I just want to be fun, however it is my daily driver and I would like to have decent fuel economy, which isn't much with our cars.

What would be the best gear ratio for me?

Most threads are for LB9 t5 or a4 or L98 auto. Can't find anything n L98 5 speed.

Thanks.

 

Assuming it's a V8 T5, do between 3.42 and 3.73.
The TPI intakes choke high rpm potential; you won't get as much out of 3.73s as you would with a Q-jet. But it's not a terrible combo by any means.

 

As of now I'm thinking 3.42's. Will 3.73's be too low for the TPI even though its a 5 speed?

Will 3.73's kill my mpg?

 

My very first conversion on a thirdgen was in 1991. The car was an 89 iroc 5.7 700r4 it ran 14.2 all day unless the retarded 700r 4 shifted too soon!!!! Only mods were cut airboxes k&N filters, pulley kit and chip..runs were at sea-level aswell.. Being competitive with all 5.0 mustangs I converted my car to a 5speed and ran 13.7 with 3.27s then got my hands on a 3.45 rear it went 13.5 finally got Hooker Shorties 2.5" custom Y pipe and ported the upper Plenum. Netting me 13.0s with traction problems on tire 12.8 this was the demise of the first t5 LOL 1.7 60' and powershifting=DEATH
I would only use 3.73s or 4.10s if I had a cam and ditched the TPI for a higher RPM intake

 

I have 3.73 and the gears seem short but it sure does fly. I recently swapped in the deeper 0.63 5th and that helps on the expressway.

You should be able to use 5th at any speed over 40.

 

92droptopws6 , thanks for the info backed up by actual numbers!

midias .How is your gas mileage? Can you even use first gear?

 

Any other input? I want to make sure I don't by gears that I regret installing.

 

My TPI 5speed,3.45 gear,headers managed 27 MPG. with no problem

My Lt1 6speed, 4.11 gear,etc... 29.5 MPG on a 450 mile trip

 

My mpg blows but I think it is more my carb running rich.

I get about 11 with pure city and about 14 combined.

I also only drive 4 miles back and forth to work so that hurts MPG and it is all stop and go.

Yes I can use first just fine
http://www.apexgarage.com/tech/gear_ratios.shtml
I have 25.16" diameter tires and a 6k redline so max of

41 1st
62 2nt
90 3rd
120 4th
194 5th

Usually I shift around 3-3.5K and I turn about 2200 rpm at 70 mph in 5th

3.42 will get you about 200RPM less at the same speed so about 2000rpm at 70mph

 

I used to have a t5 back when my car was mostly stock, think it took .2 seconds off the 1/4 mile. That was with the 3.27 rear, so I would say 3.42 would be perfect myself with that combo.

 

First off are we talking about a 10 bolt or a 9 bolt?

If it's 9 bolt you'll be limited to what you can find around normally 3.27s or 3.70s in the aftermarket. Unless you get lucky and find something on eBay or want to pay a bunch for shipping from overseas.

 

Its a 9 bolt.

I'm still torn between 3.42 and 3.73.

 

Have you priced 9 bolt gears? 3.70s are cheap. 3.45s aren't unless you can find them used. In fact I'm unaware of any us company that sells them.

 

My 87 l98 has factory 3:42s