Funky final drive?
 

Okay, now that i have my 240 street legal, its time to address some issues. My first beef is that my 240 gets terrible mileage. I think this is because of the final drive ratio in the rear end. I was wondering what RPM everyone is running from 70 -85 mph. I run about 3500 @82 mph if memory serves me correct, and that is awfully high IMO. My old Acura Legend used to run about 2800 RPM at 80mph, and got pretty good mileage, but my 240 burned a quarter tank (from full) in about 80 miles. Is this normal? I was thinking that it was either the wussy final drive or an O2 sensor, because i have a lot of black soot on the inside of my exhaust tips, and ive only had the car legal for like 2 weeks. Im also running no cat, so i think that has something to do with the soot. Any info would be greatly appreciated

Unless somebody changed your final drive it's not that. I can almost guarentee it's the o2 unless you need to do a tune-up. 80 in a half a tank is terrible......i just got back from a 1200 mile trip...i have 350 miles on the tank with a 1/4 tank left.

oops... sorry i meant a quarter tank. Yeah if i burned half a tank in 80 miles id be kinda alarmed... anyways, the car doesnt need a tune-up, i changed the plugs, wires, cap and rotor last summer, and ive only driven the car about 200 miles since then... Im going to check my timing, but thats for a different reason. What RPM does your car run at 70 mph?

about 70mph @ 3k rpm

you should be getting about 22-24 mpg under normal city driving

I have an auto right now (last few days....preping for the swap FINALLY :) ) and I get 80mph at 3k. 80 Miles on a quarter tank is good actually.

yea 80 in 1/4 tank isnt bad, i have sr but my rpms are around 3500 at about 80 as well.

okay, so the final drive hasnt been messed around with.... i wonder if i can change it to have a little more top end to it by having a shop build me an LSD?

I have another question which pertains to possible crappy mileage... I get a LOT of black soot in my exhaust tips, more than i think should be normal, and a lot of times if i shift at high RPMs, itll backfire through the exhaust. Im running a pacesetter exhaust, and a high flow test pipe/cat, so im not getting rid of the unburned hydrocarbons, could that be my problem, or is the car running rich?

stock runs 7% rich (so ive heard). if you dont have a cat youll get unburned fuel coming out of your exhaust; which if it heats up enough itll ignite there.

yea id say ur running rich, do u ever smell gas from the motor bay? i know when i had the ka i smelt gas sometimes and i had a lot of black soot buildup..

you can put a R230 rear end from a TT Z32 with a lil patty cake back there. not sure what all needs to be done but it'll put you in the 180 MPH range.

Not from the engine bay, but it stinks up the car like a lawnmower when i take off hard!

lol yea im sure thats what it is then, better rich than lean!

...yeah as far as engine longevity, but not so much in the wallet longevity... what causes an o2 sensor to go bad?

they wear out (carbon build up, burning oil etc etc)

hmm... any way to test em?