time for some gears!
Thread Starter
Burning Brakes
Joined: Sep 2003
Posts: 866
Likes: 22
From: Savannah GA
time for some gears!
I'm dropping a few bucks into the car to freshen it up a little bit before I get back to the states. Considering it has a mild cam and heads now waiting to go on it, I'm thinking it might be time to step up to some lower gears when I take it apart for hardened axleshafts and inspection.
It's a '98 M6. I usually cruise around 77 MPH. I really DONT want to kill the mileage, this is a DD car, and as is pulls 33-34 MPG with a cam and some bolt ons. Hoping I dont kill the mileage off with a fresh shortblock and heads/intake install.
I'm torn between 3.73's and 3.90's. Which would you use and why? Keep in mind, the mileage factor here. I spend lots of time on the interstate, at least up to this point. Also would you build a unit or buy one from a place like DTE?
I'll be installing some new GM CV axles, wheel studs and a DTE brace at this time as well. For now the torque tube will get a new aluminum bushing unless I find a newer torque tube I can afford (so I can upgrade). I'll also be freshening up the tierod ends and other components for preventative maintenance, so I dont want to drop too much in one area. I have been considering a 402 L92 buildup down the road, but it'll be awhile from now if I decide to do it.
It's a '98 M6. I usually cruise around 77 MPH. I really DONT want to kill the mileage, this is a DD car, and as is pulls 33-34 MPG with a cam and some bolt ons. Hoping I dont kill the mileage off with a fresh shortblock and heads/intake install.
I'm torn between 3.73's and 3.90's. Which would you use and why? Keep in mind, the mileage factor here. I spend lots of time on the interstate, at least up to this point. Also would you build a unit or buy one from a place like DTE?
I'll be installing some new GM CV axles, wheel studs and a DTE brace at this time as well. For now the torque tube will get a new aluminum bushing unless I find a newer torque tube I can afford (so I can upgrade). I'll also be freshening up the tierod ends and other components for preventative maintenance, so I dont want to drop too much in one area. I have been considering a 402 L92 buildup down the road, but it'll be awhile from now if I decide to do it.
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
from 3.42 to 3.73 is a 9% change
from 3.42 to 3.90 is a 14% change
since you have a 6 speed already (with two overdrive gears), I doubt that gas mileage would be affected much while cruising the highway in 6th.
from 3.42 to 3.90 is a 14% change
since you have a 6 speed already (with two overdrive gears), I doubt that gas mileage would be affected much while cruising the highway in 6th.
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Racer
Joined: Nov 2002
Posts: 412
Likes: 1
From: CT
Racer
Joined: Feb 2006
Posts: 383
Likes: 1
Because it is nearly impossible to get 36 mpg on a STOCK C5 with stock gearing. I guess you could get close on a stock C5 if you were traveling 55 mph on the highway, which nobody does. Sorry, not with 4:10's.
Drifting
Joined: Feb 2007
Posts: 1,446
Likes: 0
From: Cranford NJ
Traveling at 70 mph average with no traffic I've done 31 mpg between Northern NJ and Washington DC. I verified it a couple of time. Both on the way there and on the way back (I used to have a girl friend who lived there so I made the trip almost weekly). These are things that I used to do to keep myself entertained on those trips 
.
If you have an automatic, then it's a different story.
Whether you believe it or not that's what I got. I've heard the same from others. I didn't believe it myself till I got the same results.
6th gear is so steep that the gears really don’t raise the rpms that much, and actually makes the gear more useable.
Max
.If you have an automatic, then it's a different story.
Whether you believe it or not that's what I got. I've heard the same from others. I didn't believe it myself till I got the same results.
6th gear is so steep that the gears really don’t raise the rpms that much, and actually makes the gear more useable.
Max
Racer
Joined: Feb 2006
Posts: 383
Likes: 1
Traveling at 70 mph average with no traffic I've done 31 mpg between Northern NJ and Washington DC. I verified it a couple of time. Both on the way there and on the way back (I used to have a girl friend who lived there so I made the trip almost weekly). These are things that I used to do to keep myself entertained on those trips .
If you have an automatic, then it's a different story.
Whether you believe it or not that's what I got. I've heard the same from others. I didn't believe it myself till I got the same results.
6th gear is so steep that the gears really don’t raise the rpms that much, and actually makes the gear more useable.
Max
.If you have an automatic, then it's a different story.
Whether you believe it or not that's what I got. I've heard the same from others. I didn't believe it myself till I got the same results.
6th gear is so steep that the gears really don’t raise the rpms that much, and actually makes the gear more useable.
Max
Thread Starter
Burning Brakes
Joined: Sep 2003
Posts: 866
Likes: 22
From: Savannah GA
I'm thinking right now 3.73's might be too small of a step to justify cost, and 4.10's might be questionbly steep. 3.90's seem to be a good compromise. Somebody prove me wrong! lol
I'm thinking the heads and intake might hurt me more in mpg right now. I'm getting 33-34 at 78 with the A/C on. Mileage is also the reason I'm afraid of stepping up a little from the 226/230 thats in the car now.
-Dave
Melting Slicks
Joined: May 2006
Posts: 2,936
Likes: 260
From: Westchester County New York
I'm interested in hearing the difference in cruise RPM at 70. If I remember right I was cruising at like 1500ish at 70... like 1700 aroung 77-78 where I normally cruise. I'm guessing 2200 at the same speed with 4.10's?
I'm thinking right now 3.73's might be too small of a step to justify cost, and 4.10's might be questionbly steep. 3.90's seem to be a good compromise. Somebody prove me wrong! lol
I'm thinking the heads and intake might hurt me more in mpg right now. I'm getting 33-34 at 78 with the A/C on. Mileage is also the reason I'm afraid of stepping up a little from the 226/230 thats in the car now.
-Dave
I'm thinking right now 3.73's might be too small of a step to justify cost, and 4.10's might be questionbly steep. 3.90's seem to be a good compromise. Somebody prove me wrong! lol
I'm thinking the heads and intake might hurt me more in mpg right now. I'm getting 33-34 at 78 with the A/C on. Mileage is also the reason I'm afraid of stepping up a little from the 226/230 thats in the car now.
-Dave
Chuck CoW installed mine and I cant seem to wipe this S%$*T eating grin off of my face...mileage?..havent noticed a significant difference...fun to driveness (a new word)....through the roof!!!
chuck did mine, and man was he right. oh, and his tune is awesome!