MPG Hit with 4.10?
10-19-2017, 05:30 PM
#1
Burning Brakes
Thread Starter
MPG Hit with 4.10?
What kind of MPG hit are people seeing with 4.10 gears in a manual C5?
I find that other than freeway, I never get going fast enough to use 6th gear so I'm considering 4.10s. BUT, I don't want to entirely trash my good fuel economy (I'm getting 30+MPG on the highway).
I find that other than freeway, I never get going fast enough to use 6th gear so I'm considering 4.10s. BUT, I don't want to entirely trash my good fuel economy (I'm getting 30+MPG on the highway).
10-19-2017, 07:09 PM
#2
Drifting
Before I installed 4.10s I had a hand-calculated 27.4mpg for a cross-country trip from Biloxi, MS to Walnut Creek, CA. Cruise control was set as often as possible at the speedlimit +5mph. For the exact same run 4 months later in late September with 4.10s I got a hand-calculated 22.8. A real disappointment. Everyone claimed they saw "only" a 2-3mpg drop; some guys who I never believed claimed a negligible (and suspicious) "only 1-2mpg loss". They musta all been in AZ, OK, or KA, because the rolling hills of MS, LA, NM, west TX and CA sure must be the areas killing my mileage.
I've made that run at least 8x and for the last 3 runs I never got as much as 23.5. It seems that "enhanced memory" was the bait that hooked me into hoping for better. Do I care? not hardly. The 'extra' $$ penalty prolly amounts to less than $400 per year for 15,000 miles. That's prolly $4 or as much as a whole extra $5 per fill up--I fill up anywhere between 1/2 - 1/4 tank left depending on where I am (remote west TX, I'll fill up whenever I can). I never let the tank drop below 1/4. Financially, I don't feel it at all since it's "pay as you go" (yes, pun intended
).
Oops... forgot--this is an 03 z06.
I've made that run at least 8x and for the last 3 runs I never got as much as 23.5. It seems that "enhanced memory" was the bait that hooked me into hoping for better. Do I care? not hardly. The 'extra' $$ penalty prolly amounts to less than $400 per year for 15,000 miles. That's prolly $4 or as much as a whole extra $5 per fill up--I fill up anywhere between 1/2 - 1/4 tank left depending on where I am (remote west TX, I'll fill up whenever I can). I never let the tank drop below 1/4. Financially, I don't feel it at all since it's "pay as you go" (yes, pun intended
).Oops... forgot--this is an 03 z06.
Last edited by dork; 10-19-2017 at 07:09 PM.
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ChrisLSx (10-19-2017)
10-20-2017, 09:09 AM
#4
Melting Slicks
Member Since: Sep 2000
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I "could" do the math, but my slide rule is buried deep down in a box somewhere. But, I believe you could simulate 4.10 gear/6th with stock 3.42/5th.
5th stock on your M12 would be .84 X 3.42= 2.87
6th on a 4.10 would be .56 X 4.10= 2.29
Well, running in 5th on your stock setup will give worse mileage than 6th with 4.10. I think I'll go back to bed now!!!
5th stock on your M12 would be .84 X 3.42= 2.87
6th on a 4.10 would be .56 X 4.10= 2.29
Well, running in 5th on your stock setup will give worse mileage than 6th with 4.10. I think I'll go back to bed now!!!
10-20-2017, 10:54 AM
#6
Drifting
If you go here: http://www.csgnetwork.com/multirpmcalc.html
and plug in your numbers at the bottom calculator, you can figure out the hypothetical loss.
For my 03 z06 I used these comparative numbers:
OEM Ring / Pinion : 3.42
Tire height : 26.1"
MPH : 79
Trans final gear: .56
RPM calculated: 1948
R/P : 4.10
TH : 26.1"
MPH: 79
TFG: .56
RPM: 2335
1948/2335 = .834
Multiply my OEM-diff-gear gas mileage of 27.4mpg x .834 and the calculator's estimate is remarkably right on the nose for what I get as an average--the calculator says 22.85--I prolly get ~22.8 for an average over 4 cross-country trips. I've done better and worse on different trips--as low as 22.2 and as high as 23.4, so I'd say the calculator is pretty accurate but you might do better in AZ if your currently getting 30+ because that indicates to me that you're mostly on "perfectly" flat ground.
Using your number "30", it looks like you'll come in around 25.3mpg cruising at an average of ~75-85mph. (That's the speed at what my fuel mileage is calculated. It also includes prolly 8-10 incidents of WOT from "Xmph" to X+25mph before I let off when passing.)
and plug in your numbers at the bottom calculator, you can figure out the hypothetical loss.
For my 03 z06 I used these comparative numbers:
OEM Ring / Pinion : 3.42
Tire height : 26.1"
MPH : 79
Trans final gear: .56
RPM calculated: 1948
R/P : 4.10
TH : 26.1"
MPH: 79
TFG: .56
RPM: 2335
1948/2335 = .834
Multiply my OEM-diff-gear gas mileage of 27.4mpg x .834 and the calculator's estimate is remarkably right on the nose for what I get as an average--the calculator says 22.85--I prolly get ~22.8 for an average over 4 cross-country trips. I've done better and worse on different trips--as low as 22.2 and as high as 23.4, so I'd say the calculator is pretty accurate but you might do better in AZ if your currently getting 30+ because that indicates to me that you're mostly on "perfectly" flat ground.
Using your number "30", it looks like you'll come in around 25.3mpg cruising at an average of ~75-85mph. (That's the speed at what my fuel mileage is calculated. It also includes prolly 8-10 incidents of WOT from "Xmph" to X+25mph before I let off when passing.)
Last edited by dork; 10-20-2017 at 11:18 AM.
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ChrisLSx (10-20-2017)
10-20-2017, 01:09 PM
#7
Team Owner
I prefer 3.73 nice performance, more usable with heads and cam or more power. I lost roughly 3mpg on the hwy with heads and cam.
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ChrisLSx (10-20-2017)
I had 3.73s in my 01 Z28 w/ heads and cam, but always felt it didn't have enough gear. Later I did 4.56 gears and loved it (but big time mpg hit).
10-20-2017, 01:53 PM
#9
Drifting
I wanted to increase the HP/torque to just this side of needing to beef up the driveline--I didn't wanna hafta pay for new parts and an R&R of the tranny and half shafts, nor braces for the trans nor diff. All the sources said that meant 450rwhp or less. That ruled out an SC, but still allowed for your route, H/C/I.
My problem is, I'm in Podunk, Mississippi. The closest "reputable" speed shop is ~200 miles away. I wanted to leave the car for "one session"--no 'come backs' for tweaking "minor adjustments" or 'errors', or anything. Maybe the only posters on the forums are the squeaky wheels--the guys who've had problems with their H/C/I installs--but I didn't wanna take the chance that some renowned shop and/or some tuner might make a small mistake and/or assemble an incorrect/incompatible combination of parts or a bad tune that would require me to drive all the way back for another adjustment session--godforbid I'd have to leave the car there.
So I opted for the "brainless" R&R--a gear swap. It would have no effect on the engine, BCM, tranny, half-shafts, etc., only seat-of-the-pants and gas mileage. Better yet, since I was needing a new clutch, the labor for the R&R was 'free'. It only cost the price of a new gearbox; financially, I think I made out better, not that that matters. I wish I could have trusted the shop to deliver a perfect result, but with my luck, I'd have needed a tweak session, and I just wasn't willing, or I'd have done H/C/I, too.
Last edited by dork; 10-20-2017 at 01:56 PM.
10-20-2017, 03:40 PM
#10
Team Owner
4.56s could be great on slicks at the track. It all depend on goals and what your aiming for.
I have friends locally who are very happy doing mail order tunes from Frost tuning.
That's the goal I was originally pondering, but several things influenced my decision to go with 'just' 4.10s.
I wanted to increase the HP/torque to just this side of needing to beef up the driveline--I didn't wanna hafta pay for new parts and an R&R of the tranny and half shafts, nor braces for the trans nor diff. All the sources said that meant 450rwhp or less. That ruled out an SC, but still allowed for your route, H/C/I.
My problem is, I'm in Podunk, Mississippi. The closest "reputable" speed shop is ~200 miles away. I wanted to leave the car for "one session"--no 'come backs' for tweaking "minor adjustments" or 'errors', or anything. Maybe the only posters on the forums are the squeaky wheels--the guys who've had problems with their H/C/I installs--but I didn't wanna take the chance that some renowned shop and/or some tuner might make a small mistake and/or assemble an incorrect/incompatible combination of parts or a bad tune that would require me to drive all the way back for another adjustment session--godforbid I'd have to leave the car there.
So I opted for the "brainless" R&R--a gear swap. It would have no effect on the engine, BCM, tranny, half-shafts, etc., only seat-of-the-pants and gas mileage. Better yet, since I was needing a new clutch, the labor for the R&R was 'free'. It only cost the price of a new gearbox; financially, I think I made out better, not that that matters. I wish I could have trusted the shop to deliver a perfect result, but with my luck, I'd have needed a tweak session, and I just wasn't willing, or I'd have done H/C/I, too.
I wanted to increase the HP/torque to just this side of needing to beef up the driveline--I didn't wanna hafta pay for new parts and an R&R of the tranny and half shafts, nor braces for the trans nor diff. All the sources said that meant 450rwhp or less. That ruled out an SC, but still allowed for your route, H/C/I.
My problem is, I'm in Podunk, Mississippi. The closest "reputable" speed shop is ~200 miles away. I wanted to leave the car for "one session"--no 'come backs' for tweaking "minor adjustments" or 'errors', or anything. Maybe the only posters on the forums are the squeaky wheels--the guys who've had problems with their H/C/I installs--but I didn't wanna take the chance that some renowned shop and/or some tuner might make a small mistake and/or assemble an incorrect/incompatible combination of parts or a bad tune that would require me to drive all the way back for another adjustment session--godforbid I'd have to leave the car there.
So I opted for the "brainless" R&R--a gear swap. It would have no effect on the engine, BCM, tranny, half-shafts, etc., only seat-of-the-pants and gas mileage. Better yet, since I was needing a new clutch, the labor for the R&R was 'free'. It only cost the price of a new gearbox; financially, I think I made out better, not that that matters. I wish I could have trusted the shop to deliver a perfect result, but with my luck, I'd have needed a tweak session, and I just wasn't willing, or I'd have done H/C/I, too.