Best Power & MPG With 31's ( 3.73 Or 4.10 ) ?

killian96ss · Post by **killian96ss** » Thu Nov 18, 2004 5:41 pm

I am running 31" tires with the stock 3.73 gears. When you recalculate rear gear ratios, 4.10 would put me right back where I was with the stock 28" tires. Would I gain or lose gas mileage with 4.10's. I am also wondering if there is a noticeable acceleration increase with 4.10's and 31's. Some of you have done this mod, and I would like to hear your opinions on doing this.

Steve

Justin · Post by **Justin** » Thu Nov 18, 2004 9:08 pm

you will get more power but your rpms will be a bit higher resulting in lower mpg. I believe hobbie did this and he averaged 12mpg...I have 31's and 3.42. Get me on a straight and i bet i could get a good 16-18mpg but i average 14-15 which isn't bad. I speed up before hills on highway to cmpensate for loss of power

a2b · Post by **a2b** » Thu Nov 18, 2004 11:59 pm

ya i went from 3.42's to 4.10's and it was a HUGE difference....with the amount of torque and power we have, i would say 32's or light 33's would be better.

killian96ss · Post by **killian96ss** » Fri Nov 19, 2004 8:23 am

Justin wrote:you will get more power but your rpms will be a bit higher resulting in lower mpg. I believe hobbie did this and he averaged 12mpg...I have 31's and 3.42./

If I had 4.10's with my 31's I would have the same rear ratio as stock, so I would think that my gas mileage should be about the same as stock. There should only be a drop of 1-2 MPG from the extra wind resistance and rolling resistance of mud tires. Does this sound right?

Get me on a straight and i bet i could get a good 16-18mpg but i average 14-15 which isn't bad. I speed up before hills on highway to compensate for loss of power

When I switched to 31's I noticed that my truck kicks in and out of OD constantly when going up hills or mountains like the Sierra's. It never did this with the stock size tires, so I am wondering if I am actually getting worse gas mileage with my current ratios.

Steve

Justin · Post by **Justin** » Fri Nov 19, 2004 8:49 am

Well, how often do you kick out of verdrive on the hihgway? It's kind of a paradox because 1) you can get better gas mileage with lower rpms then 2) you will never downshift on the hihgway with 4.10's, however your rpms will be higher.

There are alot of factors
1) wind resistance with BL
2) height and weight of 31's
3) gear ratio
4) drivers foot

The way I look at it...my truck did fine with 3.42 and 28's. GM builds the zr2's with 3.73 and 31's.....If you really want more power and have the $1000 to put in the new gears and the extra $200 a year on gas, go for it

Post by **HenryJ** » Fri Nov 19, 2004 8:50 am

I can't say for sure where the mileage will go, but my bet would be slightly lower.

Most people make all these changes and never re-calibrate the speedometer, merely guessing or calculating the change / effect on the odometer readings.
This can lead to grossly incorrect mileage figures in either direction.
With the taller tires I have no doubt that the readings would show less mileage since you would travel further than the odometer would accumulate.

Even if you do re-calibrate using advertised diameters and your HPPIII, the figures can be off.
I check mine with the GPS to get as close as possible.
A radar/sign check station would also be a good option?

At first I really wanted to make the switch to 4.10's in order to maintain the final ratio that I had with the 3.73's and 29" tires. That was the ideal ratio, IMO. But things have changed now.
Since I did not make a gear change, which was not cost effective for the small change in ratios (3.73 to 4.10), I added other modifications to improve engine performance and transmission performance in order to compensate.

Things have come together pretty well. I have what feels like a 25-50% improvement in performance, and my mileage is nearly the same to slightly better than stock.

Even though I did not make a gear change, I now have brought the performance to the point that I can spin the tires as well as I did stock , even though I now have 31x10.5"s

killian96ss · Post by **killian96ss** » Fri Nov 19, 2004 9:17 am

HenryJ wrote:Even if you do re-calibrate using advertised diameters and your HPPIII, the figures can be off.

I was able to get pretty close as my tires are 30.3" and I set my HPPIII at 30.25", so as they wear out it should be even more accurate, assuming the programmer is doing what it's supposed to.

At first I really wanted to make the switch to 4.10's in order to maintain the final ratio that I had with the 3.73's and 29" tires. That was the ideal ratio, IMO. But things have changed now.
Since I did not make a gear change, which was not cost effective for the small change in ratios (3.73 to 4.10), I added other modifications to improve engine performance and transmission performance in order to compensate.

This is about how I am feeling right now with my current setup. Even with the bigger tires and BL, I definitely have more power than I did stock. I am curious about some mods that most of you haven't tried like the CFM Tech throttle blade, and EGR limiter. When I did the throttle blade mod I noticed a big increase in power and throttle response ( probably only 5-8hp, but it seemed big ), and a slight power increase and hesitation drop with the EGR limiter. I have not had any problems come up as a result of these mods. How come the other members are not trying these mods?

Steve

Post by **HenryJ** » Fri Nov 19, 2004 9:44 am

killian96ss wrote:... I am curious about some mods that most of you haven't tried like the CFM Tech throttle blade, and EGR limiter. ...How come the other members are not trying these mods?

Some may be worried about meeting emissions standards?

I found the CFM throttle blade added throttle response, but almost too much when in low range. The EGR limiter was a "pita" to get dialed in, but a necessary mod to use the throttle blade. I can't say it added much for me, but definitely did reduce the intake deposits.

Your set-up is very close to mine

I think it will grow on you performance wise. Have you thought about adding a MSD? What about E-fans?

killian96ss · Post by **killian96ss** » Fri Nov 19, 2004 10:26 pm

HenryJ wrote:Some may be worried about meeting emissions standards?

With my current setup I have already easily passed California's newest smog program, which is one of the hardest emissions tests in the country right now.

Your set-up is very close to mine I think it will grow on you performance wise. Have you thought about adding a MSD? What about E-fans?

Yes to both, and a Powerdyne TB spacer, K&N FIPK II, MSD wires, Accel cap & rotor, and Gibson or JBA headers. Another idea that I've been thinking about is, full roller rocker arms ( Comp Cams does makes them for the Vortec V-6 ), but the valve covers would probably have to be different ( maybe an older V-6 with the steel valve covers would work, or spacers for the current plastic ones. This is definitely another 12-15hp. With all the bolt on mods I can think of ( less supercharging ) then I would say another 30-40hp is possible.

quickbiker · Post by **quickbiker** » Sat Nov 20, 2004 5:09 am

I get anywhere from 17-21. I got 31's and 3.73's. I can get 300 miles or so out of a tank on the highway. I really think it's a combination of things. Most of it being the HPPIII. I got it tuned for 93 octane, and reprogramed the shift points. I got a detroit locker and I can squeel the rear tires off a start, but whoo, takes off like a rocket.

Maximous · Post by **Maximous** » Sat Nov 20, 2004 10:32 am

well what the heck is wrong with my truck, I am completely stock and have never seen 300 miles on my odometer unless I forgot to reset the trip, and second, how is it you can "squeel" and HJ can "Spin" 31's with 3.73 and i can't "Squeel" or "Spin" 29's with 3.73

F9K9 · Post by **F9K9** » Sat Nov 20, 2004 10:40 am

Maximous wrote:well what the heck is wrong with my truck, I am completely stock and have never seen 300 miles on my odometer unless I forgot to reset the trip, and second, how is it you can "squeel" and HJ can "Spin" 31's with 3.73 and i can't "Squeel" or "Spin" 29's with 3.73

Only performance mods I have is the Airaid intake and HPP III but, I just put my Geolanders on and they tend to "squall" very easily when pulling out in traffic. My Goodyears never did that unless I was on an incline

Post by **HenryJ** » Sat Nov 20, 2004 11:01 am

Maximous wrote:well what the heck is wrong with my truck, I am completely stock and have never seen 300 miles on my odometer unless I forgot to reset the trip, and second, how is it you can "squeel" and HJ can "Spin" 31's with 3.73 and i can't "Squeel" or "Spin" 29's with 3.73

First I would say have you ever checked your speedometer to see if it is correct?
Mine was off 3 mph stock. As if it had been calibrated for the stock tires instead of the optional offroad tires.
How about...have you tried running 89 octane fuel? I get 2 mpg better mileage on it. Mileage seems to be the same for 91 octane.

Next I would say that bone stock I could not slip a tire no matter how hard I tried. It only takes a few mods to wake things up a bit.

Have you opened up the exhaust yet?

jeff024 · Post by **jeff024** » Sat Nov 20, 2004 2:26 pm

i am also able to smoke them on dry road at takeoffs MAX with stock 235/75 GYs with the 3.73 rear only mods have been the intake and exaust and i average 20-22mpg most i have let it hit on a tank was 320.

Maximous · Post by **Maximous** » Sun Nov 21, 2004 10:14 am

you guys suck, i need exhaust and intake work done, i had the gas light come on last night w/a total trip of 230something miles, i know i can take out my muffler with no problems, but what about the pre-cat, not to start a new tread i know that some people think you need it due to back pressure however we have plenty of backpressure as is, i am just wondering the warranty issue this could be turned into, anyone know?

Post by **HenryJ** » Sun Nov 21, 2004 10:27 am

Maximous wrote:...i need exhaust and intake work done... i can take out my muffler with no problems, but what about the pre-cat...some people think you need it due to back pressure...just wondering the warranty issue ...

Just changing out the muffler will help, the pre-cat is not helping anything but cold start emissions, and that is a "maybe".I really don't think we need two cats

The main cat offers more than enough back pressure.

If you remove the pre-cat, I'm pretty sure that IT's warranty will be void, as for the rest of the intact system, I think it will be fine. Do you really plan on using the warranty for service on the exhaust system before the warranty expires?

BTW, there is no way they could justify pre-cat removal as a basis for denying warranty service on a failed waterpump, if it is that kind of thing you're worried about.

bubaloo1983 · Post by **bubaloo1983** » Sun Nov 21, 2004 1:31 pm

i had 4.10s and 32 for a bit...the power was great but the milage did suck. but i dont care to much about milage i just wanted the power...and i meanif your orried about milage with this truck you bought the wrong vehicle anyway! lol

gofast505 · Post by **gofast505** » Tue Nov 23, 2004 8:04 am

I did the bl to 31's and my gas mileage dropped too, I am very happy when i get close to 300 miles from a tank, when i was stock i actually got 360 miles from a tank, once i even made it from Durango Colorado to Hot Sulphur Springs Colorado (where i live) on one tank and my gage still said i had 1/8 a tank, and that was going over 3 mountain passes. Stock my truck could squeel no prob, i had a zr2 before the zr5 that would squeel in first and second. My next mod is the catback system, i was planning on getting that done this friday but our VW westfailia's exhaust just fell apart, so my extra $ will prob go to get that fixed.

bl

adrenalnjunky · Post by **adrenalnjunky** » Wed Nov 24, 2004 1:20 pm

HenryJ wrote:First I would say have you ever checked your speedometer to see if it is correct?
Mine was off 3 mph stock. As if it had been calibrated for the stock tires instead of the optional offroad tires.

Have you opened up the exhaust yet?

My Blazer was the same way -- Came with the smallest uniroyals (225-70-15), and I went to my 30's. I figured my speedometer would be off by a couple mph, but the next week I took a roadtrip following my mom's trailblazer the whole way -- using 2-way radios i found that my speedometer was right on with hers, and then the local Sherrif parked one of those trailer mounted "Your Speed Is..." Radar displays at the end of my road -- my speedo and it were dead on. I never recalibrated anything.

coffeedrnkr · Post by **coffeedrnkr** » Wed Nov 24, 2004 8:21 pm

I got a detroit locker and I can squeel the rear tires off a start, but whoo, takes off like a rocket.

Im pretty sure that has to do with the locker, b/c my friend with a 4runner that a person on a bike could beat in a race can squeal his tries now that he has a locker. I think it is due mostly to the fact that there is no power loss in the carrier, it is all just locked.

As far as my gas mileage I can't really tell b/c I cant run my tank lower than 1/4 or my gas gauge starts freaking out (I have already ran out of gas twice b/c my gauge says I have like 3/4 of a tank, then the engine dies)

ace · Post by **ace** » Sat Mar 05, 2005 11:24 am

I was looking over this post. I know it's old but I was thinking how people were talking about adjusting their speedometer for their change in tires etc. but what about the odometer? Does the HPIII change that too or are the taller tires and changed ratio's giving false mpg too.

bubaloo1983 · Post by **bubaloo1983** » Sat Mar 05, 2005 12:04 pm

in terms of gears i would say even with he 35s im running and the 4/10s i still have more off the line then alot of trucks i have driven. of course it dies after that but off the line i have good get up and go

F9K9 · Post by **F9K9** » Sat Mar 05, 2005 1:12 pm

ace wrote:I was looking over this post. I know it's old but I was thinking how people were talking about adjusting their speedometer for their change in tires etc. but what about the odometer? Does the HPIII change that too or are the taller tires and changed ratio's giving false mpg too.

The Hpp III adjusts your speedometer as well. I just finished my monthly beer run to the closest legal place to buy alcohol (55 miles away) and noticed that I have to tweak my tire size with the HPP III a little more. My speedometer was reading 2 MPH faster than my GPS units.

killian96ss · Post by **killian96ss** » Sat Mar 05, 2005 6:01 pm

ace wrote:I know it's old but I was thinking how people were talking about adjusting their speedometer for their change in tires etc. but what about the odometer? Does the HPIII change that too or are the taller tires and changed ratio's giving false mpg too.

When you adjust for the correct tire size and/or gear ratio with the HPPIII you are also automatically correcting the odometer reading as well, however if have been running a different size tire or gear ratio for a long period of time your odometer will never have the correct actual mileage again.

Steve

bwenny247 · Post by **bwenny247** » Sun Mar 06, 2005 4:14 pm

besides driving behind or next to someone and comparing speeds, is there a way (like glovebox code, etc...) to determine what tires came stock with your truck, either 225/70/15 or 235/75/15? is it linked to the gear ratio: 3.42's have the smaller tire, 3.73 have the bigger tire?
i bought my crew with 50,000 miles on it and Wrangler 235/75/15 rt's, which i just assumed to be the stock size. but if my speedo is set for the smaller tire, then i guess i've been speeding this whole time.

just curious for a proper recal. with the HPPIII.
thanks

Post by **HenryJ** » Sun Mar 06, 2005 4:27 pm

bwenny247 wrote:besides driving behind or next to someone and comparing speeds, is there a way (like glovebox code, etc...) to determine what tires came stock with your truck?...

Yes, and you nailed it- Deciphering the glovebox RPO codes

It is all in there.

marks10cc wrote:QBF Tire, P235/70R15 Black Wall, All Season
QBG Tire, P235/70R15 White Wall, All Season
QCA Tire, P205/75R15, White Wall, All Season
QCB Tire P235/55R16, Black Wall, AL2
QCE Tire, P205/75R15/N Black Wall, All Season
QEB Tire P235/75R15/N White Wall, All Season
QJJ Tire 31X10.50R15LT/C Black Wall, OOR
QLN Tire 235/70R15-103H Black Wall, All Season
XBF Tire Front P235/70R15 Black Wall
XBG Tire Front P235/70R15 White Wall
XCA Tire Front P205/75R15 White Wall
XCB Tire Front P235/55R16 Black Wall
XCE Tire Front P205/75R15/N Black Wall
XEB Tire Front P235/75R15/N White Wall
XJJ Tire Front 31X10.50R15LT/C Black Wall
XLN Tire Front 235/70R15-103H Black Wall
YBF Tire Rear P235/70R15 Black
YBG Tire Rear P235/70R15 White
YCA Tire Rear P205/75R15 White
YCB Tire Rear P235/55R16 Black
YCE Tire Rear P205/75R15/N Black
YEB Tire Rear P235/75R15/N White Wall
YJJ Tire Rear 31X10.50R15LT/C Black Wall
YLN Tire Rear 235/70R15-103H Black Wall
ZAA Tire, Spare Compact
ZBF Tire, Spare P235/70R15 Black Wall
ZBG Tire, Spare P235/70R15 White Wall
ZCA Tire, Spare P205/75R15 White Wall
ZCE Tire, Spare P205/75R15/N Black Wall
ZEB Tire, Spare P235/75R15/N White Wall
ZJJ Tire, Spare 31X10.50R15LT/C Black Wall
ZLN Tire, Spare 235/70R15-103H Black Wall

adrenalnjunky · Post by **adrenalnjunky** » Sun Mar 06, 2005 5:40 pm

but - to confuse things even further--my truck came with the Uniroyal 235/75/15 AWR's (Crappy tires) and when I replaced them I went with BFG ATKO 30x9.5's

The weekend after that I followed my parents to Dallas in mom's new Trailblazer--brand new off the lot maybe a month before.

I expected my truck to be showing 2-3 mph lower than what I was actually going because of the larger dialeter tire with no recalibration.

I was dead on with the speedo in her trailblazer. Unfortunately, there is no way of knowing if my truck was always calibrated off a little, or if hers wasnt right from the factory.

Either way I havent recalibrated anything on my truck.