dodge guy
Chicago, western subs.
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Joined: 03/23/2004
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FWIW, I am at 1900 or so at 65 in O/D when towing with the 4.30`s. albiet a little larger diameter tire than the op! in 3rd I`m at approx. 3000. with the 3.73`s I was at 1600 and 2700 respectively. those are approx. as it`s been 2 years since the switch to 4.30`s. obviously with the 3.73`s you can see where where my performance problem was at. the truck didn`t like O/D when towing and towing in 3rd the truck just felt a little sluggish. now with the 4.30`s I can hold O/D on anything but a hill and when it kicks down into 3rd it`s at the proper spot in the power band to hold the speed. as you can see a few hundred rpm can make a significant change in towing performance as I posted previously. something that "just running in 3rd gear" can`t do.
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07 Cherokee 32B
02 Excursion 4X4 V-10 4.30 gear
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BillyW
North ID
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Joined: 10/08/2003
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dodge guy wrote:
Gear ratios have nothing to do with emissions. if they did the manuf. wouldn`t offer the different ratios they do! the PCM programing in a vehicle with 3.55 gears is the same as a one with 4.30`s. the engine just operates at a different rpm.
Technically incorrect. If you're RPMs are increased at a given speed, your emissions will also increase. They have to.
Honestly I have no idea if/how such a thing would be enforced. I was simply stating what was told to me more than once at shops in Spokane, Wa.
I realize this isn't what the OP really wanted to know. I just threw it out there for consideration. I will tell the OP that my gear change was awesome for towing. I don't think I need anything more than 4.10s, even though I almost always push the weight limits of my 4.6L powered F150 and tow in the northern US Rockies.
'97 F150 4X4
'04 Pioneer 18T6
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dodge guy
Chicago, western subs.
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BillyW wrote:dodge guy wrote:
Gear ratios have nothing to do with emissions. if they did the manuf. wouldn`t offer the different ratios they do! the PCM programing in a vehicle with 3.55 gears is the same as a one with 4.30`s. the engine just operates at a different rpm.
Technically incorrect. If you're RPMs are increased at a given speed, your emissions will also increase. They have to.
Honestly I have no idea if/how such a thing would be enforced. I was simply stating what was told to me more than once at shops in Spokane, Wa.
I realize this isn't what the OP really wanted to know. I just threw it out there for consideration. I will tell the OP that my gear change was awesome for towing. I don't think I need anything more than 4.10s, even though I almost always push the weight limits of my 4.6L powered F150 and tow in the northern US Rockies.
While that does make sense, the very, very small increase in the emissions would be nowhere near enough to create a problem for passing emmisions tests. and if the emissions were high enough to cause it not to pass, it would also turn on the check engnie light! on 96 (OBDII) and newer anyway.
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smkettner
Southern California
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Joined: 03/21/2005
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BillyW wrote:dodge guy wrote:
Gear ratios have nothing to do with emissions. if they did the manuf. wouldn`t offer the different ratios they do! the PCM programing in a vehicle with 3.55 gears is the same as a one with 4.30`s. the engine just operates at a different rpm.
Technically incorrect. If you're RPMs are increased at a given speed, your emissions will also increase. They have to.
Emissions testing for the public is based on Parts Per Million of hydrocarbons and NOx and % of CO in the exhaust. While the vehicle may emit more total exhaust the ratio or concentration of pollutants measured does not necessarily increase.
I understand new car development testing is different in that all exhaust is captured and total pollutant per mile is measured. The low gears would probably hurt this type of testing just as you said. But again secondary testing of the cars on the road are not tested like this.
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mkirsch
Rochester, NY
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Joined: 04/09/2004
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BillyW wrote:Technically incorrect. If you're RPMs are increased at a given speed, your emissions will also increase. They have to.
Technically true, but they put a hose on your exhaust pipe and idle it for a few minutes. They don't run the truck at 65MPH.
The stuff that comes out the tailpipe doesn't change at all when the truck is sitting there idling, whether you have 3.08 or 4.88 gears.
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LeeShearer
Royersford, PA
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Joined: 01/25/2006
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mkirsch wrote:BillyW wrote:Technically incorrect. If you're RPMs are increased at a given speed, your emissions will also increase. They have to.
Technically true, but they put a hose on your exhaust pipe and idle it for a few minutes. They don't run the truck at 65MPH.
The stuff that comes out the tailpipe doesn't change at all when the truck is sitting there idling, whether you have 3.08 or 4.88 gears.
In PA they do test the emissions at a certian speed. I do not know for sure but something like 55 mph .
2005 Fleetwood Resort EXT 25SB
1999 Chevy K3500 short bed dually
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RVbikers
Red Hill, PA
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i believe the emmission test in pa is at a specified rpm, not mph. i think its 2000 rpm. so a gear change wouldnt affect the emmisions, rpms are rpms.
It's not the destination, but the journey that counts!
1995 Chevrolet Suburban K1500, 5.7L, Flowmaster, K&N Intake
1999 Dutchmen 30BH2
1998 Sportster 1200
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Twins4us07
Virginia
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RV Bikers We have a similar setup. How does you Sub pull your TT? Is your Burb a vortec?
1997 GMC Yukon, Firestone Airbags,K&N Intake,Flowmaster,Tekonsha P3, Hensley Arrow,Mckesh Mirrors,VR3 Rearview Camera.
2009 Cougar 29BHS X-Lite,Kippor 3000W Generator(quiet as a Honda but cheaper).
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Loaded 'Burb
Davenport Ia
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Joined: 06/21/2008
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Your Yukon should have an 8.5" 10 bolt rear axle. The carrier break is at 2.56. No new carrier will be needed to swap to 4.56's. I would be very leery of shops saying otherwise.
Searching salvage yards for this set up is also pointless because GM rarely puts 4.56's into anything this size. (Needle in a haystack.)
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