CLASS RACER FORUM - View Single Post - questions on 8.1 motor in 2004 Chevy truck

Alan Roehrich · 05-22-2016, 04:42 PM

I don't think a truck with 3.73:1 gears can pull both 6th gear and a trailer, and almost certainly not with tall tires. I think the 4.10:1 and 6th gear with tall tires may work, and with some of the previously mentioned modifications, I'm sure it will. A 300-500 drop in RPM can be worth as much as 2MPG in the 8.1L trucks.

If you change to taller tires, not only is the speedometer and odometer off, but also all of the shift strategy and logic, and some of the tuning. It does make a difference to have one retuned and the speedometer buffer corrected. I noticed it immediately when I swapped those 19.5" tires and wheels on.

05-22-2016, 04:42 PM	#13
Alan Roehrich VIP Member Join Date: May 2006 Location: Murfreesboro TN Posts: 4,915 Likes: 996 Liked 1,044 Times in 274 Posts	Re: questions on 8.1 motor in 2004 Chevy truck I don't think a truck with 3.73:1 gears can pull both 6th gear and a trailer, and almost certainly not with tall tires. I think the 4.10:1 and 6th gear with tall tires may work, and with some of the previously mentioned modifications, I'm sure it will. A 300-500 drop in RPM can be worth as much as 2MPG in the 8.1L trucks. If you change to taller tires, not only is the speedometer and odometer off, but also all of the shift strategy and logic, and some of the tuning. It does make a difference to have one retuned and the speedometer buffer corrected. I noticed it immediately when I swapped those 19.5" tires and wheels on. __________________ Alan Roehrich 212A G/S