I'm trying figure out the variables of what people have to see why I can't get any better mileage. 15.2 is the best I have gotten and that is 70% highway running 78mph. I have a bed cover and a RCSB 4.8 with a 3.0 pulley. I am pulling 8-10"of vacume at that speed and my a/f is right around 14.7. 5 speed with 3.73's and 31.8" tall tires (275-55-20's). My timing fluctuates between 25-32 degrees at cruse. I am thinking that my timing is too low. Also to help the problem out we leaned it out below 2800 to the 12.5:1 range while in PE. It did help a little and mainly quit sooting up my bumper. Before it would jump to 10-11:1 as soon as it went into power enrichment. I have heard of people on here getting 22-23mpg with the radix and i'm trying to figure out what i'm doing wrong. If I was getting 17-18 I wouldn't be worried. On average I drive fairly consevatively trying to keep it out of PE as much as possible and only getting on it 3-4 times a tank. Any suggestions would be appreciated. I know cruising slower would help but that is out of the question

 

Well 20's, supercharger,3.73,Nice size cam, and LT in my opinion doesnt really equal a good gas mileage truck...

Nothing performance wise is really going to help your gas mileage..

This is my opinion though, alot of people will disagree with me!!

15 is good..

I had a supercharger on my truck with 4.10s and a smaller cam and was getting like 10-12mpg on highway

 

6.0/224-228 cam/2.02 heads/4.10/lt's/3.0 pulley/20's/extended cab/hard cover...I'd **** if I had 15mpg. There is still some tuning to be had but I don't expect to see over 12-13. 13 if I drove around w/cruise control all the time maybe....lol. I agree with ya mj though I do wonder reading these threads sometimes about some of these quoted mpg...subtract your last fill up mileage from your new fill up mileage...divide by the gallons it took to fill this time. I bet some people multiply it by 1.5 or something. LOL. blownchevy gets 18 I believe, he's crew cab...he's still in 5.3 I believe.

 

my average (according to the DIC) is about 14MPG now with my Radix on. I drive 80% highway and never run over 75mph.

 

i run approx 90% hiway and get 20.0 to 21.5 driving like you about 77-78 mph.if i romp on it quite a bit it will go down thou but mainly ride on dbl lane roads( interstates) and dont have to haul *** around others....i have not seen anything under 19.0 average a tank full since the radix install.

 

You have 3.73's I take it?

 

nope...3.42's

 

Well that's pretty sweet then, and explains your mileage numbers. I would have be driving 60 MPH to get what you're getting at 70 MPH. Not gonna happen.

 

Have you guys considered inclines in your driving areas? I have a lot of hills in my local area and a heavy vehicle so I end up in boost a lot. PE fueling AFR ratios are not conducive to good mileage!

 

There are very few hills where I live, so in general I don't go into boost unless I want to. I can set the cruise control and get 17.5 MPG (or so) all day. With 3.73's that number was closer to 20 MPG.