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73-87 Chevy _ GMC Trucks => Performance => Topic started by: will.mccay on January 31, 2014, 11:10:39 am

Title: 18mpg. True or False
Post by: will.mccay on January 31, 2014, 11:10:39 am
Hey everyone. This is my first post. Im picking up a 1986 k10 Monday. It is a 350tpi, 700r, 373 rear end with 35's. The guy im getting it from is pretty highly thought of in the area for the trucks he builds. He says he consistently gets 18mpg just driving around town. Im just wondering if that's a real possibility or maybe a bit of a stretch. Does anyone have any input?
Title: Re: 18mpg. True or False
Post by: dvdswan on January 31, 2014, 01:01:39 pm
my 1st thought is.... is the speedo correct?  99% of the time when intalling larger tires the owners don't do anything with the speedo so it will register miles less, then when it comes to calculating MPG the use the fudge factor to thier favor.

i.e. speedo says 60 mph when the truck is actually doing 66 mph.
Title: Re: 18mpg. True or False
Post by: zieg85 on January 31, 2014, 04:34:07 pm
my 1st thought is.... is the speedo correct?  99% of the time when intalling larger tires the owners don't do anything with the speedo so it will register miles less, then when it comes to calculating MPG the use the fudge factor to thier favor.

i.e. speedo says 60 mph when the truck is actually doing 66 mph.

Then the mileage would be calculated lower... 18 seems to be in reach if it is driven with an egg between the foot and the go pedal if set up right.  Even with the 35's that trans with a 3.73 shouldn't struggle at all to get going.
Title: Re: 18mpg. True or False
Post by: bake74 on January 31, 2014, 09:40:28 pm
     I agree with zeig, but being realistic if you bought the truck, could you drive it around all the time and never go over 25 mph ?
     Dvdswan has a valid point also, unless he has re-calibrated the transmission with the proper spedo correction attachment, the mph on the gauge will probably not match the actual mph.
Title: Re: 18mpg. True or False
Post by: Irish_Alley on January 31, 2014, 11:26:50 pm
tpi or tbi?
i dont see 18 in city. now once hes up to speed the 35s will act like a second od and the engine wont be working as hard to turn. but like dvd said. he may not have corrected his speedo and is adding more mileage than he should to try and calculate his mileage
Title: Re: 18mpg. True or False
Post by: will.mccay on February 01, 2014, 08:42:09 am
Thanks for the input. I didn't think about the speedo being off. I'll check on that. It is tpi.
Title: Re: 18mpg. True or False
Post by: VileZambonie on February 01, 2014, 09:10:22 am
He's lying but you don't drive one of these trucks if you're looking for fuel efficiency. You drive them because you love them.
Title: Re: 18mpg. True or False
Post by: Captkaos on February 01, 2014, 12:08:29 pm
Ditto.  He isn't getting that mileage something is off.  Either is speedo and/or gears.

Chris Lucas
73-87chevytrucks.com
captkaoscustoms.com
squarebody.biz

Title: Re: 18mpg. True or False
Post by: will.mccay on February 02, 2014, 08:02:23 pm
Well yeah I have a 350 with a 4 barrel edlebrock and I know how crappy the mpg is. My question is if with the right tuning on a tpi if that's even possible. Ill let y'all know here in a couple weeks what I really get.
Title: Re: 18mpg. True or False
Post by: Irish_Alley on February 02, 2014, 10:33:01 pm
I know with my 38s 4.10 sm465 and 350 I can get 9-10. But that's keeping her at 55 nothing over. So the od might help and 35s help and taller gears and the tpi I guess I could see 15 with that setup so maybe 18 Idk only time will tell and verify speed with your GPS
Title: Re: 18mpg. True or False
Post by: Engineer on February 03, 2014, 09:05:04 am
Around town that is a 10~11 mpg truck at best.

14 highway. Maybe.
Title: Re: 18mpg. True or False
Post by: ehjorten on February 03, 2014, 02:17:13 pm
A 2013 4WD Silverado with a 5.3L is only getting an average of 17 (15 City/21 Hwy) on gasoline.  No way that '86 is doing that with 3.73:1 rear gears!
Title: Re: 18mpg. True or False
Post by: greasemonkey54 on February 05, 2014, 10:03:51 am
my 86 with 305/700 and 2.73 gear gets 16-18 mix of city/ highway, the more highway the better. around town where I live means traffic and if I do mostly city I get 10 or so