What kind of mpg should I expect after a engine swap? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Plunkett · 08-03-2010, 01:28 AM

Ok, so to start off. My truck is an86 chevy silverado with a 305/700r4 transmssion, 6" lift, 35" tires,and 4.56 gears. I don't ever expect this thing to get amazing fuel mileage. I'm currently looking at twodifferent engine swaps. One being swapping in a gen3 5.3 motor and bolting it up to my 700r4 transmission, the other idea was doing a 350 with a street avenger carb, comp cams 268 cam, and lt headers. I don't drive this truck hard. What kind of fuel mileage can I expect to get from both swaps?

**N2TRUX** · 08-03-2010, 08:55 AM

What are you getting now?

glock35ipsc · 08-03-2010, 10:49 AM

I can only speak for the 5.3, but considering my setup is:

4L60E trans (2wd), 3.42 gear, 28" diameter, .70 O/D ratio, at 75 mph = 2155 rpm

Yours should be:

700R4 (same gear ratios as the 4L60E), 4.56 gear, 35" diameter, .70 O/D, at 75 mph = 2298 rpm

I get 20-21 mpg on the highway. You should expect a little less than that due to the height of teh truck, tire diameter, friction loss from the transfer case, etc. At least I am assuming with a 6" lift and 35's that it's a 4wd.

Plunkett · 08-03-2010, 12:00 PM

Quote:

Originally Posted by N2TRUX

What are you getting now?

The speedometer is off due to the gear change and larger tires.I was getting between 10 and 11 before the lift and I'd say it's around the same b/c I drive the same amount each week and use the same amount of gas.

Glock, the truck is a 4wd.

RaysK20 · 08-03-2010, 01:30 PM

Cant comment on the over drive, but my 73 k20 gets 13 highway with a well worn 350 edelbrock performer intake and carb, stock manifolds and dual exhaust. I am running 235-85-16 tires threw a th350 and 4:56 gears. While the truck is not lifted, I just swapped off the wide 33-12.50 tires to the 235 and my mileage went from 11 highway to 13. I am currently planning on a 350 rebuild similar to above but raising the compression, a comp 260 cam and headers. I expect to be up around 14-15 mpg with a fresh setup.

*C-10 simplex* · 08-03-2010, 02:01 PM

The 2005 silverado 4x4 with the 5.3 i rented got just about 20mpg and this was with "normal' tires. So, i would guess under 20 for your app.

08-03-2010, 01:28 AM	#1
Plunkett Registered User Join Date: Nov 2009 Location: Chattanooga, TN Posts: 140	What kind of mpg should I expect after a engine swap? Ok, so to start off. My truck is an86 chevy silverado with a 305/700r4 transmssion, 6" lift, 35" tires,and 4.56 gears. I don't ever expect this thing to get amazing fuel mileage. I'm currently looking at twodifferent engine swaps. One being swapping in a gen3 5.3 motor and bolting it up to my 700r4 transmission, the other idea was doing a 350 with a street avenger carb, comp cams 268 cam, and lt headers. I don't drive this truck hard. What kind of fuel mileage can I expect to get from both swaps?

08-03-2010, 08:55 AM	#2
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,023	Re: What kind of mpg should I expect after a engine swap? What are you getting now? __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

08-03-2010, 10:49 AM	#3
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Re: What kind of mpg should I expect after a engine swap? I can only speak for the 5.3, but considering my setup is: 4L60E trans (2wd), 3.42 gear, 28" diameter, .70 O/D ratio, at 75 mph = 2155 rpm Yours should be: 700R4 (same gear ratios as the 4L60E), 4.56 gear, 35" diameter, .70 O/D, at 75 mph = 2298 rpm I get 20-21 mpg on the highway. You should expect a little less than that due to the height of teh truck, tire diameter, friction loss from the transfer case, etc. At least I am assuming with a 6" lift and 35's that it's a 4wd. __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE Last edited by glock35ipsc; 08-03-2010 at 10:52 AM.

08-03-2010, 01:30 PM	#5
RaysK20 Registered User Join Date: Jan 2010 Location: Sweet Home, Oregun Posts: 49	Re: What kind of mpg should I expect after a engine swap? Cant comment on the over drive, but my 73 k20 gets 13 highway with a well worn 350 edelbrock performer intake and carb, stock manifolds and dual exhaust. I am running 235-85-16 tires threw a th350 and 4:56 gears. While the truck is not lifted, I just swapped off the wide 33-12.50 tires to the 235 and my mileage went from 11 highway to 13. I am currently planning on a 350 rebuild similar to above but raising the compression, a comp 260 cam and headers. I expect to be up around 14-15 mpg with a fresh setup.

08-03-2010, 02:01 PM	#6
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: What kind of mpg should I expect after a engine swap? The 2005 silverado 4x4 with the 5.3 i rented got just about 20mpg and this was with "normal' tires. So, i would guess under 20 for your app.



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