Author Topic: more power = better fuel economy  (Read 14996 times)

Offline Dieselfume

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Re: more power = better fuel economy
« Reply #30 on: September 24, 2009, 01:26:48 AM »
I'm sorta surprised no one mentioned what rear end ratio they had installed until the last post here from Jimbo. Gear ratios (or really the whole trans, axle and tire size combo and resultant hwy speed & RPM) is sort of a key item here.

The original post from Irish_Alley doesn't surprise me considering stock manifolds and emissions choking the engine. His follow up about the engine originally getting 13 mpg in the 86 he pulled it out of makes me wonder if there was something noticeably different with trans, axle, or tire size.  The weight difference will have some effect, but not that much. If the pic from his signature is any indication, a lifted 4x4 with big tires is going to make a noticeable difference compared to a 86 1/2t 4x2. Turning 3/4t or 1t running gear compared to a 1/2t will make a little difference too.

Captkaos, that's some pretty good mileage on that R-10 305/700R4. What tire size and rear end gear do you have?  Any canopy or tonneau cover? Lifted/lowered? Stock or mods?

To add to the other data points out there, my stock 87 R-10 stock TBI305/700R4 with 2.73's and 225/75R15, and a 32" tall shell (about 11" above cab) near sea level on Seattle's typical 87 octane brew with unknown % ethanol (guessing 5-10%) gets 16.5-17 mpg hwy. 

Considering how tall my camper canopy is, been toying with the idea of experimenting with VGs (vortex generators) if I can find a good quick way to measure change in power required. I've thought perhaps manifold pressure, but If there was a good scanner to plug into the ALDL and display live injector pulse width or similar fuel flow parameter that could work too.  (eventually will do some basic engine mods for mileage, but I'm an aero guy so...)

I agree with SUX2BU99, today's trucks really suck for mileage compared to where they could be. The trucks are porkers weight wise, and only recently have they approached Captkaos' 22 mpg. There really hasn't been much effort to extract more energy out of the fuel burnt. About 70% of the fuel energy goes out the tailpipe as heat. We haven't even tried to apply 1940's technology to extract more energy out of the exhaust.
81 Buick Regal Limited, Olds LF9 5.7L (The Neglected Project)
93 Olds Ciera S 3300 daily driver, 253k+
87 Chevy R-10 Silverado 305TBI/700R4 52k, stock 2wd 33x10.5-15 BFG AT, camper shell, Janesville Assembly

Offline Captkaos

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Re: more power = better fuel economy
« Reply #31 on: September 24, 2009, 12:42:45 PM »
Mine truck was basically stock with nothing extra.  Stock tire size: 235/75/15.  Stock rear gear 2.73.  Stock 1989 305 engine (original was replaced by PO).  Stock suspension and an open bed.

It looked JUST like this:

It now has Impala SS wheels and a Extang Tonno:

Offline Lt.Del

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Re: more power = better fuel economy
« Reply #32 on: September 30, 2009, 07:24:23 PM »
First time reading this thread...pretty interesting.  I gotta say, my 79 Big 10 stroked 383 quadrajet with rv cam, th350c, dual exhaust, and 2.80 rear gets around 10mpg, 12 if on the highway and keeping my foot out of it. Of course, If i play with the HP and have fun with it, she easily drops to the single digits.

4x4s I have never seen get above 17mpg EXCEPT in a diesel app.

Well Chris, my 4x4 1991 V2500 5.7 sub tbi with 33's and 3.73 ratios gave me 18mpg on the interstate last year during a long particular trip to OBX....i purposefully drove it really easy just to see what I could get, even though my whole family and luggage for a week were on board.  I thought that was real good for the sub.   I can routinely get around 16.5 on the interstate not really caring how i drive.  In the city, well, easily take 6.5 off that average. 

I'm leaving Monday for another week trip to Nags Head and Hatteras, so, I'll see again what I get.

« Last Edit: September 30, 2009, 07:30:50 PM by SgtDel »

Offline murraygmc

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Re: more power = better fuel economy
« Reply #33 on: October 01, 2009, 07:30:09 AM »
wow iv got a stock 305 and only get 13 mpg lol 85 gmc 4x4 3.72 gears (stock)
85 gmc high serria 4x4

Offline screamin86

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Re: more power = better fuel economy
« Reply #34 on: October 08, 2009, 05:33:20 PM »
Well i got roughly 10mpg in my 86 k10 with the le9 and all the emissions stuff except cat removed. It has long tube headers single rin exhaust high flow cat and a factory aluminum 4bbl intake. Im hoping with the new 350 that just went in the added power well help bring my fuel mileage up some. I put the same cam in that 350 as is in my 305 that i have in my 82 ta and when i had 3.42 gears and a 2800 converter and th350 i got ab out 18 being very easy on it in town. The truck has a th350 and a 2800 converter and 3.42s (for now) but it has a 350 with about 9:4.1 so im hoping i can atleast get around 16 being very easy
86 k10 lwb 4x4:350 .040 214/224 444/466 112lsa performer rpm 1406 lt's summit racing th350 2800stall
03 yukon xl:tint debadge full boltons
86 ta:lm7 hot cam boltons