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Gas mileage with tbi

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az84chevy

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I have already done some searches but couldn't find too many threads dealing with this question.

Currently i am running a qjet carb and am getting about 8-10 mpg. I am thinking about switching to TBI and am hoping for an good increase in mileage (maybe 12-16?). It seems most people here do it for offroad capability and that would definitley be a big plus but i mainly want the better gas mileage out of it.

For all that have done this conversions from a carb, how much did your mileage improve?
 
I am getting ready to do the swap, so I can't tell you a MPG improvement. I do have an opinion to share though. If your engine is in good tune now, I would not expect too great of an increase. The TBI computer will optimize fuel/air mixture and timing, but this is minimal on a properly tuned engine. If your carb or dizzy are old, then you stand a better chance of gaining mpg...
 
you wont see 16. i doubt you'll even see 15. ive got a 700 (overdrive), 5.13's with 37's and the most i ever got was 12.5
 
I have a 350/700R4 with 4.56's and 35's and around town (which is mostly what i drive) i get on average 10mpg. My rig weighs in at 5,880 lbs also. I suppose if i were to get a good straight hiway run i would probably get around 14mpg or so.
 
ive got the same setup as 4x4high, i usually get about 10mpg if i drive normal. best mpg i've got so far city/hwy is 13.5, but thats with driving like a grampa and not going over 65.
 
Well your in AZ , do you know the PHX area ?

With my Q-jet , and religious upkeep , 305/700/208/3.73's/33's , I get awesome mileage .

This Sunday I filled up at Sossaman and Southern , drove to Lindsay and Baseline , freeway to Florence Junction to wheel , back home to Ellsworth and Broadway , to and from there to Scottsdale Road and McDowell and back Mon-Wednesday without touching the freeway ..... and I am sitting on 1/4 tank left right now .

Keep your truck tuned , lubed , and your foot out of the secondaries :D
 
No idea.

Sorry, could'nt resist. :D

I have a TBI setup but never checked mpg.
 
i got 13 when i had 350 (lt1 though, mpfi not tbi, more efficent than tbi too) 400,208, 14bsf-4.10's and 33"s.
 
my v3500 dually forest service truck... 350 tbi.. 3 inch exhaust and a k and n got 15 religously... and that was with a huge service body on it... stock 16s, 4.56 gears... driven easily

fully loaded down it went down to 11-12
 
10 mpg 454 tbi 5:13's 39" tires, sm465 (1977 Blazer).
10 mpg 454 tbi 3:73's 31" tires, sm465 (1990 v3500).
12 mpg 454 tpi 3.73's 31" tires, 4L80E (1998 Suburban).

If your looking for mileage, go with gearing that puts your average rpm in the peak torque area of your engine.

Hey what was the final consensus of adding acetone to gas for improved mileage?
 
1979 K5 4.10's - 35's - TH350 - 11-12mpg...usually closer to 11 unless i'm on the fleeway.
Recently did an out of frame on the stock 6 year old gm crate. Added reman crank... rings..tbi (late86) upheads and a slightly upgraded tbi cam. 0 miles on the motor as we are doin major gear and drivetrain work. Hopefully we'll end up with overdrive of some sort...which i figure will net the most mpg.

1976 K5 Chalet 3.73's - 31's - Th350 - 11-12mpg...not bad when you have a factory camper on your K5. Speedo is off inthe neighborhood of 6-8mph as verified this trip up to wyoming with my gps...so 65 is really 75 and that seems to be the sweet spot for the chalet. It to will be recieving OD in the form of a 700R4-NP241 combo i have in a cheap 89 Jimmy i just bought.

1990 V2500 Burb 3.73's - stock tires - TH400....wife gets 12mpg....but towing a trailer to arizona it drops to 10mpg....the return trip allways includes a new to me k5 of some sorts and the mileage drops to 8mpg. Considering i'm towing a tandem axle trailer with a k5 i'm still getting better mileage than a semi truck....but the v2500 burb should have came with a 454...as the 350 is kinda anemic when it comes to moving the trailered load up hills...

Doug W.
 
my k5 would get ALMOST 13 on the highway keepin it in 3rd, doing 65-70...ive also got 7" lift, 33s, 3.08s and a 700R4 (not that that matters much since i couldn't use OD). Motor was always kept running good (new plugs and wires every few thousand miles) and just had a clean paper filter (cheap $4 one from advance auto, i just get those and change them at every oil change) and a TBI spacer...i know the spacer doesn't make much difference on the highway but you can feel it SOTP...

around the city im sure i was gettin 10-11 if i was fairly easy...i did have my 8 mpg days tho :D

Its also going to be interesting to see the mileage i get when i get my new 14bff in there with 5.13s and ol 33s
 
You have to think in terms of percentages and not # of mpg. Gaining just 1mpg would be about a 10% improvment. If TBI gains you 2 mpg, that's 20% improvment, which is very significant.

Swapping to TBI won't give you the same mileage as somebody elses rig that has TBI, there are too many factors involved. What you want to find out is the average improvement seen by making the conversion. My guess is 1-2 mpg.

Figure out how much the TBI conversion would cost you. With the extra 1-2 mpg, calculate your fuel savings to see how long it will take to pay for itself. Also, what is the easy starting and ability to run off camber worth to you?
 
redneckdude said:
my k5 would get ALMOST 13 on the highway keepin it in 3rd, doing 65-70...ive also got 7" lift, 33s, 3.08s and a 700R4 (not that that matters much since i couldn't use OD). Motor was always kept running good (new plugs and wires every few thousand miles) and just had a clean paper filter (cheap $4 one from advance auto, i just get those and change them at every oil change) and a TBI spacer...i know the spacer doesn't make much difference on the highway but you can feel it SOTP...

around the city im sure i was gettin 10-11 if i was fairly easy...i did have my 8 mpg days tho :D

Its also going to be interesting to see the mileage i get when i get my new 14bff in there with 5.13s and ol 33s
Click to expand...

I drive my 87 like I love it and I get 14.7 for the last year. By the way, what does "SOTP" mean?
 
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