350 to 396

[Alex Kean]

Me and dad is about to pull the old stock 350 out of our 1987 k10 (v10 for those who know gm changed names for that one model year) and we are gonna put a mild 396 in it with efi. We are just wondering what kind of mpg it will get. Its currently sitting on a 4 inch lift with 35 mickey thompson mud tires with 4.11 gears. This 350 in it is apart of the first year chevy started fuel injection but me and my dad think we can pull better gas milelage with the 396 than the stock 350. Let me know what yall think

 

[vkh]

I'm betting 8-10. Big tires really kill mpg

 

[Charlie]

 

[HotRodPC]

So you're removing a TBI 350 in lieu of a Carbed 396 and you think you'll pull BETTER MPG??? Nope, Not gonna happen. A well tuned TBI 350 on OEM stock tires can get you into the 14mpg range, some of the good TBI guys will even claim 17mpg on OEM tires with an OD transmission. I'd go with my wager at 12mpg at best with the Carbed 396, deduct 1 mpg for being 4x4 and pushing an axle and carrying a Tcase so down to 11mpg. If oversize tires and lift on this V10, deduct from there depending on how much lift and how big the tires. Sounding like an 8-9 mpg vehicle to me. These are just my guesses of course, so I'm not claiming some expert here. They are just my guesses. I'd be happy and hope to hear you guys kill it and get much better somehow, but then I wanna know how and what you did to get it.

 

[4WDKC]

best I ever got with my tbi 350 was 12 with lift, 33s, 342s and 700r4 it was a dog.

 

[HotRodPC]

best I ever got with my tbi 350 was 12 with lift, 33s, 342s and 700r4 it was a dog.

This was also a 4x4???

In my C20, 2wd 3/4 ton with 454/Th400/3.21 rear gears with a full floater axle and the OEM tires of 31in, with right on the money speedo and odo, the best I got and keeping about 60-65 mph, no jack rabbit take offs from the stop lights I could get 13.2mpg and that was all highway to my dad's and back for a 140 mile drive with about 10 miles of it being surface street stop and go. With my normal driving and combo of city/highway I'd get 11.1 mpg fairly consistently without running AC.

 

[bucket]

best I ever got with my tbi 350 was 12 with lift, 33s, 342s and 700r4 it was a dog.

Best I could ever do was 11mpg with the same combo basically. Only difference was 8-lug and 3.73's.

My old C20 454 Burb could manage 13 on the highway on a warm day, but otherwise it was 10-11mpg.

And my little Stepside used to average 14 mpg with a 305, th350 and 2.56 gears.

But otherwise, most any 4x4 square is going to get 8-11 mpg, regardless of drivetrain.

 

[yevgenievich]

Mine was around 14mpg with stock tires, but with wider tire and 75mph speed limit have not seen anything above 12mpg

Best I could ever do was 11mpg with the same combo basically. Only difference was 8-lug and 3.73's.

My old C20 454 Burb could manage 13 on the highway on a warm day, but otherwise it was 10-11mpg.

And my little Stepside used to average 14 mpg with a 305, th350 and 2.56 gears.

But otherwise, most any 4x4 square is going to get 8-11 mpg, regardless of drivetrain.

 

[HotRodPC]

Best I could ever do was 11mpg with the same combo basically. Only difference was 8-lug and 3.73's.

My old C20 454 Burb could manage 13 on the highway on a warm day, but otherwise it was 10-11mpg.

And my little Stepside used to average 14 mpg with a 305, th350 and 2.56 gears.

But otherwise, most any 4x4 square is going to get 8-11 mpg, regardless of drivetrain.

Seems your 454 Burb was about right inline with my C20 454 Pick Up. 13.2 hwy was best it ever got, but 10-11 was it's norm mixed city/hwy keeping my foot out of it which is hard to do at times.

 

[bucket]

Seems your 454 Burb was about right inline with my C20 454 Pick Up. 13.2 hwy was best it ever got, but 10-11 was it's norm mixed city/hwy keeping my foot out of it which is hard to do at times.

Yeah, it was 3.73 gearing too opposed to your tall gearing. My new '78 C20 burb is the exact same drivetrain as my old '86, but the best I've done so far was 10. But that's cold weather and just driving to work for the most part.

 

[87scotty]

My first round was 6.25 with the 454 th400 208 and 4.10s but the Speedo is wrong due to the 36s and hadn't tinkered with the carb yet I can tell I'm doing better now Havnt paid attention though will fill a tank and find out I don't really run over 55-60 though I drive like an old man or a 16yr old with a hard on depending on mood lol

 

[HotRodPC]

I've never been one to believe that tall gears help make better mpg in a heavier vehicle with aerodynamics of a brick. Maybe a little less wear on an engine since they've only got so many rpms in them before they're done, but never believed that taller gears were good for mpg. Now having a low gears with an OD YES, because you have the best of both worlds. Low gears for less strain on the powertrain, and OD to get the rpms down into the sweet spot for highway speeds.

 

[vkh]

I've never been one to believe that tall gears help make better mpg in a heavier vehicle with aerodynamics of a brick. Maybe a little less wear on an engine since they've only got so many rpms in them before they're done, but never believed that taller gears were good for mpg. Now having a low gears with an OD YES, because you have the best of both worlds. Low gears for less strain on the powertrain, and OD to get the rpms down into the sweet spot for highway speeds.

I believe I gained some by switching to 3.21 from 3.73. But my situation is different than most. I was doing alot of unloaded freeway driving at 85 mph. And my 454 is better than stock, I figure torque wise I can't be any worse than a guy with a 350 and 4.10s.

 

[HotRodPC]

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I'd agree you would benefit since you're doing 85mph and unloaded. I'll tell you this much though, when you get ready to tow, you're going to sure know it. Even with a Peanut Ported low end torque Fo Fitty Fo, if you're towing any kind of weight at all it's going to struggle. I found out in real life. This was a 3/4 ton 2wd roller Burb with no powertrain on an 18ft trailer. So the trailer was probably right at 1000lbs compare to the known weight of my other trailers and then the Burb with no motor I'd say 4000lb maybe 4500lb for a gross total trailer weight of 5000-5500lbs and it struggled on the slightest of small short grades. Everytime I hit a little hill it slowed way down.

 

[Alex Kean]

So you're removing a TBI 350 in lieu of a Carbed 396 and you think you'll pull BETTER MPG??? Nope, Not gonna happen. A well tuned TBI 350 on OEM stock tires can get you into the 14mpg range, some of the good TBI guys will even claim 17mpg on OEM tires with an OD transmission. I'd go with my wager at 12mpg at best with the Carbed 396, deduct 1 mpg for being 4x4 and pushing an axle and carrying a Tcase so down to 11mpg. If oversize tires and lift on this V10, deduct from there depending on how much lift and how big the tires. Sounding like an 8-9 mpg vehicle to me. These are just my guesses of course, so I'm not claiming some expert here. They are just my guesses. I'd be happy and hope to hear you guys kill it and get much better somehow, but then I wanna know how and what you did to get it.

Actually I said a 396 with efi. I never said anything about a carb. Efi stands for electronic fuel injection