i have been thinking, im in trouble now

[68GMC454]

ok as you know i got a 68 gmc lwb..i have been seriouly thinking that when i do put a motor in it, im gonna do a straight 6..i think a v6 might work, but not sure n that...now my truck is a factory v8 truck.. i have never went with a smaller motor when building anything..what am i gonna need if i do this..motor mounts..the rest of the stuuf should work..it has a 350 turbo tranny in it..
the reason for this is i already got a big block truck that i cant afford to drive, and would rather drive my 68 than look at it, then drive it every now and then when i can spare some gas..

i know i can pick up a straight 6 pretty cheap..but should i maybe consider a v6 out of somethign newer...just wondering...

thanks for anyinfo

[Stocker]

Late model 4.3L Vortec V6? Based on 350, so should fit okay, and might get better fuel mileage than older inline six. Just tossing it out there, I've never done anything like it...

[TheSasquach]

These types of questions always bug me. Hopefully im not going too far out of line, buy why is it people always think smaller or fewer cylinders gets better MPG? I have built a 383 mopar bored .060 (equaling 394 cid)with a 484 cam (had a very slight lope) Carter AFB 4bbl installed it in a 3900# 68 Plymouth and got a averag of 23 MPG. Getting all your componets matched, building and tuening to maximum effency will give you the best HP torque and MPG, using too small an engine and running it under too much strain wont do it. David

[Pyrotechnic]

You know what funny ? When compared to a 5.3 LS engine in identical trucks, the 4.3 gets WORSE gas mileage and has much less power. 16 city vs. 17 city.

The 5.3 gets 1 MPG better, AND it has tons of power and torque.

If spending all the money to swap in a different engine with a computer and such, given this situation, it makes every bit of sense to swap in the 5.3

Don't bother with a 4.3 V6 at all. On top of all that, it will require relocating the motor mounts.

Try a worked over 305 V8 if you want decent mileage. It should drop into the motor mounts if that truck came with a 350. An older I6 will work as well.

[HeavyD]

The 250 6 I had in my 70 GMC was horrible on fuel. I think if you go to a 6, a V6 would be a better bet for economy.

[wild one]

Originally Posted by TheSasquach

These types of questions always bug me. Hopefully I'm not going too far out of line, buy why is it people always think smaller or fewer cylinders gets better MPG? I have built a 383 mopar bored .060 (equaling 394 cid)with a 484 cam (had a very slight lope) Carter AFB 4bbl installed it in a 39000# 68 Plymouth and got a average of 23 MPG. Getting all your components matched, building and tuning to maximum efficiency will give you the best HP torque and MPG, using too small an engine and running it under too much strain wont do it. David

I agree, I've built a few engines - the best approach is to look to make the engine as efficient as possible. I've had my hands in building small block 289's to big block 440's for personal and friends vehicles and the ones built for street use all made respectable power while delivering good mpg. In the end efficiency = power. I'd try posting a over in the engine/drive line forum and ask some for some input on making your existing 350 more efficient.

[Brad]

A well built/tuned engine is going to be more efficient at providing power and mileage than a tired engine. Hence, a well built/tuned V8 is going to be just as efficient or more so than a tired L6 and will give you overall more power not to mention cheaper in many ways.
Several guys on the engine board have offered up some really good stats for V8 builds. 'Billa' is on top of that.

Having said all that, when I'm back home I'll be working at getting 21-23 mpg out of my truck on the highway.

[jkeady]

Maybe think about doing a 350 with EFI. A little bit more of an initial investment, but with a conservative cam (and if you can keep your foot out of it), you could probably get some decent mileage. A lot of it boils down to gearing, too. Too high (2.xx) and you'll be wasting a lot of fuel trying to get the rig moving. Too low (upper 3.xx, and 4.xx) and you'll be more inefficient at cruise.

The nice thing about the stock 350 is it has very nice low end torque to get you rolling, and enough mid-range power to keep you going without opening it up too far.

[67 cst swb]

I agree with the above... rebuild your current V-8... hopefully 350... the money spent on changing to something else (the nickel and dime stuff) would way pay for more fuel...
Plus... if built correctly... a old everyday V-8 can get upper teens lower 20's MPG anyway...
I rebuilt a 283 in a '65 chevelle, when I drove it like an adult, It got 21 on the highway... My 4.8L 2006 silverado only gets 20 on the highway now...

[68GMC454]

well guys here is why i want a I6..first the truck came with out a motor. but i have the exhaust maifolds from the orginal 350 or 305 forget exactly...and some other parts for it..now my dad had a few chevys with I6 in them, one a 70 somthing and a 67 or 68..both of them got 18 plus mpg..both had over 100k on them when he got them..i got a 84 3/4 with a 454, that is my work truck if i need to haul or pull something.. i just need a daily driver.. the 84 gets 6 mpg on a good day..needs a new timeing chain but even then if it got over 8 to 10 mpg i wuld be surprised..now im a hotrodder at heart. i love speed, if i put in a 350 or even a 283, i know i will not keep my foot out of it..will be racing it, or spinning the tires, you know all the fun stuff..eventually i will rebuild the 68 and go with a big block..but for the forseeable future i need somthing i can drive back and forth to school, after they get finished with my back surgery..and it is anywhere form 60 to 100 mile round trip every day. depends on where they send me. i can not afford to buy a small car to drive, and will not ride the public bus..so i know i can pick up a straight 6 cheap..so was thinking of this for now..if i could find a good wrecked later model truck with fuel injected 350 or 305, i would go that route..but guys im on a really tight income because workers comp based my pay on the last 3 weeks before i got hurt. well that was the start of winter, and we were not even working part time hours..so this is why i asked the question i did..thanks for all the input

[Gray Ghost]

We just put a 250 6 into my buddy's '71. It was an easy swap once he got all the parts he needed. The motor mounts, belts and the like aren't too hard to find. He bought his 6 for $300...it runs great. It looked almost brand new inside when he removed the valve cover for a pic. Doesn't leak a bit and has plenty of power. Not sure what he getting in mileage, but I'd bet around 16-17.

[68GMC454]

well i live real close to a junkyard that is nothign but old stuff...th elast motor i got from him was a 283 with less than 63k on the whole truck. and i know the history on it to..it fired up and ran perfect...i can get a I6 for around 150 or less. and that incledues everything i need to put it in my truck....if he has one..havent been over there in awhile..

[67 cst swb]

I would go with a era correct I6 for fitment reasons as well as simplicity, before trying to go late model TPI, etc... just for the added fuel system stuff alone a 60's early 70's I6 would be a breeze...

[bowtieride]

you will end up spending more rebuilding a 250 than a 350. There are very few aftermarket parts and they cost more than the same parts for a 350.