I turned my big block into a Prius

[i82much]

Ok not really. But I did buy a 396-powered 72 K10 about three years ago. 3.73 gears and a turbo 350. I was getting around 9-10 mpg on 32's with a 2.5 inch lift, that was country road driving which tends to net you about as good as you are ever going to get in terms of fuel economy.

Anyway, I messed around with it quite a bit and wound up with a new MSD distributor with vacuum advance, Performer 2.0 manifold, functional heat riser, and a quick fuel 680 vac secondary carb, along with a wideband. I dropped the primary side idle feeds one step and got it to run at light throttle at about 14-15: 1 AFR.

Are you guys ready for this? Are you sitting down? Your jaw is about to hit the floor because I got ... 11.5 miles per gallon out of this baby! I know, I know, amazing, right? Especially when the first 1/4 tank or so I still had my hubs locked, although the transfer case was in 2wd.

Ok, not quite a Prius. And I will never make back the money in gas I spent on the wideband, carb, distributor, etc. But, the oil is staying a heck of a lot cleaner, I expect the engine will last a good bit longer, and the plugs should stay clean too. Right now, she isn't a bad daily driver, starts right up in the cold and you can take off, leans out once she warms up.

All in all I am pretty happy with how it turned out. I am thinking optimistically I might see 12.5-13 mpg on a summer day with summer gas and less wind resistance, might bump the tire pressure a smidge too. For a big block 4x4 without any overdrive or fuel injection, I am pleased.

[Oregon 1967 GMC]

Glad I was sitting down haha. Put some headers on there and get even more MPG.

[i82much]

Originally Posted by Oregon 1967 GMC

Glad I was sitting down haha. Put some headers on there and get even more MPG.

really? i didn't realize that. i know they make heat riser valves that will work with headers, so that is a possibility.

[Oregon 1967 GMC]

Originally Posted by i82much

really? i didn't realize that. i know they make heat riser valves that will work with headers, so that is a possibility.

you might not get much maybe a horsepower or two, kind of said it jokingly because some people think Headers are a waste of time. I'm still a teenager at heart so I always like headers.

[i82much]

Originally Posted by Oregon 1967 GMC

you might not get much maybe a horsepower or two, kind of said it jokingly because some people think Headers are a waste of time. I'm still a teenager at heart so I always like headers.

i have headers on a pontiac 505, i am sure it needs them. but not sure how much a 396 with an itty bitty cam and stock oval ports really needs them?

[bs46488]

11.5 MPG

That's a 27.8% increase!

[i82much]

No problems that I can tell, but all I can do is trust the wideband so if is off, I don't know it. I have a single sensor in the driver's side, I run manifolds with a heat riser on the passenger side.

I did have some inconsistency for awhile where my numbers really fluctuated, but it turned out to be the secondaries were not always closing properly. Now the numbers stay pretty steady. A little noisier at higher speeds which I believe is due to underhood temps, I am thinking I will try to set up a thermal air cleaner one day so I can have a year-round tune instead of fussing with the carb when the weather changes.