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]

Originally Posted by bs46488

11.5 MPG

That's a 27.8% increase!

I am sure the data is noisy ... but it's definitely better. I used to cruise at 12:1 or so and now I am often in the low 15's.

[Gromit]

You got me with that subject line - I thought "Wow - I wonder if they threw in a big box of Tampons with that Prius conversion?"

But then I realized you were joking.. But would love to see how you set up the wideband. Did you install two O2 sensors; one in each exhaust collector?

I've read the widebands don't work consistently with carbureted motors with stock heads - so am still investigating the various systems but sure want for them to work because it sure would help with tuning for mileage.

Good choice on the Quickfuel Vacuum Secondary - I have the 630 CFM version but sure am stoked with the setting that effectively adjusts the vacuum secondary spring by turning one tiny screw instead of swapping the actual spring. Just a quarter turn and the motor runs completely different.. Smart design.

[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.