MAX MPG from '96 LT1 ina 1970 Chevelle Wagon?

[Home Theater Sales]

Hello Folks

Your indulgence will be appreciated!

I currently own a 1970 Chevelle Wagon. It is factory originally and currently a Silver on Black car. Very rare for a Wagon.

What I am going to ask questions about will not make the most sense, unless I explain some things.

I know taking the route of replacing the motor with a more efficient one will take years/ lots of miles to recoup. I know this! I am not that concerned about recouping those cost.

I am also NOT concerned about speed -if it ends up pretty spunky, great, but its not a big deal either way.

I love driving this old wagon at this point, more than anything else I could drive. Call it nostalgia.

If I swap the motor out, I want to retain all the original parts, just in case it is important to a future owner. It is matching number car and basically stock. So, if it is removed, it will go on an engine stand and get dressed nicely with the 1971 LT-1 Z-28 Valve cover that have been sitting in my garage for the last 25 years along with some other shiny parts.

Anyway, my car has less than 66,000 miles on the original "307". The "307" being the "dog" that it is, it is actually in interesting motor.

It was the lowest compression motor in Chevrolet's V-8 line-up in 1970 -9.0 to 1.
Runs on the cheap stuff just fine. My investigation has revealed some other interesting things. It is cammed for bottom end grunt, so the cam and the heads run out of steam and flow at 4000 RPM with a red line of 4600 RPM. It makes (old gross rating from 1970) 300FT/LBS torque @2400 RPM.

I know headers, dual exhaust (it still has the single stock exhaust system) and replacing the rather large two barrel with anything will help.

I have put an edelbrock performer and a small Holley Economaster (400 CFM) four barrel carb. I saw a slight improvement around town (13.5), but I am still getting 15.9 on the freeway at 65-70. I believe the rear end gears are 3:31

I also found a 700 R 4 that is now sitting in the garage, waiting my next move.

After all is said and done, I am thinking I will be fighting for 15-16mpg around town, and maybe 20-21 mpg on the open road, maybe a bit better.

Then someone I recently met told me about the potential of an LT1.
At this point I should mention that my wife drives a 2002 Z-28 with M-6.

The thought had accured to me to do a swap using an LS motor, but everything about the swap seems to be "one more thing to move" to make it happen.

The guy that told me about the LT has one stuffed in to a 1992 RX-7. He believes it is easier and cheaper to get performance from a LT1 vs LS1

He convinced me that I should look into the LT1 swap, as it will be much easier, a basic drop-in to the same location motor mounts? 700 R 4 will go in place of the TH 350 with a shorten drive shaft and a relocation of a cross brace. I know there is more to it than that, but the big deal is the motor not having to be relocated.

I like that, along with the price and availability on LT1 motors.

So after a bit of research , I came across the de tuned LT1 in a Buick Roadmaster and Caprice Wagon. The Original EPA rating had the Chevy/Buick wagon at 4375-4550 LBS car rated at 17 city/26 Hi way. Since then, EPA revised rating adjusted the car down to 15/16 city/24 Hi way. Still not bad.

SOOOOOO here is what I am thinking. My wagon weighs a little more (about 3850) than a Chevelle/Elcamino (3650 -3720)from the same year.(1970)

The Roadmaster has a 2:92 rear end ratio and has no problem pushing 4550 LBS down the road and getting impressive MPGs.

If I lightened the load the motor is pulling by 700 pounds, maybe by a little more with some Aluminum heads, add headers, free flow cats and mufflers, some trick things on the fuels system/tuner stuff, could I possible see high twenties/low 30's on the freeway and high teens around town in my Chevelle wagon?

By the way, something different in the Buick/Chevy Wagon LT 1 motor vs the F-body cars tuning has it making its maxium torque at 2400 rpm, not 3600 like most SBC so GM got away with taller rear end gears (2.92) and still have enough bottom end to push a lot of weight. The Buick and Chevy wagons were also rated to tow 5000 LBS with the HD tow package. (I will be doing NO towing)

I am thinking with a lot less weight, I could drop down to maybe a 2:52 R&P
ratio in my wagon and I would see 1750-1800 RPM at 80 MPH.

My wagon is lower than stock -I know it is not as clean aerodynamically as a modern wagon but I'm not looking for high speeds, freeway speeds of 70-80 max.

So, feed back please!

Thanks,

Dean

[side2000]

wow lets get that one published. . . .

if you don't care about speed, a monster torquer cam mated with some efficient heads (cleaned up stockers would be fine) would net you decent mileage, depending on your right foot habits. LT is a good choice. . .it's reverse cool heads allow you to run higher compression ratio's on the same octane. if max mileage is what you want, high compression is also what you want. gotta decide whether you are willing to pay for 93 to squeeze some more efficiency out of it (i would). that bein' said, 11.5:1 is completely streetable for an LT on pump gas. assuming you will use stock heads, getting the decks milled .030 should put ya right around that 11.5 ratio. the smaller combustion chambers will yield a more efficient burn and more power.

in addition to ^^this, some added timing (good tune), free flowing exhaust, and free flowing intake would yield best possibility for great mileage.

i HATE automatics. . . .one of the reasons is they soak up too much of my mileage/power. might think about finding an LT/6 speed combo. they have awesome OD ratios also (5th and 6th are both OD). my SS cruises 2000 rpm @ 90 mph. IMO you wont get even close to high 20's w/o a manual.

you will definately see a substantial gain in mileage with a nice LT setup, and you'll be happy with the additional power/pedal feel.

[bigrondownhiller]

You could probably hit mid 20's max. The lt will be slightly more effecient than your carb combo. If you swapped the big body heads for some f-body or vette alum heads you will save a little weight which always helps. I think you might be a little happier with maybe a 2.73 or a 3.08 rear gear. If you got a tranny engine combo with a computer you will already have controls for the tranny. You could use the 700-r4 but I think the stock computer might throw some codes without the stock tranny.