fuel economy...

[kellyavanti]

I recently bought a 63 Avanti. It has been modified and is far from stock. The compression has been lowered to be more civilized on pump gas. It has a 600 cfm Edelbrock carb. It has a close ratio 4 speed. It has a 3.31 rear end ratio. It gets about 21.5 mpg on the road. I live in New Mexico so long distances are common. It tachs about 3400 rpm at 70 mph. It gets tiresome to listen to, and I'd like to bring the rpms down to around 2400-2600 at that speed. Any suggestions? The fuel economy is fine (great, in fact). If that is where the engine is most efficient, will I destroy the mileage by numerically lowering the fear end ratio?

Ringing ears in southern New Mexico, Kelly

[Guest dapy]

I'm about to climb back into my 1964 R2 automatic which has a just finished stock engine rebuild with overhauled Paxton. I am mechanically challenged and would like to learn more about the changes in your car. Probably better to do this by personal email so I don't show my public ignorance. Dave Pyle dap8@comcast.net. I'm Houston ex NM.

[Gunslinger]

Reducing the rear axle ratio by using a numerically lower gears increases fuel economy but hurts performance. 3.31 is a decent compromise for both but isn't optimum for each individually.

While not inexpensive, reducing rpm's without losing performance (like changing to a lower numerical rear axle ratio) is best done by swapping in a 5-speed transmission like a Tremec. I say Tremec because they're adaptable to many cars and the shifter is adjustable for positioning..as well as permanent mods to the transmission tunnel are likely not necessary like with a 6-speed. You could contact Mike Myer at Myer's Studebaker for an adapter plate to the Studebaker engine.

That swap would make for great performance and increased fuel economy...plus reducing rpm's which in and of itself is good for reducing engine wear.

BTW - an Edelbrock 500 is better for your car than the 600, but without knowing the mods to your car the 600 might be the better choice...plus the model 1406 600cfm Edelbrock is calibrated for economy.

Edited October 16, 2012 by Gunslinger

[PackardV8]

Your 21.5 highway fuel economy is by far the best I've ever seen or heard of in an Avanti. I've never gotten anywhere close to that with my R1 with the 700R4 overdrive.

However, an overdrive will definitely lessen the ringing in your ears. Since you've got the 4-speed, I'd go with a TKO500 5-speed. The conversion has been well documented here, on RacingStudebakers and SDC.

BTW, I can't make your numbers work out 3400 RPMs with a 3.31 rear gear and a typical 27" tall tire is more like 82.5 MPH. 3400 at 70 is more like a 3.73 rear gear. Is it possible your rear axle ratio and speedometer are not in sync? What is your tire height or loaded radius?

jack vines

[J Boyle]

When I had my R-1 rebuilt I too had the compression lowered. The rest of the engine is stock.

Stupid question: would lowering the comprerssion improve mileage?

I haven't tested the mpg...but it doesn't seem to be very good.

[okc63avanti]

My recent resto/mod with a R2-1/2 performance engine rebuild (between R2 and R3 specs) has Edelbrock 1406, Paxton Supercharger w/ high output impeller, R3 valves, ported heads, R3 exhaust, KB hypereutectic pistons, Tremec TKO 5 speed (OD gear is 0.64) and 3.73 ratio rear end.

At 70 MPH I turn about 2100~2200 rpm. I'm still breaking in the engine as I have about 2000 miles on it now but so far my gasoline mileage measured on long highway trip is about 13.5 to 14 MPG. The carb needs to be tweaked and jetted a little bit leaner I believe. I'm hoping for something around 16~18 eventually. Of course I like having fun with the car and really don't try and drive economically.

Edited October 21, 2012 by okc63avanti

[Charlie Kile]

Although mine isn't a 63/64 It's an 84 Touring optioned coupe.

It has a 286 rear end with positraction, and a 700R4 tranmission.At 70 mph it is turning just over 1700 RPM.

The engine is a Stage two Jasper, 350cid roller cam,Aluminum heads, large ss valves, and TPI from an early vette.

On a recent 500mile trip from Springfield to St Louis Mo including some running around in St Louis, I averaged 24.9999 Mpg !

It has a 22gal gas tank. Although I didn't check the milage, I drove from Baltimore Md to Springfield Mo with only one stop for gas and it wasn't showing empty when I got home !!

Charlie RQB3921

[kellyavanti]

I think I've decided "if it ain't broke, don't fix it". It runs well, and gets good mileage. So, it's little busy at freeway speeds. So what. I don't really know what was done internally to the engine when it was rebuilt. I was just told the compression was lowered to run better on the pump gas available now. We can still get non-ethenol premium here, so it runs just fine. I would have put on a 500 cfm carb, but the 600 was on it when I got the car, and it runs fine so I'm just going to enbjoy it for now.

Kelly