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-   -   AeroSprite! Aero & mechanically modified Austin Healey Sprite: consistent 65 MPG US (

MetroMPG 01-29-2014 02:44 PM

AeroSprite! Aero & mechanically modified Austin Healey Sprite: consistent 65 MPG US
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EcoModder has a longstanding (2011) member, xpedro01, who hasn't posted yet, but who has done (and is still doing) some really interesting things.

Things like this:

Details, from e-mail (posted with permission):
  • In the early 1970's I was driving 110 miles per day so I modified an Austin Healy Sprite and doubled its mileage over a period of years to a consistent 65 MPG (unheard of in those days).
  • This was a 1960 "Bug Eye" with an 850cc engine. It turned close to 3000 at 60 mph and gave 33mpg on average, originally.
  • It wound up with a 1600cc pinto engine (& transmission) with the camshaft retarded 2 notches (poor man's Atkinson cycle)
  • Additional (2nd) Buick transmission, reversed, to gain up to a 2.5 overdrive
  • The engine cruised at 1100 rpm @ 55MPH (Nixon days).
  • A slight incline required downshifting, but I had 12 speeds.
  • It was made of junk yard body pieces, pop rivets and bondo. Eye level was 70's skirt level.
Here was the car mid-way through its transformation:;d=1391531371

Here's the same Sprite in "33 mpg" form:

Ultimately (after a 250,000 miles), the modified car was taken off the road & dismantled for safety reasons. A student got the chassis in exchange for destroying the body. He had a Midget and could use the parts.

The builder says he prefers driving his recently acquired 2000 Honda Insight (which he is also modifying with a short aero tail) compared to the Sprite. No kidding!

Hopefully he'll join the conversation, now that the cat is out of the bag. At 87, he's got most of us on seniority (by a significant margin), but I bet he'll figure out this forum-posting business if he wants to!


Oh: the "secondary transmission mounted backwards" trick reminds me of my friend's dad's 1930's-era aero & mechanically modified Model T.


UPDATE - Feb 18

Reprinted with permission from April 1975 Kansas State Engineer magazine, an article about the car mid-way through its transformation to 65 mpg...

gone-ot 01-29-2014 03:22 PM

Would love to hear MORE about that BUICK transmission: actually an OPEL manual?

Daox 01-29-2014 03:34 PM

Very cool Darin. Old school modder, I like it!

xpedro01 01-29-2014 05:00 PM

There are a lot of cobwebs involved here as it was almost 40 years ago. As I recall the reason for choosing Buick was because of its very short output shaft which in this case went forward to connect to the output of the pinto transmission. It must have been from an older enclosed driveshaft Buick. With this type of use it had to withstand the torque of the 1600cc engine multiplied by reduction of the Pinto transmission. More than likely it was from a 1950's 70 series Buick since it was a 3 speed with no syncros in first gear. I had converted a buddies 39 buick and my crosley while in the Air Force back in the early 1950's. Behind this transmission was its clutch shaft that had to be supported. This called for an adapter plate and ball bearing + seal. The clutch hub was used to adapt to the driveshaft which was now only about 18 inches long. It ran in what used to be first gear when cruising. This was a 2.5 to 1 stepup and allowed the engine to run at 1100 rpm at 55MPH. A small incline required shifting the 4 speed down to third. Only about 7 of the 12 gears were really usable because of almost duplicates.

MetroMPG 01-29-2014 05:32 PM

xpedro - nice to see you on the forum, and thanks for sharing the project.

When you think about what was available at that time, 65 mpg is remarkable. (Even though it's a walk in the park for your Insight.)

Car and Driver didn't get anywhere close when they messed around with modifying their '74 Pinto.

gone-ot 01-29-2014 07:01 PM

I had experience with the 1600cc (FOB) engine & transmission in my 1972 Pinto:

...however, my best was ~ 36 mpg at 55 mph. And, ironically, I'd earlier owned a 1965 MG Midget (bought in Newfoundland) the cousin of the Sprite.

xpedro01 01-29-2014 07:51 PM

Old Tele Man, that was probably doing pretty good since your engine was probably turning over 3000. With my camshaft retarded 2 notches, the power stroke did not end until almost bottom dead center, and the intake valve stayed open till the piston was almost half way up. The displacement was twice the original (almost) so full throttle did not make it ping because of the Atkinson cycle effect (expansion stroke was much larger than the compression stroke). Mine was a gentle low power engine that operated in the 10 horsepower range.

MetroMPG 01-30-2014 10:44 AM

I think this is the first I've read in the forum of someone doing a "poor man's Atkinson cycle" by monkeying with camshaft timing.

(If someone else has done it, I welcome the correction.)

I wonder how it would impact an OBD-II car that needs to pass emissions testing...

Frank Lee 01-30-2014 11:36 AM


Eye level was 70's skirt level.
So did it get totalled in a wreck?!? :eek: :p

xpedro01 01-30-2014 12:40 PM

It probably would not pass emission test, but I don't think they tested in those days. There would be no nitrogen problem as the compression was lowered from 110psi to 75, and full throttle gave a cooler exhaust than before.
We also had a 1968 Cadillac that had the almost unheard of in those days of 10.75 to 1 compression ratio. In later years they dropped back to the industry standard of 8 to 1. It was pre Atkinson. The spec sheet said the intake valve closed 90 degrees after bottom dead center. It still required premium. It would ping at 60mph on regular on a slight hill. ONE cog retard solved that problem. It was happy with regular for the next 50,000 miles that we had it.

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