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Old 03-04-2023, 09:46 AM   #26 (permalink)
Isaac Zachary
High Altitude Hybrid
 
Join Date: Dec 2020
Location: Gunnison, CO
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Avalon - '13 Toyota Avalon HV
90 day: 40.45 mpg (US)

Prius - '06 Toyota Prius
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Quote:
Originally Posted by Solarpowered View Post
Well I figured an engine builder would get into the weeds some. And would know all the little tricks the layperson wouldn't, when it comes to the engine itself. He said lower rotational mass isn't worth enough to go chasing it down, and to focus efforts elsewhere. Because you'd spend $3,500 or more just the gain 0.3% fuel economy. Not even a full 1%

Still be fun for me to try if money was no object, but that ain't the case so yeah I'll just do what he says.
Exactly! When I rebuilt the 1972 Super Beetle engine I spent a lot of money on a few things to improve efficiency that I wished I hadn't afterwards. I got a solid 30mpg during the break-in period. But some of the things I spent a lot of money on didn't really seem to help in the end. Namely, a much larger oil cooler and modified cooling shroud, a plate with holes in it to put under the carburator, "1974" double heat risers to the intake manifold instead of the common single heat riser, and a weighted pulley wheel with the intent of taking some weight off the flywheel.

What did seem to make a noticeable difference was installing an O2 sensor in the exhaust and being able to adjust the carb to get leaner air-fuel ratios at low loads while not going lean at high loads (this actually made the engine run cooler, not hotter like some claim). I also increased the compression ratio to 10.0 (yes! in an air-cooled engine!). I took some builder's recommendations on what cam grind to get, and got one that was both claimed to be better for fuel economy, throttle response and would work with the 10.0CR. I also make the engine have a small quench. I installed hypereutectic pistons.

But the biggest difference was getting the timing down. I ended up buying an electronic programmable distributor I could hooke up to a computer and have an entire load/RPM map. There were areas I could hit 50 advanced and see improvement.

I look back and laugh. A 10.0CR lean running 50 ignition advanced air cooled engine that never pinged or knocked, the complete opposite of what most laymen people would recommend. But I got these ideas from actual builders who knew what they were talking about. The only problem was that then the engine ran a too cool even with a stock thermostat and an added oil thermostat.
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