1970's "30mpg" V8 cams, big car, w/14:1 CR on 87oct

[Beau]

The link to the Smokey Yunick (spelling corrected) article is: What Ever Happened To Smokey's Hot-Vapor Engine? - Hot Rod Magazine

[Beau]

PDF of original 1984 Article.

http://www.gafiero.org/docs/SmokeyYunick.pdf

[Diesel_Dave]

I'm not familiar with the stories you're refererring to, but the technology you're describing is called Miller cycling:
Miller cycle - Wikipedia, the free encyclopedia

While most people think that it's the compression ratio that infulences the effiiciency, however, it's actually the expansion ratio. For normal engines both ratios are basically the same. For the Miller cycle, the compression ratio is lower than the expansion ratio. This is because the effective compression ratio is lower than the geometric compression ratio (because some of the air is pushed back out).

It's the compression ratio that limits the engine (knock in the case of a gasser, peak cylinder pressures in the case of diesels). Miller cycling allows you to run a higher geomtric compression ratio without hitting the engine limits.

The downside of Miller cycling is that you lose power. Since you give up air, you give up fuel, therefore you can't get as much power out of the same engine. That's why it's not widely used. Some manufacurers have compensated by adding turbochargers and/or superchargers to help the power issue, but then that makes things more expensive.

Miller cycle engine have been mass produced by several companies. Mazda has made it:
MAZDA:Miller-cycle engine | Environmental Technology

GE puts it in some of it's diesel PowerHaul engines:
Eco-minded Powerhaul leads the way into global markets

The concept is not that different from the Atkinson-cycle engines in the Toyota Prius/

[Frank Lee]

I don't think the non-Yunick cams were Miller cycle.

They were probably just like any of the "RV" or torque cams, intended to move the torque band down low.

I had one of those in a 283 in my '74 Nova; IIRC I usually got 23-24mpg with it when I behaved myself.

25mpg is a hella long way from 30 though.

[drmiller100]

rv cams are entirely different than what diesel dave is describing.
an rv cam with 12:1 is a recipe for disaster.

i would think the right ramp closing on the intake would be a neat way to bleed off pressure. the trick would be to have homogonized mixture so you didn't change the mixture ratio, but maybe over time it would work out.

[slowmover]

An RV cam emphasizes low rpm lift at the expense of duration (when done correctly).

Bruce Crower (to go back to the OP) was the one with high compression experiments in the late 60's/early 70's. What Yunick was doing was a bit different.

.

[Beau]

Yes, you are correct. The Yunick concept and the Crower concept are completely different. I probably created confusion by mentioning them (and Ak Miller) all in the same breath.

[Beau]

Some additional information on the Bruce Crower high compression/late intake valve closing engine:

:::MaxChevy::: Technically Speaking - The Wizardry of Bruce Crower - 10/26/10

[War_Wagon]

I'd be interested to see the rear axle ratio used in the '32 Ford. I didn't see it listed, and put that together with a lack of information on the circumstances of their mileage "testing" leaves a lot of room for massaging the numbers. If they just drove around the city and the suburbs, then a set of gears like 4:88s would let the car move out and get to speed with very little throttle. Granted it would be limited to "in town" speeds before you had to go from barely taxing the engine to revving the crap out of it to go any faster, and while heavy by todays small car standards, a 32 Ford with a SBC would probably weigh in at what, just over 3000 pounds? Yes it's full frame, but its a small frame, and it's not like the car is full of airbags, ABS equipment, sound deadener, side impact beams etc etc. Being a hot rod, it probably had some sort of lightweight aftermarket wheels, and even narrow "pizza cutter" tires and wheels on the front. That's cutting a lot of rotational mass and rolling resistance. And at low speeds, the aero wouldn't really come into play as much.

If most of the testing was on the highway, then a gearset in the opposite direction, say 2:76s, would have similar results. It would be a gutless dog in town, but it would literally idle down the highway once it got moving. The "Mileage Maker" camshaft would probably just mellow out the engine enough so it could live with not having a lot of throttle. Team that up with a low-rise intake manifold designed for low RPM torque, and a small 4 barrel carb and it might work.

Being a 32 Ford, maybe the rear axle had been replaced with a 2 speed model, ala Bonniville salt flat racer style. Another way to make the test look good. Regardless of all this, I would love to see that original article as well, I hope someone can source it!

[Big Dave]

It this not exactly how Toyota puts an Atkinson cycle engine in the Prius? Its a Yaris engine with a different cam and the hybrid motor masks the poor low-end torque of the engine.

Holding the intake valve open beyond TDC vents off pressure, effectively reducing the compression ratio making it possible for high ratio engines to run low octane fuel.