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Old 08-25-2022, 11:28 AM   #13 (permalink)
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Smokey Yunick BSFC

Originally Posted by Logic View Post
This is one of those 'Little Nuggets' of information I always make a note of, but as its only one person saying so, this may well be better off in the Unicorn Corral..?

Quoting SMOKEY44211:
"Many years back I was racing in a rules restricted class that only permitted stock cast iron exhaust manifolds. I fabricated a water jacket to surround the manifolds with engine coolant. Picked up torque noticebly from 3,000 rpm to 6,500. Gained 15 hp at peak. This was a sb chev 350 that was in the 400-450 hp range. The purpose of the modification was to increase power but I also kept track of BSFC. In this case the #'s were favorable to suggest an improvement in fuel economy. Based on that I think finding some method of cooling the exhaust would have benificial effect on fuel economy in a normally aspirated engine...."

Thinking about how this may work:
There are studies saying that this results in decreased cylinder and intake tract temperatures, which leads to more dense intake air and automatic timing advance on electronically controlled engines.
(1hp for every 10 deg drop)

In a stock, cast iron manifold, I think the drop in exhaust gas volume leads to less restriction/back pressure and thats where a lot of the extra power/economy came from?

I know whats going to happen:
Someone's going to jump on here saying "more exhaust gas speed = lower pressure".
Well then; why don't we all make our exhaust systems the diameter of a drinking straw??
ie: Lets avoid quoting the venturi effect out of context...

Intake air is around 1/4 the volume of the hot, less dense, exhaust, and unless you have a tuned length manifold taking advantage of low pressure pulses in the right place at the right time, less gas volume is going to mean less engine effort pumping it out the same exhaust at any/all rpm's.

Trouble is extra cooling/radiator/weight and un-aero vent size reqd.

Anyone else here have any experience with cooled or finned exhausts?
For mpg you would never be operating anywhere near 3,000-rpm, so I'd recommend a detour around a very expensive proposition which offers very little probability of success.
Smoky 'cheated' the rulebooks as a matter of policy. And when third-party tested, some of his 'inventions' often failed to live up to claims.
You gotta love the guy, but I don't recommend anyone follow him down his rabbit holes.
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