Water cooled exhaust manifold: better economy
 

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...."
https://www.eng-tips.com/viewthread.cfm?qid=162827


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)

but
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?

What about the government-mandated catalytic converters?

A crack head cut them off and cashed them in.

Honda started water-cooling their exhaust manifolds in 1999 with the Insight. The purpose was not to improve economy by any interaction with the gases, but the packaging allowed the catalyst to be placed right at the exhaust outlet on the engine, and the engine got up to operating temperature far more quickly.

https://i.ebayimg.com/images/g/-X8AA...07u/s-l500.jpg

You're right in that there is a bit more to it. Exhausts tend to have their scavenging tuned for a rather specific RPM range, where the pulses are timed to create suction that more fully evacuates the cylinders. Exhaust scavenging is actually counterproductive for economy though because often you want exhaust gas recirculation - though that can be controlled by cam phasing (VVT).

I'd say it's probably too complex to generalize about.

Aside from faster cat light off and smaller packaging, an integrated cooled exhaust manifold is a lot lighter than the usual steel manifold. E.g. 4 cylinder headers might be around 15lbs while the short aluminum piece built into the head is barely 3lbs with the coolant jacket. It's also easier to manufacture, and decreases coolant warm up time.

On a car, the extra heat that the radiator needs to get rid of is negligible.

I think the subpar exhaust scavenging is actually a detriment though. The issue is that at high load you are more knock limited, so the compression ratio can't be set as high. It's better to have a high compression ratio and use cooled EGR.

I've always liked EGR heat exchangers as a means to make steam to drive a Tesla Turbine oil pan.

Tesla Turbines are:
Simple to make.
Well suited, efficiency and 'small steam' wise, to turning an alternator. (geared down)
Don't give a damn about wet steam and all those latent heat etc laws.

Problem is any such system has to have a higher power to weight ratio than the car did before hand.
But well suited to gensets and other stationary engines.

How did your pressure washer project go?

With all the engines doing this nowadays, they don't seem to be a problem freebeard.
https://www.roadandtrack.com/new-car...aust-manifold/
[IMG]https://hips.hearstapps.com/hmg-prod.s3.amazonaws.com/images/vw-1498054702.jpg?crop=1.00xw:1.00xh;0,0&resize=980:*[/IMG]

Well getting the engine up to temperature fast would help, but I do think lowering the exhaust gas volume helped too... if they didn't downsize the exhaust and muffler system too.

ie: Any exhaust can be considered more 'freeflow' if it only has to handle ~half the gas volume.
But the bean counters may have told the engineers to downsize the exhaust.