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.

Cooling the exhaust might decrease scavenging with a normal header, which would result in lower volumetric efficiency. Or it might not. I guess it depends entirely on the tuning.

One thing almost universally agreed upon in the boy racer community is that these integrated-port heads really choke an engine's maximum power. Because the convergence points need to be much closer to the head, you can't tune for scavenging at all.

Tuned length exhausts and how they provide low pressure at cylinder during the exhaust stroke at a pre defined rpm is a whole different subject Ecky.
Here I'm talking 'Overall, at any RPM' on a stock untuned manifold.

I do have a post in the making on them (calculators and all)
AND
Anti Reversion 'valves'
(Reduce backward flow below the branch's defined rpms)
and
Pressure Wave Termination Boxes
(makes the last 'into one' pipe also tuned, the rest of the system 'invisible' and has anti reversion)

These all reduce the 'exhaust into the intake tract' EGR during valve overlap you mention.
IMHO that's only better for reducing NOx emissions but does little for economy.

As you seem into all this; Have you looked at Koenigseg's Freevalve tech?
~3X the power/economy! IIRC
He wants to connect the valves to an A.I. and see what it comes up with! :)

Smokey Yunick BSFC
 

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.

Tuned length exhausts for low rpm/economy would have longer, thinner pipes aerohead. (and a matched cam and intake)

You aren't going to find one at your local exhaust shoppe.
(in most the pipes aren't of equal length anyway and are 'tuned' to lighten your wallet only)
There are calculators available online that will allow people here to manufacture such manifolds.

But lets compare the cost of such to the cost of a water cooled enclosure for a stock exhaust manifold...
And consider that this will reduce back pressure at any rpm, not just at the rpms a branch is tuned for...
(And the possibility of using the heat/steam in a separate system.
Turning an alternator of some sort for eg.)

Another option:
Then there are anti reversion ...er... 'valves'/doodats that one can place in any exhaust , that will reduce exhaust in the intake during valve overlap.
They seem to work at any rpm too.
They look to be a cheap interpretation of Tesla Valves. (which are worth a look IMHO)

There is also information on Pressure Wave Termination Boxes (David Vizard ) that will make the last collector pipe tuned, anti reversion and the rest of the exhaust 'invisible to the manifold tuning.
https://youtu.be/5keTM9eyCOg?t=1350

Is the guy who posted the same Smokey??
If so; the probability, though small, goes up a tad.

My borderline Unicorn Corral posts:
All the tried and tested means of improving economy WORK and are well documented and implemented here.
There's very little left to be said about them.
It's the stuff that hasn't been tried or talked about thats discussion worthy IMHO.
It's ...out there yes. :) But perhaps worth a 2nd thought rather than the:
"oh him talking crap again" reaction that seems to be manifesting...

As much as I may naysay about many of them, I'm glad you're asking these questions. As you say, they deserve to be asked.

Been there did that exists along with Carls Sagans requirement of extraordinary proof. After the Nth iteration, there is a need to to go for the jugular.

Reduction of Exhaust Noise by Means of Thermal Acoustics
"...We observe about 2 dB decrease of the OA dB value when the gas temperature decreases of about 100°C..."
https://sci-hub.ru/10.4271/2012-01-0804

NB that a 3 dB decrease in noise is perceived as 'half as loud' by our human ears..!
(logarithmic scale and all that too)
Surprising is the dB decrease @ lower frequencies too!

(This is a Sci-Hub link: Sci-Hub is a database of research that's normally behind a paywall.
As it's your 'tax dollar' (or money you spent on a car etc) paying for the research; you have already paid for the info in their (and my) opinion.

If you type in Sci-hub as a search you will find more than 1 site where you can paste in the heading of a paper you are interested in. This is because the 'Paywallers' spend a lot of time and money trying to get it shut down, resulting in multiple copies of the site that aren't always synced.

In my experience if the 1st 'Sci-Hub' you try doesn't find the paper, the second or 3rd one may well find it)