# Another engine theory Q - Blowers?

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#### PMD

The 935 was too valuable to race back in 98-2001ish when I was most involved with them. The distributor cap was $5000- yes FIVE THOUSAND dollars if you could find one. Thanks for the story and pics. I knew they used wishbones and rockers up front, but never noticed before that they retained the strut inner fender (no doubt one of the few actual production parts). I long ago turned my back on the world of uber-overpriced anything, but it came rushing back last week when a friend asked me how to solve the problem of a burned out tail light on his '09 Azure. In spite of what is shown in the manual, there is no bulb and the want$11 or $12k for a TAIL LIGHT!!!!! When you learn he has had only 3 years of driving in 12 years of ownership it sure makes you think twice about one's priorities in life (and engineering). #### dwalker ##### Well-Known Member Supporting Member Thanks for the story and pics. I knew they used wishbones and rockers up front, but never noticed before that they retained the strut inner fender (no doubt one of the few actual production parts). I long ago turned my back on the world of uber-overpriced anything, but it came rushing back last week when a friend asked me how to solve the problem of a burned out tail light on his '09 Azure. In spite of what is shown in the manual, there is no bulb and the want$11 or \$12k for a TAIL LIGHT!!!!! When you learn he has had only 3 years of driving in 12 years of ownership it sure makes you think twice about one's priorities in life (and engineering).
I am always amazed when I run across such things in the modern world.

#### 31Pontiac

##### New Member
The upside of a mechanically driven supercharger is immediate response. Not a big deal in an aircraft but for a drag car it matters. Here's a picture of my replica of an early 60's Dragmaster Dart.

#### TFF

##### Well-Known Member
Yep, that’s what vintage racing has become and it’s slowly dying out which is sad. I’m all for cool cars. Don’t think I would not want one, but I would not buy it as a sub for running a modern Daytona race because it’s easier to buy into which seems to be what the fast cars are. An early 70s Can Am is about as late as I’m for. Lola or McLaren, no turbos. Prefer the Cobra/ Ferrari GT era but that’s super stupid cost wise.

#### mcrae0104

##### Well-Known Member
Supporting Member
Who says there's no substitute for cubic inches?

Just compress those cubic inches into cubic centimeters, figure out how to deal with the consequences of the ideal gas law and keep the detonation at bay, while keeping operation simple enough and reliable, and you're winning. Easier said than done--I have high respect for those who have succeeded.

#### rv6ejguy

##### Well-Known Member
Supporting Member
If you look at the plethora of factory turbocharged auto engines today outputting over 100 hp/L on 87 octane and well over 100 lb./ft./L, it no longer seems that hard to do reliably. I drove a 1.4L GM turbo Cruze a few years back and a friend's 3.5L Ecoboost F150 last year on road trips. Mightily impressed with the engineers who designed these. Very flexible, powerful and economical. We can move up the ladder from there. Mercedes produces a factory 405hp 2L engine now for instance.

Turbos rule in GA for a variety of reasons over superchargers, just as they do in modern production cars. The ratio is at least 100 to 1 in both markets.

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#### trimtab

##### Well-Known Member
I don't want to generate thread creep, but for the experimentally minded:

I purchased an OEM single cylinder OHV to play with some direct injection schemes 7 years ago. After a few months of tinkering with the injection work, I ended up playing with another scheme: adsorption induction. Essentially, running the induction through an alternating two column adsorption O2 concentrator. I'm at 5000', and varying the O2 concentration from nominal to approximately 60% (higher % meant lower manifold pressures) the peak for the zeolite columns yielded a 34% hp increase at about 35% to 40% O2, or roughly twice the natural O2 concentration (the O2 concentration varied over the alternating cycle times, and decreasing the cycle times limited the maximum O2 available). The carb was adjusted more or less continuously to get a reasonably low CO/hydrocarbon level as a proxy for a reasonable mixture, which also swung widely from the adsorption column cycles. Induction pumping losses and effective compression ratios account for the fact that the power wasn't nearly doubled per the O2 levels.

I believe it may be the first time such an experiment has really been done, even as crudely as I did it. I have never found an academic paper that outlines this approach.

Whether it is feasible to have very large adsorption columns for the intake of something as powerful as a full-sized engine is more of a thought experiment than practical in my view. And the weight....

But, it does give some light on other methods of power boosting. For example, compressed O2 or LOX or nitro.

#### BBerson

##### Light Plane Philosopher
Supporting Member
Is there any oxygen compound in dust form?

#### BRAAP

##### Member
The “no replacement for displacement” argument in the context of aircraft boils down to, it’s just easier and safer.
Short version is lower specific outputs, (HP per given displacement), is less likely to have abnormal combustion process and has more chamber/cylinder surface area to effectively manage/dissipate the heat produced, thus reducing abnormal/undesired combustion processes.

Higher specific output is ultimately what we’re trying achieve here in this thread, though to safely maintain those levels of output as required in an aircraft application is where it gets tricky. The bearings, crank, rods, etc of these modern power plants are plenty robust enough for these high output environments and beyond, were seeing 1000+hp on small displacement engines with stock internals becoming more common place, the components of these engines can handle the physical forces.
It’s making sure this limited amount surface area of smaller displacement combustion chambers/cylinders can manage all this heat production from this elevated level of power being produced over long periods of operation, not just sprint applications, and with enough wiggle room for whatever abnormalities of mixture control and/or mixture dispersement that could produce abnormal combustion such as detonation doesn’t happen.
The higher the specific output we obtain and for the extended periods we require, the more demand there is for even greater precision and consistency of building and maintaining a proper combustion process and managing the heat rejection of this elevated power output, pretty sure this curve isn’t linear.

Example is the Datsun L28. In my experience with these engines over 30+yrs, specific outputs greater than 1hp per CID, detonation inevitably is present under high loads. Even with this engines paltry comp ratio and when using higher octane fuel, to attain ideal ignition advance for max output detonation would be present, even just a little. Pushing 200hp from 170CI, (little bit over stock), detonation over time would break compression rings, seen it a lot. Granted it would take sometimes years of driving in some daily drivers but it was happening. As power levels increased this exaggerated, adding boost bringing power levels up to 400hp from the same 170ci even with absurdly retarded ignition timing would pop the head gaskets. Many would blame the gasket for failing not recognizing the failed gasket was a symptom, not the problem, and they would modify for larger head studs, tougher gaskets only to break pistons, etc. (Detonation doesn’t want to be contained). In the L28 a couple issues are at play. A combustion chamber shape and intake port lead-in that doesn’t distribute the mixture as consistently as we would like and the bigger issue is coolant flow around and over the combustion chamber itself. Attempts at redirecting coolant flow all together by adding coolant ports into the head aimed at the top of the chambers was an effective means, a variation that as I understand was pioneered on the IMSA Electramotive 280ZX Turbo of Don Devendorf.

Any how, aircraft power plants being an endurance application we need to confirm that running these elevated specific outputs for extended periods can be done over the long term reliably without failure. For limited budgets and limited testing facilities/measures, the more displacement at lower specific output is less likely to have abnormal combustion process and has more chamber/cylinder surface area to effectively manage/dissipate the heat produced. It’s just easier.

#### dwalker

##### Well-Known Member
Supporting Member
A combustion chamber shape and intake port lead-in that doesn’t distribute the mixture as consistently as we would like and the bigger issue is coolant flow around and over the combustion chamber itself. Attempts at redirecting coolant flow all together by adding coolant ports into the head aimed at the top of the chambers was an effective means, a variation that as I understand was pioneered on the IMSA Electramotive 280ZX Turbo of Don Devendorf.

As an interesting aside, the shop I worked for in North Carolina actually had a couple of the heads worked by Electramotive in the shop for repair. My employer at that time was a cyl head "guru" and the heads had been sent to him for failure analysis as well as suggestions to improve them. The issues were the valves, which were not up to the task and would pop the heads off and in the resulting catastrophe suck bits of valve and cyl head all through the intake system destroying everything.
They did not listen to the recommendations give, and we had the heads hanging around the shop for quite some time.
IN another instance, lets take the 2.0 litre Porsche911 motor. PCA and HSR both wanted a 2.0 class for the cars in the interest of "costs". Most of the engine IIRC made roughly 150hp stock, and tuned to 180hp in the S. As a race engine with cams and headwork etc. 210 was not unheard of. Not bad for a 1970's SOHC aircooled motor, and at the thermal limts for power and any sort of reliability. The HSR folks were tickled, everyone was happy. Then "we" happened. Using very high compression, large valves and cams, and a lot of very high tech coatings and treatments, and of course, modern EFI, we were able to get right around 250hp out of those little monsters. And they would last season after season. I had multiple Porsche experts tell me personally it was not possible, even while we were smoking them into the dirt. They claimed we were actually 2.4litres, but nope, inspection after inspection showed we were legal. Dyno after dyno showed we had more power, which was "impossible in a 2.0 litre, the pistons would melt with the compression and we would blow the rings out of it if it didnt melt the heads first".

Then the engine we built became the new norm. We did the same thing with a long-stroke 3.5air motor in the last year of eligibility in Pro racing.

So now when I am told that it cannot work that way or is not possible I honestly stop listening.

Any how, aircraft power plants being an endurance application we need to confirm that running these elevated specific outputs for extended periods can be done over the long term reliably without failure. For limited budgets and limited testing facilities/measures, the more displacement at lower specific output is less likely to have abnormal combustion process and has more chamber/cylinder surface area to effectively manage/dissipate the heat produced. It’s just easier.

I might agree with you if it were not for the row of melted pistons, cylinders, and valves on the wall at my local A&P. Seems like a work in progress.

#### BRAAP

##### Member
As an interesting aside, the shop I worked for in North Carolina actually had a couple of the heads worked by Electramotive in the shop for repair. My employer at that time was a cyl head "guru" and the heads had been sent to him for failure analysis as well as suggestions to improve them. ...

Very cool.

I might agree with you if it were not for the row of melted pistons, cylinders, and valves on the wall at my local A&P. Seems like a work in progress.

Not sure I understand, maybe I missed something or are you saying that engines with lower specific output are more prone to melting pistons vs higher specific output?

#### dwalker

##### Well-Known Member
Supporting Member
Very cool.

Not sure I understand, maybe I missed something or are you saying that engines with lower specific output are more prone to melting pistons vs higher specific output?

I'm saying carbs stick and having manual mixture control based on egt leads to a lot of misconceptions when parts fail.

#### Aviacs

##### Well-Known Member
Is there any oxygen compound in dust form?

You apparently were a good kid that did not invest significant effort in pyro effects.
Is saltpeter still available by the pound at any grocery store?
(for pickles of course...yeah, that's it, mom's making pickles and needs a couple lbs. Oh, & a 5lb bag of sugar....Got any sulpher? Try the hardware store? OK....)

#### wsimpso1

##### Super Moderator
Staff member
I don't want to generate thread creep

Thread drift is EXACTLY what this is…

I ended up playing with another scheme: adsorption induction. Essentially, running the induction through an alternating two column adsorption O2 concentrator … yielded a 34% hp increase at about 35% to 40% O2…

Whether it is feasible to have very large adsorption columns for the intake of something as powerful as a full-sized engine is more of a thought experiment than practical in my view. And the weight....

But, it does give some light on other methods of power boosting. For example, compressed O2 or LOX or nitro.

Sounds like we expect that the oxygen enriching device would have to be compact, be internally regenerated in use, and use less energy than they add to the system. Other methods are to carry some oxygen with you. You know, like with rockets or with nitrous oxide injection.

There are a number of issues with taking an engine developed to work with our 21% O2 atmosphere and enriching the air to be 35-40% O2:
• The biggest one is that if we double the O2 in charge air, we can burn twice the fuel, but the charge air mass only went up 2.6% - temperature rise at any time after ignition is now almost twice what it was. A lot of our pieces will only stand that for a short period of time. Instead of aluminum pistons and cylinder heads, maybe those parts will all have to be steel. The steel poppet valves will probably need to be changed to super alloys like are used for hot section turbine and stator blades. Same with the exhaust system.
• Next issue is that the oxygen enhanced input air will oxidize stuff much more rapidly than it does with a 21% O2 level.
But if instead we just accept the atmosphere as it is, and use a neat little pump driven almost for free with waste heat from the exhaust system, then when we double the O2 in the combustion chamber, then double the heat output into twice the mass of air, we get about the same temperature rise from firing the mixture. This stuff is not completely linear, but we can get a pretty good idea of what is going on with this model.

Billski

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#### PMD

##### Well-Known Member
. Not bad for a 1970's SOHC aircooled motor, and at the thermal limts for power and any sort of reliability. The HSR folks were tickled, everyone was happy. Then "we" happened. Using very high compression, large valves and cams, and a lot of very high tech coatings and treatments
Ex plasma coating guy here, and long time air cooled builder. What coatings and on what parts were they using way back then?

#### dwalker

##### Well-Known Member
Supporting Member
Ex plasma coating guy here, and long time air cooled builder. What coatings and on what parts were they using way back then?
I'll post soon as I'm at my laptop

#### dwalker

##### Well-Known Member
Supporting Member
Ex plasma coating guy here, and long time air cooled builder. What coatings and on what parts were they using way back then?

Ok So here we go, and I do not consider this to be thread drift since the OP could use this information to reach thier goals.

We will start with the cylinder head. The intake, combustion chamber, and exhaust port were coated with a thermal barrier coating, this is post port work but pre-valveseats and guides. Valve seats are copper berylium and were a complete PITA to deal with, as the dust is exceedingly toxic. Valves were titanium from Del West, and we tried both the tulip and back-cut valves, I believe in the 2.0 the tulip made more power. Valvesprings were typically Ferrea with the usual titanium retainers Valve guides were typical manganese bronze. I want to say we were using 8mm valve stems, but I could be wrong, it has been almost 20 years.

The pistons were coated on top with a thermal barrier coating the same as the cylinder head, a Dry Film Lubricant treatment on the skirts, and an oil shed coating on the underside. Wristpins were "Casidium" coated, which I believe has changed trade names to "Diamond Like Coating".

Main and rod bearings were coated with DFL.

Cylinders were OEM steel/aluminum units that were honed and nikasil'ed by US Chrome.

With the exception of the exhaust system itself- Swaintech, the wrist pins (Casidium) and the cylinders all coatings were done by EMBEE Performance in California.

Oil squirters were fitted to direct oil directly on the underside of the piston crown, which is an old and trusted thing to do to cool the piston. Without the thermal barrier coating on the cylinder head or piston top the oil would burn and leave carbon on the underside of the pistons in just a few races. With the TBC on the piston alone the undersides would look like new after a season of racing. Without the TBC in the cylinder head the CHT would be very high and we broke a few rings due to carbon induced knock. With the TBC cylinder head and exhaust more heat went out the exhaust than soaked into the pistons or cyl head.

The coatings allowed us to run more compression with less overall wear and less heat issues. More compression and aggressive cams with a MOTEC (M48IIRC) and Jenvey throttle bodies from the UK that looked for all the world like a typical MFI setup, and a set of Denso coils and we had reliable spark that would not blow out under high compression/high rpm, very accurate fuel and timing delivery, and thats how me made power, reliably, season after season.

#### trimtab

##### Well-Known Member
Thread drift is EXACTLY what this is…

Sounds like we expect that the oxygen enriching device would have to be compact, be internally regenerated in use, and use less energy than they add to the system. Other methods are to carry some oxygen with you. You know, like with rockets or with nitrous oxide injection.

There are a number of issues with taking an engine developed to work with our 21% O2 atmosphere and enriching the air to be 35-40% O2:
• The biggest one is that if we double the O2 in charge air, we can burn twice the fuel, but the charge air mass only went up 2.6% - temperature rise at any time after ignition is now almost twice what it was. A lot of our pieces will only stand that for a short period of time. Instead of aluminum pistons and cylinder heads, maybe those parts will all have to be steel. The steel poppet valves will probably need to be changed to super alloys like are used for hot section turbine and stator blades. Same with the exhaust system.
• Next issue is that the oxygen enhanced input air will oxidize stuff much more rapidly than it does with a 19% O2 level.
But if instead we just accept the atmosphere as it is, and use a neat little pump driven almost for free with waste heat from the exhaust system, then when we double the O2 in the combustion chamber, then double the heat output into twice the mass of air, we get about the same temperature rise from firing the mixture. This stuff is not completely linear, but we can get a pretty good idea of what is going on with this model.

Billski
Yup. The manifold pressures remained below 16". The flame temps were over the top. The mass of the zeolite stacks for a system that could service, say, an O-470 at 2600 rpm would be around 50 kg, and the geometry of the columns for optimal performance changes with rpm. It's impractical for aeropropulsion, but possibly practical for terrestrial propulsion. The emissions are hotter, but NOx is still quite a bit less (less N2 overcomes the thermally driven NOx issue). In other words, a terrestrial diesel could benefit to overcome the impossible NOx vs particulate corner in the direction of efficiency by allowing leaner charges and higher Carnot efficiency.

Turbochargers simply make power density more favorable, but they exacerbate the NOx issues. Urea is commonly used to address the NOx issue at present, and a reason that turbo diesels will likely see regulatory setbacks in the future.

I only brought it up because of the displacement vs supercharging discussion. There is at least on other side to it.

#### rv6ejguy

##### Well-Known Member
Supporting Member
BRAAP- The Nissan L series engines go back to the '60s and I've built plenty of turbo and NA ones for street and road racing, won a couple championships with them. Never saw the problems you describe in ones built with Webers or EFI, all using stock crank, rods and fasteners. The heads were really bad flow wise for sure on my flow bench.

Comparing this engine to even something remotely modern, say from the '90s at least and you're in a different world. Few people would pick such old engine designs to power aircraft these days in turbocharged form outside of maybe VWs and Corvairs, just because they are light.

I've done a number of 2.2 and 2.5L turbo Subarus for aircraft and they've easily matched or outperformed Lyc 360s. None have blown up. Russell Sherwood's NA EG33 Glasair has destroyed all the large displacement certified engines in his SARL class multiple times. It can be done, if done right.

#### PMD

##### Well-Known Member
Turbochargers simply make power density more favorable, but they exacerbate the NOx issues. Urea is commonly used to address the NOx issue at present, and a reason that turbo diesels will likely see regulatory setbacks in the future.

I only brought it up because of the displacement vs supercharging discussion. There is at least on other side to it.
At the risk of opening yet another very deep mud puddle to wade through: the answer is and exotic chemical: hydrogen di-oxide.

There is quite a body of work with aqueous fuels, but the difficulty of maintaining an emulsion for long periods makes a dead end (in that arena, I have driven an EFI Ford van running on 50/50 ethanol/water as far back as 25 years ago. That particular engine used catalytic ignition, so an aspirated charge, but compression ignition (think the most exotic Cox 049 ever).

There has been a great deal of work done with water injection in SI, CI and turbine going back into the '30s (or beyond?). Amazing how easily we forget the lessons of the past, but this uses the energy of change-of-state from liquid to gas phase to drop cylinder temps while raising pressures. Easily takes NOx to near zero. The aftermarket extreme turbocharging crowd knows this one quite well.

Finally there is some new work being done harvesting steam from exhaust stream and recycling. Has a lot more to do with the extremely short lived chemical species of combustion and has given some incredible BTE numbers. Not sure if any of this one has yet been published and peer reviewed (as there is a considerable DARPA component).