[cforcht]

typically dynos use some sort of drum. matched to certain a degree of the expected hp of what you're testing. the engine or car is hooked to it in one form or another. the engine or car turns the drum from one given rpm to another in X amount of time. using the formula which I have no idea what it is. but Im sure Dyno would. you can calculate the hp it took to get the drum from one rpm to another in the given time. i think you can calculate the torque with this too. but the formula differs. of course Im not engineer so don't take my word for it. but thats what little I recall from looking into this subject once long ago.

Steve,
I have seen the type of advance you are talking about. as I recall it was not fancy or pretty but it was functional. I was thinking something more akin the the chevy vacuum advance found on their older distributors. wouldnt be hard to make. I would make it so you could adjust the max advance it would give you. via a set screw to limit the travel of the advance plate which would have the hall sensor attached to it under the flying magnet disk.

[cforcht]

you know. for that matter the ignition on this engine could actually be a true automotive ignition if you wanted. take the mallory unilite for instance. it uses an infrared emitter/detector to trigger the coil. it "looks" thru a slot in a disk that the distributor shaft rotates. one slot per cylinder. when the emitter and detector "see" each other it fires the coil. probably produce a much hotter spark than the WYSIWYG ignition. don't know why I didn't think of that before.

of course the hotter spark might eat the spark plugs faster too.

[dynosor]

LOL I knew you would chime in here somewhere. I thought you were working.

Yes, but I just could not resist taking a look to see what was going on here...

[cforcht]

thats ok. somebody has to be in charge of the reality check. I vote we nominate you. since you have more engineering back ground than us shade tree mechanics.

[dynosor]

does anyone have a mini dyno or know how to make one?

The simplest yardstick for power is an RC boat or aircraft propeller of specific size and pitch. If a 5 hp OS model engine can swing a given prop at its power peak RPM, and your V8 can match that, then the V8 is reasonably putting out 5 hp at that RPM. Obviously the boat prop goes in the water and the aircraft prop spins in the air.

Don't choose a prop that is too large in diameter and make sure it is well balanced or it may kill your engine bearings.

However, spinning a prop tells you nothing about the torque available in the rest of the rev range. If you want to know that, couple your V8 to a DC motor rated to at least the equivalent power range you think the V8 will produce. Use the DC motor as a generator and vary its load with variable resistances. You may need to cool the resitors or DC motor if you run long enough.

The volts and amps produced at any given setting represent the engine power less conversion efficiency: If such a DC motor is 90% efficient, then multiply the volt X amps by 10/9...

Another easy method is to monitor engine revs when you open the throttle wide against the flywheel inertia only - you can calculate torque and power from this, but you may need a heavier flywheel and rev limiter to reduce the risk of over revving...

[cforcht]

see, I knew mister wizard would have an answer. maybe you should change your screen name to MR. WIZARD. of course all caps would be required.

[cforcht]

just checked that name is available.

[dynosor]

somebody has to be in charge...

From my vantage point, the person cutting metal is always in charge.

I am just a wiseguy with a hyper-active idea generator - you are always in charge of determining if my proposals have any merit.


Neither education nor rank is a measure of a person’s intellectual or practical usefulness. Can you apply facts and logic to move towards a solution? If yes, then you have all you need.

I don’t know everything, but I don’t have to know everything to be effective as an individual. What is essential is that I have a crisp sense of where my knowledge on a particular subject ends and where the next person’s knowledge begins.


I don't think you can change your screen name - I have had this ID since 1996, so I am kinda attached to it. Thanks for the thought anyway.

[cforcht]

LOL I was just kidding. I didn't expect you to change your name.

as for being in charge. I said you were in charge of the reality check. you didn't quote the entire phrase. meaning when we decide this is going to make this much HP or torque or whatever. because we are comparing it to this or that. its your job to point out the small but ever important details of the equation we are overlooking. which in turn brings us back to reality. and of course the occasional self slap on the forehead for being so dumb at overlooking said details.

when it comes to me machining parts. you are correct, I am in charge. In fact I would be hard pressed to do it someone elses way without a really good presentation as to why their way is better. and like so many times I have done before. I will go out of my way to prove them wrong. at this point I have failed in doing this only once. Because of this nature in me it has earned a certain respect from a former employer which I still do business with. when he has something that seems near impossible he calls me.

That is not to say I will not listen to ideas. in fact I am always open to ideas. just don't tell me I'm doing it wrong without anything to back it up.

[dynosor]

So given the lack of data as to volumetric efficiency, etc and considering the supercharger and larger valves, do you think Craig's expectation of 9hp is realistic?

To answer that question I collected the displacement & power @ RPM specs for a number of 4-stroke OS commercial engines. Three engines were single cylinder models and one was a boxer four. I calculated the ratio of peak power to displacement X peak power RPM.

This ratio is a reflection of volumetric efficiency, combined with mechanical efficiency and thermal efficiency - all run on nitro-methane fuel.

If I converted Craig's 92 CC to 5.614 cubic inches correctly and assume that peak power is at 8000 RPM, then based on the average power to displacement x RPM ratios of the OS engines, Craig’s V8 could produce 7 hp without a supercharger.

To reach 9 hp at 8000 RPM the supercharger would have to boosts airflow by almost 30% - not impossible if the blower is geared right. In any event, the blower will have to make up for the low nominal compression ratio or thermal efficiency will suffer - I believe Craig has already made cylinder heads with the larger combustion chamber option?

This is without taking into account the good friction properties of the OS ball race main bearings and the possible difference in fuel energy content and effective octane.

Another difference is that the OS engines have glow ignition. I suspect that the V8 has the advantage with spark ignition, as it should allow more aggressive spark advance without detonation.

[cforcht]

before I read your post any further I have to say that the 9hp figure was based on harleys prediction of .098 hp per cc. I dont expect to get 9HP what i was saying was based on his figures that is where mine should end up.

[cforcht]

ok now I have read the entire post. for the record. I do not expect anything in hp figures. it is what it is. not to mention I have no practical way of testing is so what's the point in hoping for a specific hp when I can't tell if we've arrived there.

my goal is not to make a certain amount of hp or attain a certain rpm. its to make a running engine utilizing the manufacturing processes I know and have access to. and make it the best engine that my meager skills allow. I will be happy if it runs without any great deal of going back and doing something over again. if it cant power a boat then so be it. it will be a shelf model. the machining alone warrants a place on the shelf. or I think so anyway. if it blows up beyond repair it will become a static model.

now onto the other points in Dyno's post. keep in mind, my engine is running or going to run full bearings on everything except the rockers. so the OS really has no advantage there other than fewer moving parts. but mine has 8 power strokes even if its 4 stroke vs 2 stroke. so wer at a 2:1 ratio on that. my heads do have the combustion chambers cut but they are not to print. i am somewhere in the middle between the low compression and high compression versions. and if I needed I could up the compression in a few different ways. domed pistons, shave the deck of the block, plane the heads, or reduce the gasket material thickness. all of which would raise the compression ratio. yes any number of them would require cutting the pistons for valve relief. which may be needed anyway since I increased the valve diameter.

[TarHeelTom]

Not sure what the percentage of airflow increase is, but the air racers at Reno are running their WWII engines at around 120" MAP, or about three atmospheres more than a normally aspirated engine. Have no idea how many hp they're pumping out.

Typically those engines are run with water injection into the intake manifold for cooling.

The flip side is that the TBO, or time between overhauls, seems to be around 10 minutes on those engines. And of course, the race duration is around 10 minutes per heat.

I believe they get those boost pressures by raising the gear ratio on the centrifugal superchargers.

Tom

To reach 9 hp at 8000 RPM the supercharger would have to boosts airflow by almost 30% - not impossible if the blower is geared right. In any event, the blower will have to make up for the low nominal compression ratio or thermal efficiency will suffer - I believe Craig has already made cylinder heads with the larger combustion chamber option?

[cforcht]

typically a supercharged engine is running higher than atmospheric pressure. a normally aspirated engine can never achieve more than atmospheric pressure without something to cram more air into it. the water injection serves more than one purpose if memory serves me. it does raise compression slightly it also helps reduce the tendency for engine knock. as for cooling I don't know if it helps there or not.

[FannBlade]

heads do have the combustion chambers cut but they are not to print. i am somewhere in the middle between the low compression and high compression versions.

How are you calculating head (combustion chamber) design and compression ratio. Have you thought of making a single cylinder test center to run different combination of head designs.

[dynosor]

I do not expect anything in hp figures.

Craig, I think your philosophy towards engine power is spot on correct - exact numbers are irrelevant and there is no failure threshold. If it were my project, I would be very happy if the engine made the boat move at a speed fast enough to be fun – I am very confident that you are going to achieve this.

My power prediction for your engine was specifically requested by Harley 573. It was not intended as criticism of anything you are doing. If I had answered his question with "yes" or "no", the next logical question would have been ”why do you think that"?

You are right that there are many things you could do to raise the compression ratio, if you had evidence it needed to be done. From my perspective, a lower nominal CR is appropriate to a supercharged engine because it allows more boost before reaching the fuel's knock limits.

By the way, the OS engines I looked at were all 4 stroke, as stated in my post...

[TarHeelTom]

typically a supercharged engine is running higher than atmospheric pressure. a normally aspirated engine can never achieve more than atmospheric pressure without something to cram more air into it. the water injection serves more than one purpose if memory serves me. it does raise compression slightly it also helps reduce the tendency for engine knock. as for cooling I don't know if it helps there or not.

I may have misspoken. I was thinking that it helps cool the top of the piston and perhaps the head, and certainly it ends up reducing the tendency for engine knock.

I've read and heard many different (and conflicting) theories of how it does that, and why it's used. Of course, in transport aircraft, we mix the water half and half with alcohol. The alcohol is there strickly as an anti-freeze.

Regardless of why the water is there, I was simply pointing out that there are some engines being run at 4 atmospheres of manifold pressure. Wasn't intending to open Pandora's box.

Also wasn't suggesting that you should be doing this.

Tom

[cforcht]

nah I wasn't reading anything into it. and yes I have heard many reasons as to why you inject water. some are plausible some are not. I have no experience with aircraft and the engines they use. but I wouldn't be surprised by the amount of boost their wringing out of the super chargers in the reno racers. the normal blower on cars is usually a 6-71 or 8-71. they are set up in most cases to produce 10-12 psi of boost. but the top fuel guys are running 12-71 or 14-71 blowers. they line the rotor edges with teflon so there is zero gap. there is no air loss in the blower at all. everything that goes in gets pushed into the engine. but there is a price for this kind of super tight blower. it takes about 500hp just to pull the blower.

[dynosor]

My understanding is that water injection allows higher effective compression (static CR + boost) without knock. It achieves this by cooling the mixture to below the self-ignition threshold temperature - the heat required to evaporate water into a compressible gas (steam) is significant, so very little water makes an effective combustion chamber coolant.

The water vapor then forms part of the "working fluid" that drives the pistons down.

This cooling effect is used all the time at wide open throttle in gas engines when the mixture is run rich as a form of cooling. This allows more spark advance to be used without knock, producing more torque and power. Now there are limits to how rich an air/fuel mixture can be made before you "drown the flame", hence injection of a fluid with a high heat of evaporation that does not take part in combustion: water.


Definition of working fluid:
Working fluid - Wikipedia, the free encyclopedia

Thermodynamics eBook: Otto Cycle

[TarHeelTom]

nah I wasn't reading anything into it. and yes I have heard many reasons as to why you inject water. some are plausible some are not. I have no experience with aircraft and the engines they use. but I wouldn't be surprised by the amount of boost their wringing out of the super chargers in the reno racers. the normal blower on cars is usually a 6-71 or 8-71. they are set up in most cases to produce 10-12 psi of boost. but the top fuel guys are running 12-71 or 14-71 blowers. they line the rotor edges with teflon so there is zero gap. there is no air loss in the blower at all. everything that goes in gets pushed into the engine. but there is a price for this kind of super tight blower. it takes about 500hp just to pull the blower.

I agree. Of course it won't work on a dragster, but a turbocharger uses a lot less power to run. On aircraft, tc's seem to need a lot more maintenance than superchargers. Of course, a gear driven centrifugal supercharger is a pretty simple thing, at least in operation.

Some of them even had a gear shift lever, to change to a higher gear ratio for higher altitudes, but these didn't last long. Were first disabled, later removed.

On the other hand, a big Pratt & Whitney PT-6 engines make the same power with a lot fewer parts, a lot less vibration, a lot less noise, and only one or two sparkplugs.

Tom