418cc yanclone simulations

[larkout]

With no clear light shining forward in all the talk of turbos with these little 186 type yanclones, I couldn't help but think it would be nice if we could get some kind of simulation and see some action without so much sweat (and turbo plumbing). After months of wishing, I finally was given a username and password to chat with the Wizard of Oz and on that yellow brick road I have been skipping along. Thought some of you nerds would be interested too.
I've been running all sorts of scans on some modified parameters. I know that a couple of the parameters in the program are rough (turbo dimensions, valve lift, rod length, all kinds of assumptions about port flow), but the results are close enough to the published numbers to feel like its a good baseline.
For me, the downfall of these little motors is that I would feel like a lunatic trying to get down highway 1 without holding everybody up and making a scene. So my focus is picking up a little more power at top cruising speed (2800 rpm?? why not). Other concerns are that it shouldn't smoke any more than stock, specific fuel consumption would like to be improved if possible, maximum cylinder pressure gets a veto on everything else.
(I'm not engineer, just a really big dork. I'm crap at taking notes, this is some generalizations from what were interesting differences to me.)

First thing I found is that the stock engine is pretty dang good. It seems to take a right concern for low smoke and soot. You can actually get a little better power and efficiency by decreasing compression and injection advance. Just a couple percent though, not really enough to increase top speed. Peak cylinder pressure is a little less, and a little later, max cylinder temperature goes down and the soot goes way up. It looks like around 17* injection advance is a pretty sweet spot. Should be a little quieter too?

Turbo. Now, I'm short on the whole sheet accurate details of the vz21/rhb31 so I can only imagine that the results of these simulations were a little wonky, but the numbers were far enough out to convince me. The simulation was done assuming an intercooler of constant remarkable efficiency and enviable pressure drop. 1.5 pressure ratio (about 7psi)
With stock injection advance and compression the power actually stays about the same. Fuel consumption goes way up, like %50. Temperature and peak cylinder pressure goes way up.
Increased plenums on both intake and exhaust have great effect, but not enough to dig out of the hole.
Retarded injection, decreased compression, and even an optimized cam can't really save the day. Best case I could figure with a turbo is about %12 torque increase accompanied by a %20 decrease if specific fuel consumption. This calculates LOTs of backpressure from the turbo. 3.5-4 bar. The rule of thumb I keep seeing is that 2:1 exhaust:intake pressure is about the max for a good design. This is 3+. Burnt gas backflowed into the intake is real high, near %10 (compare to less than %1 for stock). Theres lots of pumping loss into the turbine, and dilution of the intake charge we are working so hard to get.

Stock with a custom cam. Anything is possible. Try as you might I don't think you can get better than a %5 performance gain with any sort of hot rod cam. I really wanted that to not be the case. Best I could get was %3.5 increase in torque with about %3.5 increase in specific fuel consumption. This happened by increasing overlap, opening the exhaust earlier, and closing the intake a lot earlier. The big thing I saw was that closing the intake earlier damped out some backflow action due to the piston rising and starting to pump back into the intake. Interesting curves, but not quite enough to make me pick up the phone and call the grinder.

Supercharged. This is the ticket. Seriously. I had been thinking about the turbo so much that I didn't give much thought to a blower. Pressure ratio 1.5. Intercooled. Probably bogus numbers on charger specs like the turbo, but we're all doing the best we can. Stock injection and compression ratio lead to about %50 increase in torque (sort of like you might expect just thinking about volumetric efficiency). The charger eats almost a whole kilowatt. The increase in torque is after the charger is factored in. Specific fuel consumption is way down (about %13), but then even after the killowatt that the charger eats we still have a slight few percent decrease in SFC. Max cylinder pressure is up, like you might expect, more than %50 up, from around under 100 bar to over 150 bar.
In view of other trends I screwed around with decreased compression and injection advance. I stuck with CR of 18:1 (decrease by 1 point). This is corresponds to an increase in gasket thickness of .009", I don't know much about copper gasket availability but this seems like it should be a reasonable request. At least more reasonable that making a new cam. Injection looks really good in the range of 6-11* btdc. I would choose 7* if I had to. Max cylinder pressure increases linearly with the advance. Stock advance will have about 160 bar like the turbo. 7* has about 115-125 bar depending on speed.
At these parameters the program says the engine will put out almost 12 kW (about 6.5 stock). SFC is down compared to stock. Smoke is way down. Max rate of pressure rise is way down ( I assume this would have a similar decrease in knock sound)
The output is more than the multiplication by the pressure ratio. Some of the work to drive the blower is recovered in a decrease of pumping loss during intake. There is better scavenging, as well as %0 gas backflowed into the intake. The higher effective compression ratio increases in-cylinder pressure and temperature and alleviates concerns of soot. The injection timing can then be relaxed to let combustion occur at a more appropriate time concerning the crank angle. Compression pressure is up, ingnition delay is down. Combustion pressure has less ramp up before tdc and more work done while our piston is on the downstroke.
The way it seems to me, is that the stock motor uses the effect of early combustion pressure rise (increase temperature and decreased soot) at the expense of overall output to some degree.

So I wonder this: What is a safe increase in peak cylinder pressure? This seems to have the biggest bearing on the engine components (rod, headgasket, head itself...). Corky Bell makes it sound like you can turbo a car without internal mods safely to at least 7 psi, that makes me think of a %50 increase in peak cylinder pressure like some of these simulations show... How would you know?
Can you retard the injection advance all the way to 7*?

For the other dorks: Stock BMEP is about 6.6 bar. Supercharged, with 18:1 compression and retarded injection, BMEP is a little over 10 bar.

[gearhead1951]

As I posted elsewhere here , check Roger Goldammer's HD based supercharged 600 cc single for ideas on fitting the 'charger up !!

Yes an engine driven supercharger takes a certain amount of power to run , but if the net gain is greater than the loss then you are on the right track !!

[alexanderfoti]

Lots of really good information in this simulation.

The only problem, is that 12kw up from 6.5 is nearly twice the power increase, im not sure the engines could take that without destroying some bearings?

[larkout]

Corky Bell has a nice section in 'Maximum Boost' about the stress of boosting an engine. The compressive load of combustion on the piston and connecting rod are counteracted by the inertial forces of the piston accelerating toward center stroke. An increase in torque will increase the load on the connecting rod but that load will still be less that the inertial loads alone at BDC and TDC of the exhaust stroke. Inertial loads are dependent on RPM so it seems like, load wise, the way toward engine life is to keep the revs low.
There is also a point that large increases in torque in a good design will come from a mild increase in peak cylinder pressure, but that pressure will be sustained over a greater period of crank angle. When cylinder pressure in the stock design may fall to 10 bar, the supercharged version may still be at 40 bar, 400% higher. The peak pressure is only 20% greater, but the average pressure (and torque) will be doubled.
There is a nice article about crank loading here: http://www.eng.utoledo.edu/mime/faculty ... 1-0258.pdf
The crank he analyzed looks similar to the yanclones'. My conclusion is that there is about a 20% increase in critical stress from supercharging in the option I simulated. Who knows what effect that will have on the life?

[alexanderfoti]

Aha that's interesting. So a 50 percent increase in power only adds 20 percent load to the engine.

That may drive me to dig out the air pump I wanted to use as a supercharger.

[BertTrack]

Depending on the type of fuel control you have you may need to adapt the fuel pump or fuel cam for the longer injection though?