Dyno Day- some followup

[wayne]

My good running red showed very rich initial running and overall too rich. I was reluctant to go too lean as I'm getting the impression that rotaries are tuned rich.

However, my red can be sluggish around 3800 rpm in top gear. You'll only feel it opening the throttle on a decent up slope and then it can be slow to respond. This is not the usual flat spot, hesitation, it's a power thing.

The dyno revealed a significant flat spot in power delivery that would approximate to this seat of the pants feeling.

So I kept the PMJ at stock 87.5 but dropped the SMJ by one size to a 177.5. This made a noticeable and significant difference to top gear acceleration where the bike had been previously sluggish. It was brisk to pull away, even up a hill. I rode around 380 klm like this.

But the bike didn't like it. No hesitation or anything like that, it just wasn't happy. It didn't like cruising at any steady rpm and was just "off" (although it did return nearly 46 mpIg on what was an average ride. Not fast but not a lazy ride (rained pretty much the whole way).

I'm going back to the stock 180. I'd rather a happy overrall bike for the minor inconvenience noted.

But I am noticing this across our five regular runners. The happy RE5's are the overall rich runners no matter what the stoichiometrics say. And note that the two best runners showed rich on the dyno using stock 87.5/180 jets. The M/A hybrid bike in our group can be tuned hesitation free but is just an unhappy runner. On the dyno and with the big PMJ it was the second leanest of the five tested RE's (I didn't put this chart up).

Similarly I recently fixed the hesitation in my A model and returned to an early spec stock 90 jet. No hesitation whatsoever but a cranky unhappy bike. This bike was the leanest runner by far and even lean by four stroke standards. I put in a 95 jet and it became a much nicer bike to ride (before fixing the hesitation it needed a minimum of a 100 jet to run hesitation free). I am going to also up the SMJ to 185 only to return the temperatures to the left side of the gauge middle mark.

Whether the whole fuel/air thing is correct or not, it seems that the leaner the bike and independent of hesitations, the crankier it is.

[riversidogs]

I do not know what the fuel is like in your part of the world but here in the states they add Ethanol to the fuel and it varies depending on the time of year and area of the country. The reason I mention this is I assume this is done without concern because the majority of engines now are computer controlled and can adjust the mixture as fuel changes. The problem comes up when the engine like ours do nor operate in closed loop. When the fuel changes the mixture changes. There are a few stations here that sell fuel without Ethanol. I use this fuel in my bike and it seems to work better.

Riversidogs

[wayne]

Thanks for that. Fortunately, only our 91 octane is mandated to have ethanol. Some stations still have straight 91 but I've given up as it can be too hard to find. I've never put ethanol fuel in the old bikes.

You can get 95 without ethanol pretty easily so that's what I use. It gives better economy than pure 91. Our 98 seems to give no advantage for the extra money (in the RE5) so I don't bother with it.

All the testing I do is on 95 fuel.

[ap951]

It's been my understanding (please correct me if I'm wrong) that higher octane fuel has a slower burn rate. Performance is gained by the slower explosion pushing down on the piston for the entire power (down) stroke. Because of this slower rate high octane fuel needs high compression to fully detonate. I buy my gas at the airport, (101 octane blue aviation fuel) mainly becuase it conforms to strict regulation that it cannot go bad. (this has saved me from rebuilding carbs on bikes that have sat for more then a year & it keeps the tank clean) I found out that runnig 101 octane in my very low compression GT750 does not work well at all. The idle is uneven and acceleration is rough. However when I run 85 octane (the lowest octane that I can find) the bike runs beautifully. I think because the fuel is fully detonating & with a faster explosion. It makes complete sense to me that Wayne would have diminishing returns with higher octane fuel. The RE5 has the compression to utilise 95 octane but not the 98

Bill

[wayne]

Indeed Bill, I fully agree. I think that people waste their money on higher octane fuel thinking that it will give them more power or better economy in low performance engines. No. You need the correct compression ratio to make it work.

Back in the day we used to run our bikes on the old Aussie "Super" grade thinking it was better for the bikes. I remember being unable to get it and using "Regular" (about 88 octane) in my GT380. Blow me down, it started first kick when cold and just ran better. I learned a lesson.

I have said in another post that I don't find 98 more economical in my RE5 and in fact have a seat-of-the-pants feeling that it actually runs worse ! Your information possibly backs that up.

Getting back to average Joe and his car/bike, English motoring show Fifth gear (not Top Gear) ran a test on 3 types of cars- small commuter, slightly sporty and performance using different fuels. They reset the ECU between each test. The lower compression commuter didn't benefit one bit in horsepower from the expensiver higher octane fuels but the sporty did a little bit (5hp) but the performance car (Subaru) got a whopping 23 hp improvement. For a low compression low performance vehicle, high octane is money down the exhaust pipe.

And just an aside to my original post- went back to the stock 180 SMJ on my red rider and did 280 klm- back to the sweet running bike it was. They don't like lean.

[riversidogs]

Octane, I was taught, is a measure of the temperature that the fuel will self ignite. This is to prevent the fuel in another part of the chamber to start burning and collide with the primary flame front and causing detonation (knocking). Detonation can have harmful effects on engines for example holes in pistons. Modern engines have sensors on the block to sense detonation and then the computer will retard the timing. This causes the detonation to stop but reduces MPG and power. I had one engine in a van that went from 15 MPG to 20 MPG by just going up one grade.
One of the problems we may have in our bikes is that the rotary engine has a very long chamber at TDC. Higher octane fuels may go out if the heat drops too much to complete the burn to the end of the chamber. The reverse of Detonation. There are people that add hydrogen to the intake mixture to get the fuel to burn closer to the chamber wall and increase efficiency.

Riversidogs

[ap951]

Wayne - I'm always amazed at how similar your experiences are to my own

Thank you riverside dog, compression does cause heat & what you say makes sense. I remember reading that during WWII England was way ahead of the rest of the world when it came to refining fuel. This allowed them to run higher compression in their fighter aircraft & when they started supercharging they could run higher boost pressures without the problems of pre-ignition.

I live in Denver Colorado, "The Mile High City" and at this altitude the compression is down on everything including my RE5