I hear what you say Tim, but to my mind, less advance equates to less stress on the bottom-end.
Peter B
E: Engine Comet Mongrel
- Thread starter Cyborg
- Start date
I hear what you say Tim, but to my mind, less advance equates to less stress on the bottom-end.
Peter B
That Comet big end is one of the strongest in its class and since I am aiming at around 8:1 so it should be flexible and stress free the 2020 is soon a to be a complete bike waiting its new front end, as to its top speed:
What did Bob Mac say in his interview on Stanley Scholfields TT record ahen asked the top speed of his bike?
"Ah top speed is no a concern of mine..."
What did Bob Mac say in his interview on Stanley Scholfields TT record ahen asked the top speed of his bike?
"Ah top speed is no a concern of mine..."
That's one of the two reasons why I said "debating about the twin plug head". When I purchased the ignition system, I ended up speaking with the fellow who developed it. We didn't get into a long conversation about twin plugs, but it was clear he believed there was no advantage. The system fires 3 times and he said it is quite happy with low grade fuel. He had some interesting points of view, but thought there was something wrong with me when I said I wasn't a fan of ethanol in our fuel.
It has been used on production motorcycles, but doesn't seem all that common. Ducati added it to their Multistrada and claimed improved fuel consumption and +5% in torque and Honda used it on some of their VT's which were not exactly performance oriented. It would be interesting to see the difference on a modern dyno with a standard head and then with something like a TP head etc.
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I am 100 % sure that the extra power from a TPV head comes from the much improved design of the combustion chamber and the squish band piston used with higher compression.
I am also sure that he spent a lot of time making sure his head flows well.
Bernd
I am also sure that he spent a lot of time making sure his head flows well.
Bernd
No doubt about that. What I wrote wasn't clear... what I meant was.... Running both heads on one plug and then two plugs just to get a read on the exact difference the second plug makes. That is what I would be interested in seeing, especially with the ignition system that I'm using. Ain't going to happen, I'm just sitting here consuming caffeine so I can head downstairs and gap those funny looking Specialloid rings.
If and when you do the tests it would be good to know what ignition timing gives the best results with each configuration.
I was hoping that someone like you could tell me. I have the software and just ordered up the doodad that allows me to change the maps. At this point in my life I have no inclination to spend the time or money on a dyno, at least not with this engine.... and IMHO using ones posterior to measure such things is extremely misleading. Wish I could help you out, but unless an engine dyno falls into my lap, the chances are slim. If I find anything in my search that is backed up by good data, I'll pass it along.
It is very difficult to adjust the timing for best power without a dyno. Even with a dyno, it may require hours of runs. I got to 19 degrees before I had run out of slot on the BTH and with the other adjustments I was at the end of a full day. I was still gaining power as I got to 19.
The more advanced the ignition, the less compression you are utilizing as max compression happens at TDC. Effectively, your ignition is sparking and slowing down the piston as it is trying to compress the charge. This bang as the piston is rising can be very hard on the big end.
It is probably best to measure this gain in reliability rather than power. But, the twin plugs with their retarded firing is quite efficient and not prone to detonation. That seems to be what the tuners want.
David
The more advanced the ignition, the less compression you are utilizing as max compression happens at TDC. Effectively, your ignition is sparking and slowing down the piston as it is trying to compress the charge. This bang as the piston is rising can be very hard on the big end.
It is probably best to measure this gain in reliability rather than power. But, the twin plugs with their retarded firing is quite efficient and not prone to detonation. That seems to be what the tuners want.
David
Sounds like you should try an ignition system similar to mine. (although I haven't run it yet) You never run out of slot. It is just set it to TDC. You can enter 4 different maps and toggle back and forth between them with switches. You could quickly run 4 different setups and quickly load 4 different ones (with the ability to create your own curve) from a laptop if required. If nothing else, it would really cut down on dyno time and as an added plus, you can set the rev limiter wherever you want.
Sorry Cyborg but all I can give you are approximate figures and you can choose which you think might be useful. One racing engine I have helped with has squish bands, twin plugs, Terry Prince heads and is about 1,200 cc. With all that a figure near to David's of 18 -19 BTDC seemed about right. Without the Squish bands then 21 - 24 would be about right but you have to experiment with your own riding style, fuel etc. With single plugs and no squish band, but using modern fuel, then rather than the original 39 you need something like 36 so you can see what a difference the twin plugs make. The late Phil Primmer told me that he had used twin plugs on his road going outfit on a run from the UK to the South of France and he believed that he got more miles per gallon. Problem is, I have found French fuel better in diesel cars than the UK equivalent so whether this also applies to petrol I don't know. Also Phil had other mods like a tube connecting his two carburettor manifolds.