E: Engine Comet Mongrel

[stu spalding]

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.

I don't know much about the high performance benefits of twin plugs, or the use of high tech ignition units. What I found was improved fuel consumption and a couple of mph off the minimum snatch speed in top. Twin plugs are a definite plus for regular road use. Cheers, Stu.

 

[Oldhaven]

Cyborg's mention of his ignition system prompts me to start another thread about the project I have been working on. We have been corresponding by PM for a while about it. I have been running the same optically triggered ignition he is using since mid summer on my Rapide with some success. It is adapted from a Power Arc system designed for HD . I have been working with the manufacturer to make the system more suitable for Vincents and with Bob Larmour to create a version of his housing to mount it under the mag cover. This is the same type system Old Britts sells and recommends for Nortons, and it has been succesfully used on lots of other vehicles old and new. I'll start a descriptive thread in the next day or so.

 

[Cyborg]

As you can see from the photo, the coils are reasonably small. Mine is slightly different. I can run two plugs, or if I chose to run with one, I just have to ground out one of the HT leads.

As previously mentioned I'm using a NOS Specialoid piston and rings. The rings are the ones with the beveled ends. I assume that makes no difference to the ring gap and planned on going with a gap of .0045" per inch of bore on the top ring and a tad more on the second ring. However, that works out to about .015" and the top and second ring that came with the piston already have about .025"+. Am I missing something?

 

[davidd]

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.

Unfortunately, the rules do not allow electronic ignitions that can provide different timings. I may try the Power Arc that Ron mentions, but I will have to "Pot" any mechanisms that would allow on board changes in timing. That may no be enough, but it is worth a try. I think the real value in it would be having the ability to design the initial curve to your liking.

David

 

[Bill Cannon]

When my twin was a race tuned 998, twin plugs made a huge difference to the road manners. It was much smoother at lower revs. Now with the TP heads and 1200cc still twin plug it is much harsher at low speeds. Given Davidd experience I will try considerably less advance, it is now about 30 degrees. In my professional life I have experienced many twin plugged airhead BMWs and they are much smoother and more pleasant to ride. So the real benefits of twin plugs are subjective rather than objective.
Bill

 

[timetraveller]

If retarding the ignition does not make it smoother it might be worth while checking the squish band clearance.

 

[davidd]

Stuart Hooper (World's Fastest Velo) has a 30 degree squish band on his piston, but he told me the only reason he went to twin plug was better starting.

David

 

[Cyborg]

Was it common to use more end gap with the original specialloid rings? The ones with the beveled ends. The gap on the rings that came with the piston are too wide. Even if I try rings that were labeled (assuming it's correct) .020 on the .010 over bore the gap is too wide. To get down to the .0045 per inch or a little more (Richardson says .016 to .020) I would have to use rings that were labeled .030 and file the end gaps. I know it's not a big deal to run them wider and better that than too tight, but curious as to why they are all over the spec except for the +.030 rings.

 

[Cyborg]

Final rinse before paint. When cutting the relief for the plug socket (tried to replicate the original as close as possible) I got a little bit of self excited vibration. Using a small repurposed Honda (Kowa) valve seat cutter, (just because the flutes were close to the correct shape) but a couple of revolutions by hand cleaned it up. End mill was used for the plug mating surface so turned out ok.

 

[eglijim]

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.

All I can say is when we ran two otherwise identical 1150 engines on Leon Moss's dyno (in 1998) there was little or no measureable difference in power output. The engine with twin plugs needed 5 degrees less advance than the (my) single plug engine. One of the main reasons we ran twin plugs in the racers in the early days was if one plug fouled the other should keep the pot on the boil til the end of the race. Most of this became pointless when we had pistons ,rings and valve guides which kept the oil out of the combustion chamber. A good thing as I was not looking forward to starting my road bike with the Mellor Motors centre plug mod which by repute needed 100 degrees of advance. Subjective reports from people with bored and stroked race engines suggest that the max advance can come below 25 degrees.