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Old 06-12-2011, 12:47 PM   #46
supershaft OP
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Quote:
Originally Posted by Lornce View Post
Gentlemen,

I've never taken an electronic bean can apart beyond prying the inspection door off and spraying the guts out with contact cleaner. Planning to dual plug the GSPD when it goes back together (using a pair of brown Dyna 1.5ohm coils because A. I have them [thanks Rapid Dog] and B. The GSPD has run for 40k miles with a 3ohm Buell coil without issue) and am wondering how to achieve the necessary advance curve to suit dual plugs. My only experience with dual plug ignition involved the pre '79-style whose exposed advance weights and springs were fairly easily modified to suit.

Can similar simple spring and post tricks be played with the advance mechanism in the bean can electronic ignition units?

My limited understanding (based solely upon what I've been told and what I observed through my arse at tracks like Grattan, where I was sure my single plug engine pulled harder at the top end, though softer off the bottom) is that the stock curve is useful from idle but needs to be contained 4 degrees or so at maximum advance.

I am at your mercy. Do your worst.

The advantages of dual plugging are really the advantages of running higher compression. It improves off cam performance and midrange the most but it surely doesn't hurt high rpm performance either. Snowbum claims that single plugs work better at high rpm and they don't. Most dual plugged race engines are not that concerned with low rpm performance. XR750 Harleys are a perfect example. Absolutely everyone has been dual plugging them for decades. Drag race engines are another perfect example.

Restrict (don't extend it like Snowbum suggests) the curve by bending the weight stops. Extending the curves rpm range is tougher because the weights still need to hit the stops but you do it the same way by removing weight and testing.
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Old 06-12-2011, 02:37 PM   #47
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Lighten up a little, Shaft. I've enjoyed reading your posts on both forums.

I agree with you regarding restricting the advance by bending the stops. I tried just retarding overall timing when I first put my RS back together, but I didn't like how it idled and started.

To me, bumping the compression and dual-plugging is a no-brainer to squeeze more power from today's alcohol fuel blends that have less energy per unit of volume.
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Old 06-12-2011, 04:13 PM   #48
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I have never found a need to twin plug, on my road or race engines, and I now have over 100bhp at the rear wheel. you need to look closer at combustion and not follow the trend like sheep.
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Old 06-12-2011, 04:19 PM   #49
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It sounds like I need to in your case DM. Thanks for the heads up! Surely you can't blame for being a bit touchy for all the crap I still get from some of that crowd.

They run so much better not timed like Oak, Snowbum, and Cutter suggests from their articles that I have read.
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Old 06-12-2011, 04:29 PM   #50
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Originally Posted by moorespeed View Post
I have never found a need to twin plug, on my road or race engines, and I now have over 100bhp at the rear wheel. you need to look closer at combustion and not follow the trend like sheep.
Now that's a loaded comment! Your bucking a lot of airhead tuners as well as tuners and designers of other engines from all across the motorsports spectrum.

Trend? How many decades does it take to not be considered a trend any more?

I would love to see it!
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Old 06-12-2011, 04:40 PM   #51
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Quote:
Originally Posted by moorespeed View Post
I have never found a need to twin plug, on my road or race engines, and I now have over 100bhp at the rear wheel. you need to look closer at combustion and not follow the trend like sheep.
Sounds like you're a devotee of Mr. Chapman.
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Old 06-12-2011, 04:55 PM   #52
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Quote:
Originally Posted by moorespeed View Post
I have never found a need to twin plug, on my road or race engines, and I now have over 100bhp at the rear wheel. you need to look closer at combustion and not follow the trend like sheep.
Mr. Moore, can you please elaborate? I'd love to hear more from a man of your experience.

To me, the dual-plugging and is an inexpensive way to increase combustion efficiency without spending huge dollars, or pounds, on a set of custom pistons. I'm working with factory BMW parts.
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Old 06-12-2011, 05:43 PM   #53
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Old 06-12-2011, 05:50 PM   #54
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Old 06-12-2011, 06:12 PM   #55
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I'm going out on a limb here and guessing that ambient temps and fuel quality are likely factors in Mr. Moore's tuning direction. Cooler temps and better fuel (in addition to Mr. Moore's attention to detail in the combustion chambers) might just negate the pressing need for dual plugs?

Anecdotal and completely accidental evidence - My bike runs fine with single plugs at comparatively high compression ratios. And it runs even better in the cooler months. I'm dual plugging in hopes of finding even higher levels of efficiency throughout the rev range. My local HP guru has been advising it for years.

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Old 06-12-2011, 08:51 PM   #56
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Please don't make me close this thread. Leave the baggage of other forums behind, please.
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Old 06-13-2011, 01:00 AM   #57
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Supershaft, can't answer your original question, however I mucked around quite a bit with spark timing when I dual plugged my 1981 R100RS (first of the bosch electronic ignition with hall effect beancan) including conducting an experiment to work out which was better: Stock beancan with timing retarded at idle or modified bean can (weights/springs & travel) with timing at idle set to around normal.

Did back to back dyno runs with both beancans. The shape of the charts were crap for other reasons but they did serve to illustrate the difference between the two timing approaches. Though not fully definitive, the test showed that leaving the timing at idle close to the stock figure and modifying the beancan to stretch the timing curve up to a maximum of 28-29 degrees resulted in a marked improvement over just retarding a stock beancan. The magic 28-29 dgrees is a number that quite e few people have independantly arrived at.

Bit off topic but folks might find it interesting.
I wrote about it in a blog including details of how I modified the beancan, too wordy to repeat here but here's the link:
http://www.cafebeemer.com.au/blog.htm

BTW, I took the advice readily found from sources already mentioned and used 2 x 0.7 ohm twin post coils in series, copper leads and 5000ohm NGK caps. The coils are PVL, which is a tried and tested brand popular in Europe and available here in Aussieland from a couple outlets. Keep in mind, this is for post 1981 bikes with the Bosch electronic ignition.
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Old 06-13-2011, 02:15 AM   #58
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I tried dual plugging but saw no benefits what so ever. I used the 6v aircraft coils supplied by Steve Scriminger http://www.scriminger.co.uk/10380/info.php?p=8&pno=0

Don't waste time messing with your bean can settings. Boyer do an ignition module replacement (with the correct curve for dual plugged airheads) and will even supply it with a pair of coils for less than $200.
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Old 06-13-2011, 03:21 AM   #59
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Originally Posted by Rob Farmer View Post
Don't waste time messing with your bean can settings. Boyer do an ignition module replacement (with the correct curve for dual plugged airheads)....
As do Silent Hektic, Omega, Dignition - All of whom offer a range of curves to choose from. But thats all too easy! What's left for us incurable fiddlers to fiddle with? Ok..don't answer that..

Actually, the beancan mods are pretty straight forward if you have an ounce of mechanical nouse. Cheap fun for this little black beemernerd.

Interesting link BTW
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adrenal screwed with this post 06-13-2011 at 03:35 AM
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Old 06-13-2011, 03:30 AM   #60
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Quote:
Originally Posted by Jasper ST4 View Post
What Craig explained to me was that the combustion chambers were redesigned for the gas and running the unleaded stuff in the earlier engines were the ones benefiting from dual plugs.
The valve seats were changed for unleaded then changed again by the time it got to your model.
The combustion chamber shape is AFAIK identical to other models.
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