twin plugging an air head BMW
 

Has anyone out there had an air head bm that has been twin plugged, if so, how did it improve the bike from the stock single plug head ???

I was a bit disappointed, after having my R80GS twinplugged. I thought that this would improve (reduce) the fuel consumption, but there was hardly any difference, although I also had the cylinder head smoothed out on the inside, to get the sharp edges away.

It starts better, runs a little smoother. Thats it. Although, for the 100GS it should make more of a difference. The R80 runs smoother than the R100 before any changes done. The effect is said to be much greater on the 1000cc engine.

Hans

Tom Cutter has written the book on this topic. Contact him at:
http://www.rubberchickenracinggarage.com/

Also see:
http://www.airheads.org/content/view/281/98/

www.airheads.org is the only resource you need for airhead stuff... Unless you speak German, then there are a few others out there.

Kevin

------------------
Kevin

http://www.nohorizons.net

I twin plugged my R100GS (Canadian model, 40mm carbs). I was told to expect an increase to power (5-10%), a reduction in fuel use (5-10%), smoother running, and less or no 'pinging' on <92 octane fuel.

I can say that the pinging on 89/87 octane fuel was reduced to the point where it wasn't a problem. Maybe a slight increase to power, Maybe a slight reduction to fuel economy, but nothing I could clearly measure. I'd do it again, but wouldn't consider it necessary unless you expect a steady diet of <91 octane fuel.

I had the following mods done on my "89R100: 32mm heads dual plugged, polished intakes. Dyna coils. The result was sharper acceleration, with minor inrease in power and fuel consumption. Motor has to be timed -2 to -3 degrees, i can't remember which. I only burn the cheepest gas, so far i've been happy with the performance, no problems. The bike is also easier to start when cold.

the main improovement i found with my 100 was it now starts easy peasy on the kick. also added the black box from a kickstart model which also helps.

Been running twinn plugged since about 1992.
This summer/fall is the first time I ever have had it running well... 16 years of hassle and head-ache!
I've run 800cc 8.2:1, 9.2:1, 10.3:1 32mm carbs, 40mm carbs, different air-intakes, different exhausts, jetting laborations, etc and so on...

IF you are to go twinn plugged - be prepared to read-up first(!), then be prepared to get a lot of flack.

The difference is 1 gearshift at 2000-2500rpm, better and easier cold starting, better burn, slightly lower mileage (some claim more - I have not experience that on my bikes).
Would I twinn-plugg my next air-head ? YES!

What made my air-head work as it is supposed to after 16 years of testing, reading, etc ?
This did:
Daniel Dicke: Doppelzündung
http://www.derdicke.de/mot/img/doppelzdg.jpg
This German recommendation is strickly contrary to Tom Cutter, Oak Oshlen, SnowBums writings. I have NO explanation for this. I can only say that on my R80 this did the trick.

Mileage increase on R60/6
 

For what it's worth, I had my 1975 R60/6 dual plugged last winter and put about 13,000 miles on it this summer. My main motivation was to help reduce pinging, particularly as I plan on taking it through central Asia next year. I kept track of mileage both before and after and have had a 3.8 mpg increase on average. I did some other things as well and so admittedly, as an experiment, the variables have not been well controlled. I did reset carb pins to a leaner setting when at higher elevations throughout the summer and switched back from electronic ignition to points at the same time as the dual plugging.

Was it worth it? I think so. It certainly has made a huge difference in the pinging, I think I have more power (hard to say) and there seems to be an overall increase in mileage. It is interesting in that after doing a bit of rough road riding, I notice that it was vibrating and running overall crappy. A little investigation showed that the bottom left wire had been snagged and pulled off the plug. Put the wire back on and back to smooth... so yes, there must be a power difference between single and dual plugging. But maybe not much.

Oh yeah... and be prepared to take crap from those who haven't done it.

BMW themselves released the cure for pinging, cylinder base gaskets at about £7 each.
I have asked on the BMW forums, and no one has answered. Why do BMW's need dual plugging? Other air cooled bikes seem to manage fine without. It does allow later ignition timing, but I sometimes wonder if the timing was retarded without dual plugging wouldn't it still allow the engine to run smoother. It seems to me abit like the big bore kits. The extra CC's produce less power than the original cc's.. IE 20% increase in swept volume=15% increase in 'claimed' power. Mostly things claime dby people who do teh conversion come down to it 'feels like' so and so is better. I can positively state here, every time I clean my bike it feels like it is 5mph faster in all gears, and runs smoother. Very rarely do you get a catagoric measured difference. If you dont belive me try for your self. clean your bike , check the oil and air pressures and ride, It will feel better.
As an aside, on top gear they did a test recently and spent £15K adding go faster bits to a car. The road test speed increase was barely measurable. The most effective thing was doing a standard service.

:thumbup1:excellent couldnt agree more, add in a sunny day and smooth road.............:mchappy:

Who need dual plugging?
 

I guess the general consensus is that not all airheads need dual plugging. Not sure that anyone ever said that they did. Mid-late 70's high-compression models are the only ones I know that really benefit from it. They don't do well on swill, and often ping on even Chevron Superduper when under load. Dual plugging helps there. The thicker base gaskets lower the compression but can also lead to lower combustion temperatures, increased carbon, pre-ignition and eventually higher compression and here we go again.

When looking for a bike for my trip, I was trying to avoid one with a high-compression engine, but got swayed by the other good characteristics of the /6's. I figured that dual-plugging needed to be worked into the cost of the bike. And pinging my way all the way up the hill to my house on it's maiden run was just as expected. Had it dual plugged and now it's quiet even on regular. :thumbup1:

That's all I know. Don't know about big bore kits or 15k go-faster kits.

The Egyptian Police commissioned a special edition of the R80. 800cc barrels with 1000cc 44/40 heads and 40mm Bing carbs.
This should result in about 7.0:1.
This edition was only made for and sold to the Egytian Police.

To get the best mileage L/dollar one needs to raise the compression ratio.

The plug is places off set in the beemer and VW air-cooled heads. Krauser 4-valve heads have the plug placed at the center which is the best position.

The 1200 oil-heads have 11:1 and dual plugs...

Recomended reading:
* 4-stroke performance tuning, Graham Bell, Haynes Books
* Internal Combustion Engine Fundamental, Prof Heywood, MIT.
* Oak Oshlen - Dual Plugging
* Tom ... ABC home-site - Dual Plugging
* Snowbum - Dual Plugging
* Daniel Derdicke - Dual Plugging
* Technik BMW 2-Ventiler
etc
Then test a dual-plugg vs a single plugged; do not guess - test and try for yourself before you decide what you think about 4 vs 2 plugs on the 2-valves.

As far as I know there are no available Dyno Tests on signle vs dual plugged 2-vales. All I have found is one (1) test, and that was on a Duccati by an American motorcycleshop.

A co-worker dual plugged his old R100 RS (maybe he bought it that way). He didn't comment on any power increase, but he was very happy with the extra 10 MPG increase.

You can't just dual plug and ride off. You then need to reset the idle ignition timing and limit the amount of ignition advance.

I am curious, How did he know he had a 10 mpg improvement if he bought the bike dual plugged?

If you spend the same amount of time doing a normal service ( include diaphragms, needles and needle jets I believe you will get the same or better results. Running a low compression will reduce the mpg slightly, but early post war 1945-50 Triumphs had 7:1 and would run happily on 'pool pertrol' ( 65 octane). One of the reasons I chose my BMW was because that model was designed fo modern fuel and has an 8,2 CR. It runs absolutely fine on 3 star. It has been stated that the pre monolever bikes with high compression engines are the ones with the problem. To fix the compression ratio ( poor modern fuel) problem lower the compression ratio with BMW's own fix at £7 a go. Spend the rest on petrol and beer. Only BMW's seem to suffer, no other biking forum I am on mentions it. I think in part it is caused bytheir use of a wasted spark which heats up the plugs more than a non wasted spark system.

You are so right in posing this question. I have been looking into dual plugging since about 1992. I have still to find even one correctly done "study"...

When I changed from Bing 40 (worn) to dell'orto PHM 40 (new) mileage dropped from about 6.5L/100km to about 5.6L/100km. The dell'ortos are tuned for 8.2:1 single plugged heads and were used with dual-plugged heads with 10.5:1 (venolia pistons) 45/40 highflow valves... my plugs were quite black... so mileage will be much better when the carbs are properly tuned.
BUT - as you point out; not even I have tested to run my engines with single properly tuned and then retuned to the dual-plugged heads.
The only "testing" I have done was back in 1992/93 when I did not have the dual-pluggin set-up - my bike consumed about 6.7-7.0L/100km and dropped to about 6.5-6.3L/100km when the second plug was activated. Coincidens ?... The bike have been running really hot causing lots of overhauls and repairs since 1992 - up till this very summer, 2008, when I fiddled with the ITU in accordance to Derdickes homesite/tips - now it is running well, but mileage is still at 6.4L/100km or so (and topping 6.7 or there about now at winter with the studded tires).

Summation:
- I agree. On what does these milage claims rest ? Service, wishfull thinking or facts ?
- If there are solid facts; please do present them -:)
- My view on dual-pluggin does however remain as solid as ever; I'm for it -;)

Maybe he did and maybe he didn't buy it dual plugged. Or he may have had an identical bike previous to that one to compare it to. Its been quite a few years. I know him and trust his numbers...we work in a test lab so he is quite analytical.

I do remember going over the timing and advance issues with him over coffee in the cafeteria.

Fact is, if the burn is incomplete, you are wasting gas...less power...less MPGs. And when you have a large diameter piston coupled with certain shaped combustion chambers, you will probably not get a complete burn. So you have two spark plugs to initiate two flame fronts. That speeds up the combustion process which is why you need to alter the idle timing and advance.

Ever wonder why the RPM decreases by about 150 RPM in a piston engined aircraft when you switch the magnetos from BOTH to L or R during your pre-takeoff checks?

IMHO the discussion shows again that this is a "nice to have" but not necessary in absolute terms.

The Dakar HPN Beemers in the '80s were not dual-plugged, had a higher compression and more cc (1040) compared to the standard Beemers and still performed excellent.

IMO the main advantage is that the engine definitely runs smoother, resulting in longer engine life, less vibs - esp. at lower revs. I found the change in fuel consumption to be negligible. Power gain ????? Maybe, but from nominal 50 hp to maybe 52 - also negligible.....

I think there are multiple reasons why people have various experiences with dual plugging. The technical differences can be:

• Modifications of top (squish-band, porting, polishing ++)
• Type of heads (valve size etc)
• Type of petrol used
• Type of carburetors used
• Setup and state of carburetors
• Type of exhaust/air filter
• Compression
• Types of pistons
• Ignition timing (static firing point, firing-curve, coils etc)
• Driving style
• ++++

When people change to dual-plugging they often change some of the other factors, maybe they “only” overhaul the carbs which often gives great improvement. Maybe some modifications where done to the bike prior to the rebuild, maybe the cleaning of the tops alone has changed the way the bike worked.

It’s true that the old Paris Dakar bikes didn’t use dual plugging; the compression for some of the years was like this:

1980 9.3:1, 798cc, 55hp, HPN
1985 8.5:1, 980cc, 70hp, HPN
1987 9.0:1. 1050, 85hp, HPN
But what type of petrol did they use? What other modifications were done to the engine?

Today HPN recommends the use of dual-plugging, at least with high compression engines, but dual plugging is only one of the factors which are changed. These engines also have different camshafts, different pistons, rebuild heads and a completely different ignition-system and a few other changes.

Personally I believe in dual-plugging, but I think that if you want a good result you have to change a lot of other factors.
So I haven’t done it and there are a lot of things I would like to change with my engine before I do, it will probably never happen.

There is one part of dual pluggin that I have been utterly unable to solve - timing.

When looking at physics it is quite clear that there will be about a 40% faster burning, and hence slightly more efficient burning of the mixture. The slightly more efficient burning is what has been attributed to as the major factor of the better mileage - but I see no published testes confirming this statement.
As for timing, it should be adjusted accordingly to the faster burn; 6' at idle should thus be set at 4' which would equate about 4mm on the flywheel if I recall correctly. Al "gurus" claim that timing is best at OT, which is about 12mm from the flywheels idle adjustment point. However, with a 32' max advance (is that figure correct? I have not been able to find it in any BMW litterature) a 40% change of the advance should result in about 19'; a difference of 13' and each degree is about 1.78mm which is about 23mm...
To reset the timing with 23mm at idle is not possible...
So... this pre-ignition by about 13' is probably what has caused the "overheating" of my engine since 1992 uptill this summer 2008 when I blocked the flyweights to about 19'. I have reset the idel to about 1' less, and that seems to be the best position on this very engine.

There is one interesting thing that I have come across and that is that most (all?) that claim OT to be ok are riding brakerpointed engines... a friend of mine uses Boyer Bransden replacement kit for brakerpoints and claims that that is working perfectly. What about the 1981 and on engines ? Mine are not working well at all with the OT setting - but run well with the flyweight stops... any idea as to this difference ?
Silent Hektik and Omega Ignitions would probably present the needed timing curves to get the dual plugging perfect.

There are so many claims - and so scarse hard data; what are we to believe ?

One indisputabel fact is that the 1200CC's have dual-plugging due to the hard California emission regulations - and those of us using dual-plugged 2-valves probably have the same comment on how the exhaust fumes smells with and without the second plug operating ?
:scooter:

I had my 83 R100RT dual plugged by Ray Peake (RJ's) in Australia. He has done many of these conversions on old boxers over here. I think it has definately helped with starting the bike, and stopped a lot of the pinging that I got when they stopped selling leaded petrol over here. I used to get around 320-350 a tank (24,litres) I now get 350-390, even up to 400 depending on the speed I ride at. It did not cost me a lot to get it done, ( I had to get the heads done anyway) so it was an easy choice for me, just do it! I definately think the old boxers benefit from it if the person who dose the conversion knows what they are doing.
Rob...

As my r80gs (60000 miles) is now used mainly for two up travelling I decided last year to upgrade to 1000cc for the extra torque and so fitted a siebenrock kit, the bike was fine but did pink a hell of a lot, I overhauled the carbs which helped as they were in need of a good pull through but the pinking remained a problem. In january I decided to rebuild the heads with new valves springs guides etc, while it was all apart i took the descision to twin plug the heads. I decided to get the second plug hole to be the same size as the standard fitment so this involved building up the outer face of the head where it was to be drilled with weld - to give enough depth (18mm) for the new plug. Holes were drilled, flame front cut into the plug seats on the inside of the head this guides the flame into the crown of the head for better burning,Guides were relined and Valve seats were reprofiled and cut to 45 degree inlet, 30 degree exhaust also the Tulip in the inlet port behind the valve head was cut back taking the step out of it where the valve stem comes through both the inlet and exhaust ports were lightly reshaped to improve flow. when I put it back together and after setting up the bike it runs excellent, Carbs were set with mixture screw 5/8ths turn out, timing retarded 3 degrees. There is no hint of pinking a notable increase in torque in the low to mid range and excellent acceleration and pick up. I have not done the fuel comparison for mileage yet as I need to do a few miles yet.
The Photo shows the head with the flame fronts cut into the spark plug holes, I cannot however get my other photos below 49kb to fit the limits on the site attachment manager. They show close ups of the cuttings and inlet tract work.

Great thread
 

Thanks for the update Jake, let us know how it works out with the fuel economy when you've got some distance on it. Did you want to e-mail me the pictures and I'll see if I can upload them? I just use Flickr and haven't had a problem uploading.

Ekke, ta for the ofer I have sent you three photos that I can not get to size thanks.

Jake's Photos
 

Here are Jake's photos of the dual plugging on his R80GS (With Siebenrock kit)

http://farm4.static.flickr.com/3359/...0225194b_o.jpg


http://farm4.static.flickr.com/3603/...b05d204c_o.jpg


http://farm4.static.flickr.com/3352/...fc21aef8_o.jpg


Jake, maybe you can comment on what each photo represents? Thanks!

Ta Ekke, I did not take two many photos however the 1st in Ekkes comment above shows a close up of the new plug hole with a hollowed out area that acts as a flame front to guide the burn of fuel towards the crown of the head maximising the efficiency of the combustion. The second shows both plug holes and bits of the valve heads and the last very hard to get with my camera - shows (badly lit) the tulip in the inlet tract where the valve stem comes through, previously this had a step around the base of the valve stem this was cut away to aid efficient flow the tract was further lightly flowed to take away cutting/ moulding edges and finished with a brushed finish to aid turbulance to mix the fuel/air. I did not get any other photos of note. Having just done 300 mile run this weekend the bike is very torquey and pulls extremely well from low revs and has a notable improvement of mid range power between 2300 to 4000 revs much better pick up on acceleration everywhere more so in the roll on speeds in top gear where before a change of gear was often a safe bet its no longer required.

Has anyone read this?
 

I found this a couple of days ago, and found it interesting.
Published in 1994 I think, so cost figures are likely a bit out by now.

I'd be very interested to hear what others think of this. The changes to MPG and power they got seem significant.


Get More Punch out of your boxer - ADVrider

CC = San Jose BMW Motorcycles - The Largest BMW Motorcycle Dealer in The Bay Area ; SJBMW Racing
Luftmeister = ? California BMW Triumph Motorcycles: Motorcycle Parts, Accessories, BMW Apparel, KTM Parts ? Vanished in 1995.

Motorworks - BMW Motorcycle Spares - home will make dual plugged heads for you.
Moto-bins - BMW Spare Parts and Accessories for Motorcycles - Index I think they will do dual plugged heads as well.
Siebenrock - BMW Motorräder & Teile ...alles ab /5 makes them.
hpn makes them.
www.israel-motoren.de makes them - this is the only remaining tuner company since CC and Luftmeister was swallowed up back in the 90-ties.
Just to name a few known companies.

Please read this as well:
Svenska BMW MC Klubben &bull; Visa tråd - Trasiga ITU - Tändimpulsgivare /7 1981-1995
http://www.horizonsunlimited.com/hub...oken-itu-41532
Daniel Dicke: Doppelzündung

I strongly disagree with the CC concept using SuperTrapp mufflers/silencers. The s/s mufflers made in Australia is far better choice. The s/s megaphone are really nice. Parts sold in Sweden by www.midland.se

You will get more effect at once by just swapping Bings for dell'orto PHM or Mikuni Flat slide or equivallent Keihan. I am playing with the idea to get a carburetor rack from a 1100-1300cc japanese bike = 4 carbs at rather good prices.
The max power will hardly be affected. I fair guess is 1-3% based on the difference between the R80 and R100 air-intake (I have a dyna test showing the difference on one of my engines). What you will get is the power when you want it and mileage will drop more than dual plugging - however... if you combine dualplugging and throttle carbs you should be able to expect about 10% (or even slightly better) mileage improvement -:)

Down-sides:
- the old articles you have read and found on the net are based on one original article from late 1970-ties... braker-point engines... It took me over 15 years to understand and accept that these articles are -not- applicable to the 1981-on semi-electronic ignition but applicable the the brakerpoint aftermarket conversion supplied by Boyer Bransden Electronics Ltd ... i.e. we're ... we who have the semi-electronic ITU... if it wasn't for Daniel Derdick and his site -:)

Options available:
- dual parallell ICU; like Derdicke presents. I prefer that.
- single special ICU from Kallenbach Electronic; Q-Tech Homepage

For the last two years I have been hestiating whether or not to dual plug yet a R100 I have. Since I managed to get my R80/100 back rolling with dual plugging since I repaired my ITU this fall - I will dual plug this bike as well!

The costs:
- the drilling of the 2nd sparkplug hole.
- modification of the ITU.
- parallell wires/cables for 2nd ICU
- new plugs
- new gaskets and sealings for the barrels and heads
To do at the same time, main things e.g.:
- check valves, guides and seats
- check pistonrings
- check conrod bearings
- camfollowers and cam for pitting

If you do the jobs that does not require machining yourself the cost should stop under 450-500 GBP (2009/2010).

I think the main issue is to get the timing right and I think it’s nearly impossible to do this without placing the hall unit in a motor-driven jig and modify it to get a proper ignition-curve.
When (you think) the ignition is correct and your carbs are overhauled you can start to worry about jetting, exhaust etc.

IMHO twinplugging is not necessary for all airheads. It depends on a lot of factors.
I’ve a bike with 80 Nm torque at 3500RPM and the mileage is typical 17.2 km/liter. It’s not twinplugged. But I will start to build another engine shortly and it will be twinplugged.

After running the bike for quite some time now on the twin plugged heads, I had a few problems with the soot build up on the plugs and some blistering it was also not so great on the fuel. I have after trying different settings come up with the following settings and found the bike has now ran perfect for many months of use. It appears to run far smoother throughout the rev range, slight improvement in fuel usage, better spread of low down torque and sharper acceleration. None of the improvements are going to pull your arms out of the sockets but when put together make the bike feel and run far better than it ever did before in any configuration and I would be as bold to say probably as well if not better than almost all the airheads I have owned in the last 30 years. It is also very easy to kick start even from very cold conditions with snow etc.
I Have changed the plugs to a BPR7ES so upped the heat range - this makes sense as the ignition is retarded - two plugs doing the spark more fuel burning the burn quicker and I suppose hotter ? - and the heat as a result was affecting the standard plugs which could not dissapate the heat quick enough - this single change made a big improvement to the running,
After another 2000 miles I also junked the y piece in the exhaust and re fitted the standard centre box this done I found it was easier to set the carbs and it ran better than before and I also ran them a bit leaner on the mixture screws 1st to 2nd phase in the carb operation was much smoother - still retaining excellent burn throughout the range with no excess fuelling - so saving fuel. I would say on average over differing conditions fuel has improved between 2 and 4 mpg. i think the centre box in the exhaust has made a big difference to the smooth running and low down torque, but its not possible to seperate all the component changes to see what has done what it all works together and gives an overall improvement each part doing its bit I suppose.

I've had good luck
 

When I lived in Venezuela a few years ago I bought a '78 R100RS. As you know, this bike came stock with a 9.5:1 compression ratio, which normally requires high octane gasoline. After the purchase, I looked closely at the bottom of the heads and noticed it had been dual plugged but the job had not been finished. There was a broken off spark plug at the bottom of each head, indicated the heads had been machined, but the coils had not been modified, etc. I bought a set of dual tower coils and finished the job, and was immediately rewarded with a bit more oomph. I also later found out that when the PO had the heads reworked, he had neglected to replace the piston rings. Although the bike ran better with a functioning dual plug system, it really didn't run optimally until I redid the entire top end of the engine. In addition, it is critical that the timing and carbs are also properly adjusted. I've been able to run regular gasoline in this bike without issues, but I wouldn't recommend dual plugging simply to allow the use of cheaper gas.

Personally, I hope I never see any of those!!

On a slightly less anatomical note, I recently posted a very similar question on my Ural owners forum, as I had read that dual-plugging on these venerable B;W analogues could be helpful for torque, power, starting, smoothness and fuel economy (by goodness, Urals need all the help they can get).

The only firm advocate was a guy who was also a pilot and drew parallels with the extensive use of D/Ping in aircraft engines. Personally, I can't see how it would nopt be beneficial once set-up properly. Perhaps one difference is that in the Ural, the two plugs are both located in the cylinder head in opposite positions and I seem to recall that with some BMs the second plug was not a mirror image of the first but in a slightly different position meaning you would need to get the spark just right so the flame fronts work together rather than against.

However, I may be wrong on this count: it is a vague recollection and therefore even more prone to inaccuracy!!

Dual plugging has its advantages, and disadvantages...

What would have a potent effect on the Ural 750cc are two other things to beging with:
- larger inlet valves
- higher compression ratio
...or/and put some more cc there... -;)

Dual plugging will aid to get a bit more of of the energy in the petrol, and with gas prices as the once we have today even a small improvement makes quite a difference in the wallet in the longer run.

Do not spend hundres of pounds ripping the engine apart to save a few pennies on petrol! Plan modifications to be done at the normal major overhaul intervalls, or if the engine needed to be opened by some other reason (leaking pushrod tube e.g.) - then the extra costs are quite moderate -:)

Ural have small bore and low compression so I wouldn’t bothered to dual-plug it unless it is heavy modified.
I believe all 750s have the Ducati-ignition and it’s impossible to alter the ignition-curve without changing the black-box.

Doesn't Ural have "stock" ca 82mm BMW barrels?
BMW 800 have ca 84mm.
BMW 1000 have ca 94mm.
ca 71mm stroke.
Compression ratio varies on BMW from 8.2-9.5 with the exception of the Egyptian Police special edition which -I guess- had about 7.0:1.

If so - he should expect just about what I got on my 800cc, right?

Doesn't Ural have the old BMW brakerpoint system?
Altering such a system is very well described in Oak Okleshen article 13 pages "Dual Spark Plug Ignition, Part 1" (last revised in 2002 as far as I know):
Airheads Beemer Club - Oak's Tech Articles
First published by BMW Owners of America “BMW News” November 1980.
Then there are:
Tom Cutter's article Tom Cutter's book on Dual-Plugging Airheads- Available now! - - Airhead Tech Archive - - Airtech BMW Archives - The Airhead Museum - Message Board - Yuku
http://www.nwlink.com/~paulcl/at/tc/pointsplate.gif
and
Scot Marburger Airheads Beemer Club - Dual Plugging The R100GS

There are -very- few ho have tested dual-plugging on airheads on less cc than 1000cc... and even fewer who have tested it on the old 750cc and 600cc... less one have personal experience of the dual-plugging on less than 1000cc one should avoid repeating opinions on wether or not these will benefit from dual plugging. I know for a personal fact that my 800cc, with 8.2:1 => 9.2:1 => 10.3:1 did benefit very well; and then 750cc with 9.0:1 should be expected to do it too -;)
Wether or not the old 750cc that Ural users also does it... I do not know, and since I have no engine data on them I can not make an informed guess either - but what I can say is that I would expect it to have -an- effect and -am- looking forward to hear from someone who have tested dual-plugging the Ural engine -:)

A very good point though is that if the compression ratio is too low... I guess dual plugging may cause more headache...

As for the part of where to place the plug... well, it will not work -against- the original plug, but it may aid it well or less well. As for the beemer heads... there is one (1) possible position for the second plug... the tricky part is not the position, but the making of the plug hole and threads. Look at Scots pics - then you see what I try to say.

It has 78 mm bore (square engine).

The Ural has 8.6:1 and a smaller bore then your R80 so I would think less effect then you got. There will be some effect, but as long as the bore is small and compression is low I wouldn’t expected much.
Personally I think a boost in compression and some tweaking of the heads will be better. It’s fun to drive a tuned Ural and the engine is smooth.


Ignition is full-electronic, not like BMW. It’s a nice system (Ducati) but it’s impossible to alter the ignition-curve.


But I agree that no-one can tell for sure unless they have tested it and it would have been fun if someone did! :thumbup1:

Spending pennies again - Next two improvements to come along on the bike will be carried out soon. Having already ran an endurolast 450 charging system I have bought an electronic ignition system with a selectable ignition curve for both single and twin plugged bikes - bit like silent hectic stuff but cheaper and works with the enduralast alternator. I have also bought a siebenrock sb2s exhaust sytem. I was going to fit a assymetric cam but siebenrock state this wont work as it was designed for the r100gs would need r100gs carbs and ideally cylinder head so thats a no go. (mine is an r80gs with siebenrock 1000 conversion) will update once i get into the garage and get it all done.

I haven't tested the asymmetric cam but I use a 296° cam (with the same Siebenrock-kit as you, standard carbs and slightly modified heads). The 296° cam gives a lot of torque at low RPMs and a bit less at high rpm (above 5500RPM).
This setup works rather nice!

Thanks for that ali I may pull he bottom end down later this year as it needs a new cam chain and a few seals are weeping a bit - so will maybe fit the 296 cam while I am on. have had to scrap the HPN frame idea it was booked in this month, but change of circumstances and the high Pound/euro rate make it too expensive at the moment. Tchus Jake.

Food for thought: Other models using dual spark are the latest 1150 boxers, the 2 valve Ducati 1000, the F650 GS single, the 1200 boxer and even my trusty DR650 has 2 spark plugs. I'm curious, doesn't pinging happen due to pre-ignition, before the spark plug fires? Are we talking about the same thing?

Yes we are talking about the same thing, you might wonder how twinplugging affects pre-ignition when pre-ignition happens before the spark?

There are mainly three things that leads to pre-ignition: Octane-rating, compression and heat in the combustion chamber.
If you run the highest octane-rating you reduce pre-ignition but high octane petrol is not always available and it might be expensive. You might lower the compression to decrease pre-ignition but you will reduce mileage and power.

Heat in the combustion-chamber is a bit more difficult. There are a lot of factors that makes it hot (or makes hot spots). This might be sharp edges, carbon-buildup, a hot plug, timing, mixture etc but we will focus on dual-plugging.

When the plug ignites the petrol the flame has to travel to all ends of the combustion-chamber. The bigger the bore is the longer the flame has to go. When the flame has to travel far the combustion will go slower and the temperature increases (which might lead to pre-ignition).
So basically big bore increases the chance of pre-ignition.

A DR650 has bigger bore then the R100. The new BMW S1000RR sportsbike has smaller bore then the R80.


If we look at the picture Adventure950 posted we will see that the original plughole (right) is not in the center of the head. The distance the flame has to travel is pretty "large". If we put in another plug (left) and fire both plugs at the same time the distance is reduced dramatically and the mixture will burn faster and cooler. This reduces pre-ignition.

http://www.horizonsunlimited.com/hub...w-p1010007.jpg



Because of the faster burn you should fire the plugs a bit later (esp on lower revs).
This is done in numerous ways and I think this is one of the reasons why people have different experiences with dual-plugging.
Timing is very important and if you fail you will not gain the improvements twin-plugging gives you. A lot of people bolt on their new parts twist the beancan a bit and ride, that's like buying a set of expensive running-shoes without tying the laces.

The faster burn will also lead to higher efficiency (esp on lower revs) and therefore reduced petrol consumption. It also reduces the levels of unburnt carbon and reduces the CO emissions at low rpm.
You can also run a twin-plugged engine leaner.

A given engine will normally have the best performance right before pre-ignition starts. That's why newer BMWs have a system that senses pre-ignition and it alters ignition (and mixture?)
to stay as close to pre-ignition as possible.

Thats a great explanation, thanx :thumbup1:. I never thought about the heat factor which puts everything into perspective.

Brilliant explanation AliBaba.

My wife has noticed a gas smell behind my R100 (especially when riding in countries on the left like the U.K. so that the exhaust pipe is pointed almost directly at her). I've leaned out the mixture as much as possible, just short of having it buck on low throttle and she still gets a whif every now and again. Perhaps twin plugging and then leaning out the mixture even more will reduce this smell. The trickiest part is exactly what you mention with getting the timing right.

I found as I mentioned earlier that I needed to change the heat range of the plugs as well as retarding the ignition 3 degrees the bike seems to run very well- this is still using the bean can - I am about to change this for an endurolast ignition with digital ignition curve (fits the enduralast charging system I have already fitted) - for twin plugged heads so should get a better response again. I have also decided to also stick in a 296 cam for more torque as well as a purpose built siebenrock sgs 2 exhaust system built for the set up I have (siebenrock 1000 upgrade with 80 gs carbs and lightly modified heads) so hopefully all these mods together should get my bike running as well as it possible can without going the 1070 cc route.
Its been a long time getting to this point a bit at a time but I decided to splash out this year on quite a bit of engine and gearbox work - as i am not travelling this year at all.

Just an update have put on the siebenrock sgs2 exhaust, really wonderful bit of kit, fits better than the original, no front balance pipe so each side can be removed independently most of the joints are tension spring connections so allow a bit of movement and the Y piece is in 4 pieces allowing it to fit and move enough to be easy to centre up and remove. there are no gaskets or stuff either. It sounds very deep but not noisy, torque delivery is very smooth top gear easy pulls cleanly fron 1500 revs straight through and will ride smoothly at these low revs in top gear, Pick up right through is cleaner and more positive - no huge jumps in power but noticable changes. Also weighs 5 kg lighter than standard system. Electronic ( euromotoelectrics) ignition system and 296 cam also lower first and higher top gear will be done in the next few weeks. :thumbup1:

ADV950 - Nice to see some feed back on the SGS2 exhaust. What style did you get - low, mid or high? I'm wondering about clearance to luggage etc. Look forward to hearing about your other modifications also.

I'm wondering about the benefit of dual plugging when travelling - i.e coping with bad or low octane fuel. Can anyone relate any experience to this?

I'm thinking about upping the compression on our US spec GS and dual plugging to suit, but my instinct is to leave it stock for a big overland trip.

Igor