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Old 11-25-2010, 05:26 AM   #16
2xdisco
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i have experience with these models. dual-plug the bike while doing this eather shave the heads or add HC pistons(better).... have the bike timed and tuned proper!.. i have found that most shops do not know how to do this right.... they do it ok but miss out on the total potential of the motor.... with it timed right. the motor will pull so hard from 1500-5500 that u actually have to hang on. after 5k the bike will accelerate extremely fast. this way u can leave everything else stock , exhaust, 40 bings, ect.... this mod will also increase fuel millage.. i have this same set up on a r100rs/s i get 45-50mpg at 75+ loaded. HP with this done right, will put u in the 75HP range. and torque will be lowered due to the retardation of the timing and a widening of the advance range...
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Old 11-25-2010, 10:53 AM   #17
supershaft
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Quote:
Originally Posted by 2xdisco
i have experience with these models. dual-plug the bike while doing this eather shave the heads or add HC pistons(better).... have the bike timed and tuned proper!.. i have found that most shops do not know how to do this right.... they do it ok but miss out on the total potential of the motor.... with it timed right. the motor will pull so hard from 1500-5500 that u actually have to hang on. after 5k the bike will accelerate extremely fast. this way u can leave everything else stock , exhaust, 40 bings, ect.... this mod will also increase fuel millage.. i have this same set up on a r100rs/s i get 45-50mpg at 75+ loaded. HP with this done right, will put u in the 75HP range. and torque will be lowered due to the retardation of the timing and a widening of the advance range...
75hp at the rear wheel from dual plugging alone? Even at the crank would be a miracle! I wouldn't count on that happening twice here on planet Earth.

Dual plugging? I am all for it. Remember that I didn't raise my compression? It's because I wouldn't raise my own compression without first dual plugging and I opted out. Besides, my boss and a bunch of mechanics I worked with the last time I had my heads off said that you HAD to raise the CR if you put in a 336. Wrong! For 1000cc, my 8.7 is about as high a CR as I would run single plugged. It runs on regular just fine when it isn't too hot and when it is hot it needs premium to keep from pinging. That's about as close as you can get to the highest CR doable IMO.

I have seen F'ed up machining on a lot of dual plugged heads. Usually the plug is way off center and if it is off center towards the exhaust seat too much, the head will crack between the spark plug hole and the exhaust seat. I have seen a lot with Fed' up threads right out of the shop too. I have seen some that have had coil inserts installed right out of the shop because the first attempt at cutting the threads was a fiasco!

I have seen even more dual plugged setups timed wrong. There are two schools of thought on this subject. One works WAY better than the other. Oak and Snowbum on on the wrong side of THAT fence.
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Old 11-25-2010, 01:02 PM   #18
2xdisco
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good read.

http://www.advrider.com/forums/showthread.php?t=510070
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Old 11-26-2010, 11:17 AM   #19
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That article has got some good, some bad, and some ugly. First off, Chris is a real good guy and has set up the best running airheads I have ever been around but he doesn't have an aeronautical engineering degree. He said himself just a while back on this forum what kind of degree he has. It's an aviation management degree or something like that. It's really no secret.

I wonder how this myth of /6's and /7's getting 55mpg got started. I worked at a BMW dealership when those bikes were being sold brand new. Back then as now, it would take getting on a thumper to get that kind of mileage. At least at decent speeds. I have ridden with so many /6's is isn't funny. They have all needed to stop for gas about the same time I do on my non /6 and /7 airheads. I am not saying I couldn't maybe get that kind of mileage out of one or any other airhead but I would want a safety car behind me with flashing yellow lights!

60+ rear wheel hp from a stock R100GS? Sorry but that just ain't going to happen. BMW "claims" 58(?) at the crank! By the time I worked with Chris, he knew his dyno that a local guy had made read high. If I remember right, he had the program re-wrote to get the numbers down and we still recalculated the figures to get them down into reality. But then most others make out of this world claims so what are you going to do? You tell your customer that we got 20% more power out of his bike and the power is now reading 58hp and the customer will scream that it made 60hp stock! SURE it did! Not YOUR engine but a FINELY tuned and setup prototype somewhere deep in the bowls of BMWAG on THEIR dyno and AT THE CRANK! Why do people even bring up claimed hp or weight? It's la la land! Sure, BMW stretches the truth a LOT less than most other companies but still!

That article reads like he didn't yet have a gas analyzer but I don't know. It reads pretty out there in spots. I am sure it would read very differently if Chris himself wrote it. His recent posts were GREAT!

I hope I am not going too far sharing my experience with Chris. For instance, I have never revealed what I saw some of his race bikes make on the dyno and other things I would consider proprietary. It's just that I have to deal with people wondering why their RS doesn't make 70hp or why their bike isn't getting 55mpg ALL the time.

supershaft screwed with this post 11-26-2010 at 11:28 AM
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Old 11-26-2010, 07:24 PM   #20
bmwrench
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My more-or-less stock R100/7 (modified airbox, RS Fairing) routinely got 50 MPG. A friend's R90/6 with an R60 rear drive(!) also got 50+ MPG. We weren't in any danger of being run over, either. This was back in the late 70s, when gasoline was far better than what we can buy today. The best mileage I've got in recent years was on my K1!
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Old 11-26-2010, 09:06 PM   #21
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Quote:
Originally Posted by zenben
Smaller valves, carbs, and more restrictive exhaust keep the torque curve down in the low and mids.
Wide open everything can generally only be driven wide open with good results.
I've built them both ways, and mild tuning is always nicer to drive all around.
I agree w/ this guy I have a 1977 r100/7 w/ 32 mm carbs and smaller valves and give riders on the rs/s/rt fits up to 100 mph. Then after that point their hp wins. Bit if you are after more torque less id more. Ron
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Old 11-27-2010, 11:41 AM   #22
supershaft
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Quote:
Originally Posted by bmwrench
My more-or-less stock R100/7 (modified airbox, RS Fairing) routinely got 50 MPG. A friend's R90/6 with an R60 rear drive(!) also got 50+ MPG. We weren't in any danger of being run over, either. This was back in the late 70s, when gasoline was far better than what we can buy today. The best mileage I've got in recent years was on my K1!
I really try to avoid mileage stories even with some of my good friends. Same goes for tire wear. Man! Think of all the pipes that have been packed and lit and journal entries made on those topics! Usually, I raise my arm and point as far away as I can and advise that the Star Trek convention is THAT way! Still, I don't remember ANY of our customers reporting anything like that back then. Some low to mid forties and mostly mid/upper thirties are the stories we heard "back when gas was good".

Besides alcohol, what has changed in gas that effects mileage? I have been riding my own beemers for 30 years now and I have noticed no change in mileage except for the predictable results of 10% alcohol added.
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Old 11-27-2010, 07:02 PM   #23
bmwrench
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Lower Octane! We used to be able to run 9.5:1 or better, with full advance on pump gas.

With the introduction of ethanol, I find I am forced to re-jet amost every bike I work on. We know that ain't going to improve mileage.
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Old 11-27-2010, 08:25 PM   #24
supershaft
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Quote:
Originally Posted by bmwrench
Lower Octane! We used to be able to run 9.5:1 or better, with full advance on pump gas.

With the introduction of ethanol, I find I am forced to re-jet amost every bike I work on. We know that ain't going to improve mileage.
Funny, I remember ALL kinds of our customers installing thick base gaskets and dual plugging to reduce pinging "back when gas was good".

OK, higher CR will increase mileage but NONE of our touring customers were raising compression. They were LOWERING it for pinging! If it ain't pinging, higher octane won't help anything. 83 octane has got the same amount of calories in it that 110 octane has.

Why are you forced to re-jet with the introduction of ethanol? I never have. I have never needed to. Neither has anyone else that I know till now. Once a little off idle, the stock jetting is PLENTY rich enough to coupe with 10% ethanol. ESPECIALLY the earlier airheads! I jetted my R100 down to 130 mains for MORE POWER on 100 octane race gas and it runs just fine on 87 octane with 10% ethanol. That is until the ambient temp gets high, then it needs 91 octane!

supershaft screwed with this post 11-27-2010 at 08:31 PM
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Old 11-27-2010, 10:02 PM   #25
Airhead Wrangler
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Quote:
Originally Posted by supershaft
OK, higher CR will increase mileage but NONE of our touring customers were raising compression. They were LOWERING it for pinging! If it ain't pinging, higher octane won't help anything.
I actually get slightly better mileage on mid grade than regular at 8.2:1. Explain that. No, this was not a single tank freak occurence. A guy I was riding with told me he got slightly better mileage running mid grade in his thumper, so I called bullshit. I alternated between regular and mid grade for 3000 miles in Argentina and sure enough, I consistently got better mileage on the mid grade. There are various degrees of preignition. It can be much more subtle than audible pinging. Though smaller amounts of preignition won't necessarily damage your engine, they won't help your gas mileage either.
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Old 11-28-2010, 11:06 AM   #26
supershaft
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Quote:
Originally Posted by Airhead Wrangler
I actually get slightly better mileage on mid grade than regular at 8.2:1. Explain that. No, this was not a single tank freak occurence. A guy I was riding with told me he got slightly better mileage running mid grade in his thumper, so I called bullshit. I alternated between regular and mid grade for 3000 miles in Argentina and sure enough, I consistently got better mileage on the mid grade. There are various degrees of preignition. It can be much more subtle than audible pinging. Though smaller amounts of preignition won't necessarily damage your engine, they won't help your gas mileage either.
I think most call pinging detonation since it is usually post ignition but I agree with you that there is pre-pinging pinging. I don't know what the correct term for it is.

Preignition is when something sets the mixture off before the spark plug does or, in the cause of ignition wire cross fire, before the spark plug is SUPPOSE to spark.

I have noticed pre-pinging pinging through better performance of higher octane gas than compared to lower octane gas even though there was no audible pinging on the lower octane. That's why I run 91 octane in my R100 most of the time although, for the most part, when I have noticed a difference it has been on two strokes. I don't know if I have ever noticed a performance difference on my R100 between 87 and 91 octane but I have between 91 and 100 although at least a big part of that is that the 100 octane doesn't have 10% ethanol in it.

I have never noticed any difference in my mileage between burning lower and higher octane. If there is, it ain't much. I have noticed differences in mileage from differently loaded bikes, jetting, ignition timing, elevation, headwinds, tailwinds, and, by far to the largest degree, how I ride. How I ride can change my mileage by 20mpg and it would probably be by an even larger margin IF I could slow down a bit more. Basically, my riding and headwinds vary too much to analyze my mileage down to a nat's ass. I think that holds for most of us.
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Old 11-28-2010, 11:35 AM   #27
caponerd
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Shaft, you're really taking an unpopular stand here.

Personally, I tend to agree with you about the fuel milage thing though.
When I first got my 1982 R100RT, everyone told me to expect 50 mpg with it.

I had the bike gone through by Steve Prokop in Oregon right after I bought it (turned a $2500 bike that I bought for $3000 into a $5500 bike that was only worth $3000!)
It's never returned much better than 40 mpg, and that didn't become commonplace until I installed an RS fairing for summer riding. I don't baby the bike, and I think 75 mph is a fair average speed when I'm on the road with it. If anyone claims 55 mpg (or maybe even 50) for one of these, I'd have to assume they really aren't tracking their milage very well.
I got in the habit many years ago of recording all fuel purchases/odometer readings because I was doing a lot of driving for work and I needed to keep good records. This became enough of a habit that I keep a record of fuel purchases for all my motorcycles.
It makes a huge difference to have an ongoing record. Just noting odometer reading and fuel amounts isn't sufficient because no matter how careful you are, the tank's not always going to be filled exactly the same, and the readouts on many gas pumps are often inconsistent, in spite of DOT rules and certification of pumps.
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Old 11-28-2010, 04:26 PM   #28
supershaft
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Boy Howdy caponerd! It's never stopped me before especially when I think the alternative view needs saying! Thanks for your input. It makes 110% sense to me. I know that our position is out there big time but it is rarely on the web for some reason. Maybe the internet is a little too close to that Star Trek convention I joke about and point to to fellow pipe smoking beemer riders like ourselves! Ask just about anyone that doesn't ride beemers and they will tell you that just setting on one will get you half way to that convention without even moving an inch!
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Old 11-30-2010, 02:20 AM   #29
Beemerboff
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Nobody ever mentions that unleaded gas burns faster than the leaded that was around when BMW set the advance figures 40 years ago.

I do my tuning , including ignition timing, on the road, up a decent steep hill.
I ended up with 26/27 degrees advance on my twin plugged 1000 cc R80 G/S, 2/3 degrees less than most self styled experts recommend.
It has factory low comp pistons in a unmodified head. That got me up the hill around 5/6 KPH slower than my buddies 86 Suzuki GSXR 750R.
And 50 KPH slower than his Honda SP2.

Other mods, like removing the snorkels from the air box which are supposed to kill midrange actually improved my speed up the hill.

Like Supershaft I find a lot of what is written on airheads is just bunkum, which has gone unchallenged for years.

Pity there is nothing authoritative out there, even getting someone who knows the optimum squish clearance is almost impossible, and that is a basic and essential figure to have.
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Old 11-30-2010, 10:21 AM   #30
supershaft
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Quote:
Originally Posted by Beemerboff
Nobody ever mentions that unleaded gas burns faster than the leaded that was around when BMW set the advance figures 40 years ago.

I do my tuning , including ignition timing, on the road, up a decent steep hill.
I ended up with 26/27 degrees advance on my twin plugged 1000 cc R80 G/S, 2/3 degrees less than most self styled experts recommend.
It has factory low comp pistons in a unmodified head. That got me up the hill around 5/6 KPH slower than my buddies 86 Suzuki GSXR 750R.
And 50 KPH slower than his Honda SP2.

Other mods, like removing the snorkels from the air box which are supposed to kill midrange actually improved my speed up the hill.

Like Supershaft I find a lot of what is written on airheads is just bunkum, which has gone unchallenged for years.

Pity there is nothing authoritative out there, even getting someone who knows the optimum squish clearance is almost impossible, and that is a basic and essential figure to have.
Leaded really doesn't burn any faster than unleaded. That is a common but oversimplified way to look at it. Lead was added to gasoline in the very late twenties for one reason and that one reason is almost all it did. That reason was to reduce pinging. That is all octane rating is. The comparative ability of gasoline to resist pinging as tested by listening to it ping or not ping in a test engine. High and low octane's flame front burn rate from the spark plug is the same regardless of whether it has lead in it. The difference is in the mix getting squeezed by compression AND the flame front that is IN FRONT OF THE FLAME FRONT. THAT is where higher octane gas burns slower and even that is misleading. High and low octane gas burn at the same rate as the flame front is compressing it and consuming it. That is until the lower octane gas in front of the flame front explodes instead of burning. That is pinging. Higher octane gas doesn't burn slower, it explodes less. Other than that trait, there is virtually no difference between high and low octane rated gasoline as far as the energy involved and the "burn rate" is concerned. That's my $.02 on that subject.

I thought I would add that those facts are why you can see evidence of pinging by reading piston tops. The very outside edge of the piston top all the way around will will suffer from the carbon getting chewed up versus a washed look if you were diagnosing improper ring seating. A little more and you can see some shiny just melted aluminum poking up through the chewed up carbon. A little more than that and the piston starts melting around the edges. A little more than that and what often happens is bits of melted piston from the edge all around goes down and sticks the rings and that is when the smoke starts pouring out the exhaust! Look for all that going on within about a half inch of the outside diameter of the piston all the way around its circumference.

supershaft screwed with this post 11-30-2010 at 10:37 AM
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