ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 10-22-2012, 01:45 PM   #46
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,355
Quote:
Originally Posted by RGregor View Post
Just for curiosity, what's the basis for this statement?

I'm not sure what SS's basis is, but I'd agree with the statement. The bore to stroke ratio is well over square (94:70) and that by nature makes it an engine that is happier reving higher than lugging at low RPMs. The more over square an engine is, the more it depends on revs to make HP than torque. For a given displacement, a longer stroke will give you greater torque as the piston has a longer moment arm to turn the crank. With the same displacement, a larger bore (and thus shorter stroke) allows larger valves for better breathing as well as more piston surface area for combustion pressure to push on, but less mechanical advantage to turn the crank and thus lower torque. Since it can have larger valves though, it can breath better and rev higher. Since HP is a function of torque and the number of combustion events per unit time, over square engines depend more on revs to make HP than large amounts of torque. Square and under square engines by comparison depend more on big torque to make their power because they can't rev as high due to increased piston and rod accelerations due to the longer stroke as well as less ability to breath due to smaller or fewer valves.
__________________
R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.

Airhead Wrangler screwed with this post 10-22-2012 at 03:04 PM
Airhead Wrangler is online now   Reply With Quote
Old 10-22-2012, 05:39 PM   #47
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,287
Quote:
Originally Posted by RGregor View Post
Just for curiosity, what's the basis for this statement?
Well, I started riding them in '75 when I was 14 but my dad put an end to that when he noticed I was grinding the rubber off the bottom of his brand new R75/6's foot pegs. I didn't ride them much but maybe around the shop after that until five years later when I bought my own. That was in '81. I have been riding the stink out of them every since. That and how they are made. Short stroke/relatively long rod. Pretty much everything about them says rev me except for their mile long pushrods. But most importantly, they just don't make good power until they are reved up a lot. Our shop was also a Moto Guzzi dealership. Overall, they are just the opposite. They are typically grunters. Other engines too. Not our airheads. I have pretty much never had any arguements on this subject or the other but there's always a first time.
supershaft is offline   Reply With Quote
Old 10-22-2012, 05:58 PM   #48
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,287
Quote:
Originally Posted by Airhead Wrangler View Post
I'm not sure what SS's basis is, but I'd agree with the statement. The bore to stroke ratio is well over square (94:70) and that by nature makes it an engine that is happier reving higher than lugging at low RPMs. The more over square an engine is, the more it depends on revs to make HP than torque. For a given displacement, a longer stroke will give you greater torque as the piston has a longer moment arm to turn the crank. With the same displacement, a larger bore (and thus shorter stroke) allows larger valves for better breathing as well as more piston surface area for combustion pressure to push on, but less mechanical advantage to turn the crank and thus lower torque. Since it can have larger valves though, it can breath better and rev higher. Since HP is a function of torque and the number of combustion events per unit time, over square engines depend more on revs to make HP than large amounts of torque. Square and under square engines by comparison depend more on big torque to make their power because they can't rev as high due to increased piston and rod accelerations due to the longer stroke as well as less ability to breath due to smaller or fewer valves.
That's the thing about airhead riders that I don't understand: Everybody calls the R65 a short stroke engine and the R100 has the EXACT same 'stroke'. 94x70.6 and 82x61.5. They both come out to 1.33:1 bore and stroke ratio. Yes, a R65 IS a short stroke but so is a R100!
supershaft is offline   Reply With Quote
Old 10-22-2012, 06:47 PM   #49
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,374
Quote:
Originally Posted by Voltaire View Post
I had to go back to 2009, # 269 was doing 1:11 lap times, he was 5th and the fastest was 1:06 on a 900SS.

I was surprised when he said 2.91 was not tall enough as my 3.0 wont hit redline in 4th on the same bit of the rising track.

I knocked 5 seconds off my previous best time with virtually no mods to the bike, so thats just me improving, I

can see a few more seconds coming that way....I'm pretty slow off the start and the first lap.

I can track the rest of the field on previous races and it would appear you plateau at some point as a rider...?

I did a bit of spectating and observed that nearly all the riders were turning in early on the hairpin...contrary to the

Super Bike school teachings of brake late, deep in, countersteer, throttle on......get on the gas asap.

The pre 89 Jappers are pretty fast in a straight line but some of cornering was pretty slow....I'm no expert but

thats where I think I make up my times on the high HP bikes.

Bummer about Super Bike School as I thinks its really worth while, following others around the track would have

taught me bugger all.

.......of course in the real world I ride an R65 and a Commando and there are cars coming the other way so I

don't worry about HP , butt, dyno, imagined or otherwise...

Did you see on Access Norton where one of the guys got all the Commando heads, flowed them on his bench

and posted up the charts.....showed that my Combat head was the worst.....only made power by the cam and

carbs.


I just had a look at a couple of Hampton Downs videos and I'm surprised that you'd need a 2.91 around there. It doesn't look as fast as Pukekohe. Just from a video, ( and I know it's a bit of guesswork, I'd fit a 3.0 .
The vid I watched was a 600 jap bike but it never seemed to get rally going in top gear.


If I ever get back to Pukekohe I'd have to pull my finger out. I can't remember the times but I think I was 1.11 or around there. Are the 2001 results online anywhere?
__________________
The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt.
Bertrand Russell
pommie john is offline   Reply With Quote
Old 10-22-2012, 07:35 PM   #50
Voltaire
Beastly Adventurer
 
Voltaire's Avatar
 
Joined: Jun 2011
Location: Auckland,New Zealand
Oddometer: 1,235
Quote:
Originally Posted by pommie john View Post
I just had a look at a couple of Hampton Downs videos and I'm surprised that you'd need a 2.91 around there. It doesn't look as fast as Pukekohe. Just from a video, ( and I know it's a bit of guesswork, I'd fit a 3.0 .
The vid I watched was a 600 jap bike but it never seemed to get rally going in top gear.


If I ever get back to Pukekohe I'd have to pull my finger out. I can't remember the times but I think I was 1.11 or around there. Are the 2001 results online anywhere?
Its not as fast as Pukekohe, but that's what he said.....I was running a 3.0.
I bought a set of big valve 1977 heads after Puke....then it was mentioned that the D port R80 heads are the better ones to start with.....got a set of these too...... head work on BMW's seems to be cloaked in secrecy.....

The BMW sidecar dropped a valve seat before even doing a lap..... and the ring lands were pushed together a bit.... Maxheadroom ( Nick) found a stock r100 head, swapped over the valves and rockers....carefully took the rings out...dressed the piston in the lathe.... and....

With this set up they managed a 3rd and a 4th...newish rider and different swinger.
I suggested they put it on the Dyno, disconnect one lead at a time and see which has more power.....
Apparently it ran the same but riders leg tended to blocked the carb
Voltaire is offline   Reply With Quote
Old 10-22-2012, 11:24 PM   #51
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by supershaft View Post
Well, I started riding them in '75 when I was 14 but my dad put an end to that when he noticed I was grinding the rubber off the bottom of his brand new R75/6's foot pegs. I didn't ride them much but maybe around the shop after that until five years later when I bought my own. That was in '81. I have been riding the stink out of them every since. That and how they are made. Short stroke/relatively long rod. Pretty much everything about them says rev me except for their mile long pushrods. But most importantly, they just don't make good power until they are reved up a lot. Our shop was also a Moto Guzzi dealership. Overall, they are just the opposite. They are typically grunters. Other engines too. Not our airheads. I have pretty much never had any arguements on this subject or the other but there's always a first time.
I see, it's your experience.
Having started with an R75 (/5) as well I would guess it was not the experience with that, as reving a stock R75 won't take you very far. It simply doesn't like it.
So probably it's the experience with your engine.
That confirms my experience with duration cams (not the 336, but e.g. Schleicher 330): you get an engine that likes to rev high, but, compared to it's power at high revs, is a bit weak at bottom revs. Overall you get a mild torque boost, but over a wide rev range.

So far so good.
From personal experience I know that with the right cam and, most important, exhaust setup you can reach a torque level at or near the magical 100Nm/litre level.
Resulting in an engine that can be, that even likes to, but not necessarily needs to be reved to have fun.

I know better engines than this one but it will give you an impression of what I'm talking about.
http://www.advrider.com/forums/showp...1&postcount=41

What I want to say: IMO there isn't "the beemer". The variety of what you can get with different setups is that high, you simply can't lump them together.
RGregor is offline   Reply With Quote
Old 10-22-2012, 11:29 PM   #52
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by supershaft View Post
Our shop was also a Moto Guzzi dealership. Overall, they are just the opposite.
Compared to Guzzis beemers do have some disadvantages
http://harley.wolfcrews.com/misc/BMWc.jpg
RGregor is offline   Reply With Quote
Old 10-22-2012, 11:36 PM   #53
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by supershaft View Post
That's the thing about airhead riders that I don't understand: Everybody calls the R65 a short stroke engine and the R100 has the EXACT same 'stroke'. 94x70.6 and 82x61.5. They both come out to 1.33:1 bore and stroke ratio. Yes, a R65 IS a short stroke but so is a R100!
Maybe they just aren't good at maths?
RGregor is offline   Reply With Quote
Old 10-22-2012, 11:37 PM   #54
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by pommie john View Post
If I ever get back to Pukekohe I'd have to pull my finger out.
Where? Out of the nose (that's a spell over here to get fast)?
RGregor is offline   Reply With Quote
Old 10-22-2012, 11:43 PM   #55
alex117
Adventurer
 
Joined: Jun 2011
Oddometer: 18
power increase with steady ride

I wanted to go fast stop fast and go into the twisty bends at speed.
I had Roger Benett of Motoworks (bins?) build me a motor . He uses 97 mm J&N pistons big port big vale heads aka 77 rs, I use a 40 mm exhaust , 9.5:1 twin plug 336 cam the rest is stock. I can RAPIDLY ACCELERATE IN 4TH TO 100MPH SHIFT TO FITH AND IT KEEPS ON PULLING so far up to 135 mph and there is more to go.

Frame r90S 1974 is fully braced ala HPN style with diagonal side braces, R100R forks reworked with Race Tech valves and springs for my weight , very light Magnesium Wheels single front brake 310-320 mm? with 4 pot Brembo, Ohlins rear with proper springs for me

Ride like it is on a rail and superb handling. Stops on a dime . Of all my airheads I like this the best I can keep up with the guys on the sports bikes sort of but the bike is faster then me.

It has dramatically improved my ability on the road and was worth the time and effort to build.
alex117 is offline   Reply With Quote
Old 10-22-2012, 11:46 PM   #56
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,374
Quote:
Originally Posted by RGregor View Post
Where? Out of the nose (that's a spell over here to get fast)?

"Pulling your finger out" is an strange English phrase that means to do some hard work , to get on with something properly, to put in some effort.
I've no idea where it comes from.
__________________
The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt.
Bertrand Russell
pommie john is offline   Reply With Quote
Old 10-23-2012, 12:51 AM   #57
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by pommie john View Post
"Pulling your finger out" is an strange English phrase that means to do some hard work , to get on with something properly, to put in some effort.
I've no idea where it comes from.
"Nimm den Finger aus der Nase" ("take your finger out of the nose") is a german phrase sometimes referred to when talking about finding a means to increase speed.
I tried to find an online version of a cartoon from the german cartoonist Holger Aue about that topic, unfortunately couldn't find one.
RGregor is offline   Reply With Quote
Old 10-23-2012, 07:32 AM   #58
Uncle Pollo
happy cachiporra
 
Uncle Pollo's Avatar
 
Joined: Jun 2006
Location: Albuquerque, Neue Messico
Oddometer: 47,408
I love this thread. Lots of experience pooled togheter.
Uncle Pollo is offline   Reply With Quote
Old 10-23-2012, 11:16 AM   #59
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,287
Quote:
Originally Posted by RGregor View Post
I see, it's your experience.
Having started with an R75 (/5) as well I would guess it was not the experience with that, as reving a stock R75 won't take you very far. It simply doesn't like it.
So probably it's the experience with your engine.
That confirms my experience with duration cams (not the 336, but e.g. Schleicher 330): you get an engine that likes to rev high, but, compared to it's power at high revs, is a bit weak at bottom revs. Overall you get a mild torque boost, but over a wide rev range.

So far so good.
From personal experience I know that with the right cam and, most important, exhaust setup you can reach a torque level at or near the magical 100Nm/litre level.
Resulting in an engine that can be, that even likes to, but not necessarily needs to be reved to have fun.

I know better engines than this one but it will give you an impression of what I'm talking about.
http://www.advrider.com/forums/showp...1&postcount=41

What I want to say: IMO there isn't "the beemer". The variety of what you can get with different setups is that high, you simply can't lump them together.
No. I am not talking about my own bikes. I am talking about the hundreds of stock beemers I have rode from /3's up to the last ones. Can't lump them all together? Generally speaking you sure can. All of them are better off being reved up. At least the way they come from the factory.
supershaft is offline   Reply With Quote
Old 10-23-2012, 12:00 PM   #60
RGregor
User Awaiting Email Confirmation
 
Joined: Oct 2007
Location: Bavaria
Oddometer: 437
Quote:
Originally Posted by supershaft View Post
No. I am not talking about my own bikes. I am talking about the hundreds of stock beemers I have rode from /3's up to the last ones. Can't lump them all together? Generally speaking you sure can. All of them are better off being reved up. At least the way they come from the factory.
Well, I've not ridden hundreds of them.
But for all I know it's a matter of setup, not a natural law.
So at least for tuned beemers it's not a "must" but a "can".

For stock beemers, after thinking about it, I believe you're right.
They have to be reved to give power, having peak torque rather high.
Last time I rode a stock 2V beemer was at least 3 years ago (the year of the GS anniversary).
It was an R80GS Basic, right from BMW Classics, and it had literally no power at all.

EDIT: really stupid, I ride a stock R100RT from time to time. Probably forgot it as I don't connect it with Power ...

RGregor screwed with this post 10-23-2012 at 12:27 PM
RGregor is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 08:11 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014