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 06-25-2012, 04:41 PM   #106
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
Is that a 750 or 1000?
__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-25-2012, 04:42 PM   #107
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,308
Quote:
Originally Posted by bmweuro View Post
Is that a 750 or 1000?


750.

It went to 92 hp when I took it out to 1000
__________________
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 06-25-2012, 04:45 PM   #108
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
Quote:
Originally Posted by pommie john View Post
750.

It went to 92 hp when I took it out to 1000
My best is 72HP. It gets expensive once you get over 50HP.
__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-25-2012, 04:50 PM   #109
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,308
Quote:
Originally Posted by bmweuro View Post
My best is 72HP. It gets expensive once you get over 50HP.

From a 750? I agree it get crazy money after a while. Mine started out as 750 but I took it out to 1000 after a season.

The 68hp engine here had a 336, Venolia pistons ( the short ones, I bought from CC as they were called then) I can't remember what valves were in it but Jim Cray built it. As you can see on the graph it had Amal 38mm smoothbores and showed a slight improvement with 38mm Dells.
There wasn't too much else in the engine, modified oil system of course.
__________________
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 06-25-2012, 05:43 PM   #110
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
Quote:
Originally Posted by pommie john View Post
From a 750? I agree it get crazy money after a while. Mine started out as 750 but I took it out to 1000 after a season.

The 68hp engine here had a 336, Venolia pistons ( the short ones, I bought from CC as they were called then) I can't remember what valves were in it but Jim Cray built it. As you can see on the graph it had Amal 38mm smoothbores and showed a slight improvement with 38mm Dells.
There wasn't too much else in the engine, modified oil system of course.
For me it was a set of my own pistons, sport cam, larger valves, porting the heads, 36mm round slide carburetors and the biggest improvement was a 2/1 exhaust that I designed.
__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-26-2012, 12:00 AM   #111
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,308
Quote:
Originally Posted by bmweuro View Post
For me it was a set of my own pistons, sport cam, larger valves, porting the heads, 36mm round slide carburetors and the biggest improvement was a 2/1 exhaust that I designed.
I never had much luck with 2:1 exhausts. I made one that made decent power at the top end but it had a big hole in the torque in the mid range.
The simplicity of a 2:2 with something like a Supertrapp on the end has a lot going for it. Somewhere I have dyno charts comparing them. I'll dig them out in the next few days.
__________________
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 06-26-2012, 12:24 AM   #112
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
Quote:
Originally Posted by pommie john View Post
I never had much luck with 2:1 exhausts. I made one that made decent power at the top end but it had a big hole in the torque in the mid range.
The simplicity of a 2:2 with something like a Supertrapp on the end has a lot going for it. Somewhere I have dyno charts comparing them. I'll dig them out in the next few days.
We lost 5-7Hp with off the shelf 2/1's and we gained almost 10HP with mine. Merged header and a big collection pipe before the muffler.
__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-26-2012, 01:30 AM   #113
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,308
Quote:
Originally Posted by bmweuro View Post
We lost 5-7Hp with off the shelf 2/1's and we gained almost 10HP with mine. Merged header and a big collection pipe before the muffler.


Was it a bit like the Gordon Blair Norton pipe? Very short headers, maybe 16" long into a single collector at least twice the length of the primary?
__________________
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 06-26-2012, 01:36 AM   #114
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
Quote:
Originally Posted by pommie john View Post
Was it a bit like the Gordon Blair Norton pipe? Very short headers, maybe 16" long into a single collector at least twice the length of the primary?
I wont give out the specs but here is what it looked like.

__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-26-2012, 02:01 AM   #115
moorespeed
Adventurer
 
Joined: Sep 2010
Oddometer: 55
yes i am the moorespeed, and i have never had less than 74hp at the rear wheel short stroke or standard stroke . the short stroke starts to pull from 6400 and makes max power at 9450, the standard stroke is about 1000rpm less. i have my own pistons 83mm and 88mm.
moorespeed is offline   Reply With Quote
Old 06-26-2012, 02:01 AM   #116
pommie john
Beastly Adventurer
 
pommie john's Avatar
 
Joined: Apr 2008
Location: Brisvegas, Australia
Oddometer: 1,308
Quote:
Originally Posted by bmweuro View Post
I wont give out the specs but here is what it looked like.



Interesting. Surprisingly long primaries.
__________________
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 06-26-2012, 04:39 AM   #117
bill42
Old-School BMWs
 
bill42's Avatar
 
Joined: Dec 2011
Location: Long Island, NY
Oddometer: 351
How much approximately is the actual horspower of a 1981 R100 motor that BMW rated as having 70HP at the engine?
bill42 is offline   Reply With Quote
Old 06-26-2012, 05:19 AM   #118
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,206
Quote:
Originally Posted by bill42 View Post
How much approximately is the actual horspower of a 1981 R100 motor that BMW rated as having 70HP at the engine?
Probably about 55-60... downhill... with a tailwind.
__________________
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 is offline   Reply With Quote
Old 06-26-2012, 07:47 AM   #119
bmweuro
Mad Scientist
 
bmweuro's Avatar
 
Joined: Nov 2003
Location: Chico, California
Oddometer: 3,282
The driveshaft eats up 20% so that would take it from 70hp at the flywheel to 56hp at the rear wheel.
__________________
BOXER Metal
BMW Biker Scum
BMW Mad Scientist!
VBMWMO #7770, BMW MOA #48694 & Airhead BMW Club #600
bmweuro is offline   Reply With Quote
Old 06-26-2012, 11:17 AM   #120
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 7,602
Quote:
Originally Posted by bill42 View Post
How much approximately is the actual horspower of a 1981 R100 motor that BMW rated as having 70HP at the engine?
How much actual hp at the crank? I know of no one that has measured the power at the crank other than the factory. I suspect there rating is a bit high but they don't stretch the truth near as much as many manufacturers. At least here in the states I think the only airhead rated that high was '77 RS's half way into the '78 model year? I think a US '81 R100 was rated at 67?

I don't think our drive line eats up 20%. Oil alone makes a big diff but . . . . It's close! Different dyno's read different figures. It all depends on the dyno AND operator. The dyno I was around that dynoed a lot of airheads you were super lucky to get 56hp. Most were from 48 to 54hp and that's R100's.
supershaft 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 12:41 PM.


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