Date: Tue, 21 Jul 1998 09:38:28 -0400
From: Frank Palmeri
I happened to be browsing a book on big block chevy upgrading, and was wondering if any of these techniques could be applied to motorcycles, specifically the Commando, to increase horsepower. I understand that because of the Commando bottom end, with only 2 main bearings supporting that big crank, you get dangerous crank flex any time you add significant horsepower. Let's just forget about that for this discussion. Since there is a one piece crank available for many $$, potentially even that restriction could be solved.
The first thing the chevy book said to do was get a less restrictive exhaust. What does that mean for us, open pipes? How restrictive is the stock 750 or 850 (balance pipe) exhaust? Can more power be added by changes in this area?
Next they recommend carb improvement. I've put on a single carb for increased midrange, better mileage, and easy starting. However, lets assume 2 carbs are better for more power. They really warn about putting on too big a carb; you whack the throttle open, and all of a sudden there's more air than fuel so your way lean and there's no power. They recommend the Holley "pumpers", which inject more fuel under these conditions to match the increased air. Doesn't Dell'Orto make "pumper" style motorcycle carbs as used on Italian bikes? If so, could the proper size (not too big, say 32-34mm depending on displacement) pumper be fitted to the Commando? I can't recall ever seeing Dell'Ortos on any Commando. I wonder why, since it seems a pumper would solve the lean problem on quickly open throttle like on the big block chevy.
Next is mechanical, like better cam, lighter valve train parts, etc. At this point I'm just happy my 850 seems to not have one of the many soft cams that are out there. I'd almost be afraid to replace it for fear of getting a soft (not properly heat treated) cam. Assuming a better cam exists, what would be the best one for more power for a daily use ridden bike?
Then of course there's boring. Apparently the big block chevys have sufficient "meat" in the cylinders to stand overbores. I don't thing that's the case with the Commando, however. I think there used to be after-market barrels available, but I seem to remember quality and reliability problems with them. Let's say because of these factors an overbore is not an option.
I already have the Boyer so I'm covered in that area. Maybe a hotter coil and better wires could be added, but that's about it electrical wise.
So what can be realistically done to the Commando engine to gain, say,
20 HP at the rear wheel? Keeping it mind the bike is to be ridden as a
daily/tourer bike, not a strip/track machine.
___________________________________________________________________________
Frank Palmeri
USNOA #7386
1975 Norton 850 Commando Interstate
ridden daily/cleaned less
1987 Honda Z50R
my son's dream bike, but I like it too
1967 Montgomery Ward's/Benelli Riverside 350 sitting in boxes
awaiting my
attention
___________________________________________________________________________
Date: Tue, 21 Jul 1998 15:52:31 +0200
From: Espen Olsen
At 09:38 21.07.98 -0400, you wrote:
>Doesn't Dell'Orto make "pumper" style motorcycle carbs
>as used on Italian bikes? If so, could the proper size (not too big,
say
>32-34mm depending on displacement) pumper be fitted to the Commando?
I
>can't recall ever seeing Dell'Ortos on any Commando. I wonder why,
since it
>seems a pumper would solve the lean problem on quickly open throttle
like
>on the big block chevy.
I have seen two of these carbs fitted to a '73 non-Combat Roadster.
The owner was very proud of them and said they really made an improvement.
--
Espen Olsen
LA6MGA/LA1K, SST#5, DoD#7962, <*>
'57 Triumph 5T, '72 Norton Commando 750 Combat, Slow old computer,
NOK 5,-
In theory, there's no difference between theory and practice, but in
practice, there is.
Date: Tue, 21 Jul 1998 14:12:36 -0000
From: C. Arthur Xanders
----------
> From: Frank Palmeri
> Subject: MORE HORSEPOWER FOR THE COMMANDO
>
> I happened to be browsing a book on big block chevy upgrading, and
was
> wondering if any of these techniques could be applied to motorcycles,
> specifically the Commando, to increase horsepower. .....I
> The first thing the chevy book said to do was get a less restrictive
> exhaust. What does that mean for us, open pipes? How restrictive
is the
> stock 750 or 850 (balance pipe) exhaust? Can more power be added
by changes
> in this area?
MAC makes downpipes that have a larger diameter, they can be combined with Emgo's Dunstall replicas to make a less restrictive exhaust. We used to run this on our Commando racer (now we run S pipes and megaphones - for increased ground clearance) Leo Goff once told me that the longer the exhaust pipe is before it make the first bend the better it is. Pictures of his drag bike show a long initial run of exhaust pipe.
> Next they recommend carb improvement. I've put on a single carb for
> increased midrange, better mileage, and easy starting. However, lets
assume
> 2 carbs are better for more power. They really warn about putting
on too
> big a carb; you whack the throttle open, and all of a sudden there's
more
> air than fuel so your way lean and there's no power. They recommend
the
> Holley "pumpers", which inject more fuel under these conditions to
match
> the increased air. Doesn't Dell'Orto make "pumper" style motorcycle
carbs
> as used on Italian bikes? If so, could the proper size (not too big,
say
> 32-34mm depending on displacement) pumper be fitted to the Commando?
I
> can't recall ever seeing Dell'Ortos on any Commando. I wonder why,
since it
> seems a pumper would solve the lean problem on quickly open throttle
like
> on the big block chevy.
Stay at 32 or 34 mm. You can run Mikunis cheaply, especially if you already have jets and jetting experience from another Mikuni equipped bike. We run AMAL MK2s on our race bikes, easy to tune and use the same jets as Concentrics. Match up the manifold to the head with a Dremel tool.
> Next is mechanical, like better cam, lighter valve train parts, etc.
At
> this point I'm just happy my 850 seems to not have one of the many
soft
> cams that are out there. I'd almost be afraid to replace it for fear
of
> getting a soft (not properly heat treated) cam. Assuming a better
cam
> exists, what would be the best one for more power for a daily use
ridden
> bike?
Megacycle makes great street camshafts for Commandos. We are currently putting one in Barry Armitage's (the editor of the Norton News) MK3. Megacycle cams are never soft. I have yet to run into a bad one. Lighten the valve train with Alloy Tech pushrods. Polish your valves before installation. You can grind down and polish the rocker arms - this is covered in Dunstall's Norton Speed Tuning book.
> Let's say because of these factors an overbore is not an option.
Correct.
> I already have the Boyer so I'm covered in that area. Maybe a hotter
coil
> and better wires could be added, but that's about it electrical wise.
A big old yellow Accel coil of a HD is what we run on all of our hot Nortons.
> So what can be realistically done to the Commando engine to gain,
say, 20
> HP at the rear wheel? Keeping it mind the bike is to be ridden as
a
> daily/tourer bike, not a strip/track machine.
The stuff that I have listed above (plus head porting and breather modification) are most of what we do to our AHRMA racers. Very few Sportsman 750 bikes make significantly more HP than our bikes do. Art X
Date: Tue, 21 Jul 1998 10:38:36 -0400
From: DUBEY, KEN
> The first thing the chevy book said to do was get a less restrictive
> exhaust. What does that mean for us, open pipes? How restrictive
is
> the stock 750 or 850 (balance pipe) exhaust? Can more power be added
by
> changes in this area?
Frank,
The main idea of these improvements is to get get more fuel/air mixture into the cylinder, and then be able to get it out again. Power is directly related to the amount of fuel/air mix being pumped through the motor. Turbo and Super charging work so well by forcing the air in and not requiring the engine to try and pump the increased volume by itself.
I found than a K&N air filter, and Dunstall mufflers made a substantial difference in the air flow, I had to rejet the carbs for the increase in air entering and exiting the motor. That alone is probably worth one or two HP on a two cylinder engine.
In the V8 Chevy world, a balance pipe in the exhaust is actually better, it allows both banks of cylinders to use the entire exhaust system to reduce restriction, this would also apply to a two cylinder MC engine. A side benefit is lower exhaust noise with the balance pipe, and smoother running due to a decrease in back pressure thru the system.
> Next they recommend carb improvement. I've put on a single carb for
> increased midrange, better mileage, and easy starting. However, lets
> assume 2 carbs are better for more power. They really warn about
putting on
> too big a carb; you whack the throttle open, and all of a sudden
there's
> more air than fuel so your way lean and there's no power. They recommend
> the Holley "pumpers", which inject more fuel under these conditions
to
> match the increased air. Doesn't Dell'Orto make "pumper" style motorcycle
> carbs as used on Italian bikes? If so, could the proper size (not
too big,
> say 32-34mm depending on displacement) pumper be fitted to the Commando?
I
> can't recall ever seeing Dell'Ortos on any Commando. I wonder why,
> since it seems a pumper would solve the lean problem on quickly open
throttle
> like on the big block chevy.
There are formulas used to determine the optimum size of the carb venturi for any given displacement. One of the problems of too large a carb is the loss of Venturi effect.
If the engine is not able to draw enough of a volume of air through the larger opening to maintain the increase in air speed through the Venturi, then poor fuel atomization and inefficient cylinder filling will result result in poor performance that you note as being lean. This is partially compensated for by using accelerator pumps to stuff more gas in the cylinder to speed the engine up and regain flow at the venturi.
> Next is mechanical, like better cam, lighter valve train parts, etc.
At
> this point I'm just happy my 850 seems to not have one of the many
> soft cams that are out there. I'd almost be afraid to replace it
for fear of
> getting a soft (not properly heat treated) cam. Assuming a better
cam
> exists, what would be the best one for more power for a daily use
ridden
> bike?
>
> Then of course there's boring. Apparently the big block chevys have
> sufficient "meat" in the cylinders to stand overbores. I don't thing
> that's the case with the Commando, however. I think there used to
be
> after-market barrels available, but I seem to remember quality and
reliability
> problems with them. Let's say because of these factors an overbore
is not an
> option.
>
Different cams with longer duration and higher lift enable the cylinders
to draw more fuel/air in, however increasing lift and duration directly
determine the effective rpm range of the engine. The bigger the cam, the
higher and narrower the power range of the motor becomes. Proper cam selection
is a key factor in getting the motor to run the way you want, bigger is
not always better, especially in a heavily used street motor.
The 920 kit is probably the easiest way to get more stump pulling power from a Commando motor, forget minor increases like .030 or .040, the displacement gain here isn't really a noticeable power gain. What an increase to 920cc would do to the stock bottom end is another factor to consider, however Carillo rods and a stouter crank would be a wise thing to do if going that route.
> I already have the Boyer so I'm covered in that area. Maybe a hotter
coil
> and better wires could be added, but that's about it electrical wise.
>
> So what can be realistically done to the Commando engine to gain,
say, 20
> HP at the rear wheel? Keeping it mind the bike is to be ridden as
a
> daily/tourer bike, not a strip/track machine.
To get another 20 hp from a Commando and still expect it to run the way it does now probably isn't realistic, it will need to rev'd higher and will be much more sensitive to carb and valve adjustment as well as timing settings. Try the little things first and see how each affects the power before going for the major changes. Two carbs, a freer flowing exhaust, and maybe a gearing change would be a good starting point.
Ken
71 Commando Fastback LR
72 Commando Fastback
82 Honda FT 500
82 GMC S-15 LT1 V8
Date: Tue, 21 Jul 1998 23:46:46 +0900
From: Charles R. Lipton
Frank Palmeri wrote:
> Doesn't Dell'Orto make "pumper" style motorcycle carbs
> as used on Italian bikes? If so, could the proper size (not too big,
say
> 32-34mm depending on displacement) pumper be fitted to the Commando?
I
> can't recall ever seeing Dell'Ortos on any Commando. I wonder why,
since it
> seems a pumper would solve the lean problem on quickly open throttle
like
> on the big block chevy.
It has been done ... and done quite well. Ron Wood and C.R. Axtell used various Del Orto carb types and sizes on the Wood Norton dirt track bikes of the late 70s and had them producing over 80 bhp on a regular basis.
Reliability?!?!?!?!!!!! This is a family-oriented board, son.
The engines I remember at Ascot were short-stroke 750s and they used pumper carbs, but I don't remember what size ... somehow the number "40" sticks in my mind. Although I got a pile of re-usable engine parts out of Ron Wood in 1979, Vern Feuston -- and maybe Tom Davenport -- probably remembers more about the bikes and engines in actual use. One of the most successful tuners, Nick Delganis, used to live across the highway from me in West Covina, Ca. and maybe he can still be contacted via the SoCal Norton Owners if you want hard numbers to start with.
There is an article on the Norton flattrackers that includes the Wood / Axtell Del Orto equipped bikes in the July/August 1998 issue of Classic Racer (HK$90.00 at Bookazine in the Alexandra Building -- Ice House Street and Des Voeux Road -- in Central). It brought back a lot of memories ...
Charlie Lipton
Date: Tue, 21 Jul 1998 11:14:01 -0400
From: Frank Palmeri
At 10:38:36 on 07/21/98 "DUBEY, KEN" Wrote:
[snip]
>In the V8 Chevy world, a balance pipe in the exhaust is
>actually better, it allows both banks of cylinders to use the
>entire exhaust system to reduce restriction, this would also
>apply to a two cylinder MC engine. A side benefit is lower
>exhaust noise with the balance pipe, and smoother running
>due to a decrease in back pressure thru the system.
I had a feeling this was the case. I know the Norton 850 headers have a tendency to break and are harder to fit, but I think I'm going to look for a pair.
>There are formulas used to determine the optimum size
>of the carb venturi for any given displacement. One of the
>problems of too large a carb is the loss of Venturi effect.
>If the engine is not able to draw enough of a volume of air
>through the larger opening to maintain the increase in air
>speed through the Venturi, then poor fuel atomization and
>inefficient cylinder filling will result result in poor performance
>that you note as being lean. This is partially compensated
>for by using accelerator pumps to stuff more gas in the
>cylinder to speed the engine up and regain flow at the venturi.
I'd like to know how the formulas take into account how the bike will be ridden. Street vs. track is a big difference. It just seems like the Dell'Orto pumpers would work well with the pump action, I wonder why you never saw them on any British applications.
>Different cams with longer duration and higher lift enable
>the cylinders to draw more fuel/air in, however increasing
>lift and duration directly determine the effective rpm range
>of the engine. The bigger the cam, the higher and narrower
>the power range of the motor becomes. Proper cam selection
>is a key factor in getting the motor to run the way you want,
>bigger is not always better, especially in a heavily used street
>motor.
Isn't there supposed to be a 2S Commando cam available that's supposed to be better than stock for street use? More midrange but not too wild. My fear is I'll put that sucker in and it will have the stupid soft lobes! You just never know with Commando cams.
>The 920 kit is probably the easiest way to get more stump
>pulling power from a Commando motor, forget minor increases
>like .030 or .040, the displacement gain here isn't really a
>noticeable power gain. What an increase to 920cc would
>do to the stock bottom end is another factor to consider,
>however Carillo rods and a stouter crank would be a wise
>thing to do if going that route.
Wouldn't it be great if the 920 kit came with a new crank with an extra big, fat bearing in the middle:). In my dreams...
>To get another 20 hp from a Commando and still expect it
>to run the way it does now probably isn't realistic, it will
>need to rev'd higher and will be much more sensitive to
>carb and valve adjustment as well as timing settings. Try
>the little things first and see how each affects the power
>before going for the major changes. Two carbs, a freer
>flowing exhaust, and maybe a gearing change would
>be a good starting point.
A very informative post Ken, and thanks for taking the time. The reason I brought the subject up in the first place is that the Commando is *such* a nice bike to ride, a little more ponies would really make it perfect. Mines running so well these days, after years of getting it sorted out, that I'm using it all the time and really wringing it out. Ben and I regularly (well, sort of regularly) ride with big Ducatis and Guzzis and keep up with them except for big long straights. And this weekend, riding 2 up and loaded down, you really start to run out of steam in certain situations.
I wish that stupid Nemesis project, if it really is true and not just another attempt to bleed money out of the famous Norton name, would have announced a big twin with 3 bearing crank. Sort of like a vertical twin Buell, instead of this $50,000 V8 nonsense. The Commando is such a good base, with a modern (updated engine), this 400 pound platform would be a world beater.
Oh well, I'd better stop dreaming and fire up the browser and look for some used Dell'Ortos...
Frank Palmeri
Date: Tue, 21 Jul 1998 15:45:49 -0400
From: Latte' Jed
> There are formulas used to determine the optimum size of the carb
> venturi for any given displacement. One of the problems of too large
> a carb is the loss of Venturi effect. If the engine is not
able to
> draw enough of a volume of air through the larger opening to
> maintain the increase in air speed through the Venturi, then poor
> fuel atomization and inefficient cylinder filling will result result
> in poor performance that you note as being lean. This is partially
> compensated for by using accelerator pumps to stuff more gas in the
> cylinder to speed the engine up and regain flow at the venturi.
This is only a real problem at full throttle openings, at partial throttle you've still got the venturi. A 50mm carb opened just a little bit would still have good speed across the needle/jet where you want it. The ideal point is when the carb offers the same restriction as the rest of the intake system (like the intake valve or port), that's when the carb is big enough. The easiest answer to the problem of the bike choking when you whack the throttle open all the way at low revs is simpler than a throttle pump - don't do it! When I put the VM34's on my GS450 it took about three times of the bike choking before I acclimated to how far open the carbs needed to be at any point, I haven't noticed it since. This is the reason that CV carbs became so popular: people didn't have to learn how to use the throttle, they could just whack it open and the bike would go.
My personal experience is that a 34mm carb is a good size for a 250cc
cylinder, or 500cc twin. The carb should get smaller as the redline goes
down of course, since the amount of gas passed is smaller. I have a 34mm
DellOrto pumper on my Ducati 250 and it runs great, and I've got 34mm Mikuni
VM's on my Suzuki GS450 (225cc cylinders). Both of these are fairly revvy
machines, but both also idle perfectly and have a good enough low end (neither
is blessed with much of a low end with the stock carbs anyway), a good
midrange, and a really good top
end.
I'd consider 36mm to be conservative for a road-going 850, I'd probably go with 38mm. I've never tried these sizes on a Norton, you'd probably be hitting the limits of the head at those sizes, but if you opened the intake ports up a bit I'd bet you could go bigger. My experience with this has been with 750 Ducatis, which are similiar to a Commando in the torquey power delivery. 38mm DellOrto pumpers are a common conversion for the Weber-carbed ducks, they give good mileage, good idle, and the same midrange. The redline is 9K, but it's pointless to chase it that far, you're well past peak torque.