Max HP with reliability?
- Thread starter Tony F
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As a CNW owner, he probably wonders if the 35mm Keihin's are a must as far as achieving the potential of the powerplant.
Panic - is there an easy CFM calculator for engines that would tell Tony if how much flow his engine combo needs? I recall doing something similar for my engine and came up not with a CFM number but a carb size (might have been out of the Dunstall tuning book) and came up with 34mm.
Tony, there's a lot of work that's needed to make the bottom end of the long rod parallel-twin bomb-proof so that you can spin the rpm's to make peak power. For instance, a Maney short-stroke 750 (his barrels, case-halves, lightweight crank) with custom pistons and rods mated to a Johnson j380 cam, head, etc. will make about 8,000 rpm without running the piston speed too high. Set up right, you could hit 80hp. Looking at about $12k for the motor.
However, if you put the effort (and money) in - you can probably make 65+hp pretty easily and without fear of catastrophe. If you're just looking at bolt-ons, you're a bit more limited though.
Panic - is there an easy CFM calculator for engines that would tell Tony if how much flow his engine combo needs? I recall doing something similar for my engine and came up not with a CFM number but a carb size (might have been out of the Dunstall tuning book) and came up with 34mm.
Tony, there's a lot of work that's needed to make the bottom end of the long rod parallel-twin bomb-proof so that you can spin the rpm's to make peak power. For instance, a Maney short-stroke 750 (his barrels, case-halves, lightweight crank) with custom pistons and rods mated to a Johnson j380 cam, head, etc. will make about 8,000 rpm without running the piston speed too high. Set up right, you could hit 80hp. Looking at about $12k for the motor.
However, if you put the effort (and money) in - you can probably make 65+hp pretty easily and without fear of catastrophe. If you're just looking at bolt-ons, you're a bit more limited though.
While I was at N-V, our prototypes were in what my boss called "Stage 3" tune. They checked out on the dynamometer in the competition shop at 83 bhp, but that was just the engine - no transmission hooked up. We had a big fan blowing air over the engine for cooling as part of the dyno system. The engine was complete - using its own oil pump.
I'm going from memory, but I think that was at about 6500 rpm. They had the stock twin-Amal carb set up.
I don't remember doing any endurance work on the dyno, but our track testing at the Motor Industries' Research Association track, near Nuneaton, involved 8 hours a day at 100 mph with stops only for rider changes and fuel (and for chain adjustments when we had the 1/4 inch chain!). We ran probably 12,000 miles on those tests, all on one bike.
The only "hand grenade" we got was when a final drive failed at about 105 mph.
We ran on-the-road endurance on the second prototype, and eventually were doing 1000 miles a day on two 8-hour turns (4 a.m. to noon and 4 p.m to midnight). One rider went off road through a hawthorn hedge at about 70, and another hit a cow pat in the middle of a 60 mph turn and came off, but those were our only incidents.
We did have failures in the first couple of weeks, so we stayed on a figure-8 course around the Midlands. That way, the rescue van didn't have a long drive! After that we went farther afield (Lake District, Yorkshire) with no problems. Great fun, particularly when you're getting paid to do it.
I'm going from memory, but I think that was at about 6500 rpm. They had the stock twin-Amal carb set up.
I don't remember doing any endurance work on the dyno, but our track testing at the Motor Industries' Research Association track, near Nuneaton, involved 8 hours a day at 100 mph with stops only for rider changes and fuel (and for chain adjustments when we had the 1/4 inch chain!). We ran probably 12,000 miles on those tests, all on one bike.
The only "hand grenade" we got was when a final drive failed at about 105 mph.
We ran on-the-road endurance on the second prototype, and eventually were doing 1000 miles a day on two 8-hour turns (4 a.m. to noon and 4 p.m to midnight). One rider went off road through a hawthorn hedge at about 70, and another hit a cow pat in the middle of a 60 mph turn and came off, but those were our only incidents.
We did have failures in the first couple of weeks, so we stayed on a figure-8 course around the Midlands. That way, the rescue van didn't have a long drive! After that we went farther afield (Lake District, Yorkshire) with no problems. Great fun, particularly when you're getting paid to do it.
Frank,
I love having you on the boards. Your history with N-V is a tremendous asset.
What year was the 83hp motor? My Racing Norton's book has numbers somewhere in that power range for the monocoque framed 1973 JPS bike. It was a short-stroke 750 with 11:1 comp, re-angled oversize valves, 7s cam and (I believe) 34mm Amal Mk2's.
I'd assume it wouldn't be terribly streetable, but it does give creedance to the 750ss Maney motor's power claims. You'd spend more on the motor than you would an 80hp Ducati Monster though.
Tony - I found a Dell'Orto carb sizing chart that put's 60hp twins in the 32-38mm range. For a warmed over Norton, that'd put the Keihin's right in the middle of the size recommendations. Vastly oversimplified way to go about it and I'm sure I'll get a tongue lashing from Panic - but there it is.
If I recall correctly, gearbox failures were a huge problem in 1973. (When weren't they?) That brings up another point - even if the motor's not a ticking time bomb, the primary and gearbox will need help on a bike making substantially more power than stock. I've got a Maney outrigger bearing on mine, which necessitates a belt drive.
Fun stuff to write about on a drizzly Saturday in western Washington State though.
I love having you on the boards. Your history with N-V is a tremendous asset.
What year was the 83hp motor? My Racing Norton's book has numbers somewhere in that power range for the monocoque framed 1973 JPS bike. It was a short-stroke 750 with 11:1 comp, re-angled oversize valves, 7s cam and (I believe) 34mm Amal Mk2's.
I'd assume it wouldn't be terribly streetable, but it does give creedance to the 750ss Maney motor's power claims. You'd spend more on the motor than you would an 80hp Ducati Monster though.
Tony - I found a Dell'Orto carb sizing chart that put's 60hp twins in the 32-38mm range. For a warmed over Norton, that'd put the Keihin's right in the middle of the size recommendations. Vastly oversimplified way to go about it and I'm sure I'll get a tongue lashing from Panic - but there it is.
If I recall correctly, gearbox failures were a huge problem in 1973. (When weren't they?) That brings up another point - even if the motor's not a ticking time bomb, the primary and gearbox will need help on a bike making substantially more power than stock. I've got a Maney outrigger bearing on mine, which necessitates a belt drive.
Fun stuff to write about on a drizzly Saturday in western Washington State though.
I'm not sure if that "Stage 3" configuration made it into the production bikes. Both prototypes supposedly had it and were derivatives of the 1866 Atlas motor.
Our dyno was a clunky old thing, so maybe we (or it) were optimistic about the results. Our endurance testing certainly didn't show any gearbox or primary drive problems and the only engine item was a tendency to burn through the head gasket.
We sure weren't gentle with the prototypes, as the objective was to see if we could break things in hard use. The only component that didn't get tested was the center stand. The Commando was in full production before I ever saw one.
Also, before I left, we hadn't started doing any testing of production bikes to see if there were any big differences. We were pretty heavily committed to the works motocross effort the last 5 months or so before I bailed out.
Our dyno was a clunky old thing, so maybe we (or it) were optimistic about the results. Our endurance testing certainly didn't show any gearbox or primary drive problems and the only engine item was a tendency to burn through the head gasket.
We sure weren't gentle with the prototypes, as the objective was to see if we could break things in hard use. The only component that didn't get tested was the center stand. The Commando was in full production before I ever saw one.
Also, before I left, we hadn't started doing any testing of production bikes to see if there were any big differences. We were pretty heavily committed to the works motocross effort the last 5 months or so before I bailed out.
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All motor planing starts at the cam and works out from there.
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"For instance, a Maney short-stroke 750 (his barrels, case-halves, lightweight crank) with custom pistons and rods mated to a Johnson j380 cam, head, etc. will make about 8,000 rpm without running the piston speed too high. Set up right, you could hit 80hp. "
Well there's not much Norton left in an engine like that is there?
My race motor puts out 68bhp at the rear wheel with only a 5S cam, 10.5 pistons and 36mm Mk2s. No oversize valves or anything too fancy or expensive. It even has genuine Norton con rods and bottom end. The head had been flowed a bit, but to build a motor like mine would cost little more than you would spend on a normal rebuild.
Well there's not much Norton left in an engine like that is there?
My race motor puts out 68bhp at the rear wheel with only a 5S cam, 10.5 pistons and 36mm Mk2s. No oversize valves or anything too fancy or expensive. It even has genuine Norton con rods and bottom end. The head had been flowed a bit, but to build a motor like mine would cost little more than you would spend on a normal rebuild.
Re: "Are flat slides mandatory in that neighborhood"
If you mean "do I need to buy this specific product for this purpose", the answer is no, a pair of Amal GPs will do quite nicely if you want to spend money and have people congratulate you on your choice.
If you mean "do it need 35mm carbs for this purpose", the answer is no.
You could use pretty much anything - if it's too small the pumping loss will go up, and the fuel curve will go to hell; if it's too large the response will be bad unless jetted very rich. Carburetors do not flow X CFM, they flow X CFM under Y test conditions. Change the condition = change the flow.
750cc × 7,000 RPM × 95% VE is 44 CFM per throat by the usual formula.
Jennings suggests using D=K×(C×N)^.5, where:
K is a constant (use K values between .60 and .70 for most pushrod OHV engines based on their volumetric efficiency and rod to stroke ratio)
D is the throat diameter in mm
C is the displacement in liters
N is peak power RPM
The Norton has fair VE and low R/S ratio, try .7:
.7×(.375×7,000)^.5 = 35.9mm
My guess: unless the head is professionally prepared, going more than 2mm above your intake port size won't add much power, and then only at a speed that invites driving over the crank.
If you mean "do I need to buy this specific product for this purpose", the answer is no, a pair of Amal GPs will do quite nicely if you want to spend money and have people congratulate you on your choice.
If you mean "do it need 35mm carbs for this purpose", the answer is no.
You could use pretty much anything - if it's too small the pumping loss will go up, and the fuel curve will go to hell; if it's too large the response will be bad unless jetted very rich. Carburetors do not flow X CFM, they flow X CFM under Y test conditions. Change the condition = change the flow.
750cc × 7,000 RPM × 95% VE is 44 CFM per throat by the usual formula.
Jennings suggests using D=K×(C×N)^.5, where:
K is a constant (use K values between .60 and .70 for most pushrod OHV engines based on their volumetric efficiency and rod to stroke ratio)
D is the throat diameter in mm
C is the displacement in liters
N is peak power RPM
The Norton has fair VE and low R/S ratio, try .7:
.7×(.375×7,000)^.5 = 35.9mm
My guess: unless the head is professionally prepared, going more than 2mm above your intake port size won't add much power, and then only at a speed that invites driving over the crank.
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ludwig said:
Ludwig - i agree, but am curious how you shed 140 lbs??
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ludwig said:
wow - i think it would be easier (and cheaper) to have liposuction or go on a serious diet/exercise plan :lol:
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