Schwany
VIP MEMBER
- Joined
- Apr 22, 2020
- Messages
- 3,831
Just giving you a bump to see how it is going getting ready.
750cc Norton Commando Salt Flats Build
- Thread starter Zachary Brown
- Start date
Zachary Brown
VIP MEMBER
- Joined
- Nov 11, 2018
- Messages
- 64
It's been going kinda slow. Not alot to do other than work out trailer, tuning options, and getting a race suit. I'm working on getting time and a dyno in the next month or so. That's been more challenging since there's not alot of dynos in my area that do bikes. In the meantime I've been taking out for some short runs on the local straightaway breaking it in and tuning what I can by feel. So far it all feels pretty solid all the way to 7k RPM. Don't have enough room to get it past 3rd-4th gear but it pulls like mad all the way through.
Schwany
VIP MEMBER
- Joined
- Apr 22, 2020
- Messages
- 3,831
Wish I had a local straightaway. All I have around here is a speeding ticket waiting to happen. 
I feel ya on the dyno operators. The young men running them on motorcycles near me are not accustomed to turning the throttle on engines that don't wind up to 11K or more. Would be a bad expensive day if they blew up my engine and charged me $225US to do it. They are not responsible for anything. I'm just going to stick with seat of the pants tuning.
Zachary Brown
VIP MEMBER
- Joined
- Nov 11, 2018
- Messages
- 64
To be fair my straightaway is a potential ticket as well, but its very remote with limited side streets. Do what I gotta do every so often
I feel ya on the dyno operators. The young men running them on motorcycles near me are not accustomed to turning the throttle on engines that don't wind up to 11K or more. Would be a bad expensive day if they blew up my engine and charged me $225US to do it. They are not responsible for anything. I'm just going to stick with seat of the pants tuning.
I did find someone that does vintage bike dyno out in NC so we'll see how soon I can get time to get out there. Rather have someone experienced than a newby used to tuning 800-1000cc modern machines. Haha.Zachary Brown
VIP MEMBER
- Joined
- Nov 11, 2018
- Messages
- 64
So finally got an update to share. Made the drive out to Jake Hall at HCV in Ashville, NC to get some dyno time. Made a few pulls to get the machine warmed up before making a base run. Base run showed that the tuning was rich, but given about a 2000ft change in elevation I was pretty much on the money back home just going off plug checks. Now this wasn't a full RPM pull so the ~55hp number was a little low to start with.
We did a little tweaking on the main jetting to get the AFR number closer the perfect number and made a few more runs changing the timing to see if we could pull some more power out of the motor. But no adjustments we made to timing gained anything in the HP numbers. After several more runs we got it to pull 60-61rwhp @ 6,500 RPM. We did discover that the left bank was lean compared to the right (blue line on the AFR chart in the middle) so there's probably a little more balance to be gained there.
Here's a video of the last couple pulls we made before calling it a day.
During the debrief we discussed a few options to try out to squeeze the max out of the motor that needed more time and tools than we had available. First would be possibly advancing the cam a few more degrees to push the power band a little higher. Jake felt like there's more power in the motor than we were seeing. He was hoping to see 65rwhp and thinks its still possible. The other would be going for a narrower tire to drop the weight the motor is fighting against. But the obvious trade off there is potential loss of traction surface.
Another thing we found was the drive side crank seal started puking out oil after back to back pulls. Gonna have to check the crank ventilation setup for restrictions. If nothing apparent shows up I may have to look into hooking up a vacuum system to help pull the crankcase air out.
I plan to start with checking the cam timing to see if its possible to advance a few more degrees. If memory serves its currently at 3 degrees advanced. I don't know if I'll be able to make another trip for a dyno session before heading to the salt so I'll just have to go on feel again. At the end of the day Jake still said that it was the highest producing 750 he'd seen and as it sits the motor would be competitive on the road race circuit. (Obviously not possible in current configuration haha).
Hoping to get time to check the cam timing this week and take it out for a test hit and see if the power feels improved.
We did a little tweaking on the main jetting to get the AFR number closer the perfect number and made a few more runs changing the timing to see if we could pull some more power out of the motor. But no adjustments we made to timing gained anything in the HP numbers. After several more runs we got it to pull 60-61rwhp @ 6,500 RPM. We did discover that the left bank was lean compared to the right (blue line on the AFR chart in the middle) so there's probably a little more balance to be gained there.
Here's a video of the last couple pulls we made before calling it a day.
During the debrief we discussed a few options to try out to squeeze the max out of the motor that needed more time and tools than we had available. First would be possibly advancing the cam a few more degrees to push the power band a little higher. Jake felt like there's more power in the motor than we were seeing. He was hoping to see 65rwhp and thinks its still possible. The other would be going for a narrower tire to drop the weight the motor is fighting against. But the obvious trade off there is potential loss of traction surface.
Another thing we found was the drive side crank seal started puking out oil after back to back pulls. Gonna have to check the crank ventilation setup for restrictions. If nothing apparent shows up I may have to look into hooking up a vacuum system to help pull the crankcase air out.
I plan to start with checking the cam timing to see if its possible to advance a few more degrees. If memory serves its currently at 3 degrees advanced. I don't know if I'll be able to make another trip for a dyno session before heading to the salt so I'll just have to go on feel again. At the end of the day Jake still said that it was the highest producing 750 he'd seen and as it sits the motor would be competitive on the road race circuit. (Obviously not possible in current configuration haha).
Hoping to get time to check the cam timing this week and take it out for a test hit and see if the power feels improved.
With out the accurately done cam timing numbers for both the intake and exhaust and the valve lifts, 3 degree advance doesn't mean much to me, And if it is not done properly, It means nothing. I do understand lobe centers, which is one of the best ways to set up cams.
Fast Eddie
VIP MEMBER
- Joined
- Oct 4, 2013
- Messages
- 23,083
That’s a surprisingly linear, in fact civilised, power curve for an engine of that tune!
I would have thought you’d have had a bit more up top to be honest.
IMHO, I’d be looking at exhaust pipe options, a big cam is very sensitive to pipes.
I would have thought you’d have had a bit more up top to be honest.
IMHO, I’d be looking at exhaust pipe options, a big cam is very sensitive to pipes.
Zachary Brown
VIP MEMBER
- Joined
- Nov 11, 2018
- Messages
- 64
Jake was the one running the throttle during the pulls. We're both sure it's got more in it. Just need to work to find it before heading to the salt.
If I could find someone local that would be willing to bend tubes in these small diameters I'd be all over it. Sadly no one that I've been able to find in a 50-60 mile radius wants to touch anything less than 2" dia. Thought running 1 5/8" would give plenty of breathing room.
Correct. My mistake. Sleep deprived from a 10+hr road trip. My brain timing is a bit retarded today
Fast Eddie
VIP MEMBER
- Joined
- Oct 4, 2013
- Messages
- 23,083
I tried 1 1/2 pipes on my hopped up 850 and they were a sizeable step BACKWARDS !Jake was the one running the throttle during the pulls. We're both sure it's got more in it. Just need to work to find it before heading to the salt.
If I could find someone local that would be willing to bend tubes in these small diameters I'd be all over it. Sadly no one that I've been able to find in a 50-60 mile radius wants to touch anything less than 2" dia. Thought running 1 5/8" would give plenty of breathing room.
Correct. My mistake. Sleep deprived from a 10+hr road trip. My brain timing is a bit retarded today
Why not beg / borrow a set of stock 1 3/8:down pipes and try them, just to give you an idea ?
Zachary Brown
VIP MEMBER
- Joined
- Nov 11, 2018
- Messages
- 64
Suppose its worth a shot. I'll see what I can scrounge up.
hybridracer
Basic
- Joined
- Feb 21, 2013
- Messages
- 366
Don’t forget that a heavy crankshaft is best for top speed.
maaseyracer
Basic
- Joined
- Apr 28, 2015
- Messages
- 237
At 6500 rpm, that is closing in on 110% VE. Very impressive.
That full auto head is bumping up against the limits of air flow, a JS2 might actually make more power in the 6500 rpm neighborhood on that setup. The big cam has too much duration, curtain area, and curtain time. Along with that the big cam is likely giving away torque and cylinder pressure without giving much useful top-end benefit. Valve size is the big limiter, and if you go to a larger valve port size will be the limiter. Also above this power I would look into steel rods.
I suspect there are some good gains optimizing this setup. Great start.
That full auto head is bumping up against the limits of air flow, a JS2 might actually make more power in the 6500 rpm neighborhood on that setup. The big cam has too much duration, curtain area, and curtain time. Along with that the big cam is likely giving away torque and cylinder pressure without giving much useful top-end benefit. Valve size is the big limiter, and if you go to a larger valve port size will be the limiter. Also above this power I would look into steel rods.
I suspect there are some good gains optimizing this setup. Great start.
Schwany
VIP MEMBER
- Joined
- Apr 22, 2020
- Messages
- 3,831
Generic stream of babble not meant for anyone in particular, but feel free to be offended: 
I have to wonder if the old cam profile the JS04 is based on was ever used with a Norton head that had the reduced exit D exhaust ports. If the D port concept on an old twin head is as good as people selling it claim, why would a 1 1/2" exhaust of the correct length make any significant difference? I seriously doubt anyone making significant HP with a Norton engine aimed at racing on the salt flats is running 1 3/8" diameter exhaust pipes. Then again are people talking I.D. or O.D.?
If the excessive crank case pressure issue blowing out the main seal is not resolved the engine will be up against a compressed air wall on piston downstroke and never produce what it is capable of.
The JS02 I had in my engine for a while was strong and felt like it did not run out of legs, but I'll never know how much power it made because my bike has never been on a dyno. The JS02 didn't feel any stronger than my old SS cam though. I actually prefer the SS because it is a little more violent when it comes on. It also works a little better on the street with a lighter crank. but i digress
I have to wonder if the old cam profile the JS04 is based on was ever used with a Norton head that had the reduced exit D exhaust ports. If the D port concept on an old twin head is as good as people selling it claim, why would a 1 1/2" exhaust of the correct length make any significant difference? I seriously doubt anyone making significant HP with a Norton engine aimed at racing on the salt flats is running 1 3/8" diameter exhaust pipes. Then again are people talking I.D. or O.D.?
If the excessive crank case pressure issue blowing out the main seal is not resolved the engine will be up against a compressed air wall on piston downstroke and never produce what it is capable of.
The JS02 I had in my engine for a while was strong and felt like it did not run out of legs, but I'll never know how much power it made because my bike has never been on a dyno. The JS02 didn't feel any stronger than my old SS cam though. I actually prefer the SS because it is a little more violent when it comes on. It also works a little better on the street with a lighter crank. but i digress
