750cc Norton Commando Salt Flats Build

Zachary Brown said:

They are not. MPS is a partial streamliner class where MP is a "open" class with no streamlining. Current record is 138MPH for 750cc MP-PG and 137 for MP-PF according to the 2025 handbook.

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Just giving you a bump to see how it is going getting ready.

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.

Zachary Brown said:

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.

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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.

Schwany said:

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.

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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 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.

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.

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.

Who was twisting the throttle? You or Jake?

Sounds good.

I'm surprised the engine didn't make more power above 6500 RPM with that JS04 cam in it.

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.

Retarding the cam pushes the power band up higher, not advancing it. Exhaust systems as well as Nigel said. Graham

Schwany said:

Who was twisting the throttle? You or Jake?

Sounds good.

I'm surprised the engine didn't make more power above 6500 RPM with that JS04 cam in it.

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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.

Fast Eddie said:

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.

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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.

velo54 said:

Retarding the cam pushes the power band up higher, not advancing it. Exhaust systems as well as Nigel said. Graham

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Correct. My mistake. Sleep deprived from a 10+hr road trip. My brain timing is a bit retarded today

Zachary Brown said:

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

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I tried 1 1/2 pipes on my hopped up 850 and they were a sizeable step BACKWARDS !

Why not beg / borrow a set of stock 1 3/8:down pipes and try them, just to give you an idea ?

Fast Eddie said:

I tried 1 1/2 pipes on my hopped up 850 and they were a sizeable step BACKWARDS !

Why not beg / borrow a set of stock 1 3/8:down pipes and try them, just to give you an idea ?

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Suppose its worth a shot. I'll see what I can scrounge up.

Don’t forget that a heavy crankshaft is best for top speed.

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.

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

Schwany said:

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.?

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I too will add to the stream of babble, and lend my amatuer thoughts.

I have talked to Jim Dour at Megacycle about exactly this. The Original Norris/Sifton 480 was created for a Triumph, and D ports were not common on Triumphs in that era. In those days both Norris and Sifton made a profile and adapted it to everything they could. The cams existence was to push the limits of mostly lift and tappet strain on a Triumph. This was all done long before computer cam design was available to independent cam grinders.The closest thing to computer design in those days was Jim Dour would go to the Boeing offices in San Francisco after hours, programming punch cards and then take the feed sheet print outs and use a dividing head on a mill with a dial indicator that read in ten thousands and subdivide those lines by eye in hundred thousandths to make cams for Dick Mann's A65 and A70 race bikes.

Needless to say the JS4 cam has been significantly been reworked by Jim Schmidt since the Norris days and it is a very different cam, the lift is probably the only thing that is similar.

I am probably over simplifying this, but with the pipes the larger OD of the pipe will effectively create more duration. The pipe will change how long the cylinder keeps moving exhaust after the valve opens, and how much it pulls in during overlap. The pipe helps to create a time area for the escaping gases and the time area is slower with a larger pipe and faster with a smaller pipe. It does not change pressure wave as much, but it does change velocity of the gas. At lower RPM, the pulse can be slower. But at higher RPM, when the engine is moving a lot more gas, the larger pipe can keep flowing after the smaller pipe would start becoming a restriction. A smaller pipe is usually easier to manage as the exhaust gas velocity helps minimize the effects of reversion. However, it is limiting as well in other ways, which gets us into the nuance of cross over pipes, x pipes, merge collectors, etc.

If the excessive crankcase 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.

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The question(s) I have is, did the cam/valve size/port size create an airflow mismatch that made more cylinder pressure leak past the rings? Are the rings are fluttering or is this detonation? Is the lack of air flow or port velocity creating reversion with at high lifts and working past the rings? If so is this intake or exhaust reversion or both? My personal suspicion is that a lot of exhaust gas is pushing back into the chamber during overlap as velocity is lost due to inadequate flow at high valve lifts. But this still may only be a symptom and not be a root cause, there could be too much windage for this much pressure, or the reed valve is not large enough for the needs of this engine, a bad seal, or a million other things. But this is the optimize the system part of building a race bike.

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

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Also advance your JS2 a degree or two and compare it the SS cam, I would be curious to hear your thoughts on the comparison.

maaseyracer said:

The question(s) I have is, did the cam/valve size/port size create an airflow mismatch that made more cylinder pressure leak past the rings? Are the rings are fluttering or is this detonation? Is the lack of air flow or port velocity creating reversion with at high lifts and working past the rings? If so is this intake or exhaust reversion or both? My personal suspicion is that a lot of exhaust gas is pushing back into the chamber during overlap as velocity is lost due to inadequate flow at high valve lifts. But this still may only be a symptom and not be a root cause, there could be too much windage for this much pressure, or the reed valve is not large enough for the needs of this engine, a bad seal, or a million other things. But this is the optimize the system part of building a race bike.

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I believe I found the culprit of the breather issue. There was a slight kink in the breather hose that was restricting or completely stopping flow. It was hidden behind plastic hose guard I'd put over it to stop damage from rubbing. SSo at a glance everything looked normal. Re-routing the hose fixed the problem. Can't really check it with the motor running right now due to the weather we're currently having to confirm.

Zachary Brown said:

I believe I found the culprit of the breather issue. There was a slight kink in the breather hose that was restricting or completely stopping flow. It was hidden behind plastic hose guard I'd put over it to stop damage from rubbing. SSo at a glance everything looked normal. Re-routing the hose fixed the problem. Can't really check it with the motor running right now due to the weather we're currently having to confirm.

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Hold onto your bars brother. If that hose was actually entirely blocked you are in for a nice ride and getting to 65HP should be a breeze.

Repeated story: When I switched to the SS cam (modifications were done to make that possible on a P11) back in the late 1980's or early 1990's I didn't know squat about the timed breather machine work missing from the SS cam I got. Must have been a Combat version that expected to have the breather on the back of the crank case. Anyway, I hooked up the timed breather hose and plumbed it to the oil tank, but had no clue it was null. I spent a lot of time trying to figure out why I couldn't make the bike go over 60mph. I eventually was told what the problem was by Bob Raber and I came up with a weird steam punk dual hose setup on the back of the timing chest. Woke the motor right up some. However, my 2 into 1 exhaust was not right and a limitation. Went to a Brit swap meet show and ran into a retired Norton racer showing his Yellow proddy race bike. Got to talking to him and told him about my issue. He said make your exhaust longer back to where it is about even with the back of the rear rim, and vent one of your rocker covers. Night and day difference after making those modifications. That's when I though maybe I won't need a modern bike to keep up with the boys when riding up on "the hill". Total fantasy with a skinny 7" SLS brake, but I was able to get the old bike up to 108 mph.

maaseyracer said:

Also advance your JS2 a degree or two and compare it the SS cam, I would be curious to hear your thoughts on the comparison.

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Unfortunately not going to happen, too friggin old to keep tearing the same engine apart. I'm down to one motorcycle. Garage is not full of bikes like it was 30+ years ago.

I advanced the cam timing 2 degrees on the SS cam when I reinstalled it. I retired the JS2 cam and all the associated lifter parts. I did keep the JS beehive springs in the engine. I also increased the valve spring pressure a little, but did it with thicker shims without measuring anything. That is how I roll. Shade tree engineering.

Both cams are very similar top end performance wise. It's easier to lighten the front end accelerating with the SS cam, but to be fair I've done some things that improved the overall package after I removed the JS2 cam and installed the SS cam. Maybe not apples to apples any longer.

I'll read the rest of what you said later, but won't comment. Not my place and I lack the tech talk.

Schwany said:

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

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A couple of years back , I ran my stock ( except blackcaps swapped for 74 type 850 silencers) 850 MK3 slug against a hopped up 750 with D exhaust ports, reshaped intake ports, raised compression and a PW3 cam. There is a video of it somewhere on this site.
It was pretty much a dead heat to 80 mph, at which speed we had agreed to shut off.
My friend kept his 750 pinned past 80 so I did too. As my stock cam 850 went past its power peak and his 750 PW3 went into its powerband, his bike pulled away.
When I finally put the MK3 in top gear at about 100 mph, his bike stopped pulling away.
If we ever have a rematch I will know the stop at 80 thing isn't happening, so I'll shift into top gear at the right rpm. With that, the bikes will be very close to equal for acceleration from 0 to 110 mph.