Baffling good results for 2 into 1 on P11

This is not of any use to P11 restorers. It's a performance thing.

So I went looking for somebody to do a baseline dyno run on my P11. Can't do that and get any AFR info with a SuperTrapp unless I install a wideband sensor in my collector. Nah, I decided to make a baffle and replace my obnoxious SuperTrapp at the end of my 2 into 1 exhaust. I have a fairly long megaphone, so I came up with a baffle idea that is stuffed in the megaphone until it butts up against the diameter inside the magaphone that matches the baffle end. It is held in place with a tight fitting SuperTrapp competition end cap. I had to open the end cap up from 1 1/2 inches to 1 3/4ths inches. Did that with a round file. That was the most time consuming part of the job.

The baffle is made up of 2 18" lengths of slip fit exhaust tubing. One 1 3/4 x 18 and one 1 7/8 x 18. I cut the 1 3/4 to around 9 inches, and slipped it into the 1 7/8 length and secured it with a 10x32 round head allen screw. The larger slip fit joint end of the 1 7/8 exhaust tube is what butts up inside the megaphone. The end cap is pressed onto the 1 3/4 inch pipe, and secured in the end of the megaphone like a SuperTrapp disc setup normally is.

I did all the drilling on a drill press. I bent the larger holes with a punch so the exhaust could exit the baffle if it so desired. All the holes are theoretically there to reduce noise. I did not use any baffle packing material around the baffle.

End result is it is a lot quieter than the SuperTrapp, I can put the bike on a dyno if I ever get around to it, and it stopped a really crappy exhaust inversion issue (maybe what people used to call back pressure) that made my FCR carburetors rattle. They are quiet now, I can hear the motor. It's not a sewing machine like an inline 4, but it is a lot quieter without those FCR flat slide rollers rattling. It runs very close to on the money, but I have not looked at the plugs yet. It is a little flabby right off idle, but still very nice to ride. An exhaust change usually requires some tuning, but it is surprisingly good. Another big plus is my ears are not ringing after a ride anymore. It is really nice to ride, but still barks some if I turn up the wick.

Some pics

I would love to see some dyno results if you ever get around to it- the only performance numbers I’ve seen were factory claims from the 60’s.

I’ve only built one engine on which I did before/after dyno runs, a Honda XR650r. Using the same dyno and operator we were able raise it from 42 to 55bhp, while keeping a flat torque curve. It was a very fun bike and the linear power delivery made it super easy to ride.

The surprise to me was how low the starting numbers were, given that proported power output for this machine was 55-60 in stock “uncorked” form (the XR650r arrived at dealerships with an intake and exhaust restrictor, as well a lean jetting to match). This was a very well maintained bike that ran perfectly- and looked fantastic inside when pulled down for the build. Notwithstanding the differences in dyno reading between devices and operators, this did drive the point those that much of what is claimed may be hyperbolic, and that the best use of a dyno is to measure relative change rather than absolutes.

I felt good about the percentage gain but will forever be skeptical of power claims.

Still, a dyno run of your P-11 would be super cool!

I, too, would be interested in any P-11 dyno results you may ever obtain. Less because of your exhaust and more because of the JSM parts you put into it. Mine would be less of course, because I went with the milder cam, but I'd still be interested.

Not to be a Debby Downer but that exhaust hanger looks like it will crack at some point...

Yer man did 270 mile round trip last week, so probably stronger than it looks....

How long are your head pipes? Sorry if I missed it

Onder said:

Not to be a Debby Downer but that exhaust hanger looks like it will crack at some point...

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Anything is possible.

That hanger has 11,096 miles on it. The bike has been over many a bump in the road. The megaphone cracked the first year I put the pipe on the bike decades ago, but it was a single 3/4x1/8 inch steel chrome strap hanger with a single bolt attached to a tall flat triangle welded edgewise at the megaphone. Terrible setup. Started out as a Bub pipe made by Dennis when he was a one man operation in San Jose CA, but I made it longer gutted it and added the SuperTrapp end so that it actually worked on the top end with a 2S cam. The attachment at the megaphone is working so far. It has 4 bolts in it; 2 in the cut down triangle and 2 in rivet nuts in the megaphone. Looks funny, but it works well enough. I know people don't like it and that's what I like about it.

The bike is a one of a kind oddball. I'm going to ride it a little more now that it doesn't sound like a 4 cylinder drift car. It sounds almost like a Norton.

Dyno: I probably waited too long to get serious enough to do a run in 2022. We are just about back in the rainy season here. I won't ride the bike in the rain. I don't own a box trailer. If I did, I would definitely do it as soon as they can get me in. I won't get to it until next year unless they can do it before Friday. Rain, or the Seattle 4 month drizzle is coming after that.

Closest dyno operator wants $125US+ tax for a baseline run, and they are busy with modern bikes. A baseline run is not particularly cheap like people say it is. And, as has been mentioned in other threads somewhat meaningless. On the plus side I would imagine the first baseline run would show low numbers and these young bucks are going to tell me they can make improvements. So those numbers might tend to be somewhat accurate.

The numbers are not going to be typical of a stock P11, or a stock 750 Commando. They will either be far worse, or a few HP better.

Power is better with the baffle arrangement. Power comes on sooner than it did with the SuperTrapp discs in the end. Probably because the reversion pulse is reduced to near nothing and the motor is not working as hard to overcome whatever that was doing inside the head. I should have made the baffle long ago. Had too many 2 wheel toys then though. Now I can concentrate on just the one. Better late than never.

mean gene said:

How long are your head pipes? Sorry if I missed it

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Gene I'll get you that number later today.

mean gene said:

How long are your head pipes? Sorry if I missed it

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1 1/2" OD 34" length. 2 of those length inches are inside the collector.

Schwany said:

Closest dyno operator wants $125US+ tax for a baseline run, and they are busy with modern bikes. A baseline run is not particularly cheap like people say it is. And, as has been mentioned in other threads somewhat meaningless. On the plus side I would imagine the first baseline run would show low numbers and these young bucks are going to tell me they can make improvements. So those numbers might tend to be somewhat accurate.

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$125 isn't bad. My local guy quotes $200/hour and $200 minimum. On the other hand, he is very experienced.

Ken

lcrken said:

$125 isn't bad. My local guy quotes $200/hour and $200 minimum. On the other hand, he is very experienced.

Ken

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The two owners are not that old, but claim to have 20 years of Dyno tuning experience. They look like teenagers to me. They have a race team with Japanese inline 4's.

I have a feeling they are going to want to rev the hell out of my bike since they work with high revving Japanese motorcycles all day long, and I don't need them to tune anything. My tune is very close to if it aint broke don't fix it riding around on the street. I only want to see the roll-on numbers to 6500 RPM. If it is still building HP at 6500 RPM that number will be good enough for me, and possibly a miracle. I'll be surprised if it breaks out of the 50's.

What is the right way to dyno a Norton engine?

I want to treat these guys with some respect and ask them to do it the right way for a Norton without any we know what's best drama if they have no experience with Nortons.

The motor is definitely making power sooner with the exhaust modification, cuz now my clutch slips when I turn up the wick quick. Slips when the frictions are cold for a few minutes. Works better when the clutch is heated up. I think the light synth oil in the primary is not working as well as I thought it was with the new earlier increase in power, or I need to replace the clutch springs and crank them down a little more and use ATF in the primary again. Something to address as the riding season here winds down.

The occasional high revving seems to be taking its toll. The bottom end got noisy after a few of the clutch slipping episodes and my childish tendency to get on the HWY at 80mph in 3rd before shifting up into 4th. Motor may be coming out for a look at the crank, and other parts if it gets any noisier.

Good thing I didn't book a dyno appointment. The slipping clutch would have made it a complete waste of time. Will do it next year though after I get things squared away.

Schwany said:

What is the right way to dyno a Norton engine?

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I'd think they'd take it through the gears to red line. And if your tune is right now, it was probably wrong before (if you didn't change it). Changing the exhaust has a huge effect on the tune, especially if it was very restrictive before. Were your plugs fouled by chance? If you've leaned out your AFR (by opening the exhaust) to ~13 my guess is you may exceed 60 HP if it's timed right, which another component to tuning. They should be able to dial that in (if they know how to adjust it). If you go for a lot of advance (which is where the power is), you'll want richer jetting, or use ethanol blend to prevent detonation.

Do they have experience tuning carburetor bikes, or is it all FI?

TomU said:

I'd think they'd take it through the gears to red line. And if your tune is right now, it was probably wrong before (if you didn't change it). Changing the exhaust has a huge effect on the tune, especially if it was very restrictive before. Were your plugs fouled by chance? If you've leaned out your AFR (by opening the exhaust) to ~13 my guess is you may exceed 60 HP if it's timed right, which another component to tuning. They should be able to dial that in (if they know how to adjust it). If you go for a lot of advance (which is where the power is), you'll want richer jetting, or use ethanol blend to prevent detonation.

Do they have experience tuning carburetor bikes, or is it all FI?

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Hmmm, I want to see the numbers to 6500RPM not to Redline. The motor will spin until it flies apart. I'd prefer to blow the motor up myself rather than watch two guys with their baseball caps on backwards blow it up. lol

Plugs look good and always have. I tuned it for the exhaust as it was before with the SuperTrapp and again as it is now with the baffle I made for it. Difference with the straight through baffle arrangement is the reversion back pressure is gone, so it has freed up some HP. And it actually ran a touch richer initially with the baffle. I've dropped the needle one clip position and leaned out the low speed fuel circuit. Seems good, and plugs look fine. Tuning FCRs is fairly simple as long as one starts with a good tune. The Sudco tune is a good start for a race motor.

I could run it leaner and have, but it has no top end when run lean like some of the members here like to run their stock Nortons with FCR carburetion fitted.

28-29 degrees of timing all in at 3000RPM is good on this engine.

The dyno shop specializes in messing with ECU programming for fuel injection. I'm not looking for a tuner.

Sorry, may have not been clear. Was not suggesting you lean it. I was just saying that the work you did on the silencers probably leaned it. Now the question is was it rich before and is now good or was is it good before and is now lean. When they do the dyno, they'll probably put on a tail pipe AFR sensor.

Schwany said:

Hmmm, I want to see the numbers to 6500RPM not to Redline. The motor will spin until it flies apart. I'd prefer to blow the motor up myself rather than watch two guys with their baseball caps on backwards blow it up. lol

Plugs look good and always have. I tuned it for the exhaust as it was before with the SuperTrapp and again as it is now with the baffle I made for it. Difference with the straight through baffle arrangement is the reversion back pressure is gone, so it has freed up some HP. And it actually ran a touch richer initially with the baffle. I've dropped the needle one clip position and leaned out the low speed fuel circuit. Seems good, and plugs look fine. Tuning FCRs is fairly simple as long as one starts with a good tune. The Sudco tune is a good start for a race motor.

I could run it leaner and have, but it has no top end when run lean like some of the members here like to run their stock Nortons with FCR carburetion fitted.

28-29 degrees of timing all in at 3000RPM is good on this engine.

The dyno shop specializes in messing with ECU programming for fuel injection. I'm not looking for a tuner.

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There might be a joke in there between baseball caps and peak power....... but I can't be *rsed to look

TomU said:

Sorry, may have not been clear. Was not suggesting you lean it. I was just saying that the work you did on the silencers probably leaned it. Now the question is was it rich before and is now good or was is it good before and is now lean. When they do the dyno, they'll probably put on a tail pipe AFR sensor.

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I've been tuning carbureted motorcycles for over 50 years and have a good handle on it by now. I have never taken a bike to a dyno though. I have always been happy with what I am able to accomplish. Still am. I just want to see some HP numbers for grins.

My exhaust is a 2 into 1 one off exhaust. (One silencer) Not another exhaust exactly like it on the planet. Nothing special about it. It is just unique.

This thread is about me replacing the SuperTrapp setup I had in the tail end of the 2 into 1 exhaust with a straight through baffle I made so a dyno operator could put a sniffer into the tail pipe. They can't do it with a SuperTrapp on the end. That is all this thread was supposed to be about. I'm not looking for tuning advice from members here or a dyno operator. Assuming I ever take it to a dyno, I can read the graphed AFR, RPM, and HP output from the dyno and figure out what I need to do. I suspect it won't be much of anything given how well it runs. I did wonder what people say to the dyno operator that the operator will listen to. That is my only question.

The tune was good before with the SuperTrapp, but on the rich side intentionally. It was not optimal however with the reversion issue. I mentioned it in the thread somewhere. Contrary to conventional wisdom the baffle made it too rich, which is why I did some minor leaning out of the tune. The other BS I mentioned about trying a leaner tune in general was done a few months ago, and it was a total fail with the current motor configuration. The leaner tune did however work fairly well with the previous motor configuration that had the Norton 2S cam and heavier pistons and rods with the SuperTrapp in the arse end of the 2 into 1 exhaust. Is what it is.

Thanks for taking a look Tom.

mean gene said:

How long are your head pipes? Sorry if I missed it

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Just for grins more numbers: The short header pipes go into a 2 into 1 collector with a 2" inside diameter exit. The collector to the end of the megaphone is straight through and decreases from 2" to 1 3/4" the last 8 inches. Collector to end of megaphone adds 36" to the 34" headers. There are 4 SuperTrapp discs before the end cap as well. It works. Is it better than dual exhaust? Probably not, but it's different looking, flows well enough and is not as loud as a hollow megaphone.

I recently took off the Super Trapp megaphone from my G80CS. It worked pretty well. I originally tuned it for a straight pipe and did well on the scrambles track with the short-track HS cams. Time passed and that setup wouldn't pass muster on the street. On went a new Armour's replica of the factory silencer. The bike would barely run. The Boss had a specially made 2-foot hole saw with a 1" cutter. We used that to relieve it. Then it was as loud as a straight pipe but more obnoxious with a high pitch. It also didn't run as well but at least looked legal. I idled past the 12th Ave police precinct house.

I ran it that way until a) I went deaf and b) I moved to an area with lots of woods roads and trails. On went a short, black Supertrap megaphone with all the discs. They claim it's Forest Service approved but I never went by the FS office to check. Now the bike was about as noisy as the cut out Armour's silencer but WHAT a difference in performance; pulls right from the bottom and hard all the way to as fast as I care to turn it.

Still too noisy and the fire risk just too great and I gave up woods riding; so, I bought a universal 20" Megatron reverse cone silencer from Walridge Motors. Nicely made. Price is right. This is on the end of a 44" straight pipe which is a bit longer than came from the factory, I believe. The result is that it sounds way more mellow but not necessarily quieter and it pulls noticeably harder in the mid range.

In all this fooling around I never changed the jetting on the 32mm MKI Amal. It's been 280 main, middle notch and .106 needle-jet since the scrambles days. I'm not as sophisticated as Schwany nor as apt to fiddle with the tune to find perfection, so there's probably a lot of potential left on the bench. But it gets nearly 60MPG so what's to complain. Besides the Commando needs fetteling before being put up for winter and the Atlas is on the stand waiting for an alternator rotor and a friend's Subaru needs head gaskets before winter and it snowed yesterday in the hills...