My first build - 75 Honda CL360 Scrambler
- Thread starter djsmiles
- Start date
crazypj
Split personality, I fake being smart
It's not the mufflers, it's total exhaust length thats important. Realistically, high level pipes are impossible to get long enough (unless you run through open section of frame and exit on opposite side) They should be ending around rear edge of rear tyre to be even close to tuned length. Sticking 12" Emgo's on there at present will exit directly at rear shock, probably 'cooking' the seal?
+1
My buddy's CJ360 had his pipes cut off right behind the foot pegs and he ran super lean for a while. Even after jetting up to something crazy like 122 secondaries, he still had trouble topping 80.
On my 360, I have the pipes going right to the end of the rear tire and that length seems about right. I haven't dynoed the bike, but it's weird; you can almost tell you have things correct by the sound and the feel on this engine. It's not quite the same, but not entirely dissimilar to "getting on the pipe" on a two stroke. My engine is pretty far from stock, but I hit 70 mph in second on mine and I don't think that'd be possible with shorter pipes.
Also, the sound is great on these machines when you get it right.
Quick vid of my little beast:
https://www.youtube.com/watch?v=FmYW7GBX4y8
My buddy's CJ360 had his pipes cut off right behind the foot pegs and he ran super lean for a while. Even after jetting up to something crazy like 122 secondaries, he still had trouble topping 80.
On my 360, I have the pipes going right to the end of the rear tire and that length seems about right. I haven't dynoed the bike, but it's weird; you can almost tell you have things correct by the sound and the feel on this engine. It's not quite the same, but not entirely dissimilar to "getting on the pipe" on a two stroke. My engine is pretty far from stock, but I hit 70 mph in second on mine and I don't think that'd be possible with shorter pipes.
Also, the sound is great on these machines when you get it right.
Quick vid of my little beast:
https://www.youtube.com/watch?v=FmYW7GBX4y8
crazypj said:
Yeah... I grabbed an 18 front from a CB450 and ground it down to the correct width. I'm on a 33 rear (which I think is stock on the CJ?) and swapped out to an early CB transmission for the better spacing between 2nd and 3rd.
In theory, I should be able to hit 141 in 6th, but I'm doubting I have the grunt.
So are all these bikes we see photographed with shorty pipes just for display purposes? eye candy? pretty bikes to look at but not to ride? I really didn't want my exhaust to be that long. I'm not trying to make this bike reach a top end of 141mph. 60mph is fine with me. If I need to go faster I'll take my car.
djsmiles said:
More or less, yeah.
As long as you know that you're sacrificing performance and possibly rideability, the decision is yours to make. It's perfectly fine to have goals that differ from other peoples', we're just trying to ensure everyone understands the consequences of their decisions before they make them.
Essentially, you need the length of pipe to scavenge the exhaust. Running shorty's or more open pipes take away most of the performance from the bottom 3/4 of the throttle range, but it's possible to gain on the top end if you can jet it right. If you're running non-stock carbs, you'll probably be able to more performance through jetting with any set of pipes. There isn't enough adjustment in a set of stock carbs to find peak performance.
crazypj
Split personality, I fake being smart
Generally you don't want or need 'back pressure' in exhaust system. You have various harmonics and pressure waves in there, the 'secret' is to get everything coming together at the correct time to improve performance. Too much back pressure can overheat exhaust valves, harmonics happening at the 'wrong' time can increase fuel consumption or create 'flat spots' plus various other running issues making correct carb tuning virtually impossible (it's always a compromise, just depends how much you want to compromise)
You could use 1-1/18" outside diameter pipe, but, it looks pretty weird and doesn't actually address the problem. Sound waves and exhaust gases still travel at the same speed. 1" internal diameter pipe is actually way closer to correct size for a stock 360 motor and should improve torque by keeping gas speed higher.
You could use 1-1/18" outside diameter pipe, but, it looks pretty weird and doesn't actually address the problem. Sound waves and exhaust gases still travel at the same speed. 1" internal diameter pipe is actually way closer to correct size for a stock 360 motor and should improve torque by keeping gas speed higher.
Without head work and perhaps a bump in compression/displacement, I suspect there wouldn't be a great difference.
On a stock motor, your exhaust options usually fall into one of two categories: "adequate" and "inadequate". If you want to move into the "good" range, there are other systemic shortcomings that need to be addressed first.
For your current setup, I'd probably aim for something like the attached image (but a bit longer).
On a stock motor, your exhaust options usually fall into one of two categories: "adequate" and "inadequate". If you want to move into the "good" range, there are other systemic shortcomings that need to be addressed first.
For your current setup, I'd probably aim for something like the attached image (but a bit longer).
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djsmiles said:
I had short scrambler exhaust on mine for a while - top speed was about 70~ MPH (no speedometer so I relied on my buddie's honda accord speedo riding next to me) bike got there pretty good, just didn't have the power to move faster.
I've since decided to do longer exhaust by swinging it under the frame and up the right rear to some reverse cone mufflers - a 2-2 system. Yo can certainly bring the exhaust into the "triangle" area and add 12+ inches to the length that way and still get a scrambler look
crazypj said:
Sound (pressure) waves move at the speed of sound and that varies with temperature of the gas it's traveling through. The gas itself moves way slower. Large pipes hurt gas velocity and disrupt harmonics.
Long pipes restrict flow and gas velocity, but with pipes that are way larger than ideal, that is not an issue. In fact it helps considerably. Exhaust harmonics are generally well understood by exhaust manufacturers but there's a lot of incorrect info out there. In theory, you want the wave to travel down the pipe and be reversed at the open end and to reach the head as both valves are open to pull burned gas out of the head and to pull fresh mixture in. Then that wave travels back down the pipe and this time it is reflected as a positive (stuffing) wave which should be timed to arrive just before the exhaust valve closes.
In practice that is just not really an available option, so exhaust designers start to look at timing of second and 4th and 6th harmonics as the waves go back up and down the pipe. For us mere mortals, it's possible to get a copy of articles by David Vizard on exhaust design or refer to the book by AG Bell or even better look at some of the more technical publications for inspiration.
And for the rest of us, think of exhausts as short and large let the motor rev but with no guts - just empty noise. Longer smaller diameter pipes tend to sound better and to add torque which is the ability of an engine to do work i.e. to get our sorry asses into motion. That's a gross oversimplification, but close enough.
Long works better. Short looks sharper but doesn't work or sound as good on the road.
I neither have the talent/skill nor the money to make a whole new exhaust setup unfortunately. As I near the end of this build my 'budget' is pretty drained. I found this muffler which is 16" long and very reasonably priced.
https://www.jpcycles.com/product/450-298/universal-tapered-muffler?mrkgcl=444&mrkgadid=3207647304&utm_source=google&utm_medium=cpc&utm_term=341779227964_product_type_vehicles_%26_parts_product_type_land_vehicles_product_type&utm_campaign=PLA+-+Shopping+Campaign&product_id=450-298&utm_content=pla&adpos=1o2&creative=42040109650&device=c&matchtype=&network=g&gclid=EAIaIQobChMI4pOYgaX52gIVSlYNCh0UtwTQEAQYAiABEgJuIPD_BwE
It has a 1 3/4" opening. Since I'm at work does anyone happen to know the OD of the stock exhaust pipes? I'll need to find the right size collector to make this all fit together.
https://www.jpcycles.com/product/450-298/universal-tapered-muffler?mrkgcl=444&mrkgadid=3207647304&utm_source=google&utm_medium=cpc&utm_term=341779227964_product_type_vehicles_%26_parts_product_type_land_vehicles_product_type&utm_campaign=PLA+-+Shopping+Campaign&product_id=450-298&utm_content=pla&adpos=1o2&creative=42040109650&device=c&matchtype=&network=g&gclid=EAIaIQobChMI4pOYgaX52gIVSlYNCh0UtwTQEAQYAiABEgJuIPD_BwE
It has a 1 3/4" opening. Since I'm at work does anyone happen to know the OD of the stock exhaust pipes? I'll need to find the right size collector to make this all fit together.
I don't think they are exactly 1.5" - they are like 1 5/8" and I've had to use the emgo adapters like from 4-into-1 for any aftermarket mufflers.
