Hey guys. I've got a 1980 Cx 500 C that I recently stripped down. I like the Cafe look on these bikes and most likely going that route. I've seen folks remove the H-Box and go with just straight pipes. Does this hurt performance in anyways? Should i leave it in? I will be going with Pods, no air box, and if no hbox, what kind of jetting am I looking at? Any input on this topic would be greatly appreciated. BTW- Thank you Cobram on the Ignitech Module. I am trying to redo the whole bike properly (dependendant on cash flow.)
jkoch72
There can be problems. You're probably going to need 85-90 main jet and 120-130 main jet. There are 2 jets per carb and they are both called main jets.
Yes - you will have performance problems with no H-box and straight pipes. This bike is very dependent on back-pressure for performance. I've tried several different combinations for pods, mid-pipes and mufflers - the best combination for performance is 90 - 120 jets and the harley mufflers that 50gary sells at a real good price (without the H-box and with pods). You can use the harley mufflers on the stock headers and they also work very well with the Mac 2 into 1 header pipes with the Harley muffler. If you go with straight pipes - you'll be missing out on all the fun that these bikes can deliver - and you can crank the throttle open without having to worry about popping an ear drum... If you still want to do straight pipes - keep the H-box - it will help a little with back pressure and the 90 - 120 jet combination will still work OK.
get cheap azz pod air filters and a 2-1 pipe then youll be looking at 90 and 120 mains and shimming the needle other than that i cant help
I run Harley Sportster pipes(stock 883) on my 80VX500C with no airbox, but with Ebay pods, and have had no problems.
If your running straight pipes(no baffles), then you're going to need the jets changed for sure.
A friend of mine uses his stock airbox but runs the bike without the top cap, which opens that filter intake nearly triple and the bike runs well with his stock CX pipes.
After any change run new plugs 50-100 miles and check their condition. They'll tell you if it's running Lean/Rich or Goldylocks mode(Just Right).
Also, watch the header pipes for bluing and temp running hotter, also signs of Rich/Lean respectively.
If your running straight pipes(no baffles), then you're going to need the jets changed for sure.
A friend of mine uses his stock airbox but runs the bike without the top cap, which opens that filter intake nearly triple and the bike runs well with his stock CX pipes.
After any change run new plugs 50-100 miles and check their condition. They'll tell you if it's running Lean/Rich or Goldylocks mode(Just Right).
Also, watch the header pipes for bluing and temp running hotter, also signs of Rich/Lean respectively.
I replaced the collector box on my GL500 with plain pieces of exhaust pipe between the headers & the mufflers because the collector was in the way of how I wanted to make the sidecar subframe. I never drove it with the collector in place so I can't tell you how it compared to stock, but it seemed to work OK to me. When I set up the 650 I used the same subframe so it also has no collector & works fine.
When you say "straight pipes" do you mean plain "pieces of exhaust pipe that replace teh collector" or do you mean "no baffles"? I hope you don't mean no baffles, because all that does is annoy your neighbours and encourage lawmakers to pass legislation restricting modifications to bikes.
When you say "straight pipes" do you mean plain "pieces of exhaust pipe that replace teh collector" or do you mean "no baffles"? I hope you don't mean no baffles, because all that does is annoy your neighbours and encourage lawmakers to pass legislation restricting modifications to bikes.
Thanks for the input. I was not clear about what I meant about straight pipes. I meant having an exhaust system with mufflers just no h-box installed. I understand there has to be some restriction for engine performance. That probably could be done thru the muffler system somehow for back pressure, I would imagine.
Blindstitch. You referenced two Main Jet sizes there. Are they they the same profile jet, just different openings?
I'm very new to the motorcycle scene and especially the CX500, being my first motorcycle. As such please take my advice/comment "with a grain of salt" if you will. I can get fairly technical so if you're not a fan of that just skip to the end of this post.
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For the majority of the last 10 years I've been very involved in automobile tuning and I'm sure a lot of the theories can be applied here as well. For instance, the misconception of back pressure. No amount of back pressure is acceptable if more HP is your goal. I'm sure we're all in agreement that the more fuel and air your engine can convert into kinetic energy the more HP you'll have. So more air and more fuel going in is obvious but we often forget that all that stuff needs to come out as well. Sticking a big ol pipe on there will do nothing for performance generally with naturally aspirated engines like mine. It's all about exhaust velocity. How fast can you get that hot air out so that it doesn't stay in there and block the new hot air that's coming. When you have a large pipe your high pressure exhaust pulse leaving the cylinder meets cooler stagnant air and expands, slowing it down and often stopping it in it's tracks until it's "pushed" by the next pulse. Resisting the flow a.k.a back pressure. No good!
What you want is a smaller pipe that will be able to maintain the exhaust velocity as it's heat is dissipated. Since cooler air does not expand as fast and therefore moves slower through the conduit, we want it to be ejected before it loses too much velocity. However, making a conduit smaller has a drawback of allowing less volume to be able to pass. Take a garden hose without nozzle, press the opening and the hose tenses and water shoots out at high velocity. But so you know the same amount or even less water will flow due to the restriction. This is because water can not be compressed to the extent that air can. It's a bad example but point made, hopefully. Needless to say that is will mean that the pipes need to be sized for a particular volume / flow so it would work at it's peak efficiency for that application. I.e. Tuned to "ride around town shifting at 5.5k RPM" pipes are a lot different from "Track burning 10k RPM type" pipes. It's nice to have a café racer but if you're not going to race with it don't tune it for racing.
Then there's something called exhaust scavenging. If you will, please think of the exhaust pulse as a wave compression of air, exactly like a sound wave. There is an area of high pressure sandwiched by low pressure, traveling in a certain direction. So now you have hot air that's pushed out of the chamber by the piston on the exhaust stroke. It enters the exhaust manifold / pipe as the valve shuts. Now you have that low pressure vacuum behind that exhaust pulse. Honda engineers have sized the piping and cam lift durations to synch that micro vacuum with TDC (both intake and exhaust valves cracked open). In turn allowing the pulling of intake air into the cylinder before the piston has started it's downward assent. A earlier onset of intake makes for more air/fuel volume to be taken in then if the piston alone would have create the vacuum.
Another side benefit of exhaust scavenging is that when hooked up to other cylinders (The H pipe) the exhaust pulse of one cylinder will create the vacuum to help pull the exhaust of the other cylinder. The end result is higher exhaust velocity, more air through.
So in summary, Honda engineers get paid good money to tune the Cx500 for max efficiency as a go around town type of vehicle with a little headroom for spirited riding and to mess with it will throw off the carefully calculated equation. If you still want to make changes or just want enough power to get by, do all the mods you want but plan on making up your own equation. (Carb Rejetting/modification, Cam/Crank profiling, Engine internal mods, Dyno, new exhaust/header/muffler, running pure xylene with 13.962:1 compression ratio, Hoosier slicks, frame mods, etc...) Google exhaust scavenging and you'll find endless volumes of reading on exhaust theory. Well, cheers and fair winds at your back!
For the majority of the last 10 years I've been very involved in automobile tuning and I'm sure a lot of the theories can be applied here as well. For instance, the misconception of back pressure. No amount of back pressure is acceptable if more HP is your goal. I'm sure we're all in agreement that the more fuel and air your engine can convert into kinetic energy the more HP you'll have. So more air and more fuel going in is obvious but we often forget that all that stuff needs to come out as well. Sticking a big ol pipe on there will do nothing for performance generally with naturally aspirated engines like mine. It's all about exhaust velocity. How fast can you get that hot air out so that it doesn't stay in there and block the new hot air that's coming. When you have a large pipe your high pressure exhaust pulse leaving the cylinder meets cooler stagnant air and expands, slowing it down and often stopping it in it's tracks until it's "pushed" by the next pulse. Resisting the flow a.k.a back pressure. No good!
What you want is a smaller pipe that will be able to maintain the exhaust velocity as it's heat is dissipated. Since cooler air does not expand as fast and therefore moves slower through the conduit, we want it to be ejected before it loses too much velocity. However, making a conduit smaller has a drawback of allowing less volume to be able to pass. Take a garden hose without nozzle, press the opening and the hose tenses and water shoots out at high velocity. But so you know the same amount or even less water will flow due to the restriction. This is because water can not be compressed to the extent that air can. It's a bad example but point made, hopefully. Needless to say that is will mean that the pipes need to be sized for a particular volume / flow so it would work at it's peak efficiency for that application. I.e. Tuned to "ride around town shifting at 5.5k RPM" pipes are a lot different from "Track burning 10k RPM type" pipes. It's nice to have a café racer but if you're not going to race with it don't tune it for racing.
Then there's something called exhaust scavenging. If you will, please think of the exhaust pulse as a wave compression of air, exactly like a sound wave. There is an area of high pressure sandwiched by low pressure, traveling in a certain direction. So now you have hot air that's pushed out of the chamber by the piston on the exhaust stroke. It enters the exhaust manifold / pipe as the valve shuts. Now you have that low pressure vacuum behind that exhaust pulse. Honda engineers have sized the piping and cam lift durations to synch that micro vacuum with TDC (both intake and exhaust valves cracked open). In turn allowing the pulling of intake air into the cylinder before the piston has started it's downward assent. A earlier onset of intake makes for more air/fuel volume to be taken in then if the piston alone would have create the vacuum.
Another side benefit of exhaust scavenging is that when hooked up to other cylinders (The H pipe) the exhaust pulse of one cylinder will create the vacuum to help pull the exhaust of the other cylinder. The end result is higher exhaust velocity, more air through.
So in summary, Honda engineers get paid good money to tune the Cx500 for max efficiency as a go around town type of vehicle with a little headroom for spirited riding and to mess with it will throw off the carefully calculated equation. If you still want to make changes or just want enough power to get by, do all the mods you want but plan on making up your own equation. (Carb Rejetting/modification, Cam/Crank profiling, Engine internal mods, Dyno, new exhaust/header/muffler, running pure xylene with 13.962:1 compression ratio, Hoosier slicks, frame mods, etc...) Google exhaust scavenging and you'll find endless volumes of reading on exhaust theory. Well, cheers and fair winds at your back!
I don't want to get into a technical debate in which we will both loose, but I feel that, while your comments are well written and mostly spot on, a couple of points need to be addressed. I should also mention that I have a background in loudspeaker design so I have a pretty good grasp of acoustics, which is what makes the exhaust system do what you are talking about.
Small pipe vs. large pipe: I had never given this much thought, but what you describe makes perfect sense to me. It also occurs that there must be an optimum pipe diameter and that it must vary with exhaust pulse frequency (= engine RPM). This is only conjecture, mind, but I think the engineers would have made an educated guess art what RPM the engine would need the pipe to help most at and designed the original exhaust system to scavenge best at that frequency. As I have said many times, the basis of good design is choosing the best compromises.
I imagine that, 25+ years later, what most of us are doing is not what they designed for. For example, I doubt that they ever considered the changes in load that adding a sidecar would make.
Or what would happen if the airbox that they so carefully designed (& modern engineers would consider laughably crude) was replaced by pod filters.
Or that, 25+ years later, owners would find that OEM replacements for their now rusted out mufflers would cost almost as much as they paid for the bike and "pattern reproductions" (that look more or less the same on the outside but are often nothing like the originals on the inside) about 2/3 of that. But you can get Harley Davidson mufflers that were changed before delivery of brand new bikes (usually for something that exemplifies the principle that the best way to convert gasoline to noise without the annoying byproduct of horsepower is to burn it in a Harley) for $10-15 each and they were easily adapted to Hondas (&, of course, sound better on those Hondas than they ever did on their original Harleys
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Or even that so many of these bikes would last long enough that new exhaust collectors would no longer be available.
So we are left to our own resources to do what we find necessary to make these bikes do what we want them to.
And besides, what do you say to a 28 year old 500+ Lb 650 that has the original headers but straight pieces of exhaust pipe to replace the collector and Harley mufflers on the ends of them when I tell you that I have to lean forward a bit to keep the front wheel on the ground when accelerating hard from stopped, and that while pulling a 200+ Lb sidecar? How badly butchered can that exhaust's function be?
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Small pipe vs. large pipe: I had never given this much thought, but what you describe makes perfect sense to me. It also occurs that there must be an optimum pipe diameter and that it must vary with exhaust pulse frequency (= engine RPM). This is only conjecture, mind, but I think the engineers would have made an educated guess art what RPM the engine would need the pipe to help most at and designed the original exhaust system to scavenge best at that frequency. As I have said many times, the basis of good design is choosing the best compromises.
I imagine that, 25+ years later, what most of us are doing is not what they designed for. For example, I doubt that they ever considered the changes in load that adding a sidecar would make.
Or what would happen if the airbox that they so carefully designed (& modern engineers would consider laughably crude) was replaced by pod filters.
Or that, 25+ years later, owners would find that OEM replacements for their now rusted out mufflers would cost almost as much as they paid for the bike and "pattern reproductions" (that look more or less the same on the outside but are often nothing like the originals on the inside) about 2/3 of that. But you can get Harley Davidson mufflers that were changed before delivery of brand new bikes (usually for something that exemplifies the principle that the best way to convert gasoline to noise without the annoying byproduct of horsepower is to burn it in a Harley) for $10-15 each and they were easily adapted to Hondas (&, of course, sound better on those Hondas than they ever did on their original Harleys
Or even that so many of these bikes would last long enough that new exhaust collectors would no longer be available.
So we are left to our own resources to do what we find necessary to make these bikes do what we want them to.
And besides, what do you say to a 28 year old 500+ Lb 650 that has the original headers but straight pieces of exhaust pipe to replace the collector and Harley mufflers on the ends of them when I tell you that I have to lean forward a bit to keep the front wheel on the ground when accelerating hard from stopped, and that while pulling a 200+ Lb sidecar? How badly butchered can that exhaust's function be?
Its the exhaust collector box that is mounted directly below the engine. Because of the two inlets at the front and the two outlets at the back it is shaped more or less like the letter H so it is sometimes called the H box.
This is the H box. And it's design was highly crafted for it's time. The function does all the simple and complex processes described above.
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Not really much to the "power chamber" is there. The engineers have learned an awful lot more about how exhaust systems since then so you don't see that sort of thing any more.
On the race track (&, to a limited degree, in the real world), the horsepower to weight ratio is more important than the horsepower number. Sometimes you can gain more speed by putting your effort into reducing the weight than you would by putting the same effort into engine improvements. Eliminating one muffler removes a lot of weight, at least in theory. To keep the same flow the single muffler needs to be bigger but to help keep the weight down it can be made of thinner material (won't last as long, but on the track that is a secondary consideration) or thinner & stronger materials (more expensive but lasts better)(remember what I said about choosing the best compromises?). Even little things can make a difference -if the muffler is made of stainless steel you eliminate the need for the heavy layer of chrome.
Cruiser/chopper guys copy what they see at bike shows so that their bikes will have "the look", whether they understand the reasons the custom builder had for those mods in the first place or not (these days a lot of "builders" don't know why they make those mods either so they end up making caricatures of the customs of the past that really don't work well). The sport bike crowd are a lot like them in that they often copy what they see on the track so that they have the right "look", whether they understand or not. A 2 into 1 exhaust is often one of the first "performance" mods done, especially to a bike that is a few years old and probably needs a new exhaust system anyway (or at least new mufflers).
In reality, an exhaust system designed with current knowledge and an understanding of how the machine is going to actually be used, can provide significant gains in performance. If you look at the catalogue of an exhaust builder that knows what he is doing you may see several different systems for the more popular models that look very much alike on the outside but the one for the street and the one for racing each provide different improvements.
I don't know the Motad system, but unfortunately, you are not likely to find such a system for bikes this old. What you will find is something made for "the look" using an off the shelf muffler. If you are lucky the headers will at least be close to the same length, but sometimes they just route them as directly as possible. I have even heard of systems that were designed with no consideration for routine maintenance so that you have to remove all or part of the exhaust system to get at the oil filter!!!
BTW: One of the minor side benefits of bypassing the collector and using the shorter than original Harley mufflers is that, if you are careful, you can set it up so that the mufflers don't interfere with removing the rear axle. I can't think of any good reason that a properly working street bike's mufflers should need to be removed very often, but I go through a rear tire every 10,000-15,000 Km.
On the race track (&, to a limited degree, in the real world), the horsepower to weight ratio is more important than the horsepower number. Sometimes you can gain more speed by putting your effort into reducing the weight than you would by putting the same effort into engine improvements. Eliminating one muffler removes a lot of weight, at least in theory. To keep the same flow the single muffler needs to be bigger but to help keep the weight down it can be made of thinner material (won't last as long, but on the track that is a secondary consideration) or thinner & stronger materials (more expensive but lasts better)(remember what I said about choosing the best compromises?). Even little things can make a difference -if the muffler is made of stainless steel you eliminate the need for the heavy layer of chrome.
Cruiser/chopper guys copy what they see at bike shows so that their bikes will have "the look", whether they understand the reasons the custom builder had for those mods in the first place or not (these days a lot of "builders" don't know why they make those mods either so they end up making caricatures of the customs of the past that really don't work well). The sport bike crowd are a lot like them in that they often copy what they see on the track so that they have the right "look", whether they understand or not. A 2 into 1 exhaust is often one of the first "performance" mods done, especially to a bike that is a few years old and probably needs a new exhaust system anyway (or at least new mufflers).
In reality, an exhaust system designed with current knowledge and an understanding of how the machine is going to actually be used, can provide significant gains in performance. If you look at the catalogue of an exhaust builder that knows what he is doing you may see several different systems for the more popular models that look very much alike on the outside but the one for the street and the one for racing each provide different improvements.
I don't know the Motad system, but unfortunately, you are not likely to find such a system for bikes this old. What you will find is something made for "the look" using an off the shelf muffler. If you are lucky the headers will at least be close to the same length, but sometimes they just route them as directly as possible. I have even heard of systems that were designed with no consideration for routine maintenance so that you have to remove all or part of the exhaust system to get at the oil filter!!!
BTW: One of the minor side benefits of bypassing the collector and using the shorter than original Harley mufflers is that, if you are careful, you can set it up so that the mufflers don't interfere with removing the rear axle. I can't think of any good reason that a properly working street bike's mufflers should need to be removed very often, but I go through a rear tire every 10,000-15,000 Km.
Bill, you will also notice they are of different diameter. My understanding is that they have an equal tuned length, even though not actual length.
Joel in the Couve
Joel in the Couve
The left cylinder is ahead of the right cylinder so the left header is longer than the right one. Unless I am mistaken, the total length from the exhaust port to the end of the pipe inside the collector is the same on both sides.
Google image search found this but the original is not on Photobucket any more.
Its hard to tell in a pic that small, but I don't think the pipes have holes in them. They do look like they are the same size, though, and the difference in length is about the difference in header length.
Its hard to tell in a pic that small, but I don't think the pipes have holes in them. They do look like they are the same size, though, and the difference in length is about the difference in header length.
Attachments
Many modern motorcycles still use,"Collector" boxes.With better technology like CAD they have been re-designed much smaller.The Motad 2 into 1 has a very small one and works exactly like the Stock exhausts,unlike the Mac 2 into 1 system.
Having had Stock pipes and a Motad 2 into 1 both tested on an EGA(Exhaust Gas Analyzer) they all can do their job of balancing the engine's exhaust emissions and providing the correct exhaust gas scavenging and Valve fuel input assistance and mix required for power and economy.
Any changes to the stock system usually affect one or more of the Power-bands and have to be allowed for e.g you may be able to get more power at higher revs but then lose some at lower revs unless you spend some money on other things to compensate.
With the CV carbs on these bikes and their design it's very hard to change the low speed and other circuits hence some people have found it better to go to the older,"Slide"(Mikuni comes to mind) type carbs for tuning.I've wondered a few times if anyone might venture into a,"Fuel Injection" carb system just for S*ts and giggles if they have the time,money and will.
As as been mentioned before.With the size of these engines if you want more power and are carrying excess body fat then losing weight will increase performance more than most tweaks that can be done to the engines.Since quitting smoking I've been struggling with weight but am slowly trying to lower mine for the up-and-coming good weather/season but it ain't easy
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Having had Stock pipes and a Motad 2 into 1 both tested on an EGA(Exhaust Gas Analyzer) they all can do their job of balancing the engine's exhaust emissions and providing the correct exhaust gas scavenging and Valve fuel input assistance and mix required for power and economy.
Any changes to the stock system usually affect one or more of the Power-bands and have to be allowed for e.g you may be able to get more power at higher revs but then lose some at lower revs unless you spend some money on other things to compensate.
With the CV carbs on these bikes and their design it's very hard to change the low speed and other circuits hence some people have found it better to go to the older,"Slide"(Mikuni comes to mind) type carbs for tuning.I've wondered a few times if anyone might venture into a,"Fuel Injection" carb system just for S*ts and giggles if they have the time,money and will.
As as been mentioned before.With the size of these engines if you want more power and are carrying excess body fat then losing weight will increase performance more than most tweaks that can be done to the engines.Since quitting smoking I've been struggling with weight but am slowly trying to lower mine for the up-and-coming good weather/season but it ain't easy
So I had a '74 CB750KFour a couple of years ago and I modded my air box (cut the bottom out and left the edge as a retaining ring to hold the filter in place) cut the back of my frame off for a cafe racer seat (didn't reconnect the sides/ rear of the frame with a hoop),and I found 2 tiny 1/16 pinholes in the bottom of each of the four exhaust pipes where they enlarge for the baffling. so I sawzalled all four pipes just past the the foot pegs. Keep in mind I didn't use the common sense to look up if there were any drawbacks like back pressure and stuff.. until right after I got done cutting her up anyway.. then researching online about it made me think I'd just destroyed my bike, but I finished my mods and took her for a ride and honestly... it sounded ridiculously mean, didn't notice much drawback, and opening her up on the highway has an entirely new feel!also.. pulling the choke full up and immediately down to like 1/4 choke as Id downshift to fourth and throttle up would shoot me like a bat outta hell and keep me side by side crotch rockets, which is pretty impressive considering I'm 6'2 220+ lbs lol
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Black and red was basically how I bought her
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Purple was my start of mod/building and green was my end result
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P.S. leaving the rear end "separated" without a hoop or anything just made it incredibly responsive to my movement. I used a brake lock as a "cruise control" and could maneuver no hand through turns and all. Obviously blind luck and good karma never beat out sound conventional wisdom so I recommend definitely listening to everyone else's advice. and maybe y'all just use my anecdote as a cautionary tale.
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A'lo'ha
Black and red was basically how I bought her
Purple was my start of mod/building and green was my end result
P.S. leaving the rear end "separated" without a hoop or anything just made it incredibly responsive to my movement. I used a brake lock as a "cruise control" and could maneuver no hand through turns and all. Obviously blind luck and good karma never beat out sound conventional wisdom so I recommend definitely listening to everyone else's advice. and maybe y'all just use my anecdote as a cautionary tale.
That's up to you but 1) if it didn't survive like that for tens of thousands of miles it wasn't really successful and 2) why are you telling us about it in a 12 year old thread about a completely different model?
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