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Has anybody cut open an H box? Whats inside if anything at all? Is anything inside that could be rattling or vibrating if the bike ever suffered a hard dumping by a previous owner.[which it did] I'm pretty confident the noise I'm hearing is not coming from inside the rear engine casing. I know it's not the cans because I yanked those to make space for harley mufflers. Any ideas?
 

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They rust like any exhaust, could be that one of those pipes have rusted off and is now rattling around...I just turffed mine and fitted a S/S "H-box"...
 

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The diagram bear posted shows why and how the back pressure is so important to these bikes when it comes to the carb balance and jetting. The engine needs this specific back pressure to get the fuel and air flow in and out of the engine just right. Just like the original sticker on the exhaust says, "modifying this system will decrease performance". So, unless you take that into account when modding, you will never get the thing to peak performance, all things considered. (Simply to compared to stock, that is.) Sure, some things can be increased, but other areas will suffer. It's all in the balance.
 

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1978 CX500 "The Grub", 1983 GL650I "Nimbus"
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Has anybody cut open an H box? Whats inside if anything at all? Is anything inside that could be rattling or vibrating if the bike ever suffered a hard dumping by a previous owner.[which it did] I'm pretty confident the noise I'm hearing is not coming from inside the rear engine casing. I know it's not the cans because I yanked those to make space for harley mufflers. Any ideas?
What model is it for? I've got an extra from a 500 Custom. You can take it with you on Saturday, if you'll be there.



R
 

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man I am trying to take mine off right now, just so I can clean her up.. I have the bolts off and am wondering if I can get it off without taking off the header pipes?? Pain in the ass it has sat sooo long, I can tell that rust is holding it in place, any input?
 

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I have taken off the whole exhaust in 1 piece but I won't do it again. I would suggest taking the header pipes off. Get out the WD-40 and let soak.
 

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Discussion Starter · #9 ·
Thanks guys. This bike at one time went over really hard on the right side by the previous owner really bending the brake lever high above the foot peg. I learned a long time ago from an old farmer how to use a wooden broom handle to isolate noises within engines and transmissions and this one really baffeled [no pun intended] me. I'm pretty sure my rear engine noise is coming from the box and not from inside the case. The engine has 28K but runs and redlines like a scream. Thanks Randall for the offer but it's a 650 and I grabbed a parts 650 a couple of weeks ago so probably this winter I'll tear into both of them and make the good one even better.It amazes me the technology that honda put into these old bikes.It also amazes me how these bikes can be brought back to life and purr like kittens sometimes with minimal effort. See ya'll in Zumbrota on saturday. Take care. Michael.
 

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The Custom and Regular H-Boxes are interchangeable however the heat shields are different.



The design also explains how you can run two 250 cc cylinders through those tiny exhaust exit tips on the silencers, it pretty much comes out of both pipes on each exhaust pulse. You can eliminate an H-Box but it's advisable to have some sort of crossover pipe in there and you'd need to have some restriction somewhere such as inserts with a small diameter inside the end of the silencers you use. It will never be as perfect as the completely oddball "makes no sense" H-Box that Honda designed for them having X inches of exhaust header before and Y inches behind them but a heck of a lot better than trying to put regular straight pipes back to something like Harley silences.
 

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The custom and standard Collector/Balance box are not interchangeable.They have different downpipe angles and dimensions.



If the the collector box is removed the engine will never be correctly balanced unless the differing lengths of the exhausts is allowed for.This is the Main function of the collector/balance box as it well as smoothing the exhaust gases.The left hand side pipe in the Collector box is shorter than the other to allow for the twist in the engine.



HTH
 

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Odd, we took ne that was supposedly for a regular CX500 and it fit right on my Custom, maybe it was from a Custom to begin with - either that or Old Okie figured out a way to mount it in there however it looks like it belongs. The Custom being a slightly shorter bike with different silencers you would think they were different. I've got another and a set of silencers for a Regular or Deluxe (sorry, they're sold to someone on the forum) along with the H-Box. WHen I had them side by side they sure looked about the same.
 

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If the the collector box is removed the engine will never be correctly balanced unless the differing lengths of the exhausts is allowed for.This is the Main function of the collector/balance box as it well as smoothing the exhaust gases.The left hand side pipe in the Collector box is shorter than the other to allow for the twist in the engine.



HTH
Shep I can't measure them but I see that the pipes inside the collector box are in fact very close to the same length, with the left hand one seeming shorter because it bends further into the box. The other bends first and seems longer but they are probably close to the same length and offer therefore the same back pressure to each cylinder.



I am not sure that all this matters very much except at maximum HP or maximum revolution conditions. I have been running one of my GL650's with GL500 headers for several years and over 50k kms, with no noticeable motor performance difference and yea they do fit.
 

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Air velocity is what makes engines go quicker/slower. You need a large opening at the headers and gradually reducing to the tips. Smaller hole with same pressure equals more velocity.



Think of a drag car engine, inlet/carbs up way high, and headers directly opposite in the head, gives maximum velocity.



So, the tiny pipes in the silencers are designed to be small.



Hmmmm.....may need to lighten up on the meds.
 

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As you can see from this picture not only are the inner pipes of the Balance box different lengths they have also been designed with different diameters,







If you look at the rear of the bike you will see that the exhaust ends are normally level.For them to appear to the,"Twisted" engine as the same length to keep the exhaust scavenging,"Back Slug" correct Honda designed the box to allow for this




How much difference this would make if removed and straight through exhausts I wouldn't know as I don't have the sophisticated test equipment required to know.You may well gain more power at different revs but the the exhausts will be of different length and of course affect economy and noise level which may not be of concern to the user.
 

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Guys what it appears like is honda was 40 years ahead of the drag race guys.What they built is what we call an exhaust termination box.What these are, are boxes with approx 8 times the volume of one cylinder that your header collector dumps into giving the effect of running the correct length collector in an open exhaust while allowing a full length exhaust system and mufflers with no power loss.

The end of the tubes is what the engine sees as the end of the exhaust pipe and the exhaust wave begins its travel back up the pipe to the cylinder from that point.At the cylinder it reverses direction and causes a pressure drop from the wave effectively pulling harder on the open intake valve pulling in more air and fuel into the cylinder than atmospheric pressure alone could do giving better cylinder fill.

What is really happening when these bikes are straight piped isn't that a loss of backpressure (never good for power or efficiency)is causing problems, it is that you have changed the effective tuned length of the exhaust pipe which is very important esp. for power below the peak torque rpm.On a smallblock equiped drag car I have seen as much as 50hp loss by using a to short or to long tuned length collector.The theory and principle is the same our engines are just smaller and a 5 hp loss could fell like 50 on a larger engine.

This will also change jetting requirements because with the wrong length the exhaust slug for lack of a better word will not arrive at the proper time and help pull in fresh fuel and air(less signal strength)causing the need for bigger jets and general richer tune.
 

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Great reply and what I was trying to allude to but you have covered the bases much better.This engine,"Was" ahead of it's time in many aspects and many of it's innovations can now be found in later Honda motorcycle engines
 

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I think it is still ahead of it's time when you think of a rocker armed engine capable of valve train stability at over 9000rpm.nascar guys are just now getting there.When you look at hp per cubic inch or per liter for the young guys it would be 100hp per liter or in american terms a 5.0 liter would be making 500 hp with a smooth idle and good torque and economy.This only really doable now in car engines with superchargers, fuel injection and very precise computer control.Not to mention it still can't be done on 87 octane.Had honda continued on with developmeny I would not be surprised if this little engine was capale of over 100hp with good manners.I have worked on and built racing engines for most of my life and this little bugger impresses me more than the 700 hp small blocks I was building.The attention to detail and ingenuity is amazing.When you compare our engines to a modern Harley it is still like comparing a model a ford flathead to a full race smallblock chevy.The little cx wins hands down.
 

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I think it is still ahead of it's time when you think of a rocker armed engine capable of valve train stability at over 9000rpm.nascar guys are just now getting there.When you look at hp per cubic inch or per liter for the young guys it would be 100hp per liter or in american terms a 5.0 liter would be making 500 hp with a smooth idle and good torque and economy.This only really doable now in car engines with superchargers, fuel injection and very precise computer control.Not to mention it still can't be done on 87 octane.Had honda continued on with developmeny I would not be surprised if this little engine was capale of over 100hp with good manners.I have worked on and built racing engines for most of my life and this little bugger impresses me more than the 700 hp small blocks I was building.The attention to detail and ingenuity is amazing.When you compare our engines to a modern Harley it is still like comparing a model a ford flathead to a full race smallblock chevy.The little cx wins hands down.


I totally agree.They even defeated the gyroscopic effects of the engine/drive shaft.I've had my CX500s,"In-The-Air" a few times as we have some great,"Humped Back" bridges over here that I know well and just can't resist it when all the roads are clear and dry<BFG>








http://maps.google.co.uk/maps?f=q&s...=65NTchoaOQtxlHejv0sgig&cbp=12,58.94,,0,15.21
 

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Guys what it appears like is honda was 40 years ahead of the drag race guys.
If I could have understood 1/2 of what I read, I'd have been amazed... Sounds like you really know what your talking about, either that or you know how to confuse me into thinking you do.... I know I sure as hell don't know what you said, but it sounds like our exhaust is EXTREMELY complicated...



Anybody know if the 2-1 kit works this way?
 
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