"Doing it Right" or "How to Build a Functional Café Racer"

crazypj

Split personality, I fake being smart
I've always treated CV carbs as about 80~85% flow of slide carb. (or, to put it another way, CV is always 'too big' by 15~20%)
36mm CV about equivalent of 32mm round slide or 29mm 'smooth bore' (actually closer to 31mm and 28mm but they don't come in those sizes)
The smaller the mechanical slide carb you can use and get the flow you want will always produce better throttle response than going 'too big' on carb venturi
As for airbox not having an effect on tuned length, it depends on the intake snorkle, if it's smaller than 1.5 times area of one carb, it will have the same effect as increasing intake length, the airbox will be acting as an Elmholtz resonator
https://en.wikipedia.org/wiki/Helmholtz_resonance
 

DucatiDave

New Member
First off, thanks to Matt, Teazer, PJ and all the others for passing on this info. I knew some of the basics but not the theory behind it. What a wealth of info.
We do these builds because we can, and I get that. My question is what is the dollar cost to HP gain to actual real world increase. If I am riding, and next to me is a "built" CB350 vs my stock CB, does he pull alittle ahead, or does he walk right away? Anyone can twist the throttle on the straight road. I want to be able to out brake and out corner the other guy. That is where I am putting my emphasis, handling and braking.
For me, I am re-building a 73 CB350 with 9k miles. My thoughts were to make the motor reliable. Upgrade to electronic ignition, Ricks stator, Bore-tec cam chain tensioner, and Mikuni VM30's. I thought about doing a whole motor build but came to the conclusion that at the end of the day it is still a small motor. Would like to know others thoughts on that.
 

stroker crazy

crazy as a fox
DucatiDave said:
the dollar cost to HP gain

There comes a point where the law of diminishing returns kicks in.

It is usually cheaper to go for a larger motor than try to wring the last fraction of a horse from a small one.

That said, it can be an interesting exercise to see how much can be extracted from any given motor!

Crazy
 

DucatiDave

New Member
Stroker, I agree, there is no replacement for displacement. And you can only go as fast as your wallet is fat. So to invest alot of extra money into a small motor and still have small motor performance seems alittle excessive. I am not saying one way is right or wrong, I am a gear head and appreciate the time, skill and effort that people put into their engines. That is why I am not going the engine upgrade route. I am looking at the bike as a cohesive piece of rolling art. Carefully crafting the bike from front to back. Looking at every part that I change and make sure it flows with the other changes I have done or have in mind. I built a "best in show" Bobber, in my garage. The only things I did not do was paint, powder coat, and chroming. (I used Kraft-tech frame) The judges said they chose my bike bike because from front to back the bike flowed, all the little details were thought out well. Doing it right is a great title for this thread, but how is everyone taking that phrase. Does it mean building a Cafe Racer this way, and that is the right way. Or Doing it right, don't short cut it. Do the job the right way the first time. I am sure everyone knows what a "rat" bike or car is. There are 2 ways to make a rat ride. Build it haphazzardly, tie stuff on with bailing wire so every time you ride it something falls off. Or build it with craftmanship and have the look that you desire.
Ah if we only had unlimited funds!
 

mannydantyla

Been Around the Block
Sonreir said:
Applications - Intake Tract

OK. Up next I'd like to ramble on a bit about intake tracts. By "tract" I mean everything before the cylinder (including the valves, valve seats, ports, carbs, and filters).
...

Excellent! Thank you for this!

https://www.youtube.com/watch?v=RA5PRj7KPkE
 

Sonreir

Oregon
DTT SUPPORTER
Nitrous Oxide

It's been a very long while since I've done one of these posts, so I apologize in advance for the lapse. If any others want to take up the mantle and help pick up the slack, please do. ;)

This is going to be another one of those posts that's largely academic, since few of us will ever go this route. It's fun to discuss and the knowledge is useful, though, so I'll proceed.

The chemical formula for Nitrous Oxide is N2O, but it also often goes by the name, "NOS", which is the brand name of Nitrous Oxide Systems, one of the more popular kit offerings and parts suppliers. N2O means two atoms of Nitrogen and one atom of Oxygen. This is significant for several reasons. Primarily, the limiting factor of producing power in most engines comes down to how much Oxygen you can stuff into the cylinder(s). You need between 12 and 14 times as much Oxygen (by weight) as you do gasoline for combustion, so adding fuel is rarely a problem. Air generally found in our atmosphere is constituted of a lot of different gases, of which Oxygen represents about 1/5. In N2O, the Oxygen represents a little over a third. What's interesting is how this Oxygen is freed up. On its own, N2O is a non-flammable, relatively inert, gas. When heated to around 570°F, is begins to break down. The Nitrogen and Oxygen separate and we now have accessible Oxygen which can be put to use in our combustion. Finally, the way the N2O is stored becomes quite a bonus as well. Compressed N2O is stored in liquid form in gas tanks. When the N2O is delivered from the tanks, it decreases in pressure drastically. And because temperature and pressure are interrelated, a drop in pressure also means a drop in temperature. Releasing N2O into your intake tract drops temperatures by a significant portion. This, of course, leads to a denser intake charge, resulting in even more air making it into the cylinders.

Unfortunately, to which many a poor soul can attest, tweaking with the amount of Oxygen entering the cylinder without adjusting the fueling can lead to a bit of heart ache. Burned pistons and valves are not uncommon as well as even larger failures that stem from detonation and pre-ignition. With all of the extra Oxygen available, we need to add the fuel to match or we quickly develop a very lean running condition.

How that fuel is added is how each Nitrous Oxide system is generally described. N2O systems come, usually, in one of two flavors: Dry Shot or Wet Shot.

In all cases, the actual installation involves locating your N2O bottle somewhere on the bike and routing the lines to an electrically activated pneumatic solenoid. The solenoid then controls the flow of N2O gas into a set of injectors mounted into the intake tract. The start of the flow of the N2O usually triggered by a button near the hand controls. Many systems also include a safety that prevents the system from being used unless the bike is at wide open throttle. Use of the N2O at partial throttle positions usually ends up being fatal for the engine. To further combat any issues arising from the addition of more fuel and Oxygen, ignition timing is usually retarded a few degrees when the N2O is in use.

Metering of the N2O is usually handled by a pressure regulator as well as jets. Like the jets you find in carbs, these jets control the amount of N2O that is provided. And like carbs, the size of the jets are usually represented by a number (which may or may not be arbitrary). The combination of the pressure of the N2O system as well as the jet size is usually summarized with a rough estimate of the horsepower added to the engine when the system is in effect. 15 shot, 20 shot, 40 shot, and even 75 shot all refer to the estimated horsepower added. As with most things, more power usually means more cost, more planning, and more difficulty in engineering.

Dry Shot
A Dry Shot Nitrous Oxide System is so named because there is no auxillary addition of fueling to compensate for the addition of N2O. Dry shot relies solely on the vehicle's existing fuel delivery system to administer additional fueling. For carbbed engines, the N2O is added upstream of the carbs. The idea is that the denser charge passing through the carbs will pick up more fuel. While this is true, it's usually not enough. The same process is used in fuel injected engines, though usually with a greater effect.

A Dry Shot system is usually the easiest to install and maintain, but also the most prone to damaging the engine and its components. Also, Dry Shot usually results in less overall power than the other types. This is purely due to the failure to add enough fuel to fully utilize the extra Oxygen. Because of the lack of additional fueling, the amount of N2O that can be added is usually minimal. Things must remain matched.

Another common tactic is to intentionally richen the mixture by installing oversized main jets into the carbs. Since the main jets have the most effect at WOT and the use of N2O requires WOT, this throttle position is reserved for when the user wished to take advantage of the Nitrous system.

Because of the balance of risk involved in using a Dry Shot system versus the low gains, Dry Shot systems are not usually favored by those looking for real power or longevity, though they are much more common in modern fuel-injected engines where electronics can account for the gas addition without many other changes.

Wet Shot
A Wet Shot system is quite a bit different than a Dry Shot system in that all of the fuel necessary to utilize the additional Oxygen provided by the N2O is added at the same time, along with the N2O, usually with fuel injectors located in each intake port, after the fuel metering (so after the carbs or MAF/MAP of an EFI system).

To add this fuel, it's usually necessary to engineer a fairly complex system. If your bike didn't have a fuel pump before, it definitely needs one now. A fuel pressure regulator also becomes a necessity. Fuel injectors must be added to each port, after the carbs, so now the button press to release the N2O into the system now also actuates fuel injectors.

It doesn't sound like a lot extra, but all of these added parts on an already small machine usually requires quite a bit of forethought to pull off successfully. Furthermore, the electricity needed to run the fuel pump, solenoid(s), and injector just may not be available on some bikes.

Conclusion
Nitrous Oxide can be a game changer. Compared to most other performance options, it is generally very inexpensive to install, but it also costs money over the long term. Refilling N2O bottles can get spendy, especially for those of us addicted to torque and horsepower. A poorly executed system can also result in a lot of broken parts and it's not difficult to find videos on YouTube of installations that turn their operators into human fireballs. Well executed systems, however, can result in a lot of extra power for very little investment of time and money and usually do little to long term reliability of an engine.
 

crazypj

Split personality, I fake being smart
A 50+ hp CB350 will probably cost in the region of $7,000 for engine work.
That will be at the wheel and not crank though so pretty much double power output
It's very easy to get 32~34 at wheel but costs pretty much double to go over 40bhp at wheel (should still be under $1500.00)
 

Quintin Snell

Active Member
Ok, ive managed to read through this rather intense (to me, anyway...) information, and definitely plan on using some of it in my build. One thing i would like to clarify... you did go into 2 into 1 systems, but i want to keep my cx500 as a 2 into 2, Which wasnt really covered. will it be an issue if i make my pipes slightly longer, to ensure the muffler extends past the rear shocks so as not to blacken the springs? I will be removing the original headers and having stainless pipes made up the same size as the original headers. Im not home now, so cant do actual measurements... i have a more or less scale drawing, if that helps... before you give me a hard time, i realise the angles on the headers are too sharp, after reading this thread i went and changed my drawing a bit to have more realistic header curves
 

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crazypj

Split personality, I fake being smart
Unles your going to run it over 12,000 rpm I've always found a longer exhaust provides easier for carb mods and better overall power. You know CX motor will kill it's cam chain tensioner if you plod around at low rpm? (below about 6K)

I would probably have flanges turned up and convert to spoked wheels, really don't like Com-Star's
 

Quintin Snell

Active Member
I think the cam chain tensioner is shot, its a bit "clattery" i will check it and the cam chain when i pull the motor for its clean out and inspection. I will likely fit a new did chain as a matter of course. I am looking into a set of gl1000 spoke rims, or possibly a conversion (conversion is a last resort, shipping and customs will probably cost more than the kit itself, i would have to have one made locally ) fortunately i dont hate the comstars, so its not going to kill me to keep them. Thanks for the input i tend not to ride at low revs, so the new tensioner should be ok...
 

Sonreir

Oregon
DTT SUPPORTER
Quintin Snell said:
Ok, ive managed to read through this rather intense (to me, anyway...) information, and definitely plan on using some of it in my build. One thing i would like to clarify... you did go into 2 into 1 systems, but i want to keep my cx500 as a 2 into 2, Which wasnt really covered. will it be an issue if i make my pipes slightly longer, to ensure the muffler extends past the rear shocks so as not to blacken the springs? I will be removing the original headers and having stainless pipes made up the same size as the original headers. Im not home now, so cant do actual measurements... i have a more or less scale drawing, if that helps... before you give me a hard time, i realise the angles on the headers are too sharp, after reading this thread i went and changed my drawing a bit to have more realistic header curves

Take a look at the Acoustic Tuning sub-section and just ignore the portion about the headers. Just apply the overall lengths and diameter of your calculations to the entire pipe for each cylinder.
 

Quintin Snell

Active Member
coolness, thanks. I will do. At the moment, i am away from home for another 6 weeks, so cant do any physical work on the bike. But now, im thinking it is a good thing, it has forced me to do a lot moreresearch andplanning than i would have, saving me from mistakes i now knowi would have made, and thinking of other ways of accomplishing my goals. My build will be all the better for it. I have restored a bike before, but this will be my first custom job, totally different. Easier in the sense that parts are more available, more dificult in that mods need to be planned, you cant just follow a garage manual!
 

Quintin Snell

Active Member
Another question which shows how little i actually know about engines... when i restored my suzuki, i had a lot of smoke, so got first over size pistons and rings, then had a rebore done to accept them, problem solved, and a just noticeable power increase (maybe my imagination, but i swear it feels quicker...) was that nessecary? Could i merely have replaced the rings, or pistons and rings with new standard size? Just something for me to keep in mind if my cx decides to start smoking...
 

Sonreir

Oregon
DTT SUPPORTER
Smoking can be caused by a number of things, one of which is the rings. If you just decided to replace it and that solved your problem, you got lucky.

Often, if the rings are loose enough to be causing smoking issues, it's not uncommon for that to also cause a loss of compression. Increasing compression will DEFINITELY cause a noticeable increase in power.
 

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