Victoria! Zeke's CB175 Build

[Texasstar]

Scavenging can occur with all engines and all exhaust configurations, provided they're setup properly.

In the case of two cylinder engines that use anything except a 360° firing order, unequal length headers followed by a 2:1 collector generally yield good results.

i know we have beat this discussion to death before for a 360 degree crank but now I am just getting a picture of how it is optimized using various crank phasing and didn't know about unequal length header for such. Also is this why the superbikes use unequal length intakes? Zeke and I were looking at a suzuki that had lost 50hp because the auto mechanic that assembled the timing chain had missed one tooth and the air box was off and it had different intakes lengths which didn't seem as efficient as the Yamaha R6 with its adjustable intake length?


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[Texasstar]

So would you have more options for step tuning the exhaust at various rpms with a 180 degree crank for a small twin than any other crank phase?


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[Texasstar]

Or as Crazypj says "suck the oil out of the crankcase"


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[Sonreir]

The trick with unequal length headers is to get the exhaust pulses to enter the collector at a regular interval.

On a 180° engine, this means cylinder two's header should be roughly twice the length of cylinder one.

At 5000 RPM, we're getting an exhaust pulse from each cylinder at a rate of a little less than 42 per second, or one every .024 seconds. And because we're on a 180° engine, the delay between cylinder one's exhaust pulse and cylinder two's exhaust pulse is half that (180° is half of 360°). So cylinder one fires, and then .012 seconds later, cylinder two fires. Then, we wait .036 seconds for cylinder one again.

As you can see, we have an uneven pattern. To correct this, we need to add a delay into cylinder two's exhaust pulse. Generally, this is accomplished by adding length to the header on cylinder two. Likewise, we can also play with the diameters of the pipes to increase or decrease the exhaust gas velocity (this is what Ducati often does). Honda generally likes to lengthen the headers. You can see this in effect on most CLs. The CB400F is a good example, too.

Without looking at it too closely, we can see that if we double the length of cylinder two's header, it will have twice as far to travel before reaching the collector. After the pulses join at the collector, they are evenly spaced. Evenly spaced pulses allow for a shorter overall exhaust, which saves on pressure and reduces the overall weight of the motorcycle.

 

[Texasstar]

The trick with unequal length headers is to get the exhaust pulses to enter the collector at a regular interval.

On a 180° engine, this means cylinder two's header should be roughly twice the length of cylinder one.

At 5000 RPM, we're getting an exhaust pulse from each cylinder at a rate of a little less than 42 per second, or one every .024 seconds. And because we're on a 180° engine, the delay between cylinder one's exhaust pulse and cylinder two's exhaust pulse is half that (180° is half of 360°). So cylinder one fires, and then .012 seconds later, cylinder two fires. Then, we wait .036 seconds for cylinder one again.

As you can see, we have an uneven pattern. To correct this, we need to add a delay into cylinder two's exhaust pulse. Generally, this is accomplished by adding length to the header on cylinder two. Likewise, we can also play with the diameters of the pipes to increase or decrease the exhaust gas velocity (this is what Ducati often does). Honda generally likes to lengthen the headers. You can see this in effect on most CLs. The CB400F is a good example, too.

Without looking at it too closely, we can see that if we double the length of cylinder two's header, it will have twice as far to travel before reaching the collector. After the pulses join at the collector, they are evenly spaced. Evenly spaced pulses allow for a shorter overall exhaust, which saves on pressure and reduces the overall weight of the motorcycle.

thank you! we have been looking at the Yoshimura 400tt but those headers appear to be the same length.


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[Texasstar]

But it did have a shorter exhaust.


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[Texasstar]

Just ran the numbers on the 175 vs 200 cam. The 175 has 215 intake duration and 220 exhaust duration.

The 200 has a 220 intake duration and 225 exhaust.

So if they have the same lift the 200 cam is the 200 a "hotter" cam because it has a longer duration?


The megacycle we have is a 256 duration on both intake and exhaust.


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[Sonreir]

Yup. More duration = hotter. All things being equal, that will mean more torque later in the RPM band. Down side is more reversion at lower RPMs. Enough duration and you may need to start dealing with double carburation.

 

[Texasstar]

Yup. More duration = hotter. All things being equal, that will mean more torque later in the RPM band. Down side is more reversion at lower RPMs. Enough duration and you may need to start dealing with double carburation.

just want all future 200 owners to know that the assumption made in this review http://www.motorcyclespecs.co.za/model/Honda/honda_cb200.htm is wrong and the cb/cl200 has a hotter cam than the cb175 however if they did put the cl160 carbs on they would be happier with the performance. Or even the 20mm carbs from the cb175.


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[Texasstar]

Zeke sanded and polished his bridge

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[Texasstar]

.042 piston to head
.109" to intake valve
.122" to exhaust

200 head decked .072" and .048" off the cylinder.

We can drop one cam link? Should we or will it be too tight?
Lash was set .006"
We will degree the cam and then check the clearances again.

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[Texasstar]

projected electrode or projected shell?

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[xb33bsa]

looking pretty good but what does the cross section of the squish look like ?
is the gap actually wider out at the edge?
have you measured the trapped volume and CR ?
you can easily see if a link can be removed by simply jumping the chaih a tooth at the top but i doubt that you will be able to go that much ,more likely you will just have to carefully design the new slipper/tensioner locations
and you must do the chain tensioners before you degree the cam and check ACTUAL valve clearance
what is the confusion about spark plugs ?

 

[Texasstar]

looking pretty good but what does the cross section of the squish look like ?
is the gap actually wider out at the edge?
what is the trapped volume and CR ?
you can easily see if a link can be romoved by simply jumping the chaih a tooth at the top but i doubt that you will be able to go that much ,more likely you will just have to carefully design the new slipper/tensioner locations

squish is flat. We can easily pull the chain one link closer. We are going to use the stock tensioner at this time with a new metal sprocket. We would have to break the cases to install the the other system. We will do that later. Trapped volume don't know yet we are deciding on what plugs to use and after we degree the cam it will tell us how low we can still go... would like to have the valves within .080". We plan on using the .016" base gasket and that will get us even closer on our squish we used the .021" for this exercise. The stock plug placement is shrouded and male thread doesn't come out to the end of the female thread so we are working on that. We really need a 21mm plug not the 19mm thread length. We still have room to chuck up the pistons in a lathe and cut the squish angle and raise the dome slightly. We may or may not do this.

Tonight we need to degree the cam before we go any further.


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[xb33bsa]

you can actually go far enough on the cam chain, 2 teeth,
to remove a link ?
i still don't understand why you have never cc'd the trapped volume it is extremely easy to do and without doing it you are missing the absolute most important data bit, it is the first thing you should have done with the piston and head combos

 

[Texasstar]

Why is it the most important data bit?


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[Texasstar]

What do y'all think? http://www.google.com/patents/US20140009058

Denso IXG24 IXG27 22mm better heat dissipation?


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[xb33bsa]

Why is it the most important data bit?


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because it is impossible to calculate cr without it

 

[Sonreir]

How are you planning to make those plugs fit? Are you going to add metal to the head?

 

[Texasstar]

because it is impossible to calculate cr without it

agreed we just disagree on when to do it. Now if you were using that data to decide what pistons you wanted to use then I would agree with you. We are talking 11-14cc so getting there is more important at the moment. The valve geometry is different in the 160 vs the 175 and 200 so the valve clearances have been important to us and the 160 has less clearance with a milder cam than 200 with a bigger cam.

Besides we didn't have a bore done till a couple of weeks ago. We will do it. If you remember we did do the combustion chamber along the way and we have calculated the piston domes and done the math. We will get to a final compression ratio and what it is it will be.


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