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Discussion Starter #1
I'm looking for help in establishing pipe and Megaphone lengths.
I'm running 175cc with Mega-cycle full race cam and intend to use twin pipes. Any help would be appreciated.
 

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Hi,
Branson can probably cover this better but for starters I'd go with about 1.25 od pipe for approx 39 inches, use a long 3inch megaphone (between 22-24 inches in length which you can probably get from Branson as well).


Aaron
 

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Aaron,
I was trying to find my specs for a 2-2 system but can't locate them right now. I can't swear to this but I think the head pipe length is close to the same as we use on our 2-1 systems...but no collector. In other words...like a 24" head pipe, and then right to the megaphone without adding the 15 inches for the collector. The added collector length is something specific to 2-1 systems. I don't think head pipe length changes when going from 2-1 to 2-2, still about 24", just added the "mid pipe" when making a 2-1.

Bertlil, I'd strongly advise not using the Megacycle 122x4 camshaft...way too pipey and very hard on the valve train. Most of our bikes run much better on the 122-20 cam. I'd also suggest a 2-1 exhaust system. If you are dead set on the 122x4 cam I've got one I'll sell you since I don't ever plan on using it again :)
JohnnyB

PS.. yes I can make you the megaphones
http://www.jrbranson.com/BikeParts/CDR-Parts.htm
 

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Discussion Starter #4
Well it looks like I have the Dreaded 122 x 4 Cam, sure wish I had found you guy's sooner.
Is it the lift or the dwell that's the issue with this cam profile.
Of course I've got a few bucks tied up now.
Any suggestions ?.
 

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Bertlil,
Well, most of us made the same mistake. Well with a lift .040" more than the -20 cam, and a duration only about 10 degrees less the valve train accleration rates seem pretty high. And with the lift they are very uncompromising about valve/piston clearance. I only bent valves about three times before I realized that even the slightest valve float would lead to immediate valve bending...and the x4 seems to produce float a lot sooner than the -20. Which means you have to go with even heavier springs to prevent it, which means you tear up your valve train even quicker. I should have been suspicious of the specs of the x4 before I bought. Strangely symetrical intake and exhaust numbers...like someone just "thought" it would be a good idea.

All this aside... I would have lived with the problems if it made usable power on a race track. It doesn't seem to, very narrow powerband, high up in the range. And seems to have some strange anamolies that make it more difficult to find a good carb and exhaust setup. It feels a whole lot like a drag race cam to me.

Well...if we were dealing with anyone besides megacycle you could probably return an unused camshaft. Or...you could save it to sell to an unsuspecting person...that's what I'm doing but haven't had the heart to do it yet. Megacycle gets stupid prices for regrinding these cams ..otherwise I'd just say send it back and regrind it...but they'll charge you full price all over again.

What pistons are you using? I think the valve/piston clearance with OEM pistons and a x4 cam are very marginal. I'd want about at least .080" with that cam.
Maybe you could sell it to someone you'll be racing against :)

Strangely enough..some of us are thinking about experimenting with STOCK camshafts. Stock cams seem to rev pretty freely up to 10,000 plus rpm. With porting and valve work probably well beyond that. And these little engines really like to have mid range power...they already make decent power at high rpm. Actual on track performance seems to go up and the cams get more "mild".
JohnnyB
 

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Discussion Starter #6
Jonny B. Many thanks for the information.
When you read the Mega-Cycle cam description Full Race Cam seems to be the logical choice when building a Roadracer. Again nothing beats track experience.
I would'nt mind trying to regrind this cam myself, and maybe give it a try.
Reduce the lift by 0.040" and check out the resultant Dwell/opening/closing peroid. Anyone tried that Yet ?.Seems I have nothing to lose.

As for Pistons I was going to use Stock CB/CL175's and adjust for a 11:1 compresion ratio.

I got the loan of a 1964 Factory CR93 Fairing and am just finishing a Mould to make a dupicate Fairing,Air-tech does not make this item so I had to suck up to a family member in Ireland to send it over.
I also wish to stay with the 2-2 exhaust system as I wish to keep this project as close to the CR93 as possible

Bert
 

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Bertlil,
Ahhh pistons and compression on the 175.

Before I step into this, perhaps one of my fellow 175 racers could vouch for me as I don't want to seem too much of a know it all. Suffice it to say I've done a bit of research and development in this area and with the 175's as a whole.

The short story is that actual cc'd static compression on a stock 175 is in the low 8:1 range. And....there is absolutely no way to arrange matters to achieve compression higher than about 9:1 with stock pistons. And even at that it will involve milling the head to a point that will compromise the cam chain geometry to the point that you will have problems there.

The problem is you are talking about a 52mm bore, and a 41mm stroke...there is just very little volume to use to build compression...so the combustion chamber must be filled to the absolute max to reach desirable compression ratios. Which means higher and higher domes, which even on this small bore size starts to create problems with flame propagation when you go to extremes.

Here is the way I solved it.

http://www.jrbranson.com/HondaRacer/CB175/pistons.htm

Despite what the page says at the moment, even with these pistons compression is much closer to 10:1 after valve pockets have been deepened and plug notches cut. These images are of the "Phase 1" pistons..... we are now up to "Phase III" which are being made as we speak.

I could go on for pages about this subject and the work myself with the help of others have done of these engines. So far we've got 23hp at the wheel on a 200cc version of the 175 (have dyno charts), and with the changes we are making this winter hope to hit about 25hp by spring. It hard to say without sounding like an asshole...but let's just say the bike I built goes pretty good.

I work with Aaron Phinney in developing these bikes, who is also on this forum, and also a great source of info for what works and doesn't on them. He likes to try to break them at Daytona every year so he's an authority on what doesn't work :)

By the way, you probably mentioned it elsewhere, but where do you race? Are you in the Northeast US like many of us?
JohnnyB
 

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Discussion Starter #8
Johnny B. again thanks for the information.
I'm a VRRA member, located in Ontario Canada . I live real close to Ogdensburg NY.
I started my 175 project to race in the 200cc class here in Ontario but it seems they may drop the class due to poor grid numbers.
I do intend to finish the bike and race it in the States.

I'll check out the Piston site, again many thanks for your reply's

Bert
 

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I raced at Shannonville and Mosport last year.

Won the "Lightfoot" Trophy at Mosport. Eric Pritchard is going to be pissed that he can't run his BSA if they drop 200gp.

I'll have to keep an eye on that, 200gp is the only reason I go up there to race. I was planning on going to Shannonville for sure next year.
JohnnyB
 

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He ran that Duc at least once at Loudon this year. The FIM meet. He finished 2nd behind Fast Phil Turkington and his Bultaco (very very fast guy). I finished 4th in that race behind Eric and another Bultaco. I remember the race well, I had a great race with the 3thrd place Bultaco but Eric and Turk were well away after only a few laps.
JohnnyB
 

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Discussion Starter #12
Johnny, talked with the VP of the VRRA. He indicated all the classes you ran in last year will still be available next year.
Seems they only dropped Period 2 200 class Honda MT125's they have been moved into another class.

Regarding the 175 pistons, can you email me details (cost etc)
Bert
 

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Bert....that's you?

Didn't I talk with you at Shannonville this year? I'm the tall guy with the blue trailer and the wife that races. I know I wrote down your email or phone number somewhere, sometime.

JohnnyB
 

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Bert,
Just found your card, with your email and phone number. I think I talked with you at Mosport also.

Our Period 2 200gp is called ULSV...that's where our MTs,TAs etc run. There was one big guy on a MT at Mosport that would pull past me down the long straight... I was impressed with the way he had that thing going.
JohnnyB
 

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Discussion Starter #15
Johnnyb, yep that was me you talked to at Shannonville. My wife and I have just moved and relocated to Smiths Falls Ontario, real close to NY state. We are now 1 1/2hrs. from Shannonville. There is a new track being built North of here in Calabogie, a Ski resort/Spa location. We are all hoping it turns into a "class A" act.
Also the excell Email address I probably gave you at Shannonville is now Dead. But you have my new one.
I did recieve you email Re: Pistons and will get back to you.

Best Regards Bert
 
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