Pipe Design !!Pictures!! on page 4! Nasty fast.

[RubberSalt]

Well I'm gonna get started on my pipe soon. I haven't check my clearances yet on how big it can be. But from what i can tell so far, the pipe isn't going to be an all out race pipe by any means. It's going to be a mid RPM range that should pull from I'm estimating at least 5k and top out at 8k RPM.

This works out well for me, as i designed my porting around mid to top end. After running the bike out at the dunes, I took note on how the engine ran. Ran better than expected but the RPM range was right where i wanted it. Power kicked in at the right time and everything. Now i just need a pipe to fully utilize my design.

Problem I have is the pipe it self, if i want it to match my porting perfectly, it will need to be an out of frame style or I'll need to cut my fenders. Neither which i want.

The pipe will hold my engine back a little, but it will be WAY better than stock.

This little software will help design my cones, so they match up evenly. http://www.pulserate.com/ It's free
Now for the interesting part, here is where i got these numbers, it compensates for a 90degree bend in the pipe already.




I'm not sure of my compression just yet, but I will be checking that in a day or so.

[BGP]

Fun stuff. Just out of curiosity, with all that blow down time area you're now running with the addition of those auxiliary exhaust ports, widening and raising of the main exhaust port and the fact that you're shooting for a peak of 8000 rpm, did you leave your transfers "that low" on purpose? Are you thinking that by the time your transfers open, cylinder pressures will be such that you'll actually "draw" from the base through your transfers? Or did you not shop at CC specialty tools to get a proper right angle handpiece? ( poking fun at you here...) Also, what makes you think that your engine's state of tune will let you use a mean effective pressure of 9.41? Lastly, nowhere in your values do I see and anticipated gas temperature... does the software loosely extrapolate values based on fuel type and BMEP?! At this point, if you're doing all this work, I'm sure you've read a bunch of books; who are you mostly coming back to? Jennings, Graham Bell or Blair?
Btw, go back and read Jenning's thoughts on the 2 stage vs. 3 stage diffusers, their lengths and effects on power distribution in the rpm range and see if you still want to build that pipe. Can't wait to see what you come up with.

[RubberSalt]

I've done most of my reading with bell.
I did leave the transfers that low on purpose, didn't feel like messing with them. I did raise them on my other cylinder, just time consuming. I've gone through, some more thinking and I'm going to go for a 7500RPM peak. The manual for the YT175 shows 8200RPM when looking at ignition timing. The ports i set up pull very hard from the mid range up to the top with a stock pipe. I feel a pipe designed to take better advantage of that would be peaking around 7-8k. But I'd like my pipe to be inside the frame. Being it's in the frame, I have decided to go with a broad range of power with a skinnier pipe.

The temperatures is something that has got me on this program. It doesn't factor in compression at all, but it does suggest an exhaust wrap with these pipes. I'm going to have to go with the loosely extrapolated values based on fuel type. It gives 3 settings for fuel. Now being this engine is air cooled, I'm probably going to use a slightly larger stinger than the program suggest. Might hurt power some, but it'll keep the heat down. I've got a silencer off a blaster, so the stinger is going to fit that thing.

Now I have a few other programs to help with the pipe design, 1 gives what it calls "average gas temp" at 600*c. This give sound a speed of 592 m/s. This is with 8000RPM, same port timing/size, and power development at roughly 29hp.

For the most part, just about ANYTHING is better than stock lol

[BGP]

Here's your pipe Sunshine:

[IMG][/IMG]

You know, if you don't feel like messing around building a pipe, an old RD350 pipe like a DG or an FPP might be a good start for you if you can find one (or a set) rather than something off a YZ or CR125. Those temps seem high for what your pipe will see riding around; so the pipe would be a little shorter for the rpm your aiming at with speed being lower. How many gears on your 175? How close of a ratio is the gearbox? Look at the pic and visualize a shorter first diffuser with a slightly longer belly... To me that pipe looks like it'll want to be between two gears more often that you like... I like the "reversion" cone however. Btw, how do the values compare to the stock unit?

[RubberSalt]

I've got a YZ125 pipe, with some modifications, it could work. You know, extending it in a few places. But the power wont hit like I'd want it to, im sure of it. But the header pipe is the same diameter as my exhaust flange. I might rig that up to see how it does, but I'd like a custom pipe. If everything worked out well, I could share with the world and tell them how to build it.

The 175 has 5 gears and they are pretty tall gears too. When i shift from 2nd to 3rd when wide open at the top of the powerband, the pipe falls short of 3rd gear, it doesn't quite get on it for a little bit, atleast 5 seconds. Most of my riding is dones in 3rd gear, 4th was hard to get too - but I'm sure i may be a little lean still(gotta check).
The stock pipe is.. not that big i want to say it was 80mm at the fatest part. That doesnt mean the baffles either.. The header pipe has some factory placed dents in it to keep it close to the frame. It's really not a good design and most everything can be better. I found a picture of it, but it was in the toilet, so i found 1 off google for ya.

About what temps should i shoot for? This area is a part that eludes me as it's an odd area. Air cooled riden very hard. Cooler is better, but cooler has to hurt the power.

I could go as far as just putting a cone with a belly on the back of diffuser, near the drain plug lol. Pipes with drain plugs just yell "HORRIBLE" lol


Thanks for all the help on this btw, i am taking it all into consideration. Do you have a program you use for this? Or just experience/Mathmatical formulas?

[BGP]

YUK! That whole thing belongs in the toilet! The problem with temps is how fast it falls off when you're not "on it" and where/when you ride. A pipe that's been cycled in a dyno room might show tremendous values and fall flat on it's face out on an icy cold lake the first time you grab a handfull of throttle. Like I stated, however, it's not such a bad thing for someone like you in a sense that the thing will be too long and help you come out of the proverbial "hole". If it were a clutched snowmobile, you'd get off and urinate all over it out of frustration because it wouldn't peel the skin off pudding! So, use a lower BMEP in your case... say 8ish. Second, have you ever touched your pipe's belly right after stopping on the trail? Let me tell you that my FMF belly isn't as hot as a pan of fries comming out of the oven at 425 deg F. They cool fast! I'm just saying that most of the time that you get on it, the pipe won't be there until 3rd gear or so. With me so far? That doesn't, however, mean that you should use a 375 degree value! It's just not a drag sled or a race bike.

Having said that, i'd calculate dimensions for say, a range of lower temps in your case. Keep in mind that the 600C you're using is 1112 F; a few inches down the port with a stoichiometric ratio, yes, but not for a mean temp. Let me go back to some notes and suggest something for you later. You'll also want to play with the stage factor value. Those will give you a sense of how much difference is involved between each level of tune ( read BMEP and exh gas temp in the pipe, hence, sound velocity ). In most cases, you'll find that you can get as much or more variance in fabrication tolerance and execution than you would from temps. Don't forget, as you know, you can save yourself by tuning the stinger diameter and/or gradually wrapping the pipe if it signs off too early. In other words, build it "long" and regulate the heat rejection to tune it... as long as you start with a decent design.

Great, you got my mind going again! Better sharpen some pencils and dust off my notes...


Funny story, when I first started seeing your posts on porting and "third porting" It took everything I had in me not get on here and blast you like the "idiot" I thought you were, dilling ports with a cordless holding the cylinder by hand and porting with a dremel !!! Ugh! Have some pride dude! But then I remembered doing my first "porting job" at 13 using my mom's nail files and father's saw sharpeners on an MX175 just because it all looked "wrong" to me. Loe, the thing ran way better when I was done! I guess we all need to start somewhere and on a budget... One thing is for sure, someday you'll be shopping at CC Specialty tools too. (hint)

[Billy Golightly]

This thread is starting to seriously interest me... keep the discussion going guys. i dont have much to add for the calculation aspect of pipes...but ive tried to build and section one, and im a pretty good tig welder and fab guy, and the pipe kicked my ass. so bad infact i threw it away without ever even taking pictures of it.

[atc007]

Easy to do ! Cleaning up ports is easy,this stuff here?? The less I know the better!! There are some places I just draw the line!! I knew you'd be all over this Billy! Good stuff! BGP,if you were American,I could prolly guess who you are! But,I don't know anyone North of the border cept my Nephew and his in laws.I spent a few afternoons at Silver Speedway,and other tracks,Repairing cones ,and taking out dents,,sometimes the guys SWORE they ended up w more power and or different powerbands. I have nothing to offer but to watch! And oh yeah,,rubber,,don't let the naysayers stand in your way,,you have some good ideas,but you already know that! But,,wear your helmet!

[beets442]

1 street(denco)expansion chamber, which is a great mid range pipe from a Kaw triple 500 would be good for a 167cc cylinder and a 28mm carb. Is that close enough to work with? I know making your own has a better cool factor and thought it was close to what your looking for. Those early 70's Yamaha enduro 175's were one of the best mid range kickers too.

[NINJA]

Listen to BGP.

[RubberSalt]

I took more measurements off my cylinder and the frame. I reentered the data with a lower BMEP. Now the pipe, for the most part, is tucked away from a lot of air flow, but I think i will wrap it with an exhaust wrap. Keep the heat inside the pipe and off the engine. The pipe does come within 1 inch of the cylinder head. Yamaha designed the head with a few fins cut short to fit the pipe above it. Thats half the reason i will be welding fin extensions to the engine.





Going for the 8000RPM peak, according to the program, this is more of a motorcycle pipe with a wide power band. As much as I'd like to have the higher hp, my gears are tall, and the wider power band would probably suit the bike better. The other pipe had the "track bar value" on the 2nd picture, set to 3.

I have noticed this program is giving a longer total tuned length with higher "Target Power Developed", all other variables the same.

[RubberSalt]

Now I've started writing a program, who knows if I'll finish it. It consist of taking the 'cones' and dividing them up. As an example. The pipe shown only gives 7 segments. These 7 segments cant me welded together to fit the bike, have to break them up into more segments.
Segment F1 is 284.8mm long, with a small end diameter of 40mm and a wider end at 52. That wont fit my frame without a nice bend. If i divide that into 8 chunks, it will flow so much smoother with a nice gentle curve. Each segment would be 35.6mm long, only thing that needs calculated would be the diameter of each end of the cones. And this software would do the rest http://www.pulserate.com/.

Now if you guys have a program to do this, GIMMIE' IT. Otherwise i will continue to create 1. I can do the math no problem on paper, but i feel everyone would benefit from some software.

[Billy Golightly]

I have the paid pulserate software and it works very well

[RubberSalt]

Does it allow for you to divide the cones up? If so, i might buy it.

[BGP]

EDIT: Cut out most of this... repetition and useless info.


Back to Salt's issue.
Speed of sound Ao=√[g*R*(TC+273)], where g=1.4, R for exh gases is 290.6 (287.1 for straight air) and TC is mean exh temp in degC. Jennings says 1670~1700ft/sec. is a good value to start with. Fine, what makes him think so? Well, in1973, he took some “good” pipes and reverse engineered them with Lt=Eo*Vs/N (Lt is tuned length, Eo is exh duration and N is rev) to find those values. So, what temp is 1670~1700 ft/sec (509m/s) anyway? Well, plugging it into the first eq, you find that the temp is a very weak 364C. Right, so be careful about plugging stuff into equations that say nothing of how they became.

For you Salt, I would start with around 475C and work out different scenarios up to ~575C. . Let's see what 500C gets you: 185*1837/8000 or 42.5” (1079mm) Sound familiar? BMEP is high on that input so you can say that the 500C is likely high too.

Also, Blair uses this equation for LT: LT=83.3*EP*Ao/rpm in mm... so for 500C; 83.3*185*560.7/8000=1080mm Ah, the magic 1080mm...

I'll post the rest of Blair's length and diameter ratios for you to compare between your program, Bell and anyone else...

Also, think it terms of pulses, BE the pipe, think of what is asked of you. Does your owner respect the fact that you have a power band to work with of the non-rubber kind? Are you drag racing? Hill climbing? Frozen lake racing or just pissin'about in trails? It all starts with heat assumptions.