Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

I did a lot (A LOT) of testing on 125/250cc kart engines with different pipes from various manufacturers and experts. Most never stood up to the advertising, for a variety of reasons. But I do remember EGT being a big factor.
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

redwillissuperman said:
I did a lot (A LOT) of testing on 125/250cc kart engines with different pipes from various manufacturers and experts. Most never stood up to the advertising, for a variety of reasons. But I do remember EGT being a big factor.

I think in almost all cases, there are sacrifices made in adherence to the design for practical sense of building and fitting the thing. For example, multi-stage diffusers are used in almost all cases to shorten the pipes up a little bit. The "step" in that diffuser adds and makes power in some places, but doesn't in others. If you look at the two stroke drag racers, almost every pipe is built out of frame. They are either short and very large in diameter with a short and quick taper back down to the stinger (Blair Formula) or more longer, smaller in diameter anaconda like things (Jennings or oldschool design).

A friend of mines CR500 powered trike has one of the oldschool designs on it. He paid good money to a builder for it, and having been to a lot of other races and looked at a lot of other pipes expected a more banshee looking pipe, quicker taper up to a huge diameter, then back down to the stinger instead of this. But you know what, his bike runs like crazy mad good, and the guy that built it told him "Just tryi t and let me know what you think..."


Pipe built with longer more gradual taper (not mine)

Pipe build with Blair / Modern formula (Not mine).

My first pipe I built used the more modern Blair design. I'm happy with how it performed (Other then I'd like to have moved the peak power down a bit because it goes so fast RPM wise its a little spooky). I'm just trying to find a happy medium of a good performing pipe that isn't fricken huge to fit and snake around the bike. If I can use the older formula and save a bit of diameter, it makes it easier to fit. Hopefully, anyhow :) In any case, I think I'll probably wind up with atleast 2, probably 3 different pipes to experiment and try with on this thing at the end of the day.
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

My only advice (you were wanting some right?) is to make a "compromised" pipe that makes it driveable and easy to use versus agonizing over the "perfect" pipe. If it's down 10hp but you ride it a 1000miles, no one will care.
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

redwillissuperman said:
My only advice (you were wanting some right?) is to make a "compromised" pipe that makes it driveable and easy to use versus agonizing over the "perfect" pipe. If it's down 10hp but you ride it a 1000miles, no one will care.

Hey I'm with ya! I'm a realist.
 
Got started on the first iteration. Stainless steel material.



Also did a little more trimming on the subframe, got the bike back up on the table and starting trying to experiment and figure out rear sets placement. That is going to be a tricky one! Are there any good threads here with a hash of information on thoughts/theories on placement? From the little bit of sitting on the the thing and experimenting it looks like they need to be about 2 inches lower and probably 4-5 inches at least further back than the ATC pegs for it to be semi comfortable/tolerable positioning wise. I took some pictures but apparently my phone corrupted them during the saving process.
 
If there is a formula for seat/bar/foot rest placement I have not seen it. I always start with the seat height the rider wants. That is pretty easy to figure out from how they ride and how big they are. I mock up the bike at the target ride height (sometimes this has been pretty much just the bare frame and front end) and set up a seat at the height wanted. Then it is just a matter of having the owner sit on the bike while trying out peg and bar set ups. Usually on the first go round there is no simple way to mount pegs on the bike so I just use concrete blocks, bricks, boards etc to make an easy to adjust foot rest. Placing your foot on the front top edge of a concrete block actually mimics a peg pretty well, is easy to move around or shim up and down, and stays in place fairly well. Once I think it is reasonably close I get them to sit on the bike for at least 15-20 minutes with their feet on the "pegs" and both hands on the grips. That may seem like some sort of torture (pretty much is) but totally worth it in the end. Usually there are changes and it takes at least couple of "sittings" to get things just right. 20 minutes is a short ride, but sitting on a stationary bike that long reveals a lot about what is comfortable. Of course it does not take into account the effect of the wind at speed or the operation of the foot controls, but bars are easy to adjust for air drag (I usually err to the low side of perfect bar height when stationary) and foot controls are sort of a learned operation between different bikes anyway. Trust me, if you are comfortable sitting on your bike for 20 minutes standing still, it will be a joy to actually ride.
 
Jennings pipes are old school for sure and still work well enough. I have tried a few different software programs for pipe design and prefer to use Bimotion. That software allows the user to change a few different parameters. They can then be plugged into a simulation program such as EngMod2T or MOTA and see what thate software thinks of the different pipes.

After that you can play with all manner of variables to see what it can be made to do. Sometimes you can spend weeks and barely move HP much at all and other times you find that copying an existing pipe from a similar bike works better for reasons that are not obvious. For those of us that don't get paid to do 2 stroke exhaust R&D, that can be a lot of fun or it can be a complete waste of time.

Karts are a world unto themselves with variable header lengths and adjusting jetting on the fly. The last 100cc Comer pipe I worked on took months of work to stretch the curve after peak power and that was worth 1 second a lap and won a championship. That same pipe on a different but similar motor just didn't work well at all. The differences were tiny but with closely matched racers that is what it takes. On the street or off road, it would have been a waste of time.

For a regular bike where we are not running week in week out at MotoGP level, small differences are not noticeable.

A Jennings pipe or copy of pipes that work with that top end and similar stroke will probably be pretty close to ideal in the real world. I am guessing that you want stump pulling torque at any revs and any throttle opening and not a peaky all or nothing pipe.
 
On rear set placement- lower and forward is better. Why?! Most people are not dragging their elbows through corners and comfort will win over max corner angle. Also remember to wear your riding boots/pants and not tennis shoes. Concentrate on shifter actuation versus rear brake.

On pipes- my point was to get something that fits versus "perfect". Riding the bike with a 15% reduction in power is always more fun.
 
jpmobius said:
If there is a formula for seat/bar/foot rest placement I have not seen it. I always start with the seat height the rider wants. That is pretty easy to figure out from how they ride and how big they are. I mock up the bike at the target ride height (sometimes this has been pretty much just the bare frame and front end) and set up a seat at the height wanted. Then it is just a matter of having the owner sit on the bike while trying out peg and bar set ups. Usually on the first go round there is no simple way to mount pegs on the bike so I just use concrete blocks, bricks, boards etc to make an easy to adjust foot rest. Placing your foot on the front top edge of a concrete block actually mimics a peg pretty well, is easy to move around or shim up and down, and stays in place fairly well. Once I think it is reasonably close I get them to sit on the bike for at least 15-20 minutes with their feet on the "pegs" and both hands on the grips. That may seem like some sort of torture (pretty much is) but totally worth it in the end. Usually there are changes and it takes at least couple of "sittings" to get things just right. 20 minutes is a short ride, but sitting on a stationary bike that long reveals a lot about what is comfortable. Of course it does not take into account the effect of the wind at speed or the operation of the foot controls, but bars are easy to adjust for air drag (I usually err to the low side of perfect bar height when stationary) and foot controls are sort of a learned operation between different bikes anyway. Trust me, if you are comfortable sitting on your bike for 20 minutes standing still, it will be a joy to actually ride.

That sounds like a really good idea. Not sure why using something like wood blocks or a CB to figure out the peg height and position didn't occur to me. I was trying to sit on the bike and take measurements of my feet unsupported where it felt okay at. Thanks for the thoughts and tip!
 
teazer said:
Jennings pipes are old school for sure and still work well enough. I have tried a few different software programs for pipe design and prefer to use Bimotion. That software allows the user to change a few different parameters. They can then be plugged into a simulation program such as EngMod2T or MOTA and see what thate software thinks of the different pipes.

After that you can play with all manner of variables to see what it can be made to do. Sometimes you can spend weeks and barely move HP much at all and other times you find that copying an existing pipe from a similar bike works better for reasons that are not obvious. For those of us that don't get paid to do 2 stroke exhaust R&D, that can be a lot of fun or it can be a complete waste of time.

Karts are a world unto themselves with variable header lengths and adjusting jetting on the fly. The last 100cc Comer pipe I worked on took months of work to stretch the curve after peak power and that was worth 1 second a lap and won a championship. That same pipe on a different but similar motor just didn't work well at all. The differences were tiny but with closely matched racers that is what it takes. On the street or off road, it would have been a waste of time.

For a regular bike where we are not running week in week out at MotoGP level, small differences are not noticeable.

A Jennings pipe or copy of pipes that work with that top end and similar stroke will probably be pretty close to ideal in the real world. I am guessing that you want stump pulling torque at any revs and any throttle opening and not a peaky all or nothing pipe.

Believe it or not, that big monstrosity I built to begin with actually kept the power pretty smooth. The RAVE valve on the exhaust probably helped with that. It still felt like a 2 stroke, and didn't just pull and then fall flat on its face like some "grunt" pipes I've ridden. It put the power higher in the RPMs than I would have liked, but it was a pretty smooth transition and ramp up there. A few friends that rode it, I had to tell them to stay in a gear a bit longer than you would think before shifting because thats just where the power was at. On the road that'd probably be even easier to do. The stainless one I'm starting now is a second set of templates I had that is the same as the first one I built a few years back. They have been laying around here ever since I finished the first one, so I'm going to build it out and then also a second one with the Jenning's formula and see which ones work better (fit, practicality, power) and then go from there.

I have MOTA actually. I found an old copy on ebay years ago that came with the dongle and it did function, but its been years since I used it. Last time I had it installed and used it, it was still a little more than I could reasonably use and wrap my head around. If I'm to buy another software package any time in the next few years, it will probably be BiMotion which I've heard extremely good things about and the developer is regular on updates and support which is worth its weight in gold.
 
redwillissuperman said:
On rear set placement- lower and forward is better. Why?! Most people are not dragging their elbows through corners and comfort will win over max corner angle. Also remember to wear your riding boots/pants and not tennis shoes. Concentrate on shifter actuation versus rear brake.

On pipes- my point was to get something that fits versus "perfect". Riding the bike with a 15% reduction in power is always more fun.

Yes, thats the one thing I noticed is going to be a bit tricky. The shifter linkage. My pegs are going to wind up being wider than on the 3 wheeler, and obviously moved back a bit also. so I'm going to have to either get a real aggressive angle coming over on the rod end, or make some sort of a splined shift-shaft extension to weld the receiving rod end bracket to. Lots of little things for sure. Lower and further back felt better to me the little I was playing around with it last night, but I will take all ya'lls suggestions to heart here and keep playing with it as I know that'll make or break the comfort level of the thing.
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

BillyGoat4130 said:
Yes, thats the one thing I noticed is going to be a bit tricky. The shifter linkage. My pegs are going to wind up being wider than on the 3 wheeler, and obviously moved back a bit also. so I'm going to have to either get a real aggressive angle coming over on the rod end, or make some sort of a splined shift-shaft extension to weld the receiving rod end bracket to. Lots of little things for sure. Lower and further back felt better to me the little I was playing around with it last night, but I will take all ya'lls suggestions to heart here and keep playing with it as I know that'll make or break the comfort level of the thing.
You can do an intermediary shaft that moves it over. Some rearset - intermediary - transmission
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

redwillissuperman said:
You can do an intermediary shaft that moves it over. Some rearset - intermediary - transmission

Thats kind of what I was thinking. Use the splined portion off an existing shifter and weld it to the end of a piece of heavy wall small diameter tubing (So it didn't flex), and extend out as far as need be, and then hook the rod end onto that.
 
Struggling with perspective, we need to see you sat on it, feet on pegs.
Probably should have a Simpson bandit on and be flipping the bird for the correct effect ;)
Hooligan style


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Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

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Guessing you don't own a selfie stick?!

I set up my wallmart GoPro years ago to record myself on my bike trainer so my (internet based) tri coach could check my bike position, it was a pain in the ass, but in the long run saved me a lot of actual pain in the ass.


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Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

Is this being built specifically for use on train tracks?

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app
 
Re: Building my own two-stroke "Mongrel" - Inspired by CharlieT & TedT

clem said:
Is this being built specifically for use on train tracks?

Sent from my SAMSUNG-SM-G920A using DO THE TON mobile app

LOL.
I'm ready to see some tires on this thing.


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That has been the subject of so many jokes with friends, I'm almost keeping it that way to keep it continuing on...lol
 

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