Big bore stinger project

[Bowtie316]

Like the title says, this project was to enlarge the stinger diameter to big bore size.  There has been much debate about the need to increase stinger diameter as you increase the size of your motor.  Some say 310 or above, some say not until you are over 370. I wasn't able to get much response about how it would change the characteristics of the motor, like would I loose low end torque, would it be louder etc., so I decided to give it a shot and post my findings.  if it doesn't work out, I will just have to buy a new pipe and post this one for sale.

My combination is a 330 ESR cylinder setup and ported by K&T, on a +4mm stroker crank.  ESR trx5 pipe, 38 A/S carb, boyesen reed cage, stock ignition, stock airbox with K&N.

So first things first, here is what my trx5 stinger measured.  1" ID except where the bending process reduced the width.

The ESR stinger material was .060" thickness, so I came up with 1.120 od.
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At the bend, it was quite a bit less.
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Here is what the cone to stinger interface looked like.  This is exactly like they came apart, there was no slag in this pipe whatsoever.
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And another showing in the ends.
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Old 1" id next to new 1-1/8" id.
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Now, after that I got busy and didn't take any more pictures until I was done but it's pretty straightforward.  I trimmed off and opened up the end of the cone to match the new stinger id.  Then I started with the bend coming off the stinger, cutting it to the right length. It sucked trying to get it flared to go over the cone, I don't have the right tools for that. Then once I had that I cut a piece of 1-1/4 ID pipe to be used as a slip-fit sleeve, slid it over the new stinger and just kept working my way back.  I didn't really start welding anything until I got the pieces all to fit together like I wanted them.

For the silencer, I cut the mount tab off the bottom of the stinger and cut the pipe off the end of the silencer.  I opened up the silencer to accept the 1-1/4 od slip-fit piece, this will be used to slip the perforated core in one end and the stinger welded in the other.  At both of my slip fit connections, I made my tube lengths such that there is no gap between the 1-1/8 od pipes.

This is how it turned out,  I'm certainly no Pumashine but it'll have to do.
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I don't have a lathe so I opened up the silencer end cap with a die grinder. It could be better but should work for now.  I might have one made later on.
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And, here is an idle video.  

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First impressions are, well, it's loud.  Is it any louder I don't really know, this big bore is just loud.   I took a quick spin around the yard and didn't really notice any loss of low end at all.  I'm going to have to go back through the jetting and more time on it before I can comment on everything.

[zarathos]

Looking good! :eagerness:

[Pumashine]

Well done. You know it was not as easy as the pics show.

[KASEY]

the only issue I see is you put the joint on backwards,,,  its going to force the pipe goo out of the joint

[Bowtie316]

the only issue I see is you put the joint on backwards,,,  its going to force the pipe goo out of the joint

Yeah I actually did that on purpose. I was tired of cleaning junk off the shock and spring.  Figured this way it would atleast be out easier to get to.  I'll probably seal it up a bit when I confirm that it is going to work okay for me.

[rsss396]

Nice job! somebody actually listened

You will probably notice a little more lowend power, that is because the pipe will have slightly less "effect" and thats a good thing when its "effect" is timed incorrectly like at low rpms. A pipe works perfectly in a narrow band outside that its "effect" may be worse than if you just had a straight pipe.

[Bowtie316]

Nice job! somebody actually listened

You will probably notice a little more lowend power, that is because the pipe will have slightly less "effect" and thats a good thing when its "effect" is timed incorrectly like at low rpms. A pipe works perfectly in a narrow band outside that its "effect" may be worse than if you just had a straight pipe.

You know, I'm glad you say that.  I didn't want to jinx it and say anything but it did feel a bit more torquey on the bottom.  I figured it might be due to it being a little leaner because I haven't had a chance to work on jetting any. Either way it certainly didn't loose anything down low.  I can't wait to get it back out and rip on it.

[Jerry Hall]

...............................Some say 310 or above, some say not until you are over 370. I wasn't able to get much response about how it would change the characteristics of the motor, ..............

It seems the majority of the internet pipe formulas and out of date books on two-stroke pipe design tie the stinger ID to some non relevant metrics like engine displacement, exhaust port area, head pipe diameter or maybe what date there will be a full moon . The optimized stinger ID depends upon the amount of power the engine is capable of making with the exhaust system dimensions that are between the inlet of the stinger and the exhaust port.


The optimum amount of back pressure created by the stinger ID may need to vary from one pipe/port design combination to the next. I am an engineer and I have not found or been able to derive a formula that will accurately calculate the optimum stinger size.  I have to resort to using the dyno to optimize the stinger size by conducting a series of instrumented tests on the dyno.  The number of bends, how many degrees are in each bend, the radius of the bends and the volume of exhaust that needs to flow though the stinger, determines the overall flow capability of the stinger/muffler combination.



A few rules of thumb for those that are playing with pipe restriction:
 

An under-restricted pipe will usually increase the low end slightly with a large loss in peak power and power after the power peak.  An under-restricted pipe will usually require a much larger main jet to provide the optimum air/fuel mixture for best power.

A slightly over restricted pipe will come on the pipe a little late, make good peak power, have good over-rev, and generate an excessive amount of unnecessary heat on the  piston crown and on the exhaust port side of the piston.  A slightly over restricted pipe will usually require a leaner main jet so that it does not have a rich misfire in the over-rev portion of the power curve than a pipe that has the optimum back pressure.

A pipe that has the optimum restriction for the power output of the engine design will typically have good power over a wide range if the port/pipe dimensions are complimenting each other.  A pipe that has the optimum restriction for the power output of the engine design will typically be easier to tune and keep tuned.  A pipe that has the optimum restriction for the power output of the engine design will typically not be plagued with piston seizures, sagging piston crowns and or holed pistons.

[Bowtie316]

It seems the majority of the internet pipe formulas and out of date books on two-stroke pipe design tie the stinger ID to some non relevant metrics like engine displacement, exhaust port area, head pipe diameter or maybe what date there will be a full moon . The optimized stinger ID depends upon the amount of power the engine is capable of making with the exhaust system dimensions that are between the inlet of the stinger and the exhaust port.


The optimum amount of back pressure created by the stinger ID may need to vary from one pipe/port design combination to the next. I am an engineer and I have not found or been able to derive a formula that will accurately calculate the optimum stinger size. I have to resort to using the dyno to optimize the stinger size by conducting a series of instrumented tests on the dyno. The number of bends, how many degrees are in each bend, the radius of the bends and the volume of exhaust that needs to flow though the stinger, determines the overall flow capability of the stinger/muffler combination.



A few rules of thumb for those that are playing with pipe restriction:


An under-restricted pipe will usually increase the low end slightly with a large loss in peak power and power after the power peak. An under-restricted pipe will usually require a much larger main jet to provide the optimum air/fuel mixture for best power.

A slightly over restricted pipe will come on the pipe a little late, make good peak power, have good over-rev, and generate an excessive amount of unnecessary heat on the piston crown and on the exhaust port side of the piston. A slightly over restricted pipe will usually require a leaner main jet so that it does not have a rich misfire in the over-rev portion of the power curve than a pipe that has the optimum back pressure.

A pipe that has the optimum restriction for the power output of the engine design will typically have good power over a wide range if the port/pipe dimensions are complimenting each other. A pipe that has the optimum restriction for the power output of the engine design will typically be easier to tune and keep tuned. A pipe that has the optimum restriction for the power output of the engine design will typically not be plagued with piston seizures, sagging piston crowns and or holed pistons.

Jerry, thanks for the input.  I am curious now though, what happens when a combination comes in somewhere between 1"id and 1-1/8 id?  Do you jump up to the 1-1/8 size and add restriction somehow?  

I figured if this combination exhibits the underestricted side effects I would slide a short piece of 1"id pipe inside where they slip together and see if that helps. Could possibly play with the length of the insert to add or remove restriction while still being less restriction than a complete 1" stinger.

[rsss396]

since you have bends,a connection point and a silencer it is more restricted than if it was a straight stinger. The center mount ESR pipes kind of fall in between since there is less bends.
It would probably take a dyno to see the power difference but you will see a difference in the field when it comes to detonation, you will be much safer now.

[Jerry Hall]

Jerry, thanks for the input.  I am curious now though, what happens when a combination comes in somewhere between 1"id and 1-1/8 id?  Do you jump up to the 1-1/8 size and add restriction somehow?  

I figured if this combination exhibits the underestricted side effects I would slide a short piece of 1"id pipe inside where they slip together and see if that helps. Could possibly play with the length of the insert to add or remove restriction while still being less restriction than a complete 1" stinger.

Our modified pipes actually have a much larger stinger/silencer and we use machined inserts to adjust the restriction.

[Bowtie316]

since you have bends,a connection point and a silencer it is more restricted than if it was a straight stinger. The center mount ESR pipes kind of fall in between since there is less bends.
It would probably take a dyno to see the power difference but you will see a difference in the field when it comes to detonation, you will be much safer now.

Yeah, I was really just doing it for reliability, but the kick in performance will be nice if I can get it dialed in. Just going to a mandrel bent 1"id stinger would have been an improvement on what I had.

Our modified pipes actually have a much larger stinger/silencer and we use machined inserts to adjust the restriction.

Good deal, sounds like there is hope for this project yet.

Thanks to both of you for the feedback.

[Jerry Hall]

.............Just going to a mandrel bent 1"id stinger would have been an improvement on what I had.
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The bends on the ESR stingers look like they were using a pipe bender for electrical conduit.  

Looking at the picture of the junction of the stinger and your tail cone is different from the ESR pipes I have had in our shop.  The end of your old stinger is cone shaped and fits over the outside of the tail cone.  This is the way we do it as well as the majority of the other pipe builders.  Using this type of junction at the stinger and tail cone moves the weld zone to much larger diameter and allows the entrance of the stinger to flow well if there is a sloppy weld.

[KASEY]

I believe ESR just started doing the stinger that way recently,, I have 2 of their pipes and the newest one is that way and the older one is not,,,,

[udontknowme]

found this info on another site. it seems to match what jerry said. " The required flow restriction depends solely on the amount of generated exhaust gas, and that is directly proportional to the generated horsepower"

somewhere i thought i saw a adjustable venturi located at the stinger inlet. not sure if that would be a simpler way than inserts but either way im sure you  would get the same results in the end