tuning pipe (old school)

[rbh]

Back in the day (maybe yesterday ) guys would tune a pipe for their 2 stroke engine by painting a line down it to the stinger.
They would take it out for a good run and after, at the point that the paint did'nt burn off they would cut the pipe and move the stinger up to that point.
First, I can't remember what paint to use, it must not burn at anything "under" 900- 1100 degrees F + -???
(aluminum melt's at 1150ish F ???)
(heat+ speed of sound stuff???)
AH lack of memory.

 

[tdrudd87]

Re: tuning pipe (old school)

I had always heard on hotrods (V8s) that you use regular paint, and it is where it does burn off that you cut or put your x-pipe.

Just muddying the waters
Terry

 

[PGFISHER]

Re: tuning pipe (old school)

Another neat idea is to weld the tailpipe on so that some of it is inside the chamber. It must not go in further forward than the wide part of the last (outlet) cone. This will quiet the exhaust by taking the sharp ringing out of it, and seems to have no affect on performance.

 

[JustJason]

Re: tuning pipe (old school)

What your talking about doing is called exhaust scavenging. It works by setting a specific backpressure point in the exhaust system in which acoustic pressure waves can hit, bounce off of, and return up the pipe back towards the exhaust valve. Then if you can time the opening of that exhaust valve in correlation of the exact moment the pressure wave hits that, bounces, and starts running back down the pipe, the wave will create the illusion of negative pressure within the exhaust pipe, and in essence help pull the new exhaust gasses out of their cylinder in a faster manner than the gas would normally escape.
Not sure if painting and cutting up your exhaust is the most scientific method to do it. You only really see it set up properly in 2 stroke moto bikes and some select (suzuki) high performance rice rockets. Other than that you may be doing more harm than good in mucking up a factory exhaust system. Because if some how you screw up the backpressure point, you'll send exhaust right back into a cylinder that's on it's exhaust stroke already, and you wont get the full spent charge out.
On engines that run heavy valve overlap. Scaveging also helps in drawing in a new air charge when the intake valve is starting to open. So you could screw that up as well.
Probably best to leave it alone.

 

[kenmyfam]

Re: tuning pipe (old school)

Aluminum melts at 1220 degrees F
Use some temp sticks and see where they melt.
What are you tuning ???

 

[rbh]

Re: tuning pipe (old school)

I have an old mid 70's alpine 640cc twin track snowmobile that I use for work and the original exhaust box rusted out, so I retrofitted a pipe and exhaust off of a 700cc tripple polaris.
The first thing that I did was remove and replace the tillitson HD carb for a
38mm mikuni, WOW what a difference, the added a comet 109 clutch.
now it goes like a bat outa heck but It has lost its bottem end tourqe.
"I know that clutching is a massive part of the ski doo", but I am just curious about the pipe.

 

[rbh]

Re: tuning pipe (old school)

What your talking about doing is called exhaust scavenging. It works by setting a specific backpressure point in the exhaust system in which acoustic pressure waves can hit, bounce off of, and return up the pipe back towards the exhaust valve. Then if you can time the opening of that exhaust valve in correlation of the exact moment the pressure wave hits that, bounces, and starts running back down the pipe, the wave will create the illusion of negative pressure within the exhaust pipe, and in essence help pull the new exhaust gasses out of their cylinder in a faster manner than the gas would normally escape.
Not sure if painting and cutting up your exhaust is the most scientific method to do it. You only really see it set up properly in 2 stroke moto bikes and some select (suzuki) high performance rice rockets. Other than that you may be doing more harm than good in mucking up a factory exhaust system. Because if some how you screw up the backpressure point, you'll send exhaust right back into a cylinder that's on it's exhaust stroke already, and you wont get the full spent charge out.
On engines that run heavy valve overlap. Scaveging also helps in drawing in a new air charge when the intake valve is starting to open. So you could screw that up as well.
Probably best to leave it alone.

Yes, I understand that stuff (this is the land of the tricked out snowmobile), the paint trick was told to me years ago and I have never tried it.

 

[Tig]

Re: tuning pipe (old school)

I did a dirt bike years ago. Ending up taking a 1/2 inch out of the expansion chamber. I'm sure it changed something in a measurable amount but in all honesty the change was imperceptible during use.
I think you are on the right track when you say "clutching is a massive part of the ski doo". It's like the prop on a boat, except it's tunable.
Sounds like a cool sled you have there. What do you do with it?

 

[rbh]

Re: tuning pipe (old school)

I did a dirt bike years ago. Ending up taking a 1/2 inch out of the expansion chamber. I'm sure it changed something in a measurable amount but in all honesty the change was imperceptible during use.
I think you are on the right track when you say "clutching is a massive part of the ski doo". It's like the prop on a boat, except it's tunable.
Sounds like a cool sled you have there. What do you do with it?

Well if it had been running last year it would have pulled men, tool's and antennas up to a tower site for a week (had to use the 700cc summit and a tobagan, OH that was a pain)
Before we would use it for making tracks down a off road pole leed then pack the guys and tools and pull the cable in, much better than snow shoes.
(we found a ski-bouse for it, looks like the snowmobile equivalent to a 18 wheeler)

 

[kenmyfam]

Re: tuning pipe (old school)

Sounds like a lot of fun !!! Did a couple of small 2 strike motorcycles in the mid 70's. Spent an awful long time getting a few more MPH !!!

 

[PGFISHER]

Re: tuning pipe (old school)

2 stroke engines have a very small power band. Expansion chambers are designed to produce power at a certain RPM, and you dont get much power above or below that RPM. When I was racing 2 strokes in the '60's I had 3 sets of pipes; for short, medium, and long tracks. Each set of pipes had jet charts for temperature, altitude, and humidity. As you have probably figured out by now it's a little more complicated than painting a line.

 

[perchin]

Re: tuning pipe (old school)

Well if it had been running last year it would have pulled men, tool's and antennas up to a tower site for a week (had to use the 700cc summit and a tobagan, OH that was a pain)
Before we would use it for making tracks down a off road pole leed then pack the guys and tools and pull the cable in, much better than snow shoes.
(we found a ski-bouse for it, looks like the snowmobile equivalent to a 18 wheeler)

I also work in the tower industry...... last winter we used two snowmobiles to pull us and gear up a ski slope. About 6 years ago we took 5 snowmobiles across lake Michigan pulling gsm tech. Radio cabinets to mackinac island...... fun stuff.

 

[puddle jumper]

Re: tuning pipe (old school)

Yes, I understand that stuff (this is the land of the tricked out snowmobile), .

Yup spend $30,000 more on a $10,000 sled to get 6 inches higher on a hill and have bragging rights. Yup seen that game played.

 

[rbh]

Re: tuning pipe (old school)

Yup spend $30,000 more on a $10,000 sled to get 6 inches higher on a hill and have bragging rights. Yup seen that game played.

UH kerry-
Do you think these guy's to the south know what we ride through here??
I bet it would freak the livin XXXX if they knew how steep and deep it really was.

 

[puddle jumper]

Re: tuning pipe (old school)

They may know about it in Rockies just south of the boarder. Where you live is the center of the universe when it comes to hill climbing and snowmobiles. It takes real guts to go vertical on a sled for that long and not wreck.

 

[Tig]

Re: tuning pipe (old school)

As I reminisce about the times I've gone over high side on my little hill climbs I'm not so sure it was guts that got me there. Although there was one memorable occasion when I took a tree in the gut on the way down. Back then there was no bailing out if you also wanted to shut the engine down. You had to try to hold the kill button until the engine stopped.
I use my sleds for ice fishing now. The only guts are provided by the fish.