expansion chamber performance

[STEVE FRENCH]

With expansion chambers, how does stinger dia. affect performance?
I have a set of twin fixed wrap over chambers I'm working with on my 302. A couple people at Lock Haven told me to kneck down the stingers. They are currently 1 1/8".
WHY?

19p

[sam]

Stinger diameter and length control the pressure in the pipe ... which directly increases power ... heat increases, too ... too much restriction = too much heat, too much heat and you melt a hole in the piston or seize the piston in the bore.

With no stinger the expansion chamber probably gives less than half its potential power increase

Since we very rarely see a C mod with problems directly attributed to a too small stinger - for several years my opinion has been that they are being set up and run very conservatively ... and that when someone gets brave (after dialing it in with a hand full of burned pistons) they will pull ahead of the pack

The correct stinger diameter and length would be just larger than what causes the motor not to be able to achieve full rpm on an over long straight .... but changing props or set up starts you over on optimizing the stinger

[nbass]

Stinger diamiter

Sam has some very good points to keep in mind, or buy lots of pistons. A good starting point is a diameter 75% of the leadout elbow diameter. You can go as low as 50%, but that will burn quite hot. The leadout diameter for a 302 should be in the range of 1.374 inches diameter. If the leadout is too large the pipe will never come on. If it is too small you loose top end. So, a stinger between 0.7 to 1-inch in diameter and about 8-inches long. Have fun, you are at the beginning of a long and enjoyable learning experience. If you burn it up, don't call back.

[pro350hydro]

Sam has some very good points to keep in mind, or buy lots of pistons. A good starting point is a diameter 75% of the leadout elbow diameter. You can go as low as 50%, but that will burn quite hot. The leadout diameter for a 302 should be in the range of 1.374 inches diameter. If the leadout is too large the pipe will never come on. If it is too small you loose top end. So, a stinger between 0.7 to 1-inch in diameter and about 8-inches long. Have fun, you are at the beginning of a long and enjoyable learning experience. If you burn it up, don't call back.

Sam and Bass both make some very good points. I agree that 1 1/8 is too large for a 302. We have found that 1" works great on the 102 and 302. However, play at your own risk. No warranties expressed or implied.

[17W]

Pipe Article...

Steve,

I get a sled magazine called SnowWeek. The Sept. 26, 2005 magazine had an excellent article on "Pipe Performance". www.snowweek.com

[David Weaver]

Stinger Adjustments

You can set up your base-line conservative stinger and then adjust it with inserts at the end to provide the constriction. Some alky races will adjust race by race based on the prevailing conditions.

Something similar could be used to adjust the length of stinger. On one set of my pipes, we kept breaking the stingers off from the small "teat" at the end of pipe. So we added a rubber hose at the end held on by hose clamp. Then we can insert different sized stingers (inner diameter and length). Also, we quit losing so many stingers.

[jsilvestri]

This goes along with the chamber question. Do the mufflers, that the European's use, negatively affect the performance of the chambers?

[David Weaver]

Slilencers

I believe that these silencers will change the performance somewhat, but on the PRO engines the moderate decrease in performance can be returned through tweaks in the carburation and timing. At least, I believe that is what I thought somebody said.

Would be nice for Mike Schmidt or Steve Litzell to jump in and really explain what happens and how to overcome it.

The Europeans run very well with the silencers.

[nbass]

Silencers

The stinger is nothing more than a metering devise to bleed off pressure. Restricting discharge from the pipe has a rough adjustment by changing the diameter and a finer adjustment by changing the length. Hence, longer is more restrictive relieving less pressure.

A properly designed silencer will not hurt performance. In fact, a couple of years ago I watched a 350 driver put on the silencer pipes because they were slightly more restrictive hence giving the engine more top end for the 1 & 2/3 mile record run.

If you are considering altering the pipe in any way, I strongly support reading everything you can find on the subject. I have made a number of pipes for different drivers only to find that those who do not understand the basic function cannot do the fine-tuning to make them really good. A calculated design seldom hits the mark. On-the-water testing and adjusting is necessary to get the right balance of corner speed, punch, and top end. The diameter and length of the leadout is critical to just working. The length and diameter of each megaphone step, angle of the reflective cone, stinger diameter and length will all partly determine tuned length, acceleration and top end. Then powerhead drives many of these issues. Induction, transfer and exhaust timing, lean or rich, exhaust temperature, and RPM range all play a part. Great subject, go and do great things!
Good Luck,
Neil

[sam]

Silencers

A silencer like the Super Trap muffler (which is adjustable) should be able to maximize performance and greatly reduce offensive noise at the same time.

The adjustable part of the Super Trap muffler is a stack of crimped rings bolted together and capped at the back. Adding more rings opens up the flow, taking rings out decreases flow.

Some combination of internal or hidden stub stinger and adjustible plate muffler is probably the best.

[Bill Huson]

Aaarrrgghh ! My Ears!!!

My previously owned Harley had Super Trap (Super Crap) mufflers, although "mufflers" is a misnomer. Frigging things were so freaky loud my nieghbors taped their windows to cut down on loose, flying glass when I cranked the Hawg up. 10 minutes into a ride my ears hurt. 20 minutes and my ears would bleed. Trashed the Super Craps for real mufflers. Course, If I had bothered to check I could have adjusted the ring thingies and maybe saved the Super Craps.

Loud pipes don't save lives, loud pipes make you go "Huh? What say?"

[Dick Tyndall]

Quieter tuned pipes..............

A silencer like the Super Trap muffler (which is adjustable) should be able to maximize performance and greatly reduce offensive noise at the same time.

The adjustable part of the Super Trap muffler is a stack of crimped rings bolted together and capped at the back. Adding more rings opens up the flow, taking rings out decreases flow.

Some combination of internal or hidden stub stinger and adjustible plate muffler is probably the best.

One way the R/C boat guys are making their engines quieter is to install a small piece of thin tubing ( in this case brass ) up into the stinger that goes all the way into the the pipe to where the big diameter of the pipe ends. Or, I guess you could say the full length of the convergent cone ( the tapered part of the pipe that the stinger attaches to ). From what I'm hearing, this does not affect the performance, but just quiets the noise to a more comfortable level. This is something that is in a book titled, " Two Stroke tuners Handbook" by Gordon Jennings, printed in the early 1970's. There is one section in this book that details the in's and out's of tuned exhaust systems. If you can find one of these books, you better get it!
Sam and others here are right on the mark with their comments. With the R/C boats we would make the pipes longer for more punch out of the corners and shorten them for more top end power. By making the stinger longer it would give us more punch coming off the corner and also cause more back pressure in the pipe, increasing the heat in the engine. Former outboard racer Jim Irwin made me some quiet pipes back in 1995 for a .21 cubic inch Mono hull boat that never ran more than 45 MPH with a regular tuned pipe. When Jim's quiet pipe was installed, I picked up 5 MPH!!! I also won US-1 titles that year and in 1996 with a boat that you could not hear with other boats running. Muffled or quiet pipes don't slow the boats down..............just look what the Europeans are doing with them; model boats and big boats!

[STEVE FRENCH]

I have an old set of AAEN chambers off a snowmoble that I cut at the back of the first cone and adapted to a Bayer stack. They have the stinger running the lenght of the rear cone taper and glass pack stinger/silencer on the ends. Tried running one on my 25MOD OMC but with the deflector piston/port design it did not work. Looking for exhaust plate for Bayer elbow to try on my 202/302. Will give Jerry Davids a call.
Have seen same/similar set ups work on Yamatos. Jim Robb Jr. ran one and Ford City and it ran well.

The wrap over pipes I have on the 302 now look like dirt bike chambers. A stock side cover was modified with outlets/flanges for the pipes. the inside of the manifold is worked to seperate the cyls. Capped the the stock pipe in tower.
Ran it a couple times but lacked any low end punch. they had no mid/straight section and very little reverse cone. Probably were ment to work with a muffler and the advantage of the multiple ratios of a bike transmission.
Cut the pipes at the back of the first cone and welded on the mid section and rear cones with stingers from another set of snowmoble pipes with reg stingers.

I realize the easy way would (and will wind up being) to write a check for someones proven system, but I seam to have this stubborn habbit of trying things my own way first.

Going to test this weekend in Oil City,Pa. at Charlie Fry's FUN-RUN.

Will make base run with 1 1/8" stingers.
Then try with a set of clamp on silencers from a RD/RZ-350 Yamaha road racer bike. Then rivet in 1" reducers and rerun.

Will probably bolt the stock exhaust cover back on and run faster but.........

Also taking my 202d/osy-400 motor and my stock/closed-up 22 OMC BSH prototype.

Weather is supposed to be in mid 60's .... and the Coor's light will be in the mid 30's............

Will post some pics in "general discussion" section next week.

19P

[les]

2stroke tuners handbook

I have tried to find this book, My copy is most likely in a box of Dr. Seuse books somewhere. I did find a copy online, but it's a big PDF file scanned in. Better than nothing...

http://edj.net/2stroke/jennings/

Larry

[sam]

Steve, the snomo chambers adapted to the Bayer stack not working does not surprize me. The correct tuned length for a motor's particular porting and operating rpm is absolutely critical. An inch off of perfect for your motor's porting & rpm can make a pipe completely worthless ... half an inch off of perfect for your motor's porting & rpm might mean it is mostly worthless.

BUT when you get it right you will know ... when the motor "comes on the pipe" it will feel like the boat has been kicked by an elephant