Yeah i have one of those black cat mufflers and they are quiet but real restrictive,so im working on modding mine.
What's the maximum RPM you"ve reached?
- Thread starter Outrunner
- Start date
Cabin,
Heres what we used to do to squeeze what we could out of them.
Notice that the stock exit tube is offset from the center. Drill a small 1/4" hole in the bottom center of the muffler next to the stock exit tube. You'll increase power without increasing the noise. Its hardly noticeable and easy as pie to do. Doubles the amount of air released. Drill through the first layer then stop. The drill bottoms out about 1" in. Thats the cat and its solid as a rock..
The exhaust port can also be matched to the exhaust mount flange on the muffler. The part w the 2 bolt holes and the large center hole. Use a reamer or a file or rasp to smooth the exhaust mount flange of the muffler.. Remove enough material so the exhaust mount flange ID matches the rest of the tubing inside it. Just finger there lip to make sure its smooth. Use the standard gasket on the exhaust.
Not tons more you can do with the black cat besides cutting it in half and/or throwing it in the trash.
Justin
Thanks, i will try the hole, i would like to cut it in half or get a new one that actually comes apart.
i do have pics of a black muffler cut in half,maybe i'll study the pics of how its put together.
i do have pics of a black muffler cut in half,maybe i'll study the pics of how its put together.
The Morini i have S6T supposedly revs at 11000 rpm's it is smooth and sounds like a high speed sewing machine. I love the hugh torque it has -you can keep up to cars taking off at stop signs its only 50cc but produces 5.8--6.3 hp i beleive.
The HT engines, "out of the box", will top out just above 7,000 R.P.M. 7,300 on a push, unless they're scrap...I've had a few. 
30-32 MPH flat out with a 170lb. rider on a 26" bike with a 44T is typical.
Please don't use the above comment as a source for debate...These figures are what I get at the shop, using tools and years of knowledge.
Riding a cheap department store bike with an engine on it at 30 MPH is "less" than safe...it is a recipe for disaster!
Jim
30-32 MPH flat out with a 170lb. rider on a 26" bike with a 44T is typical.
Please don't use the above comment as a source for debate...These figures are what I get at the shop, using tools and years of knowledge.
Riding a cheap department store bike with an engine on it at 30 MPH is "less" than safe...it is a recipe for disaster!
Jim
In testing, does the billet intake allow higher rpm? Or does it help improve power in the existing range? Currently I have used a matched stock steel intake, and a longer, offset intake tested back to back. The long/offset one helped low rpm power, and restricted high-rpm pull. ie; on my test-uphill, the engine would lose rpm accending until it reached the high-torque mid-range @ about 30 mph w/ a 27t sprocket. The matched stock intake stayed up high in the rpm range, but I feel is still restrictive. Air does not like to change direction.
I have a pic from a china website of a black cat muffler with a low cost palladium insert that acts as the catylic converter part, you can see in the pic the directionof the tubes.
Its to bad the muffler doesnt come appart except the bottom unscrews and comes off.
Its to bad the muffler doesnt come appart except the bottom unscrews and comes off.
Attachments
In my mind, a two stroke tach should be different than a four stroke tach, right? At least in calibration.
Case in point:
A two stroke fires everytime the motor is at top dead, but the four stroke fires every other time. So a tach calibrated for a four stoke accounts for that fact, ie four stroke RPM is the number of spark firings times two.
If you then throw that tach on a two stroke, it would indicate twice the RPM. ie two times for each fire. Hence it would read TWICE the RPM as the same tach on a four stroke.
Ain't that right guys?
Rich
Case in point:
A two stroke fires everytime the motor is at top dead, but the four stroke fires every other time. So a tach calibrated for a four stoke accounts for that fact, ie four stroke RPM is the number of spark firings times two.
If you then throw that tach on a two stroke, it would indicate twice the RPM. ie two times for each fire. Hence it would read TWICE the RPM as the same tach on a four stroke.
Ain't that right guys?
Rich
Most aftermarket tachs take that into account and are "settable" for not only number of pistons but 2 & 4stroke as well - but yer right, it would be best to check this first
With the stock port timing that these HT motors have, it is not possible to get them above about 9,000 rpm(on a 66cc). I have a big carb, big ports, SBP expansion chamber, and Accel spark wire, and the motor only revs an estimated 1,000 over the best stock setting. 41mph GPS verified 32 tooth sprocket. Anyone claiming Tach numbers of 14,000rpm should divide by two, and get real. My CR125 doesn't even rev that high, and my CR250 makes peak power around 8,500 in full race trim.
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Actually itchybird, A tach that that records the spark plug firing will still be correct weather
it's a 2 or 4 cycle engine. The reason, is that a 4 cycle engine only fires on the 3rd (power stroke)
of the 4 stroke cycle, whereas a 2 cycle will will fire every compression stroke. There are some
4 cycle Motorcycle engines that do fire on the compression and exhaust but that is not the norm.
Another thing about it, is that it would be VERY obvious if your 2 stroke engine displayed a top rpm of 3000-4000 rpm wouldn't it?
Robin, you're correct, but itchybird is also correct about calibration. A tachometer that reads spark impulse and is designed for a four-stroke motor would show twice the true rpm on a two-stroke. That common type of aftermarket tach doesn't know how many revolutions the crank makes, only the spark impulse per minute. Tachs are available for both 2 and 4 strokes, some tachs can be programed for either, and cost more.
