Eternal Modding Optimism

[Wheelman-111]

Greetings:

The name's Casey. Ben Casey.

It's all about frequency. Scooters operate at a nearly constant one after the messy issue of the 0-5 is negotiated.

No surprise that an open fiter can work just fine. No restriction at max output.

Don't take my word for it. Google Yamaha R6 and look up how much energy they put into the thorny issue of the compromise between low end and top end.

[noiseguy]

See also designs with variable intake tract length to optimize power across the band.

It's been several months since we discussed this last. Somewhere I scrounged up the intake length to RPM optimum length calculation... I think it's to establish a 1/4 wave in the intake...

Experiment: Blow across the top of a bottle, get a noise. Fill 1/2 with water, blow across, get a higher noise. That's a 1/4 wave you're hearing. Note that you only get 1 noise. Flat intake inlet is like this, only good for 1 note, 1 frequency, 1 RPM.

Trumpet mouths (velocity stacks) allow the tuned length to set up at multiple points along the mouth. I suspect this is the reason that actual trumpets (musical instruments) have this shape but I've not researched it.

[Lunytune]

Trumpet mouths (velocity stacks) allow the tuned length to set up at multiple points along the mouth. I suspect this is the reason that actual trumpets (musical instruments) have this shape but I've not researched it.

Five years in band and missed that one. The sound in a brass instrument is caused by the vibration of the lips. Otherwise, it's just air blowing in the wind. Each mouthpiece is designed different, primarily in order to allow or force the lips to a different tension or frequency. BTW, it takes toned muscles to play proper. The flatness or sharpness can be partly controlled by the lips and partly by the adjustable slides, lengthening the pipe/air passage. A French Horn (my primary) has a smaller mouthpiece than a cornet (my secondary) or the bigmouth tuba. The French horn is more in the high frequency range, as opposed to the low frequency bass.

NOW! How are you going to translate that into tuned intakes? May not mean anything, but then again, it might give definition to help tune the intake.

Now then, for those of us old enough to remember automotive carburetors, years ago, aftermarket gimmickry guys marketed a fan like device to go on top of the carburetor, supposedly to create a vortex, supposedly to atomize the fuel better for better combustion. What does this mean to us today with 2 strokers? I don't know.

[mookie]

Trumpet mouths (velocity stacks) allow the tuned length to set up at multiple points along the mouth. I suspect this is the reason that actual trumpets (musical instruments) have this shape but I've not researched it.

Five years in band and missed that one. The sound in a brass instrument is caused by the vibration of the lips. Otherwise, it's just air blowing in the wind. Each mouthpiece is designed different, primarily in order to allow or force the lips to a different tension or frequency. BTW, it takes toned muscles to play proper. The flatness or sharpness can be partly controlled by the lips and partly by the adjustable slides, lengthening the pipe/air passage. A French Horn (my primary) has a smaller mouthpiece than a cornet (my secondary) or the bigmouth tuba. The French horn is more in the high frequency range, as opposed to the low frequency bass.

NOW! How are you going to translate that into tuned intakes? May not mean anything, but then again, it might give definition to help tune the intake.

Now then, for those of us old enough to remember automotive carburetors, years ago, aftermarket gimmickry guys marketed a fan like device to go on top of the carburetor, supposedly to create a vortex, supposedly to atomize the fuel better for better combustion. What does this mean to us today with 2 strokers? I don't know.

you owe each one of us 30 seconds.

[mousewheels]

It's been several months since we discussed this last. Somewhere I scrounged up the intake length to RPM optimum length calculation...

{noiseguy's partial post, link follows}
"OK, I researched this to refresh my memory:

Here's a simple formula: 42000/RPM = length in inches. Length from reeds to intake mouth. For 4000 RPM, that's 10.5" Guys at mopedarmy were discussing this; this equation in similar form is in at least one internal combustion engineering books I've read so I think it's right:"
http://www.hondaspree.net/phpBB3/viewto ... ake#p59339

[Bear45-70]

Trumpet mouths (velocity stacks) allow the tuned length to set up at multiple points along the mouth. I suspect this is the reason that actual trumpets (musical instruments) have this shape but I've not researched it.

Five years in band and missed that one. The sound in a brass instrument is caused by the vibration of the lips. Otherwise, it's just air blowing in the wind. Each mouthpiece is designed different, primarily in order to allow or force the lips to a different tension or frequency. BTW, it takes toned muscles to play proper. The flatness or sharpness can be partly controlled by the lips and partly by the adjustable slides, lengthening the pipe/air passage. A French Horn (my primary) has a smaller mouthpiece than a cornet (my secondary) or the bigmouth tuba. The French horn is more in the high frequency range, as opposed to the low frequency bass.

NOW! How are you going to translate that into tuned intakes? May not mean anything, but then again, it might give definition to help tune the intake.

Now then, for those of us old enough to remember automotive carburetors, years ago, aftermarket gimmickry guys marketed a fan like device to go on top of the carburetor, supposedly to create a vortex, supposedly to atomize the fuel better for better combustion. What does this mean to us today with 2 strokers? I don't know.

That "turbo" crap didn't work on carbs on 4 strokes and it won't work on a 2 stroke either. You don't want a swirling air flow. You want a smooth linear air flow because that is how the "venturi effect" works best. A velocity stack smooths out the air flow by eliminating turbulence. Ant turbulence in the air flow into and through the intake systems is a bad thing. That is why there are no square corners. It is also why a "V block" reed system in more efficient than the flat reeds the scooters are running.

[Wheelman-111]

Greetings:

The formula suggests a 6" reed-to-bellmouth length for peak intake performance at 7K. That would include the carb body, the insulator, and the intake pipe with its kinks. Easily more than 8" total, but I haven't measured directly..

Perhaps this gives some indication why a stock Honda is resistant to efforts to make it rev much higher than 8K?

The shorter CT mani with its V-block reeds measures 4 3/8ths on its centerline, but the bigger carbs add most of the length back.

A Yamaha specialist recently told me, half-jokingly, that Honda intake charges have "a long way to go" between the carb and case. I thought nothing of the remark at the time,, but maybe that partly explains why modded Yamaha 2-strokes are reputed to rev much higher than Honda's?

At the end of its 2-stroke develoment' Honda had a horizontal Dio of its own. Interesting!

[Lunytune]

Bear, That's why I called it "aftermarket gimmicky". In same class with STP and Slick 50.

The formula suggests a 6" reed-to-bellmouth length for peak intake performance at 7K. That would include the carb body, the insulator, and the intake pipe with its kinks. Easily more than 8" total, but I haven't measured directly..
-----------
Perhaps this gives some indication why a stock Honda is resistant to efforts to make it rev much higher than 8K?....
----------
A Yamaha specialist recently told me, half-jokingly, that Honda intake charges have "a long way to go" between the carb and case....

So then, the Honda is too long between reeds and intake? In that case, an aftermarket filter would shorten the distance and be better than the OEM airbox? Or am I going backwards on this?

[noiseguy]

Yep, that's the post.

Yes, all this would suggest that the stock Honda intakes might be a bit long for high RPM tunage. Keep in mind, though, that's still just peak. If you're trying to get an engine to 10000 RPM top speed, you'll tune for slightly under that (say 9000) so that the engine will drop off at 10000, making peak power at 9000.

A box intake will be broadly tuned anyway (working OK across a variety of RPMs,) whereas what we're talking about is something that comes on strong at a smaller range of RPMs.

[Lunytune]

A box intake will be broadly tuned anyway (working OK across a variety of RPMs,) whereas what we're talking about is something that comes on strong at a smaller range of RPMs.

In that case, I think I would be content just to find a less dense foam. I'm well satisfied with results with an open airbox, but foam and cover drops power.

[Bear45-70]

Bear, That's why I called it "aftermarket gimmicky". In same class with STP and Slick 50.

The formula suggests a 6" reed-to-bellmouth length for peak intake performance at 7K. That would include the carb body, the insulator, and the intake pipe with its kinks. Easily more than 8" total, but I haven't measured directly..
-----------
Perhaps this gives some indication why a stock Honda is resistant to efforts to make it rev much higher than 8K?....
----------
A Yamaha specialist recently told me, half-jokingly, that Honda intake charges have "a long way to go" between the carb and case....

So then, the Honda is too long between reeds and intake? In that case, an aftermarket filter would shorten the distance and be better than the OEM airbox? Or am I going backwards on this?

You must remember that the Spree was meant to run only 30 mph and with no trans or variator they needed to tune for mid-range power for added low end torque for improved acceleration. The top speed was easy.

The trouble with tuning for peak power is the the horsepower and torque curves are very peaky and narrow that without a 6, 7 or more geared transmission you take an eon to get to the power curve.

[Lunytune]

You must remember that the Spree was meant to run only 30 mph and with no trans or variator they needed to tune for mid-range power for added low end torque for improved acceleration. The top speed was easy.

I was speaking in theory, not specifically Spree. I've got a variety from non-variated SB50 to Dio AF18.

[Wheelman-111]

Greetings:

The point I was driving at wasn't clear in my first post, so I'll try again.

The point was supposed to be that Honda's intake tract is so long (is it around 7" long from reed block to carb bellmouth?)that if we follow the "formula" submitted by Mouse we arrive at a peak output RPM somewhere just north of 6K. Anything added to the air column - like the stock airbox or a velocity stack - increases the effective length and thereby focuses peak power at an even lower RPM.

[Lunytune]

The point I was driving at wasn't clear in my first post, so I'll try again.

The point was supposed to be that Honda's intake tract is so long (is it around 7" long from reed block to carb bellmouth?)that if we follow the "formula" submitted by Mouse we arrive at a peak output RPM somewhere just north of 6K. Anything added to the air column - like the stock airbox or a velocity stack - increases the effective length and thereby focuses peak power at an even lower RPM.

Not sure if everybody caught it but I did. However, in afterthoughts, I wonder why people say the Honda won't run without the airbox. I've run my Banshee without an airbox, and that's when it has its most power. Seems to me that with airbox properly installed, cover and all, you've added SEVERAL inches to the air column and RPM would be cut drastically. This causes me to be in question of Mouse's "formula". Or is it like a synewave and finds another peak? That's the way things work in ballistics.

[Wheelman-111]

Greetings:

The eloquent Mr. Tune submits:

This causes me to be in question of Mouse's "formula". Or is it like a synewave and finds another peak? That's the way things work in ballistics.

I had the very same thought, but I'm so dismal in Math that I lacked the verbal skill to express it so succinctly.
The Formula doesn't state the engine makes NO power except at the calculated RPM, just that the peak - strictly in terms of the intake column length - will be found there. Maybe there is indeed another peak if you double the length?