Forced induction 100cc

[DEATH_INC.]

.aside from the difficulty of geting a reverse wave at atmospheric pressure to pass into a combustion chamber which is above atmospheric pressure most of the time - certainly when any reverse wave arrives...the last thing you need is charge contamination with hot gasses at a critical point in the cycle. Carburation is easier to set too as there is no reverse flow whatsoever.

Lol...um the reverse wave is at less than atmospheric, that's why it works. It does not cause hot gas to pass into the chamber, it draws it out, and it certainly does not cause a reverse flow at the carb...that's caused in the intake tract....

[DEATH_INC.]

Where I'm really struggling though, is why a supercharged engine is not making as much noise as an N.A motor. I know why a turbo motor is quieter, at least I thought I did, and it had nothing to do with the forced induction.

Turbo's are quieter...until they make boost.
I also struggle with how a supercharged engine is quieter. How can a bigger bang be quieter? All the s/c engines I've ever heard are loud as f*ck.

[DEATH_INC.]

Basically, you can't go wrong with plenty of silencer volume.

This is true. The speedway guys at the springs discovered this when all the whingers made 'em silence down the cars/bikes. The same core with a larger capacity can was substantially quieter.

[pete376403]

Turbo's are quieter...until they make boost.
I also struggle with how a supercharged engine is quieter. How can a bigger bang be quieter? All the s/c engines I've ever heard are loud as f*ck.

Turbo is quieter because the energy it is using to drive the compressor would, in a normally aspirated engine, be released to the atmosphere as noise.

[Drew]

Turbo is quieter because the energy it is using to drive the compressor would, in a normally aspirated engine, be released to the atmosphere as noise.

Until it spools up and the waste gate is open. Then it would be noisier than an NA motor with the same displacement, because of the bigger bang.

[Ocean1]

Until it spools up and the waste gate is open. Then it would be noisier than an NA motor with the same displacement, because of the bigger bang.

Except the waste gate is a pressure-varied restriction, (as is the turbo exhaust rotor) a pretty good silencing trick in it's own right.

[Grumph]

I don't believe I've said at any point that a blown motor is inherently quieter than a NA one...what i will say is that silencing one presents an easier problem given enough room for silencer volume.
A NA motor - particularly a single - is reliant on exhaust resonances to make much of it's power. Get the pipe wrong and there goes a lot of power.
A blown motor does not need or want any exhaust resonances at all - period. It therefore becomes an easier job to build a pipe which won't lose power.

Turbos mufflers have an easier job too - the turbo takes a lot of the energy out of the exhaust gases before they reach the muffler.

[Brian d marge]

you can absorb the energy by either, expanding it (volume) or by absorbing it .. from memory the motogp are kind of like a kn filter but inverted , the gas has mass , and gets some boudry layer disturbance..so basically rockets on through , the energy contained in the gas..( sorry cant remember in what form or position ) expands out into the absorbtion material
now as motogp dont need a hell of a lot of absorbtion .....the muffler isnt so big ....or long...
stephen
sorry ...tapping this out on the phone on the train...so please excuse

[Sketchy_Racer]

Well the first exhaust has been made, it is completely non calculated and has been made just to fit.

Cheers to Richban for letting me tax his exhaust bends. (got new ones at work will drop em off soon)

It looks ok and combines parts of a CRF250 header pipe with a chinese muffler that I stole off the turbo bike. I will re-pack it but it does sound great at 11500 RPM

Thinking of exhaust designs I would believe that in the case that Grumph is explaining with a supercharged motor then I agree that exhaust is irrelevant and big is better but only is there is considerable valve overlap. This would mean that the positive pressure in the exhaust cycle would completely negate any form of scavenging.

However in a system where there is no valve overlap then sure I believe some sort of scavenging will have an effect. I plan on testing both methods so time will tell however I do believe that experience trumps pretty much all theory so have no doubt that Grumph is correct.

The next project that me and a mate are looking at is making a inertia dyno. More on that at a later date.

[bogan]

The exhaust looks pretty exhaustlike, but I think we'd rather hear how it sounds

The next project that me and a mate are looking at is making a inertia dyno. More on that at a later date.

Skip the inertia bollocks and go straight to an eddy current dyno. Once all the other dyno costs are factored in I think the extra tuning ability would be well worth the budget increase.

[Moooools]

The exhaust looks pretty exhaustlike, but I think we'd rather hear how it sounds



Skip the inertia bollocks and go straight to an eddy current dyno. Once all the other dyno costs are factored in I think the extra tuning ability would be well worth the budget increase.

Agreed. Or even just a couple of old car brakes and a load cell. Especially for FI engines. Need a good amount of time at steady state to tune it up real nice.

How does the software work? I am assuming it is an array of cells for TP vs RPM?

[richban]

Agreed. Or even just a couple of old car brakes and a load cell. Especially for FI engines. Need a good amount of time at steady state to tune it up real nice.

How does the software work? I am assuming it is an array of cells for TP vs RPM?

One of these maybe. Looks simple enough.

http://www.mustangdyne.com/mustangdy...MD-ScooterDyne

[speedpro]

Some sort of power absorber brake thingy from trucks. They are an Eddy current type of brake but checking their specs they could draw a lot of current but I don't know what sort of power they would absorb at that current, or as stated a regular car disc brake and load cell on the cailper torque arm.

[Yow Ling]

a 60kw eddy current brake costs us$1400 fob china
a truck absorber will use one or two hundred amps at 24v depending on size
you can get 90 and180 volt ones as well

eddy current brakes or absorbers aren't that common over here, they are in Europe", hydraulic absorbers are more common here

the extra complexity of an absorber dyne does not make it very attractive, you need a closed loop control and just more electronics compared to an optical reflective or hall effect sensor for an inertia dyno

ese seem to manage ok with an inertia one

[Brian d marge]

im at those same crossroads......3d scanner , welder, or a very rare scotch whiskey

stephen