Forced induction 100cc

[pete376403]

Also on the supercharger front, I have finished the two lobe rotors and made a second set of gears, fits together great and have gone with 0.1mm wall to rotor clearance, 0.08 endplate clearance on both sides and 0.1 rotor to rotor clearance.

Given that compressing the air will heat things up, have you made allowance for rotor expansion?

[Drew]

Given that compressing the air will heat things up, have you made allowance for rotor expansion?

Have you read the whole thread? This got covered early on in the piece.

[pete376403]

Yeah I have and I'm not trying to knock the guy - I'm in awe of his talents, and I would love to see it running.

I just had a look at 0.1mm on my caliper (about the thickness of standard bond paper) and given the amount of metal in the rotors I'm guessing ("guessing", you will note) that they will expand more than the housing. Will be delighted to be proven wrong.

Rotor expansion is a big problem in top fuel blowers, they inject fuel before the rotors (as well as after) for the cooling effect.

[Drew]

Yeah I have and I'm not trying to knock the guy - I'm in awe of his talents, and I would love to see it running.

I just had a look at 0.1mm on my caliper (about the thickness of standard bond paper) and given the amount of metal in the rotors I'm guessing ("guessing", you will note) that they will expand more than the housing. Will be delighted to be proven wrong.

Rotor expansion is a big problem in top fuel blowers, they inject fuel before the rotors (as well as after) for the cooling effect.

Slight difference in pressure though. A top fuel blower takes more power to drive the thing, than a standard 426 hemi makes.

[Grumph]

Yeah I have and I'm not trying to knock the guy - I'm in awe of his talents, and I would love to see it running.

I just had a look at 0.1mm on my caliper (about the thickness of standard bond paper) and given the amount of metal in the rotors I'm guessing ("guessing", you will note) that they will expand more than the housing. Will be delighted to be proven wrong.

Rotor expansion is a big problem in top fuel blowers, they inject fuel before the rotors (as well as after) for the cooling effect.

I tend to agree...as i've said earlier on here we finished up with .50mm clearance on rotors aprox 150mm long. The rotors are always hotter than the case as there's no good heat path away.
The classic sequence is run it, seize it, enlarge clearances, repeat sequence until it doesn't seize....
By the end of our sequence we had lost 2 psi but the bastard never seized again.

There's always water injection....or just get the rider to piss in the intake if you don't want the weight of a tank.

[F5 Dave]

Rider is a skinny bstd so better hope for short races, or maybe a camel back

[pete376403]

I tend to agree...as i've said earlier on here we finished up with .50mm clearance on rotors aprox 150mm long. The rotors are always hotter than the case as there's no good heat path away.
The classic sequence is run it, seize it, enlarge clearances, repeat sequence until it doesn't seize....
By the end of our sequence we had lost 2 psi but the bastard never seized again.

There's always water injection....or just get the rider to piss in the intake if you don't want the weight of a tank.

Nah, water would already be 98 degrees F.

[TZ350]

Nah, water would already be 98 degrees F.

Nah, that’s ok as it’s the latent heat of evaporation that will do the cooling, stinky but.

[DEATH_INC.]

You really want to have that injector spraying down before the valves. That way when it is picked up in the air stream it gets diverted onto the valves.

You also might want to to some spray pattern testing. Just apply fuel pressure and hook the injector up to 12V.

Coirrect me if I'm wrong, but don't you mean 3v? (or was it 5) 12v will fry the injector quick smart if applied for long.
Apparently you move the injector position relevant to the rpm you wanna use. I'm thinking for this sort of application it'll be just fine where he has it, there'll be masses of turbulence to mix it up.
As for the charging system, or lack of it, put one on, you'll need a high pressure fuel pump, they suck a bit of power. Or at least you'll need a decent size battery to keep the charge up.

[Moooools]

Coirrect me if I'm wrong, but don't you mean 3v? (or was it 5) 12v will fry the injector quick smart if applied for long.
Apparently you move the injector position relevant to the rpm you wanna use. I'm thinking for this sort of application it'll be just fine where he has it, there'll be masses of turbulence to mix it up.
As for the charging system, or lack of it, put one on, you'll need a high pressure fuel pump, they suck a bit of power. Or at least you'll need a decent size battery to keep the charge up.

You might be right there. Probably 5V. From memory we just used 12V and you only need it on for half a second. Or maybe there was a resistor in series. Can't remember.

[bogan]

And instead of reving it right out, short shifting and driving it on the torque curve was the go.

This reminds me of an interesting discussion I was having. On the RC-31s (aka Hawk Gt, aka Bros650) the crank is pretty weak, and is prone to flying apart up near 100hp @10krpm. Now I've heard most of the crank stresses are from the centrifugal forces as it spins. So what I was wondering, if it is blown, and only revved to say 6krpm, will it be able to make more power with less chance of shredding cranks? Or will the extra power required for the blower make it snap earlier?

[Drew]

This reminds me of an interesting discussion I was having. On the RC-31s (aka Hawk Gt, aka Bros650) the crank is pretty weak, and is prone to flying apart up near 100hp @10krpm. Now I've heard most of the crank stresses are from the centrifugal forces as it spins. So what I was wondering, if it is blown, and only revved to say 6krpm, will it be able to make more power with less chance of shredding cranks? Or will the extra power required for the blower make it snap earlier?

Have you managed to define "centrifugal force"? I ask because no one else has.

The enertia is what makes the crank fly to pieces, closest thing to what people think of as centrifugal force, is good old fashioned momentum.

Now that the real basic physics lesson ois over, lets consider the problem. If the motor is blown and does achieve the same output at lower revs, the forces on the crank/bearings/casingings is, exactly the same as wht you started with.

That is all.

[k14]

Have you managed to define "centrifugal force"? I ask because no one else has.

The enertia is what makes the crank fly to pieces, closest thing to what people think of as centrifugal force, is good old fashioned momentum.

Now that the real basic physics lesson ois over, lets consider the problem. If the motor is blown and does achieve the same output at lower revs, the forces on the crank/bearings/casingings is, exactly the same as wht you started with.

That is all.

Well if you deem a real basic physics lesson as complete bs then you have given just that...

Inertia is not a force, it is a constant. Analogous to mass in linear mechanics. Bogan is on the right track, centrifugal force is the correct way of describing what would tear a crank apart if the metal is not strong enough to withstand it. Centrifugal force increases as the speed of the rotating mass increases and thus at a certain speed things fly apart. Once you have assembled the engine the inertia doesn't change (well apart from when it flys to bits!).

[Drew]

Well if you deem a real basic physics lesson as complete bs then you have given just that...

Inertia is not a force, it is a constant. Analogous to mass in linear mechanics. Bogan is on the right track, centrifugal force is the correct way of describing what would tear a crank apart if the metal is not strong enough to withstand it. Centrifugal force increases as the speed of the rotating mass increases and thus at a certain speed things fly apart. Once you have assembled the engine the inertia doesn't change (well apart from when it flys to bits!).

OK, my bad.

Provided you think that matter is being thrown off the crank due to it's rotation, then he's right. I've never seen that happen though, usually the bearings just fail and shit snaps. That's just caused by friction.

[DEATH_INC.]

OK, my bad.

Provided you think that matter is being thrown off the crank due to it's rotation, then he's right. I've never seen that happen though, usually the bearings just fail and shit snaps. That's just caused by friction.

Nope, I'm pretty sure you were thinking the right thing to start, cranks usually break due to the force it takes to stop the piston and rod and pull em back down again at high speeds. Not the centrifugal force coming from the crank itself...but kinetic energy or ½ mv² if I remember right...
Occasionally you may see one break from too much twisting force, or harmonic vibration or a couple of other things too...