What is the sound on 5% throttle?

[LeeW]

I noticed this so much more when I fitted the louder exhaust, and I can't seem to find any answers on search:

When you apply a tiny amount of throttle you get this little grumble sound. You usually hear it briefly everytime you give the car gas or again briefly when you come off the gas. If you're really gentle you can hold the throttle at the exact position (around 5% as a loose number) and it will grumble constantly.

Please explain to me what is happening in the PCM/engine and why. I'm constantly thirsty for knowledge.

Thanks in advance guys, over you to...

[wiggles]

I get this as I'm pulling into the road from my "drive" going less than 5mph it just burbles along

[LeeW]

I get this as I'm pulling into the road from my "drive" going less than 5mph it just burbles along

If you try, being gentle you should be able to get it at any speed. I seem to be able to...


Im going to guess that its this area of the map/fuelling that people heavily modify and alter to get the mental pops and bangs. I could be wrong, but that's where my brain wandered to!

[PeteH]

A few suggestions:
1) The fuel and ignition maps are specified at certain engine revs and throttle openings. The pcm will try to "fill in the gaps" by interpolating between the map cells, but if you hold a set throttle and revs then the engine might find itself hunting between cells, and therefore sounding a bit rough.
2) The engine mounts will be designed to damp the engine vibrations when the engine is at idle. If the engine isn't at idle speed then there might be resonances that can be transmitted. You won't notice these resonances at higher speeds, but at low speeds you might.
3) With a fully shut throttle the intake is effectively sealed off from the engine (not quite, but nearly). But at small throttle openings you open the intake tract up to the chambers, and so you might hear the engine through the intake system.

Best I can think of at the moment.

Ps, Pops and bangs is all about deliberately over-fueling during lift off at high revs. I doubt they would touch the map at low revs.

[LeeW]

A few suggestions:
1) The fuel and ignition maps are specified at certain engine revs and throttle openings. The pcm will try to "fill in the gaps" by interpolating between the map cells, but if you hold a set throttle and revs then the engine might find itself hunting between cells, and therefore sounding a bit rough.
2) The engine mounts will be designed to damp the engine vibrations when the engine is at idle. If the engine isn't at idle speed then there might be resonances that can be transmitted. You won't notice these resonances at higher speeds, but at low speeds you might.
3) With a fully shut throttle the intake is effectively sealed off from the engine (not quite, but nearly). But at small throttle openings you open the intake tract up to the chambers, and so you might hear the engine through the intake system.

Best I can think of at the moment.

Ps, Pops and bangs is all about deliberately over-fueling during lift off at high revs. I doubt they would touch the map at low revs.

Think no.3 might be the closest to what Im hearing. It's like a flutter or burble. The car still feels like its coasting down on no throttle, so it's like theres an air path being opened up with no fuel. Makes sense... I know its not a problem or a fault, just curious to find out more about whats going on. Cheers!

[warpc0il]

On a standard map there is no fuelling on the overrun.

Some custom maps change this, anything from a touch of fuel to aid smooth pickup, to a significant slug to provide "pops'n'bangs".

BTW this is another reason why an "OMP delete" is a much more major undertaking on a Renesis, as no fuel would also mean no lubrication, if you were relying just on premix; unlike all previous rotary engines that still added fuel on the overrun.

[AndyBrad]

with the overrun maps (pops and bangs) why doesnt it cause borewash etc?

[warpc0il]

Who says it doesn't?