Timing advance

[Gerbutt]

Hiya

 

I’ve been pondering about timing advance and I understand what happens when you do it, it sparks a little earlier. What I don’t understand is why this is an advantage and how come it seems to give more power? I’ve seen vids where a 200/201 had been done and it looked quite a lot better, faster in the cut and holding rpm better. Why is this?

[openspaceman]

2 hours ago, Gerbutt said:

 

Hiya

 

I’ve been pondering about timing advance and I understand what happens when you do it, it sparks a little earlier. What I don’t understand is why this is an advantage and how come it seems to give more power? I’ve seen vids where a 200/201 had been done and it looked quite a lot better, faster in the cut and holding rpm better. Why is this?

 

Basically it's because the flame takes a finite amount of time to propagate through the mixture  and burn it. As  the power stroke takes such a short time and for efficient conversion of heat to propulsion you need the pressure to develop before the piston has moved down very far. It becomes worth  expending a bit of the motion of the piston's energy  to overcome the increased pressure as it approaches TDC in order to expand from the highest pressure on the power stroke.

[Gerbutt]

Hiya spaceman, yes that makes sense, thank you for explaining [emoji106] I may have a dabble at doing it on my 390xp. I hear folk saying 1/3 of the key. I wouldn’t want to go to far so I may do a 1/4 and see what happens first!

[Gerbutt]

Well I’ve just done it and it does seem more responsive [emoji106]

[openspaceman]

20 minutes ago, Gerbutt said:

Well I’ve just done it and it does seem more responsive

That was quick Gunga Din. Don't confuse  my explanation of the theory with any sort of expertise in modifying engines. I've done it in my youth in a crude way but am too ham fisted to be much good at it.

[Gerbutt]

Yeah it’s easy enough with diamond files, and I just did it a little bit. It does feel more nippy, and I’m sure it started a tad better too [emoji106]

[spudulike]

You did that on a 390XP

[Gerbutt]

You did that on a 390XP:scared1:
[emoji6]

Oh no, it’s that a bad thing?

[spudulike]

No, just pulling your leg

[Gerbutt]

Tee hee thank goodness [emoji28] Whilst you’re here sir, should the max rpm be around 13,000?