Lifan 150 running higher compression

[darren89]

sorry to be a pest guys.
but i just wanted to double check to make sure my head was thinking properly at the moment.
My lifan 150 is going to have alot more compression soon, when i get the parts and fit them, afterwards i would retard timing (the pick up or wateva its called when adjust the stator plate on that backing plate)? correct? not advance it ay? (it has the daytona style outter rotor kit with the adjustable plates)

sorry to be a pest,
cheers,
Darren

 

[thump*140]

yes mate, i'm pretty sure you would need to retard the ignition timing.
Cactus Jack should be able to confirm this, he understands the concept of compression Vs timing far better than i do.

 

[Cactus Jack]

Yes , you'd back the advance off to suit the faster burn rate of the higher compression charge if you're using standard unleaded ... IF you run high octane race fuel which has a slower burn rate , you can run more advance ...

 

[darren89]

thanks for your help, greatly appreciated!
i always run high octane fuel (from servos not a race fuel) in my bikes, so it will be alright to run it more advanced? or is that only if i was to use a special high octane race fuel mixture?

 

[Cactus Jack]

One way to find out is try it ... but IF your engine starts kicking back when you try to start it ... then your question will be answered ... You can actually LOSE power by running higher octane fuel in an engine built to run on lower octane ... but it will have a bigger safety margin against abnormal engine temperatures ... IF you run too much compression or ignition advance to suit the fuel , you'll damage the engine very quickly ... Basically ... you build an engine with a compression ratio to suit the fuel you're going to be using ... THEN time the ignition to suit the combo using the LEAST amount of advance that's required to make the best power ... The cam specs also play a big role in how much static compression you can safely get away with using a given fuel ...

I had this info ready to post the other night but saved it ... so here it is ...

[The best way to find out what ignition advance curve works best in any engine and the max advance you can safely run would be to dyno test the engine at various revs ...

You can also do standing start stop watch testing over a measured distance and use the least amount of advance that gives the quickest time ... Be VERY wary of detonation ... Make sure your engine is as hot as it can get when setting the ignition advance ... otherwise it'll detonate if it gets any hotter ...

It's best to initially back the timing off until there's zero kick back on start up ... then gradually bump it up during testing ... but ONLY if your elapsed times are improving ... A bit less is far better than a bit too much ... Get it wrong and you'll be repairing things ... Watch that engine temp ... Don't punch the static advance up to give the hardest bottom end hit if you are going to go revving the motor up high where it could start fighting against itself (that's where all the damage occurs) ... You really need a programmable digital ignition which allows you to alter the initial advance without increasing the top end advance ...]

Here's a link to a thread on ignition advance vs compression in a car forum ... car engine , bike engine ... they're all 4 strokes and react similarly to the same factors ... It's VERY hard to find info on bike forums since most bikers 'aint got a clue on such subjects ... Anyway ... read up on what they're saying ... then apply the info to your own application to work out what you can or can't get away with safely ...

Ignition Timing Vs. Compression Ratio - LS1TECH