CR500 timing curve comparisons

[Tommy_J]

Gen 3 AF with 92 motor and 96 250 ignition. I'm currently running about 5 degree advance. No detonation and starts first kick. I plan to keep playing around looking for more top end.

[thestuz]

guys, call me stupid but ive had not much experience with ignition curves but i always thought the advance was ment to raise as the rpm got higher right?

so why does the timing advance drop as the rpms increase?everything after 3000rpm is down hill?

skip the sarcasim please.

[britincali]

No its the other way around, big advance off idle and then drops off to stop pinging.



My truck goes from 15degrees to 50 degrees then gradually drops to 13 at WOT.

[Cholo]

In 2 strokes there´s more advance at low rpm because the cylinder is "empty" of gases and we need to produce spark sooner to attain correct combustion. At higher rpm the effect of resonance in the exhaust system load the cylinder, the pressure in the cylinder is higher and we don´t need much advance to attain correct combustion. If the advance at higher rpm is too much, it could provocate detonation. Excuse me for my english

[stu460]

If the timing drops off at 24 degrees / 4500 rpm on the 01 does this mean the engines losing potential power thru to say 6500??

or does an ignition curve have to drop off well before max rpm to allow it to open up and rev,,,,i just noticed how all the curvs drop off rather rapidly,i would have thought it would have kept its max degrees till the end of its rev range but obviously not???

I just read the previous post by cholo i think that sums up what im asking,i guess ill throw out anything i know about 4t timing..

[rsss396]

More timing is needed when combustion rates are low.

The 2 biggest factors for slow combustion at low rpms is:
-Low squish velocities
-Residual spent gasses left in the combustion chamber.

Some left over gasses from the last combustion stroke are not completely pushed out the exhaust port and now are mixed with the fresh incoming fuel/air mixture.
These spent gases do not burn and slow down the combustion speed.

The squish velocities are also lower at lower rpms and this creates less turbulence slowing combustion rates
The squish band widths and clearances in the head is what dictates the speed of the velocities.
A high rpm motor will have a narrower squish band and/or wider squish gap to keep the squish velocities from getting to high and creating detonation. but this design means slow squish velocities until the upper rpms.
Wide squish bands and/or tight squish gaps increase squish velocities sooner but the max rpm must be lower or detonation will occur.

Then once the motor is "on the pipe" and exhaust gases are removed more efficiently and squish velocities increase causing combustion rates to increase, advanced timing is no longer needed to effectively burn all the fuel before the exhaust port opens.

[maddog1927]

Cool graphs.

I would love to see one for the 93-96 CR250 ignition

[dubious01]

bump.
I found a dyna ignition cdi for 2001 cr125, with 4 maps switch for $80.
Gonna give that a go.

[OUTKAST INC.]

do you know if 91 and later cr500s are all the same curve i have 91 ,95,98 boxes just wondering if they are all same curve thanks

[dubious01]

not sure of pre 93 changes, except the 85,86, 87 changes.
93-01 are the same.

so in essence I personally can not confirm 88-92 changes, 93-01 are same

[bowser]

did anyone happen to have a copy of these graphs? interested to see the vortex results

[blownbillybob]

I have a pic of them but not with the vortex system in the graph so not sure if it would help ya????

[bwalker]

Can anyone repost these curves?

[blownbillybob]

I forgot how to post pics ???

Hhahahaha!!!!

I can text them or ya!!!!