My engine deto'd and grenaded...wtFFFF!?!?!

[skithis]

I built a 61x this year that was ported and piped. I was running a Riva ignition enhancor until last week when it failed. I swapped it out to a 6m6 CDI and it ran great. After the porting with the westcoast head i was only making 150psi. So I assumed since I was running OEM ignition and close to OEM compression I would be good on 87 octane. Guess I was wrong. It detonated itself to death! Does porting change detonation characteristics on stock compression and ignition???

 

[Matt_E]

Porting can lower cranking compression, leading you to believe you were "only making 150psi". Your running compression may have been higher.

 

[SurferSmurf]

how can you tell what cranking psi is and running psi?

 

[5810]

x2

 

[Matt_E]

A better way to go about determining octane requirements is to figure the mechanical compression ratio. It's calculated uncompressed volume/compressed volume.

Also, the engine's squish bands may have been too narrow or the ignition advanced too much.

 

[SUPERTUNE]

A better way to go about determining octane requirements is to figure the mechanical compression ratio. It's calculated uncompressed volume/compressed volume.

Also, the engine's squish bands may have been too narrow or the ignition advanced too much.

Yes, you always should use a fill volume method using the displacement cc of one cylinder to calculate compression ratio's on ported engines.
More than likely too wide of a squish band not necessarily too narrow as a narrower squish band willl lower MSV, a wider squish band will have more MSV. With too high MSV number against the other factors of fuel and timing does cause this to happen very quickly.
Ignition timing also plays a role big role in controlling detonation.

 

[SurferSmurf]

Yes, you always should use a fill volume method using the displacement cc of one cylinder to calculate compression ratio's on ported engines.
More than likely too wide of a squish band not necessarily too narrow as a narrower squish band willl lower MSV, a wider squish band will have more MSV. With too high MSV number against the other factors of fuel and timing does cause this to happen very quickly.
Ignition timing also plays a role big role in controlling detonation.

and this is why you are the man. every time you explain things i end up scratching my head and saying WTF does that mean and how the heck did you learn all this. im a very mechanically inclined person and i understand alot about motors but just when i think i get it you post up more info that causes my brain to melt down.

 

[ATS_Aaron]

MSV - Maximum Squish Velocity rates the maximum velocity of the fuel air traveling across the squishband just before the piston reaches TDC. If MSV is to low the flame front will not burn the fuel air mixture effectively. If MSV is to high, detonation will occur and cause engine damage. The TSR programs calculate MSV for various types of heads.

 

[ATS_Aaron]

I googled that. I'm not that smart.

 

[SurferSmurf]

I googled that. I'm not that smart.

good cuz i was thinkin that im pretty dumb after reading it.

 

[SUPERTUNE]

Years ago when trying to learn all I can... I bought most of the TSR computer programs and applied them to the engines I was building and testing at the time and did learn a few things on how to keep a full blown XIR Kawasaki stroker w/MRD injection together in pro mod 785 runabout.
Sorry for not explaining about what MSV was! I wasn't :thinking:
P.S Not all of these trick programs are god for the engine builder, you still have to learn how to apply what works and what doesn't for your setups.

 

[jMike]

So how would these settings change when a cylinder is ported? by allowing more air/fuel mixture into the combustion chamber? If a guy was running stock heads or at least an aftermarket built to the specific specs for the piston shapes to my brains the MSV and squish band should stay the same?

Also I found this and I helped me visualize what these mechanical marvels are talking about http://www.muller.net/mullermachine/docs/squish1.html

 

[kevbo]

Stock Superjet ignitions have no high rpm timing retard. Setting up a proper squish will require you to back off the timing and that kills throttle response. Stock ignitions require thick and/or narrow squish with more spark lead for good freeride performance. A programable ignition provides the best throttle response and lowest octane requirement. Stock Kawasakis have had nice retard curves and high rev limits since 94, Yamaha never improved their standup ignitions. To answer your question, you found your engines minimum octane limit. Either buy better gas or lower the engines requirement. Opening the top screw on the carb will probably do it.

 

[skithis]

Well to answer everybody's Q's Ill be running 93 ONLY after this little mistake. Also, My timing plate is set to stock or less than 1' advanced. At the time I threw 87 in it and ran it but now that I look back on it, it was pretty ignorant. Thanks for the info supertune, I learn something every day.