Under these conditions why would detonation STILL be occuring??

If you're detonating WITH an a/f of 12.5:1 AND your timing is appropriately retarded AND your gas is high-enough octane (93+), AND YOU'RE STILL EXPERIENCING DETONATION then WHATS causing the detonation?

Also, the engine does not misfire....

Could it be spark/coil related? Weak/inconsistant spark? Bad wires? Plug problems? WTF could it be if you've covered the primary and basic causes of detonation and it's still detonating??

I know you guys have thoughts and opinions on this...lets here em!



[Modified by greyzone, 7:05 AM 12/15/2001]

 

you never mentioned if the motor is getting enough fuel. Is it? Or are your injectors too small?

 

If the a/f is reading 12.5:1 wouldnt that indicate that fuel supply is good?? This is only at 7.5lbs boost, but a/f was 12.5:1 and still detonating...doesnt make sense to me.

 

good wuestion, i dont know either

 

about all I know on this one is I dont know...but at least I know what I dont know and thats knowing something

 

Are you running a catch-can? Maybe you've got oil going into the cylinders in addition to the air/fuel. It will significantly reduce your motor's resistance to detonation.

Sonny

 

Ok, let me see if I can make some sense of this.

Now let me cover some of the basics of a the otto cycle or how a 4 stroke engine works. You have a 4 strokes, intake stroke, comression, power, and exhaust stroke.

Now, Picture your piston at Top Dead Center TDC. As the piston goes down that is called the intake stroke and it inhales the air and fuel. The piston is at the very bottom of the cylinder now which is Bottom dead center BDC and there is fuel and air kinda in a seal container all in the cylinder and on top of the piston.

The second stroke is called the compression storke where the piston is moving upwards from BTC to TDC. At Bottom Dead Center (BDC) the cylinder is at its maximum volume and the intake valve is closed. Now the piston moves backward the Top Dead Center (TDC) and compresses the air/fuel mixtures. The pressure is increased and the volume is decreased. The necessary work for the compression increases the internal energy of the mixtures - the temperature is increased. Now this is where detononation comes into play. Because you have some heat or timing advanced too high that pre-ignites the mixture. So the mixture has "caught on fire" too soon before TDC which we call detonation.

Now, the mixture is now burned but where does it go? Keep that last statement in mind.
This leads us to the next and 3rd stroke the power stroke. this is the stroke after TDC and its moving in the down direction. The force drives the piston downward to crank shaft (the valves are closed). The volume is increased and the preasure is decreased. No more energy is added and because of this the internal energy of the gas is decreased as so as the temperature.

Now the 4th and final stroke, the exhust stroke. At BDC the exhaust valve is opend and the piston moves up the cylinder. Remember you I said where does this mixture go? It was in the cylinder the entire time. So even tho the mixture was burned at, before, and after TDC the air to fuel ratio wouldnt change.

A good air/fuel mixture will not always prevent detonation. You need to look at other things like ignition, plugs, and timing. Im sure you have looked at these things but there is something that is causing you to pre-igninte the mixture. It appears the fuel is there, but maybe heat of some sort is causing you to detonate. Im sorry this was soooo long, but its just something to look at.

Im out of breath.

 

I just read in an other post that you have block guard. I dont know, maybe something to look at. Im not telling you, its just mearly a suggestion. As you know I dont like them, but it seems to work for other people like yourself.

art

 

Damn Art, thats one of the best explanations Ive heard of concerning stroke sequnce. THis by the way is not my engine, it's JFKs...He was origionally asking me about this and I couldnt figure it out so I reposted it as a new question.

But your answer makes good sense (thanks for the thourough reply) and I'm thinking overheating could be the answer. I was wondering about ignition, spark and plugs etc, but didnt know if those would cause detonation, per se. HOWEVER, all the things I stated could be occuring WITH detonation IF the engine is running hot for any given number of different reasons...thats incredibly obvious and I never thought about that...perhaps it's to obvious so you'd think that couldnt be it.

Massage those fingers Art, they do great work around here


[Modified by greyzone, 9:59 AM 12/15/2001]

 

coolant temp, and air temperature will also cause detonation.

 

did you never consider that your block guard is maybe the cuz!!!

 

Are we talking about detonation or preignition?

 

Well isn't detonation the result of preignition? And if you do preignite the mixture, won't you get detonation?

 

preignion can cause detonation, however it is not the only cause of detonation.

 

Why do you say you are getting detonation, are you hearing pinging or knock? What rpms? when?

 

uhh, ya know what, this is not my car and I don kno the answers to these questions, Im gonna try and get JFK to respond to this as its his car and converstaions I was having with him...I couldnt figure it out so I posted it as a new question...

this is a bit more complicated than I thought...can anyone post info on the "basics of detonation / pre-ignition" that covers this issue??

Thanks for the replies...this board rules



[Modified by greyzone, 9:06 PM 12/15/2001]

 

I kinda was taking about both even though I used preignition when I should have use detonation in the post above. Sorry, it was late.
Anyhow, they both are different but related to each other. But there is a difference. Look here: Article on detination and preingnition.
The article is somewhat old, but it would still apply to internal combustion.

art

 

Hey, JFK here. Yes this is my car we are talking about. I'll try to explain this thoroughly.

Stock D16Z6
Greddy Turbo TD04-15G
Blue Box
'91 Eclipse intercooler
Stock ignition
MSD wires
NGK BCPR7ES-11's gapped .30
Ignition timing at 5 degrees retarded
92 octane Texaco with NOS octane boost
Walbro 255lph
B&M commandflo
FP set at 42 psi
Redline water wetter
Heat wrapped downpipe
Straight pipe
Greddy EVO exhaust
Valve cover breather filter
Mobile 1 5w-30 full synthetic

My car was set up like this at the track and on the dyno. At 7.5 psi I get loud pinging, sounds like a marble fight under the hood starting at 4500-5000 rpm. My a/f ratio is 12.5:1 at WOT on the wideband, so my fuel should be good. Most people with this kit run only 1-2 degrees retard at 8 psi on pump gas, I was running higher than normal octane and 5 degrees of retard which should've been more than enough. My ignition system is in good condition and works fine, I've never had it misfire or anything like that. My coolant temp gauge never reads high.

At the track it was pinging loudly, but I was pissed so I did 8 runs like that but it never blew. I felt no surging or anything like that while it made the noises. It seemed to pull fine. My EGT probe is mounted like 2" down on the downpipe. It usually reads 1100-1200 F, 1250 max at WOT. I did a compression test afterwards, and all cylinders were 185-195 psi so it doesn't appear any damage was done.

Air temp doesn't seem to matter 40-85 degrees it still does it. It was 60 degrees when on the dyno with hood open and fans on the intercooler. It started pinging at 6400 rpm on the dyno. There was a 15 min rest between runs. All runs were done in 4th gear which took 18.7 seconds of WOT. There was a lot of oil vapor pouring out of the valve cover filter above 5000 rpm. We tried running a hose from there to the intake pipe pre-turbo, it made no diff. Exhaust smoke was light grey above 5000 rpm, there didn't appear to be any blueish tint to it. Engine has 60,000 miles on it.

Does this sound like preignition or detonation? I gave up on it and just ran 5.5 psi for a month, but that got old fast.

Well, I recently upped the FP to 62 psi and on 92 octane and 2 degrees of retard, it runs fine at 7.5 psi of boost now! But that means my a/f ratio must be overly rich now. Why is it that with a perfect 12.5:1 a/f ratio, lots of octane, and lots of retard it pings, but with less octane, less retard, and an a/f ratio richer than 12.5:1 it doesn't? I'm confused.

Many people with this setup say they run 8-10 psi with 1-2 degrees retard on pump gas with no problems. My bro runs 9 psi with 2 degrees retard no problem. His car dumps a ton of dark grey smoke at WOT. But he and most of the others are using a vortec BDFPR instead of the blue box. I'm sure they are all running really rich and they don't detonate. Is it necessary to be overly rich to cool the cylinders down so that preignition doesn't occur?

 

I don't know much about this, but I know increasing the fuel going into the cylinder will help to cool things down. Could it be that a few seconds after going WOT the cylinder temps were rising enought that your timing retard, and higher octane were not enough to prevent preignition?

Now, with the increased amount of fuel, your cylinders are recieving the cooling they need?

This would kinda explain why the pinging doesn't start until you get higher in your rpm range....it takes time for the cylinders to heat up.

Isn't it with DSM's that they run a really rich a/f ratio to help cool the cylinders, and they have a knock system that retards timing ALOT once detonation is detected?


[Modified by HXMan, 6:59 PM 12/15/2001]

 

JFK,

I thinking the stock ignition may play a part of this....you dont have the quality or intensity of spark there to adequately do the job under higher levels of boost, so it's not about a/f quality, but the quiality of your spark. Then, when you get it overly rich, theres enough spark to burn an excessive amount of gas.

Just a thought, but Im only guessing on this one. I thought you had a full ignition w/coil.


[Modified by greyzone, 3:55 AM 12/16/2001]

 

Art
that was worthy of websters.
im calling them tommrow
gonna get that added to detonation.

 

i'm not sure but, it could be that your timming belt is stretched. my car back fires, so is that like detonation too.

 

Now Ive heard it all...

 

does that mean it gets better from here?

Tom

 

hehehe, never a dull moment