what is detonation?

Is it from rich or lean fuel ratio?

 

It's not inherently from one or the other though a lean condition can result in detonation.

Detonation is basically when the fuel air mixture is injected through the intake valve into the cylinder and then ignites EARLY during the piston's compression stroke, BEFORE the spark plug actually fires at the beginning of the power stroke.

This is caused by the fuel-air mixture reaching its flashpoint before the plug can fire it as a result of A) cylinder pressure and B) heat.

In short, when a gas engine detonates, it's functioning on exactly the same principle as a diesel engine which PURPOSELY uses compression to ignite a fuel/air mixture rather than a spark plug.

As a gasoline engine is not designed for compression ignition, detonation (also called knock, pre-ignition, dieseling, etc) can be devastating to engine components.

When detonation occurs in a cylinder, the explosion puts a DOWNWARD pressure on the piston while the other pistons are still driving it UP via the crankshaft. You can obviously see how this causes a problem when it happens several times in rapid succession.

Lean conditions can contribute to detonation because a leaner mixture burns hotter.

 

Thank you very much for your reply

lets say your engine with procharger - 4psi and you put 83lbs injectors but you couldn't adjust the Air\Fuel ratio Perfectly do you think with time it will damage the engine?

This morning i sent my ZO6 to the workshop to change the injectors to 65lbs and i think it is good for this level? after that i will re-tune it.

 

Maybe maybe not. It's hard to say from the other side of the world. I would make sure the air-fuel and timing curves are right before driving it.

Randy

 

Perfect!

Well, I don't i understand what you mean. With 83lbs. injectors, you are not able to adjust your AFR? What you have to look into with injectors, without getting technical, is your duty-cycle. But your AFR is is adjusted by your PE table. If your running out of fuel because your out of injector, is one thing, but your PE is what is used to get your AFR inline.

What AFR is the car running at right now? Timing?

 

I would think 65 lb injectors would be ok for that boost level. I run 9 psi on 60 #ers although you do have a little more displacement.

The size of the injector is NOT the only factor though.

Having enough injector simply guarantees that the physical parts of the fuel system CAN supply the required amount of fuel to keep you from going lean. HOWEVER, if the PCM is not tuned correctly to tell them exactly how much fuel to supply, they're not going to do their job correctly.

Running rich isn't great either....it's (for the most part) safer than running lean (until you get REALLLLY rich) but a severe rich condition is going to spit and pop, may foul spark plugs and oxygen sensors, will obviously hinder gas mileage and can actually wash oil off cylinder walls.

Just make sure your car is tuned by someone who KNOWS supercharged LSx engines. If you do that, I think you'll be fine at that boost level.

 

it is between 11 to 12.5 like that all the time my friend who tunned the car told me that i can't adjust the AFR coz of the injectors are too big for this level you have to buy the 65lbs injectors to adjust the AFR.
I bought it alread and i sent my car to him but i wonder why he couldn't adjust the 83lbs injectors in my ls7 engine? do you think there is a solution for the 83lbs or i have to throw it?

 

This is a good read.
http://www.streetrodstuff.com/Articl...ne/Detonation/

 

it is hunting between 6 to 12.5

 

Nope, that is pre-ignition, and it is often confused with detonation. Detonation is when part of the mixture burns "outside' the normal flame front, and it is indeed bad, but it is caused/initiated BY the firing of the plug. Pre-ignition is the burning of the mixture BEFORE the plug fires.

Read Jason's link posted above - very good.

 

You have just described preignition.

 

Not quite.

 

the AFR gauge (above)

 

If you guys want to really get nit-picky, detonation also occurs when nothing is wrong - how else would the engine run to begin with?

I have to go with the fact that "detonation" is a slang term for "pre-detonation" just like pre-ignition. And for the record, I did a little googling and found plenty of definitions that lump "detonation" in with pre-ignition.

I'll bet that plenty of folks who want to get picky about the definition call engines "motors" - one of my real pet peeves.

 

I don't know about tuning a supercharged engine. But, I am now dabling in tuning on two different cars. One an 07 Z06 the other a Mast Motorsports LS7, which uses a wideband to control the AFR.

I have quite a bit of experience with junk wideband sensors. Some of the sensors, like the Innovate LC-1 are total junk. I've had two of them in the two aforementioned cars and they are not reliable and work intermittently. Innovate will not acknowledge that these gauges are for neophyte car guys and thus (in my opinion) you are totally wasting your money on any wideband gauges that are not professional grade. That being said, I am currently using the "new" Innovate LM-2 models and am having good results with their reliability. Anyway, my recommendation is to get an LM-2, either single or dual channel just to verify your AFR. You might want to bump around on the HP Tuners website forum and/or buy a tuning book "Designing and Tuning High-Performance Fuel Injection Systems (Paperback)" by Greg Banish, it's the 2009 one, (the most up to date). This is just for your reference so you have some clue about what a tuning might be doing for you or to you. There are a lot of very well meaning nice people tuning cars out there, some of them on this forum, that frankly don't know as much as they might have you believe. I have experience with this. That's why I've given up on relying on "tuners" and I am self teaching myself. Anyway, that's just my 2 cents. I think you will be happy with learning about your monster under the hood.

 

I'll bet that plenty of folks who want to get picky about the definition call engines "motors" - one of my real pet peeves.

So which one is it engine or motor?

 

Sorry, this is not one of those times where there is no substantial difference between the two. One happens before and without the plug even firing. The other happens when the plug fires so technically it is correct as far as spark timing goes, but it happens outside the normal flame front, and sometimes with a slight delay. The two mechanisims (before plug firing vs. after plug firing) are not even close. Those of us pointing out the correct definition of the two terms are not being nit picky in the least - we are being accurate.

 

Apparently.....I did not know that....thanks.

 

That's a great article...one I will keep for reference.

Thanks,

Tom

 

There are so many good, easily accessed articles about this on the Internet that there is no reason not to get the proper understanding about it. Here is another good link;

http://www.enginebuildermag.com/Arti...eignition.aspx

....two good definitions from the article;

"Detonation
A good one-word definition of detonation is "autoignition." In other words, it is ignition caused by something other than the spark plug. (Unfortunately that’s true of pre-ignition as well.) That’s not to say that the spark hasn’t taken place, because one of the key points in the distinction between detonation and pre-ignition is that detonation occurs after the spark. Parts of the fuel charge ignite the mixture of fuel and air in the combustion chamber due to the pressure and temperature increases from the expanding flame front. This is important because pre-ignition takes place because of ignition before the spark even goes off.
Pre-ignition
Let’s switch gears now and talk pre-ignition. As we said earlier, one important characteristic is that pre-ignition takes place before the spark. As a result, the temperatures and pressures are much higher than they are in detonation. Another characteristic is the short durability of pre-ignition. It typically lasts only a few seconds and really tears things up in that short period. The reason is that, with the extreme temperatures everything in the combustion chamber feels it and can’t last very long. "