Boost leak and knock

[gorf]

I have been doing a lot of reading here and the general opinion is that, boost leak can cause knock. I know that I have a boost leak and think it is from the o-ring on my td05 housing. I can still hit 20 lbs with my 14b.

My question is why would this cause knock? Logically, if your maf is reading a certain amount of air and adjusting your injectors to supply more fuel, but not all of that air is getting to your intake manifold - then you should be running rich. It is my understanding that running lean cause the knock.

If I replace that O-ring, will my knock lessen?

 

[The_EE]

Too much fuel can cause knock just as too little can. Boost leak would mean, more fuel being added then air in the system causing a rich condition.

 

[nube90]

Yes running lean causes the knock or detonation to hot combustion temps, your running stock injectors right? If you are thats your problem the stock 450's cannot supply enough fuel for 20 psi. Any black smoke?

 

[gorf]

Yes running lean causes the knock or detonation to hot combustion temps, your running stock injectors right? If you are thats your problem the stock 450's cannot supply enough fuel. Any black smoke?

Currently running 450's. A LOT of threads indicate that with a 14b 450's are enough, especially with a rewired walbro 190.

I have a set of EVO 560's, just have not installed them yet. I know that I have to resolve the boost leak, and was planning on doing that first to see if it helped the knock. Then I was going to install the 560's.

 

[Quasimondo]

Even though the boost leak will fool the ECU into running on the rich side of things, the overworked turbo ends up operating well below it's efficiency range. Inefficient turbos create lots of heat, which is probably beyond what your intercooler (if it's still stock) is capable of taking care of, and that ends up heat soaked pretty quickly. Even at 20 psi with no leaks, that intercooler will heat soak quickly. You should consider turning the boost back down to 11-12 psi until you figure out the boost leak problem, as well as the knock situation.

Running lean is just one factor in causing knock. High intake temperatures is another factor that you haven't taken into account.

Which o-ring are you talking about, btw? If you mean the one that goes on the compressor inlet, that isn't the source of your boost leak. Your leak is somewhere between the compressor outlet and the cylinder head, to include the fuel injector O-rings, throttle body shaft seals, gaskets for the compressor outlet and BOV, all of the piping in between, and even the intercooler itself if something damages it badly enough.

 

[gorf]

Which o-ring are you talking about, btw? If you mean the one that goes on the compressor inlet, that isn't the source of your boost leak. Your leak is somewhere between the compressor outlet and the cylinder head, to include the fuel injector O-rings, throttle body shaft seals, gaskets for the compressor outlet and BOV, all of the piping in between, and even the intercooler itself if something damages it badly enough.

The housing O-ring. When I do a boost leak test, it leaks down very quickly and it sounds like it is coming form the backside of the turbo. See this thread
http://www.dsmtuners.com/forums/showthread.php?t=208072&highlight=boost+leak+turbo

I have not checked it yet but I am pretty sure this is where my leak is also.

 

[daren_p]

Even though the boost leak will fool the ECU into running on the rich side of things, the overworked turbo ends up operating well below it's efficiency range. Inefficient turbos create lots of heat, which is probably beyond what your intercooler (if it's still stock) is capable of taking care of, and that ends up heat soaked pretty quickly. Even at 20 psi with no leaks, that intercooler will heat soak quickly. You should consider turning the boost back down to 11-12 psi until you figure out the boost leak problem, as well as the knock situation.

Running lean is just one factor in causing knock. High intake temperatures is another factor that you haven't taken into account.

Exactly what I was going to say Defently turn the boost down until you can figure out your knock situation.

 

[Quasimondo]

If you're leaking from there, then that's definitely a problem. Fix that before you do anything else.