does a crack on exhaust manifold cause boost leak

[deviousgst]

so last night i raced and my intercooler coupler ripped and didnt let me boost how i usually do...i replaced it and still boost less than i do...but i have an exhaust leak(jst happend same night i think)on the exhaust manifold where the gasket between exhaust manifold and turbo go...can this cause my car not to boost ### it usually does...
thanks

 

[TSiAWD666]

that's not a boost leak, but yes it can limit your turbo from receiving energy from the exhaust.

 

[Backinajiffy12]

O YEAH like huge. esspacally because its pre turbo just replace the gaskets and check the couplers again

 

[deviousgst]

that's not a boost leak, but yes it can limit your turbo from receiving energy from the exhaust.

koo..thanks...
### kind of gaskets would work best

 

[vanilla gorilla]

stock gasket works best

 

[JusMX141]

that's not a boost leak, but yes it can limit your turbo from receiving energy from the exhaust.

Any airflow leak between where the turbocharger MAKES air (compressor) and where the airflow is channeled into the turbine housing (this INCLUDES CRACKED MANIFOLDS) would be a boost leak.

If 18psi is entering the engine, then 18psi will be leaving the engine as well....that is, until it runs into a leak at the exhaust manifold.

This is the same concept that manifold-mounted external wastegates use....the only difference is external gates do not cause a leak until the turbo has reached a certain boost level. In the O.P.'s case, his "external wastegate" is always slightly open.

 

[TURBOGSX]

use permatex copper spray a gasket on the new gasket awesome stuff

 

[Whophlungpoo]

use permatex copper spray a gasket on the new gasket awesome stuff

Yeah, my exhaust would just push the OEM gasket out, so I tried that copper spray a gasket and I haven't had any problems yet.

 

[ScottH]

that's not a boost leak, but yes it can limit your turbo from receiving energy from the exhaust.

+ 1 , Couldn't have worded it any better then that.

 

[TSiAWD666]

Any airflow leak between where the turbocharger MAKES air (compressor) and where the airflow is channeled into the turbine housing (this INCLUDES CRACKED MANIFOLDS) would be a boost leak.

If 18psi is entering the engine, then 18psi will be leaving the engine as well....that is, until it runs into a leak at the exhaust manifold.

This is the same concept that manifold-mounted external wastegates use....the only difference is external gates do not cause a leak until the turbo has reached a certain boost level. In the O.P.'s case, his "external wastegate" is always slightly open.

Eh arguably the exhaust gases are pressurized, but what relevance does that have? The majority of the energy scavenged by the turbine is from the heat energy leftover from combustion. Regardless of whether you want to argue that is "boost", I'd say you might be one of a handful of people that would use the term to refer to anything other than post-compressor/pre-engine pressurized intake gases. The term is used in relation to the pressurized intake tract and that's pretty much it.

 

[clockworktoy]

Eh arguably the exhaust gases are pressurized, but what relevance does that have?

Then Why do you explain using a gasket and preventing exhaust leaks pre turbo? A big exhaust leak between the exhaust manifold and the head will definitely have an affect on your spool time.

 

[jrohner]

On my car, an exhaust manifold leak makes a lot more of an impact on performance than a boost leak.

Make sure and have your exhaust manifold planed by a machine shop or at least put it on a belt sander so it's smooth and straight. The manifold may be warped, which would cause a bad leak.

 

[webconnect]

OK QUESTION: I am assuming yes, it will cause the turbo to spool slower, however, will it effect the a/f ratios and maf like an actual BOOST LEAK would. I am guessing not.

 

[TSiAWD666]

Then Why do you explain using a gasket and preventing exhaust leaks pre turbo? A big exhaust leak between the exhaust manifold and the head will definitely have an affect on your spool time.

If you paid attention to the little side discussion we were talking about the term "boost". Not the effects of exhaust leaks. It's quite obvious to all in the thread with some experience the effects of a pre-turbo exhaust leak, which you've reiterated again.

 

[gofer]

stock gasket and copper gasket spray from autozone whatever you do don't buy the metal gasket, stronger isn't always better... the metal gasket expands from the heat and will cut into your manifold to turbo bolts everytime.

Any airflow leak between where the turbocharger MAKES air (compressor) and where the airflow is channeled into the turbine housing (this INCLUDES CRACKED MANIFOLDS) would be a boost leak.

If 18psi is entering the engine, then 18psi will be leaving the engine as well....that is, until it runs into a leak at the exhaust manifold.

This is the same concept that manifold-mounted external wastegates use....the only difference is external gates do not cause a leak until the turbo has reached a certain boost level. In the O.P.'s case, his "external wastegate" is always slightly open.

not to get into an arguement about what a boost leak vise an exhaust leak is but hear me out...

the turbo creates "boost" from the exhaust gases coming across the turbine side of the turbo which in turn spins the compressor wheel creating boost into the cold side. you can only leak boost from the cold side of the turbo, anything leaking from the exhaust manifold // turbine (hot side) // wastegate // o2 housing is not a boost leak, its definitely an exhaust leak.

your 18psi in then theres 18psi out theory is definitely
the external wastegate causes a controlled "exhaust leak" pre turbo to control the amount of exhaust gases coming across the turbine. it doesn't use 18psi IN to 18psi OUT though... the vacuum line that runs from the wastegate to the cold side of the turbo is how the wastegate sees how many psi your running through the system and when it sees 18psi on the BOOSTED side it opens the EXHAUST side to control boost and hold it to that amount (18psi)

hope i didn't lose anyone and i think that needed to be cleared up

 

[webconnect]

+1 amen thread closed

 

[JusMX141]

the vacuum line that runs from the wastegate to the cold side of the turbo is how the wastegate sees how many psi your running through the system and when it sees 18psi on the BOOSTED side it opens the EXHAUST side to control boost and hold it to that amount (18psi)

The reason the boost is regulated on the cold side (BOOSTED) is because it would take too long to respond to any change on the hot side (EXHAUST). By the time you saw 18psi at the exhaust manifold the turbo could be producing 25+. The exhaust side is also inconsistent as different engines with different port sizes will flow different amounts of air, thereby effecting airflow velocity as well as pressure.

But I'm curious....if you're pushing 18psi into an engine, how much pressure is seen at the exhaust manifold after the combustion chamber but BEFORE the wastegate and turbine housing? Perhaps you could enlighten me on this.

 

[Turb07]

Yes it will cause a loss in PSI because the exhaust gas is not turning the turbine wheel and shaft (which is connected to the Compressor wheel) and not allowing the compressor wheel to do its job and compress the air.

And it will affect the Air fuel ration because if you have enough fuel to run 18 PSI and only actually running 15 PSI then it will run rich.

Just my $.02

Turbo

 

[webconnect]

I know I probably have an exhaust leak. I still hit my full boost of 8 lbs (wastegate pressure). So full, boost, plus leaking = Should my a/f ratio be messed up? Fuel+control is stock. - No it shouldn't. same thing as a wastegate!