DanaT

Hi all,

I remember reading a while back that an exhaust leak between the head and turbo on a 951 can cause some serious HP losses.

Please school me, why would such serious losses occur? I could see reduced exhaust gas pressure would not allow the turbo to spool up but assuming you are getting enough boost why would this hurt so much.

The only thing I can really picture in my head that would cause monster HP losses is that an exhaust leak typically makes a "pff -pff - pff" sound or a ticking sound. A ticking sound may cause the knock sensor to think that there is detonation and retard the timing killing both mid range power and spooll up.

What would be the other causes to create such HP losses?

-Dana

Ski

engine sucking air at a calculated volume, this volume is transmitted to all engine parameters to determine fuel ratio through DME or other engine mangmnt system . One of these parameters is resistance to the fuel injectors. the more air you are trying to suck in then pump in, the more exhaust going to spin the turbo for boost. If this ratio is off, meter measuring air being sucked in usually has major influence on fuel delivery, more fuel than air that is being now forced in results in not as much hp as possible as it is with a proper A/F ratio. that's why exhaust leaks cause a loss of hp, resulting in a loss of boost which usually makes for rich mixture - not a great environment for max hp.

cracked manifolds, cracked crossover pipe or poor gaskets, wastegate leaking by, crush rings not sealing in exhaust system - even someone not checking their bolt/nut tightness after a rebuild and after the first couple of heat cycles can cause exhaust leaks.

Ski

no, if your MAF is sucking in a given volume through the AFM/MAF, whether it be a barn door or hot wire, that resistance there, is assisting in giving fuel to the engine. As you now turbocharge that air and force it into the engine, it is then combusted and then exhausted....now. as the exhaust goes out and leaks the turbo doesn't spool as fast, less air being pumped in but now you've already got a rich condition going on from the first onset of boost, so you have two problems now, to much fuel and an exhaust leak. the too rich condition will get you first, then the exhuast leak will continue the down fall of hp. Sorry, hell I almost "conFused" myself - but that's easy to do.

951_RS

I have a leak on my header and crossover pipe =[ I dunno what to do, they cost a crapload to replace.

toddk911

What is the best or easiest way to find exhaust leaks?

With out access to a smoke machine...

951_RS

go to a muffler shop, alot of places will give you a free quote for fixing it (then you leave haha)

OriginalSterm

spray soapy water (with those misting type spray bottles) on the exhaust and see where it bubbles. has to be cold exhaust though, keep spray as the car is idling and you might see the soapy water getting blown around.

toddk911

But how would you find leaks that only show under boost? Or does it matter if under boost or not??

RS: Good one!!

z3bra

Use a shop vac in blower mode (or an electric leaf blower or something like that) and shove it up the tailpipe. Seal it up with rags as necessary. You can take your sweet time looking that way

toddk911

Ok cool.

I'll make sure I am in clear view of the neighbors.

"what the hell is that guy doing to his car now????"

jimbo1111

An exhaust leak is simply put. Lost energy. The energy needed to spin the turbine is being lost. Once the back pressure increases more energy is lost because with more velocity more can escape. Our engines are small enough to notice a substantial decrease in performance with exhaust leaks. To put it in perspective. A 35mm waste gate when open is enough to relieve 100% of that energy needed to spin the turbine. Even if your turbo can build boost to it's setpoint It most likely can not maintain it to redline. Unless the leak is that small or the turbo that big.

stewardx

you may make more HP with the exhaust leak if you can get past the noise.

Wes