my lt1 camaro has an exhaust leak where the exhaust pipe bolts up to the cat,how much horsepower do you guys think im losing do to this?im going to the my local drag strip for the first time this week,and i dont want to go there and lose to some stinkin import or something.

 

At minimum the exhaust leak would introduce oxygen into the exhaust stream which would make one bank run rich. That could foul your plugs and not deliver the full spark you'd normally receive. At worst, it would introduce enough oxygen to create some serious heat on the backside of the exhaust valve and pull (or suck) a valve.

If you know where the leak is, then the recommendation is to fix it first. If not, let me know and I'll get you the steps to find the exhaust leak.

Good luck.

 

If you aren't getting any knock retard, then you are actually GAINING HP, since you have more free flowing exhaust now. (although it's in a manner that is not normally chosen )

Dan

 

With one bank running rich how would it create heat on my exhaust valve considering lean conditions is what causes valves to heat up or become burnt?I kinda guessed if anything i would lose horsepower do to the exhaust leak slowing the velocity of the exiting exhaust gases down resulting in backpressure.either that or effect the accuracy of the o2 sensor.

 

There is not going to be be any adverse effect as far as performance goes, since the exhaust leak is downstream of your o2's. The only noticeable effect will be the noise, and poor emissions.

 

I should update my previous post. The exhaust leak is before the cat and since it is a 1994 it is probably a single pipe exhaust. You won't disturb a specific bank but you can throw off your BLMs (aka LTFT). Since it is before the cat, you'll introduce oxygen into your cat which is essentially what your AIR Injection Pump does on start up to heat up the cat. Introducing false air before the cat can heat up the Platinum/Rhodium cat and eventually melt it down. A restricted/melted cat will restrict exhaust. Not to mention a new cat will cost $$$... OEM is the only way to go for emissions. If you only want a cat to pass emissions (if that is a concern) you can get an aftermarket which may last 6 months to 3 years (for a really good one).

Yes, you will have less backpressure on acceleration, but at cruise to deceleration (and Idle) you'll be sucking in oxygen.

 

Someone correct me if wrong,but doesnt a car that is running lean result in more oxygen content in the expelled exhaust gases,and a lower voltage reading from the 02 sensor?

 

To answer your second question. Any exhaust manifold leak at the flange to head will introduce oxygen into the exhaust. That does two things: 1) send false air to the O2s that you are running lean and will richen the mixture which can foul plugs that may lead to ignition misfire, and 2) oxygen directly on the back of the valve head increases heat... like a blacksmith pounding a horseshoe and using a bellows to introduce air to make the metal glow red. The rich mixture will mess with combustion and ignition while the oxygen on the back of the valve increases heat to that valve.

However, since your concern is after the O2 the worst you have to worry about is a melted cat.

 

Regarding your third post... exactly. IF the leak was at the manifold then the O2 will be picking up false oxygen indicating a lean burn which will result in the PCM richening up the injectors to richen the mixture and result in fouled plugs and fuel soaked oil in the crankcase. If you O2 is a Zirconia (and it is) lower readings are indicating that the O2 is reading low oxygen and result in low mv readings. You are correct. Which results in a wider pulse width from the injectors. But since your car isn't leaking at the manifold, the concern is the cat.

While your leak is before the cat, your are introducing oxygen at that point. Heat will be created in your cat at that point. That is your only risk.

 

thanks alot for the advice,I consider myself to have some pretty decent automotive knowledge,but you definetly know stuff I dont.What are blms im not familier with what that stands for?

 

BLMs are Block Learn Multipliers... that is a given value for setting fuel trim.

LTFT = Long Term Fuel Trim... same as BLM.

The Short Term Fuel Trim will try to compensate for any brief fuel anomalies. However, if the concern goes on for a period of time, the Long Term Fuel Trim will intervene and raise/lower the fuel trim value. Both banks should be relatively close. If one side is richer/leaner than the other by more than a value of 6, then you should start looking for intake/exhaust leaks.

In your case, since your leak is at the CAT well past the O2, it isn't likely that you'll affect your BLMs.

I have two recommendations:
1) Check for exhaust leaks to see if there are any other mystery leaks. Run a SeaFoam clean or simply use Auto Trans Fluid (ATF). On a warm and running engine, disconnect the booster vacuum line from the booster, the engine will surge and sputter due to the air leak you have just created. If you have a buddy available, raise RPM to 2000. Then slowly pour in ATF or SeaFoam.... you will soon see smoke. Under ideal conditions, you will see smoke only out of the tailpipe. If you have leaks, they will puff smoke. That way you can see if you have any stray puffs. Does your CAT have 2 bolts at the leak? Have you cleaned the surface and re-tightened the connection?
2) You can get an Off Road Pipe. I use one made by MAC and it works well. Then for smog or street, I swap the CAT back on. Then you don't have to worry about any leaks and overheating the CAT.

Good Luck.