My car is tuned for a 3" test pipe. The tune is solid. AFR's are all between 10.8 and 11.2. Knock is a non-issue and the power band is smooth. The car pulls like a raped ape. It has cams, IX turbo, pump, cam gears, TBE, etc, etc.

I'm starting to get tired of all the off-throttle noise associated with running a test pipe. I'm ready to put the 3" HFC back on. My only concern is the tune. Am I just asking for some knock on the top end or should I be OK?

 

it shouldnt effect your tune at all. I have a BR350IX with the stock cat.I asked Dave Buschur if i put a test pipe on if i would need a re-tune and he told told me i wouldnt.

 

That's because a test pipe will be less restrictive than a HFC. I'm going the other direction.

 

Getting a tune for every single part on your car is unneccessary, and is only recommended by tuners because it boosts their profits. There isn't any difference between a HFC & straight pipe to the ECU, except may be o2 level readings which might through a check engine light.

 

I appreciate the advice but I'm not 100% sure that's true. It's my understanding that there will be increased knock if you swap in a catalytic converter when a car has been tuned with a test pipe. Whether those knock levels are/will be acceptable is what I need to know. Maybe I'll just reinstall the HFC, go back to my tuner, have him plug the laptop into the ECU, and log a couple WOT pulls to see how it looks.

 

Where did you get this info from? Why would a switch from a test pipe to a HFC increase knock?

 

you'll lose power.

 

Two different tuners have mentioned it to me. Is that incorrect?

I will lose a little. I'm OK with that.

 

Uhhh yeah, a cat that will cause knock...maybe you should also get a tune everytime you get an oil change!

 

Ok so the cat will add a bit of backpressure...backpressure may increase temperatures (doubt it) and may cause some knock (doubt it)....Just put it on and log.....My guess (from the professionals that I have spoken to ) is there will be no issue.

 

Is the sarcasm neccesary? The questions I'm asking are not amateurish. If you're frustrated that you can't organize your thoughts into words it would be a good idea to avoid threads asking for insight. This is not the general forum. It's specialized. When I asked the original question and you posted your experience of going in the opposite direction I could have easily been a complete *** but I chose not to. It would have been nice if you could have tried to sustain the same level of maturity.
Would the most potential for problems be at high RPM WOT, or under low RPM boost. Is it more a load issue, a backpressure issue, or little of both?

 

finally one logical response for the poor guy.

My personal opinion would be if you're worried to swap it and log a couple pulls. I wouldnt think the difference would cause anything drastic to happen, but I'm no expert lol.

 

only one way to find out. Do the swap, make a few runs and let us know.

 

Thats what I say.....swap the cat in and then log, that will give you your answer? Then you dont have to listen to 500 different opinions. Seems logical to me?

 

I agree you have to datalog to find out if it is causing any harm. Logically a HFC will add some back-pressure compared to a test pipe, so a lot will depend on how aggressive your tune is and how high of a boost pressure you are running. If it is aggressive I would assume you would have to turn down the boost due to the added back pressure, all else being constant.

Better safe than sorry ...