zzjakect

I have the LG longtube headers and x pipe. Currently have Cats installed. Kit came with bypass pipes. If I install them will I need a re-tune?

itomh

If not you will throw codes

Turbo6TA

Yup ... Remove the cats, and you will get a check engine light.

But, it will not hurt the performance or the drive-ability of the car at all.

If you don't want to stare at the check engine light all the time, the same software that is used to dyno tune the car can also make sure your check engine light don't come on after the cats have been removed.

It's up to you whether or not you want the check engine light all the time or get rid of it.

Turbo6TA

I think your making a mistake by removing the cats.

Very little HP gain at all ...

Dano523

Your losing about 3HP total with the high flow cats in play on the exhaust system.

Hence that they are doing is keeping the car cabin from stinking of un-burnt fuel every stop light.


As for if you remove the high flow cats, and install the fake high flow cats pass through pipes instead, will not need a retune, nor will you end up with codes.

Hence when the header system was installed, the rear o2 sensors where removed from the system and tuned out of the tune. The rear O2 sensors only monitor the how effectively the cats are working, and with High flow cats much farther down line from the heads not working as effectually as the oem cats, would have ended with codes to start with if they where left in play. So front O2 sensors are used for the actual closed loop of the motor tune, and the rear O2 sensors are only used to monitor the how well the cats are working (rear 02 sensor readings, againt the reading of the front 02 sensors). The high flow cats are not as effective as the stock cats, so when long tube headers are installed even with high flow cats, the rear O2 sensors are deleted, and there function tuned off in the tune.

To add, anyone that said you where gong to get codes, does not have clue, since your rear O2 sensors where deleted/turned off in the tune when the long tube headers where installed in the first place.

So again, leave the high flow cats on the car!!!!! The 3hp total you are losing from them in the system, is way, way better than sitting at every stop light with the cabin of the car stinking of un-burnt fuel isntead. Again, they are high flow cats to start with, and do what they need to do with the min of HP lose to start with.

C6in816

yup they are right i had my car dynoed this last saturday and with the qtp opened it gained 6 hp now having said that i paid 400 for the qtp and 350 to have them installed. talk about pissed




ls2 396 at wheels w them open

Not So Fast

QTP ???? And what has been done to your car ?? LS2 making that power is pretty darned good, was it a DynoJet ?
NSF

C6in816

cut outs QTP Cutouts has a hand held remote that opens the exhaust . much like the NPP ...

C6in816

i changed intake and throttle body and installed a vararam intake

zzjakect

My right side high flow cat seems to have failed. I had a bad o2 sensor that made engine run very rich, rough and produced heavy carbon deposits. Thought it might have clogged the cat. keep getting code that says right side catalyst too lean. I tried running cat cleaner through it several times. It seemed to help, but now it has returned. Not sure of next step. Was not looking for hp gain. Looking to eliminate codes.

Thanks for your help.

C6in816

you could replace the cat ... or lift car up take it apart and beat the honey combs out like i did.. i took both sides apart and beat the insides out so when you look at it you would swear it has cats in there but i also had them do a tune after

Dano523

Yep, QPT's just makes the car trash-truck loud, Throwing open flames out under the car, isntead of safely out the back; but does not gain you more than a few HP at most.

Hence both high flow cats and even the mufflers on the vet do a good job of not restricting the exhaust flow that much, so not much power be gained.

Hell even the NPP system with the gates wide open only gains you like 6hp, over the gates closed and running in quiet mode instead.

So QPT on NPP system before the cats, with high flow cats in play, your looking at gaining maybe 5 HP over NPP with gates open isntead. Hence NPP with gates open already has the muffler pipes as a straight through design to start with, and it would be just gaining back what the cats 4hp lose, and maybe another 1HP with the exhaust not having to travel so far through tube bending to the back of the car isntead.

zzjakect

You guys stole my thread. Not even remotely having to do with my question. But that's okay.

C6in816

yur so right and its one of those things i did read that but just couldn't image not getting 15 or so hp.... worst investment

C6in816

sorry bro... yea replace it or pull it off and grout it out .. best advice...

Dano523

C6in816, nice way to flush money down the toilet.

Had you just spent the money on a long tube header system with high flow cats (OBX system would have less than a grand in parts), would have seen a good 25~30hp gain instead.

Hence stock manifolds do not scavenge well to pull the exhaust out of the cylinders, and the reason why such HP increase with the long tube header system isntead.

C6in816

yea thinking of putting a set on whats your thoughts on speed engineering headers 1 7/8

zzjakect

I'll just contact LG about it. Don't know how long warranty was.

Ahrmike

I added an O2 defouler - the 90 degree type from amazon (15$ or so?). Have not thrown a rear o2 code.

Turbo6TA

How do you know the OP's rear O2 sensors were 'tuned out' when he initially installed the headers and had it tuned?

There are folks here that re-install there rear O2 sensors and add wire extensions to them during the headers install.

But, your right, if his rear O2 sensors were not installed when he had the headers installed, the tuner would have already made sure he would not be getting a check engine light via the tune .... No retune necessary.