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Discussion Starter #1
Figured that title will be an attention grabber :lol:
I’ve got a full set of ARH catted longtube headers all the way back to stock mufflers. Will be installing it this weekend with the help of a buddy GM master tech. I’ve seen some various responses here over the years and I apologize to rehash this, I wanted to get the latest on what the answer would be.

I’m planning on driving the car for a hundred miles or so before getting a tune just to make sure there’s no issues with the install itself and see how I like the exhaust. Other than the potential CEL triggered by cat efficiency, any other issues that have been seen? I hope nothing that would put the car in limp mode. I’ve had a Rotofab Intake for about 8 months now. Any recent fitment issues noted by anyone?
 

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You will almost certainly get O2 codes. I would recommend against running it up through WOT without a tune, relaxed street driving will be fine.

I found fitament to be excellent, as expected with ARH's (have them on 2 LS's now). Otherwise install is fairly straight forward, with the infamous passenger's side O2 connection the worst part. Also if the car sees winter weather at all, peak at your two muffler clamps. Mine were rusted beyond recognition and had to be cut off for removal and replaced - and they are an odd euro style clamp with an e-torx fitting so not off the shelf at your local auto parts store.
 

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I ran my Kooks for some time untuned and aside from the CEL, the stock ECU compensated for the headers nicely with short-term and long-term fuel trims being excellent (low single digits). I wouldn't hesitate to run the heck out of the car pre-tune if you've got some way to monitor the fuel trims (they're also a great tool to tell if you've got any intake/exhaust leaks). I was using an OBDLink MX with the TorquePro app for monitoring.
 

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It won’t hurt anything but the check engine light will come on with cat low efficiency codes. I drove mine for about 2k miles before I did the cam and had it tuned.
 

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Don't use the gaskets that come with the headers. Use only GM gaskets. The GM gaskets can also be reused if you take the headers off once or twice to do other mods and won't leave a mess behind to clean up.
 

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6 of one have a dozen of the other. If you install the ones that came with them correctly and torqued the bolts down you are fine. Tons of miles on mine and no issues with the arh gasket. I still have my original exhaust and gaskets. If it ever does come to it (which is doubtful) I’ll change it over to the mls gasket. I’ve done plenty of these with all different gasket types. The one from arh is more like a remflex type. That is a thicker graphite one that forms to flanges and head. It’s not a pos paper gasket.

Edit: I did forget the rear clamps for mufflers will almost certainly brake if your car has been daily driven. Ask arh to include them if you aren’t changing the mufflers. They have the correct clamp for it. I did make mine work since I got two of the four slug spacers from the clamps and used longer bolts and extra nuts on the other side of them. The original bolt seized in mine and I snapped them.

That o2 sensor on the pass side was a god awful pita to disconnect. I had a really long pic that had a hook on it and got it from the bottom. No way for me to get it from top. Too tight. I also was not jacking up the engine/trans on that side. I’ve read people have done that. Best of luck with the install.

In the end it’s your car do whatever you want to it and don’t let people tell you only one specific way to do things. More than one way to skin el gato!
 

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Discussion Starter #11
Exhaust is in and the car drives and sounds amazing. Here’s breaking in the cats


I have a tune scheduled for next Thursday. In the meantime I am finding every excuse to go drive it.
Definitely needs a tune soon. The AFR is still settling, at idle if I didn’t know better I would say it’s cammed. Stutters and lopes but then rpms are reasonably steady.

I will keep reading here but would you guys mind educating me how much power on average the exhaust unlocks versus just intake and tune?
 

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Discussion Starter #12
Is it typical to idle really lumpy without the tune? At get-off it almost stumbles before it gets going. It started out ok but today was the third drive cycle and man, it’s definitely there.
 

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It shouldn't lump that much. Did you possibly crack a plug doing the headers or have a loose plug wire?
 

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Yep, i told my buddy to remove his plugs before swapping the exhaust from my parts car to his - definitely easy to damage plugs :LOL:
 

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Discussion Starter #15
Everything looks to be tight. I’ll leave her alone until I get a tune and report back. This could be because I couldn’t help myself staying away from redline. Guessing she’s hunting fuel tables.

Plugs and wires were removed and replaced with new.
 

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Could be random misfires. My engine shakes a bit occasionally. Upon looking at misfire data on gds2 it shows some cylinders randomly misfire but not the point of generating the random misfire dtc. I changed my plugs and wires and still have the issue. I’m not changing coils or injectors until it becomes a hard fault.
 

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Discussion Starter #17
Well, you called it. Something peculiar happening. The odd thing is the car isn’t complaining or telling us anything at all; no misfires, no CELs, nothing. She’s hunting for a stable AFR and shows an occasional stumble about once every 5 seconds when in gear and foot on brake. She put down 373 without a tune on a dynojet in close to 90 degree weather and about 40% humidity with the intake and exhaust. Driver side bank has a stutter. It’s either the plug, coil or injector. I’ll start with the plugs since that’s the most straight forward then I’ll have the injectors pulled and cleaned and last I’ll go for coils and we’ll see.

I’m so disappointed to walk away from the tuner without a tune but I completely agree we can’t move forward until this issue is fixed
 

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Discussion Starter #19
Something interesting to note, my tuner recommended going as low as .027 on the plug gap
 
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