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Issue.....The driver's side bullet cat is occasionally banging on the tunnel plate even though the plate has ~0.50" of spacers between it and the bottom of the car. The bullet cats have 4" bodies so I think the issue is the driver's side LG Motorsports header is hanging too low/mis-aligned.
I'm out of town but this is driving me insane so I'm planning my course of action to address it when I return. Here's what I'm thinking...
- Remove tunnel plate
- Loosen the two exhaust clamps that secure the driver's side bullet cat to the header and mid-pipe
- Loosen the bolts that secure the header to the cylinder head
- Use a floor jack and block of wood to gently push the bullet cat "up" in order to gain clearance
- Re-tighten the exhaust clamps
- Re-torque the header bolts to the cylinder head (re-using the GM gasket)
- Reinstall the tunnel plate
Any reason why this won't work? It's not going to move enough to mess with port alignment. I've been working my Google skills and no one else seems to have this issue. As such I'm going to believe it's another case of poor installation workmanship of the header by the shop that put them on. If that's not the case, it means the header itself it misaligned. Another example of I should have just did it myself
Some pics are below.
The first one shows the new cats that replaced the crap the shop installed. These are GESI G-Sport Gen 2 cats
View looking aft and you can see the driver's side cat is low/resting on the tunnel plate
Note the witness mark on the driver's side cat towards the back. Added spacers but it still intermittently bangs on the tunnel plate
No mine are AFE I tried the jacking the pipes up first and Got a bit but it still rattled so time for the plasma torch and grinder
Thanks Ernie
Not sure why so many have this issue. I can’t believe shortening the pipes by a half or 3/4 inch would have had that much of a performance impact. I’d rather have factory fitment vs the last 2-5 hp.
When does it rattle? Can you get it to do so while in the air, so you have some chance of diagnosing it? Have you driving it with the bottom plate off? If you cannot localize the source at least a little you are simple randomly "adjusting" hoping one will be right. All the best.
Just use a few thick washers on the stock bolts or how many you might need. It should clear.
It already has 1/2" of spacers and the cat is still hitting I'll see what I can squeeze out of it by moving the header. If push comes to shove I'll either hack a tunnel plate, add another 1/8" of spacers, or check out the TSP piece Dave mentions.
I did reach out to TSP a month or so ago to see if they'd sell the plate separately and get the cost. Unfortunately I got no response. Why have an email address if you're too busy to use it? Just remove the email and put a note on the website that says "please contact us via phone at xxx-xxx-xxxx for questions"
When does it rattle? Can you get it to do so while in the air, so you have some chance of diagnosing it? Have you driving it with the bottom plate off? If you cannot localize the source at least a little you are simple randomly "adjusting" hoping one will be right. All the best.
With the plate off it doesn't rattle, and there's a witness mark on the bottom of the cat that matches a corresponding witness mark on the tunnel plate It's definitely the driver's side bullet cat hitting the plate.
When does it rattle? Can you get it to do so while in the air, so you have some chance of diagnosing it? Have you driving it with the bottom plate off? If you cannot localize the source at least a little you are simple randomly "adjusting" hoping one will be right. All the best.
A lot of "Green" cats bang the bottom plate , I had the spacers but that was just to "hooky" looking for me .
It already has 1/2" of spacers and the cat is still hitting I'll see what I can squeeze out of it by moving the header. If push comes to shove I'll either hack a tunnel plate, add another 1/8" of spacers, or check out the TSP piece Dave mentions.
I did reach out to TSP a month or so ago to see if they'd sell the plate separately and get the cost. Unfortunately I got no response. Why have an email address if you're too busy to use it? Just remove the email and put a note on the website that says "please contact us via phone at xxx-xxx-xxxx for questions"
I called them , at the time it was $250
I wasted no time buying it
I would suggest tightening the header first, then the cat. That way you know the header is in the best position possible, then try adjusting the cat. All that said, the feedback above says you may need to clearance the plate for the best outcome.
I called them , at the time it was $250
I wasted no time buying it
Dave
Yes, call them. I tried emailing them about buying tunnel plate spacers and they never returned it. I called and they answered right away and were really easy to talk to. I wound up not needing the spacers but the guy I talked to was more than helpful.
Got my QuickJack assembled and operational
Pretty quick process for the cat
- Loosened the driver's side header
- Removed the tunnel plate (24 bolts )
- Loosened all the exhaust clamps
- Used my floor jack to gently push the cat upwards.
Unfortunately I only gained about 1/8". Sooooo, I reinstalled the tunnel plate with some machined 1/4" aluminum spacers. I took it for a drive today and so far so good. We'll see if anything shifts around. If that happens, I have 3/8" and 1/2" spacers I can use.
LT Header Adjustment - opinions needed
I'll see what I can squeeze out of it by moving the header. If push comes to shove I'll either hack a tunnel plate, add another 1/8" of spacers, or check out the TSP piece Dave mentions. 
It's definitely the driver's side bullet cat hitting the plate.
