Here's what I used:
GrimmSpeed Downpipe to Catback 3" Gasket 2X THICK

 

+2.

OP:

When I installed a friends Invidia I also used the same. It just wasn't worth it using the ****ty gaskets right after the header that Invidia supplies. Actually let me say that perhaps they aren't crappy, it's the design of what most manufacture's do which is stupid. The stock exhaust has a recessed area for the crust gasket after the header, which is a good design. One of the ONLY manufacture's I've found that did this same setup is Borla, (maybe Tom's, I've yet to see full pictures of their cat back exhaust not installed). Most other manufactures including Invidia have a flat flange, so they supply a flat gasket. It just doesn't makes sense in our application because as the exhaust moves it's going to introduce wear on the gasket as it keeps moving. This could probably be solved 100% if they would have just milled in an area on the flange to accept an OEM gasket, OR, just make the flange part 2.5" instead of the 2.75". There's no need to have piping at 2.75" honestly.. 2.5" is fine. But I digress.

Use the above, put sealant on both sides of the gaskets then let it cure for about 1 hours before you tighten it down. Then after the hour torque the bolts properly to spec. Check a few hundred miles later and make sure everything is still torqued properly.
So far those that have used the grimmspeed x2 thickness gaskets have reported no issues. I've always used their gaskets on my Subie and have never had an issue, so I wanted to find something and luckily they had a 3" downpipe gasket that we can use for our application.

-Nigel

 

Exactly this! I haven't gotten a cel since I've replaced my Invidia gaskets with the grimmspeed +copper silicone sealant.

 

If the flange was 2.75 like the piping the OEM gasket would actually work. For some dumb reason Invidia uses a 3" flange at the header that then tapers down to 2.75" for the rest of the piping. OEM and even PPE headers are a 2.5" outlet. Since the OEM side isn't flat it's a real pain to get a good seal.

Figured I'd point out the root cause in case anyone was wondering why you need thick MLS gaskets and copper rtv with this exhaust.

 

I just installed this in my garage with jack stands last week.
I used Apexi's gaskets and they work beautifully.
I've driven it for almost 200 miles now and hardcore with no CELs.
If y'all are having issues with CELs, then look into Apexi's gaskets.

 

+2. I still don't understand why Invidia didn't do a slightly better job at the flange. Doesn't make sense. For the price point I get it, but at the same time they are one of the FEW that actually welds the tips onto the back of the muffler. Exhaust costing double/triple still use some type of stupid clamp to hold the tips to the muffler. If I could fine a spare set of OEM pipes SUPER cheap it would almost be worth it to take it to a nice exhaust shop and saw put the flanges from this exhaust onto the invidia pipes. But until that time I think the multi layer gaskets is the way to go.


^
Apexi still uses fiberglass gaskets. They might be slightly different but they are going to be exposed to the same issues that the Invidia is. It's the movements of the headers/exhaust pipes that cause small cracks/fractures in the fiberglass gasket. As it flexes over time gasses will find a way through and then the exhaust leak starts... then it just burns more and more/quicker and quicker. The grimmspeed is s/s all the way through plus a firering in the center. No way of burning through it. Don't be surprised if eventually the apexi leak. I think Sunny had his gaskets on the Invidia for almost two years before he experienced a leak just a few months back, replacing with the thicker (not double thickness) grimmspeed gaskets.

-Nigel.

 

The 2 - OEM crush gaskets are a one time use technically…

Are the flanges seated on the Invidia side ??


Joe Z

 

I am getting cel (p013c - bank 2/ oxygen sensor 2) code from time to time after mid pipe swap (gt haus) on RCF. Anyone had similar experience and found a reasonable remedy? I have been guided towards sensor spacers (90 degree), reinstalling the sensors, oxygen sensor simulators… appreciate the feedback. Thanks.

 

if you have the stock headers, then your issue is exhaust leak at the front flange or damaged sensor wiring. Check and replace the gasket. Also make sure wires aren't overly twisted.

 

As noted by LoSt, check your gaskets and wiring. If a shop installed your midpipe more than likely they did NOT remove the o2 sensors and just twisted them a bunch of times. Also probably didn't take care in terms of making sure the gaskets lined up.
You do not need o2 spacers/defoulers for after the headers, it won't do anything at all to eliminate the problem you are getting. The only time you'd be using the 90 degree simulators/foulers is if you had headers installed.

Read through this thread and you will see the correct gaskets to buy. Many of us have used the x2 thickness 3" s/s gaskets from grimmspeed. MOST aftermarket midpipes/exhausts have a design flaw in my opinion that they do not utilize the recessed area in the flange like OEM. Therefore instead of being able to use an OEM crush gasket, a flat gasket is used to seal the connection of the two pipes. It's more of a petpeeve of mine honestly because yes it would make the exhaust more expensive but in my mind it would eliminate a lot of these issues with leaks. Just pass the cost down to the consumer. I would have gladly paid more knowing that mid pipe flange was just like OEM. Borla is one of the few that actually did this with their exhaust system. I've yet to see a Tom's exhaust, no one seems to take pictures of the flanges/connection points of that so I can't say for certain. The GT Haus is also flat, which is nuts considering their mid pipes are over $1200 alone.

-Nigel

 

@nigel821

Agreed.. Only a few experienced companies understand the importance of the CNC’d seated flanges to match the OEM manifolds…. Also PPE has done a great job on creating the seated flanges on their aftermarket headers as well..

Even more important is to know how much to seat them to make the OEM crush gaskets effective..

Below are some visuals of an X-pipe with properly seated flanges.


Close up on X Pipes



Sorry I don’t have better close ups, but you get the picture.

Also here’s a cool article from over 11 years ago..

https://motoiq.com/project-lexus-is-...eries-exhaust/

Joe Z

 

^
Yep! I just don't understand why companies don't go the extra little bit to make a superior product.

This is Borla's BTW. It's just like OEM mid pipe when I pulled mine. Looks the same. If manufactures would just do this there would hardly be any issues with exhaust leaks, short of user error.



I love that Borla did it, but I also hate how Borla uses "clamps" for the rest of their system. Again, that just seems tacky as hell to me. Why not bolt everything together? Who knows....

I'd love to see a full Tom's system just to see how that looks. No one posts pictures of anything when they get stuff for some reason here. I don't think I've seen anyone post a full TI Tom's exhaust (mind you probably due to price, at $10.5k), But Tom's actually looks like it's as close to OEM as OEM can get. The midpipe is all one piece just like OEM one is, and it appears it has cat's/resonators just like OEM. The gaskets on the side there also look to be utilizing OEM gaskets so I guess I can assume that their midpipe might have the recessed area as well.



Just seems really silly to spend $10k on an exhaust for a car that isn't an exotic. If this was a higher end P-car, Ferrari, Lambo..etc. I get it. But spending that much on a Lexus just seems silly. If it were half that price I'd probably bite on it.

-Nigel

 

None of the $5k or $10k exhaust make any sense to me… Quality 304 SS is not that expensive…

Model of the car or wallet size should not matter either

You can see the effort we put into our exhaust components, never slip fit and always fully flanged in all sections. The parts I pictured are what we used on the RC F & GS F full exhaust systems..

Joe Z