I have Bonez down pipe which is connected to the stock main cat and to the stock exhaust. I have Bonez HF cat and I wanted to install it but the flange on the bonez hf cat has lager Flange (maybe 3"). Now, to install the HF cat, what do I need to do?
Would I have to have the 3" flanges welded onto the down pipe and the stock exhaust?

Thanks!

 

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In some instances, there may be enough overlap to mate the two flanges, then use the gasket that fits the best. I had a stock cat connected to a 3" cat-back in this very manner. Gasket + GE silicoln II (clear) sealant-- worked fine.

If you find that there is not enough flange overlap to seal, you can make an adaptor plate out of 1/4" or 3/8" material (i.e., steel, aluminum, etc.) that has enough surface on it for both gaskets, one on each side, to seal. (you will use a 2-1/2 gasket on one side 3" on the other.) An aluminum spacer will work fine, I've had one in my exhaust for 3 years now, no problem--and its easy to fabricate with standard woodworking tools such as saws, files, etc..

You can use the same method to adapt the stock exhaust and it will work; however, it would be better from a performance standpoint to transition to the smaller pipe over a distance of several inches. Best results can be obtained with a 3" to 2-1/2" transition on the order of 12 to 14" long; I know this through real-life flow testing.

I also know that the stock cat-back will be you major restriction; much more so than the high flow cat. Therefore, you may want to consider doing something with it, depending upon what your goals are.

Hope this info is useful.

 

Thanks alot. I thought no one was gonna help me out on this.

I just bought RSR Single tip exhaust so I'm planning to install it along with HF cat.
How come the HF cat does not have any threads on the flange, where stock cat does. Do i need to get some long screw from Home Depot to tie down the cat to the dp and catback?