I remember reading about this in a post but I couldn't find it.

I'm getting ready to ditch my borla catback for some borla true duals with XR-1's. Got it all planned out, but I want to use borla tips as well. Problem is, the type I want to use is the type that comes on the borla catback, and the biggest inlet is 2.5".

I read somewhere that as long as the pipe is 3" up to the tips that it will not cause a restriction due to the density and temperature of the exhaust at that point. Anybody have any insight on this?

 

I believe my old Edelbrock catback had a 3" intermediate pipe and 2.5 inch tailpipes and this exhaust still improved the power numbers.

 

so did my borla, but that was on a catback. The restriction there is the single 3" pipe. It splits off into two 2.5" pipes downstream. With the duals and X pipe with all mandrel bends, I'm just worried that if I choose the wrong tips it might cost me power since the 2.5" tips on duals would be the smallest part of the exhaust system.

 

The theory sounds good and makes sense, but since you already have the tips, drive it around without the tips and then with the tips. Maybe even go to the track. Tips aren't that hard to install.
If your not really noticing a difference then the loss is more than likely minimal. If you go to the track post your findings.

 

You'll never notice the difference, honestly.

 

Or another thought is to install a 40.00 cutout before the muffler and end all the worries completely.

 

Will it cause a restriction--- yes
Will it matter--- probably not
Ya won't be able to feel it.

 

By the time the exhaust reaches the tips, its cooled so much that you don't need as much cross-section on the pipes.

Buddy of mine had a 30th SS, with the 2OTL exhaust. He cut the 2OTL tip off and had it welded to the 4" taipipe on his Mufflex 4" catback, for that "stock" look. The car ran low 9's at over 150mph with the skimpy 2OTL tips.

 

Good. That's what I thought, I just wanted to be double sure before I started buying parts to do it. If I'm building the dual setup the last thing I want is to loose power from just a poor selection of parts.