Hi Flow Cat

[snozzau]

People,
Once and for all can somebody set me straight on if I have to change to a hiflow cat when if I add extractors and a 2 1/2 ïnch sports system.
Some exhaust places say the standard cat flows fine while others insist if I dont change the cat I am wasting my time and money on the extractors.
I am only changing to extractors to try and increase my fuel economy.
Thanks All,
Snoz

[JC]

It depends on the condition of the cat.

If the cat's OK, just get them to widen the entry/exit from 2" to 2.5" (they basically cut back into the cat a little bit to do this). If your cat is stuffed, then get a new one.

[loxxr6]

The standard cat is meant to flow ok from what I am aware.

I replaced mine for the hell of it. I believe JMM introduced a higher flowing cat to their range of products but before this it wasn't a must have thing. The standard one should be right.

[xr8ute]

As has been said, by most reports the stock cat is OK for a mild 4.0L.

JC makes a very good point though, make sure the flanges they weld onto the cat are full 2.5" internal diameter.

I had some new cats made up for my exhaust with supposedly 2.5" flanges, but when i checked the rears where not quite 2.1". No big drama, just a pain in the ИИИИ to check and grind back out to the correct size.

This is more important for you i6 guys becuase you've got all 4.0L of exhaust going through the same cat.

Yeah, spoke to JMM who just said to cut the ends off and weld 2 1/2 inch pipes on the ends, they told me a hiflow cat will not be as strong as the ford one, and not flow that much better to notice the difference...

[Tri Power 289]

Originally Posted by snozzau

People,
Once and for all can somebody set me straight on if I have to change to a hiflow cat when if I add extractors and a 2 1/2 ïnch sports system.
Some exhaust places say the standard cat flows fine while others insist if I dont change the cat I am wasting my time and money on the extractors.
I am only changing to extractors to try and increase my fuel economy.
Thanks All,
Snoz

I have fitted DiFillipo extractors and Hi Flow cat to my AU XR6 but kept the standard exhaust because I don't like loud sixes and I can tell you, I am paying the price.
It has made no noticeable difference to the economy or power.

But gee it looks good under the bonnet now!!

To get the full advantage, you really need to do the whole lot.
I am investigating a way to get a "quiet" performance exhaust.

Originally Posted by Tri Power 289

I have fitted DiFillipo extractors and Hi Flow cat to my AU XR6 but kept the standard exhaust because I don't like loud sixes and I can tell you, I am paying the price.
It has made no noticeable difference to the economy or power.

But gee it looks good under the bonnet now!!

To get the full advantage, you really need to do the whole lot.
I am investigating a way to get a "quiet" performance exhaust.

Yeah ive got JMM extractors, and have a 2 1/2 exhaust, with a single muffler and rear resonator. Not loud at all, which is what I wanted, just a tough sound...

[buickman]

Originally Posted by Tri Power 289

I have fitted DiFillipo extractors and Hi Flow cat to my AU XR6 but kept the standard exhaust because I don't like loud sixes and I can tell you, I am paying the price.
It has made no noticeable difference to the economy or power.

But gee it looks good under the bonnet now!!

To get the full advantage, you really need to do the whole lot.
I am investigating a way to get a "quiet" performance exhaust.

I went through that when 1st having the extractor system & redback 2.5 pipes fitted but kept the orginal cat. I thought it was to loud after driving in a car that was like a libery inside. I got the exhaust guy to make it quiter so he modified my stock rear muffler to fit back up. I regreted it after nearly 12 months & others bagging me on the unusual sound : . So I took it back & had the rear stocky removed & a hotdog fitted & have no complaints now with the exhaust note plus the car gets better ks out of the tank & sounds as if it revs out better.

[JC]

More mufflers = quiet. Easy.