Hey guys,

This is way left feild but i thought it should be discussed as i found it very interesting and contradicting to all info on this and experience on this website.

Im gona replace my exhaust on my EF XR6 and from cat back as both front and rear muffllers are no good and while my exhaust shop was looking they noticed it was the 2 1/4inch that come on non XR falcons. I was like its sopposed to be 2.5 press bent and it seems the last owner changed it for whatever reason, anyway i asked about the 2.5 redback cat back and asked if it would improve bottem end and economy and he said no u have to give it a little more to get it going and the 2 1/4 inch is best for economy and bottem end.

When i got this answer i was it carnt be and i take his word like the bible for exhausts as he is the man is Sydney to use so i went looking on redbook and it showed standard EF GLi and Futura 12.5L/100 urban and 13L/100 urban.

What do u guys think about this answer as it sounds right to be and i thought why not a custom 2 1/4 exhaust with 2 magnaflow mufflers would give still good economy and good bottem and mid range power and torque/power increase???

Either $250.00 for stock 2 1/4 stock replacement or redback 2.5 inch with 2 mufflers $440.00

From my research it has also shown that even with extractors 38mm primary pipe is best for bottem/mid range and decent top end and JMM race series headers are 38mm primary.

I know most of u will say just stick with stock which im gona do but worth a discussion and see what people think.

2 1/4 mandrel bent will be better for economy then a comparable 2 1/2 as it won't be a restriction down low/mid and will keep your exhaust gas velocity higher meaning higher temps and less mass throughout. Regardless of whether you are talking intake manifolds/exhaust manifolds/exhausts you want to keep the exhaust gas velocity at an optimum level. Where you want to make the most torque and how much air is being displaced then determines what size piping to use, so for economy you want peak torque down pretty low meaning you want a system that would have ideal velocity in those revs.

In saying that whether you are after economy or performance there are much better mufflers to use than are used in any off the shelf system.

dude is this a serious question?
obviously the smaller exhaust will be marginally better low low rpm and the bigger better for high rpm..

there will be minimal difference between the two with fuel economy

a 2.5 is a good all round size for a stock i6 and is even better if your considering mods

Pretty sure most people on here would tell you the opposite
Your price of $440 is f**k ridiculous!

Other ppl wanted $500-550 and yeh that Sydney workshop prices 4 ya

Drive up to the central coast and get it done for $300.

buy an online one for $250 and fit it yourself. Clamp + gasket = $10.

What would u guys say is the best flowing non stainless mufflers going around???

There's a post I made in a thread of yours ages ago. I know the Borla is S/S, not sure about the others though.

http://www.fordmods.com/post1000232.html

I think the luckey race mufflers or straight through stuff flow pretty well from what i have read