Exhaust 101

[Birdman]

Originally Posted by Boston Mike

Ok, so, now assuming I'm running a stock s/c (which I am) and am not ready to swap out headers (which I'm not), would it make much sense for me to install hi flow cats while I'm putting the h pipe in. What else would I need to do? It's not so much for power gain (that would be a plus) as much as it would be for a deeper, more muscular exhaust tone. if it allows the engine to run more efficiently, even better.

Yes it would be a very good move to change to hi flow cats for both sound and performance improvements.
The cats on our car are very restrictive on this engine . A year ago I had a lenghty face to face discussion with one of the GT500 SVT engineers about this . He gave me some numbers of just how restrictive they are on the 5.4 GT500. I am not at liberty to give those numbers out but suffice it to say they were suprising indeed (more than twice as restrictive than if used on the 4.6 Gt engine) mainly because these engines flow so much more because of the great FordGT heads they have.

[Boston Mike]

Originally Posted by Birdman

Yes it would be a very good move to change to hi flow cats for both sound and performance improvements.
The cats on our car are very restrictive on this engine . A year ago I had a lenghty face to face discussion with one of the GT500 SVT engineers about this . He gave me some numbers of just how restrictive they are on the 5.4 GT500. I am not at liberty to give those numbers out but suffice it to say they were suprising indeed (more than twice as restrictive than if used on the 4.6 Gt engine) mainly because these engines flow so much more because of the great FordGT heads they have.

This actually makes a little sense to me. So sounds like it would be a good mod to do in conjunction with the hpipe install. Now, any recommendations I. Hi flow cats to look at? I'm also assuming a tune sold be required to account for the change I flow, right?

[Birdman]

Originally Posted by Boston Mike

This actually makes a little sense to me. So sounds like it would be a good mod to do in conjunction with the hpipe install. Now, any recommendations I. Hi flow cats to look at? I'm also assuming a tune sold be required to account for the change I flow, right?

It's always a good idea to have the car dynoed and fine tuned at the same time after these types of changes especially if the O2 sensors are relocated in any way.

Not sure what's available out there to make up the exhaust parts you will need when changing to the 'H' pipe but I'm sure there are a few co's who make hi-flow cats . You may need a good exhaust place to make up the rest of the stainless system dunno.

[JTB]

Originally Posted by Alloy Dave

Chef, just remember that dynos are only so accurate...the normal variation between runs can be 1/2% or so....so you may misinterpret any perceived result from the H pipe.

I ran diesel engine dynos for 8 years. I calibrated them, ran tests on them in a research center, etc. It was not uncommon for an engine to change 1/2 to 1% from run to run on the same day.

If the car baselines at 600 (you have a TVS, right?), and then with the H-pipe it runs 598, that may really mean 596 nominal with a +2 from the H pipe.

Dave

Atmospheric conditions can effect Dyno readings too.
I've pulled better numbers on the same Motorcycle in the cool crisp morning air than the hotter more humidity laden air in the afternoon.

[ItalianStallion]

Originally Posted by Boston Mike

Ok, so, now assuming I'm running a stock s/c (which I am) and am not ready to swap out headers (which I'm not), would it make much sense for me to install hi flow cats while I'm putting the h pipe in. What else would I need to do? It's not so much for power gain (that would be a plus) as much as it would be for a deeper, more muscular exhaust tone. if it allows the engine to run more efficiently, even better.

Well Mike.....sounds like you'd be happy with just the "H" pipe assembly.
Seems as though it will garner the sound you're after.
I do agree with the comment made on the FRPP shorty; with minimal mods
it might be the way to go, at least in terms of the header subject.
A local guy here had the FRPP shortys installed when he purchased his GT500,
along with the 3.73 gears. I must say it sounds great and with the gear swap'
it pulls like crazy.


ItalianStallion

[cheftjpeck]

Originally Posted by Alloy Dave

Chef, just remember that dynos are only so accurate...the normal variation between runs can be 1/2% or so....so you may misinterpret any perceived result from the H pipe.

I ran diesel engine dynos for 8 years. I calibrated them, ran tests on them in a research center, etc. It was not uncommon for an engine to change 1/2 to 1% from run to run on the same day.

If the car baselines at 600 (you have a TVS, right?), and then with the H-pipe it runs 598, that may really mean 596 nominal with a +2 from the H pipe.

Dave

thx dave.... Yeah I am not too hung up on dyno numbers... That is part of my point I mean once you get to a certain point in rwhp it doesn't matter if you lose a few rwhp for the right sound... Right?? I mean if your not a racer guy , which I am not and never will be... Who cares if your car has 545rwhp or 535rwhp right??? If it sounds the way you want it to, are you really going to miss 10rwhp???... I won't... My car is not tvs yet still stock blower a smaller pulley and my goals are still the same.... To thoroughly enjoy my daily driver and not get caught up in the power mods craze... But that's just me...so mike get the h pipe and let us know what cats you find

[JTB]

Originally Posted by Boston Mike

This actually makes a little sense to me. So sounds like it would be a good mod to do in conjunction with the hpipe install. Now, any recommendations I. Hi flow cats to look at? I'm also assuming a tune sold be required to account for the change I flow, right?

Anybody know if there will be any issues with Hi-Flow cats when comes time for an emissions test?

[Dad's72Mach]

Originally Posted by JTB Consulting

Anybody know if there will be any issues with Hi-Flow cats when comes time for an emissions test?

Emissions test? You must live in one of them there eco-frenly places. Down here we just wanna know if the horn, blinkers and wipers work. That's enough to be road worthy I reckon.

[JTB]

Originally Posted by Dad's72Mach

Emissions test? You must live in one of them there eco-frenly places. Down here we just wanna know if the horn, blinkers and wipers work. That's enough to be road worthy I reckon.

I gotta move...

[Birdman]

Originally Posted by JTB Consulting

Anybody know if there will be any issues with Hi-Flow cats when comes time for an emissions test?

No problem at all as long as your tune has correct A/F and there are no codes thrown. I once passed emissions with the Lightning on the rollers with "gutted" cats because the A/F is spot on.

[Alloy Dave]

Originally Posted by cheftjpeck

thx dave.... Yeah I am not too hung up on dyno numbers... That is part of my point I mean once you get to a certain point in rwhp it doesn't matter if you lose a few rwhp for the right sound... Right?? I mean if your not a racer guy , which I am not and never will be... Who cares if your car has 545rwhp or 535rwhp right??? If it sounds the way you want it to, are you really going to miss 10rwhp???... I won't... My car is not tvs yet still stock blower a smaller pulley and my goals are still the same.... To thoroughly enjoy my daily driver and not get caught up in the power mods craze... But that's just me...so mike get the h pipe and let us know what cats you find

[SteelSteeds]

I had passed for years with my '79 Bronco, until about 4 years ago they cracked down on "visual inspection." I had never had a cat on that truck since I bought it in '94, but that just happens to be the very first year they were required on trucks. Suddenly I was failing for not having a cat, even though my emissions were well within the limits for the 1979 model year.