Backpressure, anyone?

[MidnightStalker]

Hello, all. Im new to the panther world; i just bought a 96 MGM a few weeks ago, and this was the closest thing I could find to a panther forum. I figured there must be a fair amount *at least* of crossover between the Marauder and GM, and I had a technical question that hopefully someone could answer... and I'm sure more will follow :P

Im looking to convert my single exhaust to a dual by adding high flow cats, an H-pipe, and a glasspack (possibly removable to run straight pipes at the track) on each side. My question is this: I have heard that if not enough backpressure is kept, my engine could throw a code causing me to fail emissions. One thing i could do is put an extremely restrictive muffler on to for the emissions test, but its a bit of a hassle, so I just wanted to know if anybody knew any truth to this rumor. Thanks for any and all help.

[Local Boy]

That's NO rumor, my friend...

Back presure should be calculated into the total package (engine displacement, N/A or SC'ed...,etc...)

In general, for most, if not all, N/A motors...TOO much exhast (NO back presure) = Loss of low end torque, and a lean condition in the upper RPM's...

Are you going to keep the stock manifolds and run your new pipes from there? How big?

Where do you plan on putting the 02 sensors?

The code it will probably throw would be for a "lean" condition...or "Emissions" because high flow Cat's are not as efficient as your OEM one's...

Best of Luck...

ALOHA

[RF Overlord]

I've never heard of low backpressure setting a CEL. It CAN cause a slight loss of low-end torque, but that should be about it.

The code it will probably throw would be for a "lean" condition...or "Emissions" because high flow Cat's are not as efficient as your OEM one's...Randy, I have Dennis's Cobra system on both of my cars and it includes high-flow cats. Neither car has ever lit up a code. I've never heard of anyone getting a code from high-flow cats, either.
this was the closest thing I could find to a panther forum.There's also CVN... www.crownvic.net

[MidnightStalker]

Are you going to keep the stock manifolds and run your new pipes from there? How big?

Where do you plan on putting the 02 sensors?

Stock manifolds, high-flow cats, I would LIKE to run 3 inch piping (H-pipe) then glasspacks. However, I might have to run skinnier piping to keep more of the backpressure. Has anyone on here converted from single to dual or know anyone who has?

*EDIT*
and probably just keep the O2 sensors where they would be/drill new holes in the corresponding place

[Local Boy]

I stand corrected, Bob...;)

Although, I never meant to say that High flow Cats would throw codes...I was just stating that High flow Cats are not as efficient as OEM one's, and thought perhaps, in instances where there are 02 sensors after the Cats, it may throw an emissions code...particularly if it's (motor) running poorly...

Would it be prudent to advise, this individual, to make sure that the 02 sensors are before the Cats...?

MidnightStalker, I would suggest 2.5 piping with 2.25 H-pipe...Your call...Have fun, and be safe...

Thanks for clarifying the issue, Bob...:beer:

No code on my SSW's w/ high flow Cats...:D rear 02's eliminated...:banana:

I will defer to your knowledge...as I 'am here to learn from you and others... who are kind enough to share...:bows:

Always a pleasure reading your posts, my friend...:beer:

ALOHA

[MidnightStalker]

MidnightStalker, I would suggest 2.5 piping with 2.25 H-pipe...Your call...Have fun, and be safe...

Well, I suppose that would probably save me some cash... deal.




No code on my SSW's w/ high flow Cats...:D rear 02's eliminated...:banana:

... I wasnt aware you could do such a glorious thing... Is there by chance any walk through/guide for how to? I didn't find anything in a search. I dont suppose I could just clip the wires and just walk away.

[Local Boy]

Sorry, not that easy...

But, it is still easy!

Your tuner needs to turn it off, via the software (tune)...

ALOHA

[RF Overlord]

As Randy said ^^^, if you're going to get a tune, have the tuner shut off the rear O2s...it's very common.

If not, then you can get little plug-ins called "MIL Eliminators"...Google is your friend here.

The simplest and least expensive way to convert from single to dual on the CV/GM is to find a wrecked CVPI in a junkyard and buy the system off that. It will include everything you need for the conversion, plus it's stainless steel, so if it's not crunched it should be in good condition.

[Rockettman]

I haven't failled an emissions test but I can tell you that back in '92 I put an upgraded exhaust system on my '91 Mustang. The headers were one size bigger, and pipes were one size bigger, with flowmasters to finish it off.
Result...all low end torque - gone! :bigcry:
I really have planned to put it all back to stock sizes (although money would never allow it).
Be careful.

[ctrlraven]

Yeah for that car and the amount of power it puts out 3" would be loud and take away a fair amount of your low end off the line tq. Some will argue that it really doesn't affect it but I went from a muffler-less side pipe exhaust to the stock exhaust with flowmaster mufflers and shaved off 3 tenths off my 1/4. Granted with more open exhaust I had a higher trap speed but at a lower time and with the less flowing exhaust it was vice versa lower trap speed with a faster E/T.

Your best bet would be what RF Overlord suggested with getting a CVPI exhaust from a junkyard, slap your mufflers and tips of choice on and your good to go. Honestly unless your plan on dropping a lot of coin into the car and really boosting up the power the CVPI exhaust will do just fine for now and save you some money which you could use for other stuff for the car.

Also don't forget to look into doing the PI (Performance Improved) head swap, that will get you some more ponies and won't break the bank.

[Aren Jay]

.............................. ...

[MidnightStalker]

You could always put a fake second pipe on it. Looks the part until someone gets their knees dirty.

pass.

Haha, not a fan of the fake.

*EDIT*

P.S. I did a little research about the MIL eliminators/tuning the ECU to ignore them and I read in a thread on this site that it would cause the engine to run full rich all the time... Soo...

1. True?
2. Is there a way to change this to maybe more towards the lean side? (I have no experience with tuning, so I don't know the capabilities of the tunes.)
3. Is there anyway to install some sort of toggle switch/tune switch to enable/disable the second set of O2 sensors? (again, newbie.)
4.please don't tell me "with enough money..." :P

Thanks for helping out this far. Waiting for the summer to scavenge some wrecked CVPI...

[Local Boy]

Nah...NOT true...

This has been done for years now...

Car runs perfect, without the rear O2's...It's ALL in the tune...

No need to have a switch...

ALOHA

[ctrlraven]

^Correct you just need to get a tune first which will turn off the rear O2 sensors. It's pretty much standard with DR and Lidio's tunes for them to be turned off.

Also a good idea to get rid of the 2nd set of cats, allows a little more flow and sound. I netted a tenth off my 1/4 time after having mine removed.

[GetMeMyStogie]

Also a good idea to get rid of the 2nd set of cats, allows a little more flow and sound. I netted a tenth off my 1/4 time after having mine removed.


Dare I say "Spare the air"? If this is a daily driver, keep the cats - they won't do you any harm :fishing:

[MidnightStalker]

In general, for most, if not all, N/A motors...TOO much exhast (NO back presure) = Loss of low end torque, and a lean condition in the upper RPM's...

Well... now i have another question, is this due strictly to the ECU tune, or just the fast that air flows more freely, because the base crown vic (single exhaust) is rated at 190hp and 265 ft-lbs, while the sport is rated at 200/275, respectively. So, if i were to switch to the CVPI dual system (which I would assume the only difference, if any, between the civilian and CVPI models would be material) should I expect to see similar gains of 10/10, or should I expect something closer to 10/-10? Obviously numbers directly from the factory vary widely from one application to another, I just dont want to drop a good chunk of coin on something im going to regret. Thanks again for all the help so far.
Nic

[ctrlraven]

There is also a different tune for the CV and CVPI models but yeah if you swapped over the dual exhaust system you should feel a slight increase in power.