Has Anyone Removed The Precat From The Stock Header? If So What Kind Of Results.

 

I think it's a cast iron header, and it's just not worth the effort. If you're going to do this much work, why not just get another header, and save the stocker if you have to sell the car, or put it back for inspection? It's more expensive to replace than to get an aftermarket header...

Matt

just my take though....

 

No cast iron in a Mini S header, unless I'm missing something here.

 

I WAS THINKING OF CUTTING AT THE BACK OF THE PRE CAT AND THEN CUTTING AT THE FRONT OF THE MAIN CAT, THEN ADD A PIPE THE SAME DIA AS THE PRE CAT EXIT AND WELD TO THE MAIN CAT. HOPE THIS MADE SENSE.

 

I don't know what it's made out of, but it sure weighs a ton!

Matt

 

I have had exactly the same question.

I have heard that the pre-cat's role is confined to emissions control in cold start situations below 0 degrees C. We never see temperatures that cold here in Seattle. Don't know if these claims about the pre-cat are correct or not.

Have thought about cutting out the honeycomb innards of the pre-cat with the intention of reducing back pressure in the exhaust system. I have modified my exhaust system so that I can temporarily remove the catalytic converter and replace it with a "track pipe" for track days. As a result I can access the pre-cat from below and grind out the honeycomb if I want to. Not sure what to do.

Is there any significant performance advantage from removing the pre-cat?

John Petrich in Seattle

 

I've done this to a stock header and put it on my MCS.
Still have not dyno'd it yet so I'm not sure of the gain, but if anyone wants, I'll let em use it as long they share the results .

Cost was $80 at a custom exh. shop to cut out and replace the pre-cat.
Has not caused any fault codes either.

motor motor

 

Tuners here in Germany recommend to do this. You can get good results but you have to adjust your motormanagement. Otherwise the EML could be on.

The best results are in combination with MTH because the change the advance angle and so you could get about 10 hp and about 15 Nm.

 

Right on Peter. Haven't installed MTH yet, but will sometime soon.

good day to ya.

 

You never see temps at or below 32 F ?!?!?!?!?!?!

Do you live in Seattle, Mexico?

 

Rather than spend time & money on this why not just throw on a cheapie header?

EDIT - I didn't see MATTS post - "ditto"

 

the stock header has a very good main cat, tuners in europe feel this is a good header minus the pre cat, if you use the obx you still have to use the stock cat for best results, if you buy a good after market cat the obx is not a deal. i feel the engineers that designed this header do know what they are doing, bigger longer is not always the best. if the displacement was changed or a really big increase in charge was present i would agree with a redesigned header, this is not the case with standard mods. a good header has a purpose, to assist in scavaging exhaust gases out the exhaust. this is why i want to try this mod, i have nothing to lose but a couple of hours, if it does'nt work, i will look to the aftermarket for a header, probably the alta as it has the ss flex joint and not the cheesy stud and spring set up,plus a quality cat, at a price though. same as mth setup. time will tell as i am going to post before and after results with this mod.

cheers

 

here is a link to a german mini site were I describe the mod! (coops)

http://www.newmini-technik.de/viewtopic.php?t=1566

 

PeterKostenberger,
Thank you for the post, but, I cannot read German. What modification did you do? Did you remove the pre-cat? I am thinking of grinding out the interior matrix of the pre-cat and keeping the stock cat in place. Please clarify.

Auf Wiedersehn,

John Petrich in Seattle

 

Same as Shelby uses on his new 427s..... Just better springs, bolts and nuts. Same graphite gasket.....

Matt

 

sorry doc, the ss flex joint is much much better, than any back yard stud and spring set up. i will restate again "CHEESY" , a front wheel drive vechicle motor moves much more than a rear drive.

cheers

 

oh ya, can you post any pictures of the mod? would be great.

cheers

 

The ss flex joint is a bellows, not smooth at all. The use of a spherical graphite bushing will allow for a much smoother flow path, independant of front or rear drive. And have you seen (0r felt) the torque of a 427 with dual four barrles, while it won't move front to back like a transverse mounted front drive motor, it will sure twist the crap out of the motor mounts (frame and chassis too), and rock side to side. The only problem with the OBX isn't the gasket there, it's the "cheesy" nuts bolts and springs used to keep the price down. Use good stuff there and it will out perform (and isnt' that what power adders are about) any corregated metal bellows. That's just the physics of flow.

Matt

 

NICEEEEEEE!!!! THIS WAS WITH ONLY ABOUT 160WHP

CHEERS

 

Hey Doc, I Respect Your Opinion. I Have Never Used This Setup On A Rear Wheel Car, I Have Always Bolted The Collector To The Exhaust System And Then Used Rubber Hangers To Take The Twist, The Motor Does'nt Move Front To Back Like A Fwd, It Does Twist. You Are Right The Springs Could Be Stiffened Up To Resolve The Gasket Issue. But The Main Reason For The Mod To The Stock Manifold Is That Respected Tuners Believe The Design Is Right For The Car, And I Also Agree With Them In Theory. Know I Will Try For Myself.

 

We all know that the nuts, bolts and springs supplied with the OBX suck. What does that have to do with the design principles? I can go find photos of crappy bellows, but it has nothing to do with whether the bellows restric flow more.

Your post is a perfect example of taking something out of context.

So you go get a better pair of springs, and double nut the sucker. $10 bucks more, and the whole kit would be under $200. (Mine was $185 shipped to my door).

Matt

 

Dr. O:

I was one of the last posts in the lengthy OBX thread - BahamaBart responded to a few questions I had. I am seriously considering the OBX, but worry a little about the bolt,nut,springs issue. The bolt/nut fix seems simple enough by double-nutting, but do you have any suggestions on replacement springs and where one might get them?

 

SFJames2:

I realize you have no empirical data, but did you notice a difference with the pre-cat removed? What are your observations?

 

The one I went to had some weld-in joints with the graphit gaskets, springs nuts and bolts to use for building headers and the like. A few calls should locate something for you.

Matt

 

Willy69,

Are you talking about cutting the section in the picture below?