Kind of off topic, but if an OBX header with stock cat, hp dyno gains are around 2-3 hp and 8 ft lbs. You are saying that only the removal of pre-cat gives you 6hp? So if thats true, would an OBX header with straight pipe give you 8+ hp (2+6) and 10+ lbs. torque?

 

And HP numbers rarely add simply...

Matt

 

this is not a flame...this is only so that people who have less knowledge don't start walking around saying....WOW a 3" exhaust is going to loose me HUGE hp...

to go from a 13.9 @ 100 to a 15.9 @ 90 means you lost some 80 hp....I do not belive this number change was a result of a 3" exhaust...

that's like saying anythign over a 15% pulley or 18 lbs of boost will blow out your head gasket...

that is the error of comparing only times...that's WHY the truth meter (dyno) was invented...

 

Point taken. So maybe the loss of HP is exaggerated in his test by some error, but is it possible for a 3" exhaust to lose power over a smaller exhaust?

 

updates?

 

Yes, it's possible. Bigger is not always better... The bigger it is, the less velocity. Sure, there may be less backpressure, but most engines need a bit of backpressure to develop optimal power.

 

 

It's the velocity. If you can get the same velocity without the backpressure, you'll make more power as scavaging will improve.....

Matt

 

Maybe, but there's also a balance that has to be struck... MINIs with completely open pipes run like complete crap, sans almost all backpressure and with high velocity...

More velocity is a good thing, agreed...

As far as bigger NOT being better to address norm's 'Bah Humbug' and - it completely depends on the application, but you CAN go too big and lose power on an exhaust which is why there are general recommendations for N/A vs. forced induction, displacements, and horsepower. Just ask the ricers with the huge cat-backs - a properly sized exhaust will always make more power than one that is too big, from the manifold all the way back to the tip.

 

Plus if I recall correctly - it was not apple to apples - one set of figures (OBX) came from a dyno (WHP) and the pre-cat were G-tech figures (NHP).

 

I know this happens because it happened to me too! But that's not the backpressure being needed, it's the modified breathing of the motor changing the VE vs Load and RPM. If the car isn't tuned for it, wayyyyy to much unburned gas comes out the exhaust, and keeps burning. When I got a map for the free-flow exhaust, the issue went away, and the car ran fine. The exhaust was just too loud....

We all have to remember that anything that changes the breathing of the volumetric efficiency of the car will require a re-tune.

Matt

 

just returned from vacation, got the new header file from mth and will install today, should have some results in the pm.

cheers

 

*****, I would like to hear your feedback.. honest feedback.

 

I'm looking forward to it, too...

My Frankenheader will be completed and installed when I get my head finished - OEM manifold, pre-cat deleted, metallic core race cat...

 

Sounds good

In the mean time (if you don't mind sharing) would you tell us who's metalic-core race-cat you've gone with? Details like inlet/outlet dia. etc would also be interesting.

 

I'm either going with the Vibrant Performance 2.5" or the Random Technology 2.5" model... The Random is $75 more, but from know they make good stuff from prior experience. I'm not sure how good the Vibrant stuff is...

The Vibrant Performance one is shorter, overall, too, which would be beneficial...

Vibrant - http://stores.channeladvisor.com/verociousmotorsports/Items/7101?

Random -
http://www.martelbrothers.com/catalo...er-p-7661.html

 

i installed the mth upgrade file, very noticeable change, i tried to do some tests but had way to much tire spin, the car is very responsive and pulls very good. i will elaborate more as soon as i can get some good test results, as far as getting rid of the stock cat, i would not do this as it is pretty good and you will not gain much by changing it.

cheers

 

Right, but I've got a complete manifold sitting here sans cat as a spare... I was going to remove the pre-cat from that one and install another cat, and keep my original header in case I ever need it (say, if they pass some insane emissions law).

 

A few folks have killed the OE cat. The reasons haven't been proven, but high-temps & melted substrate due to-rpm track time was sighted/blamed. If this is a concern a metalic-core cat would prevent cat failure (clog/melt) as they can handle higher temps. This notwithstanding I have to wonder if removing the pre-cat, as you've done would lessen the chance of heat-related OE cat failure?

Seems like there are a few of us keeping a spare around. I have one complete with OE cat too. Cheap insurance IMHO.

 

I cooked an aftermarket cat. I did it by putting a real free flow exhaust on the car, and not getting a tune to support it. I'm not sure what was changed in the tune to support a header, and free flow exhaust, but without it, I think the improved breating allows a lot more of the burning to happen in the header, and the exhaust gas temps go up a lot!

FWIW.....

Matt

 

Hmmm
Doc, you were logging with Bim-com correct? Did you log any change? If you did was it a gradual or sudden change?

Seems like a combination of issues - not really the fault of the OE cat... Poor gas quality, ECU dumping fuel/pulling timing, leading to a lot of unspent fuel hitting the cat.

This is where a wide-band 02 sensor prior to the cat & real-time logging software would be quite helpful for diagnosis.

Was your head/cam OE? What software (if any) were you using, and was it custom? - Note, this is not to imply poor tune to any vendor, so folks don't go there. ...Just for clarity as to conditions. As we should all be aware MINI's differ, and no one tune, unless VERY concervative (like OE) will 'work' on all cars. Hell, even OE/JCW has problems on some cars. LOL

I'm beginning to think the folks who just went out an did a cam w/o custom tune are in for a short cat-life if they run thier cars hard. Especially anyone who's consistantly using 91 octane.

Thoughts?

 

I'm planning to get an MTH Tuner update when I install the Frankenheader, sans pre-cat and with the metallic race cat... From what I have heard, people have had issues with the Magnaflow cats - melting the brick - but, I don't know if they had a "proper" tune loaded with it... I do know one guy that melted his OEM cat with head/cam and no software upgrade that does a lot of track work...

If I install the Frankenheader before the new head/cam go on, I'll have to get yet another update after the head/cam go on...

I believe that Franz has a pretty good handle on tuning for a header, as well as a head and cam...

 

I run MTH, and at the time had the standar file. When I added the free flow exhaust, the EGT went way up, but interestingly, the biggest problem wasn't a WOT, it was during the dreaded flat spot of light throttle cruising. EGTs went wayyyyyyyy high (I have a PLX R-500) and the car ran very lean.

Getting a map that took into account a bunch of changes brought EGTs down significantly, and made the flat spot much less sever (although it's not completely gone). But I don't see EGTs > 1000 C anymore! But I went back to the one ball as well... The other exhaust was just to noisy...

Matt

 

Interesting stuff, thanks!

My car's going to come out of hibernation soon. I've been planning on a custom tune. This discussion is reinforcing my thinking/impetus. Gotta book some dyno time.

 

Any word on this, willy69?