What would be the effects of putting in a high flow header without doing the rest of the exhaust? Would the increase in flow provided by the header be irrelevant because the exhaust would still be too restrictive?

What if a high flow cat and a straight pipe was put in with stock mufflers? What kind of effects would that have, if any?

Really trying to figure out what to do, thanks everyone for your contributions

 

Doing just that portion of the exhaust will increase flow. If you want the most out of everything you should do the full exhaust, but if you do just that you should be better off than just stock.

-Luccia

 

Correct me if I'm wrong here but I was under the assumption that the cats were the most restrictive portion of the exhaust?

 

Increasing the diameter and removing or adding high flow cats allow for a much less restrictive flow. Most of the time people stick with high flow cats because of emission purposes rather than removing them all together. But yes, if you remove the cats completely you will allow for much more flow.

 

For sure, only problem as far as I know is that without a cat, emissions will be failed and I don't need that hassle.

What is the ideal exhaust diameter for optimal pressure for the stock turbo? I have been weary of changing the exhaust (a) because I don't want to fu$k with the compression for turbo and (b), don't want the volume...not just yet.

 

It depends on what state you're in too. Some do visual inspection and some only pull OBD II data. You can run catless with a tune to get rid of the CEL that inspection would see on an OBD II pull. If they do visual inspections however, you'd still fail.

That being said, I think the general consensus on back pressure for the turbo is that it doesn't matter much, at least not with the aftermarket exhausts that are available. Most of them are 2.5" and I think some may even be 3" (someone feel free to chime in on that). Replacing the downpipe is almost guaranteed to give a CEL, even if it's a high flow catted version.

Downpipes and catbacks won't really gain you much performance-wise without a tune. If you're looking for performance out of the exhaust I'd spend that money elsewhere, likely on a tune.

 

Remember were are running a I4 1.6 liter engine here, anything beyond 2.5" pipe diameter isn't going to do much for you. It would be nice to remove the primary cat because it's just a heat magnet that stores 1450-1600F inside the cat.

 

Do it right the first time. Do the header and down pipe at the same time. Before the install have an O2 bung welded into the downpipe for a wideband o2 sensor to monitor AFR's, you can plug this until you actually get the sensor. Have both exhaust parts ceramic coated. Replace your leak prone turbo oil feed line with an aftermarket one. Get a tune before your next inspection to clear the CEL.

 

^This^.

Also, I would look at other performance opportunities first, if you haven't already. Doing an engine tune and high-performance intercooler will give you a better bang-for-the-buck and not have the side effects of emissions headaches and stinky exhaust.

 

Wow this is all incredibly helpful, thank you everyone. I didn't realize that doing a tune would wipe the CEL. I have another thread here discussing tunes, it is something I really would like to do.

So is the consensus that doing a performance header and down pipe with a high flow cat would serve my needs well, while still passing all emissions.

I want to do a tune but don't want to do the full exhaust.

Without straying too far from my original questions, what is a good intercooler?
I have seen this one http://www.tyrolsport.com/minifmic-detail and it looks epic! The only problem is that its about $1000...and that is cripplingly expensive. I never expected to spend more than 600 for one. What do you guys think? Any other recommendations?

 

Helix and Forge are the most popular choices around here for intercoolers it seems. Between the two, I'd go with Helix. It's also slightly cheaper than the Forge.

 

It depends on how intense your emission laws are. Even some cars with high flow cats will fail emissions. If this does happen to you, just make sure to hold onto your stock exhaust so that you can swap it on if you don't pass with the high flow cats.

As for Intercoolers. It's not live on our site, but we do sell the Forge Intercooler for your vehicle for $720. If you're interested you can give our sales department a call at 888.280.779 as they can go over specifics. Part #FMS-FMINTR56



-Luccia

 

We will soon be releasing performance datalogs of our intercooler. The intercooler that we are releasing will be our third improvement for the 2nd Gen MINIs. This latest version has the best shaped end tanks--designed with the aid of Computational Flow Dyanmic Software for the best flow and least pressure drop. We've also improved on our already best-in-class fin density for greater temperature drop. Stay tuned...

 

If you remove the cat, a tune can keep the CEL on the tach from being lit, but the code in the ECU will still be set. So you will fail emissions based on a visual inspection (hey, where did your cat go?), an OBD2 scan (codes set for cat not working), or a tailpipe test (sky high HC, NOx, and CO). You may, or may not pass emissions with a high flow cat. It depends on the cat and the testing requirements in your state. The manufacturers may provide some guidance, Akrapovic says "not approved, track only."

Changing the exhaust, header, intake, or intercooler isn't going to do anything for you without a tune. Think of the engine as an air pump, the ECU is managing how much air is flowing through the engine and then adding the appropriate amount of fuel. Without changing the ECU targets for how much air is flowing through for a given RPM and throttle position, you're not going to get any more power. (You may get slightly more power from a better intercooler since the intake air will be cooler and therefore the timing can be advanced more, but this is theoretical, in practice I haven't seen this.)

As Helix said, a better intercooler with a tune that takes advantage of it is great bang for the buck. Only when you get to higher power levels will the exhaust become the limiting factor to the airflow through the engine, and you'll probably need a bigger turbo to get there. Look at the JCW - 208 HP. The exhaust header and turbo are modified but the downpipe/cat is the same between the S and the JCW for the N18 engine. So unless you are going for maximum power, the downpipe/cat isn't going to be the limitation.

Look at the Wagner (under $600, lots of threads on it). Also the new Helix looks really interesting, too bad I'm not shopping for FMICs any more.

 

The Wagner looks good, thank you for sending me that link, definitely the most affordable seen. I have another question, more likely will require intuition than product knowledge, regarding the Tyrolsport. It is unique in that it sits in front of the radiator. It appears to have the most unique design and looks mean from the front. My only concern is that since it sits in front of the radiator, it is blocking a bit of air from getting to the radiator.

Will this result in the motor temperature running measurably higher?
or is it inconsequential?

 

No one would even consider the use an intercooler if it cause our engines to run noticably hotter, the whole point is to lower intake air temps. The air that flows through the intercooler goes through the radiator as well, it might be a few degrees warmer but not enough to change the operating temperature of the engine.

 

^ right, from the radiator's point of view it would be like the difference between a warm day and a cold day. The thermostat would open a little more to allow more circulation through the radiator to maintain the proper coolant temperature. Consider that when you push the sport button, your coolant temp drops from about 215 to 180.

Having said all that, I recall reading somewhere of someone seeing overheating problems after a long track session with a larger intercooler -I don't recall which brand. Most of the larger intercoolers are the stepped design that only overlap part of the radiator so there is little impact on the overall radiator airflow, but the Tyrol covers a much larger area so it could be a concern.

I'll be trying out my new Wagner FMIC at the track next week and will be logging a bunch of data including intake temps, nothing like some real empirical data instead of handwaving.

 

Keep me posted I'd like to see that. Explain why the coolant is lower temp when the sport mode is on, that's interesting.

 

This isn't your dad's Buick with a fixed temperature thermostat. The thermostat is controlled by the ECU, when in sport mode the ECU opens the thermostat more.

 

That's awesome, I am just going to drive in sport mode all the time now

 

I don't like normal mode, it feels not very responsive. Sport Mode brings our Mini's to life!