[marconi118]

This topic has been beaten since many years but still no clear answer...

Going full catless (rid of secondary cats too) will lead to less torque at low rpm?
BuraQ thinks it is the case... but why?


135i guys swap their mids with N55 mids to get rid of the secondary cats...

Some aggressive N54 tuning will toast the secondary cats because of heat and flow.

My dilemma is now to go with a full N55 E92 exhaust without cats?

[idratherbesurfing]

Im catless n54 and made 446ftlbs with full catless exhaust and intakes. Thats a pretty good number i cant imagine it effects us too much

[brewnami]

I would like to see dyno results that support that claim. When I was modding S4's I'd see some folks run dumps on the dyno, aka no exhaust. Catless downpipes are a huge bump in power/torque so I don't know why removing the secondaries would then reverse those gains. There's a lot of theory going around in the tuning scene and I only buy into it if they produce dyno results to back up their claims. Unfortunately, there's a whole lot of missing dyno numbers these days.

[Milan]

Don't listen to Buraq. After the turbo the less restriction the better.

[JC335xi]

Originally Posted by Milan

Don't listen to Buraq. After the turbo the less restriction the better.

This. On a turbo car you want the lowest back pressure possible.

[Jeff@TopGearSolutions]

It's completely negligible. These cars make a boat load of torque. Go Catless and enjoy.

[shadow191]

On N/A cars, if you remove cats or go to too large of an exhaust or headers, you can lose low end torque. That's due to the loss of scavenging. But on a turbo car, there isn't any scavenging after the turbo. You simply want maximum flow so really you can't have too little restriction.

Even on N/A cars where scavenging applies, the secondary cats would be so far downstream that there would be no impact from removing them.

[BQTuning]

Originally Posted by marconi118

This topic has been beaten since many years but still no clear answer...

Going full catless (rid of secondary cats too) will lead to less torque at low rpm?
BuraQ thinks it is the case... but why?


135i guys swap their mids with N55 mids to get rid of the secondary cats...

Some aggressive N54 tuning will toast the secondary cats because of heat and flow.

My dilemma is now to go with a full N55 E92 exhaust without cats?

As to your question why my personal preference is contrary to the majority:

Its my personal experience, my research, my personal cars - 3 N54 cars, and I am one who does not jump on the same band wagon as everyone else cause someone else says so, or cause the elite says so (they have been proven wrong many times), which seems to be the trend around here. Ive always had the renegade attitude about following what others say.

Apple to apples testing: " Multiple 335is DCT cars with catless downpipes with or without deleted mids I have tuned beyond the whp of my model 335is but they still rubbed shy 30+ less wtq even the cars that were local had same identicle setup as me. The difference, I had highflow catts

So you will hear garbage like maybe they were not tuned right, but yet we BQ Tuning by WedgePerformance produce more torque than any other tuner on stock turbos / stock inlets 578 wtq on a 6AT catless DPs with mid cats. So I guess they werent tuned right either. Yet you can barely hear a hermit of a talk of someone else hitting these torque related numbers on a competely cattless exhaust system. Maybe its their tuning ?

Till this day no FBO + meth cattless N54 can break my speed trap record (stock turbos stock inlets) at our local track http://www.dragtimes.com/Palm-Beach-...e=500&carmake= which is a professional drag strip and not a hole in the wall junk strip

My latest slip is not posted on drag times but here it is https://lh3.googleusercontent.com/Og...=w1213-h683-no

and just an FYI my car was full weight with a half a tank of gass + a 260 lbs driver, me

I got plenty of cars runing with stock midcats on E60 fuel and the midcats are fine as their EGT dont get crazy stupid, btw.

To get to the nitty gritty the sound of an N54 most of the time on a completely catless exhaust is just horrifyingly awful unless your going to whip up something ie more money to spend, to get rid of the drone, and rasp sound. If you came from a ricer scene then you'll be right at home, but even said, my previous 240sx converted to a Silvia with a RB25 swap or my previous 3000GT VR4 didnt sound like a ricer as I hated that sound and they were always supplemented with highflow catts

Now the theory is less back pressure = more whp (agreed) but less emphasis on talk about wtq and this is where your research needs to be defined as people mix up whp and wtq with each other in these talks

If I was you, start with Professor Google https://www.google.com/?gws_rd=ssl#q...ressure+torque

Again, everything I said here is not based on theoretical views but based on my personal hands on experience, and R&D with other cars, the contrary views will fault the tuning side as it makes no "theorical" sense to them, but thats ok as I have results to back up my POV and they have nothing but theoritical talk.

Its all going to be a gamble either way, good luck. Go in the directly your pockets take you and learn from the errors if you make any.

[matthewo]

pervious owner of my car put vibrant resonators in the place of the stock secondary cats and it has catless dps and stock muffler and its very quiet and doesn't drone one bit. also high e85 mix smells just fine.

but you guys are right power wise for secondary cats is probably little to none, but its just one less thing to go wrong.

[marconi118]

Thanks for the answer BuraQ!

Indeed I am looking for max wTQ with stock turbos and improved inlets...


should I go with original secondaris or 200 cell metal cat?

The 200 cell should have less back pressure, so maybe less wTQ?

[BQTuning]

Originally Posted by marconi118

Thanks for the answer BuraQ!

Indeed I am looking for max wTQ with stock turbos and improved inlets...


should I go with original secondaris or 200 cell metal cat?

The 200 cell should have less back pressure, so maybe less wTQ?

IMO you will be more than fine with 200 cell upgraded secondaries and have good exhaust flow, and acceptable bottom end torque. You will need to talk with your tuner to get the best out of it though unless you know how to tune your own car

[boost junkie]

ETS dyno'd every bolt on step by step. You can make the decision for yourself:

http://www.extremeturbosystems.com/E...p-Dyno-Sheets/

[BigHoncho]

Originally Posted by BuraQ

As to your question why my personal preference is contrary to the majority:

Its my personal experience, my research, my personal cars - 3 N54 cars, and I am one who does not jump on the same band wagon as everyone else cause someone else says so, or cause the elite says so (they have been proven wrong many times), which seems to be the trend around here. Ive always had the renegade attitude about following what others say.

Apple to apples testing: " Multiple 335is DCT cars with catless downpipes with or without deleted mids I have tuned beyond the whp of my model 335is but they still rubbed shy 30+ less wtq even the cars that were local had same identicle setup as me. The difference, I had highflow catts

So you will hear garbage like maybe they were not tuned right, but yet we BQ Tuning by WedgePerformance produce more torque than any other tuner on stock turbos / stock inlets 578 wtq on a 6AT catless DPs with mid cats. So I guess they werent tuned right either. Yet you can barely hear a hermit of a talk of someone else hitting these torque related numbers on a competely cattless exhaust system. Maybe its their tuning ?

Till this day no FBO + meth cattless N54 can break my speed trap record (stock turbos stock inlets) at our local track http://www.dragtimes.com/Palm-Beach-...e=500&carmake= which is a professional drag strip and not a hole in the wall junk strip

My latest slip is not posted on drag times but here it is https://lh3.googleusercontent.com/Og...=w1213-h683-no

and just an FYI my car was full weight with a half a tank of gass + a 260 lbs driver, me

I got plenty of cars runing with stock midcats on E60 fuel and the midcats are fine as their EGT dont get crazy stupid, btw.

To get to the nitty gritty the sound of an N54 most of the time on a completely catless exhaust is just horrifyingly awful unless your going to whip up something ie more money to spend, to get rid of the drone, and rasp sound. If you came from a ricer scene then you'll be right at home, but even said, my previous 240sx converted to a Silvia with a RB25 swap or my previous 3000GT VR4 didnt sound like a ricer as I hated that sound and they were always supplemented with highflow catts

Now the theory is less back pressure = more whp (agreed) but less emphasis on talk about wtq and this is where your research needs to be defined as people mix up whp and wtq with each other in these talks

If I was you, start with Professor Google https://www.google.com/?gws_rd=ssl#q...ressure+torque

Again, everything I said here is not based on theoretical views but based on my personal hands on experience, and R&D with other cars, the contrary views will fault the tuning side as it makes no "theorical" sense to them, but thats ok as I have results to back up my POV and they have nothing but theoritical talk.

Its all going to be a gamble either way, good luck. Go in the directly your pockets take you and learn from the errors if you make any.

I appreciate your experiences and your feedback, I really do.

But I still think that the assumption is false... there ist simply no reason why less back-pressure should yield into less torque. So I think the solution is on the tune side. Maybe we will see some advances here in the future.

I myself also prefer 200cell secondaries for a couple of practical reasons (smell, smoke, drones).

[jippii ensio]

Originally Posted by boost junkie

ETS dyno'd every bolt on step by step. You can make the decision for yourself:

http://www.extremeturbosystems.com/E...p-Dyno-Sheets/

The tuning is different though for each setup and we do not know which parameters are taken into account by Procede autotuning and how exactly are they affecting the boost and ignition.

I'd like to see the difference with the tuning unchanged.

[Jaronbwall]

My logic: Every turbo racecar I've seen on TV or real life had the shortest exhaust possible, no cats and most times no mufflers.

[BQTuning]

I was waiting for someone to post a dyno. Here is my little experiment on a "load dyno" with a premature developed tune, flash only.

[cmg5461]

Originally Posted by BuraQ

Now the theory is less back pressure = more whp (agreed) but less emphasis on talk about wtq and this is where your research needs to be defined as people mix up whp and wtq with each other in these talks

Lol, bhp = btq/time, or bhp = btq * espd{rad/s}

You can't emphasize one without the other.

If you mean emphasize torque by focusing on increasing torque at low rpms (little power gain), that's controlled by volumetric efficiency. All you're doing is shifting the operating range of the engine. (or widening it with turbo cars)

Volumetric efficiency is unaffected after the turbo. The turbine blades muffle the pressure waves too much to make any use of scavenging. Even then, scavenging isn't the way to make power on turbo cars. The small benefits (energy efficiency and volumetric efficiency) and negligible compared to the gains of keeping hot, high pressure exhaust before the turbine blade and dumping it to the lowest restriction possible. Hence, you achieve a greater pressure ratio across the turbine blades. More torque is transferred through to the impeller, resulting is quicker spooling and charged air.




so.. generally, higher pressure ratios equal higher efficiency. Higher turbine efficiency = more energy to compress air = higher boost (if the tune allows) = more air in the cylinder = more fuel in the cylinder = higher pressure on the piston = more torque. (negating spark timing effects)

---

So why does your higher restriction catted exhaust give you an extra 30wtq?

At what engine speed is that extra 30wtq?

---

Oh, and 335is A vs 335is B is not apples to apples.

Apples to apples is using the same car. Get a stabilized baseline with the catted midpipes. Then compare a stabilized result with your catback removed.

Need I say to use the same calibrated dyno as well?

---

But who cares, you should be looking at area under your torque curve, not just torque or power. Aren't you the expert?

[Tiago@VRSF]

Our testing pointed towards more torque with catless downpipes, vs catted. It's the only reason we don't sell or recommend catted downpipes. Some catted aftermarket downpipes end up being as/more restrictive than the OEM's due to them using a smaller overall diameter for the cat in comparison to stock.

[csu87]

Originally Posted by BuraQ

I was waiting for someone to post a dyno. Here is my little experiment on a "load dyno" with a premature developed tune, flash only.

That Torque Spike.

Ive driven cars tuned like this. Ive even tuned cars like this, and its not my cup of tee. too much torque down low, not enough up high. Makes for a miserable drive. IMO

As far as losing torque by opening up the exhaust, this is only partly true. If the exhaust is too big on a turbo car, you will lose some low end torque. However, if the exhuast is sized properly, than removing any airflow restrictions will only improve performance.

Based on Buraq's experience, it may sugest that the exhaust system as a true dual full 3" may be too big of an exhaust for the stock turbos on the n54. Hence why the ETS dynos of a 2.5" exhaust showed improvements.

[Jeff@TopGearSolutions]

Originally Posted by cmg5461

Lol, bhp = btq/time, or bhp = btq * espd{rad/s}

You can't emphasize one without the other.

If you mean emphasize torque by focusing on increasing torque at low rpms (little power gain), that's controlled by volumetric efficiency. All you're doing is shifting the operating range of the engine. (or widening it with turbo cars)

Volumetric efficiency is unaffected after the turbo. The turbine blades muffle the pressure waves too much to make any use of scavenging. Even then, scavenging isn't the way to make power on turbo cars. The small benefits (energy efficiency and volumetric efficiency) and negligible compared to the gains of keeping hot, high pressure exhaust before the turbine blade and dumping it to the lowest restriction possible. Hence, you achieve a greater pressure ratio across the turbine blades. More torque is transferred through to the impeller, resulting is quicker spooling and charged air.




so.. generally, higher pressure ratios equal higher efficiency. Higher turbine efficiency = more energy to compress air = higher boost (if the tune allows) = more air in the cylinder = more fuel in the cylinder = higher pressure on the piston = more torque. (negating spark timing effects)

---

So why does your higher restriction catted exhaust give you an extra 30wtq?

At what engine speed is that extra 30wtq?

---

Oh, and 335is A vs 335is B is not apples to apples.

Apples to apples is using the same car. Get a stabilized baseline with the catted midpipes. Then compare a stabilized result with your catback removed.

Need I say to use the same calibrated dyno as well?

---

But who cares, you should be looking at area under your torque curve, not just torque or power. Aren't you the expert?

This post gets my vote.

[cmg5461]

Originally Posted by csu87

That Torque Spike.

Ive driven cars tuned like this. Ive even tuned cars like this, and its not my cup of tee. too much torque down low, not enough up high. Makes for a miserable drive. IMO

As far as losing torque by opening up the exhaust, this is only partly true. If the exhaust is too big on a turbo car, you will lose some low end torque. However, if the exhuast is sized properly, than removing any airflow restrictions will only improve performance.

Based on Buraq's experience, it may sugest that the exhaust system as a true dual full 3" may be too big of an exhaust for the stock turbos on the n54. Hence why the ETS dynos of a 2.5" exhaust showed improvements.

That exhaust sizing theory only applies to N/A engines. And also only applies to the headers. Typically, the exhaust is too long to make any benefit of the wave reflections after the headers. Turbo exhausts already have a huge, muffling restriction in them. The turbine. Upstream is not effected by downstream of the turbo.

An easier way to visualize this is the intake on a supercharger. The air before and after a positive displacement compressor are completely separated. Air after the supercharger has zero effect on the air before the supercharger. The turbine works the same way, except it dampens the pressure wave trying to make its way back through the turbine. The effect of that pressure wave is negligible on volumetric efficiency.

[csu87]

Originally Posted by cmg5461

That exhaust sizing theory only applies to N/A engines. Turbo exhausts already have a huge, muffling restriction in them. The turbine. Upstream is not effected by downstream of the turbo.

An easier way to visualize this is the intake on a supercharger. The air before and after a positive displacement compressor and completely separated. Air after the supercharger has zero effect on the air before the supercharger. The turbine works the same way, except it dampens the pressure wave trying to make its way back through the turbine. The effect of that pressure wave is negligible on volumetric efficiency.

put a 4" dp and exhaust off your turbo and let me know how it works. It will affect the flow characteristics of the turbo.