[Tim07e90]

Originally Posted by TheAxiom

What's missing from this is OPs goals. What do you want from your car?

This is true. OP what are looking for? Sound or performance?

[superduty]

Originally Posted by justpete

To feel an increase in horsepower it's generally agreed the increase needs to be on the order of ten percent and no catback on earth will produce ~20rwhp.

There are two issues with this statement

1) It's a generalization. Generalizations imply absolutes. There are no such thing as absolutes.

2) More importantly, horsepower isn't everything. I could give a rat's ass about horsepower. For a street car, torque is far more relevant and important. Torque is king. Given a hypothetical engine with constant torque and variable horsepower I agree that somewhere around a 10% gain is probably what is needed for the driver to notice an improvement because speed is more difficult to gauge. Given another hypothetical engine with constant horsepower and variable torque, the amount of gain in torque before the driver can detect an improvement is going to be less. The reason is simple. Torque is what pushes you back the seat, snaps your head back, and allows wheel slip to occur. In the case of the cat back systems available for our cars, the more popular ones, PE, Flowmaster, Borla, etc. are all just variations of the OEM configuration. As a result the expectation is these systems will not provide any detectable performance gain leading to the myth perpetrated on this forum to "just buy a cat back for the sound cause there are no gains possible". The SS system, on the other hand, takes a different design approach by including elements to produce larger gains not possible within the confines of the stock or stock like system. I don't need dyno runs and timeslips to reach this conclusion, all I need to do is to evaluate the design. No placebo here.

[justpete]

Originally Posted by superduty

There are two issues with this statement

1) It's a generalization. Generalizations imply absolutes. There are no such thing as absolutes.

2) More importantly, horsepower isn't everything. I could give a rat's ass about horsepower. For a street car, torque is far more relevant and important. Torque is king. Given a hypothetical engine with constant torque and variable horsepower I agree that somewhere around a 10% gain is probably what is needed for the driver to notice an improvement because speed is more difficult to gauge. Given another hypothetical engine with constant horsepower and variable torque, the amount of gain in torque before the driver can detect an improvement is going to be less. The reason is simple. Torque is what pushes you back the seat, snaps your head back, and allows wheel slip to occur. In the case of the cat back systems available for our cars, the more popular ones, PE, Flowmaster, Borla, etc. are all just variations of the OEM configuration. As a result the expectation is these systems will not provide any detectable performance gain leading to the myth perpetrated on this forum to "just buy a cat back for the sound cause there are no gains possible". The SS system, on the other hand, takes a different design approach by including elements to produce larger gains not possible within the confines of the stock or stock like system. I don't need dyno runs and timeslips to reach this conclusion, all I need to do is to evaluate the design. No placebo here.

1. No, it's not.

2. Bullshit

[hassmaschine]

Originally Posted by superduty

There are two issues with this statement

1) It's a generalization. Generalizations imply absolutes. There are no such thing as absolutes.

2) More importantly, horsepower isn't everything. I could give a rat's ass about horsepower. For a street car, torque is far more relevant and important. Torque is king. Given a hypothetical engine with constant torque and variable horsepower I agree that somewhere around a 10% gain is probably what is needed for the driver to notice an improvement because speed is more difficult to gauge. Given another hypothetical engine with constant horsepower and variable torque, the amount of gain in torque before the driver can detect an improvement is going to be less. The reason is simple. Torque is what pushes you back the seat, snaps your head back, and allows wheel slip to occur. In the case of the cat back systems available for our cars, the more popular ones, PE, Flowmaster, Borla, etc. are all just variations of the OEM configuration. As a result the expectation is these systems will not provide any detectable performance gain leading to the myth perpetrated on this forum to "just buy a cat back for the sound cause there are no gains possible". The SS system, on the other hand, takes a different design approach by including elements to produce larger gains not possible within the confines of the stock or stock like system. I don't need dyno runs and timeslips to reach this conclusion, all I need to do is to evaluate the design. No placebo here.

uhm.. how do you think you make more horsepower? HP = (TQ * RPM) / 5252. OK so HP is a bad example because the formula is more complicated than it needs to be (KW & NM would be better), but if you break it down, torque is just the force, HP is how much work the engine can do with that force.

You can't increase torque without increasing HP - although you can increase HP by increasing RPM and using that torque to do more work in a shorter amount of time, typically you won't significantly increase power either without an increase in torque. They are linked together, not separate entities.

yeah, maybe it did gain 4whp - but it's not going to transform how the car drives like limited slip does. Mostly it just makes the car loud.

When you say you care about TQ, not HP, that's basically bullshit forum talk right there. The easiest way to increase torque to the wheels would be to put in a limited slip differential with a shorter gear ratio - 25% increase is easy. Way more than a loud exhaust could ever hope to make.

[justpete]

Yeah, power is the scalar result of the dot product (well, that's redundant...) of the torque and angular velocity vectors. Doesn't get much simpler than that. So that's torque times rpm times a scaling constant equals horsepower.

[Taskmaster]

I'll say I have a awesome butt dyno.

[Tom Droze]

Originally Posted by TheAxiom

I'll say I have a awesome butt dyno.

No buts about that!

[DUI Elite]

To be honest, I'm going to end up doing both - I just like to space out the mods. I've had the car since birth and it didn't get to its current state over night so I don't mind patiently adding on to it. I have an X3 I can daily as well, so downtime isn't part of the issue.

The only thing that drives me a little insane is that my car basically sounds stock but isn't. Sound is part of the enjoyment of a "fun" drivers car.

I've tracked the car on road course 3x and have pretty much always found the power and brakes to be the limiting factors on E9X. As a related note, I'll likely try out E46 M3 race pads this year since they do fit on our calipers (source: bimmerworld). The last time I tracked was 2011 and the car was nearly stock by today's comparison but it was fun, no less.

As far as goals, I expect to do 3-4 events per year in HPDE (if that). I am not personally a fan of autocross, but will admit it is still a fun time. It is definitely intended to be my weekend "fun car" due mainly to the fact the (high number of) wear items on these non-M's is so much more reasonably priced than some M equivalents. Doing the same stuff with an E90 M3 is worthwhile I'm sure, but is easily double if not triple the cost.

Weekend use will also include fairly frequent street use.

[MFactory]

If you want performance, LSD (but I would say that )

If you want sound (at any speed), exhaust. This you do get tired of, and end up cranking up the stereo (which is futile in my case as my exhaust is louder than my stereo)

If you want the best of both worlds, LSD + shorter ratio ring & pinion. You get the extra traction from the LSD, the extra torque to the wheels due to torque multiplication, and a louder exhaust due to higher rpm's

[klick]

I will be another person who puts the vote in for the LSD. MFactory is awesome by the way. When I dealt with them last year for my LSD they took care of me very well and their warranty is very trustworthy as they will straight up replace the unit if it is defective in anyway.

Driving with it for almost a year now, I can truly say that it has made the car much more fun to drive, while making it quicker. I have to watch my speeds through turns as I accelerate without much traction loss. Since it is a helical as well, you will not need to worry about maintenance (other than replacing the diff oil 1000 miles in), which is a huge plus.

As far as exhaust goes, you seem to want to change the tone. So my recommendation for you would be to get an LSD and a muffler delete. The N52 with a muffler delete has a surprisingly nice tone to it. Definitely can get you through until you can save up for the SS exhaust if you are really set on it.

[Rob43]

OP, one of the most important things to consider when choosing a LSD is:

Whether you want/need a Helical type LSD or Clutch type LSD. Both absolutely have their pros & cons, as the owner of both types I'd tell you to Really research what one will best fit your goals.



Rob43

[Taskmaster]

Originally Posted by Rob43

OP, one of the most important things to consider when choosing a LSD is:

Whether you want/need a Helical type LSD or Clutch type LSD. Both absolutely have their pros & cons, as the owner of both types I'd tell you to Really research what one will best fit your goals.



Rob43

Go on...

[Rob43]

^

My experiences have been this:

Helical (Gear) diffs are great as DD's because they do the job you want them to & are virtually maintenance free. My Quaife LSD is completely silent which is great for typical high performance street driving, but the moment I take it to the track I can get the inner (unloaded) wheel to spin at the apex of a turn. This of course Doesn't promote faster lap times, so for this reason Helical LSD's are only a "Fair" choice as a track diff.

Clutch diffs are great for dedicated competition, companies like Diffsonline can setup the exact custom clutch type LSD for the chassis & type of competition that the car will be driven in. These types of diffs are typically the fastest on a Road Course or Auto-X Course because they won't spin the inner (Unloaded) wheel at the apex of a turn. The down side to driving a clutch type LSD on the street is they're usually noisier, require more maintenance like oil changes, & have the tenancy to feel like a locked (Welded) diff while trying to park the car.


Helical = Street

Clutch = Track



Rob43

[Kgolf31]

Originally Posted by Rob43

^

My experiences have been this:

Helical (Gear) diffs are great as DD's because they do the job you want them to & are virtually maintenance free. My Quaife LSD is completely silent which is great for typical high performance street driving, but the moment I take it to the track I can get the inner (unloaded) wheel to spin at the apex of a turn. This of course Doesn't promote faster lap times, so for this reason Helical LSD's are only a "Fair" choice as a track diff.

Clutch diffs are great for dedicated competition, companies like Diffsonline can setup the exact custom clutch type LSD for the chassis & type of competition that the car will be driven in. These types of diffs are typically the fastest on a Road Course or Auto-X Course because they won't spin the inner (Unloaded) wheel at the apex of a turn. The down side to driving a clutch type LSD on the street is they're usually noisier, require more maintenance like oil changes, & have the tenancy to feel like a locked (Welded) diff while trying to park the car.


Helical = Street

Clutch = Track



Rob43

Also, one of the big differences as well.

Helical gears cannot lock under deceleration, clutch diffs have static lock, and ramp angles that can create lock under deceleration, which aid in rear stability under hard braking.

And yes, clutch diffs are noisy, you get a very distinct gear whine with stiffer bushings.

[Rob43]

Originally Posted by Kgolf31

Also, one of the big differences as well.

Helical gears cannot lock under deceleration, clutch diffs have static lock, and ramp angles that can create lock under deceleration, which aid in rear stability under hard braking.

And yes, clutch diffs are noisy, you get a very distinct gear whine with stiffer bushings.

Absolutely.



Rob43

[Bimmer-Bob]

Originally Posted by Rob43

...Helical (Gear) diffs are great as DD's because they do the job you want them to & are virtually maintenance free...The down side to driving a clutch type LSD on the street is they're usually noisier, require more maintenance like oil changes, & have the tenancy to feel like a locked (Welded) diff while trying to park the car.


Helical = Street

Clutch = Track

I feel like the maintenance requirements of a clutch-type LSd are overblown on forums. I mean, what's the big deal? I'm about to do a break-in change of gear oil (after initial 300-500 miles) and then plan to do subsequent gear oil changes annually (although my builder said at least every two years, I don't plan on pushing it that long). It's hardly an onerous amount of maintenance. Do helicals never require fluid changes?

I guess technically by design clutches do wear, so there must be some rebuild interval, but from what I understand, for a mostly street-driven car even a clutch-type diff can be expected to last the effective life of the car. Anyway, most people who keep a car like this for 8-10 years and beyond expect to put some money into preventive maintenance. If I can get 5 years before a rebuild I'll be happy (about 8,000 miles/year w/ 10-12 AX events - I understand that regular tracking would be much more demanding).

Originally Posted by Kgolf31

Also, one of the big differences as well.

Helical gears cannot lock under deceleration, clutch diffs have static lock, and ramp angles that can create lock under deceleration, which aid in rear stability under hard braking.

And yes, clutch diffs are noisy, you get a very distinct gear whine with stiffer bushings.

I was going to say one of the major benefits of a clutched diff is static lock and the ability to specify custom ramp angles. Really, the whole set up is customizable, i.e., the amount of static lock, the rate of dynamic lock, symmetrical vs asymmetrical ramp angles.

I don't really get the noise thing, but my diff is brand new. From what I understand a noisy diff can be quieted down by either choosing a different fluid or by adding additional friction modifier to your current fluid. My builder specified Red Line 85W-140 (includes FM) and I have yet to hear a peep from the rear end. Bear in mind I haven't autocrossed with it yet, although I have felt it working on the street with aggressive cornering (40% static lock & 30/60 ramps).

[hassmaschine]

BMWs came stock with clutch type LSDs for decades until cost cutting measures came into place. They were awesome. I don't think the maintenance is that much of an issue. I've never heard one make noise either - I suppose if you get a high lockup race build, then it could chatter a bit around corners, but the stock LSDs on older BMWs were quiet.

[Bimmer-Bob]

Originally Posted by hassmaschine

I suppose if you get a high lockup race build, then it could chatter a bit around corners, but the stock LSDs on older BMWs were quiet.

For reference, these were historically 25% static lock with 45/45 ramp angles.

[hassmaschine]

Yeah, they weren't super high lock, but good enough for hooning around in.