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07-30-2013, 02:22 PM | #23 |
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One thing I noticed on the X5 is it uses 55 mm down pipes going in to a 75 mm exhaust pipe (and different exhaust manifolds). The 128i has a 65 mm exhaust pipe and since there are no clamps for it in Realoem, as yet unmeasured by me down pipes. The larger exhaust may be part of the puzzle.
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07-30-2013, 02:49 PM | #24 | |
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07-30-2013, 03:24 PM | #25 |
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This thread=
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07-30-2013, 03:32 PM | #26 |
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The 3.0si on has 315 Nm/232 lb-ft.
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07-30-2013, 04:44 PM | #27 |
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Exactly, more torque. I suspect it is mainly in DISA and tuning. Evolve certainly added torque to my powerband.
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07-30-2013, 09:28 PM | #28 | |
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Good exhaust scavenging improves low end torque (thus power). You achieve good scavenging by maintaining high exhaust velocity near the valves (i.e. narrow headers). Somewhere along the line, someone associated narrow headers with backpressure. Completely false. Backpressure is NEVER a good thing. And an open exhaust further down the line is always going to help torque production (and thus power production), throughout the rev range. The backpressure myth has been debunked left and right. Please don't continue to propagate it. Backpressure is bad. Always. Efficient exhaust gas scavenging is good. Always. Last edited by PrematureApex; 07-30-2013 at 09:41 PM.. |
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07-30-2013, 09:40 PM | #29 | |
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You cannot increase torque, and not increase power, or vice versa, for any given RPM. |
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07-30-2013, 10:39 PM | #30 | |
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You will certainly gain power and torque with a larger pipe(ie the Bimmerworld E46 M3 3.5" race pipe), but it comes at the expense of low end torque. The power is moved and enhanced in the upper RPM ranges, and completely destroys what is the irrelevant(in track terms) low end. Such pipes are great for lap times and terrible for daily driving. Who said they didn't increase the HP as well? Are you trying to pointlessly pick a fight in what should be a constructive thread?
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07-31-2013, 07:30 AM | #32 | ||
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If the larger OE system maintains sufficient velocity, while decreasing back pressure, it could easily make MORE power all over the rev range, including low RPM. Simply because the diameter is bigger, does not mean you'll lose low-end. I'm assuming that you're making this assumption because you're equating exhaust diameter to backpressure, thereby perpetuating the complete fallacy that "backpressure is needed to make low end power": Quote:
C/N: There could easily be some more diameter to give in the smaller OE setup to decrease back pressure before velocity falls to detrimental levels. You have no evidence to support that the larger OE setup in question sacrifices anything, anywhere in the rev range. Last edited by PrematureApex; 07-31-2013 at 07:56 AM.. |
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07-31-2013, 08:05 AM | #33 |
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Once again, you are reading too far into what I said. Never once did I say back pressure increased torque.
If pipe diameter was a problem with our exhaust, the R&D side of the aftermarket would be there to fix it. Instead the power in our exhaust track in found in the headers(by deleting primary cats and creating equal length piping), deleting secondary cats(for a much reduced power gain compared to primaries), and smoothing out the bends in the mid pipes(almost no power to be gained). Any assumptions about other factory exhaust components are just that, assumptions. Attempting to use them or incorporate them by the average joe is just as likely to lose power as gain power.
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07-31-2013, 08:15 AM | #34 |
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So the Ferrari Formula 1 team has had it wrong all these years. They just needed an 8 inch exhaust pipe and wham more power no ill effects.
By restricting air you can restrict horsepower but torque can still be slightly improved. WRC cars had air limiters pre turbos. Some were 300hp and over 400 lb/ft of torque.
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07-31-2013, 11:36 AM | #35 |
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Back on topic: 128i dynos now-!
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07-31-2013, 05:15 PM | #37 | |
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You were the one making the assumption without any support. That the larger OE exhaust would cost low end power. I simply stated that certainly isn't necessarily the case. Post cat diameters hardly affect anything anyway. |
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07-31-2013, 05:21 PM | #38 | |
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What you're seeing there is the effect of a restrictor. The engines breathes well enough at low RPM, but loses it's ability to move enough air in the higher RPMs. Thus, it makes comparatively more low RPM power vs. high end, than it would sans restrictor. You haven't improved low end torque (i.e. improved low end power), as you state, you've merely choked the engine from making high end power (i.e. high end torque). Still funny to see people who don't understand the relationship between power, torque, and RPM. Everyone hell bent on calling low end power "torque" and high end power, power. Pick one! It's all power people. Power is a function of torque and RPM, nothing more. Last edited by PrematureApex; 08-01-2013 at 06:58 AM.. |
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08-01-2013, 08:02 AM | #39 |
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I was highlighting the possibility of a negative outcome. Randomly swapping 135i exhaust bits is common enough that I was attempting to head this off before it became a norm.
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08-01-2013, 08:46 AM | #40 |
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The flow of exhaust gas is one of the many things that is not so simple as to be resolved to one number like back pressure. Some headers are designed, for instance, to have the flow from one cylinder create a slight backpressure on the other exhaust port joined to it through the header due to the flow. If you want the momentum of the flowing gas to work this way you must be careful about the diameter of the pipe to keep the velocity up. I mention this to say that I am very confident that at best increasing exhaust pipe diameter is a "diminishing returns" situation where some improvement from a small increase is probable but each additional increase in diameter will provide less benefit. It is also possible the effect will be negative if there is some scavenging going on due to flow velocity. I doubt it this far from the exhaust port but it's difficult to be sure with no tests or mathmatical models of the engine with exhaust. If it was my money being spent to try, I would do what STIG did and put the headers on first, then possibly go to slightly larger pipe with smoother bends possibly with a muffler with less pressure drop. When I say small, I think a 1/4 inch increase in diameter is about as much as I would try. You also have to remember that the flow area is a function of the radius squared. So it doesn't take a large diameter increase to meaningfully change flow area and thus back pressure. The benefit is likely to occur (or be measurable) only at high rpm when the engine is flowing the maximum amount of air+fuel.
The intake is an example of what I am talking about. If it was just a flow restriction sort of thing you'd want a huge venturi going into the engine without any piping. Instead, we have piping of varying length depending on the rpm range. Using this approach gives multiple torque peaks over the rpm range. That happens because the different length piping is keeping the velocity of the air/fuel mixture up increasing flow. It's just not as simple as increasing flow area = more power. Since the highest output n52 has ~3 inch exhaust piping versus our ~2.5inch, maybe a 0.5 inch increase would make sense. To be sure, we'd have to try it both ways. Jim
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08-03-2013, 05:49 PM | #42 | ||
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Generally speaking, when discussing cars, "increasing torque" means increasing low end power whereas "increasing horse power" refers to the top end. Yes, both really refer to the thing as horsepower is torque X rpm/constant, but... try to chill out a little and have a discussion.
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