My search for more NA power (Dyno time)

Originally Posted by Iceman00

The problem is the Y pipe, period. There is no loss in power going to larger and larger pipe after the merfer. The merger must expand too fast, causing the exhaust gases to cool and slow down, which is why there is a loss of low end power. I've pointed this out before.

The Single 3" pipe has just a bit more surface area than dual 2" pipes, and when the merger is designed correctly, there should be no loss in power. Period.


From Bimmerworlds graph, I don't see a loss in power, but I do see a dyno run that was started later than the inital baseline, which causes a huge dip at the begining as the engine revs under load.

First, let's make things clear. I claim 3" pipe is a definitive overkill in case of AggieE46's engine. If it was my engine, I would definitely use 2,5". Has Hoveringuy lost torque by going 2,5”? Corky Bell claims in his book "Maximum boost" that the flow through a 2,5" pipe is sufficient upto 500hp and 3" is rated to 700hp.

Next thing, Iceman00, your statement is :The Single 3" pipe has just a bit more surface area than dual 2" pipes, and when the merger is designed correctly, there should be no loss in power. Period.
Could you than explain me why header designers for our cars, when they merge 3 pipes into 1, don't use your logic, and the surface area of the pipe after merge =/= 3 x surface area of pipe before merge? Well, I can tell you why. That's because exhuast is not as simple as 2 + 2. And it can't be well designed just with a use of intuition.
An example? Sure, let’s take headers for euro s50b32. Pipes before merge are 1,8” and the pipe after is 2,4”. That gives us a diameter ratio of 1,33 (note we merge 3 into one, NOT 2) and surface area ratio of 0,6 (far from 1:1). Do you think they made mistake? If so, give them a call, they should know … at the end, we all want our bimmers to be as good as possible, right?
Now something about placing Y joint. For me, there is only one reason why the Y joint is so far in both HKS and 323 designs. And it’s simple. It’s because they are designed to pass emission tests, which mean a use of two catalyctic converters (again, as Hoveringuy demonstrated, one is not enough).
If an Y joint close to the headers is bad, why than hoveringuy’s and partially bimmerworld’s systems seem to work?
And for the end, as it goes about bimmerworld’s graph. I agree, you can’t exactly say, when the dyno operator pushed the pedal to the metal, but I’m pretty sure, that if their design was beneficial in the whole rpm range, they wouldn’t forget to tell us about it.

Sorry about my cheapo y-pipe. I didn't put much effort into that part since I live in California and I'm stuck with using stock headers so no matter what I get pretty crappy exhaust flow. Also I remember looking at that Burns Stainless y-pipe and then crying when I saw the price...

...so I just tried copying them.

Originally Posted by TiAgTouring

Any idea of weight savings over stock exhaust? Im about to install a ZHP exhaust and am wondering if its gonna be way heavy...(currently Ive got a stock 323 exhaust)

dual 0.065" wall, 2" diameter is 2.68 pounds per foot
single 0.065" wall, 3" diameter is 2.04 pounds per foot

Roughly around 24% lighter per foot for roughly the same cross sectional area.

Brady's exhaust is significantly lighter than a 70 pound ZHP exhaust.

Originally Posted by Iceman00

The problem is the Y pipe, period. There is no loss in power going to larger and larger pipe after the merfer. The merger must expand too fast, causing the exhaust gases to cool and slow down, which is why there is a loss of low end power. I've pointed this out before.

The Single 3" pipe has just a bit more surface area than dual 2" pipes, and when the merger is designed correctly, there should be no loss in power. Period.

Single 3" pipe has quite a bit less surface area than two 2" pipes though...

single 3": 2*pi*(radius)=2*3.14*1.5in=9.42in
dual 2": 2*2*pi*(radius)=2*2*3.14*1in=12.57in

3" -> 1,5" * 1,5" x 3,14 = 7,065
2 x 2" -> 1" x 1" x 3,14 x 2 = 6,28

oh, he means cross sectional area, lol. You can't really say surface area with out a surface. I thought was was talking about actual surface area of the pipe, because that kinda came into my equation when trying to figure out a y-pipe design.

I don't think the hks system uses cats i think those are resonators. The 323 has the cats in the stock headers. I'm not saying the design of the oem y pipe on a 323 is the best design. I do think the placement of the y pipe in the exhaust system was put there for a reason. The y pipe location has nothing to do with emissions. Just my .02 cents

This is what we have in europe: (323 exhaust)

European versions don't have cat'ed headers and they also run Y pipe like US.
What is the relation between y pipe and emissions -> if you place your Y farther, you can run cats parallel, which is the only way to make them work efficiently. They need a proper temperature (HOT!). Now if you place Y pipe closer to headers, you have to run one cat behind the other. Second one won't work as good as it could.

interesting... I think we all agree the y pipe needs to be moved back

Originally Posted by beemka

This is what we have in europe: (323 exhaust)

European versions don't have cat'ed headers and they also run Y pipe like US.
What is the relation between y pipe and emissions -> if you place your Y farther, you can run cats parallel, which is the only way to make them work efficiently. They need a proper temperature (HOT!). Now if you place Y pipe closer to headers, you have to run one cat behind the other. Second one won't work as good as it could.

This doesn't apply to M54 cars, and US cars in general. The Cats are in the headers, and there is no crossover/merger, just two single pipes.

Originally Posted by Iceman00

This doesn't apply to M54 cars, and US cars in general. The Cats are in the headers, and there is no crossover/merger, just two single pipes.

false. Before the facelift happened on Sedans, all E46's ran dual headers to a y-pipe to single.

Originally Posted by xixixi

interesting... I think we all agree the y pipe needs to be moved back

I don't.

My reasoning being that the proper positioning of the first set of collectors and the second set of collectors is probably going to be determined based on some physics that optimizes the exhaust to suit the needs of the engine. Measurements like "around the driveshaft" are probably not going to work when the only gains at this point are going to come from very careful engineering.

It'd probably be more worthwhile to figure things out before chopping up that exhaust which was so laboriously fitted and welded together.

Are you arguing OEM header mergers? You are aware that even factory BMW exhaust don't use a merger after the headers of ANY sort, at least not the E46 M54. In fact, only the S54 uses a merger (H pipe).

Secondly, you can't use larger diameter pipes right off the exhaust ports...well you can, but I wouldn't recommend it. Smaller primaries and collectors allow for more exhaust velocity, using a lager diameter tube would surely compromise power some place. Ask Supersprint, which is why the developed a Stepped header design (smaller diameter pipes off the exhaust ports, that gradually 'step' into larger primaries, then a collector) to produce a broader torque curve without sacrificing to much top end power, like smaller primary pipes would.

Third: piping after the collector doesn’t matter.
http://my350z.com/forum/7412469-post2.html

For any system "Y-back" you can't have too large of tubing. There is no compromise of TQ by going larger and larger. With one exception, the only thing a Y-back can do is "potentially" reduce HP if there is excessive back pressure. The one exception would be a diffuser or megaphone which can reduce pressure drop below that of an open pipe.

TQ is determined by the diameter of tubing upstream of the end of the Y-pipe. So in other words, TQ is determined by the Y-pipe primary diameters and a few inches past the merge collector.


Anyhow, Active Auto's 3" race exhaust has the cross over in what would be after the factory cats

The S52B32 is closely related to the M54B30, sharing crank and stroke.

Originally Posted by firefirefire90

false. Before the facelift happened on Sedans, all E46's ran dual headers to a y-pipe to single.

So you've seen an M54 with a dual to single? According to realoem, even the earliest M54 runs dual pipes from the manifold back.

Originally Posted by firefirefire90

false. Before the facelift happened on Sedans, all E46's ran dual headers to a y-pipe to single.

? what ? my 01 330 doesn't have a y pipe. it's dual all the way back oem. The 323's have a y pipe, I'm not sure about the 325's. Iceman, I don't really like that graph. That m3 has top side mods to be rapping out to 7500. I'd rather see their exhaust on a bone stock car/bolt on car. Either way good info here.

Originally Posted by xixixi

? what ? my 01 330 doesn't have a y pipe. it's dual all the way back oem. The 323's have a y pipe, I'm not sure about the 325's. Iceman, I don't really like that graph. That m3 has top side mods to be rapping out to 7500. I'd rather see their exhaust on a bone stock car/bolt on car. Either way good info here.

No, the graph has rpm listed at 7500rpm. The car more than likely has a software reflash (based on the 7200rpm redline where they let off, and the power figures)
I wouldn't rev an S52 up there for long.

Originally Posted by beemka

And it’s simple. It’s because they are designed to pass emission tests, which mean a use of two catalyctic converters (again, as Hoveringuy demonstrated, one is not enough).

I am also learning that one cat gets hot as a mofo.

Originally Posted by Iceman00

No, the graph has rpm listed at 7500rpm. The car more than likely has a software reflash (based on the 7200rpm redline where they let off, and the power figures)
I wouldn't rev an S52 up there for long.

Originally Posted by aggieE46

For reference, here's a better shot of the current Y.

What I'd like to change if it was mine is the two 90 degree bends and they are real close to each other. 90's slow the flow. the oem exhaust shows 45's.

but on the other hand the increase in size may make up for it?

didnt you increase the throttle body as well, or did you dyno with the other exhaust sorry i missed it

Piping after the collector doesn't matter.

Keep it coming.