45 replies to this topic

[Jimbo]

3" on a H6?

[Josh.]

 

 

3" will just make a lot of noise.

[Root Beer]

Money still stands

[crjohnson]

Hey rootbeer i'm interested to know more of what you know about exhaust systems. My understanding is that it is all about the exhaust gas speed, keep it as high as possible to get the most inertia/pressure wave effects and that backpressure is a MYTH and does nothing but bad for an engines performance.

When people say "don't go too big in pipe diameter else you'll lose backpressure" - whats actually happened is that the bigger pipe slows down the gas speed and loses the pressure waves or inertia effects.

 

Not terribly relevant here as Deltiod is using stock headers, but (from what I have learnt), header design (4-into-1), is all about runner lengths that make the negative pressure wave reach the back of an exhaust valve at the point of valve overlap. This helps draw exhaust gas out and intake charge in, all at a particular RPM relative to runner length, gas temp etc.  4-2-1 headers are obviously different and I haven't been able learn much about their design yet (teach me??), unless its as simple as multiple wave frequencies due to the primary and secondary pipes lengths? Also I know there is much more gains in the design of the collector, lengths, angles, expanding cones etc, all able to be tuned to particular engine combos (cams, intakes, heads...)

 

Also what I am yet to learn (and interested in your thoughts) is how much the pipe after the merge collector benefits/restricts engines. Has the exhaust system (from say 100mm after the collector?) done all it can to draw exhaust gasses out and charge in (and this is why you are suggesting a 3" pipe and 1 or no mufflers? ie, no restrictions) or is there more to it? From my understanding there IS some point where the pipe stops helping and starts hurting performance.

 

I still believe 3" is overkill for a standard street engine/car (running a standard manifold), UNLESS the whole point of changing the exhaust is to squeeze every miliwatt of power. Whereas all deltoid wants is a "sports sounding h6 such as a BMW or porche sound, not a fully sick commo".

 

Anyway, I'm still keen to learn if you have "been there and done that", hope none of this comes off the wrong way or offends you..

[Jimbo]

You pretty much answered your own questions but it depends purely on the application, really.

To put it in a nutshell on an N/A you have to find the blend between velocity vs. back-pressure at the ideal rpm range where you make the most power, if you were chasing the last strand of power and efficiency out of your exhaust system. This is pretty extreme for a street car and your average enthusiast, who just wants some noise, and to not spend $1000's on exhuast R&D. It's usually best to go for what's tried and true.

A lower diameter exhaust will give a higher velocity of exhaust gasses with more back-pressure where a larger diameter will flow better with less restriction at the expense of exhaust gas speed.

On a turbocharged car, it makes a negligible difference as you want no back-pressure at all, once the exhaust has left your turbo. You start making a difference when you play with the exhaust pre-turbo, however, ideally this is where you want velocity in the system to spool up the turbo as fast as possible.

Cam knows his shit with the H6, nuff said.
 

[Root Beer]

First thing's first i'm the realest.
Second of all I have never owned a NA Subaru nor will I ever.

But I have messed around with a few 6 cylinders with similar capacity's, some with massively inferior head designs, some with better. Now, it is pretty hard to compare so many different motors, but when you take a step back and stop being elitist novices, you can see that the days of a 2.25" exhaust on na being the biggest you will need are over.

As I said I'm willing to bet all costs that 3" will make more power from my other all motor encounters.

3" is over kill for a 50 year old enthusiast who just wants a little more grunt. For any other sane person 3 " is the sweet spot. Fortunately exhaust design can be simple and doesn't need crazy bends and turns. And after 1m from the collector I doesn't really matter.

Collector 'design' is pretty important as you want as smooth transition from runners to one path of flow as possible. When I say design however its pretty basic, just size.

There's pages and pages we could post on all of this, but until one of you step up its pointless.

Look at some vw bugs who run 4.5" megaphone exhausts and such.

[Morgan]

Cool so you're forcing advice on someone with no actual real-world knowedge.

[Liberty]

As I said I'm willing to bet all costs that 3" will make more power from my other all motor encounters.

3" is over kill for a 50 year old enthusiast who just wants a little more grunt. For any other sane person 3 " is the sweet spot. Fortunately exhaust design can be simple and doesn't need crazy bends and turns. And after 1m from the collector I doesn't really matter.

There's pages and pages we could post on all of this, but until one of you step up its pointless.

Are you talking about sound alone, or power and sound?

You're willing to bet all costs? Sweet. Pay for it and I'll do it to my wagon and see whether everything you're stating is correct.

Otherwise, without evidence, you are making some big claims. I've spoken to various exhaust shops and they've all said that three inches is way too big for my car. You mentioned that someone should step up, well unfortunately money doesn't grow on trees and no one is going to put money towards something that one person claims is the "sweet spot" and has no full-proof evidence of it even being successful.

My two cents.

[Niko]

I just deleted all exhaust on my car and run it straight ATMO, because back pressure kills the killawasps.

 

Also funny to find a bunch of guys on the internet arguing over inches.....

 

My contribution to this thread,and to Deltoid, is that Gary (Liberty) is looking at getting rid of his CAI, if you're interested in that sort of thing.

 

RX25SE just installed Raptor headers on his H6, think he put pics in the General Thread, check it out.

[RX25SE]

3" may well produce the largest power numbers, but if it drops mid range torque is it really worth it for a street car?

 

Without a couple of different diameter systems, tuner, test car and a dyno; I guess we'll just never know.

[Shiv]

Jase would you be able to tell me how much the Raptor headers sit lower than the stock headers? Is there much in it? 

 

I'm considering them but don't want to lose much/if any ground clearance. 

[RX25SE]

PMed you Shiv.

[skillionaire]

Hi,

 

 

First thing's first i'm the realest.
 

 

/thread.

 

Cheers,

Nik

[nickknack]

I guess you could say your exhaust design is... fancy

[RX25SE]

Guys,

 

The OP is interested in information regarding intake and exhaust for a 30RB.

 

Cheers.

[Barbbachello]

He's my mate IRL. Got his exhaust done today haha. Not sure on details but hes after an CAI still as recommended by his tuner. Dont know who that is though

[Niko]

He's my mate IRL. Got his exhaust done today haha. Not sure on details but hes after an CAI still as recommended by his tuner. Dont know who that is though

 

I say again..... Gary's Weapon R.

[Barbbachello]

 

I say again..... Gary's Weapon R.

Ive passed it on to him

[Liberty]

I was just about to say. I'm not 100% on whether I want to remove it but I'm more so leaning towards that way. Here's the topic man:

 

http://www.subyclub....y-weapon-r-cai/

[Morgan]

Good to see you pass on the free item, Gaz.