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inthewind
04-11-2002, 02:07 PM
Post deleted by inthewind

Wongsifu
04-11-2002, 02:17 PM
thats what ive heard that long runners cause more lag.

04-11-2002, 02:28 PM
You might initially think that long runners cause more lag...but it's not that simple.

A long-runner equal-length tuned manifold can take advantage of resonance, and can be tuned to give better performance at low RPM than a short-runner manifold. It's just like a header -- longer tubes move the resonant peak to a lower RPM, so longer tubes in a turbo header can give you better scavenging at low RPM and thus have LESS lag than a short-runner manifold.

Asad

inthewind
04-11-2002, 02:31 PM
Post deleted by inthewind

SLoWaSs13
04-11-2002, 02:36 PM
also from what corky bells says in his book, a long runner manifold can allow the exhast pulses to even out and become more smoother, producing better power that doesnt spike or peak, lol one thing is for sure, professional racecars have really long manifolds, and alot of the tuners (hks,Greddy,etc) have manifolds that are long but of course twisted up like pretzels so it can fit in the engine bay. i think what really makes a manifold desgin good is the exact length for the application, meaning, if ur drifitn or doin any type of low speed road course type of thing where ur not at wot all the time a longer manifold would be useful, but on a top speed car, or drag car a short more straight design would be used. this is my opionin and im not a engineer, so dont attack me with scientific s***, im makin these points from what i have learned from books, etc etc

inthewind
04-11-2002, 02:44 PM
Post deleted by inthewind

White_240sx
04-11-2002, 02:47 PM
Also: to take advantage of a divided turbine housing, don't the runner lengths have to be grouped and tuned anyway?

White_240sx
04-11-2002, 02:55 PM
Originally posted by asad137:
A long-runner equal-length tuned manifold can take advantage of resonance, and can be tuned to give better performance at low RPM than a short-runner manifold. It's just like a header -- longer tubes move the resonant peak to a lower RPM, so longer tubes in a turbo header can give you better scavenging at low RPM and thus have LESS lag than a short-runner manifold.<font size="2" face="Verdana, Arial[/img]How does resonance work in an exhaust manifold (or is that what scavenging means)? Does it work like it does in the intake manifold; except for strong negative pulses are favored over strong positive pulses?

[ 04-11-2002, 03:56 PM: Message edited by: White240sx ]

04-11-2002, 04:44 PM
Originally posted by White240sx:
How does resonance work in an exhaust manifold (or is that what scavenging means)? Does it work like it does in the intake manifold; except for strong negative pulses are favored over strong positive pulses?<font size="2" face="Verdana, Arial[/img]Yeah, it's basically the same thing. Any time there's a junction/transition (like changing pipe diameter, or joining two pipes together), you'll get a reflected pressure wave. In the case of a header, when two (or more) pipes come together, you get a reflected wave in the original pipe as well as the pipe it joins to, and this wave helps to pull (scavenge) exhaust gases out of the port (if you're at the right RPM http://www.freshalloy.com/ ).

And, yes, ideally you'd want a manifold designed to take advantage of the divided-inlet turbine housing.

Asad

White_240sx
04-11-2002, 06:50 PM
Originally posted by asad137:
In the case of a header, when two (or more) pipes come together, you get a reflected wave in the original pipe as well as the pipe it joins to, and this wave helps to pull (scavenge) exhaust gases out of the port (if you're at the right RPM<font size="2" face="Verdana, Arial[/img]So could I correctly assume that the collector is the most important part of the exhaust manifold?

I remember seeing a brand of headers in a summit catalog that had a cut-a-way of the collector and it featured a conic shape that protruded from the middle of where the primaries came together. Now was this a marketing gimmick or has that shape proven to be the most acoustically advantageous. I seem to remember reading that a cone worked well, but I don't remember too many details on it.

And say on a tubular turbo exhaust manifold, would it be advantageous to weld on some diffusers (DCOE carb. style) to the ends of the primaries where they collect at the "plenum", or does the simple fact that they converge together mean that savaging strength is maximized?

Thanks for answering all the questions Asad; I kind of hit you with a lot as of late. http://www.freshalloy.com/

04-11-2002, 08:59 PM
Originally posted by White240sx:
So could I correctly assume that the collector is the most important part of the exhaust manifold?
<font size="2" face="Verdana, Arial[/img]

Well, I don't know about MOST important...because things like tube length and diameter affect the resonant RPM and such...but the collector is certainly very important.



I remember seeing a brand of headers in a summit catalog that had a cut-a-way of the collector and it featured a conic shape that protruded from the middle of where the primaries came together. Now was this a marketing gimmick or has that shape proven to be the most acoustically advantageous.
<font size="2" face="Verdana, Arial[/img]Yeah, that would be a merge collector. They're supposed to be very effective. You can get pre-made merge collectors from Burns Stainless, if you want to try your hand at header building http://www.freshalloy.com/



And say on a tubular turbo exhaust manifold, would it be advantageous to weld on some diffusers (DCOE carb. style) to the ends of the primaries where they collect at the "plenum", or does the simple fact that they converge together mean that savaging strength is maximized?
<font size="2" face="Verdana, Arial[/img]No, a velocity stack like a carb has will actually reduce the scavenging somewhat (by reducing the intensity of the reflected wave). The fact that the flow goes in the "opposite" direction in a header vs. an intake manifold means that they're not really necessary.

Asad

[ 04-11-2002, 09:59 PM: Message edited by: asad137 ]

White_240sx
04-11-2002, 09:42 PM
So would a merge collector be beneficial in a tubular turbo manifold as far as increasing spool up time and low engine speed VE? I can't imagine that there would be a need for resonance tuning at higher engine speeds when boost is present.

**DONOTDELETE**
04-11-2002, 10:59 PM
Originally posted by White240sx:
[QBI remember seeing a brand of headers in a summit catalog that had a cut-a-way of the collector and it featured a conic shape that protruded from the middle of where the primaries came together. Now was this a marketing gimmick or has that shape proven to be the most acoustically advantageous. [/QB]<font size="2" face="Verdana, Arial[/img]I believe the term is anti reversion chamber. Basically, keeping the exhaust from being sucked back into the cylinder. I believe this is more of an issue for NA, as valve overlap and On turbo engines, both sides of the head are pressurized. On-boost, I don't think exhaust reversion is an issue. The exhaust gasses are going to flow to a path of least resistance, one of which isn't 1.5 BAR from the intake side.

Wongsifu
04-12-2002, 05:07 AM
i love this forum , its the only place where other ppl talk about cars and i sit and listen dumbfounded as opposed to doing all the lecturing http://www.freshalloy.com/

04-12-2002, 07:28 AM
Originally posted by White240sx:
So would a merge collector be beneficial in a tubular turbo manifold as far as increasing spool up time and low engine speed VE?
<font size="2" face="Verdana, Arial[/img]Absolutely. In addition, one thing merge collectors are supposed to is to broaden the resonance, so you can have a wider powerband.



I can't imagine that there would be a need for resonance tuning at higher engine speeds when boost is present.<font size="2" face="Verdana, Arial[/img]Well...that depends. With a small turbine, pressure in the exhaust ports/manifold is much higher than in the intake ports, so the boost isn't really pushing the gas through -- in fact, it's the other way around! The exhaust gases want to push their way back through the combustion chamber and out the intake ports (which is why you want low valve overlap on a turbo cam). I'd imagine that resonance would still be useful, but I'm not sure how the turbine affects things.

Asad

**DONOTDELETE**
04-12-2002, 10:33 AM
How about log style runners like this one:

http://www.jgstools.com/turbo/

Want are the advantages - disvantages of log-style compared to tubular?

**DONOTDELETE**
04-12-2002, 02:30 PM
Want are the advantages - disvantages of log-style compared to tubular? <font size="2" face="Verdana, Arial[/img]Wouldn't cylinder #1 and #4 be fighting eachother? This looks like a serious restriction of exhaust flow to me. Equal length is definatly the way to go IMO.

04-12-2002, 11:00 PM
Originally posted by webcrawler:
How about log style runners like this one:

http://www.jgstools.com/turbo/

Want are the advantages - disvantages of log-style compared to tubular?<font size="2" face="Verdana, Arial[/img]The they are compact and simple to build. They're still pretty heavy though, because they're typically made of thick-walled pipe.

The disadvantage is that pulses from one cylinder can affect the other cylinders in odd ways, because there's no tuning. Still, log-style manifolds can work very well.

Asad

[ 04-12-2002, 12:14 PM: Message edited by: asad137 ]