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twin 2 1/2 

 

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Posted: Fri Dec 29, 2006 9:50 pm 
Stock as a Rock
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after working on mainly diesel engines we (me and the company i worked for) found that back pressure was only real useful
on a two stroke engine. thats my two bobs worth.

 

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Posted: Fri Dec 29, 2006 9:55 pm 
Getting Side Ways
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There's absolutely no point in a twin exhaust on these 6's unless there turbod. it'll just add weight and cost. better off spending the differece between a twin and single exhaust on a wade camshaft or something benificial like that!

 

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Posted: Fri Dec 29, 2006 10:01 pm 
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sabian631 wrote:
after working on mainly diesel engines we (me and the company i worked for) found that back pressure was only real useful
on a two stroke engine. thats my two bobs worth.


i know what you mean, 2 strokes tend to splutter then stop and dont start again if the exhaust seals blow!


just stick with the 2.5", it will give you a decent sound. save the money instead of getting 3". im sure there are better mods to give you better sound.

hey if your lucky a metal bar could accidently ram thru your cat converter
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Posted: Fri Dec 29, 2006 10:02 pm 
Tyre Shredder
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a car with no back pressure will only pull at about 7000rpm, you canot run say no pipe, just extractors, on an auto, and even on a manual, say bye bye clutch, and it would run like crap so those that think back pressure is irrelevant, think again, as for 2strokes, yes taht obvious they need it, you can tell by the fact they need an expansion chamber.
... also the eb xr6 that ran duals was only 2"'s
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Posted: Fri Dec 29, 2006 10:09 pm 
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moody wrote:
a car with no back pressure will only pull at about 7000rpm, you canot run say no pipe, just extractors, on an auto, and even on a manual, say bye bye clutch, and it would run like crap so those that think back pressure is irrelevant, think again


I think this is a bit of an exaggeration considering the overlap of the average camshaft people are running on this forum.

 

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Posted: Sat Dec 30, 2006 12:58 pm 
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ea_falcon wrote:
i rang up a few plces to day it ranged from $250 to $450 just for a cat back system i wouldnt pay more than $300..
i rang up this palce called et exaust and they got realy cheAP pacemaker extractors for 350buks but they charge 450 for a cat back system which is rediculous
best thing for u to do is ring up the exaust places to get a firm price range from them


Nice find cheers.

So with cheap extractors its about $700 cheers.

Also why would you want twin it looks to ricey rice boy.

get a 2inch and a half no need for noise as long as performance.
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Posted: Sat Dec 30, 2006 4:12 pm 
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yeh, maybe a little ( :P ) nit of exageration but im trying to say back pressure is needed. 3" flows better, coz you reduce backpressure, but because you have reduced backpressure, it wont work aswell, more then likely loose power but i cant back up that it makes it loose power.
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Posted: Sun Jan 07, 2007 6:52 pm 
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would twin 2 1/4 have enough backpressure and sound good
how good will it flow
i dont like twin tips i want twin pipes
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Posted: Mon Jan 08, 2007 6:11 pm 
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Sturmovik wrote:
stockstandard wrote:
Sturmovik wrote:
After the extractors, bigger is better. Its an urban myth as far as im concerned.


There is plenty of theories either way. For example

Quote:
We've seen quiet a few "experienced" racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.

As discussed earlier, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don't want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.


Im of the feeling that exhaust are just as much an art as science (unless you have the budget of a race team to turn it into a science). If you go small, their are issues. If you go big, there are another set of issues. 2.5 to 3" pipework is the ballpark range for the "right" size for a 4.0. Why do I say this - look at the size of pipe on the cars that win dyno comps and drag days.

Having said that, i am yet to see a falcon 6 with a 3" exhaust outperform a similar engine with a 2.5. Hell even my EF makes 95mph through the traps with a budget brand 2.5" press bent exhaust. I think once you have removed the restriction of a factory system you have to be very lucky or very smart to find something that will outperform an off the shelf redback system by a noticable amount.


Plenty of evidence to show unbolting the exhaust at the headers gives a measurable hp gain on any car. Hence why on drag days and dyno comps they run open headers. (or a screamer pipe off the back of a turbo)


Southy here on these forums did a few runs with his worked EA.

Full exhaust run and straight out the extractors and he said it made no difference.

We unbolted the exhaust on the VH i just had and took it for a drive...it was even more gut less.

Not having enough back pressure can cause the motor to bog down and not work as well because the engine is tuned for the exhaust to be on there.

We had the VH and on the 202 there is a valve from the inlet to the exhaust. The gaskit was foobared there. It was tuned for that. But we replaced the gaskit and started it up and it reved alot higher cause there was more fuel being burt due to it actually working the way it was supposed to.

IMO get what ever exhaust you want...Personally i chose the 2.5Inch because that is what has worked best for people running the 4L's here.

I would go for a 3 inch if i was turboed but like i said...go with what you want. And if a twin 2.25 is gay and you have to fork out another 300 for a 2.5 single then dont complain here cause noone will want to hear it.

Good luck :)

 

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