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brockharro
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varex

Post by brockharro » Sat Mar 02, 2013 7:36 am

has anyone used a varex muffler before becuase im looking at getting some on my h6 lib
i just want to know if there safe or not

cheers brock

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RSR 555
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Post by RSR 555 » Sat Mar 02, 2013 11:00 am

I use them a lot. Never used it on a NA engine but can't see why it wouldn't work on long runs. Wouldn't be too good for your engine when just putting around town.
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Post by El_Freddo » Sat Mar 02, 2013 10:58 pm

RSR 555 wrote:Wouldn't be too good for your engine when just putting around town.
Paul, I've never heard of these mufflers, why wouldn't they be good for short runs and why are they only usually used on forced induction engines??

Curious!

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Post by steptoe » Sun Mar 03, 2013 7:39 am

RSR 555 wrote:I use them a lot. Never used it on a NA engine but can't see why it wouldn't work on long runs. Wouldn't be too good for your engine when just putting around town.
Paul ! I could have used your support in my 1st grade class, when caught out not listening - tried to tell the teacher Miss Das, or was it Miss Kaybern - when I tried to tell her P U T was pronounced putt. A young Paul could have piped up "Miss ! What about putting and putting, two different words and sounds, but same spelling" ?? Huh :( ?

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Post by TOONGA » Sun Mar 03, 2013 9:50 am

Here you go Bennie

Xforce performance mufflers

I would think that if left in race mode the long term lack of back pressure could be a worry. but hey you can ajust the noise level via the remote :)

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Post by Gannon » Sun Mar 03, 2013 10:29 am

Back pressure is not really back pressure when it comes to exhausts.
Back pressure is just laymans terms for tuned pipes and cylinder scavenging. It relates to pipe size and exhaust gas speed and has nothing to do with the restriction (or lack of restriction) of a rear muffler.

A varex in open mode may free up a bit of power in the top end, but open or closed will make no difference at low revs/general driving.

Gen 3 H6 Outback or Gen 4 H6?

Gen 3 H6's already have a variable muffler thats controlled by the ECU and dont Gen 4's have 2 rear mufflers, meaning you will need 2 varex's?
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Post by brockharro » Sun Mar 03, 2013 6:28 pm

Gannon wrote:Back pressure is not really back pressure when it comes to exhausts.
Back pressure is just laymans terms for tuned pipes and cylinder scavenging. It relates to pipe size and exhaust gas speed and has nothing to do with the restriction (or lack of restriction) of a rear muffler.

A varex in open mode may free up a bit of power in the top end, but open or closed will make no difference at low revs/general driving.

Gen 3 H6 Outback or Gen 4 H6?

Gen 3 H6's already have a variable muffler thats controlled by the ECU and dont Gen 4's have 2 rear mufflers, meaning you will need 2 varex's?

yer you need two but if you put of the same size varexs one as that come on the system that they make surly it would make any difference there and gen4 liberty

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Post by Gannon » Sun Mar 03, 2013 6:46 pm

Im sorry, but I dont understand the above post. Is it a question or a statement? Can you add some punctuation, my head hurts.
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Post by brockharro » Sun Mar 03, 2013 7:02 pm

statement sorry

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Post by Gannon » Sun Mar 03, 2013 7:32 pm

I think you are saying....

Yeah you need two, but if you put the same size varexs on as that come on the liberty from factory, surely it would make a difference. And gen4 liberty

As I said above, you may notice a difference it the upper rev range at full throttle, but at lower revs/normal driving, it would make no difference (even if it sounds like it does)

If you want to increase low end performance, you will need to go with tuned primary and secondary pipes. But I doubt its really worth it, the factory exhaust is pretty good
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Post by brockharro » Sun Mar 03, 2013 7:45 pm

i mean the same size as what xforce system has but swap the 2 mufflers off that to varexs

sorry if i make no sense didnt get to sleep till 4 in the morning last night and back up at six

and i just wanted to know if anyone has had any problems with them

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Post by RSR 555 » Sun Mar 03, 2013 11:46 pm

I've only used them on Turbo systems. I've fitted many of them without any problems, as Xforce make a good system for the price.

Gannon.. Does all Gen3 H6 have variable mufflers? I have 2 Gen3 H6 Outbacks and I can't see where they vary???

And sorry to disagree with you but back pressure comes from the muffler (plus all the other parts in the system) and is required on all 4 stroke. If you run a NA engine without back pressure, you'll end up using more fuel and increase your chances of burning out valves. Where do you get the statement that "back pressure is just laymans terms"?
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Post by Subydoug » Mon Mar 04, 2013 8:05 pm

RSR 555 wrote:I've only used them on Turbo systems. I've fitted many of them without any problems, as Xforce make a good system for the price.

Gannon.. Does all Gen3 H6 have variable mufflers? I have 2 Gen3 H6 Outbacks and I can't see where they vary???

And sorry to disagree with you but back pressure comes from the muffler (plus all the other parts in the system) and is required on all 4 stroke. If you run a NA engine without back pressure, you'll end up using more fuel and increase your chances of burning out valves. Where do you get the statement that "back pressure is just laymans terms"?
What you say is true to a particular point Paul. Back pressure in a turbo engine (turbo engines producing by far the most back pressure of any exhaust component, meaning turbos have large amounts of it) Can be utilized to stop intake gasses escaping out of the exhaust port during overlap periods while the compressor rams the charge in. Thats why changing exhausts (turbo back) can increase peak HP because you reduce the back pressure in the turbine, which in turn reduces engine back pressure at high rpms. Its also another reason why turbo engines mostly run different cams to a N/A or a supercharged engine.

On N/A engines though, most of the time the better term to use is Velocity. More back pressure means more velocity and visa versa. Usually, on race engines you optimise for High flows at High rpm because the aim of the game is max power and torque (remember, race engines are mostly tuned to produce max torque and max HP at the same time, usually also at rev limit). Velocity is what gives scavenging. Back pressure is a byproduct of velocity. Street cars usually rely on torque for drivability, so usually the pipe is tuned to match velocity at max torque RPM. A pipe that is too big lacks velocity so it has no back pressure. This will inhibit scavenging under the hp curve because the exhaust isnt helping to suck fuel into the cylinder (havent reached the torque curve yet). The other extream is too small exhaust which has great velocity. It scavenges great, but as soon as you try ramming more air down it at higher rpms, it gets overwelmed my backpressure.

Supercharged engines are slightly different again. Because it doesnt have a turbine in the exhaust stream, the back pressure is very low (with retorspect to turbo and N/A). And because your forcing air into the cylinder, scavenging isnt needed as much as it is on a N/A engine. Usually running less overlap is benificial to prevent charge from escaping out the exhaust. You can also run an exhaust tuned for max RPM and HP. The downfall of this is the massive fuel consumption, compared to scavenging, because if your going to run a SC, you want power so your not going to whimp out on low boost levels ;).

Unfortunately, basic Engines can really only be optimised for a single RPM range. However, newer technolegy is allowing for improved engine performance across larger rpm ranges. Variable valve timing and, to remain on topic, Velocity (back pressure) adjustable exhaust systems. Lambo's and Ferrari's and other sports based road cars use systems like this. Small money road cars perform well enough for systems like that to be neglected.

Think of a air compressor. It has a tiny air duster on the end, which squirts air out at increadible velocity (if you hold it up to some light, you can see mach dimonds in the stream), but the tank takes 5 mins to empty. Now if you were to put a 3 inch ball valve on it, that tank will be empty in a matter of seconds, but the velocity will be slower.

I hope this ramble makes sence.

Regards

Doug

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Post by Gannon » Mon Mar 04, 2013 8:08 pm

Gannon.. Does all Gen3 H6 have variable mufflers? I have 2 Gen3 H6 Outbacks and I can't see where they vary???
Sorry, my mistake. I thought I had read somewhere they had the same rear muffler as the B4, but the FSM says otherwise
And sorry to disagree with you but back pressure comes from the muffler (plus all the other parts in the system) and is required on all 4 stroke. If you run a NA engine without back pressure, you'll end up using more fuel and increase your chances of burning out valves. Where do you get the statement that "back pressure is just laymans terms"?
Back pressure isnt anything to do with restriction. Any restriction in an exhaust is bad for performance and economy.
What most people call "back pressure" is actually choosing a pipe diameter large enough not to cause restriction but small enough to maintain high exhaust gas speeds. When done right, it causes a scavenging effect of the cylinders and this increases power and economy. This is why tuned headers start small at the primaries, and then are larger for the secondaries, its all about making use of the momentum of the pulses to pull extra gas out of the cylinder, making room for more fresh air on the intake stroke.

Maybe "laymans terms" was the wrong term to use.
What I meant was that when most people use the term "back pressure" they are actually referring to what I explained above, not restriction. No restriction in a muffler will ever increase power or economy.
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