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Discussion Starter · #1 · (Edited)
Niallyc raised a query here re having quiet exhaust when required but beasty when required, which has been discussed on that thread. I outlined a method to give the best of both worlds, now here's a how to with diagrams to make it easy. Level of difficulty - with this how to, Novice, time to complete - 2 hours, cost, £5 approx.

The exhaust system on many of our Skylines already has the ability to open a "straight through" path at a predetermined rpm, that's the normal Nissan setup, standard setting is 4000 rpm under acceleration. But that's a waste of potential, which is why I've done the mod, this way I decide when I want straight through performance and when I don't.

The dual mode active muffler fitted to numerous Skyline's has a novel feature, at 4000 RPM it opens a valve in one of the two tailpipes, providing a straight through exhaust path for a short burst during heavy acceleration.

The mod below allows those with the Nissan twin output dual mode muffler to make considerable performance and sound gains virtually for free, whilst being able to stay within the law. (as and when required by flicking the switch) The mod allows you to manually select between straight through and normal exhaust modes, so no problems with roadside VOSA tests and MOT's etc.

Now that MOT's are computerised and VOSA has been allocated the funding for increased roadside tests, this mod could be a godsend.

The mod shows how to fit a switch circuit, allowing manual selection of the straight through and normal paths. With the switch fitted to open & close the flap in the exhaust on demand, the Nissan dual mode muffler provides two exhausts for the price of none.

Look for the "choke flap" inside the right hand tailpipe on these twin pipe back boxes. The flap is normally closed in the straight through right hand pipe, which does not go through the "silencer" section of the back box. At street speeds exhaust flow is forced by the closed flap in the straight through tailpipe to go via the "silencer" section, but at around 4000 rpm under acceleration the flap opens, creating a straight through system path.


The link below shows a similar system:

http://www.skylineowners.com/forum/attachment.php?attachmentid=31669&d=1182330502


The actuator on the Nissan system is tucked behind the boot trim on the passenger side, though control is excercised by the engine management systems. It certainly does change the exhaust note, quite a lot, but in it's normal setup only for short bursts during heavyish acceleration.

The actuator requires 12v + to close and 12v - to open, for my initial tests I wedged the flap in the "straight through" tailpipe section wide open, beautiful, so decided to make it a permanent feature. To this end I fitted a switch on the central console, I used the space provided for coin storage.

I can now run with a legit system or a straight through system at the flick of a switch, how cool is that?

Requirements: a few metres of 4 core cable, a switch as per my diagram included below, an inline fuse & holder, 4 diode's and a soldering iron.

The diode's are a belts and braces device to prevent stray voltages, and allow me to safely reconnect the original feed into the loop to provide the normal action when the new manual switch is set to closed.

I have not yet checked to see if the voltage needs to be maintained, or whether it can be disconnected following actuation. I suspect only a pulse voltage is required and it could be dropped after operation. In which case a non locking switch could be used, but I prefer the locking switch as I know at a glance which mode I'm in.

This mod provides two totally different exhaust system results, one for shopping and one for bopping..the straight through mode will not rip your guts out with base pulses but it's as much as I'd ever want and toooo much for the wife! Beauty is I can be legal or straight through at the flick of a switch!

At the end of the day this mod costs a few pounds and an hour or so's work, unbelieveable value, you really have to do this if you have the dual mode muffler, and if you haven't then get one! There is not a better way to spend a few hours and a few punds this weekend, this time you can keep your promise to the wife, it really will only cost a few pounds and take an hour or so!

I have a few tips to make it quicker..

To run the cables from the actuator to the centre console where I mounted my switch, the following saves time.

Remove the bolt from the front of the rear seat squab on passenger side. Now find something flexible but robust to use as a cable pull, I used a length of 1/4" plastic tube from a nos system. Feed this from the boot at the left side of the battery, there's a gap through to the rear seat squab. By pushing it through the available space it will go under the seat on the passenger side, you will then be able to pull it through form inside the rear of the car. Tape the wires (x 4 core 0.5A is ok) to the tube and pull through to front of rear seat squab. Now feed the tube with wire attached under the carpet and come up in the void under the centre console.

You are now ready for the install, the rest of which is simple if you follow earlier posts and the diagram below.

Have fun, you will afterwards!


Aitch
 

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Discussion Starter · #3 ·
As Nissan have several "stock" mufflers and I can't see yours from here, I'm afraid I'll have to leave that bit to you to determine.

As I said in my post, the first thing you need is the twin tailpipes, then you need to look up the righthand tailpipe of the two. It will have a "choke flap" type fitting in there if it's the right type for the mod. The flap is operated by an actuator behind the passenger side boot panel.

Aitch
 

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my gts25s used to have this type of flap. it seems that the previous owner of this gts4 had it removed cos i have a twin taile pipe straight through with no flap. sounds pretty awfull at low speed ....but give it some when warm abd its not half bad.
 

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Discussion Starter · #8 ·
No idea, only know the Nissan unit, but also aware Toyota do a version as do Ford, Nismo also do a version and others may do so too. The only way is to look into the tailpipes, (though some have the device on the backbox inlet!) you'll see the flap if it's there.

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Discussion Starter · #9 ·
Hesh, if your's has a twin "straight through" back box it's not only going to be very noisy it's also probably going to fail MOT. A roadside VOSA test could also invalidate your MOT and insurance if the box is indeed "straight through", though that can depend on state of tune and other factors.

So do you really mean "straight through" or is it actually as many aftermarket back boxes are a twin pipe system with the minimal legal silencing capacity?

To avoid confusion, in the Nissan system for which I've discussed the mod, the right hand pipe with the flap is truly "straight through" in the true sense of the description, though of course only with the flap open. So when modded with the switch it can be left that way as long as you like, and switched back for tests etc., thus avoiding any and all risks.

The thing I like about this mod apart from the exhaust note improvement, is that it has allowed me to be "totally legal", but at the flick of a switch I can get down and dirty.

In synopsis, I've removed the decat pipe and replaced with a legal sports cat, which whilst it is heaps better than the standard cat does not quite provide the same gains as the decat pipe did. The mod I've now done to the Nissan dual mode back box IMHO restores everything to the same power levels as with the decat pipe in place. The additional benefits are that the exhaust note is hugely improved and no need to change parts around for MOT, plus no risk at roadside VOSA tests, which are set to become a feature of the motorists life in the near future apparently.

So Hesh, for clarity, is it really straight through?

Aitch
 

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Discussion Starter · #10 ·
Addendum

My diode addition did not work as expected, so I now have just the options of either closed or open via the switch. I currently cannot switch back to the original mode where the flap opens via the engine management system at 4100 rpm when the switch is in closed position, but no problems, the mod is really very useful!

I need to identify a switch which in addition to the common poles and two optional switch modes has an additional pair of neutral poles, allowing the option to connect back to original route.

At the moment I'm happy with the open or closed options, but I do like to squeeze the lemon!

Aitch
 
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