x pipe needed?

[LukePitt]

Hi everyone, I'm looking into finally getting my uprev done at Horsham soon. So far on my 2005 gt I've changed the rear section of the exhaust, got a pop charger, Horsham d's silenced decats, ams light weight pulleys, ultra light weight flywheel & exedy clutch, and a d1 throttle controller. Do I need to change the x pipe to get maximum gains or is the stock one ok? Also I am adding a plenum spacer whilst having it mapped, should I see good gains? It's got 58000 miles and I've always used shell v Power since I've had it.

[rtbiscuit]

The stock exhaust is a Y pipe. If you want a custom built x pipe or h pipe I know of a company.

[LukePitt]

Do I need a h or x pipe? Will the stock one restrict me enough to stop my remaps potential?

[rtbiscuit]

Lots change the Y pipe, is the stock pipe restrictive? If I'm honest I can't remember. X and h pipes will only fit if you have a tree dual system. If you haven't then you need an aftermarket y pipe. Have a chat with tarmac Sportz they have possibly the widest selection on offer. Also cougar store and redline styling have stuff on offer as well. My advice look around, do some research and then find the trader that offers you the best product for your budget.

[wls350]

Go with an x pipe it sounds awesome!

 

Sent from my GT-I9300 using Tapatalk

 

 

[Tarmac@TarmacSportz]

 

Motordyne do an XYZ pipe which is probably the best on the market, or Stillens Ypipe is excellent too.

 

I don't know of any off the shelf Xpipes but as biccy says you could possibly get one made up

[rtbiscuit]

^{standard exhaust comes off either side of the engine; so you have 2 routes of exhaust gas. these then merge in the y pipe and converge into 1 pipe as it heads through the system. it gets to the rear box which is baffled where it then has 2 points of exit. in order to have an X or an H pipe you would need a whole new exhaust from the cats back. as the X pipe is designed to allow exhaust gases to scavenge from either bank, as the rest of the route they remain separate from the manifold all the way to the rear, where there are usually 2 back boxes, one for each bank of the engine. as you have replaced the rear of your exhaust already, you're only real option is an aftermarket Y pipe.unless you wish to change the whole system.}

[LukePitt]

Thanks for the advice. I'll do a bit of research as suggested! Just want to get the full potential from the remap. Cheers guys.

[Dblock]

^{standard exhaust comes off either side of the engine; so you have 2 routes of exhaust gas. these then merge in the y pipe and converge into 1 pipe as it heads through the system. it gets to the rear box which is baffled where it then has 2 points of exit. in order to have an X or an H pipe you would need a whole new exhaust from the cats back. as the X pipe is designed to allow exhaust gases to scavenge from either bank, as the rest of the route they remain separate from the manifold all the way to the rear, where there are usually 2 back boxes, one for each bank of the engine. as you have replaced the rear of your exhaust already, you're only real option is an aftermarket Y pipe.unless you wish to change the whole system.}

 

Not on the zed engine. A guy in the USA did a huge review with many different types of exhaust. Scanenging only happens on the manifolds on the zed and not in the cats or y pipe.

[rtbiscuit]

AFAIK scavenging can only happen where either bank can pull gases from the opposite bank,

[Dblock]

AFAIK scavenging can only happen where either bank can pull gases from the opposite bank,

 

Copied from Hydrazine off the my350z forum

 

Back pressure (at least on our engine) is NEVER a good thing for NA applications.

 

It is a widely spread myth that some back pressure is good, but it is 100% FALSE.

 

There clearly are situations where smaller diameter pipes can outperform larger diameter pipes but this is not because of back pressure. This is because of scavenging. And when tuned properly, scavenging actually reduces back pressure as seen by the engine.

 

But be careful in the assumption that smaller automatically equals better performance. It is highly dependent on where the smaller diameter pipes are being used.

 

Small pipes near the engine can be good for scavenging and power, but as the pipes move farther and farther away from the engine the effect of scavenging rapidly diminishes. If scavenging cannot be taken advantage of, then small/restrictive pipes must be completely avoided.

 

Back pressure can only reduce power. Do not confuse this with scavenging.

Scavenging actually reduces back pressure on a tuned cyclical basis.

 

With each pulse released during the exhaust stroke of the engine, the pulse travels like a shotgun blast down the exhaust pipes. The high intensity blast creates a shockwave with a large positive pressure at the wave front. This wave front is traveling so fast that even when the piston reaches TDC and all the gas is expelled by the piston, the fast moving slug of exhaust gas doesn't stop and it rarefies the gas and creates a vacuum behind the shockwave.

 

It is the vacuum behind the shockwave that sucks out any remaining exhaust gas from the cylinder. This vacuum also pulls more fuel/air mixture through the intake valves during the intake/exhaust valve overlap period. And this is how more power is made. This is the scavenging effect. It vacuums exhaust gas out of your engine!

 

Adding back pressure can only kill off this vacuum that you want.

 

NOW HERE IS HOW THE MYTH STARTED.

IT WAS A MISINTERPRETATION OF TEST RESULTS.

 

Sombody a long time ago probably did the same series of dyno tests I did on varying pipe diameters. Like I did, they probably found that smaller diameter pipes can yeild higher HP and TQ. They probably mistook this for back pressure and put it out in the public. Smaller diameter pipes can provide higher performance when used properly. But small diameter pipes are only desirable when they are very close to the engine.

 

For example:

I did a series of dyno tests on various diameter test pipes ranging from 2.5", 2.25" and 2.0".

 

Before conducting the tests, my initial guess was that the larger diameter pipes would produce the highest HP with lowest TQ. And the smaller diameter pipes would produce the lowest HP and the highest TQ.

 

Well... I was 1/2 right...

 

As expected, the dyno testing showed the 2.5" diameter test pipes made the lowest TQ. And as expected, the dyno testing showed the 2.0" diameter test pipes made the highest TQ.

 

But here's the kicker. The 2.0" test pipes made 2 more HP than the 2.5" test pipes! ...It left me thinking "COOL. Smaller diameter test pipes make more TQ and more HP. That's a wining combination!"

 

So sombody a long time ago probably misinterpreted the smaller diameter as adding performance by being more restrictive. But this is not the case. It is because of increased scavenging. Smaller diameter pipes near the engine increase the velocity of the shockwave and thereby increasing the effect of scavenging. It was a misinterpretation of the results.

 

So I continued down this line of testing at the Y-pipe primaries. Using the 2.0" test pipes, I then tested various Y-pipe primary diameters. 2.0", 2.25" and 2.5".

 

The expectation was to see similar results... but not quite this time. At least not at the Y-pipe.

 

The 2.0" Y-pipe primaries did indeed provide the highest TQ, but it brought a good portion of the HP down. 2.25" primaries were better but could still be improved upon. The 2.5" Y-pipe primaries provided the best peak power and the best average power.

 

So dyno testing proved the best test pipe diameter is 2.0" diameter and the best Y-pipe primary diameter is 2.5".

 

I then continued further down this line of testing on the mid-pipe and made some more interesting observations. Testing mid-pipe diameters at 2.5", 3.0" and then a fully open Y-pipe.

 

What I did find was that there was no scavenging effect possible after the Y-pipe. There was nothing to gain from the smaller diameter what so ever. In fact, the only thing that had any effect was simple back pressure.

 

Using a open Y-pipe as the baseline I found that connecting a 3" single exhaust had no effect on TQ and with only a small 1.5 HP decrease.

The 2.5" midpipe slightly reduced TQ and was ~2.5HP down from than the 3" midpipe.

 

This series of tests established:

1) There was no scavenging possible after the Y-pipe.

2) A smaller diameter midpipe can only decrease HP&TQ

3) There will be rapidly diminishing returns beyond a 3" midpipe

4) With power to weight ratios taken into consideration a 3" midpipe can be considered optimum. 3" also allows more headroom for medium boost FI applications.

 

Going from 3" to a 3.5" midpipe may at best provide a 0.5HP increase. So from a weight point of view, going larger than 3.0" would be counter productive for NA applications.

 

I then conducted another series of tests at the end of the Y-pipe.

1) Attaching a 3" diameter butterfly valve with variable position restriction plate.

2) Attaching a 6" diameter parabolic diffuser to reduces pressure drop below that of a 3" open pipe.

 

The purpose of the butterfly valve restriction plate was to directly test the effect of raw back pressure on performance. And the results were very clear.

BACK PRESSURE RAPIDLY REDUCES PERFORMANCE.

 

I dyno tested the valve at various levels of flow restriction. From wide open to almost fully closed as back pressure was increased, performance rapidly decreased.

 

 

This set of dyno plots is proof positive that back pressure is the enemy of power and torque.

 

Let the myth of back pressure be permanently dispelled from the vocabulary of this forum!

 

After that series of tests I started another set of tests that decreased exhaust pressure beyond that of a simple open ended 3" pipe.

A 6" diameter parabolic diffuser was clamped onto the end of the Y-pipe. This was used to decrease flow resistance below that of a open pipe.

 

Dyno tests of the diffuser showed an instant 4-6HP increase over that of a open Y-pipe!

 

This picture below is a picture of a 5" linear diffuser. It doesn't perform quite as good as the 6" parabolic diffuser but the 6" diffuser is completely impractical for fitment and production reasons.

6" is too big for fitment under the Z and the parabolic shape also gives it a curvature that makes the production process MUCH more difficult.

 

This is the diffuser used on the MD ShockWave single exhaust system. It can also be attached directly to the Y-pipe for drag race applications.

 

 

 

So while there are rapidly diminishing returns with going to larger and larger diameter tubing after the Y-pipe, significant gains can still be made by use of diffusers.

 

The back to back dyno testing shown below was a simple open Y-pipe as the baseline and then with the diffuser attached.

[rtbiscuit]

You need to read your own text. Most of that I knew, but the guy says no more scavenging after the y pipe. An x or h pipe replace the y pipe. And if built properly are set slightly back anyway. Which is where the scavenging happens. That whole text is on how pipe diameter affects exhaust pressure. It makes perfect sense but it completely agrees with what I said originally.

[Dblock]

There is also scavenge on 4 cylinders or 6 cylinder cars not just between banks though.

[rtbiscuit]

What they refer to as scavenging I've always known of it as pulsonic wave theory. And seen scavenging as a seperate part of it. They seem to see it all under the scavenging title. And on a 4 cylinder car you still have pipes intersecting. At the manifold which gives the same scavenging principals.