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I DO have flex joints... 6" long once at that (I was paranoid after the first pair of cracks).

G

 

Gurgen,

The Stillen pipes do not come with flex lines. Did you install these yourself?

I have been thinking of doing the same thing because of the possibility of cracking the OEM manifold but now that you have a cracked manifold it suggests a flex line may really be needed.

In Theory, practice and theory are the same.
In Practice, practice and theory are not the same.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

 

yes i did install the flex pipes after the fact

g

 

You know I mentioned this issue to Stillen some time ago but they blew me off and said it wasn't a problem. I suppose we will see what happens a year or two from now.

Not having the flex pipes sounds like a problem waiting to happen. I'll put them on soon.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

 

Can you explain what or how the PE system disconnects the PCV system? I'm not that familar with the PE system.

And not one car I've added a turbo system or made serious turbo swaps on had ever eliminated the PCV or changed it's operation in anyway. So I'm a bit curious as to what they did.

But even if it's somehow building up vapors the oil you have in the photo above seemed excessive to be from the crankcase without significant blow-by.

 

I'd like to see pictures of these washers. Whether the bracket supporst the turbo or the downpipe, if it prevents expansion, it can cause stress on the parts. I don't really see the point of the bracket anyways. If the manifold is designed well and built strong it should not crack from the weight of a turbo. As far as the weight of the exhaust components much of it should be supported by existing exhaust supports. If the brackets do not allow for enough expansion or is too stiff then it can put far more stress on the components than the relatively small amount of weight the exhaust system might put on it.

And this is of particular concern with the PE manifold from the photos I've seen. As all ports empty into a common tube, the heat in the section furthest away from the turbo will be cooler than the section closes to the turbo. The section closest to the turbo gets 3 cylinders feeding it where the section furthest away only gets one. This results in an even greater amount of expansion beyond the third port then you might see with a manifold where each port has a dedicated runner up to a single collector. And this is where allowing expansion to the rear is going to be critical.

However, this is probably not the cause of your cracked mani. I'll suspect the head flange is the likely culprit. But hard to say without seeing the crack or the bracket itself(along with the rubber washers you speak of).

 

I doubt the OEM mani will be a problem without flex joints. The main reasoning is that the expansion you are going to be most concerned with will be that which causes the exhaust pipes to lengthen to the rear of the car. The factory rubber mounts are designed to handle this type of expansion You'll usuallu find flex pipes on cars with tranversely mounted engines where the fore and aft rocking of the motor work to try and bend the pipe rather than simply expanding it. Longitudinally mounted engines tend to try and twist the pipe a little but over a large section of pipe so the stress is minimal. The other place you might see a flex pipe is a external wastegate dumppipe that is routed back into the main exhaust stream. Since the wastegate is not always open it heats and cools often while the mainpipe changes much less. The flex pipe allows the two to be able to expand at different rates without causing stress to the components.

 

<blockquote><font class="small">In reply to:</font><hr>

You know I mentioned this issue to Stillen some time ago but they blew me off and said it wasn't a problem. I suppose we will see what happens a year or two from now.

Not having the flex pipes sounds like a problem waiting to happen. I'll put them on soon.

<hr></blockquote>

My experience has been pretty negative with their tech support AFTER you purchase their product. So, that response is pretty typical of Stillen, as per my experiences.

 

Ckwik

The PCV valve on the p-side rocker cover connects to a tube extending from under the front edge of the lower intake manifold. Given that the manifold sees over 1 atm pressure (absolute) at boost, the crankase would be exposed to positive and not negative pressurs (bad). That is of course if there is no meaningful PCV valve on that rocker cover which will prevent flow in the direction of the crankcase. That is not the case with this VQ motor.... the PCV valve is very effectve (unlike other motors),

PE's kit instructs the closure of that lower manifold tube with a supplied plug and moving the PCV hose (connected to the PCV valve) onto a nipple on the intake tube (p-side).

 

Ckwik

You are precisely right on the heat that each part of the manifold is exposed to. The first time each of the manifolds cracked, the crack was right at the top of the manifold (at the weld) right before the flange (not at the weld immediately at the flange). This is of course where the temp is highest.

This time, i bet it is in the same place. As far as the rubber washer is concerned, it is very much like the stock rubber washer/grommet that is installed between the bracket and the tranny over the mounting bolts, only with a slightly greater thickness, that's all. it is inserted between the bracket and the transmission.

As far as not using the bracket alltogether, i thought about this long and hard. Yes it will allow for more movement. However, we will lose the stability of the whole assembly... as the engine moves when the car hits potholes, road bumps/dips, the engine/tranny assembly moves considerably. Having the bracket fasten the downpipes to that assembly will keep everything in one piece and prevent stress in these circumstances.

Maybe we need to design a full rubber mount, not unlike the hangers found further aft, which accept the SS hangers welded to the muffler, etc... But again, that would not provide sufficient support in the stated circumstances.

Gurgen

 

Ckwik,

Thanks for the input but I'm not sure I can agree. Although thermal expansion can be an issue I think it is much less of an issue than the engine rocking back and forth.

Without flex lines the entire exhaust pipe system is effectively a very long, heavy and rigid torque arm bolted to the OEM exhaust manifold. The Stillen exhaust system is suspended on rubber suspenders, but with the stainless 2.5" pipes being such a long and inflexible torque arm, it isn't of much help. Those stainless pipes are very rigid but the engine will continure to rock at every stop light, at every 1/4 mile launch and with every stab or lifting of the gas pedal.

Every time the engine rocks it will put an elastic torque stress on the area where the manifold pipes meet up to the flange. Eventually the metal will become fatigued and fail.

Also, every time you go around a turn or go over a bump the rubber suspenders will allow the exhaust system to bounce, swing or move but the OEM manifold is still hard mounted to the long, heavy, rigid torque arm. There has to be a lot of torque stress placed on the manifold because of this.

I am sure Nissan put flex lines in the OEM exhaust system for a reason.

In fact, it kinda makes sense that Gurgens manifold failed so early. With the TT, he has way, way more torque than the average G. That means his engine can rock even more forcefully. This in combination with the long torque arm of the Stillen exhaust is an invitation for failure.

2004 G35 6MT Blk/Blk Sedan Stillen Air, Stillen Exhaust

 

Sounds to me like the guys at PE are going to have to design cast iron manifolds.

04 G35s 6MT BS Aero Kit/Nav/Prem
Warning: Objects in Mirror Are Losing!

 

RacerX

You area mind-reader. They have been on it for a couple of monts. They will be migratingto the cast manifolds (which will also lower the cost of the kit considerably) by November.

G

 

Nissan/Infiniti obviously use them for a reason. I'm not convinced it's for thermal expansion though. I see flex pipes and flanged swage joints used in FWD cars with horizontally mounted engines. And the reason is not for thermal expansion. A FWD motor will try to lift or push down the rear of the exhaust system significantly as it rocks. If say the engine rocks 3 degrees. With the average length of a car being about 15 feet, I willl say the fulcrum of rotation to the end of the tailpipe will be about 10 feet. This equates to just over 6 inches of movement at the tailpipe. On the other hand a RWD car will have it's tailpipe about 2 feet from the fulcrum(extendint id down the vehicle from the motor to the tailpipe). With 3 degrees of motion that works out to 1.25" at the tailpipe.

I can only speculate as to the reasons for the flex jopints used on the G and Z, but it would only be speculation. I don't think the G has any significant issues of movement over any other RWD car I've worked on. It's certainly not to say the flex pipes won't absorb some of these movements, but the question in my mind is why do they need them if most other FE/RWD car doesn't? I just think there is more to it then the movement.

 

It doesn't sound like they are bypassing the system as much as they are re-routing it. Which is fine and should not pose any issues with it's operation. The 240sx has the breather tube routed right in front of the throttle body. With the my turbo kit, it was routed just before the turbo. It worked fine. And my turbo kit on that car had some relatively long plumbing compared to most others.

*Edit - Additional info:

Where exactly is the PCV valve itself located then? Typically you should find the PCV valve located between the crankcase and the manifold. And then there should be another tube connected to the intake tube so that the engine can draw fresh air from the intake tube through the crankcase through the PCV valve and into the manifold. Under boost the PCV valve will automatically close itself and at that point all blow-by will be going out into the intake tube. if it were do be doing what you are saying the oil would not be finding itself out in the intake boost until you boost. The PVC valve will stay open until the manifold no longer sees any vacuum.

Here's a pretty good explanation of a PCV system:

www.autoshop101.com/forms/h63.pdf

<P ID="edit"><FONT class="small"><EM>Edited by CKwik on 09/17/04 02:38 PM.</EM></FONT></P>