My experience has been completely different than yours, but I believe you. Exhaust leaks at the manifold can cause a lean condition, but most any other leak south of that point usually only causes noise. Leaks at the exhaust manifold cause lean conditions and a major lack of power due to negatively impacted exhaust velocity. I think the problem is definitely exhaust related, but his dyno plots are very clean suggesting to me that his G isn't suffering from an exhaust leak at the manifolds or cat.

I agree with you that the lack of flex sections in the Stillen X pipe and Borla y-pipe should be a cause of concern in terms of exhaust leaks, especially leaks at the exhaust manifold. With the OEM flex sections, the engine is able to twist without putting a major load on exhaust. Without the flex sections. all that engine torquing will be transfered directly to the exhaust. If I would have kept my Borla, I would have installed flex section in it.

And before someone says this, revving the engine in neutral to look for engine movement will not truely show how much the engine moves in it's mounts. When the engine is under load and especially on shifts, it will move quite a bit.

 

Trey,

That "pfft" noise is pretty common on VQs when you change something with the cats. My 96 Maxima had a precat in the y-pipe just south of the exhaust manifold and then the main cat downstream just below the center console. The biggest bang for the buck mod is to buy a aftermarket y-pipe that removes the precats. Once this is done, you get a nice increase in power, but you get more exhaust noise including "pfft" sounding on off throttle deceleration and also a hissing noise above 5000rpms. We called these noises the "bees in a can".

Good luck and keep us posted.

 

The best way to see how much the engine moves is either on a dyno or put the cars parking brake on tight and put the car in gear and give it some gas where it forces the engine to rock. Then watch to see what the exhaust does as well during this moment.

 

It seems different REVUP engines have different reactions to exhaust mods. I have seen some go well and others that didn't... I wonder how much of it has to do with the exhaust valve timing. There may be some degree of variability in the exhaust cam position sensors that results in variability of the cam phase angle. This could cause a greater sensitivity to exhaust mods.

Going back to stock cats is a good idea, but if possible, have the dyno shop measure each A/F bank on the extra bungs before you take out the cats.

You could get one more vital data point before the opportunity is gone. If you put on the stock cats and still find the same problem it will be more difficult to diagnose and isolate the problem.

 

I don't know if I am reading this correctly but we are trying to ELIMINATE the rattle or as Trey put it the "pfft" sound (I disagree on the "letters" used but hey...). This does not sound anything like a *wanted* sound and is quite irritating in some cases as it gives a sense that something is loose.

 

Update -
I asked a few guys around town for some help, suggestions for local shops, etc. Specifically, I was looking for a local shop that could install widebands into my extra bungs for some a/f checks(temporarily, of course). Or even a shop that could monitor the voltages of the onboard sensors. Unfortunately, there's just no one so equipped.

So I posted up on g35frenzy, figuring there would be some shop in Atlanta that could do the work. I got a response directing me to z1motorsports. I gave them a call this past saturday, and got some pretty good information. If I choose, I could make a day out of it and have the car strapped to their dyno(not sure what type). The shop could monitor the voltages of my onboard sensors. They could also install a wideband in each cat(to measure each bank), *and* use the wideband-in-the-tailpipe method. By converting the voltages of the onboard sensors, we could compare the a/fs at each location. What would I hope to accomplish? Well, one of my fears is that with the stock O2 sensors being removed from the stock cats, reinstalled in the kinetix, removed from the kinetix, and reinstalled in the crawfords, that maybe one(or both) have become possibly fouled, or succeptible to too much pressure when being torqued down, or something else entirely; thereby either damaging a unit or causing it to read out of whack, but just within tolerances to not throw any codes. I don't know how likely it is for any of this having happened is, but I cannot deny it as a possibility. Another possibility is that the dyno just wasn't reading properly. Again, less likely, but possible nonetheless. Regardless, the intent would be to make sure the ecu is seeing what was indicated by the dyno. If not, then I would be chasing a wild goose.

That's an option. An option I've chosen not to exercise. Over the weekend, I noticed that my tailpipes are filled with soot. Granted, I got the exhaust used, but it was semi-clean. After just 3 weeks, it's completely black. After looking at my oem muffler, it was just as dark. I found this observation extremely interesting. This soot would indicate a rich condition, opposite of what the dyno tells us. Confusing huh?

At this point, I'm tired of chasing the problem down. Hell, I'm tired of trying to figure out my options. The curious part of me wants to be methodical, but I don't have the patience. At this point, I'm going to try to find a local shop to swap out the cats back to stock. I've got a hunch that one(or both) of the cats is blown out. But that's another unknown. Let's assume that one or both are blown out. Running rich over time can cause cats the fail. I didn't examine them before I put them on the car, and neither I nor Doug know how many miles were on them prior, so were they blown before I put them on the car, or afterward? If I swap out the cats, am I treating a symptom, or the cause?

I'm going to gamble, swap the cats, and hope for the best.

 

You are probably right with your hunch.

Good luck.

 

Um, I have mixed news.

I had the cats put back to stock today. I knew the exhaust volume would be lessened, and the tone changed, but I didn't expect the differences to be so dramatic. The car is now, much, *much* quieter. I almost cried when I drove it home . Part of me hopes it gets louder; when I did the ecu reset almost two weeks ago, the exhaust was much quieter(though not as quiet as now), but it slowly returned to it's pre-reset volume. On the plus side, the tone is much less muddy. The best way to explain it is to use a subwoofer analogy. In my den I have a used 15" sub(I got it for $50), and although it is quite loud, and provides a good punch, it is extremely muddy. Being the audiophile I am, I would gladly trade volume for more precise bass reproduction. The new exhaust note is like that; it's more defined, and easier to hear the engine's behavior transmitted through the exhaust. Though I will miss the volume.

I didn't do an ecu reset. I still haven't decided that I need to. I'm not quite the believer in the magical learning properties of the ecu that some others are. Regardless, I noticed the car lost quite a bit of power, just like when I reset the ecu 12 days ago. I only hope that the ecu will adjust to the new, or old(depending on one's viewpoint) cats.

The most noticeble difference is the exhaust odor. When the car had the stock exhaust system(including cats), the odor was inoffensive, almost non-existent. When I had the kinetix, there was an "oily" smell, somewhat similar to pulling into a gas station. It was temporary, only noticeble when cranking or shutting off the car, or after some good thrashing. The crawfords also had an odor, similar, but yet distinct. The addition of the stillen exhaust added another flavor, but I think that was because it was in storage for a while and needed everything burned off. It went away within a week or so, returning to the crawford style of odor. When I cranked the car for the first time today, though, I was greeted with a very strong offensive odor. It can best be described as putrid. Driving home, it was ever present. It was quite nice today, so I got to ride with my driver's side window down, so I'm sure that contributed to the smell's strength. The car never smelled like that stock, and I just hope it goes away. The whole drive home, I was trying to identify it(smelled similar to something I couldn't put my finger on). Then I realized what it smelled like: it's almost exactly the same as when I burnt up my clutch back in September when the clutch got stuck. Though I'm absolutely sure this odor is not the clutch(no slippage experienced whatsoever), it does concern me.

Overall, I'm disappointed. I had fallen in love with the exhaust. Although it arguably sounds "better", I miss the volume. I'm also quite disappointed in the performance. I'll just have to put some miles on it and hope it corrects itself, then possibly dyno. If I am still not seeing the same power as everyone else at that point, I think I'm just gonna race the **** out of the car in it's current trim, and forget about further go-fast mods.

Oh, there is a bright side. Visual inspection of the cats show they are in fact in good condition. Both of them. The honeycomb is still present. So I might be able to sell them and re-coup some of the expense incurred in this goose chase. And I also noticed something else; only the passenger-side cat has the extra bung, not both.

 

Note to self, if I buy a Rev-Up G, do not buy aftermarket cats or a true dual exhaust

I'm sorry to hear about all the problems. I really don't think the cats were causing the problem. I still think it's the catback. I'd put the stock exhaust back on and add an aftermarket muffler if you want the volume. I think with the stock exhaust back on there, the MREV will spring to life. IMO, the TD is somehow flowing to much air for the Rev-Up variable I/E cam timing. That's the only thing that seems to make any sense to me.

 

True Dual Exhaust has nothing to do with his problem. It's the Cats and possibly his car. Others haven't seen this problem.

 

I guess we'll see who's right when you get your Stillen TD put on

Well, he says the OEM cats are back on there with no change to the performance which means the aftermarket cats had nothing to do with the problem.

Look at his plots and you'll see that there really isn't anything "wrong" with the engine. The power delivery is smooth and linear. Often an engine that's having problems will have a somewhat jagged plot and sometimes the power drops hard at certain points. The other possibility is that MD accidently sent Trey a Rev-Up lower manifold, but I think Trey would be smart enough to notice the same sized intake horns. The non-Rev-up manifold with a spacer should instantly make a healthy surge in midrange power. It's a given with the longer runner design. My contention is that much increased exhaust volume of the TD exhaust is somehow effecting the variable cam timing. Since the Rev-Up motors don't seem to be taking to exhaust mods like the previous gens, it makes sense to me that either higher flow Rev-up manifold or variable intake cam timing is the culprit since the non-Rev-Up motor don't have these systems.

 

And we all know his butt dyno isn't accurate.

So now your stating it as a fact that it has nothing to do with it when he has yet to get it dynoed without the cats.

The exhaust has nothing to do with the problem where there are other 05s out there that dynoed much higher with stillen td, mrev, and other items.


Thank you for your assumption, but it is wrong.

 

I like your reasoning, but there is more evidence supporting the positive effects of TD exhausts on the revups than the other way around. Look at the post from Diesel350 about his HKS in combination with the MREV. The gains weren't what he was expecting, but he saw some pretty good gains on top of those of the MREV. Then look at thawk408 on my350z. He's got a revup, with full bolt-ons(crawford package, borla exhaust) on his z, with no mrev, cams, heads, or ecu, and he's pulling around 282 dynojet the last time I saw.

 

G35CR = Coupe w/rev-up engine
350ZR = 350Z w/rev-up engine

 

I guess we'll see. MREV gains of 10-25wtq from 3000-5500rpms should be easily felt by the old butt dyno, even Trey's miscalibrated dyno BTW, nothing I said was stated as fact. It was purely opinion. I even said that many times. You on the otherhand and telling me I'm completely wrong and as usual you're simply flaming me for no real reason and in your typical fashion, offering up absolutely no help or insight concerning the thread.

Trey, I wish you the best. Not having mods work like you hope is gut-wrenching and terribly frustrating. Sometimes it makes you want to just say f-it and want to go back to stock. Keep experimenting and you'll eventually figure it out.