Then yes you missed the point completely.

 

At this point, I'm going back and forth on the cats and exhaust. On the one hand, I think it's the cats. Since I dyno'd in November with the kinetix, I have not been able to replicate my 250hp numbers. What confuses me though, is that I felt a tangible torque increase with the crawfords versus the kinetix, and I had a slight improvement at the track as well(9 tenths and 1mph), though admittedly that could have been just better driving.

Part of me wants it to be the cats and not the exhaust. I went to a lot of trouble getting that exhaust, and it sounds so sexy. If it turns out the exhaust note is mutually exclusive to the gains of the mrev, I honestly don't know what I'd choose.

However, another part of me doesn't want the issue to be the cats. These are Doug's actual cats, the cats off his 350z. They have extra 02 bungs in them that I can use for a wideband if I chose. I really don't want to get rid of them.

If it is in fact the cats, then that makes me even more proud of my 13 second runs back at the beginning of December.

 

Update ---
Looks like I flipped out a bit prematurely. I've spent a bit of time analyzing my runs, and I have determine that I in fact have gained power; it just depends on how one looks at it.

Back in November, I had kinetix cats versus the crawfords, but I also had my stocker 18 inchers with oem rubber(235/45/18), versus my current 245/40/18, which is roughly 2.5% shorter. I had forgotten about the changing of the wheels/tires.

When I compare my runs against my runs in December( in which I had my current wheels/tires), I observe a slight gain. I'm still not seeing anything anywhere close to what I should, so I still have concerns about the a/f, but I don't feel nearly as bad right now.

When changed the graph to display time vs. speed, I noticed that I am in fact accelerating faster than in December. For example, at 8.2 seconds into my 4th gear pull, I'm going 113.04mph, versus the baseline of 110.41. Also, comparing acceleration from 60mph to 90mph, in 4th gear, I am now there by 0.191 seconds quicker.

This is not a huge improvement, but I expect an even larger difference if/when I get the cats figured out.

 

Hi Trey,

I just got a chance to look at your data and the run down of the various mods.
There are indeed several changes going on at once so it makes it difficult to say what mod changed what factor and how much.

Given that your A/F is so high, I would check for exhaust leaks. During the scavange phase of the exhaust pulse, an exhaust leak will draw in air and rapidly throw off the aparent A/F ratio. The same leak could also reduce scavanging of exhaust from the cylinders.

Check the weld joints on the cats and also check the flange to flange interface seal for any possible leaks.

Tony

 

Thanks Tony. If I get a chance this weekend, I'll go by the exhaust shop and get it on a lift to check it out.

Now, here's something interesting. I did some *more* analysis, and noticed some oddities regarding air/fuel.

Back in August, on my first dyno, the a/f looked just like everyone else's, except it was a tad rich. At that time, I had a 350z midpipe.

In November, the a/f looked fine again. It was leaner than in August (much cooler), but the profile of the a/f looked fine. At the time, I had ztube, k&n, kinetix cats, and 350z midpipe.

In December, I noticed my a/f was extremely lean, and very erratic. It seemed to jump around a lot; it displayed a lot of bounce. At the time, I had crawford cats instead of the kinetix.

On the same day in December, I ran without my rear muffler. Without the muffler( but with the crawford cats ), not only was I running *richer*, the signature resembled the "correct" a/f's; didn't exhibit nearly the same erratic behavior.

Then last night when I dyno'd(k&n, ztube, mrev, crawford cats, and stillen exhaust), my a/f was again mega-lean, and again very erratic.

I have attached a chart of my a/f's.

Key:
BLACK - August - 350z midpipe
RED - November - ztube, k&n, kinetix cats, 350z midpipe
ORANGE - December - ztube, k&n, crawford cats, 350z midpipe
GREEN - December - ztube, k&n, crawford cats, 350z midpipe, NO MUFFLER
BLUE - February - ztube, k&n, mrev, crawford cats, stillen catback

 

Good analysis you have there Trey. Its certaintly helpfull.

The plots are indicating the problem first started sometime between November and early December. So you can pretty much exclude modifications outside of that time frame as being the root cause.

What you did do at that time is exhust modifications... (It looks like the A/F really went out of control when the crawford cats were installed.) And then the problem appeared to fix itself when you removed the muffler for the dyno test???.... I'm getting the feeling you may have an exhaust leak somewhere that may have been temporarily jarred closed in some way during the muffler removal test.

Assuming its not too cold in your area, you can check for a leak by getting underneath the car and listening carefully, or by using a mechanics stethiscope.

Check everywhere from the exhaust manifold/head interface to at least the mid pipe end flange. Check for stealth cracks, lose bolts or off axis/non parallel flanges.

 

IMO, if he had an exhaust leak, he'd know it. VQs with even minor exhaust leaks have a very farty sound. Take it from a guy that has had over 6 different exhaust systems and multiple exhaust leaks on his VQs

 

Regardless, you should be seeing an elevatated powerband from 3500-6000rpms. All the other MREV dynos I've seen show a significant midrange gain. On your dynos, you can see the MREV choking above 6000rpms (normal), but the big wallop in midrange power is non-existent. You really weren't joking when you said you couldn't feel any difference in the midrange. I still think it's the TD. I'd say take the TD off first and see what happens. Or I guess you could wait until Russ gets his Stillen TD installed and dynos.

This really does suck because you're one of the few avid racers on the site that actually tests his mods and I would have figured the mods you selected would have gained the car a substanial amount of power.

 

LOL, not really. I have a exhaust leak at the join where my rear muffler meets the mid-pipe. Stock exhaust. And I didn't know it. I just saw black all around one part of the seal.

 

By nature, exhaust systems aren't completely airtight. My 03 exhibited the same thing you're describing. If you were to have put hand near the flange you wouldn't have felt air coming out. Why do you think exhaust systems tend to rust at the flanges? Beause the water trapped in the exhaust system will leak at these flanges when the exhaust is cooling down or cold. This rust will then break down the gasket a little and sometimes you'll see the black carbon build up you're describing.

A real exhaust leak (what I'd consider "minor") can be heard. The exhaust will emit a farty noise that can easily be heard and the air can be felt with the hand. A major exhaust is very audible and ugly sounding. A leak at the exhaust manifold gasket is deafening and a major power loss would be felt. If you don't believe me, so be it.

Trey's power loss does not suggest an exhaust leak and his dynos show it. There's something else going on.

 

That's possible, but consider Treys analysis of A/F ratio Vs the progression of modifications. (That was really good of Trey to keep all that data BTW)

With the data presented so far, the problem is more likely to be exhaust related. Note the onset of the symptoms began between modifications and only after the prior modification was shown to be acceptable.

This suggests the anomaly is probably related to the Crawford cat installation that followed. And it would have to be either poor cat performance or an exhaust leak.

It is doubtfull the catalytic converter is the problem, but there have been a few posts about cracking beads at the weld joints. Exhaust leaks could so easily cause these symptoms.

I'm also wondering if installation of the rigid X pipe exhaust could have contributed to crack propagation.

 

I have to disagree. I had an exhaust leak at the exhaust header flange where it caused a significant loss of power and a very high A/F. It really messed up the idle and performance.

During my trouble shooting phase I checked underneath the engine and chassi with a stethiscope specifically to listen for leaks but I simply couldn't find any. All other possibilities were investigated and eliminated. It wasn't untill after I removed the headers that I could visually see where the leak path occured. Carbon and oxidized chrome.

The problem was fixed when the headers were changed out.

What could have caused it?...
There was a bent U bolt on my Stillen exhaust that was further down stream. In any case the heavy gauge bolt was bent as if it hit a big rock or ran over something very solid. For the bolt to be that bent it must have transfered a lot of force and shock into the surrounding exhaust system. And the exhaust headers were the only part of the exhaust not suspended by rubber supports. The headers were hard plumbed to the rigid X pipe and heads. The bent U bolt connected to the X pipe wasn't far down stream. I think the headers were damaged (bent) by what ever damaged the U bolt on the X pipe. But the point is that I never heard the exhaust leak that so readily caused a loss of power and a high A/F.

I wouldn't exclude an exhaust leak so soon.

 

I have quite a lot of more information to share.

I went to an exhaust shop yesterday to check for any leaks. We put it up on a lift for a visual inspection. We looked at all of the components, and the welds, and we couldn't find anything of any signifigance. I then related that I am experiencing an odd noise(more on that in a second), so we pulled the car down, I got in it, and put it back up on the lift. I then preproduced the "noise" several times, and 4 different guys were checking it out. With the car actually running, we did discover a tiny exhaust leak at one of the welds on the midpipes. The Stillen midpipes have self-sealing slip-over flanges, but Zimbo (original owner) had these flanges welded when he put on his TT kit. Regardless, the leak was tiny, so small that a pin head could not be inserted. It was only noticed due to a very small bit of condensation present around the leak. It was the general concensus that the leak was acceptible, would not cause any codes to be thrown(I haven't experienced any) because it was after the 4 02 sensors, wouldn't affect performance, and that I shouldn't worry about it. However, if I want a more thorough/complete leak checkout, they can hook up a smoke machine. I elected to not use the smoke machine just yet.

Now let me describe this "sound". I installed my kinetix cats in late October, myself. I described the fitment issues I had with them. After I installed them, I would hear a noise any time the engine spun down, at about 2200 rpms. The noise sounds like "pffft", and only lasts for maybe a half-second. At first I thought it was an exhaust leak, and had it found to be negative. I then decided that it must be hitting the heat shield, which was also incorrect. I could never identify the cause of the sound.

In mid-November I drove to Nashville to help Doug prove that his cats fit 05 Sedans built on/after March of 05(there's a thread over on my350z about this). I did it just because I thought it would be cool to meet Doug, and I was off that day(so were the wife and kid), and figured we could hang out in Nashville for the day.

After Doug had installed the cats and taken pictures, he asked me if I wanted to buy them(used) at a discounted rate. I had no intention of swapping to the crawford cats, but they fit. Plus, these were *his* cats, and they had extra O2 bungs if I ever wanted to go with a wideband. I decided I couldn't pass it up, and told him to leave them on. I drove it around, and noticed I got back some torque that I had lost with the kinetix cats. However, they were rubbing the heatshields on the driver's side, so we got it back on the lift to adjust the heatshields. At the time, I noticed that "pfft" sound again, and pointed it out to Doug. We spent about 20 minutes trying to find the source of the sound, and finally determined it was coming from my stock ypipe. It seemed to be coming from one of the flex-sections when the engine spun down. We figured that I must have somehow damaged when ypipe when I installed the kinetix cats. He happened to have a few extra ypipes lying around, so he gave me one for free, to swap out when I chose.

I've been living with that pfft noise ever since. I decided not to swap out the ypipe because I knew I would be getting a full catback in a few months. So I got the Stillen, had it installed, and to my surprise, the pfft was still there. Exact same sound, occurring under the exact same circumstances.

So yesterday when my car was on the lift, the exhaust guys traced the sound(with their ears), to the xpipe. How odd is that? After I explained it couldn't be the xpipe, the best they could come up with was maybe it was a vacuum effect being created in the exhaust system at that rpm, and the gasses were rushing back through the xpipe(and the ypipe before it). That's just a guess, and may be completely wrong.

cliffnotes:
So I've got this really weird pfft noise that is happening, that eminates from after the cats. It started after the kinetix cats, persisted through the crawfords cats, and was present on the stock ypipe and stillen exhaust.

Regardless, I don't know if this pfft sound is a leak, and I'm fairly certain that this sound is not the cause of my erratic a/f ratios. Why? I was experiencing this sound when I dyno'd in November(with the kinetix cats), and my a/f's were fine.

Thoughts?

 

It sounds like you should take advantage of thoes extra O2 bungs on the cats. It may shed some light on what is happening and where.

 

Part 2 -
I called Doug yesterday to inquire about his cats. I explained my situation, and he said that the cats *can not* affect a/f ratio. The ecu uses for forward 02 sensors in the exhaust manifolds to adjust fuel, and use the lower 02 sensors in the cats for emissions. Therefore, the brand/operation of a cat will not affect a/f's. I don't know if I completely agree with him, but hey, I'm don't have his experience, nor do I manufacturer hiflow cats.

Anyway, he mentioned Tyler(thawk408 on my350z), whom has the complete crawford package on his 05 revup Z(no mrev) plus a borla exhaust. Tyler's car is running fairly rich, which appears to be cmmonplace for the revup engines.

Regardless of Doug's opinion, I have decided that I am going to remove the crawford cats. One reason is because I'd like to put my cat brace back on. The second reason is after even *more* analysis yesterday, I noticed that my car exhibited an odd performance characteristic.

When stock(actually with the 350z midpipe), I dyno'd in August and when my horsepower peaked, it stayed flat all the way to redline. It dropped 2hp from peak to redline. We all know this to be common to the revup.

When I dyno'd in November, my car stopped holding peak power. The only changes were the addition of the kinetix cats, k&n, and ztube. From peak at 6400 rpms, I lost 10hp to redline.

Why the sudden loss? Sure, I peaked higher than I did stock, and at redline I was making within 2hp with the kinetix as I was stock(within margin of error), but why didn't the car hold it's peak power? I hardly doubt it has anything to do with the k&n or the ztube.

I just noticed this yesterday when I was playing with winpep. The car has since exhibited the same peak-to-redline-loss trait, with the kinetix cats, with the crawford cats, with and without the muffler, and obviously with the MREV(known mrev trait afterall).

So, I'm going back to stock cats and go on from there.