from CustomMaxima.com today. I got the last Y-pipe on the group deal.

As some of you know, I held back on buying a Y-pipe for a long time. I had heard that by removing only one pre-cat, CA/NLEV-spec Y-pipes could unbalance the exhaust flow between cylinder banks and lead to long-term engine damage. But thanks to some technical information I read to the contrary as well as the efforts of several members of this forum, most notably Desert Pearl, I'm convinced that a CA/NLEV-spec Y-pipe will not cause engine damage.

My other concern was the "bees in a can" sound many Y-pipe owners complain about. I researched that subject pretty thoroughly in a couple of polls I posted recently. Based on the results of those polls, it appears that the Cattman Y-pipe is my best bet for avoiding the pests. Plus, as everyone knows, Cattman makes the best Y-pipe on the market right now from the standpoint of materials and craftsmanship.

So Y-pipe . . . here I come!

 

y2kse - the exhaust imbalance issue was also my concern. Is that technical info you mentioned available on-line?

 

I am also looking to order a cattman pipe soon. Perhaps within this month. Was the exhaust imbalance issue because of the rear O2 sensor positioning? If those sensors only check for the presence of pre-cats, then things should be fine, right? Probably the front O2 sensors prior to the pre-cat measure exhaust and adjust air/fuel ratio accordingly.

 

If it exists at all, the imbalance has nothing to do with the positioning of the O2 sensors. It has to do with leaving one pre-cat in place and removing the other.

 

This is a back-pressure imbalace caused by removing only the rear precat and it only applies to 2001 max's. I think all 2000's the I'm still not convinced that this is insignificant enough to not cause some long term damage or at least accelerate engine wear. If you're planning on keeping your Max for 40-50K miles, then getting another car (2003 Max!) I wouldn't worry about this at all. But if there's a possibility you'll keep your car longer then this may be something to think about. That's why I'm going for the Cali/Fed conversion - besides, Desert Pearl showed that losing the front precat will give you a couple of extra ponies too!

Relocating the rear oxygen sensors doesn't involve an exhaust imbalance at all. It was just a question of does the ECU use the rear sensors to regulate the air/fuel ratio. If so then relocating the sensors behind the larger main cat could cause the ECU to mis-adjustments this ratio. But I'm assuming that these sensors aren't used in this manner by the ECU unless the front sensors start too fail - at least this is the way the 4th Gen's three sensors seem to work.

 

Again, the post I read dismissed this "back-pressure imbalance" theory, sleepermax. And Desert Pearl's empirical evidence does pretty much the same thing. But as I said before, I can't find the post I read right now. So I'll reluctantly defer to you for the moment. This much I can tell you. I intend to keep my Max for a lot more than 40-50K miles and I'm not about to lose any sleep over "back-pressure imbalance".

Having said that, Desert Pearl's Cali-spec to Fed-spec conversion is arguably a better way to go UNLESS your warranty is important to you. If it is, I'd suggest that it will be much easier to reinstall your stock Y-pipe before taking your car to your dealer for warranty repairs than having to convert your entire exhaust system from Fed-spec back to Cali-spec.

 

Woohoo! New mod!

 

Congrats on finally getting a Y!!! I'm sure you'll like yours as much as I like mine.

 

http://forums.maxima.org/showthread.php?postid=209153

So much for the idea of exhaust flow imbalance.

As further evidence, I would submit that Desert Pearl's results can lead to one of only three possible conclusions:

1) The front pre-cat is not restrictive enough to create a flow imbalance between the cylinder banks with the rear pre-cat removed.

2) As Random Technology indicated, the Cali-spec ECM is balancing the A/F ratio between the cylinder banks electronically.

3) God doesn't want Desert Pearl's car to go any faster!

Interestingly, conclusion number 2 draws us back to conclusion number 1. The reason, quite simply, is because there was virtually no difference in performance between the Cali-spec manifold and the Fed-spec manifold on Desert Pearl's car. So either the front pre-cat is a non-issue from a flow perspective OR the ECM is expecting to see the front pre-cat and is adjusting the A/F ratio between cylinder banks accordingly. There's only one way to be absolutely certain, of course. Desert Pearl would have to replace his Cali-spec ECM with a Fed-spec ECM and then dyno his car again. If the Fed-spec ECM yielded a substantial performance increase, we could reasonably conclude that the front pre-cat was an impediment to flow and the Cali-spec ECM was adjusting the A/F ratio to compensate. If it didn't increase performance appreciably, then conclusion number 1 would be the only reasonable conclusion that could be drawn short of divine intervention.

 

I would like to install a Cattman Y pipe as well as a cat-back from Cattman once they're available. Some other mods I'm considering are: Eibach springs, CAI, rear anti-sway bar and a FSTB. What are these mods going to do in terms of engine life and ride? Honestly, how noticeable is the HP gain? I want a little meaner sound from the car, would a Y and a cat-back provide this? Sorry if I sound like an idiot, it's not the first time and certainly not the last.

Thanks, Dave

2001 SE with about 450 miles on it. Can't wait til the 1000 mile break in is up.

 

Welcome, Dave.

First, I'd suggest you read through the Frequently Asked Questions (FAQ-U) thread at the top of this forum. I'd also suggest you look through the FAQ section of the main Maxima.org website (www.maxima.org/maxfaqs/index.shtml). Then I'd recommend you use the search function at the upper right corner of the page to search for specific items of interest.

If you don't get all the answers you're looking for, post a new thread and we'll respond.

 

Cool - I wish I'd run across that thread earlier. Another thing I hadn't thought about is most of the time I'm not running my engine between 3-6K RPM, well I try not to anyway Most of the time I'm operating it below 3K RPM where this possible imbalance would be close to, if not totally, nil. And the ECU compensates for any possible effect on the A/F ratio anyway, which is important as far as minimizing engine wear, increased deposits, fouled plugs ect - so I feel better about trying this mod now without replacing the front exhaust manifold. I think the only thing to really make sure of, and which takes on added importance with this mod IMHO, is to check the O2 sensors earlier than whatever the recommended interval is, say at 50K - 60K along with the plugs, if not sooner. They do get more and more sluggish with time and you don't get a check engine light until they are significantly sluggish.

So I guess the main restriction on the stock exhaust is the Y junction itself, (in addition to the deep crimp right after the main cat)?

As far as problems with warranty service - I'll take my chances.
I think the main things that seem to be problematic with 5th gens are the following - let me know what I've left out:

1. TCM/solenoind - mine is a 2K1 built after September'00, so this doesn't apply.

2. Wheels improperly torqued (might warp rotors too soon) - I checked the lugs were on my left front tire - they were all exactly torqued at 85 ft/lb's so I guess they've addressed this issue at the assembly plant. I didn't bother to check the other tires. I figured either they are all OK or by an incredible coincidende all lugs on a randomly picked tire are at the correct torque!

3. rattles - none so far.

4. bad ignition coils - none so far as I can tell. I'm using Chevron gas exclusively.

5. Paint chips - not a prob so far.

Anyway, sorry for rambling on - thanks for the help. I've found this forum to be an invaluable resource, especially for someone who is horsepower obsessed like myself.

 

HP gain with a Cattman Y-pipe, cat-back and CAI is about 30hp at the crank. That should be enough to knock over half a second off your 1/4 mile time. You might want to rethink teaming up the Cattman Y-pipe with the Cattman cat-back unless they do some more work to quiet it down. MrBurner has this setup and it's LOUD!