Well, I finally solved the low-end torque loss I'd been and whining about after trying an Ooglie Cali/Fed conversion. I replaced the Cali manifold and partially gutted pre-cat with a Fed spec manifold (many thanks to Desert Pearl for answering all my e-mails!). I got it from a local salvage yard off a '95 model for $50. It was either this, or spend about $500 bucks for a new pre-cat, or just live with it and a rougher idle as well.
Now in addition to getting back the torque I'd lost, the car runs/idles as smooth as when it was stock, the exhaust is just a little deeper, and the little bit of top-end I gained remained! I sure didn't think a partially gutted pre-cat/Cali manifold would be so different from a Fed spec manifold as far as exhaust flow characteristics.

The manifold removal and install was a pain in the b**t. Not to mention I had to remove/re-install the y-pipe yet again for this. I definitely have to agree with Desert Pearl that as far as the slight gains I experienced it was not worth the trouble at all, and I would have been better off just leaving the front precat alone. However, as far as driveability characteristic, meaning very smooth and just as quick acceleration, and just the way the engine seems to run much more smoothly in general as it did when stock, I'm glad I did it and I think it was worth it (these things are important to me you know ). But if this doesn't really matter as much to you - don't bother. I just wish I had better know-how regarding all the various steps to doing this before starting it.

 

Well unless I'm mistaken, you've just taken away Desert Pearl's bragging rights as having the one and only CA-spec to Fed-spec Maxima in the world.

That's all right, Desert Pearl. We still luv ya!

 

nice job

 

Yeah - he was the first to do it though, and I'll probably be the second and last!

UMD_MaxSE - it was a pain but in a weird way I did enjoy doing it. I just get a kick outa working on my car in general.


Have you guys though about doing the valve body mod?

 

I wouldn't necessarily say that, sleepermax. I'm constantly amazed at the things people are willing to spend their time and money on. Both you and Desert Pearl had legitimate reasons for doing your conversions, of course, and valuable information was gained as a result of your experiments. But in both cases, the information gathered points to an inevitable conclusion:

There is nothing of value to be gained by modify your Cali-spec front exhaust manifold.

On the other hand, I've learned never to underestimate the power of denial. So who's next?

 

how do i find out which spec my car is? and which is better to have? thanks

 

I won't be next, but once the warranty is up I WILL perform the cali-fed conversion! There is one FACT that you have forgotten. The unbalanced flow of exhaust gasses due to leaving the ONE remaining precat WILL lead to premature engine damage. Whether or not it will occur during "your" ownership is unknown, but it's a risk I'm not willing to take.

 

y2kse - I have to agree with you on one point and partially on another. First, the power of denial was one motivating factor in my trying all this in the first place, lol!

Second, modifying a Cali-spec front manifold (I take it you mean gutting or partially gutting the pre-cat) is not a good idea at all. However, I think replacing the manifold with a fed spec manifold may be something to think about doing for some of us. Especially those of us with ultra power parasitic Nissan auto trannies. And those of us who may be keeping their Max for the long haul. [Why doesn't Nissan get auto trannies from GM like BMW does? If there's one thing they've got down pat it's their trannies.]

Having tried the following set-ups over the past several weeks:
1. stock
2. y-pipe with pre-cat
3. y-pipe with partially gutted pre-cat (after relocating the rear o2 sensors)
4. y-pipe with fed-spec manifold

I can honestly tell you I like #4 the best (taking warranty concerns out of the equation). Sure, the peak performance gains are minimal over #2 - you can feel a power difference but barely. But what I really like is the way the power is delivered - acceleration and power delivery is very smooth, and the motor seems to be running in a more clockwork-like manner. Basically it feels like stock but with lots more power. With #2 the power certainly felt better than stock but not as smoothly delivered. Granted, these are all butt-dyno impressions, but having experienced set-ups 1-4 very recently I think I've got a fresh enough memory of each to make a pretty valid comparison.

My other reason for trying this was the hashed and re-hashed (and now re-re-hashed!) backpressure difference question. I'm now fairly certain that this will not present long term harm. We've already established that the O2 sensors adjust the air/fuel ratio accordingly thus carbon deposits should be about the same over both cylinder banks over time. Also, supposedly the engine really doesn't care if one cylinder bank experiences different backpressure as long as the a/f ratio is adjusted accordingly by the O2 sensors.

However, I'm not 100% certain there won't be long term drawbacks. Since I'll probably be keeping this car for the long haul and it is my primary mode of transportation at this time, I feel much better knowing that both cylinder backs are experiencing the same backpressure, will have about the same carbon deposits, and will likely wear evenly. Again, in all honesty, I think leaving one pre-cat on probably won't have any noticeable effect on the motor (ie rougher idle and power delivery, reduced power ect) until probably 100K miles or so but I kept my last car to 175K miles and it was still running strong until it got totaled (not my fault) and I may very well keep my Max this long.

I feel it was worth it for ME. It's really a mod that's 75% preventive maintenance and peace of mind, 25% performance. It was a whole lot of work though. At least now I have a better idea of how to do this and if anybody is interested I can tell you how I did it (no need to take the radiator off by the way).

Anyway, if this mod eventually takes off, I think it should be called Desert Pearl's Fed Spec Conversion or something like that since he was the pioneer!

 

I think y2kse had discussed this before with some pretty knowledgable people. They had all said that uneven exhaust flow will not harm the engine. Not only that, but the front precat is not very restrictive as is evidenced by the very minimal gains achieved by swapping it for a stock fed spec manifold. y2kse: do you care to elaborate on this some more?

sleepermax: I know what you mean about working on your car. I like it a lot as well. I am thinking about getting the VB mod. Perhaps in a few months. Next up for me is the UDP...

 

You stated it perfectly, UMD_MaxSE. The only thing I would add is that the knowledgeable people you refer to work for Random Technology. I'd say RT knows a little something about catalytic convertors and flow characteristics.

I also intend to keep my Max for a long time. And I'm not the least bit concerned about "uneven exhaust flow". But I am concerned about the possibility of having to pass smog some day. So I think I'll leave the front manifold alone in case I have to reintall my stock Y-pipe to accomplish that.

 

UMD - Here's a thought... you may want to save your pennies and get the VB mod first (you'll probably need to factor in the cost of a rental while your car is out of commission). The pulley is nice to have, and is an improvement over an ok stock pulley, but I think its' benefits are more noticeable on a 5 speed. The VB mod on the other is not only an improvement but addresses a glaring defficiency on the stock VB and how the auto tranny shifts. I really wished I would have done this first because when I consider performance benefit gained per dollar spent, the VB mod is way better in my opinion.

The removal and install is really pretty easy too. You just have to keep track where every screw goes, keep everything very clean and torque everything as closely as possible to the specified torque. I've had absolutley no problems since installing mine (and probably look kinda weird smiling all the time while driving).

 

I know the VB would be more worthwhile than the pulley. But, I am going to try and coordinate the VB mod with some vacation time probably later on towards the end of the year. Plus, there is a group deal on the UDP going on now which is pretty good. Hopefully, coming up with the $$$ won't be a problem later on Thanks for the advice