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· Registered
477 Posts
The environmental impact...long

Removing the cat may or may not affect your tailpipe test. This depends on the condition of your engine, and the levels of pollution allowed in your area. If your engine is very efficient, the levels of NOx may be low enough to pass without the CAT installed, but if your engine was running poorly and had the CAT installed, it would still pass. So, it can be a gamble, depending on how confident you are with the tune of your engine.

Case and point: My engine is a 2.8L with triple webers and while tuning it, it was hooked up to a exhaust analyzer. It turned out that my 2.8L put out only 200ppm more NOx than a typical 280Z with fuel injection and CAT installed. The reason for this is that my engine is more efficient. However, if I was to install a CAT, my emissions would be much lower than that of the stock 280Z, since I'm already more efficient to begin with. Personally, I'd keep a CAT if I had one. I'd just get a free-flow design. Many companies make such CATs, and they don't rob horsepower like they used to. The stock Datsun CATs are quite old (15+years) and were of an older design. I wouldn't be surprised if they were robbing significant amounts of hp, due to them falling apart, and becoming a restriction. Just replace it with a new one. I used to have a HONDA, and always ran the CAT. There was only a SLIGHT increase in hp with it removed. Actually, the engine liked the backpressure that it provided. It had a better torque curve with the CAT installed. So I voted to keep the CAT installed, and have cleaner running engine (and air), for the sake of a few hp.

The CAT is used to convert NOx (Nitrogen oxides) back into Nitrogen and Oxygen using a catalyst (hence the name catalytic converter). NO engine is 100% efficient. Fuel injection, powerful sparks, re-designed combustion chambers, etc... all help to make the engine more efficient. But, man has yet to make a 100% efficient internal combustion engine. You can get emissions extremely low (Honda has a ULEV Accord), but they still exist, and will not go away completely.

Alternative fuels (propane, hydrogen) do not need a CAT. This is because they are of a different molecular compound than gasoline, and the product of their combustion is not the same.

Of course less emissions are better than more. This is why a CAT is used. It cleans up the unburned gases and reduces them back to their original elements. Otherwise these 'radicals' can begin reacting with other elements and create smog, which causes lung problems, which causes acid rain, which eats away at buildings, paint etc....

Guess my California upbringing is evident now.

Just my .02

· Registered
477 Posts
Re: environment and ? (long)

Yeah, it's kind of hard to keep the air clean, when crap from China just floats on over in the jetstream, but hey, we've got to start somewhere. I actually read an article about the Honda ULEV engine. They said that if you drove that car around L.A., you would actually be CLEANING the air!! The Honda puts out less pollution than what's already in the air.

Mine is a 1978, stock engine
> with 134,000.

> high speed results: reading limit

> HC ppm 4 500
> CO% .01 3.0
> CO2% 13.1
> O2% 19.9
> RPM 2411

Wow, 4 ppm is quite low. Are you sure they tested it right?? That is one of the cleanest readings I have ever seen. Most I've seen run about 150-250 HC ppm. My car was about HC 400ppm. I don't have a printout, but next time I go to the dyno, I may have one done. I guess Nissan knew what they were doing way back in 1977 to get a car to run that clean.

> idle results

> HC ppm 58 500
> CO% 0.0 3.0
> CO2% 12.7
> O2% 19.8
> RPM 804

These are also extrememly low. Sure you didn't pay the guy taking the test?? :) I would say that if you removed your CAT, you would still be well within limits, if your car runs this well. Of course all the HC and CO would go up, but still passable I would imagine.

The value that indicates rich/lean, would be the CO and HC. The higher these values, the richer your engine is running. The HC is UNBURNED fuel, which obviously means there is too much fuel, or a rich condition. Your car is running very lean. Does your car run hot?? Leaner conditions make cars run hotter. A basic rule is to run rich rather than lean. As there are more consequences to running lean than there are running rich.

· Registered
477 Posts
Some ideas to ponder...

The reason I feel running rich is better than running too lean is for two reasons.

1) You don't lose as much hp, by running rich. The leaner you go, the more rapidly hp begins to drop off.

2) Lean conditions cause pinging, and hot running engines. Unless the engine is designed to handle that effectively, you can cause serious damamge. As opposed to just having carbon buildup from a rich running engine and occasional backfiring. I'd rather have the carbon than the pinging. Wouldn't you??? Of course the magic 14.7:1 ratio is the best. It's a stoichiometric ratio (meaning it's the ratio of fuel:air at which 100% combustion is possible).

> Any ideas on what I should do next?

Well, now you're getting into a whole different bag of tricks. There are many ways to go with this, depending on what you want.

> Cam (reccomendations)?

Unless you are porting the head for higher flow, a high lift cam (.500+) isn't going to do anything for you. One thing you can do, is to install a longer duration cam. You can actually have your current cam reground to make it longer duration. I think 265-280 duration works great. The longer duration will allow you to rev STRONGLY up to 6500. Although the 280 duration can be a little lopey. If you get the 265-270 duration, you might actually help the engine stay clean, as Z cams are notorious for being undercammed. Although they are very easy to overcam as well.

> Exhaust?

Here's another area where it's easy to gain a few hp. 2 1/2 is a very popular setup, although 2 1/4 can work quite well. The 2 1/2 is a little louder, and can rob some low rpm torque. The 2 1/4 works best for all around daily performance. Just have a shop make one up for you with a high quality muffler. e.g. Dynomax Ultraflo, Borla, etc....Careful, these can get LOUD!!

> Headers?

I wouldn't bother unless I had the exhaust & cam already. Since you need to smog your car, the Nissan Motorsports are out of the question. You might pass the tail-pipe test, but you'll fail the visual inspection. I think the Motorsports Auto 3-2 setup is crap. The 6-1 design is alot better, although it can't compare to the Nismo.

> K&N?

Highly recommend it. I ran K&N on all my other cars, and what a difference. Besides, you can just clean it when it's dirty, and re-install it. I like the idea of not having to buy a new filter every 6 mo., and actually get a few hp to boot.

> Is there really a good bang for the buck? I
> suspect it's like what I did; they all help
> a little and add up when done together.

You're absolutely right. You have to think of the engine as a system, and need to consider all aspects of it when making a change. This is why I would recommend getting a cam after the exhaust and K&N. Otherwise, it won't be able to do it's job, and pull in more air, because you've still got restrictions. The key to modifying an engine is BALANCE. You want the amount of air in to = the amount of air out. Any difference will change the characteristics of your engine.

> How does your car run? Approximate 0-60s or
> HP. What else have you done besides the
> triples?

I've done alot to my current engine, and am doing more as we speak. It's a long list of mods. Basically, I'm running 9.6:1 compression, fully ported polished head. Port matched intake manifold. Nismo headers with 2.5 exhaust(soon to be 3).

Right now, my engine puts out about 220hp (gross). I based this on information gathered from some reputable engine builders in the area. With my new cam, and 3 exhaust I should be approaching 250hp(gross). I'm still running the stock 240 cam, so I'm missing out on ALOT of top end. My engine runs out of steam @6000rpm. I'm going to dyno it this summer.

So far, I've run [email protected] I think that works out to about mid 6 second 0-60 range. This is with a 280Z 5spd and stock R180 3.364:1 diff. I'm planning on upgrading to a 3.7 or 3.9 R200 this summer. Should improve my times to mid 14's and low 6 second 0-60.

>Would it really make that much difference to go to a 3.9:1 rear-end?

Sure will. Might be shifting a little more, but it'll help you get going.


· Registered
477 Posts
Nismo & other suggestions...

> How much do the NISMOs run and shouldn't I
> do them when I do the exhaust?

$300.00 and if you do them with the exhaust that would be great. It's easier to do everything at once. But, don't expect to get the most hp out of the headers until you install the cam and modify the intake and other items. A degreed cam gear might be a good idea as well.

You can order a catalog from:
Nissan Motorsports
P.O. Box 191
Gardena, CA 90248-0191
(310) 538-2610 voice
(310) 538-1462 fax

Also, how do
> you get a muffer shop to shoot a pipe
> straight out the back, when the car (78)
> calls for a CAT. Isn't that illegal for them
> to do? Or do you just find a specialty shop
> that doesn't ask questions?

Have them fab a pipe from the header to the CAT, then from CAT back. Then when you get home, you can either keep the CAT, make a hole appear in it with a broomstick, or buy a high flow version. Depends on what your conscience tells you to do. Yes, it is illegal for them to remove smog equipment, and if you find someone who'll do it, you're lucky. They can get HUGE fines for such things.

> On the cam, I've heard you can decrease the
> valve lash spec, and get a similar result to
> longer duration. Any knowledge on this and
> how much you can go before you've gone to
> far and lost your ramp?

Yes, that does affect the overall duration. It is effectively keeping the pad in contact with the cam lobe for a longer time, thus keeping the valve open longer. Don't expect more than a few degrees from this mod though. And, you have to be careful as to how tight the valves are, because you don't want them to get too hot. They need to fully seat in the head when closed to transfer the heat into the head. If the clearance is too small, they will not fully seat when everything is up to temp, and may burn on you. The smallest clearance I'd run on the Intake would be .005 and .006 exhaust.
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