[Z-Rex]

Re: Why rebuild?

> I have a 1978 Datsun 280Z running stock
> intake, fairly well tuned, but has a knock
> developing on number 5. The exhaust consist
> of OEM pipe to the hollow cat. out to a
> Cherry Bomb glass pack. I went in for
> testing yesterday and my car passed with
> flying colors. In TX the highest your
> reading can be is 750 ppm, I don't remember
> if this is CO or what but it relates
> directly to the cat. Anyway at idle my
> reading was 118ppm and at running speed it
> was 12 ppm. The inspector said the 96 Ford
> Taurus in just before me didn't test that
> well. All of the other reading on my car are
> also very low. I am not saying cut off your
> cat. I am just stating that if a car is
> tuned to utilize all the HP the motor can
> produce and is in good working order, most
> emission control is unnecessary. I have no
> EGR or other such non-sense on my motor. She
> runs clean and strong, I think this might
> not be legal, but at least my moral problem
> with polluting the air is gone.

> John Cooney

> Clean but not legal....

Then, why do you want to rebuild your engine? It sounds great! Is it because of that knock? You can take care of that with out rebuilding, it may not even be a valve, could be the rocker arm, or something...

 

[Unknown User]

Re: Why rebuild?

> Then, why do you want to rebuild your
> engine? It sounds great! Is it because of
> that knock? You can take care of that with
> out rebuilding, it may not even be a valve,
> could be the rocker arm, or something...

Well I know the knock is from down under... Thats not so good. I used a scope and listend very carefully, the knock happens when I tap the accelerator from idle, it is the loudest right next to the pan/block gasket on #5. The smoke is from a failed valve seal and too much backpresure in the block. Probly from blow by in the rings (#5?) I can lessen the smoke by opening the PCV hose on the top of the block. But the knock just gets louder every day. Click click click.....

 

[Unknown User]

Re: Why rebuild?

> Well I know the knock is from down under...
> Thats not so good. I used a scope and
> listend very carefully, the knock happens
> when I tap the accelerator from idle, it is
> the loudest right next to the pan/block
> gasket on #5. The smoke is from a failed
> valve seal and too much backpresure in the
> block. Probly from blow by in the rings
> (#5?) I can lessen the smoke by opening the
> PCV hose on the top of the block. But the
> knock just gets louder every day. Click
> click click.....

My friends z knocked and it turns out he had a busted bolt on his exhaust manifold

 

[Unknown User]

Re: Why rebuild?

Had 2... Fixed them.. still knocking, but thanks for the advise. Keep them coming and I will keep trying.

 

[Phantom]

Cat or no Cat

Bean bandit -
The catalytic converter was only required in California up through 78. The 79 280ZX was the first Z to be catalytic equipped for sale in all 50 states. The readings you referred to are, in fact, CO. I have a catalytic equpped '77 280Z that gets simailar to yours but it has all the stuff still on it and runs like a bandit. The catalytic converter, however, has nothing to do with CO emmissions - it neutralizes some other nasty by-products you get when burning unleaded fuel. The stuff that was added when tetra ethyl lead was removed. It also works great as a resonator and causes almost no back pressure. I will continue to run mine so my conscience won't suffer - at this point my performance doesn't either.

> Had 2... Fixed them.. still knocking, but
> thanks for the advise. Keep them coming and
> I will keep trying.

 

[Unknown User]

cat with no back pressure, you gots to be kidding

The catalytic converter is the weak link of all
exhaust systems. It might be true to say that
free flowing cats create little back pressure.
The back pressure created by the stock muffler is
nothing compared to the stock cat.
I'm not trying to insult you but it sounds that
you've read some advertisements that were a bit
discerning. You should read some hot rod magazines to get back to the basics of exhaust systems.

Antony

> Bean bandit -
> The catalytic converter was only required in
> California up through 78. The 79 280ZX was
> the first Z to be catalytic equipped for
> sale in all 50 states. The readings you
> referred to are, in fact, CO. I have a
> catalytic equpped '77 280Z that gets
> simailar to yours but it has all the stuff
> still on it and runs like a bandit. The
> catalytic converter, however, has nothing to
> do with CO emmissions - it neutralizes some
> other nasty by-products you get when burning
> unleaded fuel. The stuff that was added when
> tetra ethyl lead was removed. It also works
> great as a resonator and causes almost no
> back pressure. I will continue to run mine
> so my conscience won't suffer - at this
> point my performance doesn't either.

 

[240Dave]

Can have very little pressure though

> The catalytic converter is the weak link of
> all
> exhaust systems. It might be true to say
> that
> free flowing cats create little back
> pressure.
> The back pressure created by the stock
> muffler is
> nothing compared to the stock cat.
> I'm not trying to insult you but it sounds
> that
> you've read some advertisements that were a
> bit
> discerning. You should read some hot rod
> magazines to get back to the basics of
> exhaust systems.

> Antony

New cat's are extremely high flowing. The older original equipment found on Z cars is of a pellet design, which you may well know is VERY restrictive. But, replacing it with a newer honeycombed brick design is extremely beneficial. You can gain performance, as well as have a clean running engine. No sense in ripping out a cat for 2 extra hp in the high rpm. I kept all the cats on all my cars that came with them, and had plenty of performance. I would never remove the cat for a few hp. It just isn't worth the extra noise and emissions.
Try looking through a new honeycomb cat. You can see right through it. This is indicatvie of the new designs, extremely high flow. Try looking through most performance mufflers, unless they are a straight design, they will have bends in them, such as 2 chamber flowmasters etc.... This makes the muffler more restrictive than the cat at this point. Most N/A engines need some backpressure to produce a decent torque curve, and if you eliminate all backpressure your N/A car will not run right. If you don't believe me, try this experiment. After driving your car around with the muffler/cat/exhaust, remove the entire exhaust system except for headers. What you will notice is more power, but the power band has changed to such a high rpm, and LOTS of low end can be lost. This is the reason you need some backpressure on an N/A engine. Of course, with a turbo, you want as large and free flowing exhaust as possible, becuase the turbo provides all the backpressure the engine needs. You don't want any pressure after the turbo, becuase it would have to work harder, and performance would suffer. My advice is keep the cat, just replace it with a high performance design, this way you get a few lost hp, and will pass emissions. These cats are more efficient to boot, so you can actually have a cleaner engine by installing the new cat also.

 

[Phantom]

Re: Can have very little pressure though

Thanks for clarifying my position Dave. Don't wask me how but my '77 has the free-flowing wafer design vs. the pellets.
There are a few axioms that I have come to stand on:
1) Adds, commercials, etc. are created to sell a product and the truth is usually only incidental and you have to look hard to find the shred that the add is based on. Obviously I stake very little on adds.
2) Foroms like this are populated with sincere enthusiasts who, like myself, are generally long on enthusiasm but also profoundly ignorant. Fortunately ignorance can be cured - thus the justification for the forum.
3) You never ever modify a component on a vehicle without first determining why the OEM made it that way and then also identifying the other systems that will be affected by the change. I learned that when I was going to put headers and low restriction mufflers on a '70 'Cuda with a 340 ci V-8 only to find out that the MOPAR cast headers and mufflers borrowed from the 426 Hemi were considered equal to any aftermarket system available at the time. A little investigation saved me a lot of money.
It's like the way headers are combined on a six so that three cylinders that fire 120° out from each other are routed into a common pipe so they won't fight each other and actually help scavenge each other so the combination is more effective than individual straight pipes.
My car still has a stock intake and exhaust except tfor the muffler itself. Nissan designed the sytem the way it is for several reasons. Until I sort out all the ones that need to be kept I'm not about to start changing a bunch of stuff because it seems like a good idea. The reason for a larger diameter exhaust is so that more air can flow down it with an equivalent back pressure to original. It's like changing wheel sizez and tire profiles so that the new combination has the same rolling diameter as the old so the speedometer doesn't get screwed up.
Oh well - enough rambling for now. Keep the exchange going guys - I'm learning a lot - not only of what I can do but also what I shouldn't do.
Phantom

 

[Unknown User]

Alright, so you've proved you know your stuff but

can anyone explain that when I went to gut my
cat, all I found in there was a wire mesh wound
up ball. After finding my cat already missing its internal I was quite upset because I wanted something to do. So I take out the wire mesh thingy and from 2800+ rpm I could feel a difference. Then later on I had to take my muffler off and drove around without any restrictions except the cat housing. Basically it was as free flowing that you can get a stock exhaust without adding anyother parts. This made the car pull a lot harder at highway speeds
(75+). This goes to show that more people can benefit from a straight through exhaust than just racers.

Antony 83NA

 

[Phantom]

Can't argue with experience

Antony,
There is no way I'd argue with the results you have personally experienced. Theory is one thing - actual experience is another. I'll go with experience nearly every time.
As a engineer in a manufacturing plant, however, I've noticed that frequently a certain result may get misinterpreted and the credit or blame for something is awarded to the wrong source. Your description indicates that you had a converter that had experience mechanical failure and was literally stopping up your exhaust. In your case - pulling the plug was the right move. You removed a restriction that wasn't included in the design parameters of the engine and got your performance back to where it should be. If a person has a converter in good condition, though, it's just not worth the effort.
Remember - the automotive industry is very competitive. Their engineers are always looking for the best way to improve their products - and it's generally a holistic approach - IE: they don't improve one thing at the cost of another. Example - my son has a Pontiac Firebird with the 3.8 liter V-6. His car is heavier than my Z and the engine is bigger and has more horsepower. so, even though he's heavier he can out accellerate me and the gearing and engine management system allows him to get over 31 mpg on the highway which knocks the wind out of my Z there too. It can do that because it benefits from an additonal 20 years of engineering refinement my Z doesn't have. Bummer! My only saving grace is the Z doesn't have a stupid governor on it so I can out run him on top end. I guess not all progress is good.
Keep looking for the edge - you'll find some. Let me know when you do.
Phantom

 

[kasper]

Re: Alright, so you've proved you know your stuff

> can anyone explain that when I went to gut
> my
> cat, all I found in there was a wire mesh
> wound
> up ball. After finding my cat already
> missing its internal I was quite upset
> because I wanted something to do. So I take
> out the wire mesh thingy and from 2800+ rpm
> I could feel a difference. Then later on I
> had to take my muffler off and drove around
> without any restrictions except the cat
> housing. Basically it was as free flowing
> that you can get a stock exhaust without
> adding anyother parts. This made the car
> pull a lot harder at highway speeds
> (75+). This goes to show that more people
> can benefit from a straight through exhaust
> than just racers.

> Antony 83NA

Don't just gut your cat is causes a flow RESTRICTION. I know, we did some flow tests to prove this. If you want free flowing exhaust but with the apperance of the cat still in place, then you must put a pipe though the inside of the cat. This will giev you good flow but leaving just the gutted cat may acctually cause you to lose power.

 

[Unknown User]

Re: Alright, so you've proved you know your stuff

I know but I don't mind for now. I guess when I get a complete 2.5 exhaust, I'll have to buy a new free flowing cat (with really big faces on both ends).

> Don't just gut your cat is causes a flow
> RESTRICTION. I know, we did some flow tests
> to prove this. If you want free flowing
> exhaust but with the apperance of the cat
> still in place, then you must put a pipe
> though the inside of the cat. This will giev
> you good flow but leaving just the gutted
> cat may acctually cause you to lose power.

 

[Unknown User]

Re: Alright, so you've proved you know your stuff

I know but I don't mind for now. I guess when I get a complete 2.5 exhaust, I'll have to buy a new free flowing cat (with really big opening surface areas on both ends).

> Don't just gut your cat is causes a flow
> RESTRICTION. I know, we did some flow tests
> to prove this. If you want free flowing
> exhaust but with the apperance of the cat
> still in place, then you must put a pipe
> though the inside of the cat. This will giev
> you good flow but leaving just the gutted
> cat may acctually cause you to lose power.

 

[john]

Re: Alright, so you've proved you know your stuff

After reading through this message thread I realize the ignorance of my ways - here's the long & short of it:
Bought a '77 Z from a used car guy that looked great & seemed to need very little. He guaranteed inspection but when his guy inspected it said it needed a new muffler to pass emissions. Okay, he gets Meineke to customize one, costs about two bills and now I'm getting some serious exhaust fumes in the car. I'm thinking exhaust manifold is leaking, but you guys, who obviously have a great deal of past experience in this subject lead me to believe that Meineke doesn't know jack!
Could the back pressure from this new muffler be causing a leak into the engine compartment? I can't detect any leaks.
I'm going back to Meineke but I'm thinking my next step should be a high-performance custom exhaust...
Thanks for your patience regarding my exhausting ineptitude!

 

[Phantom]

Re: Alright, so you've proved you know your stuff

John,
The most probable cause of the exhaust smell in your car is a leaking hatch or tailight gaskets. This is a really common problem in Z's. I'm on my second '77 and both have had the same problem. Car smells fine when cruising down the road with the window up, pretty much OK with the window down too UNTIL I decellerate off the highway. Then I almost choke on the fumes. The down window cause a vacuum inside the car which, during decelleration, sucks all those extra fumes into the cabin past the seals in the rear of the car. There are a jillion of them. around the hatch, around the tailights, in the bottom of the hatch, underneath the deck where all the fuel lines go through, etc. It's a bugger toseal them all up on a 20+ year old car.
Meineke probably didn't goof. Oh - adding insult to injury - you paid way too much for the muffler unless they did a lot of tailpipe work along with it.
Phantom.