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Old 01-12-2008, 03:13 AM   #1 (permalink)
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OEM Air Injection, Yay or nay?

My Datsun 240Z has an air injection system, and I have been thinking about removing it. For those unfamiliar with air injection, its 1970's emissions technology. Basically, the engine turns an air pump, which is connected to tubes in the exhaust manifold that inject air to oxidize CO and HC's...to make CO2 instead.

This is definitely a good thing, I mean we're all trying to reduce CO2 emissions, but CO2 is nowhere near as bad as CO. However:

-The exhaust manifold tubes increase exhaust flow restriction

-The air pump increases engine drag

-The whole system adds weight to the car

Basically, the exhaust itself is cleaner in the sense that there is less CO and HC's, but it reduces gas mileage so there is more exhaust. It becomes a compromise between a smaller volume of dirty exhaust, or a greater volume of cleaner exhaust. Heres how I think I can improve FE and emissions by removing the system:

-Engines produce most CO and HC's at idle and other closed throttle conditions, so the air injection system is most beneficial during idle and engine braking (carbureted engines at least). However, I always turn off my engine at stoplights and have begun using EOC while driving.

-In its place I can install headers and a free flowing exhaust system that will increase MPG.

-If I want to further reduce CO and HC's, I can install a high flow catalytic converter.

-My car is registered under "classic car" status...I'm only required by law to get an emissions test every 5 years. This is important because I can avoid the visual inspection of not having the OEM air injection...and I can throw it back on there for an inspection if I have to.

-I can always lean out my carbs more to reduce CO and HC's.

Basically, I just think its an ancient band-aid fix to poor carburetor tuning...and that I could improve the FE and emissions using more modern methods and driving techniques.

So what do you think, remove the air injection or leave it in place?

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Old 01-12-2008, 08:36 AM   #2 (permalink)
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Lightbulb Your ideas are better than OEM

Having been in the biz since the '70's (when rock was new technology), I can tell you that air injection of that era was in-efficient at best.
We (me and all the other wrenches I knew) would joke that the AIR system was just watering down the dirty exhaust with fresh air. (think big glass with 2oz milk,,then pour in 14oz water). the gist of the joke was; The EPA was too stupid to realize the car companies hadn't "fixed" anything, just diluted it so total volume would seem cleaner. You take 'dirty ' exhaust at the manifold, inject clean air from the front of the vehicle, you get diluted exhaust out the tailpipe, (where emissions are read). Duh.
We all understand that by adding fresh air to the exhaust stream you may, possibly, perhaps, if the conditions are perfect re-burn some of the loose hydrocarbons. Real world experience tells me thats a bunch of Krap.
Make a cleaner engine in the first place and the rest falls into line.

I say Yes, go your route, I would even get the emissions tested after mods to see where you stand. The Reg's back then were fairly lenient, and I am of the belief that they can't force you to make a 1979 auto meet 2008 Reg's.

If ya gotta getta cat then so be it. There's plenty of high flow cats out there.
Drive safe. S.
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Old 01-12-2008, 11:26 AM   #3 (permalink)
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I would be very careful about leaning out an L-24 engine. They were prone to lean detonation in their day, and are more so with modern unleaded gasoline. I would not do this without having a properly functioning stand-alone A/F meter installed (or at least a quick reacting EGT).

OTOH, while air injection systems do all those things you mention, in combination with a modern generic cat they also dramatically clean up your car's HC emissions. The car will produce slightly more CO2 than it does now, but compensates by dropping its HC emission to near-zero. I helped a friend do this to a similar vintage Toyota that was getting busted for HC emissions, and a generic Chevy 350 cat with the right in/out tube sizes dropped HCs to nearly nothing.

Long-tube 4-2-1 headers uncork the exhaust side of the L-24 very nicely and bring a nice little bump in performance/FE. If you buy an unpainted set, you can have any muffler shop weld in an air injector bung and an A/F or EGT bung, then have the whole thing ceramic coated. A header like that will save considerable weight over the OEM cast iron manifold, improve FE and last the life of the car.

For better FE I also recommend looking at swapping to one of the taller diffs that came in later Z-cars (like the 280Z 2+2). Check out the many websites dedicated to those cars for details.

It's all good!

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Old 01-12-2008, 11:41 AM   #4 (permalink)
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How about an electric air injection pump off a new car and an rpm switch that turns it on under 1500 rpm?

A lot of new cars have an electric air pump. RPM activated switches are pretty common a lot of people use them for their nitrous systems and can be had new for under 50 bucks. Used is much cheaper if you can find one.

You might even be able to pass visual inspection since it still has an air pump, not sure how they do it though since I have never seen an emissions test done.
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Old 01-13-2008, 05:36 AM   #5 (permalink)
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metroschultz:

If it really does just dilute the exhaust as opposed to oxidizing CO and HC's...then its just a sham and I should go ahead and remove it. Cats actually work since they have the catylyst plates that convert CO and HC's at the chemical level...the better way to go.

Stan:

I've played with the carbs on the engine quite a bit...and I also have a chart that give tuning specs (in terms of turns from closed of the main fuel jet) as a function of altitude and temperature...so I have some baseline data that I can work from without leaning them out so much that it detonates. I also have a colortune device that I use when adjusting the carburetors.

As far as reducing HC's with an air injection/cat converter combo...I would be willing to bet that the cat was responsible for most of the actual reduction in emissions. If I did get a cat...I would use one of those high flow cats meant for modern high performance engines...to make absolutely sure restriction is minimized.

Did you mean to say 6-2-1 headers (the L24 is an I6, not an I4). Actually, the stock manifold is a 6-2-1 design that works well with the engines firing order. The OEM manifold is actually a fairly good design...dyno tests have shown it to be comparable performance wise to many of the available aftermarket headers...using a 2.5" exhaust from the manifold back however has been proven to increase both power and gas mileage. I think the ultimate set-up would be an equal length 6-1 header with a 2.5" exhaust (equal length header combined with free flow exhaust is hard to beat).

I actually already have one of the tallest geared diffs (3.36:1)...but I could convert to a 5-speed from a 280Z or 280ZX one of these days, which would do the same thing.

Coyote X:

Even if I made the pump electric, it would still cause engine load through the alternator. Besides that, I almost never have my engine under 1500 RPM...because I do very little idling and cruising at that RPM means lugging the engine...I think its better to just remove the pump and air injection altogether and use other methods for emissions reduction.

As far as the visual inspection goes...I don't need one for 4 years. That and I go to the pre-1982 emissions place...which is kind of a hole in the wall Mickey Mouse operation anyways. The old guy who runs the place probably wouldn't know or care that the car is supposed to have air injection as long as the tailpipe emissions are within specs...I don't even know why I'm worried about the visual part.
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Old 01-13-2008, 10:25 AM   #6 (permalink)
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There is actual science behind the addition of air pumps, I am speaking from observation that in their fledgling use they really accomplished nothing.
The idea was
> Hot Exhaust +
> Unburned Hydrocarbons +
> Fresh air =
> less unburned hydrocarbons.
The earliest Catalytic converters were not capable of removing NOx.
NOx was reduced with EGR.

Catalytic Converters Require fresh air to work efficiently.
The new electric air pumps use Very Little current.
(My daughters Jetta has one and I can not even measure its draw with my antique amp meter)

I stand by my rec. Remove what you have and test your Emissions.
I believe you will be Happier with the results.
The early air pumps and related components were HEAVY.

THEN, If you need to add a cat. get one with a feed pipe and use an electric pump. (for the weight savings)
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Old 01-13-2008, 11:29 AM   #7 (permalink)
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Quote:
Originally Posted by Dane-ger View Post
Stan:

I've played with the carbs on the engine quite a bit...and I also have a chart that give tuning specs (in terms of turns from closed of the main fuel jet) as a function of altitude and temperature...so I have some baseline data that I can work from without leaning them out so much that it detonates. I also have a colortune device that I use when adjusting the carburetors.
Great...sounds like you have a handle on it!

(Hard to tell from your initial post how much you knew about the details of the car -- didn't mean to tell you stuff you already knew. )

Quote:
As far as reducing HC's with an air injection/cat converter combo...I would be willing to bet that the cat was responsible for most of the actual reduction in emissions. If I did get a cat...I would use one of those high flow cats meant for modern high performance engines...to make absolutely sure restriction is minimized.
Yes, absolutely...the cat is doing virtually all of the work. Cats have to have have free oxygen to work efficiently, though, which is where the air injector comes in. By adding oxygen to the exhaust stream, the air injector system assures that the cat can work efficiently under all conditions. Summit Racing has a good selection of Universal Cats to choose from.

Of course, I offer this with the presumption that you are interested in maintaining the car emissions legal. I understand your next check is in 4 years, but I see little down side to maintaining low emissions while working to improve your car's FE.

It's obviously your choice, though...

Quote:
Did you mean to say 6-2-1 headers (the L24 is an I6, not an I4). Actually, the stock manifold is a 6-2-1 design that works well with the engines firing order. The OEM manifold is actually a fairly good design...dyno tests have shown it to be comparable performance wise to many of the available aftermarket headers...using a 2.5" exhaust from the manifold back however has been proven to increase both power and gas mileage. I think the ultimate set-up would be an equal length 6-1 header with a 2.5" exhaust (equal length header combined with free flow exhaust is hard to beat).
Yep, my bad! I have a '72 Dime. For non-Nissan folks that's a Datsun 510. Its spare engine still has the cast iron header, which is, as you note, much better than the standard Detroit cast iron exhaust manifold. The header actually in my car is a long-tube 4-2-1 design that feeds into a 2.25" exhaust pipe. The L-24 in your car is the exact same engine with two cylinders added in the center, so I bet a 2.5" pipe would do the trick.

Quote:
I actually already have one of the tallest geared diffs (3.36:1)...but I could convert to a 5-speed from a 280Z or 280ZX one of these days, which would do the same thing.
Sounds like you have all the easy stuff lined up and yes, a taller 5th gear would definitely help.

Still, you have chosen a car with a massive overbite and attendant drag 'shute front end. Good thing they're such handsome cars, eh?
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Old 01-13-2008, 12:19 PM   #8 (permalink)
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Quote:
This is definitely a good thing, I mean we're all trying to reduce CO2 emissions, but CO2 is nowhere near as bad as CO.
While CO2 is bad and all - it's not the only emission that is kept in check... NOx, for example, is pretty nasty... I mean, we can get great mpg numbers if we just ignored NOx... The problem is, the effects from NOx exposure are deadly - and we need breathable air Not sure if air injection changes any of that - just putting that info out there
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Old 01-13-2008, 01:43 PM   #9 (permalink)
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I think I've asked you this before treb, but do you have any links on how NOx is so bad? It undoubtedly isn't good as a precursor to smog and is likely a carcinogen, but from what I've read the most dangerous culprit is PM<2.5.
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Old 01-13-2008, 02:54 PM   #10 (permalink)
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Originally Posted by roflwaffle View Post
I think I've asked you this before treb, but do you have any links on how NOx is so bad? It undoubtedly isn't good as a precursor to smog and is likely a carcinogen, but from what I've read the most dangerous culprit is PM<2.5.
Yeah, particulate is pretty bad too....

NOx and PM responsible for 2,880 deaths per year in CA

Only the Abstract

The good news is - NOx production has fallen from state to state (but not sure if that includes automotive emissions)

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