exhaust flow and routing question,,
as it is today,,the D-150 has a single exhaust running to a cat running to a flow master muffler that splits to duel exhausts running across the rear axel, and back to the rear quarters. The flowmaster stuff is courtesy of my sons from when they drove this vehicle.

Question is,,, whether I run dutra's or a header, I plan to run into a single cat like one of these,
http://www.summitracing.com/search/Bran ... onverters/
from there to the existing muffler where it will split and feed dual exhaust outlets. Going to replace the cat on the assumption that my current one (original ?) is shot,, but really don't know. Would like to have some level of pollution control,, but in central IN,, there are no emissions inspections,,
Question,,,
1) would a cat and shared muffler provide the same effect as an x pipe? 2) Any thoughs on why some cats are 60.00 and some are 110.00 ?

I do plan to install an exhaust cut out ahead of the cat for the moments the D-150 ends up on the strip. At least it will be comparably loud.

is this a good plan,,
thanks
DT

John, run true duals and forget the cat if you have no inspections. If you have the truck well tuned a cat really doesn't make much difference.

I smogged my Duster many times (We have testing here) with an empty cat and it passed every time.

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Official Cookie and Mater Tormentor.

interesting, so you think a single pipe running to my existing muffler that splits to duals would be good? I like the cost factor.The cut out is part of the plan.

currently with a stock motor the exhaust at road speed is not heard,, that is because at 60 MPH there is so much NVH from wind and road noise the exhaust is not audible,,however at idle and low speed it has a real nice note.

I am anti dual exhaust, since it is not a functional advantage over a good single. They are purely for looks on a Slant. It is same reason I don't like convertibles (or even hardtops) - less stiff platform is less fun to drive, so you can forget your sun and I'll drive the crisp sedan.

I put a cat on my '68 Dart to try to help it pass CA emissions, and it did nothing from the tests they did (tailpipe sniff, no load, no dyno). I had to ditch the holley 2bbl and run a 1bbl 1920 to get it to pass. I think the gain in emissions from just a cat by itself is minimal. I did put one on Slantkota to pass visual inspection here.

On Slantkota, I went from Clifford shorties into a crappy homemade Y pipe (2X2") into 2" single, to a Flowmaster Y (2X2" into 2.5") with a single 2.5" out the back with Jones exhaust muffler and it got no louder but picked up almost 3 tenths in the 1/4.

Lou

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Home of Slant6-powered fun machines since 1988

I have a set of Hooker super Competition headers. The primaries are 1 5/8 and the collectors are 2.5. I'm planning on running a single exhaust system all the way back using 2.5 tubing. Given that this is more a street motor than a race motor, does keeping the tube diameter the same for the entire system make up for the lack of back-pressure I'll lose with the larger primaries?

The cost difference is usually standard versus "heavy metal". HM have a higher amount of platinum, to clean the exhaust. More precious metal = more $$.

I'm with the others, skip the cat. The money saved could go towards something else that would have a more profound impact on emission (HEI mod, fresh tune up, etc)

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1976 Dart Lite /6 3 Speed

Carburetors and catalytic converters were a "shotgun wedding" that never got along well and still don't. A carbureted fuel system just is not precise enough to keep the fuel/air mixture stoichiometric, and a stoichiometric mixture is what an exhaust catalyst needs to do an effective cleanup job without melting down. If you want or need to have a catalytic converter, get one with a large inlet and outlet, rated for an engine much larger than you intend to use it with, get the more costly variety which has higher platinum loading, place it as close as safely possible to the engine, and use thermal wrap on the headpipe(s) between the manifold outlet and the converter inlet. Keep the engine in very careful tune. I would use Dutra Duals on such a configuration, not headers (too much heat loss with headers; you need to keep the exhaust temp up or the catalyst can't do its job efficiently).

Feedback carburetion (with O2 sensor and electronically-controlled carburetion) was a halfaѕѕed, low-cost way of avoiding doing it right (fuel injection) and meeting tightening emissions regulations in the 1980s. Many of the systems were poor in terms of driveability and durability of tune. Some of them were okeh. The 1981-'84 318 cars (Diplomat, Gran Fury, New Yorker Fifth Avenue...) got a feedback Carter BBD 2bbl carburetor that worked reasonably well, certainly better than the 6145 feedback 1bbl on some '81+ slant-6s. I have never done it, but I (and Hemi Andersen and a few others) have had it in mind for a good many years that such a carburetor would probably work well on a slant-6. The idea would be to use the computer only for control of the feedback carb (basically looking at the O2 sensor, engine temp, and manifold vacuum and controlling the carb's duty cycle solenoid), but not the computer's ignition timing control -- instead, put in a well-curved conventional electronic distributor with vacuum and mechanical advance. Probably with the HEI upgrade. It would not be difficult to go to a heated O2 sensor to further update the system. I have a new appropriate BBD on the shelf, and it would bolt right onto a Super Six intake, but the odds are I will never get around to putting it on anything; I've got too many pre-catalyst cars to put together already!

I've had good results with Catco's converters on newer vehicles. Better prices from Discount Converter. The ones with the high catalyst load are the "California" models listed in red. Look at a 712006; the 2½" inlet and outlet can be step-adapted to the exhaust pipe size you're using (I would go with 2¼"), thus minimizing restriction from the converter (most of which comes from the inlet and outlet, not the catalyst bricks themselves). If you're using Dutra Duals or another twin-headpipe system, you could use Doc's favorite Wye connector to bring the two headpipes into the cat.

Single pipe from cat to muffler (Walker #50051), single tailpipe.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

thanks,, good info and tips

Well said, Dan.

Lou

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Home of Slant6-powered fun machines since 1988

Um.... no.

It makes a phenomenal difference, but only when the engine is running at stoichiometric ratio (Lambda = 1). Actually, it works even better if the ratio switches rapidly between rich and lean (as with narrow-band O2 sensor systems), so that it can continuously switch between oxidation and reduction. Without this precise control, as Dan mentioned, it simply doesn't work on a carbureted engine.

One of my engine management books by Charles Probst is quite clear about the benefits, and I discovered a scan of his graph HERE. Reductions of 90% of the harmful gases are quite a difference, indeed. Whenever the NOx readings are sky high, on a car where everything else is running well, it almost certainly needs a new cat. At some point, I'd love to try putting a high-flow cat on a slant 6, but only after firmly establishing that a fuel injection system is working appropriately. Before that, it not only doesn't really help, it wastes money by destroying a cat.

Some catalytic converter tips, for all who need to know this for a newer daily driver: unless a cat is so old that the thin coating of precious metals has worn off (abrasion?), it generally doesn't die on its own. It gets poisoned. (Remember the definition from chemistry class, that a catalyst is something that helps a reaction occur but does not get used up in the reaction?) If the emission test station tells you to buy a new cat, make sure you figure out why the old one is nonfunctional first! Possible contaminants include the well-known leaded fuel issue, but also excessive oil burning, or a microscopic coolant leak from a head gasket. (Don't ask how I know.) Overheating issues are caused by too lean a mixture, including engine management failures (O2 sensors), or even a pinhole leak anywhere in the exhaust prior to the cat that will allow in extra oxygen. (Don't ask about that, either.)

When working, cats work well. When anything isn't quite perfect, they're finicky little bastards, willing to give up the ghost on a moment's notice. And in California, they're twice as expensive to buy as in the rest of the 49 states. (Each unit must be certified that it been tested on the exact make, model and year car for which it is sold. Never mind that part numbers interchange for, say 1990-94 Mazda and Ford Escort. If you own a 92 with a particular size engine and maybe even a particular color of windshield wipers, you'd better buy one that was actually tested on a similarly-equipped 92. And mfrs have to pass along those stupid costs, of course. Does this scheme smell like someone actually cares about clean air? Or that they want to make it as expensive as possible to fix older cars?)

Hmph.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.