Dual exhaust for a 307 Olds

[kustomkyle]

Hello, I have a 1986 Buick Regal Limited with a 307 Olds/200-4R with 85,000 miles and considering installing dual exhaust. It has a single pipe currently with a glass pack, and the catalytic converter was removed temporarily because it was clogged (the engine lost power/starting making a valve or lifter type noise). The removal of the converter made a huge difference in power, and it has not "ticked" since, but I think the old glass pack is starting to go bad, and inspection is coming up this fall (they only use a sniffer, but it previously barely passed emissions with the converter after three tries). I want to use dual converters and glass packs (Flowtech?) with 2 1/4 pipes. My main questions before I do anything are:

-Would dual exhaust with catalytic converters hurt/help emissions?

-Does dual exhaust affect the ECM/emissions controls in any way?

-I've read that modifications to the 86' and later swirl port 307's actually diminish horsepower unless everything (cam, headers, exhaust, etc.) is changed. Is this true if I add dual exhaust and nothing else?

-Would dual exhaust help/hurt high speed cruising and off-the-line acceleration?

-Do low restriction converters make a difference in power, and would they work better than larger OEM style ones for any reason?

Thanks for your time and if you have any other suggestions let me know (keep in mind I don't have the money to swap engines any time soon).

 

[megaladon6]

dual cats will help lower emissions, especially since the 80's type cats were extremely inefficient.
the only real problem control wise is that you need an O2 bung in the headers/downpipe and the sensor will only read 1 bank, that's if you go with a true dual.
adding a y-pipe back exhaust won't really change power. a true dual exhaust should add power, but not much on a stock 307. but they will help any mods you make later.
exhaust mods generally increase power across the RPM range, unless you go too large. in which case you'll mostly notice it at high rpm's only.
low-res cats compared to a modern OEM cat--not much of a difference. compared to an 80's OEM cat--much better flow.
my advice, 87 monte's used a cat back dual exhaust. try and find a cheap one and if necessary for emission there should be room for a second cat. but remember, cats are not a cure-all for emissions inspections. the best thing you can do is have the engine running as well as possible.

 

[joe_padavano]

dual cats will help lower emissions, especially since the 80's type cats were extremely inefficient.

I agree that the 80s pellet-style cats are awful and replacement with newer matrix-style cats will help a lot. The emissions will probably not change. The only issue is that you may fail an emissions test visual inspection. The reason is that the two cats and dual exhaust will cause the cats to take longer to heat up. This can result in failure to meet cold-start emissions requirements. Since annual tailpipe sniffer tests can't test for this, the stations are required to perform a visual inspection to ensure the system is the same as stock. It depends on how flexible (and reasonable) your test technician is. The local station where I get tested used to be pretty reasonable, but they must have gotten busted by the emissions police, because they are a lot stricter now.

 

[kustomkyle]

For inspection/emissions in Delaware, last time I went, you just go to the DMV and wait in line for the inspection station. First they use the sniffer, then they make you go through your lights, and then you do the brake test. They never looked under the car or under the hood. I'm not sure if it is still like that. I think a lot of people around here have newer trucks with true duals though.

Also, I didn't mention that the engine smokes sometimes (usually acceleration from a stop). We had to do whatever we could to get it to pass with the single pipe with catalytic converter. I was thinking that duals would reduce the emissions they would pick up because they only use the sniffer on one side. Is there any truth to that, or would it be worse for some reason?

 

[joe_padavano]

I was thinking that duals would reduce the emissions they would pick up because they only use the sniffer on one side. Is there any truth to that, or would it be worse for some reason?

Emissions constituents are measured in either parts per million or percent. Either way, dual exhaust doesn't matter, because half the exhaust flow has the same percent or PPM as the full flow. That's why they spec it that way. The only way this would help is if you had one cylinder that burned oil and they happened to sniff the other side.

 

[kustomkyle]

I know this is a stupid question, but is it possible that a restrictive exhaust would cause an engine to foul it's plugs/smoke? The car most likely has a bad valve guide or something similar in the drivetrain. I was hoping freeing up the exhaust would make it run better. Looking at the factory crossover pipe makes me wonder how the car runs at all.

 

[joe_padavano]

I know this is a stupid question, but is it possible that a restrictive exhaust would cause an engine to foul it's plugs/smoke?

Highyl unlikely. Fix the source of the smoke and fouling first, then change the exhaust. Is the smoke black, white, or bluish-white?

 

[montessaj]

I am sooooo happy I don't have an emissions inspection. I can run whatever I want under the monte all day as long as there are no exhaust leaks.

 

[85 Cutlass Brougham]

I am happy that I live in one of the only states ever to eliminate emissions inspections once they got them!

That being said, you have to ask why the cat went bad. It is not just due to old age or high miles- my DD has 287,000 miles on it's original cat. Most likely, the car was running rich and this flooded the cat with fuel, so much so that it over heated due to excessive reactions. This killed the cat. I have seen that happen before in other cars. So, I would see what went wrong in the engine management system. It could be a bad O2 sensor, or even a leak in the exhaust before the O2 sensor, causing the ECU to read it as lean and thus over richen the MC solenoid. A bad check valve in the AIR system can also cause this to happen as can something as simple as a bad exhaust manifold gasket. If I were to guess, I would say that your hydrocarbon readings were excessive, and that is why you had a hard time passing.

 

[kustomkyle]

I'm pretty sure there is something wrong in the heads somewhere, I don't think the last owner changed the oil much and they probably messed something up. It's a shame because the car has such low mileage.

I keep hearing about "AIR" tubes/system causing problems. What is that/where is it located? There are so many emissions canisters, valves, tubes, wires, and vacuum hoses that it is hard to figure out what is what. Is it a specific part to the 307 Olds system? It seems like dual exhaust is out of the question for this car.