innertwist

iTrader: (3)

A previous owner cut out the little secondary exhaust pipe that runs alongside the main exhaust (probably because it was rusted to hell) and welded up the hole for it on the downpipe. I'm sure this is at least one reason why my car has never come close to legitamately passing emissions. My question though is how bad is this on the performance?

Also, there's been a bit of confusion on the board about what the lobe that's directly bolted to the downpipe is. Many say it's the heat exchanger, but the Victoria British/Black Dragon catalog lists it as a catalytic converter. So, assuming it is a cat, will I have to worry about it prematurely failing because of this mod?

Yark79

The only way its a cat is if it were installed by the previous owner for whatever reason. Otherwise, it's a heat exchanger. While it may look similar to a cat, I believe the internal composition is different. If your air pump is still installed, I can't see the output pipe for it being plugged up as being a good thing. Do you have to pass emissions testing? Being over 25 years old, I wouldn't think that it would have to.

RXDad

iTrader: (2)

As you surmise, plugging up the secondary exhaust will kill any chances to pass emmissions. It should not significantly affect performance, however. The engine exhaust will not see much more back pressure than if it was a later FB with stock exhaust manifold.

The unit on the downpipe is the heat exchanger, not a cat. The thermal reactor works by heating air in the heat exchanger and using that heated air to react with any unburned hydrocarbons in the exhaust, just as it exits the engine.

The reason why VB lists a cat, is that the heat exchanger/reactor combination is not available, and if it was, would be very expensive. VB substitutes a cat that fits in the place of the heat exchanger to restore emmissions performance.

The only problem is the life of the new cat would not be the longest. I had a cat from VB last only about 1 1/2 years.

I think Bonez has cats that with modifications potentially will fit and last significantly longer.

RXDad

innertwist

iTrader: (3)

I guess then the question should be, cats aside, does an SA have a freer flowing exhaust than an FB?

I still don't understand how the heat exchanger works. The pipe from it seems to connect to the air pump through the intake manifold. Why would it need a fresh supply of air if it's just drawing heat from from the exhaust? Does the combustion continue even after the thermal reactor? I disconnected the tail end of it at one point (couldn't get the downpipe end to seperate) and looked inside, and it looked like the barrel of a silencer, with all the air forced through the holes of that barrel. I couldn't see the other side of it, but I'm guessing it transfers the heat by conducting it through the metal of the downpipe - is that correct?

As for emissions, I wouldn't have to worry anymore if I was still in NY, but I just moved to NC, and it's an emissions county. Appartently, right before I got here they removed the 25 year exclusion, so that all cars since emissions testing began must pass it. That's 1977 (or 78?) and up. And here I can't even pay off the tester. *shakes head* I haven't registered the car here yet :-/ I figure though, since they're only testing for carbon monoxide on this year, if I run it pig rich I could pass. maybe

Thanks for the heads up on the catalytic converter btw!

RXDad

iTrader: (2)

Fresh air is pumped into the heat exchanger where it heats up. The air then travel thru channels back up the down pipe back to the reactor which is attached to the engine at the exhaust ports. The hot air then mixes with the exhaust which burns off the excess hydrocarbons in the exhaust. The hot exhaust then travels to the heat exchanger to heat the fresh air. The secondary exhaust was to help cool the shell of the heat exchanger to prevent from overheating.

I would think that the back pressure from this system was no more or less restrictive than the FBs cats. Want less backpressure you will need headers and a good flowing exhaust system.

The mixture on SAs was pretty rich to begin with to support the thermal reactor. Don't know if it will pass without a cat. What is the requirements for CO in your state?

RXDad

peejay

YOU NEED THE SECONDARY EXHAUST PIPE TO BE OPEN.

It's not an "exhaust" pipe in the sense of exhaust gases. It's the exhaust for the COOLING AIR that is pumped around the thermal reactor to keep it from melting down.

Just take the cap off. It doesn't really NEED to extend all the way to the rear of the car. But it does need to be open!

innertwist

iTrader: (3)

YIKES, well that would explain why the downpipe gasket burned through! I don't think I'll be able to unclog the weld (there's a fat bolt stuck in that it's welded around) so I'm going to try and find a "new" one.

For emissions, I just looked it up. I was wrong on the details, it's for both carbon monoxide AND hydrocarbons, and it's 1975+. The details are here. I'm not sure if there's a visual inspection, I have to go to an inspection station and find out details, but if there was I'm pretty sure adding a cat would be illegal... if they could even tell the difference. Of course, if they didn't do the visual I would (eventually) get a header instead, and save the trouble of finding a "new" downpipe. Either way, it looks like I'll have to be running my rotary on alcohol in order to pass. The last time it was hooked up to a sniffer it failed everything almost ten fold, for 04' NYC standards. For instance my CO reading was around 6-8.

Back to the original question, how bad. I've driven this 10k miles now and god knows how long it's been like this with the former owners. I've gotten a number of comments *cough* on how efficient the foot warmer was (this was my first rotary and thought this was normal. Hell, maybe it is). So when I get the downpipe should I assume the heat exchanger is damaged and replace it too? Should I be looking for any other damage?

trochoid

iTrader: (6)

Since the entire SA exhaust systen is NLA, most states allow emissions to be upgraded to later, better, systems. You may wish to check with your State regulatory agency that covers emissions. Unless the testing station has diagrams of all of the stock systems on hand, you should be able to get by with an FB exhaust mani, an aftermarket cat that will hold up to the rotary exhaust, coupled with a working air pump and they would never know the difference..

I have read about some CA members upgrading to the entire FB system to pass emissions and CA has the toughest regs in the States. I believe they do need an inspection and CARB sticker for the upgraded change.