3.6 swap exhaust for SMOG

[Synchromesh]

Long story short, I picked up an '87 G50 coupe with a 3.6 swap from an early 964. The car runs and drives very well but is still on the raw side of cooked. One thing going on is that it's running an BnB exhaust which sounds lovely but obviously will not pass SMOG since it's lacking a cat. Aside from a lightened flywheel engine is stock otherwise running a proper 964 DME. As part of the package I got a 964 catalytic converter and a 3.2 muffler separately.

I've been reading lots of threads on the subject but nobody seems to come to a proper consensus. Can someone tell me in plain English what's the best exhaust to pass California SMOG properly?

I see people are recommending a Carrera 3.2 exhaust but it seems like it needs to be modified to fit the 3.6 and then it's a bit restrictive due to pipe size. Is the the easiest way to go? Is it ok to keep that exhaust on permanently? Any other suggestions? I'm pretty open. Thank you.

[winders]

Well, if you go by CA law, you need to get the car inspected and a sticker installed detailing that the car has a n engine from a later model year car and must pass smog for the year of the engine. It must pass visual for the year of the engine as well.

[Synchromesh]

Well, that's a major additional headache so I'll probably forgo that altogether. Engine is very much stock, I doubt they'll be able to tell the difference, especially with a stock-looking exhaust.

[dannobee]

Scott's right.
Take it to the referee and see what he says. Yes, it'll need a catalytic converter and all smog equipment that the 3.6 came with (which it sounds like already does). One thing that trips up people after a swap is the evaporative emissions system. Make sure it's hooked up and functioning.

[Synchromesh]

If you read my original post it has a BnB exhaust with no cat whatsoever. Installing a full blown 964 system is a major undertaking which will require body modification because the pipe exits in a different place. I'm not going to do that as the body is very clean and uncut. All I need to do is just pass the basic SMOG in this thing and that's what I'm aiming for.

[Bill Verburg]

Originally Posted by Synchromesh

If you read my original post it has a BnB exhaust with no cat whatsoever. Installing a full blown 964 system is a major undertaking which will require body modification because the pipe exits in a different place. I'm not going to do that as the body is very clean and uncut. All I need to do is just pass the basic SMOG in this thing and that's what I'm aiming for.

As I recall the stock 964 exhaust also interferes w/ clutch actuation.

Just guessing here but you might be ok w/ a stock 3.2 Carrera exhaust, It looks similar to the 964 just w/ slightly more compact dimensions.

Way back when the states started promulgating their smog rules B&B used to offer a muffler w/ cats in the muffler outlets, to my nose they worked ok, but I haven't a clue as to CARB's view on the matter

[dannobee]

In the eyes of the CARB/BAR, the catalytic converter is part of the chassis, not the engine. Just like fuel evaporative emissions. But obviously in the case of a 911, everything is already in the back. The referee would likely accept the 3.2L exhaust system. And even more so if you ask/tell/remind him that the exhaust is from the original car and isn't it part of the chassis with respect to engine swaps?

Just make an appointment with the referee and let him see what you have. He will make a determination that you'll have in writing. Since you're swapping in a later model engine, it shouldn't be a difficult process. OTOH, if you were swapping in a 77RSR engine, then they'd tell you to pound salt.

FWIW, I had a CA Smog license for over 30 years. I kinda know what I'm talking about.

[Steve W]

The I.D. of the 3.2 heat exchangers is the same as the 964. Just fit the 3.2 exhaust system on the motor, it basically bolts right up. On the plus side, I think you will find there is no power difference or loss over your B&B exhaust, and it will be a lot quieter and have heat.

[Synchromesh]

Originally Posted by Steve W

The I.D. of the 3.2 heat exchangers is the same as the 964. Just fit the 3.2 exhaust system on the motor, it basically bolts right up. On the plus side, I think you will find there is no power difference or loss over your B&B exhaust, and it will be a lot quieter and have heat.

Thanks. That's what I'm thinking about doing. Couple of questions about that though.

1. do I need to reverse the flanges on the 3.2 exhaust? Some threads mention that but since I have an earlier engine (1990 iirc) does it apply here?

2. I have a 964 cat by itself. Will it fit into the 3.2 setup or is it different?

[Bill Verburg]

Originally Posted by Synchromesh

...
1. do I need to reverse the flanges on the 3.2 exhaust? Some threads mention that but since I have an earlier engine (1990 iirc) does it apply here?

2. I have a 964 cat by itself. Will it fit into the 3.2 setup or is it different?

No, only the 993 used the rotted flanges on the right side, and evn then the heads had provision for either style flange

stock 964


stock Carrera 3.2


stock 993

flipped rt. 993

[Synchromesh]

Thanks, that's a good breakdown!

Are all 3.2 exhausts exactly the same or do they differ year to year?

Also, where could I find some part numbers for the exhaust pieces?

[FrontGarage911]

Originally Posted by dannobee

In the eyes of the CARB/BAR, the catalytic converter is part of the chassis, not the engine. Just like fuel evaporative emissions. But obviously in the case of a 911, everything is already in the back. The referee would likely accept the 3.2L exhaust system. And even more so if you ask/tell/remind him that the exhaust is from the original car and isn't it part of the chassis with respect to engine swaps?

Just make an appointment with the referee and let him see what you have. He will make a determination that you'll have in writing. Since you're swapping in a later model engine, it shouldn't be a difficult process. OTOH, if you were swapping in a 77RSR engine, then they'd tell you to pound salt.

FWIW, I had a CA Smog license for over 30 years. I kinda know what I'm talking about.

If you have a 3.6 you will need 3.6 cats to be California legal.

5. Exhaust System - All exhaust after-treatment devices (catalytic converters, Diesel Particulate Filters (DPF), Diesel Oxidation
Catalysts (DOC), Selective Catalytic Reduction (SCR), etc.) the donor vehicle was certified to use must be present and
positioned under the vehicle in the same linear position within the exhaust stream as measured from the exhaust manifold
outlet.

https://ww3.arb.ca.gov/msprog/aftermkt/ca-bureau-automotive-repairs-engine-change-requirements-6-8-18-arb-website-download.pdf

[bluvan]

Here is my experience with a 3.6 swap and smog. It does not directly address your exhaust question but may help with some parts of what you are embarking on.

Last year I went through the BAR referee process to get the coveted engine swap sticker. I put a 95 OBD1 motor into a 1988 coupe. The referee I got was knowledgeable on how the 95 motor was originally certified in CA and was looking for all things intake to exhaust to be intact as OE including the SAI. We got tripped up on the intake warm up circuit in the 88 car, the DME serial number, a functioning OBD I CEL as installed in the 964 to 95 993s, and the evap system. The engine swap was done under my stewardship with support from this forum. I mention this because I was adamant that things like the SAI stay with the motor. If you have good knowledge of the build and believe all the parts are there you are not far from the legal sticker route. PM me for more on the subject and help making a CEL work if you go that route.

For exhaust, my car passed with the stock 993 exhaust cut off just past the cats. It was miserably loud but passed the visual and sniff tests. Since then I went full custom with removable magnaflow cats. In May next year I will need to get it the smog renewal so I will try with the new exhaust which will pass the emissions but fail the visual. If that does not work I have the cut 993 system.

My evap fuel vapor system was a series of rotting and pinched cloth braided fuel lines and the charcoal canister. I used a plumbing test manifold from the hardware store and rigged up a connection to the vent system on the fuel tank. With a bike pump I brought the pressure to about 2 psi. If it holds you will pass that part of smog if it fails you will smell where. Keep patching hoses until it holds.

Lastly, check with a couple indy shops. They may share some thoughts on the more knowledgeable smog techs.

[dannobee]

Originally Posted by FrontGarage911

If you have a 3.6 you will need 3.6 cats to be California legal.



https://ww3.arb.ca.gov/msprog/aftermkt/ca-bureau-automotive-repairs-engine-change-requirements-6-8-18-arb-website-download.pdf

Did you forget the other part? Some swapped engines have the converter built into the exhaust manifold (not available separately from the manifold), so the inch parameters apply. Again, he should go see the referee and get his ruling in writing.

If the device is integrated with the exhaust manifold, it must remain that way. Tolerances for this measurement as are
follows:
a. On the close-coupled end (nearest the engine), within 6 inches, and no closer than the stock configuration
b. On the other devices (rear catalyst, DPF, DOC, SCR, etc.) within 12 inches of the stock configuration
No other exhaust system changes are allowed, unless they occur downstream of the last emissions control device i.e. (Oxygen
sensor (O2), NOx sensor, etc.). For example, the muffler location(s) may be modified

[JonT]

Originally Posted by bluvan

Here is my experience with a 3.6 swap and smog. It does not directly address your exhaust question but may help with some parts of what you are embarking on.

Last year I went through the BAR referee process to get the coveted engine swap sticker. I put a 95 OBD1 motor into a 1988 coupe. The referee I got was knowledgeable on how the 95 motor was originally certified in CA and was looking for all things intake to exhaust to be intact as OE including the SAI. We got tripped up on the intake warm up circuit in the 88 car, the DME serial number, a functioning OBD I CEL as installed in the 964 to 95 993s, and the evap system. The engine swap was done under my stewardship with support from this forum. I mention this because I was adamant that things like the SAI stay with the motor. If you have good knowledge of the build and believe all the parts are there you are not far from the legal sticker route. PM me for more on the subject and help making a CEL work if you go that route.

For exhaust, my car passed with the stock 993 exhaust cut off just past the cats. It was miserably loud but passed the visual and sniff tests. Since then I went full custom with removable magnaflow cats. In May next year I will need to get it the smog renewal so I will try with the new exhaust which will pass the emissions but fail the visual. If that does not work I have the cut 993 system.

My evap fuel vapor system was a series of rotting and pinched cloth braided fuel lines and the charcoal canister. I used a plumbing test manifold from the hardware store and rigged up a connection to the vent system on the fuel tank. With a bike pump I brought the pressure to about 2 psi. If it holds you will pass that part of smog if it fails you will smell where. Keep patching hoses until it holds.

Lastly, check with a couple indy shops. They may share some thoughts on the more knowledgeable smog techs.

I have a system with 993 cats with flanges flipped to fit a 964 and the 993 cat with tips cut ready to bolt on to a 964 for sale in classifieds if you are interested. Might help get you past the smog test. It is loud but it sounds very aggressive in a good way.

[Synchromesh]

Ok, an update and another question. I obtained the full 3.2 exhaust with cat and all. Oil line changed back to stock (maaaaan what a pain that was) and it was all ready to go except one thing. It appears the 3.2 exhaust has rings that stick out of the flanges that are pressed in while the aftermarket exhaust doesn't (pic below). Is there an easy way to get those rings out or do I need to grind them out hard? I think they're pressed in which makes it a tad complicated.

[911obgyn]

And the flanges are thicker, the plot thickens.

[Synchromesh]

I addressed that with longer 3.2 studs. It's just the rings at this point.