Exhaust System for Olds 307 Vin 9

[T.Wagner]

I always suggest mandrel bent pipes instead of crushed. I perfer older hotrod type shops for custom exhaust work myself.
And IMO 2 1/4" will be fine for your set up.

I will definitely search out some good shops to take it to. I'm currently in the process of acquiring some manifolds, the crossover, and the front exhaust pipe. Then all I need will be the cat, pipes, and the mufflers which are far easier to get.

Do you have any particular cats and mufflers that you suggest? I heard the Hooker Aero Chamber mufflers and they sound really good. Supposedly they help to increase the flow as well.

 

[DoubleV]

If you want to be legal you have NO choice but to go with manifolds and that means 307 manifolds with the heatriser and the O2 sensor. Of course you MUST run it on the computer with ALL the emissions crap too. With this being the case, the stock style exhaust system will ckoke even a 307 down....

The pipe you're referring to is called the downpipe. If you can get away with it, you can get a custom mandrel bent 2.25" crossover pipe and maybe something like a 2.5" to 3" mandrel bent downpipe into a high flow cat. Then just run an aftermarket 2.5" cat back ( even though 2.25" would be all you really need ).

Yeah, if you live in CA and you need to stay legal you're absolutely SCREWED as far as adding any real performance to your car.

 

[T.Wagner]

If you want to be legal you have NO choice but to go with manifolds and that means 307 manifolds with the heatriser and the O2 sensor. Of course you MUST run it on the computer with ALL the emissions crap too. With this being the case, the stock style exhaust system will ckoke even a 307 down....

The pipe you're referring to is called the downpipe. If you can get away with it, you can get a custom mandrel bent 2.25" crossover pipe and maybe something like a 2.5" to 3" mandrel bent downpipe into a high flow cat. Then just run an aftermarket 2.5" cat back ( even though 2.25" would be all you really need ).

Yeah, if you live in CA and you need to stay legal you're absolutely SCREWED as far as adding any real performance to your car.

Unfortunately that's California for you 🙁

I wish I had a car pre '74 so I didn't have to worry about emissions... As it is the car probably has too much flow now and isn't performing at it's best, so going back to the original setup with a high flow cat and the aero chamber mufflers might actually benefit me! Do you think that I will see a performance increase by having a custom crossover and down pipe made vs. using the stock ones?

 

[DoubleV]

I'm not buying the 'you have TOO much exhaust flow'. That ain't your problem.

Will you get gains from bigger than stock crossover and down pipe into a high flow cat? Over stock, I would say 'yeah a little' but it's going to be worse than what you already have though.

Aerochamber mufflers aren't going to make any difference over any other decent muffler. Just get something that sounds good and sound is subjective so.....

 

[williamattop]

You could spend good money on some expensive trick parts and get some above average results. But what is it really going to equal to? 10-20 extra hp? I mean, its Cali, and your motor is stock anyway, correct? You wont get much out of it in stock form no matter how much money you throw at it IMO. For the money Id buy a decent factory style stainless set up (with manifolds) and be done with it. Unless you plan on moving to a diffirent state anytime soon.

 

[T.Wagner]

You could spend good money on some expensive trick parts and get some above average results. But what is it really going to equal to? 10-20 extra hp? I mean, its Cali, and your motor is stock anyway, correct? You wont get much out of it in stock form no matter how much money you throw at it IMO. For the money Id buy a decent factory style stainless set up (with manifolds) and be done with it. Unless you plan on moving to a diffirent state anytime soon.

That is exactly my thinking. It's a stock 307 rated at 180hp... I think in the end it would be better to just have a legal car that is that much closer to original. I'm looking into some original manifolds, a crossover, and a downpipe right now. If I get those then all I need is a cat (maybe a high flow one), mufflers, and most likely a custom stainless steel exhaust. I don't want to spend tons and tons of money just for a small boost in performance. At this point the main goal is to get my car legal and then I can go from there. All I do is cruise around in her anyway so it's not like I need the performance. Someday I'll get a '72 Cutlass convertible and I'll have my power in that car :lol:

Thanks for all the insight and help guys!

 

[jiho]

What others said, everything between the heads and the cat has to be stock, or else CARB certified aftermarket (EO number). I doubt there's anything certified aftermarket for a 307.

The cat has to be CARB certified now, too. Whether the tech checks it or not is another matter, but if he does, it's supposed to be marked and he's supposed to look it up.

 

[DoubleV]

You don't need a custom exhaust ( not counting the crossover and downpipe if you wanted mandrel bent and a bigger size ). A Hooker cat back would be a good choice and be legal.

 

[jiho]

If you want to be legal you have NO choice but to go with manifolds and that means 307 manifolds with the heatriser and the O2 sensor. Of course you MUST run it on the computer with ALL the emissions crap too.

The OP hasn't addressed this point. With headers and no cat, it seems likely whoever did that would also remove the smog pump, there being nothing to hook it up to.

If the computer was removed, but it still has the computer-controlled QJet and HEI, that could explain why it runs even worse than it should.

Then there's the EGR, the ThermAC air cleaner....

 

[kustomkyle]

Unfortunately I need to have a cat to pass emissions so I will need to go back to the "stock" setup. I need to do some more research but I am thinking of going back to manifolds if I can just because my headers leak like crazy all the time. Then maybe a high flow cat like 88hurstolds suggested. I also like how those aero chamber mufflers sound! I will most likely just go to a muffler shop and have them custom make all the pipes if I decide to do it. Does 2 1/4" pipe sound good for the stock 307 setup or should I do a different size?

Do you guys have any pointers on what I should be looking for in a muffler shop? I know there is a certain bending technique that I want to make sure they do, right?

Also, can you tell me what the front exhaust pipe is? The crossover goes from the left manifold to the right one, then the front exhaust pipe connects that to the cat? Is that correct?

The "front pipe" connects the RH exhaust manifold to the catalytic converter. The crossover just connects the two exhaust manifolds. There is no real y-pipe in the exhaust, but the RH exhaust manifold is one more or less. This is sort of what makes the factory exhaust a little complicated. Actually, the "front pipe" extends the exhaust manifold down to right about where a header collector would be.

I will post a picture of mine when I installed a new one. The original's flat flange rusted so thin it was folding in on itself.

Keep in mind, you might spend more sourcing original and original replacement exhaust parts than a decent header/dual exhaust system. I think I spent over $130 in just the pipes and gaskets, not including a cat, which I reused from the previous cobbled exhaust. That was with a bare bones discount (I'm a store employee).

My ultimate goal is to put headers (with oxygen sensor bung and sensor), dual high flow universal cats, to factory style/placement 442 mufflers and tailpipes. I don't see why that wouldn't be better than factory emissions output, other than the oxygen sensor placement might be tricky in order to get a correct reading so the CCC isn't thrown in a loop.

The only problem I would think would be a visual inspection. But how would the person know what they are looking at? Do they have exhaust diagrams and emission routing for every car at the inspection stations?