Exhaust System for Olds 307 Vin 9

[T.Wagner]

Thanks for that write-up Brother Al... very informative! 🙂

Just an update! I have found the original manifolds, crossover, and downpipe. They should be coming next week. I also located an original H/O/442 dual snorkel air cleaner in good shape! I am looking forward to having the car that much closer to original. I am going to have the exhaust re-done soon back to factory specs. Also, my transmission is starting to go and I will have to have it rebuilt. I'm going to do it at the same time as the exhaust because I can save a bit in labor since they will have the exhaust off for the transmission... Once that is done, my car should be good to go for many more miles

When this whole endeavor began I was looking for the best performance while still being emissions legal. It seems like a difficult battle, and pretty much with California's laws it is impossible. All I do in the car is cruise around town and go to some shows/cruise nights. For that I don't need to spend all the extra money to get a few extra HP out of it, so I decided to restore the exhaust back to original.

Thanks for all the help everyone!

 

[pencero]

I think you are definitely making the right call. My twin flowmaster 40s kit w/ the h-pipe is one of the only other systems you can get through emissions with and I think for all the backpressure it added actually resulted in a loss of a few hp. It was definitely not worth all the effort I put getting it to pass smog all just to have spent double and have less power after all that. At least if I come up on a decent 350 rocket I can re-use the exhaust. As for that filter to the dual snorkel thing, thats very cool information but you definitely don't need to replace that. Not only would it be hard to track down but it's in theory supposed to stop the backfires right. Well I had one w a Rochester and my carb still backfired all the time. So I cut off that filter put a really strong adhesive on a plastic cap and blocked it off; no more backfires. Some theories are a lot better on paper than applied in real life and the 2nd filter is one of those theories.

 

[T.Wagner]

I think you are definitely making the right call. My twin flowmaster 40s kit w/ the h-pipe is one of the only other systems you can get through emissions with and I think for all the backpressure it added actually resulted in a loss of a few hp. It was definitely not worth all the effort I put getting it to pass smog all just to have spent double and have less power after all that. At least if I come up on a decent 350 rocket I can re-use the exhaust. As for that filter to the dual snorkel thing, thats very cool information but you definitely don't need to replace that. Not only would it be hard to track down but it's in theory supposed to stop the backfires right. Well I had one w a Rochester and my carb still backfired all the time. So I cut off that filter put a really strong adhesive on a plastic cap and blocked it off; no more backfires. Some theories are a lot better on paper than applied in real life and the 2nd filter is one of those theories.

Yeah, it all just seems like a lot of effort for little gain. It just makes more sense to me to restore it back to original (except the mufflers of course )

The air cleaner I bought actually has both filters, so I am all set! I am very excited to see how it all comes out!

 

[kustomkyle]

When I changed my cobbled (but less restrictive exhaust) to new replacement parts for the single exhaust system, I think I gained horsepower oddly enough. And it went through emissions testing and passed on the first try instead of on the 5th or 6th.

 

[T.Wagner]

When I changed my cobbled (but less restrictive exhaust) to new replacement parts for the single exhaust system, I think I gained horsepower oddly enough. And it went through emissions testing and passed on the first try instead of on the 5th or 6th.

My mechanic that has been working on my car for years suggested just that! Right now I have headers straight to the back with 2.5" pipes and and X-pipe in there. He said that I could have too much flow in there and that putting a smaller exhaust/the stock one on it may actually help performance. I am looking forward to seeing if that is true.

 

[Brother Al]

Its true... relatively stock engines need a little back pressure to function properly and also help maintain a reasonable amount of torque... and its Torque that shoves you back in your seat, spins the tires, & gets your butt up the street.

 

[T.Wagner]

Its true... relatively stock engines need a little back pressure to function properly and also help maintain a reasonable amount of torque... and its Torque that shoves you back in your seat, spins the tires, & gets your butt up the street.

Exactly. I live in Los Angeles so it's not really about speed but rather how it feels when you floor it from a full stop :lol:

 

[jae]

Cquote="88hurstolds"]Headers might be a little bit overkill for a stock 307 but it shouldn't hurt performance.
I would install an X-pipe to help with back pressure.
Oldsmobile's like back pressure, it helps scavenge exhaust from the cylinders.
2 1/4 duals are fine for a 307.
If it were me I would just put the factory setup back on with a high flow Cat and some Borla Aero Chamber mufflers.[/quote]

Can you please explain how back pressure helps scavenge the exhaust - just curious?

 

[olds307 and 403]

Back pressure isn't needed as much as velocity for small cubic inch engines or torque will suffer. The factory vin 9, 2.25" with better mufflers will beat the crap out of a single exhaust system, especially with an aftermarket cat. I got beat in my 81 Delta 88 4 dr with an Olds 307 that always had reasonable performance but seemed degraded by a little mid 90's Ford 4cyl. I pulled the half plugged cat off that car and replaced it with a piece of pipe, what a difference. Tons more power, the guy wouldn't race me again. Don't mistake back pressure with velocity. A muffler like a Super Turbo sounds close to stock inside but much better on the outside and flow much better than Flowmasters but you can group any muffler in that category. Another good gain would be a dry flow reusable filter like AEM and run dual hoses under the bumper to the air cleaner but wait to after emissions testing for the last one. I opened up the air box and added an AEM filter with a big body Super Turbo muffler in the stock pipe size on my 2000 Dakota. I did it because the 3" cat back loses torque on v6 trucks like mine. Yes some flow but mostly velocity. I can tell you it is night and day on the highway for power. In town like your car, it had good 3.92 gears so it was OK.

 

[T.Wagner]

Do any of you guys have a part number for the left manifold cover that the air cleaner pipe goes to? I can't seem to find any information anywhere.

Also, I recall DoubleV saying that there are two pieces that attach to the Manifold? A bracket type thi and then a heat shield that goes under that? I really can't seem to find any information on this.

How much should I expect to pay for these? I don't know the range that I should be expecting/negotiating to.