Exhaust System for Olds 307 Vin 9

[T.Wagner]

Hi All!

I have an '83 Hurst/Olds and I am looking at redoing the exhaust system. Right now my mechanic said it could be getting too much flow and hurting its performance. Also, it is not legal for California emissions, so I am looking to fix that as well. Currently I have headers on the car (not sure what kind) and then straight 2.5" (I believe) pipes to the back with some Magnaflow exhaust. I have a few questions regarding a new system.

1. Should I try to get exhaust manifolds for my car or keep the headers? I am looking at getting the best performance I can while still having it legal for emissions.
2. What size pipe should I get? I was thinking 2 1/4" but I am not too sure on all the math behind it.

I believe the system originally comes from the manifolds down to one pipe to the catalytic converter. From there it splits into a Y pipe into the mufflers and out the back.

Any help would be greatly appreciated. Thanks!

 

[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.

 

[T.Wagner]

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.

I was thinking about going to look through some junk yards to see if I can find manifolds for the 307. It seems that they are pretty common engines, so I'm hoping it will be relatively easy to find some... My headers leak a lot right now (and if you tighten them they leak again soon after), and if they aren't helping my performance then I might as well get it back to stock with manifolds.

As for the X pipe... is that suggestion if I keep my headers? I definitely need to put a cat back on my car and with that I don't think I can do an X pipe? Also, I am in California so I am not sure if a high flow cat would be legal here, but I will need to research that more.

Ultimately I will be going back to the stock setup, I am just trying to figure out whether to keep my headers or not and the pipe diameter. Like I said, if the headers aren't helping and I can find some manifolds then I will likely go with those.

Do you know what the stock specs were for pipe diameter? I can't seem to find that information anywhere...

 

[T.Wagner]

 

[kustomkyle]

I wouldn't say headers aren't going to help, I'm assuming all that was meant by that is it was a lower horsepower engine, and to many that means it isn't worth putting any money into. By bolting them on you aren't automatically going to have 300 horsepower. The VIN 9 exhaust is different from the catalytic converter back from the VIN Y (non-H.O.), in that it turns into a dual muffler/tailpipe outlet system, whereas the VIN Y stays a single pipe (though still 2-1/4") then down to 2" at the short tailpipe after the muffler.

I seriously think headers and duals on a 307 in perfect tune are worth 20 horsepower, just like they are on any other V8. You don't want your headers too big, as bigger tubes are only good for high horsepower and high RPM applications, which the 307 is obviously neither. X-pipe, now that is more what I would call overkill. Some say it actually does something, but I think again it's something that only works in high horsepower/RPM applications. You also run into clearance and space issues if you want to use cats, but I'm sure you can purchase them from Pypes or whatever tailor made for these cars any way you want them.

I'd stick with headers, maybe just a better set with thicker flanges is all you need? Maybe earlier Olds 350 manifolds would be alright, still better than the 307 ones, although the 442/Hurst ones were supposed to be better (but good luck finding those in a junkyard).

I have a factory replacement Y-pipe for my car that I haven't put on yet if you need those measurements for whatever reason. The "front pipe" is getting harder to come by, I think I got one of the last ones available by Merit. I don't see a part# in the Walker catalog.

 

[kustomkyle]

This is the VIN Y single exhaust system. Note how everything is the same part# ahead of the intermediate pipe. Keep in mind, if you do end up going back to stock configuration, Walker doesn't list a VIN Y 307 engine for your year, just the VIN H 305 Chevy. Why they do this I have no idea, to my knowledge the Chevy engine was only available in Canada.

 

[DoubleV]

If I'm not mistaken it's technically illegal to mod anything on the exhaust before the cat. If that's true and you want to be 100% legal, you're stuck with the fake dual exhaust setup like the stock VIN 9 engines had and that setup is horribly restricting.

If you can get away with running true duals then definitely go that rout. Headers aren't the big power adder for your application despite what some people may try to sell you.

 

[williamattop]

I believe Thorton makes some reproduction high flow exhaust manifolds to fit the 307.
I would suggest these or factory manifolds with a factory set up exhaust.

Stock motor + California = stock set up exhaust IMO.

 

[T.Wagner]

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?

 

[williamattop]

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.