henryk8398

Ok, I'll accept the fact that the most cost-effective mod for a 307 is to swap in a 350 or 403. With barely 90k on the clock, that's a "someday" thing. However, I would like to have an exhaust system in place that will accommodate a larger engine in the future and maintain emissions standards. It certainly won't make it run worse! I highly doubt that a tech would be able to tell that I swapped a 350/403 in place of the 307. With a dual exhaust that has Cats and functional A.I.R., I think I can get away with it. I intend to maintain the CCC, so I think I have a fighting chance.

So here's what I'm thinking and I would appreciate any feedback.

1. Use Tailpipes from a `94-`96 Impala SS. They should jive with the C-Body Chassis, right?
2. Use Dynomax mufflers
3. Not sure about the intermediate pipes. I don't see why I couldn't use the Impala pieces.
4. I know I'll need to modify the crossmember. Thanks to The Stickman, I know what to do!
5. Dual cats, both with air.
6. Are there any Olds downpipes in the aftermarket I can use, even if they need to be modified.
7. I will use a crossover and weld in a bung to maintain an O2 sensor.

Any other ideas/suggestions? I would really appreciate it. Thanks in advance!

The Stickman

You should oly need the O2 sensor on the passenger side. Shouldn't need to worry about welding a bung on just use the stock manifold.

Olds64

I don't know if you could use the 94-96 Impala SS parts. There was a significant body change in B bodies in 1991. I'm not sure it would work.

joe_padavano

The 1977-1996 cars all have the same chassis, so the pipes should fit fine. Pypes Exhaust sells a nice mandrel bent system for the B-body cars. They also sell Olds down-pipes, but I'm not sure if they match up to the 307 manifolds. You might need the earlier 350 manifolds, which would require welding an O2 bung to the downpipe.

The biggest problem you'll have is that the C-body has a longer wheelbase than the B-body. You'll need a couple of pieces of straight pipe in front of the mufflers to extend the B-body system. Note that the Pypes system includes an X pipe, which is a good addition to any dual exhaust system.

Olds64

You could probably have it done cheaper at a local exhaust shop. That is an additional option. I had duals put on my 71 98 for about $300.

joe_padavano

Yes, but many local exhaust shops do not have mandrel benders, which means the bends will be much more restrictive. Be sure to check first.

henryk8398

That's precisely why I want to use as many mandrel-bent off-the-shelf products as possible. I'm sure I'll need to use an exhaust shop for the downpipes and to lengthen the intermediate pipes. I don't want to change manifolds at this time. That way, I can maintain the o2 sensor, per Stickman.

Sounds like I'm on the right track, but I was wondering. If I keep the stock 307 manifolds, but cut the crosspipe, the o2 sensor would only be reading exhaust from the passenger side cylinder bank. Will that cause any problems?

Thanks!

joe_padavano

Yes, you'll only read one bank and unless you have a bad cylinder in the other bank, you will be fine.

1964F85

Hi Henryk, Adapting the Caprice factory duals may work, with some mods. Starting in 94, Chevy went to duals with the LT1 350 engine. You could go into the local parts house and tell them you have a 95 Caprice with the factory duals [former police car] and get the pipes. However, the tailpipes are only 2" diameter. You may have to cut out a section the of pipe after the axle bend. Chevy went with real duals on 94 up 350 civilian cars and police cars. They both had a "double hump" trans cross member to allow both pipes to pass. As for the intermediate pipes, the Caprice stuff may work, but with mods as well [i.e. a section removal here too..]. You will still need to get pipes bent from the exhaust manifolds to the cats. I'd run a pair of the small sized "universal cats" [if your state allows them]. The next problem might be the joining of the cat to the caprice pipe.. The stock pipe was a ball/socket type joint and the uni-cat is a slip fit. If you are handy with a mig welder, this may work out, and you could add a crossover piece too. However, the true test is to compare all the individual parts prices to the muffler shop total system price.

In the end, it may be cheaper and cleaner to get it custom bent to suit your car, especially in light of all the extra fiddling you'd have to do to get the other pipes to work. Exhaust shops around here are very touchy about the cat and insist it has to be as stock, in the stock location.. after the cat you can do as you wish.

Hope this helps. Cheers, Mike [I upgraded my 91 caprice with single to duals using the 94 cross member and parts store replacement pipes..I did have to weld ball ends on the cats though, but it worked.]

joe_padavano

This is why I suggested the Pypes kit. It is mandrel bent and comes in 2.5" and 3", along with an X-pipe.

henryk8398

I don't want to mess with trying to unbolt the downpipes from the manifolds. I was thinking I could just have the downpipes made from there at a shop, then use a Pypes pieces kit to build the rest. I would like to stay legal, and I can MIG weld, so I think this is very doable. I'll use universal converters. My biggest concern was using too many compression bends. Looks like this is very doable. Thanks for all the great advice!