From what I've been told, the factory manifolds in my '92 have a 2" collector and goes to a pair of 2.25" pipes which each have a catalytic converter. From the cats, the pipes merge into a single pipe which goes into the muffler with dual outlets. Looking through the receipts for my car, I came across one which involved installation of an OEM-style Magnaflow muffler with 2.5" tips. Bet it's gonna sound awesome once the engine's up and running!

My question is, with the exception of the aftermarket muffler, how restrictive is this overall setup on a 305? I imagine the collectors might choke the larger 350 but it really doesn't seem that bad for the smaller 305. I have no doubt that a set of long tubes with larger pipes would open things up a bit, but would this be counter-productive to the low-mid range nature of a factory Tuned Port? Maybe a pair of shorties with smaller runners would be a better choice? Also, is the single pipe coming off the Y 2.25" as well? I could certainly see swapping in a larger pipe here since it has to handle the flow of both cylinder banks.

 

Have you looked under the car yet to see if it has dual cats? Or are you assuming it has them?

If it's a single cat car, the exhaust is bloody awful. Dual cat cars have larger outlet manifolds, a better Y-pipe, and larger exhaust from the cats back. Any of the above can be improved on, but read up a bit and consider your real world goals before you start throwing parts at the car. Your horsepower goal might very well conflict with your plan of action.

 

Yeah, at the moment, I'm just assuming. I've read that the later third gen 'Birds commonly had the "N10" exhaust option, which involves dual cats. Does mine actually have that? Honestly, I haven't looked yet, LOL. But thanks for the input, the factory single-cat setup is crappy, so I'll know where to start if mine DOES have such a setup.

As far as power goals go, I'm looking to keep things more or less stock with a few of the usual upgrades. Already got a K&N drop-in filter (thanks, previous owner!), but might add a larger throttle body, headers, open up the exhaust a bit and maybe nab a slightly modified PROM to maximize the OEM setup (if there really is anything appreciable to do here). In a nutshell, my power goals aren't exactly "steep."

 

Best way to know is to peek under the passenger's side behind the front wheel and count the cats. Dual cats were required on 350 cars, it was required on Formula and GTA 305 5-speed cars, and optional with other 305 TPI cars. So with an auto, it could be either way.

 

Yeah, looks like I've got the single-cat setup after all. But, there's a plethora of universal aftermarket cats out there so I figure to nab a universal Magnaflow when the time comes. I've got one with a single 2.5" inlet/outlet on my Ram and, combined with shorties, a 2.25" y-pipe and no muffler, low-end torque and throttle response improved appreciably over the OEM setup. And it has an awesome, bass-ey rumble at idle. Now, I figure that my 305, more free-revving as it may be, isn't going to need very large pipes just because of it's displacement.

Has anyone tried the old ram horn-style manifolds? I'm sure they don't flow as good as headers but they're readily available, pretty darned cheap and I suspect will last a longer than even expensive headers. And some of them have 2.5" collectors although runner size seems a bit small overall. Are these any better than my current log-style manifolds? If nothing else, they sure look cool.

 

Ram horns wont fit you will have to use headers or exhaust manifolds specific to these third gens as far as I know. Your y-pipe is the main problem. I'm not sure if your exhaust manifolds are different from the 350 cars or not maybe someone like Drew could chime in on this. Id replace every bit of the exhaust from manifolds back and run 3in.

 

[Quote; As far as power goals go, I'm looking to keep things more or less stock with a few of the usual upgrades. Already got a K&N drop-in filter (thanks, previous owner!), but might add a larger throttle body, headers, open up the exhaust a bit and maybe nab a slightly modified PROM to maximize the OEM setup (if there really is anything appreciable to do here). In a nutshell, my power goals aren't exactly "steep."[/QUOTE]

I wouldn't waste money on a larger throttle body on a basic stock motor. Your 305 with the stock throttle body will be more that adequate until you start building a higher HP motor. The stock throttle body will support up to 400hp easily. I would work on opening up the very restrictive exhaust for sure. As for a rams horn manifold, they are still somewhat restrictive and will change the placement of your "Y" pipe. If want to change the manifolds out, I would go with shorty headers and either eliminate the cats, or if you want to keep the cats for emission testing, get a less restrictive cat. I would also work with some good tuners on here and other places and pay for a custom made tune which isn't any more expensive that a "can" tune, and you can have custom work done to your liking like disabling VATS, or EGR etc. Really on a stock motor, nothing will wake them up like a really good tune up. Plugs, wires, cap, rotor. Keep it simple and have fun.