ERA FIA undercar exhaust vs Sidepipes

[289FIA]

Hi Bob,

Found this informative link regarding how mufflers work:

http://www.howstuffworks.com/muffler.htm

Got me thinking about the “technology” differences between undercar exhaust and sidepipes. I’m looking for a quieter note on a rather tame 302 but lately have been reading various threads of how much power can be lost with different sidepipe setups. This leads me to believe the undercar exhaust restriction would vary even more.

So 3 questions:

1) What size are the primaries pipes on both setups?

2) On a 9.5:1 compression 325HP small block, what could be gained going with sidepipes vs undercar? (probably not realistic question, right?!)

3) Considering the limited space under the FIA, any recommendations on “better” performing mufflers that could out perform the stock setup? (Borla, FlowMaster, MagnaFlow, Dynomax, etc…)

Thanks,
289FIA

[imagine2frolic]

All of the mufflers listed except for Flowmaster are basically a glass pack. Straight through with a bit of a curve. The tubing passing through the muffler is perforated, and then the rest of the body has a packing of some sort, or another. I myself am thinking of a 289 275 HP with an under car exhaust. I was hoping to find a cast iron manifold application, but that does not seem possible, but one never knows. I was going to experiment with 2, or 3 long glass packs welded together under the car. What ever length I could get to fit before a bend. The bigger, diameter, the system, the better it will breathe. You lose your low end unless you are side stepping the clutch with a big system. Not good for everyday driving. You need to ask yourself, what kind of driving you will be doing, and then it is easy to decide on a system. I have done exhaust for 30 years, and tried most everything on most of my cars. Flowmasters are very loud mufflers, and not really the best breathing muffler there is.

[strictlypersonl]

The primary pipes on both setups are 1 5/8", feeding into a 3" collector.

On the undercar exhaust, the collector tapers to 2 1/4" pipe for the muffler.

The side pipe has an internal glasspack. I'm not sure about the ID - either 2" or 2 1/4"

I don't know the amount of power lost through the muffler. The amount of power lost probably depends a lot on the amount of valve overlap and the carburetor. For a 300 bhp 302, maybe 20 bhp, but that's strictly a guess.

P.S. Interestingly enough, we usually use a Dynomax muffler, the internals of which are a perforated pipe going directly from in to out, which sounds a lot like a bullet muffler.

[chuckbrandt]

I'm going to try these one of these days. A pair is supposed to support 400 HP, whereas the original dynomax are only supposed to support 200 HP.

http://www.flowmastermufflers.com/pr...8b4fd29079d23d

Chuck

[imagine2frolic]

I looked at the Flowmaster, and it looks to me like a piched down glasspack with blockage on the exit. I think for less money you can get a lot more. The most important thing is what do you want to hear, and how will you drive? Then you can make a decision. Exhaust is always give, and take. In 30 years I have not seen a muffler that gives you everything. There are several variables. When a customer comes into my shop. The first thing I ask is..."what do you want to hear, and what do you want to see." From there I can figure out something to make them happy....

[chuckbrandt]

imagine2frolic - you are probably right. On my car and I assume the FIA as well, this muffler fit the narrow confines pretty well. Jake Roulstone did a nice undercar exhaust using 2 glass packs on each side. There are of course new muffler shapes coming out all the time, I should do some more research I'm sure.

Chuck

[imagine2frolic]

Chuck, since this post I went out into the shop, and removed my stock muffler from my Caravan. Replacing it with a offset center Magnaflow muffler only 18 " long. The sound of the exhaust is almost NIL compared to before, and this is with a straight through muffler replacing a factory triple baffled muffler. Soon I will know the difference in the gas milage.

289, let me know what you want to see, and hear, and I can have a few ideas for you.....

[Cobralaraza]

I've been seeing a lot of comparisons between Flowmaster and Magnaflow. Which one's a bang for the buck?

[PeteF]

I have ERA's undercar exhaust, and have been thinking of adding resonators at the tail end to quiet it down a little. Chambered Classics makes 12 inch resonators that might just fit. Anyone tried this or have comments ? Thanks