3" too big?
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Joined: Jun 2003
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From: ok
3" too big?
It is time for a new exhaust for my ’95 bronco, stock 351 100K mi. I am planning on using a dual 2.5” in to single 3 “ Y in place of the first cat. Then going into a 3” in/out high flow cat then on to a 3” flowmaster 70 series muffler and exiting in the stock location. My questions are:
1. Does anyone have a similar setup? Any problems?
2. Is 3” too big? I don’t think it is and here is why the surface area of a 3” circle is7.065 sq in. My ’74 EB with a mild 302 has true duals with 2.25” pipes. Surface area of a 2.25” circle is 3.974 sq in. 3.974x2(duals)=7.948 sq in. Any thoughts
3. Sound? Would like a good sound but not too much of it. How loud would this exhaust be?
4. Might add shorty headers later how much louder would it be and are the performance increases worth it on a stock motor?
1. Does anyone have a similar setup? Any problems?
2. Is 3” too big? I don’t think it is and here is why the surface area of a 3” circle is7.065 sq in. My ’74 EB with a mild 302 has true duals with 2.25” pipes. Surface area of a 2.25” circle is 3.974 sq in. 3.974x2(duals)=7.948 sq in. Any thoughts
3. Sound? Would like a good sound but not too much of it. How loud would this exhaust be?
4. Might add shorty headers later how much louder would it be and are the performance increases worth it on a stock motor?
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Joined: Jul 2003
Posts: 49
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3" too big?
I have 3" on my car, not my trucks, but here is my opinions-
1) 3" pipes will give a Very low tone, and it will be hard to keep quiet. If you want loud and low, this will work good.
2) the flow characteristics through a tube are more complex than just measuring the area in the cross section. Actually, it is more of a ratio of volume in the pipe, vrs surface area (or cross section area vrs circumference). The air in the center of the pipe will flow much faster than the air next to the metal. When in physics class, I played with the numbers (don't have the equations handy now) but a 3" pipe, with its greater volume and less surface area flows much better than dual 2.25, and arguably better than dual 2.5! The answer to your question is that for performance reasons, 3" isn't too big, you can't go too big for your exhaust, expecially after the cat (on a header, that would be a different story)
3) I would guess the truck would be quite loud. if you have flowmasters on it, it will drone at some rpm (usually at cruising speed), and it will have a really deep sounding idle. It shouldn't be obnoxiously loud, but you won't ever accidently hit the starter with it running thinking it was off.
4) correctly sized headers will always help.
1) 3" pipes will give a Very low tone, and it will be hard to keep quiet. If you want loud and low, this will work good.
2) the flow characteristics through a tube are more complex than just measuring the area in the cross section. Actually, it is more of a ratio of volume in the pipe, vrs surface area (or cross section area vrs circumference). The air in the center of the pipe will flow much faster than the air next to the metal. When in physics class, I played with the numbers (don't have the equations handy now) but a 3" pipe, with its greater volume and less surface area flows much better than dual 2.25, and arguably better than dual 2.5! The answer to your question is that for performance reasons, 3" isn't too big, you can't go too big for your exhaust, expecially after the cat (on a header, that would be a different story)
3) I would guess the truck would be quite loud. if you have flowmasters on it, it will drone at some rpm (usually at cruising speed), and it will have a really deep sounding idle. It shouldn't be obnoxiously loud, but you won't ever accidently hit the starter with it running thinking it was off.
4) correctly sized headers will always help.
