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Old 07-09-2008, 01:33 PM
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Exhaust question

My car has 1-5/8" headers, 3" collectors, 3" H-pipe and dual 3" Flowmasters. Right now the motor is a H/C/I - 351W (N/A) making 400-420hp.

My question is - if I weld two 3" to 2-1/2" reducer pipes on the output of the two Flowmasters will my car lose power?

My other question is same exhaust set-up including the reducer pipes on the output of the Flowmasters but with a 418ci SBF (N/A) making 550hp at the crank?

The reasoning by this reducer pipes addition (?) is at WOT it's a friggin' cop magnet. Thanks everyone for your time.

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Old 07-09-2008, 01:44 PM
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Pretty much anything is a cop magnet at WOT. Are you thinking that reducing 3" to 2.5" will make it quieter?? Uh, ...no.
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Old 07-09-2008, 01:45 PM
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Quote:
Originally Posted by Greg T
Pretty much anything is a cop magnet at WOT. Are you thinking that reducing 3" to 2.5" will make it quieter?? Uh, ...no.
Yeah - that's my thinking. I don't know alot about exhaust. I was hoping that dual 2-1/2" exhaust holes would be quieter than it's present dual 3" holes.
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Old 07-09-2008, 02:07 PM
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Wont make a bit of difference. Want quiet? Change mufflers or keep your foot out of it.
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Old 07-09-2008, 02:11 PM
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Quote:
Originally Posted by Sixtyninemercury
My car has 1-5/8" headers, 3" collectors, 3" H-pipe and dual 3" Flowmasters. Right now the motor is a H/C/I - 351W (N/A) making 400-420hp.

My question is - if I weld two 3" to 2-1/2" reducer pipes on the output of the two Flowmasters will my car lose power?

My other question is same exhaust set-up including the reducer pipes on the output of the Flowmasters but with a 418ci SBF (N/A) making 550hp at the crank?

The reasoning by this reducer pipes addition (?) is at WOT it's a friggin' cop magnet. Thanks everyone for your time.
For a street engine, probably not. The reason is that the exhaust gases cool and contract as they move away from the engine. The muffler further reduces energy in the gases which not only quiets them but the process also cools and further contracts them. As the gases cool and contract inside a given pipe diameter they loose velocity. This can result in some amount of stagnation which will increase back pressure in the system. Reducing the pipe diameter behind the muffler will restore flow velocity of the cooling gases which will enhance getting the stuff out the rear and keeping the 1-5/8 pipes up front pulling harder on the valve.

1-5/8 pipes are suitable for a 350ish cid engine up to about 6000 rpm, they would prove to be too small on a 418. The 3 inch head pipes would be fine on the 418. For the 351 if mostly street driven, would be too large compared to the 1-5/8s headers, you get an immediate stall in the pipe with this. A 2-1/2 head pipe with a 2 inch H and 2-1/4 tail pipes would be a more effective solution.

Bogie
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Old 07-13-2008, 09:15 AM
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Re: Exhaust question

Stupid question time, when you guys quote a diameter as 1-5/8 is that i.d. or o.d.
I have 1-5/8 i.d.(41.275mm) on my 650cc single with a 41mm pumper carb.
Clive W
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Old 07-13-2008, 02:54 PM
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Normally the o.d.
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Old 07-13-2008, 03:09 PM
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Quote:
Originally Posted by Greg T
Wont make a bit of difference. Want quiet? Change mufflers or keep your foot out of it.
That is exactly what I have to do, but I drive by a police station
every morning, and they look at me, but I drive like a somewhat
responsible adult...

The only one that has complained is my neighbor...

K
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