Exhaust Inlet Size

[Divers]

All - I am researching a new exhaust system. Car is 81 FI with 4mm domed pistons and Marks 274FI cams. I thought I had a muffler chosen...now not so sure. The forums seem to state that a larger inlet is what I "need". That being in the order of 2" minimum or more. I was going to buy Danny O'Donnell's stainless muffler, but hit a snag when he stated the inlet at 1 1/4 inch (or 1 3/4...now cannot remember!) with and outlet of 3 1/2". He seems very knowledgeable on the subject so I am looking for others who would have input. Don't need input on muffler types as that seems to be personal preference...just inlet pipe size please.

Robert

[Divers]

Hello....Bueller....Bueller...

[BEEK]

depends on the rest of your exhaust system

[Divers]

Sorry...thought I posted.

81 FI
Stock Manifold
Stock downpipe
Oversized intake/exhaust valves
4mm dommed pistons
274FI cams (Marks).

Is that enough info?

[narfire]

I have a similar set up for the engine and when it came time to replace the exhaust, I went to a 2 inch pipe from where it combines the two into one (cut at the collector and welded it in). I took the resonator off, added an additional support where the resonator was, over the axle to the twin tip Ansa that hangs a bit low but has a great sound.
Chris

[BEEK]

narfire gets my vote.. great system 2" from the collector. keep the number of bends to a minimum

[Divers]

Thanks! Guess that rules out Danny's muffler!

[fiat218]

narfire gets my vote.. great system 2" from the collector. keep the number of bends to a minimum

When I got my exhaust done, I told the guy to cut most of my exhaust off and start fresh, 2" from the starting point up front to the back, he told me that not a good thing because it could build up back pressure, I said what ever , I did not get it my way, I was pissed! It a 1 5/8 tube and then the muffler is 2" maybe that why I got less power

[So Cal Mark]

you need at least 2" from manifold to the muffler if you have a 2L motor. Be aware that a muffler shop bender will reduce the diameter of the pipe when they bend it to go up and over the axle. Few muffler shops have mandrel benders. A larger diameter system will reduce back pressure. The design of the muffler can also increase backpressure. The only pro from backpressure is reduced exhaust noise. Backpressure kills performance by pushing exhaust back into the cylinders. If you're interested, google reversion and you can read volumes by current top engine builders about the subject

[maytag]

yeah, Fiat218, What Mark said!

If yer exhaust guy told you a 2" would build back-pressure, and then he put in an 1"5/8, .... well..... you should find a new exhaust dood.... 'cuz he's stoopid.

Mark is also correct that most exhaust shops will not have a mandrel bender. Performance shops will though. If you get a guy who has a reputation for doing exhausts for the hot-rodders in your area, he'll know what he's doing.

and plus 1 on the 2".

[fiat218]

you need at least 2" from manifold to the muffler if you have a 2L motor. Be aware that a muffler shop bender will reduce the diameter of the pipe when they bend it to go up and over the axle. Few muffler shops have mandrel benders. A larger diameter system will reduce back pressure. The design of the muffler can also increase backpressure. The only pro from backpressure is reduced exhaust noise. Backpressure kills performance by pushing exhaust back into the cylinders. If you're interested, google reversion and you can read volumes by current top engine builders about the subject

i got that muffler from u, and i put that on my 80. yes it seems like there something holding this car back, i can feel it as if the exhaust is being squashed
muffler is 2" inlet, and the rest forward is smaller . that is a problem, CORRECT

[fiat218]

yeah, Fiat218, What Mark said!

If yer exhaust guy told you a 2" would build back-pressure, and then he put in an 1"5/8, .... well..... you should find a new exhaust dood.... 'cuz he's stoopid.

Mark is also correct that most exhaust shops will not have a mandrel bender. Performance shops will though. If you get a guy who has a reputation for doing exhausts for the hot-rodders in your area, he'll know what he's doing.

and plus 1 on the 2".

I AGREE

[Divers]

Thank you all for your feedback. I guess I will go and get a 2" exhaust. Now...off to find a stainless muffler with a 2" inlet. Kinda wish Danny O'Donell made one.

Thanks again!

Robert

[maytag]

Kinda wish Danny O'Donell made one.

for the uninitiated: Why? What is special about his mufflers?

[Divers]

Its all stainless...will not rot.

R