necking down after collecter?

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70DusterBob

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The shop my Duster is in wants to neck down the exhaust from TCI headers to a 2 inch pipe. The collectors are 3", after the foot of 2" pipe they plan to use, the 2" extensions the headers came with, they plan on going to 3" out the back. Is this stupid or a good idea?

Thanks
 
The shop my Duster is in wants to neck down the exhaust from TCI headers to a 2 inch pipe. The collectors are 3", after the foot of 2" pipe they plan to use, the 2" extensions the headers came with, they plan on going to 3" out the back. Is this stupid or a good idea?

Thanks
What cid and cam duration?
I can about guarantee it's a stupid idea.
 
One muffler shop dude told me (and it made sense) that the exhaust is hot near the headers and cools as it travels out the back. That's why you can hold your hand over the rear exhaust pipe but not at the header outlet (too hot). Cooling gas should condense.....so the same amount of exhaust gas (volume) at the header should decrease in volume by the amount that it cools (temp) off as it travels to the rear.
 
It is a BPE 408 with the following specs:

· HP & Torque: 445 HP / 500 FT LBS
Compression Ratio: 10.1:1
Aluminum Heads
Flat Tappet Cam
Cast Steel Crank
Forged Pistons

Block:

· Hand picked seasoned block
Square and parallel decked
Align honed main bearing bore
Cylinders honed on computer controlled machine to within .0002 straightness and roundness
Cylinders are sonic tested for thickness
2-Bolt Main
4.000" Bored .040" over
2-Piece Rear Main Seal
Mech fuel pump provision: Yes

Rotating Assembly:

· New Cast steel crankshaft
4.000" Stroke
OEM type 6.123" connecting rods w/ 150,000 psi bolts
Forged pistons
External

Cylinder Heads:

· Aluminum Cylinder Heads - 63cc chamber
2.02" intake/1.60" exhaust valves
171cc intake/77cc exhaust runners

Cam Specs:

· Cam Type: Flat Tappet
.545 Intake .545 Exhaust
241 Intake / 247 Exhaust duration
@ .050 - 110 degree lobe separation

Ignition Timing:

· 34 degrees total at 2500-3000 RPM
 
One muffler shop dude told me (and it made sense) that the exhaust is hot near the headers and cools as it travels out the back. That's why you can hold your hand over the rear exhaust pipe but not at the header outlet (too hot). Cooling gas should condense.....so the same amount of exhaust gas (volume) at the header should decrease in volume by the amount that it cools (temp) off as it travels to the rear.

You're referring to what's called "tuned exhaust".... what you do.. is... you take shoe polish, and you wipe a fkn line every 8 inches from the collector on the extension.... or about 3 line...the last line of shoe polish that burns off.... is where you would attach the muffler....imo that has NOTHING to do with the diameter required...smaller would probably move that line further down the pipe even..'more heat'. Need to know what you're doing and not let some Ck biter steer you queer.
 
One muffler shop dude told me (and it made sense) that the exhaust is hot near the headers and cools as it travels out the back. That's why you can hold your hand over the rear exhaust pipe but not at the header outlet (too hot). Cooling gas should condense.....so the same amount of exhaust gas (volume) at the header should decrease in volume by the amount that it cools (temp) off as it travels to the rear.

He was mentioning something like that, that the neck down needed to be where the paint no longer burned off the exhaust was his explanation. You did a much better job of it. I'm just concerned that it is not far enough back and too narrow. I posted the specs above for the engine. I have 3 step headers on it: 1-5/8 to 1-3/4 to 1-7/8 into a 3" collector.
 
Do you really mean they want to go straight to 2" and then later bump it back to 3"??

Stupid.

Except for maybe using a choke at or in the collector, the exhaust should continue at collector diameter for some length and terminate into very large volume in order to take advantage of any wave tuning the extension might help create.

This is a good article.
 
He was mentioning something like that, that the neck down needed to be where the paint no longer burned off the exhaust was his explanation. You did a much better job of it. I'm just concerned that it is not far enough back and too narrow. I posted the specs above for the engine. I have 3 step headers on it: 1-5/8 to 1-3/4 to 1-7/8 into a 3" collector.
Check with Johnny Mac and Blue Point, I'll bet they have your answer.
 
The shop my Duster is in wants to neck down the exhaust from TCI headers to a 2 inch pipe. The collectors are 3", after the foot of 2" pipe they plan to use, the 2" extensions the headers came with, they plan on going to 3" out the back. Is this stupid or a good idea?

Thanks
Quick! Run away, very quickly. Run your *** off. There secretly anti MoPar as well as plain old fashion stupid.
 
Do you really mean they want to go straight to 2" and then later bump it back to 3"??

Stupid.

Except for maybe using a choke at or in the collector, the exhaust should continue at collector diameter for some length and terminate into very large volume in order to take advantage of any wave tuning the extension might help create.

This is a good article.

Sounded like crap to me too. I'm looking for 3" extension/collectors, Summit does not have a 3" in 3" out. Not that I can find.
 
You're referring to what's called "tuned exhaust".... what you do.. is... you take shoe polish, and you wipe a fkn line every 8 inches from the collector on the extension.... or about 3 line...the last line of shoe polish that burns off.... is where you would attach the muffler....imo that has NOTHING to do with the diameter required...smaller would probably move that line further down the pipe even..'more heat'. Need to know what you're doing and not let some Ck biter steer you queer.

Gotcha
 
Re cam that pos too.
The heads on it, should make 500
Favorite post and best next move after you run Away from that asshole lead exhaust shop that contains morons and asshats inside out being worn upside down.
the exhaust should continue at collector diameter for some length and terminate into very large volume in order to take advantage of any wave tuning the extension might help create.

This is a good article.

Smartest post yet. Possibly better yet, get the book by David Vizard.
 
Sounded like crap to me too. I'm looking for 3" extension/collectors, Summit does not have a 3" in 3" out. Not that I can find.

Like this?

You can also get 3" "reducers" made for a 3" collector that are made to weld the rest of your exhaust to. Either way works. The torsion bar cross member is typically pretty close though... So the longer extensions may be more trouble.
 
I don’t even think the stock 318 ever cam with a 2 inch exhaust. IIRC (LMAO @ that but....) stock exhaust tubing is 1-7/8. Correct?

They are TCI headers if I remember correctly. The pipes going into the collector are huge, 2" is barely half the size. I'm like?????
 
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