26 replies to this topic

[Redslur]

Depends on the engine power really.  A dual 2 inch system is plenty if it is stock. I ran dual 2 inch on my 320 HP 308 and it screamed. Anymore power and I would be considering a dual 2 1/4 or 2 1/2 system.

[rexy]

Twin 2.5 inch system on the old LX sedan and on the current hatch.

[Orange SS]

I am currently running a twin 2 inch system with pacemaker extractors and I am getting the engine up graded to a 355, hydraulic roller cam and my engine builder has recommended a twin 3 inch to the diff and 2.5 over the diff and out the back. Not sure why the need for 3 inch when it drops back to 2.5 over the diff but he definitely knows his stuff so I am inclined to go with what he has recommended.

[IMORAL]

 _{Full twin 3"  with 1 7/8" custom primaries. Tail pipes go under the diff instead of over.}

Edited by IMORAL, 09 September 2015 - 12:05 PM.

[Mort]

Just had a twin 2 1/2" mandrel bent mild steel system with 'H' pipe fitted from extractors back.

 

Exhaust had to go under diff because it wouldn't fit past the drop tank (apparently) if it went over.

[ls2lxhatch]

This is a rough guide to exhaust pipe sizing.

http://www.exhaustvi...-diameter/#easy

 

This test compared a 2 11/42"  (~ 2.25") system vs a 3" system on a 500 hp 383 SBC. The 3" system picked up 11 FWHP over the 2 11/42" system.

http://www.hotrod.co...ermarket-parts/

Edited by ls2lxhatch, 15 September 2015 - 11:05 AM.

[UCgazman]

I'm going for a 2 1/4'' twin system on the UC, but its pretty much a stock 5.0....

[Holdenbn74]

I'm going 2.25 with cats and hooker mufflers with2.5 tailpipes. Mild 304 currently

[ozyozyozy]

Mine has twin 2 1/4, x pipe and pacemakers.
Standard stroke 308, 415rwhp.

[myss427]

Twin 3.5 inch over the diff (lots of mods made for room), big engine , big exhaust!

[IMORAL]

That's good HP for a standard stroke 308. How did you mange that?

Edited by IMORAL, 16 September 2015 - 12:06 PM.

[Redslur]

Yes agree with Bomber, most people over exhaust their car. I had a dual 2 1/2 system on one of my 5000's and it sounded crap (thong slappy).  The engine produced 320 HP so I change it to a dual 2 inch system with X pipe.  It sounded way better and had exactly the same HP on the dyno with both exhausts.

[ozyozyozy]

Im not bs-ing.
Even have 2 mufflers and 2 hot dogs to quieten it down a little, take the edge off.
The shirt motor is nothing that special, factory 308 crank, scat rods, forged pistons, 11 to 1 comp now, has 4 bolt mains, bronze lifter bores, solid roller cam, come alloy heads 580 series i think, un ported, harrop manifold, 650dp carb, dry sumped.
Spent alot of time fine tuning, widening the operating range, all about making what you have work efficent not just having the biggest and best.
I made 385 with my old ported iron heads.
Has a great note too, no thong slapping, i hate that noise with a passion.

[IMORAL]

Nice. Sorry i didnt mean for it to sound like i said bs. It was meant that is a truley good number for standard stroke. Great work

[TerrA LX]

Finally I won't feel odd when I answer the next person I'm fitting a 2 1/4 twin to mine.

[ozyozyozy]

Your right imoral i didnt take it that way, had a few people question tho locally.
When it was first built it made 340, just refining areas of it has crept it up.
When you way it up twin 2 1/4 is equivalent to 4 1/2 inches of single, thats still a decent hole.

[myss427]

Does not work that way, putting 2 1/4 inch pipe on top of another 2 i/4 pipe is 4 1/2 high but still 2 1/4 wide hole.

Edited by myss427, 17 September 2015 - 03:19 PM.

[ozyozyozy]

What about the volume of air it can flow.
too big pipes on an engine can reduce the amount of scavenging affect that occurs, less power

[Bigfella237]

When you way it up twin 2 1/4 is equivalent to 4 1/2 inches of single, thats still a decent hole.

 

Not quite, the area of a 2¼" circle is 3.98 square inches, multiplied by 2 pipes gives a total area of 7.96 square inches

 

The area of a 4½" pipe is 15.9 square inches, roughly the same as 4 x 2¼" pipes

 

The total area of twin 2¼" pipes is a little under a 3¼" single (3.18" dia)

 

Volume is irrelevant as length wasn't mentioned.

Edited by Bigfella237, 17 September 2015 - 03:31 PM.

[ozyozyozy]

Math dont lie.
That gives more of an idea as to what size to run.
Thats why there is formulas for header size and length.

[hanra]

I wonder what the thinking or maths is/was for the stock 1 5/8in tail pipes after the stock 2in system?

[UCgazman]

^^They shoot peas further?