orangeapeel

iTrader: (18)

What is wrong with the true dual setup?

dirtytrucker+nurse05

how about single 5 inch?

lsx24

iTrader: (45)

You're going to be restricted by your header collector at this point. Since most (if not all) header collectors come in at 3", that is going to be a bottleneck of any system even if the piping is larger behind it.

lsx24

iTrader: (45)

On an interesting side note, you can prove that the stock 75 mm MAF sensor is a restriction, using the above formulas:

Code:

75mm  =  790 cfm = 359 hp
85mm  = 1007 cfm = 458 hp
90mm  = 1131 cfm = 514 hp

lsx24

iTrader: (45)

I would assume this is fwhp (flywheel hp), because we are talking about the efficiencies of the actual engine and what airflow it can support.

TheBlurLS1

iTrader: (8)

Exhaust gas is a *slight* bit warmer, and less dense than incoming air wouldn't you say?

This means that for every cubic inch of incoming air, there is FAR more molecules than in one cubic inch of exhaust. This formula only applies to exhaust systems.

lsx24

iTrader: (45)

That makes sense since I didn't take into account the density of the incoming air....to bad there isn't a formula for cold air I'd be interested to run some numbers through it. No wonder I was already loosing faith in the stock MAF sensor.

dirtytrucker+nurse05

This was origianally posted in "small block, big block specific". I didn't get any responses for a few days, so I tried in here. Specifically for a FI BBC 468 in a tube chassis trail rig. I don't have room for duals and I have a 3" exhaust kit but, I didn't think it would support the HP I will be making. That's why I asked about single 4". Thanks for all the responses, Mike

Ragtop 99

iTrader: (7)

Plus the exhaust has to deal with the gasoline that was used, which entered the engine from a different source. Those molecules have to come out the tailpipe too.

greysteel_M6

iTrader: (5)

I think you were right the first time. From Theblurls1's post he's saying that each cubic foot of air that flows through the pipe supports 2.2hp, thus
for every hp produced the pipe needs to flow .4545.. cfm
1cfm=2.2hp
1127cfm=2479hp

I assume that formula holds true for only na?
Looking at the numbers a 4in pipe is absurd.

SSmokin 01

iTrader: (14)

Here's something for comparison.

Revised my 3" exhaust to 4" (lost 2psi). Made a more efficient inlet hat and gained back the 2psi + 1 deg timing. Gained +58rwhp/+63rwtq

Figure roughly +40rwhp/+40rwtq without the degree of timing.

Same boost, more efficient, more power.


614rwhp/537rwtq to 672rwhp/600rwtq

https://ls1tech.com/forums/forced-induction/626013-procharger-346ci-58rwhp-63rwtq-new-inlet-hat-exhaust-1deg-timing.html

ss1

iTrader: (32)

Does it make a difference if you're talking about the ID of the exhaust as opposed to the OD? The exhaust gases are flowing through the inside of exhaust, not the OD.

I would think you'd take into consideration the thickness of the material and subtract that from the OD. Figure for 16GA tubing you lose ~.130" (.065" wall thickness) of the cross section.

I'm only mentioning this because I was figuring out the same stuff not too long ago.

purdueranger

iTrader: (11)

I have the Mufflex single exit 4" cat-back with a flowmaster muffler. I love it.

lsx24

iTrader: (45)

Actually this is not true. There are two header collectors, therefore it would be 2 x 3", or 6" exhaust before the collectors become a restriction in this system.

lsx24

iTrader: (45)

I don't believe so because there's no way a dual 2.5" exhaust will support 2479 hp...I don't think Theblurls1 meant to say 2.2 hp per cfm, rather 2.2 cfm per hp, it makes more sense that way with the pipe numbers I quoted earlier.

speed_demon24

iTrader: (6)

Wow.....

lsx24

iTrader: (45)

Or Dual 3".

ss1

iTrader: (32)

lsx24

iTrader: (45)

There are 2 headers, so therefore there are 2 collectors, and each one is 3", so the total restriction the collectors play is 3" + 3" = 6". Although I'm not sure the math comes out identical for each area (square inches).

As far as what is the equivilent pipe diameter that the start to become a restriction...

Just like 3" True Duals is 3" + 3", 2 header collectors are 3" + 3".

ss1

iTrader: (32)

Yeah, the math doesn't come out the same. You could almost fit two 3" OD pipes side by side in one piece of 6" OD pipe, and still have a bunch of area left over. I don't feel like doing the math right now though.

Maybe I just misunderstood what you were trying to say. No big deal.