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My 4BT has the H1C turbo with the small compressor housing so I don't know if that would be better off with a 4" or just leave it at 3"???

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My 4BT has the H1C turbo with the small compressor housing so I don't know if that would be better off with a 4" or just leave it at 3"???

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hopefully 4" isn't too big, that's what i got goin on.

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I'm not sure this is right.The 1st Gen CTD 6BT used a stock 4" exhaust which was fine for some very high power levels. The 3" 4BT exhaust is equivalent to a 4.5" exhaust on a 6BT. Seems to me it should allow for some pretty exotic power levels as-is.

The area of a 3" pipe is 7.07 sq. in.

The area of a 4" pipe is 12.56 sq. in.

So if you calculate that a 6bt has 6 cylinders / 12.56 area (4" pipe) = 2.09 sq. in. per cylinder.

A 4bt with 4 cylinders / 7.07 area (3" pipe) = 1.76 sq. in. per cylinder.

You would need a 3.25" pipe on the 4bt to be the same effect as the 4" on the 6bt.

Correct me if I am wrong.

I ain't no math whiz, but what I did was divide the 6BT 4" diamter by 6, and got 0.6666667. Then I divided the 4BT's 3" by 4 and got 0.75. If I take the 4" divided by 6, and multiply times 4 for 2 less cylinders it comes out to 2.667" which is smaller than 3". If I take the 4Bt's 0.75" and multiply times 6 it comes to 4.5", which is larger than a 6BT stock exhaust.I'm not sure this is right.

The area of a 3" pipe is 7.07 sq. in.

The area of a 4" pipe is 12.56 sq. in.

So if you calculate that a 6bt has 6 cylinders / 12.56 area (4" pipe) = 2.09 sq. in. per cylinder.

A 4bt with 4 cylinders / 7.07 area (3" pipe) = 1.76 sq. in. per cylinder.

You would need a 3.25" pipe on the 4bt to be the same effect as the 4" on the 6bt.

Correct me if I am wrong.

I could be off base 'cause I'm not real bright on mathematics.

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The issue with your math is that there isn't a linear relationship between 3" and 4" exhaust.I ain't no math whiz, but what I did was divide the 6BT 4" diamter by 6, and got 0.6666667. Then I divided the 4BT's 3" by 4 and got 0.75. If I take the 4" divided by 6, and multiply times 4 for 2 less cylinders it comes out to 2.667" which is smaller than 3". If I take the 4Bt's 0.75" and multiply times 6 it comes to 4.5", which is larger than a 6BT stock exhaust.

I could be off base 'cause I'm not real bright on mathematics.

when it comes to cross-sectional area of the tube, the formula is pi*r^2. so you have to compare the area/cylinders.

hopefully that explains it. I don't know for sure that the 2/3rd rule works in this case, but even if it's not 100% true, it's probably close.

i came up with the same results as Kurt (biobusgroup)

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Is there a way to go 4" out of the Turbo? I currently have a 3" downpipe and then it will go to 4".

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Now i just have to figure out routing. tailpipe is easy, it's the intermediate stuff going around 2 crossmembers that may be tricky. I may end up running it below a crossmember. not something i really want to do, but my truck will only be 2wd and won't see much dirt, let along rocks. that's what the jeep's for.

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