B6 Exhaust Piping?

[sketchman]

Mandrel Exhaust Systems says they don't make Festiva parts(I knew that already but whatever) and don't plan to.

[drddan]

I have been comparing B3 vs B6 exhaust manifolds. Measured the port openings on both and here are the measurements I found.

B3 exhaust ports are roughly 1 3/16 inch or 30 mm

B6 exhaust ports are roughly 1 3/8 inch or 35 mm

These are the ports at the head.


Measured with digital calipers, and this is the average, as the ports are not completely round.

Measurements at the outlet or down pipe side are

B3 port is 1.58 or 40 mm

B6 port is 1.80 or 45 mm


Since the B3 ports open to 1 1/2 inch down pipe, I am thinking the 1 3/8 inch B6 ports will be perfect with the 1 3/4 inch down pipe and exhaust pipe size.

Would I do okay with using the Mazda 323 as an ordering guide to which down pipe I have made or should order?

The B6 exhaust manifold is also longer than the B3.

[Christ]

A port opening slightly smaller than the pipe it dumps into is a good thing. It prevents flow reversion at the manifold surface to some degree.

[drddan]

Yes it does. I was just agreeing with everyone that suggested 1 3/4 pipe size.
So I would have 1.80" going into 1 3/4" pipe. (1.75")

It seems like if I wanted a bigger down pipe than the port, I would need 2.0" exhaust piping.

Now I gotta figure out which down pipe to get. The B6 is 3 1/2 longer than the B3 manifold. I will need a shorter down pipe than the B3 used.

Do you happen to know of a good site for figuring out down pipe length?

[BigElCat]

Also, you asked if a stock replacement gen 1 B6 (323) headpipe would fit on your car, right?

[drddan]

Also, you asked if a stock replacement gen 1 B6 (323) headpipe would fit on your car, right?

Yes I did.
I was curious if it would fit the Festiva okay enough to be able to get the rest of the piping to line up.

If it would have the bend in the right spot to go around the bottom of the motor and get to where the cat. should be?

[BigElCat]

I'm wondering the same thing. Does anyone know?

[drddan]

Just checked the bolt pattern of the flanges on the B3 and B6. Guess what?
The bolt pattern diameter of both the B3 and B6 are the same!
The bolts that stick up are the same pattern, but.... the B3 flange pattern is canted at about a 15* angle or so, where the B6 flange pattern is straight. The only other difference is the bigger exhaust hole in the center.

[Christ]

I used to have a bunch of custom exhaust sites bookmarked, but I don't use that computer anymore, sadly. I went even more minimalist than I originally was, so I basically only use my phone or other people's computers to do online stuff.

I do remember that runner length is only part of the battle when building an optimal exhaust system. The distance between air-mass convergence (the junction) and the valve also determines "boost" points in the exhaust flow (based on RPM and volume) which can effectively "supercharge" the exhaust flow based on reverb frequencies. The effect is much more pronounced in intake building, but exhaust tuning works it's way into the game just as well. This is called "Helmholtz" tuning, if you want to research it.


I also remember that after the exit from the head, you want the pipe as smooth as possible on the inner bore. At the head, the velocity is high enough due to incomplete expansion to keep the flow moving along the pipe, even after the step restriction is introduced (which slows down flow by allowing expansion and creating drag). All of your expansion/contraction points should be no more than about 12-14* angles, any bend after the header should be wider than the pipe it intersects by about 20-30%, etc.

[BigElCat]

Just checked the bolt pattern of the flanges on the B3 and B6. Guess what?
The bolt pattern diameter of both the B3 and B6 are the same!
The bolts that stick up are the same pattern, but.... the B3 flange pattern is canted at about a 15* angle or so, where the B6 flange pattern is straight. The only other difference is the bigger exhaust hole in the center.

You mean the flange that connects the headpipe to the exhaust manifold?

[drddan]

Yes. The same flange will fit both.

Correction: When I said the B3 flange was "canted" about 15*, I used the wrong terminology. I should have said "rotated" about 15*

So one stud on the flange of the B6 points straight towards the front of the car, while one of the B3 flange studs points more towards the headlight, if that makes sense.

[BigElCat]

Makes sense.

Somebody help!

Will an old style (Gen 1) stock B6 headpipe work for a Gen 1 B6 motor swap in a Festiva?

[drddan]

Here is a link to one on ebay.It looks like it would work, but not sure.

http://www.ebay.com/itm/Walker-Exhau...4176be&vxp=mtr

I am waiting on an answer as to what diameter the pipe is.

[drddan]

Ok, I have an answer on the tube diameter of the above link to a Bosal down pipe for a Mazda 323

Here is the answer I got

Dear drddan,

Hello,

Inside diameter of the inlet is about 1 and 5/8 inches. Inside diameter of the outlet is about 1 and 3/4 inches. Outside diameter of the pipe changes a little bit with the curves but is about 2 and 1/2 inches.

Thanks,
George


- pelhamautoparts

The id's & od's dont compute. 60 ga tube wall is 1/16 thick. 2 walls = 1/8 thickness, so 1 3/4 id + 1/8 = 2 inch od pipe...not 2 1/2

But this looks like it is close to what I am looking for.

Any opinions?

[Christ]

The pipe is jacketed, which is why the OD is so much larger than it should be.

PS - 1/8" and 1 3/4" is only 1 7/8".