Weighing Fueling Options

[Syscrush]

I'm eager to see what you come up with on exh. specs.

Almost every system I see seems to have primaries about double the length of the ones on my bike. I am expecting that the modeling software will suggest something close to the Schuele design given that that seems to be one of the few single exit systems that doesn't have a big midrange flat spot. But we will see.

I'm as eager and curious as you, I've been wanting to have this analysis done for a long time.

[bobcat]

I'm eager to see what you come up with on exh. specs.

Almost every system I see seems to have primaries about double the length of the ones on my bike. I am expecting that the modeling software will suggest something close to the Schuele design given that that seems to be one of the few single exit systems that doesn't have a big midrange flat spot. But we will see.

I'm as eager and curious as you, I've been wanting to have this analysis done for a long time.

Study the stock OEM system and note that the header tubes are 3 different lengths in pairs.
This is not for cosmetics or convenient routing. Each length produces power at a different
area of the power band/range and serves to broaden the power band.
If you have to stray from this 3 length design, try to stick to a length within the 3 different
stock lengths. I would also suggest not going any larger than the stock header tube OD.
Whatever the design, the focus should be on maintaining velocity. If you kill that you have
just another piece of plumbing.

My nickels' worth (no more pennies)

[Syscrush]

Haha, look at what I wrote to the exhaust design consultant on the weekend:

I want to replace this with a 6-3-1, with 1&6 paired, 2&5 paired, and 3&4 paired. I am OK with the primaries for those 3 pairs being different lengths in order to spread out the power more across the rev range.

.

[bobcat]

Haha, look at what I wrote to the exhaust design consultant on the weekend:

I want to replace this with a 6-3-1, with 1&6 paired, 2&5 paired, and 3&4 paired. I am OK with the primaries for those 3 pairs being different lengths in order to spread out the power more across the rev range.

.



$$$$

[Syscrush]

Here are my injectors being tested after cleaning. The shop gave them an all-clear:

My injectors in the test apparatus

After the cleaning Static Flow deviation is 3.25% and Dynamic Flow deviations are within 5.04% on the all linear pulse width range. Good linearity on the flow to pulse width graph, no abnormal drop or rise in flow.
Good set after the cleaning.

[Syscrush]

Yesterday I had an interesting chat with Vince, the engineer from Burns Stainless who does design consults for exhaust systems. We went over what I'm trying to do and what my reasoning is, and he shared his experience from the V8 and V6 world. And then we reviewed the numbers his analysis had come up with.

The most interesting thing that he said is that in his experience, when pairing cylinders that are 360° apart, the primary length is not very important - it's the primary plus secondary length that matters most. Honestly it's hard for me to understand how that can be true, but the number of exhaust systems I have designed and tested is exactly zero. Even so, I'll be looking for a second opinion.

The numbers he came up with were:

• Primary dia: 1-3/8"
• Secondary dia: 1.5"
• Primary len + secondary len: 25" total
• Final dia: 2"
• Total length: I lost my notes and have asked him to refresh me.

[bobcat]

Hey Phil, it sounds like he's describing "stepped out" primary tubes where the tubes
get larger halfway (or so)down from the cyl. head as I described in the 6-1 options thread
where I said my ideal would be to double wall halfway then single wall the other half,
full length outer wall with the first half length inner wall so the step out is internal and
doesn't show (instead of welding two different DIA tubes at mid tube full length.
The 2" DIA would be the collector exit.
Dave Rash suggested the total header tube be 28" to 32" (between the cyl. head and collector.
25" pri./header tubes sounds a little short to me (if I read that right) unless he meant the tube*
between the first and second collector. 6-3-1 where the first collector is a 3-1 and second
collector is a 2-1 collecting the two 3-1.

*1.5"

[Syscrush]

To be clear, we're talking about:

• 6 1-3/8" Primaries feeding into 3x 2-1 collectors.
• 3 1-1/2" Secondaries feeding into 1x 3-1 collector.
• 1 2" Final to the muffler.

His model said that the Primary + Secondary should total 25", and he says that it doesn't much matter how long or short the Primaries are, as long as they add up to 25" with the Secondaries.

That would be similar to 25" Primaries between the head and a 6-1 collector. I agree that it seems short compared with other headers that have been shown to work well on the CBX, and it's hard for me to believe that the length of the primaries for a pair firing 180° apart isn't critical.