Long tube cat bypass

[911st]

I suspect a long tube cat bypass might let the stock HE's out preform an SSI system on a 3.2 Carrera and more closely approach the performance of most larger tube header system's that seem to make up to 10hp over a stock cat bypass or SSI based system.

This makes for a longer path between each side of the motor and should help reduce exhaust events from one side of the motor from creating a high pressure environment on the other side of the motor just as the exhaust valve closes. Thus. reducing reversion and improving cylinder filling on the intake cycle.

If it works it would be a lot less expensive and extensive mod than headers. It would also make it easier for owner's that need to put the cat back on for SMOG testing.

Might look more like this:


.................................................. .................................................. ....(one side of a B&B header.)


Current bypass style:

[Ken311]

is that bypass pipe currently for sale? that design looks promising

[Flat6pac]

I like it, suprised there isnt more conversation on here, there has to be some pros and cons at some level.
Bruce

[KTL]

The 1st picture is a B&B header installed on the 1-2-3 bank of cylinders. I can see what Keith is saying about the longer path, but the downside is muffler fitment. A lot of people want to ditch the cat but still bolt on a factory-like muffler. A longer bypass wouldn't allow for use of the many muffler offerings out there. So a custom muffler would be needed?

[Bill Verburg]

Originally Posted by 911st

I suspect a long tube cat bypass might let the stock HE's out preform an SSI system on a 3.2 Carrera and more closely approach the performance of most larger tube header system's that seem to make up to 10hp over a stock cat bypass or SSI based system.

This makes for a longer path between each side of the motor and should help reduce exhaust events from one side of the motor from creating a high pressure environment on the other side of the motor just as the exhaust valve closes. Thus. reducing reversion and improving cylinder filling on the intake cycle.

If it works it would be a lot less expensive and extensive mod than headers. It would also make it easier for owner's that need to put the cat back on for SMOG testing.

Might look more like this:


.................................................. .................................................. ....(one side of a B&B header.)


Current bypass style:

the first pic is my car w/ B&B headers on a 964 engine in my '76 C3, the issue w/ it is sound volume, it's quite loud w/ a Flowmaster X flow muffler(note that X flow does not indicate a merged flow only that the gases are directed so as to traverse the muffler w/o having the flow of the left interfere excessively w/ the opposite flow) and the tight radius bends to get gas into the muffler. the issue w/ the second pic straight pipe bypass is the merge area and the volume and the transition to the rest of the exhaust

a much better design is the RoW 930/10 premuffler, these were also oem on my RoW '76(pre-cats)C3 and in that application dyno work showed it to be superior to a straight pipe

here's is what a roW pre-muffler looks like


the advantages are a better merge design and an expansion chamber where the L/R gasses can slow down but still not overly impede the following gas flow. At the exit there is an attempt to guide the combined flow back together smoothely for exit to the rest of the system.

the pipes leading into the premuffler are the main concern as they have very uneven lengths

these are oem 964s which are similar to those used on 3.2 and 3.0

note the very long and poor design for flow used on the piece that transfers gas from the opposite side. the uneven lengths of the primaries cause the merging flows to be very chaotic even when peak rarefactions do mange to coincide w/ peak compressions from other cylinder for a short period of time

[Ken311]

the ROW premuffler looks alot like the m&k premuffler that is for sale here on pelican. since you said that design was superior, i assume that is the best option available for purchase at the moment?

[Bill Verburg]

Originally Posted by Ken311

the ROW premuffler looks alot like the m&k premuffler that is for sale here on pelican. since you said that design was superior, i assume that is the best option available for purchase at the moment?

The internal shape is an important feature, I haven't a clue what the MK internals look like