Triple SU thread....

[FEnatic]

Tried to search but couldn't find, anyone have a link to it? Thanks

[johnc]

Just remember the L6 firing order: 1 5 3 6 2 4 and you'll understand why triple SUs won't work unless they are mounted on a plenum.

[FEnatic]

So, with that order, the single throat SU couldn't fire on side by side cylinders?

[johnc]

Here's a quick table that shows why its not a good idea:

 

Firing Order, Degree of Rotation

1 0

5 120

3 240

6 360

2 480

4 600

1 720 (0)

5 840 (120)

3 960 (240)

6 1080 (360)

2 1200 (480)

4 1320 (600)

1 1440 (720)

 

3-4 Intake charge every 360deg (middle SU carb)

1-2 Intake charge 480 deg, then 240deg (front SU carb)

5-6 Intake charge 240 deg, then 480deg (rear SU carb)

[Tony D]

Also, remember they are designed for a constant velocity. For the triples to work, the sizing on an L24 would need to be more like that on a 1600SSS motor (38mm).

 

When you do the math, there is no flow advantage doing it that way, and the triple 46mm units are way too much to work correctly without some serious rework.

 

This was a common argument in Corvair Circles, being the placement of the carburettors on the heads in dual configuration was always suspect. When you checked reversion pulses and firing/intake order, though it really WAS the correct way to group the cylinders. If you look at the SU manifolds, they really ARE "equal legnth" when looked at from reversion and firing order! Same as the Corvair.

 

Sometimes, just sometimes, the millions of dollars put into R&D by the engineering department really does yield a good result that wasn't killed by some accountant somewhere!

 

Refer to the Corvair instance if you REALLY want to get people going in regards to "factory added additional carburettors"... The 140HP engines had four 1-BBLs on them, the secondaries opening up like on a normal four barrel. Their placement was also hotly debated, but time has proven out they are also in about the best spot possible....