Plenums, Do They Run Lean On Rear Cylinders?

[RLF]

I'm not totaly against plenums or anything, if my car somehow came without an inlet manifold I'd probly buy a plenum but why throw out something you already have that works good for basic setups, ie 300rwk.

If I was to choose a custom plenum I'd probly go for something that holds a big volume, for some reason I imagine if it can over supply more volume than the cylinders require they should all draw in equal amounts at high rpm.

[Smoke them tyres]

Too much volume with a single throttle body= low speed of airflow= low torque= off boost unresponsive= higher atmo fuel consumption.

The plenums should also block off the long runner ports (the D shaped ones) in the bottom manifold and just run the contoured main ones. Those are cast bell mouthed and will supply all the airflow that the bottom runner to each port can supply. We want a constant acceleration of airflow to the back of the valve, not destroying energy by changing it's speed all the time via changes in volume. The manifold has to to both atmo and boost, and atmo is where you spend most of your time.

Personally, I think the FG manifold is much better with a smaller volume to provide a good mix across the entire operating sphere. So long as it can supply the air at the maximum power, why run any more volume than is necessary? Maximising the area under the power curve is the goal, not a spike of peak power.

[RLF]

If your looking for off boost torque and fuel economy down low your defeating the purpose of fitting a plenum to chase the big numbers up top.

When there's boost in the runner I wouldn't imagine air speed matters, only flow?

[Adam]

Flow is movement. Speed is movement.

Plenum's are also fitted to reduce the amount of piping and increase the over all efficiency.

[RLF]

Boost increases air speed giving more volume hence higher volumetric efficency in the cylinder. They all relate to one another but for a high boost, high horse power application n/a airspeed is irrelevant. Bigger is better in a way, and that's when plenums are better suited.

[TURBO4LT]

If I had to buy a plenum again I would probably go with the FG unit and mod it to fit the BA.

[IH8TOADS]

In light of my comments on the previous page....some food for thought.

The O2 transport delays are unique for an N/A 6, XR8 and the XR6 turbo.....why is that!?

Fuel multiplier per cylinder table. In SCT red means the tuner has increased the value/s, whereas blue means they have been decreased. This is straight from my tune.....yet I haven't physically changed the values in this table, not this one anyway! Without reverse engineering the binary I can't explain this unfortunately.

[ratter]

when you make adjustments to "injector comp batt volt offset" it makes changes to the table you are looking at

[Headsex]

SCT's f*cked up, and the "Fuel Multiplier per cylinder" table is actually the "Injector Comp Batt Volt Offset" Table..

Its commonly known that the rear cylinder runs hotter due to the water jacket design, and the fact the waters already heated from the front 5 cylinders by the time it its the back cylinder.

Changing the water system is a option. or altering the individual cylinder trims for spark or fuel.

Its pointless putting AFR in each cylinder, esp in a boosted setup. The best way is to use thermocouples..

Let me illistrate why...

This is the 8 AFRs on each cylinder of the pro stock car....

This is the same run, but 8 Thermocouples. one per cylinder

Now you tell me.. WHich one is hell of a lot easier to understand...

PS. I've purposely cut the scale out on the left, as its quite secretive information...

Edited 08/12/10 09:38 AM by Headsex

[Dirty32]

Danny - For those that playing along at home who are a little bit bemused by your findings, what are Thermocouples??

The differences in graphs are obvious, but can you explain how these differences are attained?

Cheers!