Plenums, Do They Run Lean On Rear Cylinders?

[F6R]

Thumbs up for individual cylinder tuning!

Of all the engines I've tuned with the above in mind, I have never seen a linear variation in cylinders across the rpm and load range.

[RAP1D]

Yep, IF people know how to do it, its the way to go

[turbotrana]

F6R

How are you doing your individual cylinder tuning. Are you running a lambda sensor on each exhaust port.

What sort or dyno?

[IH8TOADS]

There's a few things you can do. But I highly doubt anyone would be monitoring each port with a wideband......it's kinda done already by the PCM with a single narrowband anyway. In closed loop the PCM does an estimation based on the O2 sensor position and distance to the cylinder. It uses a time window, firing order etc to determine if a particular cylinder is lean/rich and it will adjust the fuelling for that cylinder. SO in closed loop it won't matter what type of plenum you have, the PCM will still 'learn' via the O2 sensor. Open loop WOT bit different. DUS12 makes some very valid comments IMO.

[RAP1D]

I'm not sure about BA BF but FG has some tables that let you manipulate fuel from each injector in a sense, though its not like you would for all 6 as per normal, and doesn't read like anything that would suggest it can, if that makes sense... but to make best use of the features you'd want to run EGT sensors on each runner, monitored with a stand alone system, which are widely available.

[Process West]

A few years ago I did some testing measuring individual cylinder air/fuel ratio and exhaust gas temps. This was a mammoth job.

The difference between cylinders is huge and is doesnt make any difference which aftermarket plenum or stock plenum you use. There are a dozen things after the plenum which will have an effect on cylinder balance. In my opinion the exhaust manifold makes a lot of difference. A properly designed aftermarket exhaust manifold is the way to go.

A couple of pics of the stock manifold we modded to accept individual O2 sensors and EGT sensors.

Kev

Edited 13/10/10 08:40 AM by Process West

[sexual harrassment panda]

We love you Kev

[IH8TOADS]

Haha well I'll be dammed!! Awesome initiative Kev.

[bjc]

Now that's ultimate tuning ability!

[Smoke them tyres]

I don't believe the plenums can be totally blamed, but some of them are not ones I would fit to my car....re airflow dynamics, particularly the head of steam that the airflow will have at peak power/maximum load. The manufacturers put right angle bends in their turbo model inlet manifolds so that one cylinder is not advantaged over another....a long held practice. A GTR setup with the individual throttle plates is what I would be fitting if I was after a lot of increased power.

The rule of thumb is don't blow across ports and don't funnel it down ports either. The first one will starve a cylinder, the second will favour a cylinder.

As far as I can see, there are only a few factors to losing a particular cylinder if everything is in good working order.....

-Is the fuel delivery consistent between cylinders?

Does the rail need to be fed from both ends or a bigger diameter fitted? Is the fuel system up to supplying and regulating the extra flow, and thus maintain consistent pressure? Can it consistently supply the flow without interruption?

-Is the airflow from cylinder to cylinder reasonably equal?

For this to occur, port airflow speeds need to be reasonably equal on each cylinder. A cylinder that has a bad "run" (such as with the std exhaust manifold) will definitely affect that particular cylinders ability to fill. If the same injector pulse width is applied, the mixture will either end up rich or lean. Also, it is not uncommon for engines with production hot side componentry to have an exhaust manifold pressure twice the boost level (which is also why they run so hot). Cylinder dilution from backflows between cylinders would also be a factor. I would be replacing the std exhaust manifold as part of the upgrade.

The other issue to consider is that the water flow basically goes from the front of the block to the rear, then up into the head and forward. Rough temperature equalisation will occur, but the front of the block runs cool, and the rear of the block runs hotter.

Some of the GTR guys have found that they can get the engine to live in the 800hp range if they richen up the 2 rear cylinders and also pull a couple of degrees timing out of those ones as well.

The sooner manufacturers run water flow ACROSS AND UP the engine and minimise temp fluctuations, as well as fit proper manifolding, the better off we'll be.

Edited 13/10/10 11:43 AM by Smoke them tyres