CIS FD balancing flow to injectors

[Walt Fricke]

If I had an EGT probe in each exhaust 1" below the head, I suppose I'd consider using a Mustang dyno (if that is a good term for a chassis dyno where you get to the RPM you want to look at (say 5,500) and then adjust the dyno so you are at WOT and the RPMs are holding steady.

If I were brave enough to be reaching in there with my 3mm Allen adjusting things.

Not sure how practical having six measuring devices for this would be, though. Maybe if you were a shop and were using an engine dyno?

[Walt Fricke]

Also, I have spent more time than I like to remember aiming an IR thermometer's laser dot at individual exhaust headers. Works great for finding a dead cylinder, and at some gross level of inequality would probably show up a large mismatch, I don't see it as being as repeatable and stable a method as an EGT or CHT reading. So much variation in where you point, the angle, the different reflectivity of the different runners, and so on.

Anyway, I am subjectively satisfied that the time I spent (basically while flushing the systems) getting the flow balance more nearly equal was well spent. Beyond that, marginal costs may override marginal gains.

[PcarPhil]

I agree there is a point of diminishing returns however if the car has a turbo CIS engine (mine for instance) then equal AFRs across all the cylinders becomes even more important.

I remember seeing this post that RarlyL8 posted awhile back in the 930 forum. This is a nice setup!

Originally Posted by RarlyL8

A lot of work and testing goes on behind the scenes. We use a set of headers with O2 sensors in each primary located 10" from the exhaust port. The AFRs are balances at idle, cruise, and boost. A conservative spec is used to buffer uncontrollable parameters such as CHT and ambient temperature / air density. As you know there is only so much that can be reasonable done with CIS but it is a tunable system.

[Walt Fricke]

I know the roundy round guys do stuff like this to suck out that last foot pound of torque. With EFI you could, I imagine, balance the AFRs across the whole working RPM range.

Don't see how you could do that with the CIS, though - you only get one shot at adjusting those six adjusters in the FD. I'd want to do it at higher RPMs at WOT. But one might pick cruise at part throttle.

I thought that when Porsche cut the fins off of the 930 turbo cylinders on one side, they cut off the top side, on the theory that the cooling air was coolest up top, but needed the help of fins down below to keep cylinder wall temps roughly symmetrical. Same theory as with the NA cylinders, which have shorter fins on top. And then just switched back to shorter fins on top. Do I remember that wrong?

Those headers are a thing of beauty.