Syncing dual dbw throttle servos

[parsonsj]

Hi all,

Sorry if this topic has been covered before. I searched but didn't find anything.

I've got a Radical SR8 running with a MoTeC ECU using the GPR package with Geartronics extensions. All is well except idle. When I set offset and scale for the dual Jenvey DBW servos (one per bank), I can get them pretty close -- within a percent or two. And for on-track use, that's plenty good enough. But at idle, a couple of percent makes a big difference in air flow from bank to bank -- 20/30% air flow difference.

I'm wondering if anybody has a procedure for getting the throttle percent to match airflow across dual throttle servos, especially at low blade angles such as idle.

thanks!

John

[parsonsj]

Based on some advice from another website, I've been able to sync the two banks at idle. I reset both banks' offset and scale but this time using the idle stop screw to allow better repeatability of the offsets. Then (1/4 turn at a time) I turned in the stop screw on the rich bank, and reset the offset and scale of that bank. As I did that, the lambda readings of the rich bank slowly leaned out and then matched the other bank, and so did the scale percentages, which should mean that the sync at part throttle and WOT will be good too.

Love this ECU!

[Stephen Dean]

Hi John,

That is the biggest issue with ITB's, in that unless you have an external measuring device like the old Weber Synchrometer that can be used to balance the flow between all of the ports, a small variance in the closing angle of the throttle valves will have a large flow on effect on the operation of the engine idle. Measuring flow is going to be better for balancing the individual ports compared to measuring the angle of the blades as there could be small manufacturing variances that also have an effect on the flow rate.

A variance in the angle of the blades once they are at a larger opening angle doesn't tend to be as noticable, and at full throttle usually the throttle shaft is a bigger restriction to flow than the blade angle variance.

[parsonsj]

Thanks Stephen!

I have a set of flow meters that I use to configure a bank of ITBs to all flow the same. I had both sides flowing consistently within their own banks, and I used the throttle stop to get the two banks to flow the same at idle (1-4% throttle opening, closed loop fuel less then +/- 3% and typically no more than 1% difference between banks) and idle is still at 1700 rpm!

All is well there now, and I'm happy with engine idle.