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Honda K20 VTC Cam movement clarification

Variable Cam Control Tuning

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Discussion and questions related to the course Variable Cam Control Tuning

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Hi, I am making my own standalone ECU for the Honda K series and needs some clarification regarding the K20 VTC.

1. When its "0" VTC moving to "50" does it equate to 50 crank degrees, or 25 cam degrees, or 50 cam degrees or different

2. How to measure correctly which cam degree is it at 0 VTC with relation to crank degrees


Not all ECUs do this the same way, some are crank degrees, and some are cam degrees. MoTeC uses Crank Degrees, and there is an offset so that this reads 0 degrees typically when the cam is either most retarded (intake), or most advanced (exhaust).

The cam control mechanism should have stops to prevent the ECU from moving the cam outside of the usable (non interference) range. So, you can move the cam and "learn" what the range is, because you will see the position stop at the maximum.

Right. I have never disassembled a K series engine, mechanically how is the VTC at most retarded related to crank degrees? I am going to use the 13th tooth of crank as the reference minus the time it takes to see the first tooth of the inlet cam in microseconds, then convert it to crank degrees. is that correct?

You can convert CAM degrees to CRANK degrees by multiplying by 2 for a 4-stroke engine. The crank turns 720 degrees for each 360 degrees the cam turns.

The factory workshop manual will show how you align dots on the crank sprocket and dots on the cam sprocket to achieve the proper CAM timing relationship.

Normal practice for all cam' timing is to use crank degrees, unless there is specific reference to camshaft degrees.

so I made a code and tested it with my simulator and my ecu, at 0 VTC its at 100 crank degrees, and when I give 50 VTC, it goes 50 crank degrees. Anyone with a standalone ecu besides hondata do the same?

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