Mark IV BBC LS2 Cam Sync and Crank Trigger Solution
Posted: Sat Oct 08, 2016 7:36 pm
I'm shifting entirely over to an EFI and distributorless ignition setup (LS2 style) on my new build and it's been a real learning experience over this last year. I still have several months worth of work left to finally get the Camaro back on the street, but I've made great progress so far. I'm hoping to get to dyno by mid to late November.
Old school Mark IV BBC's don't lend themselves to this sort of new-era LS2 build. Crank triggers have been around for a long time but there's not a lot of options available which provide the cam sync signal required by the ECU for DIS. Various options are available to convert your distributor to provide a cam sync for the ECU, but I'd really like to lose the distributor altogether. For one thing, it's a make-do solution and would be in the way down the road if I needed to move up to a 12-71 or 14-71 blower. A distributor style unit is definitely not compatible with that scenario.
There is a new timing cover available for Mark V BBC's which incorporate both the cam sync and crank trigger sensors, but they do not work with my old style block. There's a company which sells a distributor-type unit which provides a dual-sync signal, but again, this is not compatible with my plans to possibly hang a bigger blower on the motor.
So, I'm working on a home-grown cam sync and crank trigger solution. I'm still not convinced it's going to work. If not, I'll fall back to other options to meet the need. If this does work out, it'll be pretty cool
I came up with an approach which uses dual HE sensors mounted through my upper Comp Cams timing cover plate. I designed and had a local CNC shop machine out the new dual sync plate that mounts on the upper timing gear. The plate is both doweled and secured to the timing gear with flush-mount machine screws and uses high-temp neodymium magnets in combination with hall-effect sensors to provide both cam sync and crank trigger signals to the Holley ECU. There is a wedge of space just below my electric water pump which exposes just enough of the timing cover to allow sensor placement. I timed and located all of the magnets to align with this location. If this does work, all of this will be out of sight from above and I won't need to run a conventional crank trigger on the snout. The sensors I'm using are MSD 2348 HE sensors which have an integrated LED indicator. This makes it pretty handy to check timing for the digital rising/falling index points.
The photo above is the 1/4" plexiglass mockup I'm currently playing with. In this view I'm indexing the hall-effect sensors to the dual sync magnets. The precision required in placing the trigger points and sensors is pretty significant. Given the cam sensor layout actually represents 720 crank degrees, my 3.25" trigger circle yields about .014 travel for each degree of crank rotation. My current challenge is getting the sensors placed in the right locations and ensuring the end state provides a reliable, consistent and predictable timing scheme for the ECU. The per-cylinder crank trigger signal is used by the ECU to initiate all sequential injection and spark timing events. This is not a place I can afford to screw up - this is why I've spent so much time laying this all out. The solution is designed around a CNC-produced trigger plate, a bit of machine work to mount it to the cam gear and uses off the shelf wiring harnesses and sensors. If this does work it'll be easy to duplicate for future builds.
What do you guys think of my approach ?
Old school Mark IV BBC's don't lend themselves to this sort of new-era LS2 build. Crank triggers have been around for a long time but there's not a lot of options available which provide the cam sync signal required by the ECU for DIS. Various options are available to convert your distributor to provide a cam sync for the ECU, but I'd really like to lose the distributor altogether. For one thing, it's a make-do solution and would be in the way down the road if I needed to move up to a 12-71 or 14-71 blower. A distributor style unit is definitely not compatible with that scenario.
There is a new timing cover available for Mark V BBC's which incorporate both the cam sync and crank trigger sensors, but they do not work with my old style block. There's a company which sells a distributor-type unit which provides a dual-sync signal, but again, this is not compatible with my plans to possibly hang a bigger blower on the motor.
So, I'm working on a home-grown cam sync and crank trigger solution. I'm still not convinced it's going to work. If not, I'll fall back to other options to meet the need. If this does work out, it'll be pretty cool
I came up with an approach which uses dual HE sensors mounted through my upper Comp Cams timing cover plate. I designed and had a local CNC shop machine out the new dual sync plate that mounts on the upper timing gear. The plate is both doweled and secured to the timing gear with flush-mount machine screws and uses high-temp neodymium magnets in combination with hall-effect sensors to provide both cam sync and crank trigger signals to the Holley ECU. There is a wedge of space just below my electric water pump which exposes just enough of the timing cover to allow sensor placement. I timed and located all of the magnets to align with this location. If this does work, all of this will be out of sight from above and I won't need to run a conventional crank trigger on the snout. The sensors I'm using are MSD 2348 HE sensors which have an integrated LED indicator. This makes it pretty handy to check timing for the digital rising/falling index points.
The photo above is the 1/4" plexiglass mockup I'm currently playing with. In this view I'm indexing the hall-effect sensors to the dual sync magnets. The precision required in placing the trigger points and sensors is pretty significant. Given the cam sensor layout actually represents 720 crank degrees, my 3.25" trigger circle yields about .014 travel for each degree of crank rotation. My current challenge is getting the sensors placed in the right locations and ensuring the end state provides a reliable, consistent and predictable timing scheme for the ECU. The per-cylinder crank trigger signal is used by the ECU to initiate all sequential injection and spark timing events. This is not a place I can afford to screw up - this is why I've spent so much time laying this all out. The solution is designed around a CNC-produced trigger plate, a bit of machine work to mount it to the cam gear and uses off the shelf wiring harnesses and sensors. If this does work it'll be easy to duplicate for future builds.
What do you guys think of my approach ?