24x sbc crank trigger conversions

Discussion in 'High Tech Retrofits' started by John Wright, Apr 14, 2020.

  1. rburrow87

    rburrow87 Veteran Member

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  2. JMcDonough

    JMcDonough Member

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    John's post in Paul's CP build thread reminded me of this and I wanted to post an update now that I'm running MS2 port EFI w/ 8 coil wasted spark on a gen1 SBC.

    Cliff notes version: Works great. Still more tuning to do, need to figure out a good tach output, but no real surprises during initial setup and operation. Coil per cyl helped power slightly. EFI thottle body helped a bunch more (vs a 650 cfm holley).

    Relevant aspects to this thread:
    - Using DIY Autotune 36-1 wheel. Should have used a wheel already drilled for a Gen1 SBC crank pulley bolt pattern.
    - DIY autotune 3 wire hall sensor with a weatherpak connector added
    - Running a ~5.5" aluminum 2 row crank pulley milled down on the back side to account for the ~0.2" thick wheel so rest of pulley system stayed as-is.
    - Made a simple bracket to mount the crank trigger wheel on the lower driver side of the block. This was possible by running a type 2 p/s pump with a head mount bracket to move the p/s pump out of the way.
    - MS2 port injection with batch fire (4 injectors/driver), modified to run 4 coil driver outputs
    - Mustang 5.0 Coyote injectors at ~58psi (manifold pressure reference) with a cheapo speedmaster efi manifold and 1200cfm throttle body. Barely fits under a ~2.5" cowl hood using a slightly dropped air filter base and 3" filter.
    - 4 wire IAC valve
    - 3 wire TPS (I don't actually know the right part number for this...I had one that worked from another MS2 project)
    - D585 (LS truck) coils with custom mounting brackets for top of valve covers. Summit LS coil ceramic boot plug kit.
    - GM ECT and IAT 2 wire sensors

    Because I didn't want to break the engine in with EFI for the first time, but did want to run the EFI manifold from the start, I broke it in using a holley carb and large cap hei distributor. I then connected up 1 coil to #1 cyl and used a timing light back and forth between #1 cyl distributor to plug wire and EFI coil #1 cyl with a wire and plug hooked to chassis ground to ensure I had the exact same timing between distributor and EFI while the engine was idling. After getting the megasquirt settings spot on for Cyl #1, I checked the other 3 spark outputs using a dial back timing light and same process.

    We (Dad and I) did a few pulls with the engine running 650 carb + distributor on the new engine before running EFI or electronic spark. Running 11:1 up top and 33deg total timing, made ~360whp. Kept carb, swapped to coil per cylinder (was no-name red large cap HEI), kept timing the same as the distributor (total advance and curve), picked up ~10whp. Then I swapped the carb out and hooked up the EFI system. MS2 base map config for the engine + decent estimates for the coyote injectors made for an easy initial startup. I took all warmup and most accel enrichment out for tuning to keep things easy. Used the dyne to hold speed as I changed map via throttle and get VE datapoints all over the curve using the distributor emulating timing curve. Within about 30 min I had a really good base VE map. Ran out of time to do much spark tuning.

    Based on the dyno's MAP sensor, we knew the 650 was adding quite a bit of a restriction up top (~2.0" of Hg vaccum at peak power) and we had power to gain in AFR adjustment. Went from ~370 whp to 417whp with EFI thottle body and AFR tweaks (12.5:1 vs 11:1). Memory is a little fuzzy, but I think the vaccum up top went down to ~0.7" Hg with the 1200cfm throttle body. Spark still not fully optimized, but we might have added a degree or two to get to the higher peak #.

    I haven't figured out a good tach output (12v square wave) approach yet. I tried using AutoSportLab's tach circuit. It creates the right logic level, but those signals are all 0-5v, so not enough to drive a typical autometer tach. Putting a simple amplifier circuit on that (based on the MS2 extra manual) pulled those coil driver signals down in voltage to the point where they had difficulty driving the coils, causing misfires. So, I either need to build a dedicated tacho out circuit on the MS2 board and find another pin to use as an output (with 4 spark outputs + CAN H/L wires, I'll need to get creative) or figure out a circuit that doesn't need as much current draw from the coil driver circuit.

    Other misc MS2/EFI related lessons while I'm typing this novel:
    - Having the IAC default to full open then return to desired position leads to a big engine speed flare on startup if you immediately crank the engine after key-on. Switching to full close as the reference to fix this.
    - I've done a bunch of GM TBI tuning in the past...compared to that I LOVE megasquirt and port EFI.
    - Glad to not be tuning hugely oversized injectors where tiny changes in open time at idle cause large AFR swings.
    - Having a USB PC based o-scope is really handy. I found a DS1M12 used on craigslist for $25 locally. Good for checking trigger wheel inputs, injector outputs, spark outputs, etc.
    - Having 0, 90, 180, 270 markings on the crank damper was super handy when checking spark timing for the other three spark outputs.
    - I used weatherpak bulkhead and other connectors. I don't love them. The kit I had for terminals and the crimper I used wasn't great for 20 ga wires. Okay but still not awesome for 18ga. Ended up putting small pieces of heat shrink around the wires where the seal goes over top to ensure snug fitment. 22 pins isn't enough for all my engine bay to MS2 wires. The weatherpak connectors are also bulky. Cheap, but in hindsight, I'd go with a different route.
    - Adhesive lined heat shrink is your friend. That plus staggering non-insulated crimp butt splices keep wire bundle sizes reasonable.
    - If you build the MS yourself, a stim or a good bench setup to test is super handy and lets you catch errors before they transfer to the car
    - Megasquirt CAN output is nice to have for datalogging purposes. I use it with an Autosportlabs Race Capture Pro and SoloStorm to get engine data during autocross runs that's aligned with gps speed, accelerations, video, etc.
     

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  3. biker

    biker Veteran Member

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    Amazing. But thanks for the headache. I feel like I did as a kid trying to do a Rubik's cube.
     
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  4. sandlapper

    sandlapper Veteran Member

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    Does any company offer a trigger wheel with high tooth count that will fit inside plastic timing cover as on OE iron head Vortec 350" L31 (5.7L) or 305" L30 (5.0L); essentially replacing OE 4 tooth trigger wheel that's sandwiched between crank's timing chain sprocket & damper snout ?
     
    Last edited: Nov 15, 2020
  5. JMcDonough

    JMcDonough Member

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    See the link on the first page/post. Exists, just kinda pricey.
     
  6. biker

    biker Veteran Member

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    That would be the way to go though. Cover has a sensor hole ready to go.
     
  7. sandlapper

    sandlapper Veteran Member

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    Ouch $175 ! But thanks just the same. IIRC, the OE 4T wheel may be a powder metal casting. Perhaps that's something that could be re-engineered via 3-D print/deposition; I'll ask a gent I know who sells that equipment.
     

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