There is no reason that a properly designed EFI system wouldn't work really well in a flathead. The key is having the correct injector sizes and technology to start with . . . and an overall system design that optimizes what EFI can/should be all about. It really should be an optimal solution to fuel and spark . . .
I'm currently designing a high-horsepower setup for a blown Hemi 392 - including converting a hat injector over to EFI. Lots of details, lots of expense due to what I'm working to accomplish.
I've thought about a custom EFI for a flathead and here are some thoughts/ideas.
1)
MPI: I'd go for true multi-port fuel injection - with an injector in every runner. This can give us the ability to "tune per cylinder".
2)
Sequential Port Injection: I'd go with a CAM sync setup - such that I can run true sequential (timed) fuel injection. This gives me the ability to tune/time the injector pulse to match a certain intake valve location - all based on the cam position.
3)
New Style Injectors: I'd look into using the best modern injectors - like the Siemens DEKA 4 or the Bosch EV-14 style. They atomize fuel a LOT better than the older EV-1 style of injectors (which a ton of people still sell).
4)
I would also run COP or CNP (coil on plug - coil near plug) - and ditch the distributor completely. My preference would probably be CNP - as I'd find a way to "hide" the coils as much as possible. Having complete timing control - based on true engine conditions (rpm, load, vacuum, coolant temperature, boost, etc) - is really something that good EFI ECUs provide - so why not get rid of all the moving parts. Is this a 'cheap' way to go . . . not if you're comparing price only to a 21A crab distributor . . . but if you're pondering a high-energy magneto, MSD box, etc - then it starts to make sense. The Holley ECU I mention below does all this stuff (and more) - and obviously so do other systems.
5)
I'd probably use a Holley HP ECU - as their software is really excellent, it's automatic learning capabilities really work well and it can handle additional sensors for data collection, has data collecting logs and the ability to playback the logs over the actual fuel tables, etc.. Just a really nice product, well engineered, great software, good technical support, good user forums, etc..
6)
Holley Dominator - Exceptional and Expensive: This is their top-end ECU - does everything imaginable (and more). There are many additional features over the HP. One thing I like is the support for dual O2 sensors (and learning modes that can average between the readings). Also, you can store multiple tunes in the ECU and switch between them with an external switch. This makes it possible to have a street tune, race gas tune and an E85 tune - all in the same CPU . . . you just switch between them.
Expensive Stuff? - Yes - it is not a cheap ECU ($1100), but one rapidly learns that the whole path to EFI (to have a system as I denoted above) is expensive. But why do it if you only get 1/2 the way there? (Might as well run 97's and a crab distributor). The sensors, harnesses, injectors, everything - it costs a lot of money. BUT - I also believe that if done correctly, one would have the best possible running flathead . . . including cold-starting, fuel economy, performance . . . all of it.
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In the case of my 392, I really want to run a 60's Hat Injector on top of my blower . . . and you really can't run MFI on the street, so converting it over to EFI is about the only viable path. I should be done with the project in roughly 2 - 3 months - then onto an engine dyno for initial break in and EFI tuning.
Platform to Learn: The other main reason I'm doing this is to learn --> I've been in engineering, design and software my whole career - why not combine all the skills and apply them to some of my hotrod/race efforts. I'd really like to convert the FlatCad Bonneville engine over to dual turbo and EFI - we'd probably make 100 more horsepower (due to reduction of parasitic loss from the stripped roots blower).
If anybody has any questions about the above - feel free to ask . . . I'm deep into it! LOL
D
