EFI on our old engines--what to expect

[SwedCharger67]

My advice here would be to choose a cam profile compatible with aftermarket EFI if you are contemplating going with that over a carb. Most aftermarket EFI will require a certain vacuum level at idle for best performance with the systems operating parameters. Even the tuneable systems will have trouble with a cam that doesn't produce at least 12 inches at idle....

That's an interesting point.

There are different ways to control how much fuel is injected. I can well imagine that some systems measuring the intake manifold pressure will struggle a bit with a big cam and low vacuum, fooling the system to believe that the throttle seems to be open quite a bit.

Many high performance motorcycles use just the TPS and RPM as a reference to how much to inject (and adjust for air pressure, system voltage etc.). It works well, I have it myself in my Ducati 996SPS with dual injectors per cylinder.

I have to study those details in my own system, since I'm going to use a low vacuum cam, thanks for pointing it out.

 

[dpstark2]

Early Harley (Magnetti-Marelli) EFI had a lot of trouble due to low vacuum and small plenum volume. Even the current systems aren't great once you modify ANYTHING. On my bike, I use an auto-tune system that runs in Alpha-N, which means TPS and RPM only. The same vacuum issues can occur with reversion on a V-8 with big cams. The Alpha-N on my bike is fine, but it's by no means ideal. . MAF is great for production, but apparently hard to tune in DIY stuff- it's usually a trial and error situation that gives little benefit. I'll be avoiding it. I have a relatively mild Comp cam in my 440 that makes about 13-14" vacuum at idle, and the Megasquirt seems OK with it. However, if I had to do it again, I would opt for the same cam on a 112 LSA, or maybe a bit more cam on 114. I'd certainly like more vacuum for my brakes, anyway. And I don't know if the EFI packages have options for calibrating what vacuum means relative to load, which you can do on the Megasquirt...

 

[SwedCharger67]

Early Harley (Magnetti-Marelli) .... I have a relatively mild Comp cam in my 440 that makes about 13-14" vacuum at idle, and the Megasquirt seems OK with it. However, if I had to do it again, I would opt for the same cam on a 112 LSA, or maybe a bit more cam on 114. I'd certainly like more vacuum for my brakes, anyway. And I don't know if the EFI packages have options for calibrating what vacuum means relative to load, which you can do on the Megasquirt...

I'm going to try to reuse the cam I had in my 383...where it was a pig with 8-9 vacuum and lots of exhaust pumped into the intake, intake valve closes @ 63 ABDC and 110 LSA...it's going to be interesting to see what influence bigger cubes, significantly higher compression, and computer controlled injection/ignition will have on the behaviour of the engine.

 

[scotts74birds]

Swedcharger, a cam for an F.I. motor has different needs than for a carb. You'll need a cam ground for FI.

 

[SwedCharger67]

Swedcharger, a cam for an F.I. motor has different needs than for a carb. You'll need a cam ground for FI.

I don't understand why that would be the case?