Im going to really show my ignorance here.
I'm curious, because Im thinking about this 24/7 these days.
Compression ratio
In choosing a CR for an EFI engine. How does the EFI relate? Do I have fiddle room for more compression with EFI? Why?
Cam choice.
Do I have more room for overlap? Do I choose what I would for a carb? Can I take advantage of EFI and go bigger and still get street able (qualified) manners? Do the basic adv/retard rules apply?
Porting
What does EFI like? Same as a carb?
Feel free to add what I should also be thinking about.
Marc,
First camshafts - You can do anything if the system is adjustable enough, more if you can make it NOT adjustable....more on that in a second.
The basic premise is, the engine doesn't know what is feeding it and for the most part, with the cam, power is power. However, remember, the engine is using the O2 sensor, along with the other sensors to adjust fuel. An O2 sensor doesn't know if it is rich from unburned fuel from a bad mixture or fuel being pulled out with a big overlap cam, so generally, on the street it is better to try to run less overlap. Cam choices stay the same, but you spread the centers to minimize overlap a bit to keep idle clean-ish. That being said, as a reference, my 10.7:1 489 runs a 286/294 cam (@.020) on 110 centers on 106, so you don't have to go crazy, I just wouldn't run a huge cam on tight centers.
I mentioned making it non-adjustable...thats the good thing about electronics. Let's say the idle is dumping fuel into the exhaust during overlap. If you decide you want to go "open loop" at idle and ignore the O2 sensor, you can. It uses whatever sensors you want and still does it's thing, but it doesn't adjust the fuel tables as much and doesn't use the O2 sensor to decide. So, very common technique is with a big cam, open loop at idle and make it sort of an electronic carb, then when the throttle cracks and vacuum comes up, it goes closed loop again.
Next thing is injector timing, I adjust my injector timing based on actual cam events. There are a couple schools of thought, and it really doesn't matter at high RPM as the injectors sort of just create a fog as they fire at 90+% duty cycle, but at low RPM it can be dramatic. You can spray a closed valve and keep it cool and continue as it opens, or you can time the injector to follow the valve movement. I do the latter. I really cleaned up idle that way and it just seems happier.
Next as far as far as compression and timing, think of electronic timing control as the thing we always wished we had. Can you run more compression? Sort of, usually, in the end you can go higher because you likely can control your timing curve is ways never before able. Load, temp, outside air temp, a/f mixture, throttle position, speed, all kinds of things. So, likely, you can run more compression, but the extra 1/2 point or so IMHO could be put into airflow and/or programming experimentation. However, total timing requirements are still based on what the combustion chamber is seeing, so the thought behind total timing isn't significantly different.
In terms of the timing curve to get there though, it's awesome. If the cam is a little big, you can crank at 0, 6, or 10 BTDC, whatever the starter can handle and immediately pop to 20 when it fires, you can pull timing out with boost, even with atmospheric pressure or coolant temp or air temp. My Mustang using 10 BTDC crank and +10 when it fires for 20 at idle. That can add or lower for load, temp, etc all the things I mentioned before, so drivability, especially when mixed with the injector timing can be dramatically different than a carb. In the end, basic rules still apply, but your curve becomes multi-dimensional adjustable based on your system and what you want it to do.
And...punch line...if you decide at times like WOT you don't want that, you go open loop to keep the computer from adjusting and the curve can be exactly like a standard distributor, but with no friction, rust or sticky weights, and when you come off WOT, it goes right back to adjusting for everything.
As far as porting, less of an EFI vs carb thing IMHO, but, I think i could tune some torque into a port that is a little too big using ignition timing and cam timing. As an example, who would think a ported Victor on a 489 with a 6400 shift point would chug around at 1400 rpm in 5th? (2.63 final drive when in OD)
Just remember, it takes two things:
1 - The ability to access and control the computer (system and it's interface)
2 - the time and willingness to learn to tune (your skill)
The first is generally a function of money spent, the second is generally trial and error and time.
I am not sure the end use of this car, but my opinion is for a street car.
- Use the most adjustable port injection you can afford and one you know has internet or a buddies with experience
- Lean more toward making power with good airflow and as much as you can without getting silly (heads, intake, exhaust) so you can run a little less cam
- Think cam timing as valve events and then build a cam that you want to match needs (likely not off the shelf)
- Practice, experiment, save your files, hit "undo" when you don't like it, and keep tuning until you love it
