Going to Megasquirt, More questions Options

[bbrock]

After about 1,700 miles of driving my freshly restored car with rebuilt engine, I’ve decided I’ve had my fun with Weber carbs and distributor-based ignition and am ready to step up to modern EFI and coil on plug ignition. Even with the jetting that came out of the box leaving the carbs running rich, the performance has been fantastic. What is not fantastic is the garage stinking of gasoline, no compensation for altitude, and being generally too fiddly to set up for my taste. My trials with the ignition are documented in another thread. Yes, I know a 1-2-3 would solve those problems but for the money, I’d rather invest in modern COP ignition as part of an EFI upgrade.

My goal is a smooth, efficient, and reliable street machine that I can drive from sea level to 11,000 ft. without starving or choking on fuel. Efficiency is at least as important as performance. As long as I can get at least the stockish 100 hp, I’ll be happy and beyond that, I’d like to wring as many mpg out as possible.

The engine is a mostly stock euro-spec 2L engine. The only mod is a fairly mild Elgin 6048 camshaft with 256 duration for the carbs. A source of pride of this build is this custom 911/914-6 inspired air cleaner I made which I think looks cool and really silences the carbs.



Now for the questions:

• Single throttle body or ITB? I think I’ve made a decision but still interested in thoughts. I was thinking about welding injector bungs onto the carb manifolds and using my carbs as throttle bodies. The main appeal is that I would keep my cool air cleaner to make the other kids jealous. However, it seems the stock throttle body would greatly simplify the conversion. Also, even though the custom intake is designed to allow access for servicing and easy air filter replacement, it does crowd an already crowded engine bay and makes working in there just that much more of a challenge. My stock TB needs some TLC and might have to be sent for professional refurbishing. I think I could sell my carb setup to cover that cost but not sure. The upshot is that I’ve all but decided to go back to the stock TB, but curious what others think.

• N Alpha, Speed Density, or MAF? I’ve been reading up on this and think I understand pros and cons, but still a little confused about sensors needed. With my efficiency goal, I think MAF is the way to go. It looks to me that cutting off the tube connecting the stock air cleaner to the TB and replacing it with a MAF could be a really slick way to add MAF in stealth fashion. Has anyone done this? If not, how does one find the right MAF to use? Other than dimensions, what else needs to be considered?

Another question is about MAP + MAF vs MAF only. I’m a little confused about advantages or when a MAP sensor is needed if you have a MAF.

• Barometric correction – this is an important feature for my location, but the hardware needed to implement it is a little confusing. It seems like if you are running a MAP, then barometric correction is obtained by adding a second pressure sensor (another MAP?) to read reference atmospheric pressure to make corrections to the fuel mixture. How does it work with MAF? Do you only need one pressure sensor to read atmosphere? Or do you still need to reference it against manifold pressure? I assume a lot of this is done in the software but I haven’t looked to far into the tuning part yet. I’m more trying to figure out a shopping list for parts at this point.

• Anyone running a CAM sync and sequential spark and injection? Again with the efficiency goal, this is appealing. Looks like Mario is working on a new version which isn’t available yet, are there alternatives available? It seems people say you still need a crank position sensor even with a cam sensor in the mix. It isn’t entirely clear why though. Lastly, and this is mostly just curiosity, but is it correct to think that the lifespan (in miles) of spark plugs are cut in half with wasted spark?

I have many more questions but this is already too long so will save them for later.
TIA

[bbrock]

Good to know about the MAP sensors. Looks like most megasquirt oriented sites only sell the 3 bar version so will look at where you sourced yours.

I've made a couple decisions:

- I'm going to follow @JamesM 's idea and use the stock throttle body setup but build the harness to be able to work with ITB if I don't like the throttle response with the stock setup. Buying ITBs for this project doesn't make sense because even the cheaper ones look like will cost more than I could get for my carbs. Doesn't pencil out given my carbs would make fine throttle bodies. However, the stock setup will not only be easier, but I could then sell my entire carb setup with air cleaner to recoup a nice chunk of the EFI setup. I'm pretty sure the stock throttle body will be fine with my stock 1971cc build.

- I am going ahead with my plan to add a CAM sync and run sequential spark and injection. There are a couple reasons. One is that once this is running well, I'd like to try iridium plugs which should last longer than I'll have the car - thus eliminating another maintenance item. They are fairly spendy though and doubling their life by sparking only on compression stroke would pay for the CAM sensor. Second, reading the articles linked in Greg's blog about sequential injection convinced me it is the right way to go for my project. Remember that efficiency and emissions are AT LEAST as important to me as performance. I know that's kind of a foreign concept on this forum (IMG:style_emoticons/default/smile.gif) Getting better fuel economy and drive ability around town will be worth the expense and slightly added complexity to me. I want to bring this system into the 21st century, not just the late 20th. Looking back at the old mileage records for this car in stock (although well-worn) condition, I was getting great highway mileage but pretty poor city mileage. It will be interesting to see what I get with this upgrade. Unfortunately, it looks like that means going to Megasquirt 3 which adds another $200, although I saw there is a daughter board for Microsquirt I need to learn more about.