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]

An additional 800 miles of seat time in my car hasn't lessened my desire to ditch the carbs and dizzy. I continue researching how I want to approach this and have more questions.

- Do I need a crank sensor? To go full sequential I need a cam position sensor for sure. I've read that cam sensors are not as accurate as crank sensors but that is because of chain or timing belt slack. Type 4 cams are gear driven. Is there enough gear lash in distributor drive mechanism to affect position accuracy? I have no issue with adding a crank sensor, but it is the only part that will require dropping the engine so the question of whether it is necessary if I have a cam sensor has to be asked.

- I'd love to hear thoughts on whether modern injectors would be worth the cost if I don't upgrade the fuel rails. Still not sure what I want to do, but curious why modern fuel rails would make a difference.

- Anyone know when Mario plans to open online ordering on The Dub Shop site? It's been closed since June so he can catch up on orders and restock parts. Sure, I could reach out directly but seems counterproductive to pester a guy who is already swamped. I know some of you are in touch with him so wondered if you've heard anything.

That's it for now. There will be more.

[JamesM]

- Do I need a crank sensor?

If you want to run any ignition control it is highly recommended. If you want to run full sequential i believe it is mandatory.

I highly recommend Mario's crank trigger setup for multiple reasons, however as you mentioned it does pretty much require you drop the engine in a 914 to install and/or service it. Well, maybe not required but you are going to want to.

More recently I have came across this crank sensor setup that looks like it would be easily serviceable with the motor in the car, but i havent personally run it so i cant speak at all to how well it works. Also its expensive and looks like it probably uses a VR sensor (one of the reasons i prefer Mario's setup is it uses a Hall sensor that gives a nice clear square wave output)

https://www.clewett.com/index.php?main_page...;products_id=31

- I'd love to hear thoughts on whether modern injectors would be worth the cost if I don't upgrade the fuel rails. Still not sure what I want to do, but curious why modern fuel rails would make a difference.

I see no need to swap out the fuel rails.

These are my preferred injectors when running stock intake runners

https://www.fiveomotorsport.com/a280-a380-h...-fuel-injector/

Lots of advantages in my mind:
They are pretty much plug and play to the stock intake runners and fuel rails.
They have locking EV1 connectors
They are high impedance so no need to use inline resistors or run PWM control
They run at higher pressures for better atomization
They come documented with flow specs and voltage correction datasheet
They are brand NEW

Only potential downside is that you will most likely want to run them with a newer style fuel pressure regulator to run at higher pressures, but there are a few options there that easily install in place of the stock regulator.

I think the deciding factor though should really involve asking yourself the question, do i trust 50 year old injectors and if so, for how long?

A few years ago I was driving behind @StratPlayer out of Salt Lake on the way to RRC and wound up getting my car covered in oil when a sticky stock injector holed a piston in his brand new 2056. Given all the other modernizations you are putting in, i see no reason to stick with old injectors. Not to mention, the stock 2.0 injectors are absolutely HUGE for a 2.0L motor resulting in very small injector pulse widths at idle which produces less accurate fueling. In fact, back in the VERY early days (pre MS2) I had to run a special "hi-res" code variant to gain the resolution needed for proper idle control with the stock injectors. If you do want to run d-jet injectors the ones off a 1.7 are much more appropriately sized for the application.