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

[nditiz1]

I have only seen the crankfire setup that McMark was selling from Original Customs. With that said what is the adv to running the cam sensor?

If it was easier to install/cheaper big a significant amount/better signal/easier to setup I might entertain the idea. Are any of those advantages present? Also, I know Al Kosmal is currently working on a T4 - EFI setup.

[bbrock]

I have only seen the crankfire setup that McMark was selling from Original Customs. With that said what is the adv to running the cam sensor?

If it was easier to install/cheaper big a significant amount/better signal/easier to setup I might entertain the idea. Are any of those advantages present? Also, I know Al Kosmal is currently working on a T4 - EFI setup.

The advantage is that I like to over complicate things (IMG:style_emoticons/default/biggrin.gif) An objective is to get the best economy (especially in town) and lowest emissions I can. A cam sensor let's you go full sequential for spark and injection which in theory can give a little better driveability and economy at lower speeds, reduced emissions, and smoother idle. I know going sequential isn't going to gain me that much, but I like this kind of challenge.

The descriptions for Marios' old NLA cam sync sensor says it must be used with a crank sensor. I'm not sure if the same will be true for the new one which will have a trigger wheel instead of flying magnet. If it were possible to get by with just a cam sensor and no crank sensor, you wouldn't have to drop the engine to do the conversion. I guess that might simplify the install regardless of spark and injection mode.

[Frank S]

I have only seen the crankfire setup that McMark was selling from Original Customs. With that said what is the adv to running the cam sensor?

If it was easier to install/cheaper big a significant amount/better signal/easier to setup I might entertain the idea. Are any of those advantages present? Also, I know Al Kosmal is currently working on a T4 - EFI setup.

The advantage is that I like to over complicate things (IMG:style_emoticons/default/biggrin.gif) An objective is to get the best economy (especially in town) and lowest emissions I can. A cam sensor let's you go full sequential for spark and injection which in theory can give a little better driveability and economy at lower speeds, reduced emissions, and smoother idle. I know going sequential isn't going to gain me that much, but I like this kind of challenge.

The descriptions for Marios' old NLA cam sync sensor says it must be used with a crank sensor. I'm not sure if the same will be true for the new one which will have a trigger wheel instead of flying magnet. If it were possible to get by with just a cam sensor and no crank sensor, you wouldn't have to drop the engine to do the conversion. I guess that might simplify the install regardless of spark and injection mode.

Mario's cam sync is working togeher with the crank sync only. But you can run a missing tooth sensor in the dizzy for sequential ignition and fuel, so no need for the crank sensor. The dizzy sensors are also much easier to service if the sensor is failing...