Kit Carlson EMS in stock TIV?, How good will it work wit a stock engine Options

[Mueller]

howardchen327,

for about $100 or less, you can eliminate your points right now with a Pertronix or other brand point replacment kit.

[fiid]

I disagree..

Yes, any engine may "work ok" with carbs or FI, but it will not be optimized unless specifically built for either application!

A good case is my 912E. I built the engine for carbs only and ran it for 59K miles that way. When we installed the FI the tuning procedure took longer than normal and my idle is not at a premium due to lack of vacuum signal due to a cam ground on a 105 degree center keeping the plenum scavenged drastically. The engine runs okay, but could run and idle better with a combo made for FI.

Sure it will work, but it won't make as much power nor will it tune as easily. So, why do it half assed?

There is nothing that pisses me off more than generic things that are "universal"... One size fits all don't cut it around here.

EFIs respond to the same set of variables as carbs do, only they (usually) take into account far more variables than carbs do. Carbs respond mechanically to quite a narrow set of variables, and usually do so in a compromised way. So any set of variables that CAN be manipulated with carbs, CAN also be handled with FI. Usually with modern EFI systems, this is a lot easier because you don't have to (using the SU as an example) get different profiled needles to handle different power curves.

The clinching datapoint here is that an FI system CAN read an oxygen sensor and run closed loop (thus calibrating itself).

NOW: CAN and DO are different - poorly set up carbs are crap, and so is poorly set up FI. Correctly set up FI should be able to generate equal power to a well set up carb system, but will likely have a better emissions profile and better efficiency on the same engine.

You are right that cams with a poor vacuum profile can foil MAP (manifold pressure based FI systems. That is easy to fix with a megasquirt - you just run Alpha-N (throttle based) instead of map based. With other systems you may be able to go to MAF (mass air flow - which is basically how carbs work).

There are other ways to fuck-up both systems (lack of sufficient fuel delivery, etc etc), but at the end of the day you have much better odds of getting the ideal mixture out of FI than carbs since FI uses more input variables than carbs do, and can sometimes even tune themselves based on huge numbers of variables. You would need a carb the size of Babbages differencing engine to be able to do that with mechanical setup.

[fiid]

BTW just to be clear on my concession on one point - MAP (pressure) based FI is a hack. It is based on the ideal gas law:

pv = nRT

Which basically (applied) says you can calculate the volume of air going into the engine based on the pressure and tempurature (MAP and MAT) of what is in the manifold.

MAF based systems are actually a little better in that they measure the weight of air travelling past a "flapper" (L-jet does this) rather than doing the math, which can get tripped up by other variables.

Having said that MAP is easier to implement, and bypasses som reliability problems with MAF sensors.

[lapuwali]

MAF based systems are actually a little better in that they measure the weight of air travelling past a "flapper" (L-jet does this) rather than doing the math, which can get tripped up by other variables.

Which is also the way K-Jet works, just using an all mechanical system instead of an electronic system.

Not all MAF systems use the flapper. Nearly all (if not 100% of them) that use MAF (which is damn near 100% of current OEM systems), use the "hot-wire" MAF meter (MAF = mass air flow). MAP, throttle position, RPM, and air temp are all used in the attempt to guess how much air is flowing into the engine (thus, how much oxygen, which is really what you want to know). Measuring the airflow directly is far and away the most accurate method, which is why it's universally used in OEM systems today.

The hot-wire meter, rather than using a flapper, uses a thin wire or thin film that's designed to get hot. There's a temp sensor at one end and a current sensor at the other, and the system attempts to keep the temp of the wire/film constant. As the airflow mass increases (or the ambient air temp falls), more current is required to keep that temp the same. Thus, the current applied to the wire is directly proportional to the amount of air flowing through the meter. Relatively little airflow restriction, but there is still some susceptibility to airflow reversion confusing the meter if particularly wild cams are used.

I've not yet figured out why so many aftermarket systems tend to be MAP-based rather than MAF-based. Adaptability is my best guess. New MAF meters are expensive and relatively hard to come by. Used bits off recent cars, however, are becoming more plentiful. Depending entirely on MAF means it's harder to be able to smooth or ignore MAP under those conditions where MAP is unreliable (low-loads with wild cams), and one can use a TPS-based measurement "blended" with MAP at higher loads.

[Jake Raby]

So fiid,

I suppose that Dave just wasted the last 8 years of his life building a MAP based unit...

May as well stop testing right now, pull the system off my car and burn the bitch.

[Aaron Cox]

ouch <_<

[lapuwali]

I suppose that Dave just wasted the last 8 years of his life building a MAP based unit...

No, there is no absolute good v. bad in MAP v. MAF. For some uses, MAF is superior. MAP is better suited to being adapted to a wide variety of engines, and it a bit better suited to wilder cams. The Megasquirt stuff is all MAP based, as is SDS and nearly all of the other aftermarket units.

[fiid]

So fiid,

I suppose that Dave just wasted the last 8 years  of his life building a MAP based unit...

May as well stop testing right now, pull the system off my car and burn the bitch.

Not at all. MAP is a suitable approximation for most systems, and I have found it to work pretty damned well. It's not so hot on engines that

Similarly - carbs work for most systems.

Something doesn't have to be perfect to be better. Better is good. Next week there will be something better than todays better. Technology is just about continuously trying to better what is there today.

I have a lot of respect for the work both you and Dave have done - it's top notch stuff. (IMG:style_emoticons/default/beerchug.gif) Please don't take what I am sayin' as dispectin'.

[Jake Raby]

To be worth a damn, a system has to be simple! Too much crapola and bells and whistles sells things but that don't keep them on the road.

Dave has done an excellent job on his system, I can say that from first hand experience and 5,000 miles of proof.