Benefits of EFI over CIS on an otherwise stock engine?

[GGR]

Hi all,

this is my first post here and my Project is a Mercedes one. So I apologize in advance if I'm asking questions that have already been answered several times (I did a search though) and for them not being directly Porsche related. But here is where CIS to EFI conversions seem to be most popular.

My engine is out of a euro '78 Mercedes 500 SLC. These are still the early systems with no O2 sensors and no electronics, and the ignition is a hall effect and advance can still be tuned by turning the dizzy.

The car has stayed parked for three years, then someone started the engine and had it run well before parting the car. Engine has stayed two more years in a barn. Though it has only 88.000 original miles, over 30 years of age and these last years of neglect mean I will have to go through the CIS system before starting the engine. I don't know these systems, and I don't know what to expect.

So I have thought of converting it to EFI. I have already converted a 450 D-jet to Megasquirt fuel & spark so I'm conversant with what is involved. The 450 D-jet manifold is a nearly bolt on on the 500 and using all the D-jet plumbing and injectors makes it an easy conversion especially that I have all I need already. But there is a bit o work involved and I will still have to buy and MS brain and Relay Board.

So, here is my question: Is it worth it on an otherwise stock engine? What are the gains in terms of power, torque, driveability and MPG over a well sorted early euro K-jetronic system? I hear these CIS are quite bulletproof, very simple and very reliable. So is the conversion worth it in my case? I like EFI, but if gains do not justify the additional work and expense, I may well stay with CIS..

Thanks in advance for sharing your experience, especially on gains with EFI over CIS on a stock engine.

[Bob Kontak]

This may give you something to chew on.

Another ITB Megasquirt and EDIS setup experience

Try the advanced search function also.

[sc_rufctr]

The biggest improvement with a stock engine CIS to EFI is better fuel economy.
And that's becoming more important everyday.

You'll also get some more power. Not a whole lot but you'd feel it driving the car.

BTW Welcome. Do you own a Porsche?

[GGR]

Thanks!

No, I do not own a Porsche (yet!) but I like the 911 a lot. I've been considering buying a Carrera G50 at one time and have it look like a 2.7 RS. I think they sell body kits for that. May be one day.

[brads911sc]

the real advantage to EFI is not fuel economy. i get about the same on mine as as i did with CIS. economy is marginal and overstated when you drive it like you stole it. maybe if you drive like an old lady you will notice improved fuel economy. the real advantage is that you can tune across all RPM and MAP values so you can avoid lean (or rich) conditions. you can also tune factoring in temps, throttle position, ethanol content, etc.. with cis, if you you are good at cruise you will many times be lean at WOT. people compensate then they run rich at cruise.. You can also control spark if you desire and match advance/timing characteristics with the fuel mapping. there are lots of things to consider. not sure what your ignition looks like... but you want 35 degrees all in at 3k rpm. if you are not in until 5500 or 6k rpm, u likely wont notice a big seat of the pants difference.

[quaz]

I would have to say EFI is the ultimate in control over the engine and is the only improvement in peak power over carbs. It also offers ignition control, fuel economy tuning and better adaptability to temperature conditions. That being said, unless you plan to track the car, change engines or are having major problems with the CIS I would leave it. The process to go to EFI is not easy.

My 71 911 had Zenith carbs that badly needed to be rebuilt. Parts are difficult to get for them and setup and tuning can be a PITA. For me the cost of EFI was equal or a little less than the cost of Webers/PMOs. Also in the not so distant future I am going to change engines so I wanted to not have to change my fuel management setup again. I can just swap engine and retune.

I have a 78 VW Scirocco with a 16v swap in it right now that runs for crap on the original injection. Between a ported head, header and the engine being in a different car I can't get it to idle, start consistently and drive normally. It is getting EFI this summer. :-)

[brads911sc]

The most difficult part is the tuning. Ideally you want to tune with the EGO correct turned off, then control the last 5% with EGO correction. Also difficult is getting cold start, Accel enrichments, etc all tuned. I think the easy part is "operating temp driving". Most of the base maps guys will give you be within 20% on this...
I had a hesitation/stumble at 3000-4000 rpm at cruise. Sounds easy but it didnt make sense because the VE and AFR tables where smooth. There was no logical explanation based on my system settings... well it turns out that it was caused by a voltage spike just before the event (stumble). which is likely caused by a ground issue.
I have dialed down the injector voltage to 1/10 the starting value and it went away (.02 vs 0.2)... but I need to find some bad ground somewhere on my car. fun. and likely its not at all related to the fuel system.
This is the kind of nuance that guys dont consider when putting on some hardware.
you need to be very computer literate, understand electronics and fuel if you want to DIY.
You can spend double the hardware on tuning if you farm it out to someone else and they are charging you $100 an hour.
Choose your ECU based on who will tune it.
Just my .02.

[wwest]

You undoubtdly are already aware of this but you will need a (heated..?) oxygen sensor and a MAF/IAT module. Oxygen sensor to control idle and cruise A/F mixture ~14.7:1, MAF/IAT sensing, ~12:1, otherwise.

If your CIS is like our Porsches, '78, etc, you can remove the intake air flow sensing "flap" that controls the level of fuel injected and replace it with a simple "linear" (PWM dutycycle positional control) 12 volt electric solenoid controlled by the new ECU.

"EFI" using the CIS fuel injection system.

Gains: Engine life, emissions, FE, WOT power, did I mention engine life..?