Currently have a 2.2E/S with Webers. It runs well and makes good power, having been tuned on the dyno and further dialed in since then, but I have discovered I'm just not a carburetor person. Fuel economy isn't good enough for the size of engine/car, and the emissions bother me—both in terms of the smells in my garage and while driving the car. And yes, we've been totally spoiled by low emissions cars.

What I'm curious about, for anyone who has lived with carbs and MFI: Is MFI noticeably cleaner and/or more efficient than carbs?

Or is EFI the way to go? I'm in no hurry on this, but curious for the experiences of others. Yes, Motronic, but I actually like the 2.2 engine.

Thanks!

efi is the old school Boss..not so correct for the ecology..

call Clewett.. EFI


3.2

A properly restored and tuned MFI setup will be close in cost to a running 3.2 engine. I don’t think it’s what you really want. A properly tuned modern day efi system would do it but again, by the time your done -$$$.

Cross country I got a little better than 25 mpg with the 3.2 and stock efi. Same as my big Ford Escape. One cause of the lower mileage is the increase in speed limit across the different states. At 85 mph you are way past the inflection of the drag curve. But crossing Nebraska, you feel silly not keeping up with the Jeeps.

I can tell you one thing, MFI on an E or S when tuned well will pull super strong in every gear. On my 73 S it ran great when the MFI was synced well but the tune would fall off in not that long and then it just pulled well but not as good as just right out of tune.

CIS ran well and kept its tune for a very long time. Always started right up and ran the same (good) all the time. Monotonic always ran good for me in my Carrera.

CIS and Monotonic always worked great.

I have PMOs in 46 for my 6 and we have to work out the tuning after we get the break in of the Engen. I think the PMO 46 where like $6,000. If you are not going to run your car all the time, carbs IMHO need to be run and not just sit for a very long time or you have to dich with them.

The thing is that the EFI when dialed in run all the time.

As far as the gas mileage it never meant anything to me.

Bob B

EFI is the only way to go if you dont mind spending the money.

MFI is good for power, but not fuel economy or low emissions. Modern EFI will mop up the floor with carbs and MFI when it comes to those 2 measures.

MFI will not get better MPG or Emissions than would Webbers, but
maybe slightly better throttle response, and maybe less fuel smell.

If your 2.2 was not already a MFI engine, the cost to convert to MFI would be mega $$$$ [ouch!]

Appreciate the replies so far. Have driven MFI—I almost wish I hadn't!—but have not lived with it.

Agree that EFI mops then floor with MFI in most regards, with maybe the only exceptions being 1) fuel pressure > throttle response and 2) noise of that injection pump, particularly right behind my head. Probably the best-sounding Porsche street car I have driven this side of a CGT. Certainly one of them.

As to price: No six induction is cheap anymore. Not PMO, not MFI, and not EFI. But MFI is indeed nutty. Last I asked, it seemed like $12k~ to collect, restore, and install. And that was years ago. What's on there now is probably the cheapest option, which is old Webers—but even these aren't cheap anymore and I suppose they can be sold to offset some of the move to EFI. Already have Clewett's crankfire trigger with Electomotive "coil" setup, but the rest of his setup isn't going to come cheap. Do like that it looks like it would work under a factory airbox while looking like carbs. Hmm…

Interesting...I think most of 6 drivers don't really worry about efficiency and emissions, especially on 30 plus year engines:)

A small displacement engine on carbs tuned properly can be quite fuel efficient and not smell of fuel/etc. of course never as close as EFI and you have to adapt your driving style.

MFI is kinda the precursor to fuel injection and very rudimentary. Great power band but you drive it almost on and off throttle. Due to fuel injectors at 220psi you get better atomoization and fuel burn for efficiency and of course smell over Carbs but still way short of EFI.

I've done Webers- Simple, quick technology, pain to initially tune and LOTS of compromises.

I've done many MFI- T/E/S, even a real 2.7RS, and my own built 3.0L. Complicated to understand at first and to tune properly. But man that throttle response and sound in addicting.

That being said, unless you have an affinity or like to play with these technologies EFI is the way to go for the best of both worlds. Check out X-Faktory (Al Kosmol on Pelican) he's created some really cool EFI independent throttle body kits for small displacement Porsche (2.0L and up). I haven't seen any with small displacement try this yet but lots are raving about EFI on their old motors.

For me, regardless of the induction, I'm as often as safely possible into 6K/rpm so emissions and efficiency are until the next fill up

Cheers,

Marlon

Same for my 3.6, i get 25mpg on my road trips. That's fully loaded with gear and two people in the cabin.

My 2.2E targa MFI got 17 mpg highway back in 1982. Carb engines got about the same. No doubt MFI is cool, but crazy expensive.

https://rasantproducts.com

I have been collecting parts for a few years now to do an EFI system using MFI throttle bodies and the MFI injector ports in my 2.4 heads.

I have a set of MFI throttle bodies and stacks and they can be had for cheaper than most of the offerings on the market for ITB’s and you can bolt right up including linkages and retain the classic Porsche look and airbox/filter options.

From there I plan to use Rasant stuff. This has been done successfully by many. Al Kosmal has done it at least once, Jamie Novak several times and others over on Pelican. Jamie sells adapters to fit modern electric injectors in MFI injectors ports.

http://classicautowerks.com/mfi-injector-adapters

Overall cost should be around $6000.00. Selling Weber’s will recoup 1/2 of that.

Will be cool if I ever get around to actually finishing it instead of talking about it. Current carbs are tuned ok and Too many other projects.

My 914 with 97 Nissan 3.0L will do 29 mpg @ 90 mph between Reno & Vegas, stock ECU.

My Nissan 3.5L swap will get full aftermarket FI, MS3Pro EVO. Allows a few different tunes (street, track, highway). I can run a bit lean at 90 mph for mileage or a bit rich for cooling on the track. Also the software has 'autotune' to make initial setup & tuning easier.

You can use whatever intake hardware that fits, as the controls such as TPS MAF/MAP WBO2 TEMP INJECTORS all can be GM or Subaru or in my case stock Nissan.

I'll be all in for about $1500, which is likely cheaper than the dinosaur Porsche factory FI.

Pete,

You’ve seen my car at the EASY get togethers and have probably heard me rave about how much I love my EFI conversion with PMO ITB’s and COP’S on my 3.2 conversion in my 73 long hood. Next time we meet up I will let you take it for drive to see what you think.

For me, in addition to the significant performance boost from the conversion, which I wasn’t expecting, the other main reason I did it was to give the engine bay that old school vibe since the PMO’s look just like carbs plus I love how uncluttered the engine looks. See for yourself.

Click to view attachment Click to view attachment

What is your MPG with your 2.2? mine with good tune is really crap ?
Sorry no intent to hijack from the OP.
.

Yep, I'm in the teens with carbs—and they're dialed in. Seems ridiculous for a car that weighs 2100~ pounds. While fuel economy is near the bottom of my list of "must haves" in my 914 (and thus I am not in any rush), K5 Blazer fuel efficiency sort of grates on me.

And here I thought I was making a funny about the mpg, but… https://ck5.com/forums/threads/good-fuel-ec...y-on-k5.144786/



Your 73 is gorgeous, Steve, and I'd love to take you up on that.

There are a lot of relatively new and interesting EFI options right now, from Clewett (already have their crankfire ignition trigger with Electromotive) to Rasant to several others. Some of the newer ITB hardware is really beautiful, too, but I have to say my leanings are toward the PMO hardware you have due to compatibility with the factory airbox and likelihood of long-term support. The promise of long-term support is where carbs, MFI, CIS, and Motronic shine bright—but only two of those were offered with a 2.2.




No apology needed! This is very much the kind of discussion and data points I hoped for.

My carbed 2.4 in S trim runs good, pulls smoothly from idle to 7000 rpm and drinks gas like crazy. Never really actually checked mpg but estimate low teens.

A throttle body is nothing more than that - a body that holds a throttle plate and facilitates linkage. The MFI ones provide an idle air adjustment circuit and I modded mine so that each has a vacuum port. Nothing more or less than what the PMO’s provide for more $. And you cant get more “compatible” or correct looking than using what the factory used for period fuel injection.

Steve, bad ass street sleeper hot rod BTW! Righteous

A problem with carbs and MFI is that a lot of unatomized fuel ends up in the crankcase over the miles. 3000 mile oil changes become a requirement.
Also, the cheapest decent throttle bodies are motorcycle... 1999 to 2000 GSX-R 750 or 1000 depending on the size you want. Triumph ITBs require a manifold. I did this on a 3.2 back in 2012 with megasquirt (which I'll never use again).

I plan to do 1 of 2 things on my car.. Use my webers as Throttle body's and use the MFI ports in the heads for injector ports or use my restored 3.2 intake and make adapters for the heads and likly use the Bitz racing setup with Megasquirt.. Pretty cheap EFI at that point.

You've touched on a couple of the things that put carbs or MFI ahead of most options for a small flat six—development and support, both in the short term and the long term. Right now, of the aftermarket stuff, what is likely to still be around with parts and support in the long run? There are some very attractive custom ITB and EFI products for old Porsches out there, but it seems we have several developers vying for a slice of a fairly small pie and I wonder what living with the products in the long arc will be like. Thinking of race cars that require the upkeep of a 386 or 486 laptop to run in 2020. You hope for the best, but if it stops running 12-17 years from now?

Suzuki GSX-R750 ITBs are actually pretty interesting, as I suspect those will be supported for a very long time with new parts and still possible to look for used parts if you're in a pinch. Manifolds and other machined parts to adapt them are, so long as they're well made, unlikely to be problematic (and can be replicated down the road if need be). So a Suzuki setup might match or even beat PMOs in that regard.

Which gets back to the brain/software/etc. All of the EFI setups are going to offer superior performance over carbs (and MFI), I am just thinking about those "un-sexy" factors like reliability, fixability, support, etc. in the long term. Don't have a position on it yet, but very much appreciate the conversation going on here.

https://www.x-faktory.com/store/p3/EFI_Kit_RHD-EFI-001_.html

and this one, I bought a set up for under 1k
https://www.ebay.com/itm/Triumph-ITB-Setup-...qAAAOSwQDhbXN0H

As much as DIY people online like to say, Megasquirt is not really a 20+ year kind of thing. It’s really just not hardened, and IMO many of the control strategies are rather lacking, as is some of the hardware signal processing. I think most people who are really pro MS haven’t use high end stuff (think Motec, Life, etc) which is constructed with much stouter hardware and will last for decades. I’d be shocked to hear about something like a Life F88 which has failed even over 20 years. The computer insolence part is certainly a real issue. MS is nice here because the under community forced it to be up to date. That said, in general the guys carrying around a 486 have hardware which is now 30+ years old. It’s surprising they’d really ever have to touch it after so many years of tuning. Chances are if you do with an established ECU company, you’ll have hardware support for a long time.

I’m not a high AEM fan, even with the Infinity (probably pick just about everyone else in the high end market over them), but the Rasant package looks really clean.

I paid $300 for 8 low mileage Suzuki ITBs, with throttle cables and sensors. Then made adapters to attach them directly to the heads. They also needed spaced out more, so I also made spacers and lengthened the throttle mechanisms and fuel rails. Those ITBs are Keihin, so a ton of injector options. Honda S2000 injectors would work great for a 3 liter engine. The throttle cables are perfect length for both to attach to the lever bell crank on top of the engine.
Concur with lack of hardening on megasquirt.

http://forums.pelicanparts.com/search.php?do=process

I would give Al a call about his x-faktory kit and ask him what it would cost to get it on your car and tuned. It's not cheap but seems to be a well proven solution and you can sell your Webers for 2-3K to make back some of the cash.

Als a great guy , would make a great article too.
Is was a member ..he sold his 914

that you would be better to sell the webers and use TB's from a Triumph bike. If you still want to use the carb bodies I'd get a pair of Zeinths.

With ITB's and big carb cams you will have to run MS in AlphaN (SDS "TPS only") because you won't have good enough vacuum to run the MAP sensor. AlphaN works but tends to make the throttle an on/off switch which is a PITA at lower RPM's such as stop and go traffic. It also disables altitude AFR correction because it works off the MAP sensor.

Big cams with large duration is where MFI and carbs shine, this is especially true for hot street engine that sees a fair bit of time at lower RPM. My bug and 914 I run real hot cams, the /4 has SDS EFI with a 163/86B cam and my six 120/104 web cams, The /4 cam with 46mm ITB's has to run in TPS only. The carbs have a much smoother on/off transition compared to the FI.

This is for a /4 but you can see how much work it took me to adapt Suzuki GSX-R TB's to carb manifolds in my motorcycle TB's thread.

I've got the same cams as Mark in my Carrera 3.0 engine and decided to run 46 PMO. I've spent enough time on this car already and the PMOs, all new and properly jetted, will provide me a good induction solution at minimal effort. And why spend money and time on old 40IDA3C that will need rebuilt and rejetted when for a bit more money you can get the brand new PMO setup?

Ben already has the weber carbs, as long as the throttle shafts are good and he doesn't care about the MPG they can be made to run just as smooth as FI.
My webers for a twin plug 3.0 have 34mm venturis, 155 main jets, F3 emulsion tubes, 180 air correction, 55 idle, tuned with a WB meter and runs a solid 12.7 AFR throughout the RPMs. Paul Abbott confirmed this was about perfect AFR. I'd suggest the same set-up but your main jets may be a bit smaller.

But this is where the bulk of the fuel mileage penalty happens, the FI can lean out the AFR at cruise, where as the carb is locked into the jet sizes.

Here's the going in PMO 46 setup:
Vents 38
Mains 155
Air Correction 185
Idle 55
Idle airs 130
E tubes F16

We're not that far off. With my larger vents, looks like I may be a little leaner at higher rpm. Engine has the larger 3.0 intake ports, running 9.5 compression single plug. I timed the cams per spec, but given the cam sprocket pin placement, they are very slightly retarded.

I'd be real happy with your AFRs!

I can see where PMO carbs are attractive to someone building an engine or a car for all the reasons listed, but they don't make sense for me.

I rolled the dice and bought a set of used Webers from Pelican Parts years ago for less than what cores cost now. Had them gone through by someone very familiar with Webers before they went on the car for seals, etc. Only suspect thing was a bit of wear on one shaft...but it wasn't enough to be worth dealing with. After the better part of a day on a chassis dyno and some subsequent fiddling, they're good. Car starts first try if it's been driven within the last few days, and will start in the first couple of tries if it's been sitting—and this is without the luxury of a 914-6 choke. Engine pulls nicely from idle to 6000+, and is pretty hard to catch out. Jump on the gas too quickly and you can sometimes get ahead of the carbs, but that's about the only niggle. I'm happy in all those regards.

New PMOs would need to be dialed in, and present most of the same problems. This thread has me moving the goalposts away from MFI (cost, emissions, etc) and towards EFI, possibly on PMO TBs to keep the factory 914-6 airbox—which I really like—and because I suspect parts & support will be available for a long time to come.

That leaves which engine management system. A lot of good inputs here to consider.

I have essentially the same setup as Steve in my 914 using the Rasant harness and the AEM infinity EMS.
As far as maximizing power and tune ability this is the only way to go.
Also, by far the cheapest option to go to twin plugs.

Definitely not cheap though.

MS3pro is a completely different system than the MS 'kits'. It was designed and built to be higher end and competes with systems more than it's $1100 price tag.

Thanks for posting this—looks great, and your and Steve's positive experiences go a long way with me. Sounds like, for me anyway, EFI > carbs or MFI.

I tend to think of EFI as a "$10-15k" hurdle, but selling my running/setup Webers and Clewett/Electromotive crankfire ignition system may offset or even cover the 40mm PMO EFI setup—meaning the hurdle is more like $4850-$7200~ for AEM or Motec plus the time to do the swap and set it up. Don't need twin plugs or more power, but better drivability from a cleaner, crisper, more efficient engine certainly has its appeal.

Again, thanks for the input, everyone. This is turning out to be a very informative thread.