We (and several others) are in the process of converting our 914/4's to /6 cylinders and I suspect many more will follow. Some of the items are straight forward, exhaust, oil system (with Ben's help), mount, but fuel? Yes, it's a process but reasonably doable, assuming the $$$$.
What are most guys doing for fuel systems? My gut is telling me twin Webers, but the setup is not inexpensive. To throw a wrench into this wringer, I have two CIS systems laying around condition unknown

If the cis systems are in good shape, go for it. If they are just a pile of parts in a box, carbs are probably the way to go.

Rebuilding a wur, fd & injectors cost about a grand.

I'm a glutton for punishment.

Planning on EFI with ITB's. Would like to do Clewitt. Cost of the EFI alone will be what I paid for the car x2.

Occasionally I get tempted to do Weber's when I see them pop up on the classifieds but usually they are already worn out or at least unknown cores that may or may not have casting issues. New PMO is really appealing but nearly the cost of EFI.

I really want EFI - Fuel injection is just superior but I also love the look of Carbs and/or ITB's. Plus they just sound right.

I still need a lot of time to cash flow the rest of my engine build and conversion parts so I'm sure I'll switch back and forth at least a dozen more times before I really need to part with cash.

Ditto, I am switching back and forth daily. Webers are somewhat simple so long as they are not worn out and 50 years old stuff is often worn out. Look in the mirror recently? CIS should be simple, efficient, etc, but finding a cracker jack to assist has not worked too good for me

My six is running the stock 3.2 FI system. But I am looking into the pros and cons of this set up. Patrick Motor Sports is installing these on some of there conversations now.



AT Power has developed a unique range of Direct to Head "Drive By Wire" (DBW) Electronic Fuel Injection (EFI) Individual Throttle Body systems for the Porsche 911, 964 and 993, Air-Cooled Classics.
Each bank of Throttle Bodies are directly driven by AT Powers DBW Actuators and Throttle positional feedback to the ECU is provided by individual Hall Effect Throttle Position Sensors. The air-cooled Porsche models suits our beautifully manufactured “Shaft-Less” Throttle technology perfectly.

what size motor ,, what cams ..apples/oranges

2.7 stock motor

EFI w/ ITB and DIS Electronic fuel injection with individual throttle bodies and a distributorless ignition system is the ultimate in tunability (if you're so inclined). But they can also be a deep $$$ pit if you don't do the install and tuning yourself. CIS and carbs would be a tie in my mind for simplicity. But personal order of preference would be ITB FI, carbs then CIS (pick your version of ITB FI).

I'm running mechanical fuel injection (MFI) and programmable DIS ignition on the warmed up 2.4 (thanks @sixnotfour ) in my car. MFI is tough to tune but the MegaJolt ignition system made it easy to dial in the advance curve I wanted and, unlike a distributor, have it vary depending on engine load.

Tony Donato in Philly can rehab your cis to new specs if you decide to go that way. We used him to rebuild at least a dozen systems when I worked at the Porsche shop.

I had carbs on my four cylinder and liked them. Went with Richs PMO's on a 2.2E with S pistons and Johns Mod-Solex cams. MarkClick to view attachment

I had MFI on a 2.4ST motor for a long time in my six conversion. It had wonderful throttle response, but it was a b1tch to live with for a daily driver. Now I have Motronic on the 4.0, and the only thing I would trade it for is an aftermarket EFI with ITBs. But I have other things I want to do to the car first.

We also have a factory six with stock webers. I only keep the webers on it because that is the way it came from the factory. If I could do it without affecting the value or appearance, I would put EFI on it in a heartbeat. EFI is so much more user friendly than carbs.

Clay

Electromotive

Clewitt does seem to sell what looks like a well put together package-it always surprises me that they use such and old school controller.

Same here on the controller.

Once school of thought - go Megasquirt, Motec, or other controller but then it becomes fully DYI.

Other school of thought - Clewitt seems to have good reputation, and may have this system pretty well sorted. Don't really need a fancy controller to run a 1973 engine without knock sensors and a pretty low RPM limit.

I need to do more research for sure.

Depending on the year 914 you have you may want to relocate the fuel pump to the front then add Tangerine's SS fuel lines in the tunnel. I was gonna do carbs on my 3.4 but went with the PMO EFI and Rasant complete engine management system with COP. I was going to use a modified factory 3.2 EFI intake but choose the classic carb look instead.

You can run you CIS as long as you have all the parts and in working order. Weber or PMO carbs are what most people run for simplicity and classic look. All depends on what you want.

You can modify a factory 3.2 EFI intake to work with the 2.7. There's a few people on Pelican that have done it. I was looking at doing that for my 2.7RS build but then switched to Weber 40ida's. I just didn't like the look of the intake on the engine.

If you are looking at doing carbs go with the PMO's. Last I heard the production on them is backed up so you may want to check the status on stock.

Cheapest way I've found was partially CIS and Holley sniper

I wasn't looking to upgrade my system. The the two main reasons I'm doing the EFI on my 3.0 is because I got a smoking deal on a good used system with a known since new history and two is I also have a second 2.7 engine build that I'm slowly gathering parts for.

The SDS EM5-F6 that I got is a pro built system with injectors and ignition that was $3300 new. I paid substantially less for it used, but I do know this system, what to look for and how to tune it. And then you still need an intake, cheapest is motorcycle ITB's, to stock to spendy for PMO TB's.
EFI isn't cheap, usually x2, even x3 the cost of carbs, it also has a steep learning curve. SDS isn't too hard to program, other systems often need expensive dyno time. There's plenty of opinions on which is the best system I'm just going with the system I know and have tuned for 18 or so years.
What ever system you pick you have a huge amount of research to do before you jump in.

At best a set of good Webers will be $2500, you could get Zenith carbs cheaper but there's not as much support as with the Webers. Cheaper Webers will need a lot of rebuild work, my carbs were in very good and it still cost me ballpark $5-600 for venturies, rebuild kits, jet holders, tubes, jets, fuel level tool..... plus you need linkage rainhats, etc. Carbs are also a learning curve but a lot easier if you already have a basic understanding.
It's more than just carbs, you also need a dizzy, I was quoted $600 to get my stock dizzy recurved.

Jeff asked the correct question, a stock 2.7 is designed for CIS. Yes, carbs will run mostly fine, but you'll run into the constant compromise situation of an unmatched fuel delivery system to engine.

I agree, really aftermarket EFI is for modified engines that won't run on a stock system (cams), in fact on a stock engine it will not give you any more power than the stock system. It will work, just like carbs will run a stock engine, but it's not better than it was with the stock FI.

Also, the carbs will require more maintenance and upkeep than even the stock FI. CIS is a very well designed system, and will start and idle when cold or hot. Carbs require more finesse and more patience to keep running when cold. They also require periodic adjustments to stay in tune.

And with carbs, you can end up with this:



The carbs on Elwood were not rebuilt by me. I had them done by Zims, and they were setup perfectly. Then I spent hours syncing them to get them to run correctly and idle right. And the float still stuck in the right hand carb.

Has anyone tried the Bitzracing CIS to EFI system? While not as elegant as ITBs, it looks interesting for a street driven 6.

Charlie

The CIS adapter parts look good. For people who are totally non-technical it looks like it comes with a tune loaded so you should get driving fast and it'll likely perform kinda OK.

The issue I have with it are as follows:
1) Uses a very old Megasuirt ECU
2) No ignition control integration. A lot of the benefit you get from aftermarket EFI is on the ignition side.
3) No TPS. Acceleration enrichment based on MAP which is a little weird. They claim it's OK, maybe it is, but I've not had that experience.

You could use their hardware with a newer Megasquirt, and add a TPS and ignition control.

Clay

It is looking like CIS might be the winner, I have a complete setup on the shelf and connected with Tony in Philly. Hopefully he can get me hooked up.

I like the look (not cluttered) of Webers, but $$ are a factor. Another poster mentioned the 2.7 was built to run with CIS, personally I am not sure if that matters.

@ClayPerrine

Everytime you post that video it makes me laugh. As I said last time, I'm grateful you weren't injured by the splash. But it sure makes me laugh.

You're a good sport to keep posting it!

It is a good lesson for everyone out there. And it shows the advantages of wearing glasses, especially safety glasses.

Clay

My /6 I took a shortcut and rattle canned my fan shroud. I had issues with my carb float levels and by the time I had it sorted I pretty well ruined the finish on the shroud under the carbs.

A stock 2.7 has special piston tops to swirl the air/fuel charge. USA spec I don't think the CR is more than 8.5:1. The stock cams are also made for CIS. It will run on carbs but I consider this a low budget or I don't have the OE intake system solution.
If you want real high performance you have to start with basically a clean slate build, cams and pistons at minimum.

I have a 2.7 here I could start building, but I need JE pistons $1200 (ballpark), replated cylinders $1200 and a set of cams $1000 plus all the rest of the parts, machining, etc., etc.
Adds up PDQ and my running 914 still needs work.

CIS pistons and cams are not optimal for carbs. Rebuilding with better Pistons and cams is expensive. But if you want a motor that will run well, you need to do that, even if you run carbs.

Clay

This is my preferences least favorite to favorite and why. I have had all the options listed at one time or another.

For me carbs suck. Lots of fiddling to get them close. seams like always a compromise between idle, part throttle and full throttle mixtures. Never perfect for long. When temp or elevation changes (i live near mountains) all bets are off. When you park a hot car in your garage after a drive you will stink up the garage and if attached to the house that to. Had to park car in driveway until car was cold and then put away.
A plus for carbs is the ability to use more aggressive cams and in general you can bolt them on and get engine to run (maybe not really well) with just a screw driver.

MFI- just as fiddly as carbs. Maybe more if you are using a non stock combination. At least you get altitude and temperature correction with later systems. Expensive if you need custom parts like space cams, bigger stacks etc. Cool looking in 911 where you can see it. Pain to work on in 914 and you cant see any of the coolness. Pluses for MFI: Also allows more aggressive cams, garage doesn't smell like gas.

CIS. My experience has been that CIS is mostly set and forget. If working correctly it works pretty good but not perfect under all conditions. Does require special tools if you need to trouble shoot issues. Not very performance oriented and limits cam choices to those with low overlap (think close to stock CIS or EFI). Can tolerate some performance changes like compression, mild displacement increase etc.

Factory EFI. Similar to CIS. Works very well in most cases. no touch starting and running, just turn key. Better performing than CIS. Has similar flexibility for mild modifications like CIS. With ability to have custom chip made (can be expensive) more flexible than CIS. Can pretty much be tuned to be spot on under most conditions. Adds 3D ignition control and o2 feedback which is a plus. Can be repaired by most Porsche mechanics. Very good option for many applications.

Programmable EFI. Super flexible. Can be fiddly but its fiddly with a computer vs screwdriver. Can be used with factory intakes (MFI,CIS, 3.2 Carrera, 964 or 993) for easy install. If single throttle body system pretty easy to tune (especially if you only expect it to work as good as carbs). Single throttle systems have similar camshaft restrictions to CIS and Factory EFI. Can add ignition control as well. ITB's can be work to get right.
Can use non factory intakes, ITB or build your own . Can buy turn key kits or do total build it yourself. Good solutions for boosted applications (super charged or turbo) ITB's big cams etc. Pricing can be pretty low if you do it yourself or thousands of dollars for turnkey/High end system. The sky is the limit in what you want to do. This is my favorite because of the flexibility

Full disclosure: I work as a application engineer for industrial control systems so concepts for building system and programming ECU for engine is not something I find difficult.

john

john

Confirmed, Tony will receiving my complete system for rebuild. CIS rebuild $1.k plus or minus with no fuel odors OR Weber setup around $3. or $4k with gas odors. Simple answer. I was unaware of a CIS guru, Tony comes highly recommended.

FYI, I have Weber triple throat IDA’s on my 2.7. There is no gas smell in my garage with a hot or cold car.

Yea, He is a funny guy but really knows cis. He doesn't just clean them up and paint. He tests them to correct spec. He fixed a turbo for us that the owner spent years and $$$ trying to get it to run correctly and another engine where the guy spent $22K on a rebuild but they did nothing to the cis and it ran for crap. He once sent me a pic of the insides of a "rebuilt" FD. It was all rusty inside. All they did was a "krylon" rebuild on the cover.