EFI on an early high-compression 911?

rs911t · 12-04-2003, 08:31 AM

Folks,

So, I have a 1972 911 with a carb'ed 2.8L engine. The car generally runs pretty damn well but many have suggested I address a couple issues: replacing the Weber carbs and the engine's 10.2:1 compression ratio with single plug ignition.

Replacing the carbs is the only immediate issue - they're old and leaky. The CR issue is what it is, but the previous owner drove the car 16 years on unleaded pump gas without any apparent damage.

This winter I plan to drop the engine to fix an oil leak(s) and basically evaluate the engine's overall health. Now seems the time to think about these issues. When I do I come up with the following:

* PMOs and leave the ignition as is - $3000

* PMOs and twin-plug - $3000 + $? (drill heads, ignition and rebuild)

* Install MFI with or without twin-plugs - $? (find S/RS MFI setup)

Today I start researching EFI and find a complete TEC3 engine management system with individual throttle bodies packaged by Clewett Engineering for $5500.

Yes, it's more expensive than PMOs, but I suspect less expensive than PMO or MFI and twin-plugs. I wonder if the electronic FI would handle the marginally high CR with single plug ignition.

Anyone have any insight on this topic?

Thanks.

lendaddy · 12-04-2003, 08:41 AM

EFI is a really intensive option. I am going this route with my 930 and although the rewards are potentially huge the initial headaches will be equal. I don't see too many EFI guys here but other boards seem more in to it. I don't really care how long it takes me to get it done, but if you want to hit a goal of being on the road trouble free in the early spring then go the carb route and be done with it. If you enjoy tinkering (or have big $ to pay a tuner) then I think the rewards of EFI are definitely worth it. JMHO Also, I have not heard too many good things about the electromotive stuff, there are many other options out there. The good thing about electromotive is that they seem to be really into P cars. GL

Early_S_Man · 12-04-2003, 08:42 AM

Well, I think you left one option off your list that would be less than $1000 ... geting the Webers rebushed!

And, acquiring/adapting an MFI system to your engine is probably less expensive than PMOs.

rs911t · 12-04-2003, 09:01 AM

Quote:

acquiring/adapting an MFI system to your engine is probably less expensive than PMOs

Warren, please expand. I've no idea how to estimate the MFI cost and effort to round up all the bits.

I find the EFI option appealing if it addresses both issues. I wouldn't do it just as a Weber replacement.

Chuck Moreland · 12-04-2003, 09:12 AM

My understanding is the TEC3 system can drive twin plugs. So if you go that route, you really only need to get the heads machined ($300) and you've got EFI with individual throttle bodies and twin plug.

Properly tuned, that should yield a potent, responsive motor that actually gets decent fuel mileage.

That's a pretty interesting combination for about $6k outlay. Yes there will be some more $ spent on dyno time and tuning. I've been kicking this idea around for my '73 too.

jpnovak · 12-04-2003, 09:16 AM

Greg, I would think the simplest decision would be to follow Warren's advice and rebush the webers. You will only be out a few hundred $$. They will last quite some time after that.

If you decide to tear down the engine I would opt for a twin-plug head and electromotive type setup. I think the electromotive systems can be expanded to include EFI at a later date.

If you want the MFI, which is noble. You will need to start collecting parts. New cams with belt drive, correct engine sheet metal, mfi injection pump, fuel pump, throttle bodies, stacks, Filter system (fuel) and probably a few more bits. IF not still on the car you may need to fab up the warm air supply from the HE's or replace them. This would be required for the warm-up regulator. It may be an involved conversion and still not solve the high-comp issue. The heads will also need to be setup for MFI injectors unless they are currently plugged from the original config.

Not that I could hear it but I didn't notice any signs of pinging when we went for a ride. I think the CR is just fine.

Tim Walsh · Tim Walsh's Garage

I've basicly replaced all my MFI system. It really shouldn't be that bad. I would look for a whole MFI system on ebay, send the pump to hans or Pacific fuel injection. With a 2.8 though you'd probably want Mg stacks or plastic S stacks. I don't think the cost would be unreasonable but more than likely you will need a pump rebuild since it's not a stock engine (1k) and throttle bodies enlarged ($200 to 1.2K) and then there's the stacks which are more of an unknown (Mg stacks are easy to bore out)

Just some initial musings on MFI

304065 · 12-04-2003, 09:44 AM

Each has advantages and disadvantages. MFI is cheapest when your engine conforms closely to the T, E, S or RS spec, otherwise you're looking at a custom space cam, big bucks, only Gus can do it.

Webers allow the tunability for "custom" engine specs but will cost you a few HP over MFI or EFI.

EFI is realy the best of both worlds-- you have the ability to create a custom fuel and ignition map on the dyno-- expensive and time consuming, but the best, if lacking the Aesthetic appeal of MFI for a vintage car.

If I were you I'd do the EFI. In a couple years I'm going to build a screamer 2.2 and it's going to have EFI, plain and simple. I like the combination of crank-triggered spark, precisely measured fuel with baro and temp compenstion, with individual TB's or slide valves to really get the air moving.