914 1.8L VS 912E AFC fuel injection

[kuch]

I have a 1974 1.8l with the original stock AFC fuel injection system that I am rebuilding. The engine is apart and I am adding all the required machining and new parts so that it will be a dependable street car. While going through the process of the rebuild I was thinking of increasing the displacement to a 2.0L. I have the entire engine and injection system from a 1978 VW bus and was wondering if the 1.8L fuel injection system would work on an engine with a 2.0L displacement. I intended to just add the 2.0L crank, rods, and pistons and cylinders to the 914 thus I will use the stock 1.8L heads which have larger valves than the 2.0L. I know Porsche used a 2.0L AFC injection system in 1976 with the 912E, but do not know if or what is different between the 912E and the 914 1.8L injection system. Can some one tell me if it will work as a direct bolt on or do I need to swap out some 912E or VW bus parts to make the 914 injection system work at a higher displacement ?

[Dave at Pelican Parts]

The 1.8 heads have smaller valves than the 2.0 914 (and 912E) heads. The better 1.8 ones (including the 914 heads) have 41mm x 34mm (intake x exhaust) valves, while the 2.0 914 heads have 42 x 36. The 2.0 Bus heads have smaller valves than either.

The 912E uses several unique FI parts, including the air flow meter. Since there were only 2099 of them ever made, parts that are 912E-only tend to be hard to find and expensive. I hear from some sources that the 1.8's L-jet EFI can keep up with 1971cc displacement (stock 2.0), but I have also heard that it doesn't.

Mike Mueller on the Rennlist is doing an L-jet 2.0, perhaps you can find out how his works. He is threatening to have it done next weekend.

--DD

[kuch]

I am not sure what you are saying, I gather this injection system will work, but you are not sure how well, right? The limiting factor would be the possible restriction of the air-flow meter. If I can match up the air flow-meter will the injectors need to be replaced as well? Do you have the e-mail address of anyone currently doing a 2.0L 914 with L-jetronic fuel injection?

[Ron Meier]

It is not a question of whether it will work or not - it will. The main impediments are the calibration of the 1.8 brain vs the 2.0 and the flow rate (lb/hr) on the injectors.

The injectors can be replaced with the appropriate 2.0s. Given the corecct fuel pressure, the correct amount of fuel will be delivered.

The programing of the brain is a different story. Unless you have a friend in the business with a dyno and an eprom burner, it will be hit and miss as to whether the brain sends the correct signals to the components. You will have to use the 1.8 brain.

D-jetronic works off manifold pressure. The throttle body on D-jet controls the rate of air (throttle opening) and only has contacts for fuel pump on and wot enrichment. The MPS signal is sent to the brain to control opening duration of the injector.

L-jet works off of airflow. The vane air flow meter measures the airflow (by deflection of the vane) and sends the signal to the brain which determines the total time the injector is open for the load. The VAF used will flow the required air for the increase you are seeking.

Try it if you like, but without the proper measurement tools to dial it in, you're shooting in the dark.

[bowlsby]

Find Mike Mueller here, nice guy...I'm sure he'd help:

mmueller@netmercury.net

Im a Djet guy myself, but I would think the only tool you might need would be an air/fuel meter and tinkering with the air flow meter vane or spring to calibrate the mix. The L-jet seems to be a very tunable system. You could also add resistance to the TS2 via a potentiometer (~300 ohms max) and that would richen the mix across all loads and rpms.

Good luck.

[kuch]

I need to know where to get a air flow meter. Forgive my ignorance but I have never heard of one, are they hard to use ?

What set point values for air flow would I be setting the meter to when adjusting the airflow meter?

[Ron Meier]

You already have one (airflow meter or properly vane airflow meter - VAF). It is the big silver (& black) unit right after your airfilter.

[Va914]

I am taking my 1.8L L-jet and adding 96mm P/C's and will be keeping the F.I (I hope).

I have seen some talk on using the cold start injector as a 5th to richen the A/F ratio. I hope I don't need to go that route, but if I do richen her up I have an option. I believe all injectors fire at once, so if the 5th was to fire also it would richen all 4 cylinders, slightly.

I hope Mike will chime in on this one. I hope to have mine engine running around March'ish.

Bect of luck

[Dave at Pelican Parts]

First of all, an EPROM burner will do you zero amount of good with the 914's L-jetronic fuel injection system. The 914/1.8 was the first car in the world to use L-jet, and the computer is a relatively simple analog device. You'd have to throw it away and swap in something else and then make it work.

The fuel injectors are triggered rather differently than D-jet (i.e., 2.0) ones. I have heard that if you swap L-jet and D-jet injectors you will fry something. Frankly, I'm not sure I see how as I think the 914 D-jet and L-jet injectors have similar resistances--but the info supposedly came from Bosch, so I'd guess they might know what they're talking about. Some injectors from a larger-displacement L-jet car might be swappable.

As Jeff said, the air-flow meter is the thing bolted on the side of the air filter housing. It measures air going into the engine, and the FI uses that as the primary determinent of how much fuel to inject.

The 1.8 stuff may bolt right on and work first time. In theory, the extra air the 2.0 needs over the 1.8 would be detected by the meter, and extra fuel would be added. I don't know myself how it works in practice. I have heard (cannot confirm) that the 1.8's air flow meter is maxed out by about 4500 RPM, so I might be worried about the engine running lean on the top end. That's where the mixture gauge would come in handy.

Tuning options seem a bit limited to me. You can fiddle with the head temp sensor resistance, as Jeff said. Or you can go to a junkyard and pick up a bunch of airflow meters that would seem to fit (and have the same kind of plug). Then you can try bolting them on, and messing with the tension of the spring that pushes the metering flap closed.

You might be able to substitute an aftermarket rising-rate fuel pressure regulator to help with the lean top-end, if that actually happens. The stock regulator is constant-rate, it increases fuel pressure by the same amount manifold pressure increases when you open the throttle. Aftermarket ones can increase by more than that, giving you a richer mixture with the throttle open. If that is needed, this could be a solution. You don't want too much pressure going to the injectors, though, as they may start to leak or to not atomize the fuel very well. (No, I don't know how much "too muchh" is.)

The 5th injector isn't a very good fuel injector, frankly. It doesn't atomize fuel that well, and just dumps it into the manifold. The fuel winds up as a liquid, rather than a mist, and tends to get distributed unevenly. Remember, the 5th injector was intended just to give a very cold engine a bit of extra fuel while the starter motor was cranking--just enough to help kick it off. It wasn't designed to provide fuel to a running motor at high RPM and throttle settings.

Another option, if you really want to be able to "chip" the car, is to snag a complete system off of a later L-jet car and then adapt it to the 914. If you really like putting stuff together and figuring out how to make stuff fit and so on, this would probably be a really cool project. And you'd have a very valuable information resource for others when you're done.

--DD

[914GOD]

Using the stock FI on a 2.0L will work fine, sort of.

The amount of fuel the engine recieves in AFC is controlled (mostly) by the amount of air entering (via VAF). Therefore the engine should run fine. However, there is one HUGE caveat to all this. The VAF in the 1.8 (so I understand) is fully open around 4000 rpm. This means it will be fully open around 3500 or so in a 2.0L. After this point the engine will run increasingly lean. I believe the engine continues to deliver more fuel based on RPM but as this is a differnt sized motor, that wont work quite right.

The best way I have heard of calibrating the computer is to stiffen the spring on the VAF, add new injectors. Then fine tune with fuel pressure and temperature sensor.

I am getting ready to build either a 2.0L or a 2.1L with L-jet myself. I really hope everything I have suggested here works!

Good Luck!

Sean

[Va914]

Thanks for the input Dave. One question though...
If you connect a normal (not the cold start) 1.8L injector in the POSITION of the cold start valve, why would you have diferent atomization there then in the valve chamber. There is alittle more of a distance to the combustion chamber but not much.

Cold starts are another issue but if you don't have weather that calls for the cold starts then you should be okay.

Just curious..

[Dave at Pelican Parts]

A regular injector would atomize fuel better. But it wouldn't get the fuel distributed any more evenly--possibly worse, as the regular injectors are designed to be fired at the back of the intake valve.

It would be interesting to see how it worked, but you'd need some sophisticated equipment to tell. (E.g. four separate fast-response exhaust gas sensors.)

--DD

[kuch]

I did a little digging and gathered the following information;

I e-mailed EBS racing , they sell the 96mm big bore kit and they said that; “ the big bore kit can be fitted to the 1.8 without any modifications to the fuel injection.” They did not have any dyno numbers on the 1.8 with only a big bore modification but estimated a 10% increase in HP and torque.

Gary Helbig , a L-Jetronic fan informed me that “ the 912E had a 914-2.0L block with 914-1.8L FI parts”

A 912E fan, Clay Perrine had the following to say:

“The 76 912E had a 914 2.0L intake runners, intake plenum and throttle body, but the throttle body was fitted with the L-Jet throttle switch.

The bore on a 1.8 throttle plate is smaller than the 2.0L. They also used a different intake hose to connect the 2.0 throttle body to the L-Jet AFM.

The injectors are the same size, the additional air flow will increase the fuel injected. The 1.8L injectors are not near to max flow, so the dwell can be increased to account for the extra displacement”

Ben Watson author of “How to tune and modify BOSCH fuel injection” wrote a chapter in his book on fuel injection Performance Modifications. When modifying the L-Jet system he wrote “ Contrary to what many believe, the goal of performance modifications is to get more air into the engine, not fuel. If fuel were the key to power, then increasing performance could be as simple as raising the fuel pressure by crimping the fuel pressure regulator return line. To get more power, the engine first needs to be modified to accept the additional air. “

This information points to the Air flow meter and induction system as the key components to the conversion. Unfortunately finding the correct airflow meter designed for one application doesn’t mean it will interchange, but if they are both Bosch there is a better chance of it working. I do not have access to 912E parts but a 2.0L VW van L-Jet system is cheap and easy to come by. The guaranteed factory Porsche engineered “bolt on system” would definitely be the 912E 2.0L L-jet induction system. From Clay’s observations obtaining the 912E AFM throttle body and intakes (or maybe 2.0L VW intakes if you don’t have the 914-4 2.0L heads) and possibly the 912E ECM are all the components required for the conversion.

[Dave at Pelican Parts]

The 912E used the 2.0 914 motor, complete with the unique heads and so on. The manifolding is identical to the 2.0 D-jet stuff.

The ECU and air flow meter are unique to the 912E. The injectors were used on the 912E, the 81-86 Alfa Romeo GTV-6, the 87-89 Alfa Milano, the 80-83 Jag XJS, the 75 Opel Manta and 75 Opel 1900, the 75-77 Renault R17, and the 87-88 Range Rover.

The above info is from Bosch.

The Bus EFI was designed for a low-compression motor with a very mild cam grind and very little power (67 HP!!). How well it will cope with a higher-compression hotter-cammed engine is yet to be determined.

--DD

[kuch]

Yes the compression is low on the VW van engine, but all the solid lifter cams are ground with minimal variations. The compression ratio is the key to making more HP, a good example is the 2.0L Euro vs North American pistons.

[Dave at Pelican Parts]

My understanding is that the Bus ran 7.3:1 compression and made 67 HP. I can't really believe that bringing a Bus up to the 914's 7.6:1 compression would get the Bus close to the 914's 95 HP rating. I realize that intake and exhaust manifolding is partly responsible, but even the 1.8 914 made 76 HP with 7.3:1 compression and a somewhat restrictive intake/exhaust. And less displacement!

Hugo from the Netherlands had a page (which is now sadly gone!) which detailed cam differences in the Type IVs. The biggest differences were in cam timing, rather than duration or lift. You could tell the different cams from each other by the "rings" cast into the shaft in between the cam lobes & bearing journals. There were ones with 1 full ring, ones with two full rings, and ones with only one half-ring. I do not remember which was which.

Boy, I wish I'd done a download of Hugo's page when it was still up!!

--DD

[Va914]

On compression ratio's..
what will get the most HP and still run on pump gas with a 1.8L, L-jet and 96mm P/C's??

I was thinking 8.0:1 to 8.5:1. I believe "fly cutting" is a good method?

Thanks.

[Dave at Pelican Parts]

If you can get the 94 octane that's available on the east coast, I don't see any problem with 9.0:1 compression. In CA, we're limited to 93 octane. So 8.5:1 is probably close to the limit.

Fly-cutting is fine as long as you don't make the "deck height" too small, and as long as you don't wind up smacking valves into piston tops. People generally say the minimum deck height is either 0.040" or 0.060", depending on who you ask.

--DD

[kuch]

Does anyone know the differences in the Porsche 914 cams?

If cam timing is more important than duration or lift, who offers the best cam for the 914 in a 2.0L configuration? That is, which cam would offer the best performance throughout the RPM range while maintaining the Bosch fuel injection?

I take it the cam rings were found on the stock cams, but what about the after market cams? It has been a while since the original cam design was first offered and fuel injection is now the norm. You would think by now, someone has optimized the cam for FI.

[kuch]

Maybe I should do a new post but this is still on topic,


In summary increasing the displacement of a 1.8L 914 into a 2.0L and keeping/modifying the L-jetronic fuel injection system should work. After all that is the system used on the Porsche 912E, Air cooled technologies claim that they can take a 1.8L 914 and modify the engine to 2055cc using the stock 1.8L L-Jet system.

The main difference in the 1.8L vs 2.0L 912E engines apart from displacement is the cylinder heads, and the induction system.

To improve airflow into the engine the 912E the :
- intake manifolds have a 2.5mm larger diameter than a 1.8L
- the throttle body has a 2mm larger I.Dia. than a 1.8L
- the air flow meter is 2mm larger than the 1.8L
- the heat exchangers flow better

This forum has helped me answer a great deal but I need to know one last tid bit of information to complete the conversion. That would be is the 912E wiring harness and ECU needed to do the swap ? Or instead will the 914 L-Jet system interface with the Bosche 912E FI system without a problem?