Thread: Completed. gems 4.6 fitted to 94 classic

Originally Posted by HSE30

I hear you.... I have a small LR workshop business and have tried for years to get the 3.9/14cux injection to run better economy. I can get them to around 14lts/100. That is why, for my work RR I went for the 4.6 and running the gems 8.2 ecu. 12lts/100 is normal hwy cycle. My thor 4.6 in the p38 will do high 11's to early 12's. I do drive economcally though. The right foot has a lot to do with economy......

Would part of the problem be the injection sequence ?- (Squirting at the whole bank instead of each cylinder) .

Possibly why they run ok on LPG.... pre-mixed air & fuel fed into the manifold.

- How much value is there in adding Oxygen sensors? Difficult ?

I drive so gently.... that even SWMBO complains about it...


James in Gosnells

'95 Vogue SE with working EAS, working Cruise Control, - and like a thirsty camel.

- Also, BIM 024 Bosch IGN module fitted.

Originally Posted by superquag

Would part of the problem be the injection sequence ?- (Squirting at the whole bank instead of each cylinder) .

Yes. part of the problem is the primitive nature of the system (software/progaming) and the tune/trim is too rich for safety.

Possibly why they run ok on LPG.... pre-mixed air & fuel fed into the manifold.

Yes
- How much value is there in adding Oxygen sensors? Difficult ?

Yes o2 sensors help, but are not the solution. Not sure if there is a 02 input to the 14cux.

I drive so gently.... that even SWMBO complains about it...


James in Gosnells

'95 Vogue SE with working EAS, working Cruise Control, - and like a thirsty camel.

- Also, BIM 024 Bosch IGN module fitted.

Really IMHO if staying with a 3.9 I would go for a aftermarket ECU Haltec Motec etc. Alot of tunning runs on dyno's required, but the outcome with patients is good. More power and economy. Russell.

My RRC has 14CUX, Unichip controlling timing, o2 sensors, Thor inlet manifold, free flow muffler.

I would estimate that I could probably get around 13L/100Km at about a true 100Kmh.

The latest reading I had was last week with 17L/100Km, towing camper trailer Canberra Sydney, crawl along entire length of Pennant Hills Rd, and then commute around central coast for total 660Km on Long range tank.

The GEMS will get better economy as it has knock sensors and an very accurate timing map, that runs the timing right up against knock at all times.
The secret to good economy is not only the mixture, which GEMS and 14CUX can both control via o2 sensors or even dyno tuning with piggyback without o2 sensors, but MOSTLY the timing map.

It is IMHO impossible for the amateur or even professional on a dyno to get anywhere near the factory maps such as GEMS, as car companies spend millions on this, much of it on starting strategies and again most importantly part throttle operation. Ask a dyno tuner to optimise say 10% throttle operation and they look at you as if you are a Martian.

Everything I have read is that sequential injection is ONLY for emissions and also that over say 3k revs , the sequential injection reverts to batch as there is insufficient "rise time" for the injectors to open and close sequentially. This may now have changed with piezo injectors and or direct injection , but we are not talking about those.
Regards Philip A

Interesting....
How much would you guess, of your mileage is due to the Thor manifold ?

Or is there room for modifying the standard 3.9 shoe-box ?

I couldn't quantify it, but the ability to hold onto 4 lockup on hills towing the camper has to be worth quite a bit.
I guess one of my objectives was to not have to repass all the cars on cruise control on the next straight after they had passed me on every hill.

The engine spends much of its time now around +- 2000RPM with few excursions above 3000RPM.

It will climb Mt Ousley in 4th unlock ( with a few drops to 3rd) at 80Kmh towing the 600Kg camper trailer which IMHO is pretty good.

I tend to drop to 3rd now and hold 100Kmh more often than I used to, as even in third it would fall off previously. I hate empty semis passing me uphill, then having to repass especially in busy traffic like the Canberra road.

The TC is now very loose with a 25% slip at 1800on the flat turning into 2200 on a hill. This is from the Thor having much more torque than designed for.I would probably gain a bit of particularly urban economy by tightening up the TC, but not feasible IMHO unless I have to take it apart for another reason, eg rear main seal.

So I am all for the GEMS idea , but you need to start with a block that has the crank sensor provision and the knock sensor provision, which my 3.9 doesn't. AFAIK GEMS needs the exact number of teeth and gap of the OEM flywheel, and I have not investigated whether aftermarket sensors that go on the crank pulley are the same. Even if they are you need the exact location and fitting for the knock sensors or they will not work accurately.
Regards Philip A

Philip,
Correct me if I'm missing something....

The o2 sensors are allowing the 14CUX to run at its best.

You're suggesting (?) that better breathing - THOR manifold - is giving you the bulk of uphill efficiency, with the modified timing (Unichip) as icing on the cake.

I read somewhere on another forum that adding a spacer around 10mm under the 3.9's shoebox allowed better airflow into the trumpets, particularly the end ones. The effect was (supposedly) noticeable, but not 'licence-losing'

I'm not keen on getting any more engine noise via a free-flowing exhaust...don't particularly "enjoy" the V8 burble, and its associated resonances. Much prefer the straight six's balanced hummm.

Since LPG is getting more probable, I'd like to get the engine running as well as it can before spending on the change. Bee Utey has suggested the O2 sensors as part of the conversion.

Like to think I exist in the real world re. cars, that Nice & Easy to Drive is more useful than 1/4 mile acceleration figures. etc.

And how many service stations can be passed before refilling.

You're suggesting (?) that better breathing - THOR manifold - is giving you
the bulk of uphill efficiency, with the modified timing (Unichip) as icing on
the cake.

Well in fact theThor gives worse performance at high revs by about 10% vs the standard manifold. However the Thor gives much better torque at low revs, because the intake runners are MUCH longer than a normal 3.9, at about 1metre to the throttle vs 250Cm for the 3.9. BMW also claimed at the time they had engineered "Hemholz Resonance" into the Thor which gives a supercharging effect at one revs only, which I suggest is about 2000RPM.
People selling these 'spacers' are hoping for a difference from the longer intake , butthe change is so small that it would be unnoticable IMHO.

The timing advance control by the Unichip allows much more "vacuum" advance so that at light throttle the engine is running much closer to the knock limit and therefore more economically. Unfortunately most if not all dyno tuners have no experience in this and are very conservative as they do not want any blown engine comebacks. I have added another 3 degrees static ( to 8 degrees)to mine over and above the dyno tuners ( who have added about 10 degrees at 5% throttle) settings with no ill effects.
Regards Philip A

Originally Posted by PhilipA

My RRC has 14CUX, Unichip controlling timing, o2 sensors, Thor inlet manifold, free flow muffler.

I would estimate that I could probably get around 13L/100Km at about a true 100Kmh.

The latest reading I had was last week with 17L/100Km, towing camper trailer Canberra Sydney, crawl along entire length of Pennant Hills Rd, and then commute around central coast for total 660Km on Long range tank.

The GEMS will get better economy as it has knock sensors and an very accurate timing map, that runs the timing right up against knock at all times.
The secret to good economy is not only the mixture, which GEMS and 14CUX can both control via o2 sensors or even dyno tuning with piggyback without o2 sensors, but MOSTLY the timing map.

It is IMHO impossible for the amateur or even professional on a dyno to get anywhere near the factory maps such as GEMS, as car companies spend millions on this, much of it on starting strategies and again most importantly part throttle operation. Ask a dyno tuner to optimise say 10% throttle operation and they look at you as if you are a Martian.

Everything I have read is that sequential injection is ONLY for emissions and also that over say 3k revs , the sequential injection reverts to batch as there is insufficient "rise time" for the injectors to open and close sequentially. This may now have changed with piezo injectors and or direct injection , but we are not talking about those.
Regards Philip A

I agree with most of what you have said here. 13's is good and nothing wrong with 17's towing. And correct, tunning maps are critical to get the right result. My mention to aftermarket ecu's is more about the chasing of power and having a new system ie new electronics v's 20 year old ecu's which I might add have proved themselves to be very robust.