A lot has been written about timing the 4.5 with D-jetronic, but has anyone experimented with changing the centifugal advance springs to improve performance? These engines are notoriously thirsty at 11-12 mpg even when new. Pretty lousy for a 4.5, but not out of the ordinary for the day when the only way they knew to clean them up smog-wise was to reduce the compression from 9.5 to 8.0 from the '71 3.5 to the '72 4.5, and retarding the timing. One can't do anything about the compression without changing the pistons/heads, but the timing is another matter.

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Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
1959 Ford Thunderbird convertible/430
Past vehicles;
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang

There is nothing to stop us setting the timing to whatever we want. Many of us have set it to about 27-30 deg BTDC at 3000rpm. This usually ends up giving you about TDC at idle.

But, how the timing advances from idle to 30 BTDC is controlled by the weights and springs. Would changing the weights or springs improve gas mileage?

At one time, the weights on my car were seized and not moving at all! the car felt a LOT better after freeing up the weights. But, I now sense that it may not be working as well as it once did. Maybe it's because I did not replace the fragile fibre that the weights slide on.

I have been working on fuel consumption from a different view. The amount of fuel used is the amount that the computer tells the injectors to discharge.
I installed a full time wide band Air-Fuel gauge, so I can see how much excess fuel is being used. This allows the MPS and the idle mixture on ECU to be adjusted so AFR is close to optimum. But I have been warned that these engines like to run on rich side, so I have not gone overboard. But, if you make settings to achieve the low end of the ranges below, fuel consumption should improve.

One thing that puzzles me. the 3.5L engine puts out about same HP as the 4.5L US spec engine. BUT, the euro engine uses lower flow (yellow) injectors. This would mean that they would have to be pulsed more often than the US (blue) ones. I have heard of some people switching to yellow - they may make it easier to set up the MPS.

Finally - Several here are converting to Megasquirt. I have not heard what capacity injectors they will use as compared with the OE injectors. They will presumably try and have their new ECU set the AFR just like I am trying to do manually.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Graham, I am using Nissan 280Z Turbo 280cc hose injectors that are a staight fit in the Djet setup. Didn't fit the Megasuirt nor the engine in the car yet.

It will be interesting to see how they work out. The Megasquirt likely has the capability of controlling the duty cycle and pulse widths a lot better than the D-Jet ECU. But I imagine it will take some programming to get it right! Have any of the M116/117 owners fine tuned their MS to their satisfaction yet?

The thing that puzzles me, is why the M116 engine uses the yellow injectors with about 340cc capacity while the M117 uses blue injectors with 495cc capacity (figures depend on which reference you use!). If anything, the M116 engines produce higher BHP. Presumably this would mean that the M117 injectors are open for a shorter period (smaller pulse width). But why the difference?

I have read where Jag owners can have the D-Jet ECU modified to reduce pulse width. They do this so they can increase fuel pressure to 2.5bar and help prevent vapor locking.

PS: The 280z fuel pump can also be used on these cars. Part number is Bosch 69612 but is apparently same as 0580464005. (Pump comes in Bosch box, but was made by Unisia Jegs in Japan (Since discontinued apparently, but still can be found)

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I would theorize that a long pulse width with higher pressure flow (yellow injectors) would help atomize the fuel better when the air fuel mixture is sucked into cylinder. Sounds like blue injectors give out more of a large burst, but in a shorter time. That may be better for emissions because it may have been easier to time a short pulse better (error margin) in thos days to make sure no uncombusted fuel-air mixture came into exhaust. Also, cams are different for Euro and US M116 engines (so I am told) so that also affects pulse width.

Bert

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'70 111 280SE/c 3.5 (4 spd manual) - sold
'63 MGB
'73 MGBGT V8

Just to avoid confusion - the pressure used is same for both engines/injectors (2bar).

But I had not thought about the cams. Maybe the valves stay open longer on the M116 (longer duration) and this would allow larger pulse width on injectors. But it could also increase emissions if you get overlap of inlet/exhaust valve opening. This could very well be the reason for the difference along with the slowness on the D-Jets in pulsing the injectors.

Although mainly about the 12cyl Jag, this article provides some good background on how the D-Jet injection system works:

http://www.jagweb.com/aj6eng/djetronic.php

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Best Djet site I have found so far (courtesy of Tony H) is under

http://members.rennlist.com/pbanders/

Even has electrical diagram of ECU!

Has some part numbers and awesome ECU pin diagram with voltage and Ohm values under

http://members.rennlist.com/pbanders/djetparts.htm

Bert

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'70 111 280SE/c 3.5 (4 spd manual) - sold
'63 MGB
'73 MGBGT V8

I don't think the cam duration would have much to do with the injector pulse timing since the D-jet is a batch fire system and the injector pairs will be firing at different times relative to the piston stroke-I just don't think the D-jet is sophisticated enough to be concerned about the precise time the injector is fired. Plus as power is increased it becomes less relevant as the injector pulse gets longer. I read some info on the Megasquirt site comparing sequential injection to batch fire(all injectors firing at the same time) and the power was nearly identical with a slightly less smooth idle using batch fire. emisions might be more of a issue requiring sequential injection.
I am investigating using other more commonly available injectors when I go to Megasquirt.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

My "euro" 4.5 has no smog equipment, higher compression and advanced timing and gets 14 mpg (imperial gallons) which is about the same as 11-12 mpg US gallons. I will have a little more power but not better economy.
Personally, i think there are more economy gains to be had through changes to the transmission than the engine.

[/QUOTE]PS: The 280z fuel pump can also be used on these cars. Part number is Bosch 69612 but is apparently same as 0580464005. (Pump comes in Bosch box, but was made by Unisia Jegs in Japan (Since discontinued apparently, but still can be found)[/QUOTE]


I can tell you these pumps work as the PO of my car replaced the malfunctioning bosch unit with one! Sourced it from an ebay seller in the middle east(Saudi Arabia)

On the 3.5 vs 4.5 debate,that is a 20-25% difference in displacement.It makes sense that a smaller displacement engine would use a smaller injector.Less cylinder volume to fill.

The 3.5 gets materially (16-17 on hwy)better mileage mainly because of higher compression. That together with higher lift cams and possibly better ignition timing account for the almost equal HP. But as expected, the 4.5 has significantly more torque, which can only be achieved with 1) more displacement or 2) forced induction. Horsepower is often a somewhat disapointed matter of bragging rights these days; you really have to wind the buggers up to get any "go" results. Torque is king in everyday driving.

So, getting back to my original question, does anybody know anything about changing springs in the 4.5 distributor for better performance? Are the 3.5 springs any different?

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Berfinroy in CT
Present vehicles:
1973 300 SEL 4.5
1959 Rolls Royce Silver Cloud I
1959 Ford Thunderbird convertible/430
Past vehicles;
1958 Bentley S 1
1976 ex-Max Hoffman 6.9
1970 300SEL 2.8
1958 Jaguar MK IX
1961 Jaguar MK IX
1963 Jaguar E-type factory special roadster
1948 Plymouth woody
1955 Morgan plus 4
1966 Shelby GT350H Mustang

Get the factory specs and compare,
I recently did a 1973 450SLC 4.5 distributor and noted that there are different springs and weights on each side, asymmetrical spring weight system.

Have a hot rod shop test and re-calibrate the curve to custom.
I have spare distributors for that purpose as to not screw up an original

I would have thought that the HP required would determine the injector size. It must be that the 3.5 uses a higher duty cycle than the 4.5, but just why this is is not clear - to me anyway!

Most references say duty cycle can be up to 85% at full power. But the 3.5 and 4.5 operate much lower than that - maybe 30-50%. Again not clear whye except perhaps to allow for the slow analogue electronics.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

You are right! I had forgotten that on the D-jet, fuel is just dumped into the intake ahead of the valve with one valve being out of sequence. I gas the fuel just sits there waiting for the valve to open But actually everything is happening so quickly, it apparently does not matter and is still better than having a carb or TBI.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5