Topic: Larger Bore D Jetronic Throttle Body

[Nutz]

I was hoping that someone here would know the size of the throttle body on the V12 Jaguars with D Jetronic or other models with a larger bore than what is on the M117.Thanks in advance 

[Denis]

Hi Nutz

I hope you realize that a bigger throttle body will provide nothing at all more unless you FLOOR the accelerator.
In any other position, it results in zero improvement in power 

Besides, there is very little room on the D jet manifold. One possibility is getting a throttle body from the bigger BMWs, at least that is what I would do if french law allowed 

Of course I have an alternative plan for more power WITHOUT any apparent change 
A Megasquirt built into the analog computer housing using all normal sensors, wiring, injectors, etc.
It appears that I can get an extra 15-25% more power that way. Just studying this possibility.

Cheers

Denis

Paris, France

[Nutz]

Hi Nutz

I hope you realize that a bigger throttle body will provide nothing at all more unless you FLOOR the accelerator.
In any other position, it results in zero improvement in power 

I have a few tricks up my sleeve

Besides, there is very little room on the D jet manifold. One possibility is getting a throttle body from the bigger BMWs, at least that is what I would do if french law allowed 

That actually was was first thought,then the V12 Jaguar.I did however find today an 83mm throttle body off of
a Ford SC Thunderbird that fits like a glove.Drawback is the amount of work to get the TPS positioned correctly and
radiusing the throttle body and adapter.

Of course I have an alternative plan for more power WITHOUT any apparent change 
A Megasquirt built into the analog computer housing using all normal sensors, wiring, injectors, etc.
It appears that I can get an extra 15-25% more power that way. Just studying this possibility.

I have heard of Megasquirt but know nothing about it. 25% increase in power

Cheers

Denis

Paris, France
[/quote]

[Denis]

Interesting, unfortunately there arent any Thunderbirds here 

The power increase is for a well optimized FI + ignition control system. Our M1XX engine suffer from a primitive electronic FI or an equally primitive K-jet. Anything better, especially coupled with igntion curve mapping is going to result in more power and probably better fuel consumption 

My estimate also relies on the Euro compression of 9.5 to 1 : the more the merryer 
Getting 12 liter per 100 instead of 13.5-14 does motivate me !

Cheers


Denis

Paris, France

[Nutz]

I agree that the D Jetronic is prehistoric but it can be modified via the ECU,larger pressure sensor,larger fuel injectors and tweaking the injector pulse width to stay open 1 or 2 milliseconds longer,use of a Halls Effect transistor and an injector amplifier.

[Denis]

I have complete details on the D-jet setup and see NO easy way of getting it to perform much better.

D-jet is basically a fixed trigger technology with changes essentially based on manifold vacuum. It does not know the throttle plate position angle at all nor the exact mixture (no O2 sensor data) at any time. It cannot be fine tuned as it knows nothing about driving style, it cant tell why the vacuum level is where it is or why. The worst part is not knowing anything about ignition, something that FI only started doing in the early eighties (BMW 528, if memory serves me) with a major improvement in fuel economy.

BTW big Richard, who are we kidding with a big bore add-on ? Unless more is done, I see it as a waste of money and/or something to brag about between beers    methinks the guy who sold it is the real winner.

My real problem is that it is ILLEGAL to modify a car engine in France ! so I plan to make all these changes utterly INVISIBLE by even reusing the original D-jet injection casing 

If some authority asks me why there is an oxygen sensor on the car, I will say that it drives little LED meter in the ashtray, taht is a legal mod 

Best regards to all you fine gentlemen !

Denis

Paris, France

[Nutz]

D-jet is basically a fixed trigger technology with changes essentially based on manifold vacuum. It does not know the throttle plate position angle at all nor the exact mixture (no O2 sensor data) at any time.

The throttle switch tells the ECU when the throttle is closed,when the throttle is wide open and when the throttle is moving towards the open position.The switch consist of twenty-two contacts,with a set of wiping contacts that move across them as the throttle progresses from the closed position to the wide open position.

One wiping contact is used to inform the ECU that the throttle is closed.Another makes contact only when the throttle is wide open and a third makes and breaks contact twenty times as the throttle opens.The electrical pulses created by the making and breaking of the contacts signal the ECU to open the injectors more frequently,thereby enriching the mixture for acceleration.

The L Jetronic/Motronic throttle switch used on BMW E28s ,E30s etc...,is like what you described above,and uses a potentiometer located in the airflow meter to signal the ECU of the changes in airflow.

It cannot be fine tuned as it knows nothing about driving style, it cant tell why the vacuum level is where it is or why. The worst part is not knowing anything about ignition,

That's the trigger points function which provides the synchronizing signal for opening the injectors.

A very easy mod is to remove the plastic cover on the pressure sensor and turn the adjustment screw that adjust the air-fuel ratio if enrichment is needed after airflow has been increased.

I'm not trying to build a 10 second car for the record,I just want to improve the performance while traveling through our mountains here I go from sea level to high altitude in no time

[Denis]

Hi Nutz

Thanks for pointing out to me that here IS a potentiometer in that throttle position switch. This makes a conversion even easier.

The fixed trigger contacts work alright but that is why I say this is a basically fixed system. It is as fixed as the static ignition timing.

As for the pressure sensor, I know what you mean but my experience with them is that "fiddling with the screw" is very, very risky : the diaphragm is a very delicate thing that can easily be BROKEN with a twist of the little screw, broken as in "need a new pressure sensor right now" problem. I have saved a few by soldering after opening the units but that IS a 500 km fix.

Cheers

Denis

Paris, France