Lotus Twincam

[Lotus54]

I am new here, did some searching but could not find anything.
I have a 66 Lotus with Twincam engine. I got a crank pully with 36 teeth- but no missing ones.

Can this work? I do not see how it will ‘know’ TDC- but perhaps I am missing something basic here.
I have sent email to supplier (QED) but no response yet.

There is a base map it came with on DTAFast (T2i— 5.40 firmware) but has some errors in it (saying a 60 tooth wheel)

Any help would be very much appreciated.

Mark

[David Ferguson]

Is the engine currently running with that configuration? If so, perhaps the trigger wheel you are looking at is not being used, but rather one inside the distributor, or on the flywheel.

[Lotus54]

No, I am just not fitting the system. So it has never run with it. All new parts.

If I need to remove a tooth- that is easy, just need to figure which one. But they did send and a system - and I assumed it should all work together. (But of course, who knows?).

Mark


Edit:
There will be no distributor, there is no cam angle sensor. Just the 36 tooth (none missing) front crankshaft pulley and sensor for that.

[SMR]

Hi Mark,

Pretty sure you'll need to remove one tooth, to give a 36-1. Because the T ECU can add an offset, I don't believe it matters which tooth you remove. Refer to the manual as there's a handy drawing showing how the missing tooth position is determined.

Steve

[stevieturbo]

For fuel injection etc, you could use a crank wheel with no position reference, but then you must have a cam/phase/sync sensor

But in general, a 36-1, 36-2, whatever, always run a crank wheel with some sort of position reference. Having none, just makes no sense, even if you did also have a cam sensor.

[Lotus54]

Thanks all- I understand how to set angle in solftware, so will remove one tooth in middle of adjustment range


Thank you

[Lotus54]

Before I remove a tooth- I thought I’d better see if I understand.

In the diagram in manual, it almost appears that the trailing edge of the first tooth should be at TDC?
But I think I may be interpreting.

I did a rough measure of where the sensor is located compared to engine at TDC pulley position.
I thought about removing a tooth about 90º from TDC pulley position, since the sensor is around 168º BTDC. (Which I would measure accurately and enter in software). I do not see anyplace where you enter where the missing tooth is located (maybe it does not matter?).


I would appreciate any input to see if my thinking is right.

The white mark in right it TDC, the engine is at TDC right now. The light blue mark near top is potential tooth to remove.
The sensor is just sitting in there and pulley not pushed all the way back. Just rough idea to see if I am all messed up.

[stevieturbo]

It's not that critical, and I'd assume the T series can run the gap anywhere, like the S series ( but not older P series )

So a tooth removed anywhere around 11 o'clock would make sense and be roughly around 90 deg BTDC if that is a useful reference to remember for you.

The only critical aspect, is telling the ecu exactly where that reference is.

Page 54 of the manual

[Lotus54]

So I remove a tooth. then careful measurement of trailing edge of tooth after missing one— to where the sensor is in degrees, yes?
That seems to agree with drawing.


Do I have it right? (I see Oscilloscope and timing light verification)


I line up trailing edge to sensor, then turn engine to TDC- carefully measure degrees it took

[Rob Stevens]

Yes that's it, once running use a timing light to verify position. I get confused easy when using a wasted spark and timing light (I assume you are not using a distributer for sparks, and are using a wasted spark setup) so I enter 0's into the ignition table and look for the alignment of the sparks and pointer at TDC. Then adjust the sensor position in the software, don't rely on the oscilloscope.

QED should be able to give you a pretty good map as a starting point.