Best practical way to Twn Spark ignition 911 engine?

[911hillclimber]

I breezed though the installation instructions this morning and even I grasped it all. The XDI2 is more sophisticated, so prob not worth it for this engine.
Got to keep in mind the application.

As it was, a distrib + coil + points.
There is mention of vac off the manifold which I have blanked off atm, need to actually red this lot and go and see the rolling road man.

I just like the simplicity and no computers, the system and it is engineered for the 911 twin plug, not a mix of bits n pieces.
James' experience is re-assuring.
Needs fancy spark plug leads (Magnaflux) so I hope the connections are easy as any pre-cut leads will be too short I bet!

My thoughts about a dyno tune is that the engine can be run and corrected, the head nuts re torques and then the finished lot into the car. Not sure if I can get to the head nuts with the engine in this tight chassis though removing it etc is not hard work, just tedious.

Good grief, almost excited!

[Gary71]

Will be dead easy to dial in the standard 3.2 curve to start with an advance it from there.
Get some ‘99 octane in stock

[hot66]

This is my curve ….

1500 rpm = 11.21 deg
2000 rpm = 15.24 deg
3000 rpm = 25.09 deg

[911hillclimber]

Thank you James. It all paints a good picture.
Need to tell Mrs HC that I need one....should be ok.

[911hillclimber]

Permission granted.
Will buy the smaller accessories too, but will buy the special leads here in the UK
Fingers crossed it is all in stock.

[KS]

Graham, what plugs do you use for the second set? I presume they're smaller (12mm?), but what about heat ranges, etc?

[Jonny Hart]

The advance curve seems quite limited. Pretty much all 911 engines seem to respond to a 'bump' in the timing on cam, but this must be taken away at high rpm to avoid detonation. That's one of the advantages of having electronic ignition over bob weights, yet the Xdi box can't do that. Seems like an opportunity missed.

[911hillclimber]

Not a clue yet Keith.
There are words of advice in the instructions on the Clewett site. The size/thread of the lower ones are the same as the top.
More details are given to electrode gap depending on the engine's application.
A fresh batch of ZDi's are arriving in California on the 14th Jan, I put my order in tomorrow with some other smaller things.
Key also are the plug leads, Magnacore should be used, but will source them in the UK.

I really feel this is the right simple system for this engine and it's purpose with everything designed for the flat 6 and access to the supplier.
It was Richard Clewett himself who answered my recent questions.

I think also there will be lots of other ways to deal with this subject, and it is very hard to be sure system A is superior to all the others etc, but I have to bite the bullet due to time slipping by.

I hope this is the last BIG PURCHASE to this engine!

Cost ex California is $1600

[Jonny Hart]

On the page below, have a look at the full throttle maps for 964/993 (e.g. twin plug) and you'll see what I mean about the 'bumps' in the mid range.

https://www.911chips.com/ignition.htm

[gridgway]

Very pronounced on the full throttle 964/993, but much less so on the 3.2

[hot66]

On the page below, have a look at the full throttle maps for 964/993 (e.g. twin plug) and you'll see what I mean about the 'bumps' in the mid range.

https://www.911chips.com/ignition.htm

But with mfi and carbs the ignition doesn’t know throttle position or load etc … On mine neil did bump up the advance at the top end but it made less power . My settings were based on lots of power runs . . Clewett do sell a mappable control box for those that want more out of their ignition. I’ve got no axe to grind though as back in 2010 my only alternate was twin plug dizzy with dual cdi boxes

[Gary71]

You can dial a decline in advance from 3k to 8k, so whilst not a ‘bump’ as such as it’s not very smooth, it can have something similar if the work on the rollers show it to be required.

Those nice 3D ignition graphs are managing (in conjunction with the fuelling map) emissions and minimising fuel consumption at part throttle.

[Gary71]

Having said that…

Don’t discount the Xdi200 set up just yet Graham.

I’ve just had a read and it’s not a lot more in the scheme of things and it has a fully flexible 3D map together with the ability to run a coil on plug set up.

This would make for a neat setup without need for custom HT leads. With some measurements and consultation of the Bosch catalog you can probably find a coil on plug that fits.

Giving the tuner the freedom to dial the curve as required rather than being held back by the 3000rpm change point might release a few more ponies whilst keeping it safe from det higher up the range.

Just a thought

[gridgway]

But with mfi and carbs the ignition doesn’t know throttle position or load etc … On mine neil did bump up the advance at the top end but it made less power .

The only way I can see to do that is using the 3k-8k range setting which is linear so not really a bump at the to end as it were.

The thing I don't know anything about is how sensitive a twin plug motor is to ignition advance. And for Graham's application what's in it for him as it were.

0.5 bhp extra available? Probably not material, 10bhp? 20bhp? At 20 it's worth it, but it won't be 20, probably not 10. Just musing now!

If it's more for engine safety, that's a different matter. So much to contemplate.

[Gary71]

And it will be better when you eventually turbocharge it