Best practical way to Twn Spark ignition 911 engine?

Nine One One · Post by **Nine One One** » Sat Sep 25, 2021 8:30 pm

Why not just go for this and save yourself some time??

https://www.ddk-online.com/phpBB2/viewt ... ccd7a68b07

911hillclimber · Post by **911hillclimber** » Sat Sep 25, 2021 8:43 pm

That is interesting.
I expect this new engine to have similar mechanical conditions, just bigger dia Pistons and the more aggressive cams, GE 60 possibly much the same as your cams in the small dia Pistons.

Twin boxes to fire the lot is expensive, and this is where I feel the Clewett system to be a good package.
The current slightly tweaked engine gives a very drivable 261 BHP.
The engine today at Loton Park hill was really really nice, but I hit the limiter twice as per usual.
The deeper Rev limit I hope for will negate this and net some good time advantage allowing me to hang on to the gear far longer and still be powering on the hill.

The engine for sale is a real bargain, but this rebuild will be about 6k cheaper which will pay for the fresh tyres (1.3k) and a few other things.
I also want to do this myself, I want to do the oily bit as I always have done.

neilbardsley · Post by **neilbardsley** » Sun Sep 26, 2021 6:01 pm

Are you going to crank fire? Not that I want to send your money but isn't it a more stable spark?

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911hillclimber · Post by **911hillclimber** » Mon Sep 27, 2021 2:44 pm

The Clewett system is a crank fire, a design used by many for some years straight off the fan belt pully.
This what I like about it, no moving parts, everything set in position.

Had a very interesting conversation with someone with a modified 3/3.2 hillclimb engine about his twin sparks.
The engine had to be heard to be believed. I've never listened to such a stable tick over ever.

This is the Clewett system:

https://www.clewett.com/bmz_cache/5/5ce ... 00x481.jpg

911hillclimber · Post by **911hillclimber** » Sat Jan 08, 2022 2:13 pm

Need to pull the trigger very soon on a suitable twin plug ignition system for my 3.2.
Still favour the Clewett as it is 911 focused and an integrated system.

Will be discussing this system with the rolling road guy on Monday next.
Has anyone direct experiences tuning this system esp with twin plugs?

I think all the clever bits are included, just need leads, plug tops and some lead clamps etc.

hot66 · Post by **hot66** » Sat Jan 08, 2022 11:29 pm

I’ve got it on my engine … Neil Bainbridge tuned it on his engine Dyno and I’ve not touched his settings since.

Basically 4 rotational knobs. 3 of them are for advance at different Rev ranges … you set the first one , then the 2nd is for the additional advance over the next range and again the same for the 3rd . 4th knob is rev limiter. Pretty basic way of tuning but works well .

911hillclimber · Post by **911hillclimber** » Sun Jan 09, 2022 9:13 am

Thank you James, I knew you had the system, but was not sure if you were involved in it's set-up.
Sounds ideal to me.
Not a laptop in sight.

Do you have the settings by chance that I could suggest to Ben as a stating point?

The GE60 cams won't be so far away from your S cams.

Alternative is to take the engine down to Neil, not too far away from me, and get him to do the same to my 3.2 and so not have to do a rolling road.

hot66 · Post by **hot66** » Sun Jan 09, 2022 9:32 am

Might as well be up front and say Neil will not be cheap !

I’ll see if I can dig out the numbers,

Gary71 · Post by **Gary71** » Sun Jan 09, 2022 10:12 am

James, Does your set up use an additional MAP sensor?

hot66 · Post by **hot66** » Sun Jan 09, 2022 11:22 am

No. Basic clewett is just for twin plug ignition as I’m running MFI . I went clewett at the time as it was the most cost effective way to twin plug but as it is I’ve been really pleased with it.

I have 2 lambdas which are are connected to a dual band afr display located in the glove box that I use for mfi tuning tuning

Gary71 · Post by **Gary71** » Sun Jan 09, 2022 11:55 am

Interesting, so it’s just a 2D simple advance curve? Does the MFI car normally have any form of vacuum advance/retard on the dizzy?

gridgway · Post by **gridgway** » Sun Jan 09, 2022 12:25 pm

It's intriguing to know how the advance works in the Clewett with the three knobs to adjust it.

Mind you in the application, it's only WOT that's off interest, so advance based on revs should be fine.

It seems slightly counter intuitive though to be building a mega race engine with clever ignition that's only 2d. Having said that, I don't have any experience of the ins and outs though.

Gary71 · Post by **Gary71** » Sun Jan 09, 2022 12:40 pm

I read the manual. Yes I was bored this morning

It looks to be a good way to replicate a distributor, but is a bit limited as to where the changes can be applied.

For the application in hand i.e idle and 5k to 8k WOT it’s probably all you need. Not worried about tractability at 2k in 5th

but from James experience it seems ok at doing that as well.

Lightweight_911 · Post by **Lightweight_911** » Sun Jan 09, 2022 12:48 pm

Gary71 wrote: Not worried about tractability at 2k in 5th but from James experience it seems ok at doing that as well.

I doubt that James has ever driven his car at 2k rpm in 5th !!

.

Gary71 · Post by **Gary71** » Sun Jan 09, 2022 12:50 pm

Fair point well made, his operating window is the same as Grahams

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