To Twin Plug or Not?? That is STILL the question
 

As many of you know, I converted my SC engine and now has a turbo on it (K27-7200). I converted using 930 Euro CIS to keep it simple and also have 993 HEs MK Y-pipe and a 965 Interooler.

With this set up I am running 0.5 bar and when the bugs are worked out may bump to 0.6. My biggest issue is boost lag. Boost does not come on until 3500 or later.
The heads are ready, I just need to source the ignition parts. I plan to go the distributor route as that seems less complicated to me.

Anyway, will I benefit from finishing the twin plugging? I have heard it will help and others say there will be no great benefit. Thanks for the input.

It is not required unless you have a high dome piston. But any engine will benefit a small amount because you can reduce the timing advance due to the faster burn time. Boosted mixtures burn faster anyway though, so you might gain a horsepower, nothing big.

Flieger is correct about the high dome pistons found on normally aspirated 911 engines. There are advantages for our flat dome turbo engines also.
Twin plugs get the flame front started from both sides of the cylinder (the stock single plug is at one end) so the mixture burns faster. Twin plugs are good for a little bit of torque (since you can run a little less timing advance) and .5 point of static compression (a faster burning mixture is less likely to auto-ignite).

If I were building a race engine or already had EFI and was doing a rebuild, I'd do it. On my CIS car it wouldn't be worth the extra expense.

Yes I still have the SC CIS pistons

Jeremy,
I have a 3.2 converted to a 3.4 turbo with Electromotive tec3r twin plug. The ignition is wired to two toggle switches in the car so that I can switch off either the top or lower sparkplugs. Much easier to diagnose a miss fire which could go on undetected for a long time unless you like to pull 12 plugs out periodically. When I cut one bank off there is a decrease in throttle response throughout the whole rpm range. AFR does not go down (i.e.richer) unless I am on boost so that tells me that all fuel is burned while not on boost even with only one bank on. On boost it's another story, motor goes rich and the backfire starts. Throttle response weakens and feels like spark retardation. Twin plug gets me some boost and power at 2,200 with full boost at 3,300. Clear as mud???
Hope this helps, cheers,
Upon

You should spool up sooner and be able to run more boost safer with twin plug. Is it worth $3K for a CIS engine? Probably if combined with the other efficiency updates and will allow you some better control.

Dave Jarvis has made a nice RSR reproduction twin plug distributor with the sand blasted body and all. The caps are readily available Marelli unit from a Jaguar. The orange Bosch caps are rare as hen's teeth as they say..

Patrick MS sells these kits with MSD parts and has some nice Kingsborne wire sets too.

Be nice to see what you end up with..

Thanks guys for the advice.

Upon what turbo are you running and where does boost start when on single plug?

I can not see how the twin plug with distributor should give noticeable or any spoolup improvement. Is the mechanical vacuum ignition timing different or the same with 12 plugs?

To address spoolup I suggest to look at the areas that matters i.e. contributes to air volume, velocity and puls energy.

I had an Andial built Twin Plug.

Having twin plugs will not improve spool-up, it will make approx. 10-15 more HP than a Single plug, and improve the crispness of the throttle response.

The best thing about using twin plugs is that it gives a little detonation safety margin when using street gas.

I think the quicker spool up could come from the off-boost power increase that the twin plug gives.. My mechanic builds Porsche motors for a living and swears by twin plugging. Granted he says the N/A cars reap the most benefit but since a turbo motor is N/A till the boost hits it can only help the cause.. And since a performance rebuild is in the $10k+ range you would be foolish not to add it to the mod list. I am..

Twin plug dizzy
 

Another advantage is you can have a distributer built with a custom curve and boost retard to suit your build. You should consult a builder who can tell you what benefits he can do for your application. There's more to it than what meets the eye. Philip

if you still have a distributer ;)

Jeremy,
Re: your question. I'm using a K27 of sorts. I should really take it appart, take some pics and let this forum tell me what I really have. With respect to the boost running single bank, I do not remember at what point the boost comes in and I will not have an answer for you until next spring when my hot rot will hopefully be on the road. It would be fair to say that the less throttle response the more lag so it would have to start boosting at a higher rpm-think of accelerating at a modest pace where the boost does not really come on.
Cheers
Uwon

Jeremy,
Re: your question. I'm using a K27 of sorts. I should really take it appart, take some pics and let this forum tell me what I really have. With respect to the boost running single bank, I do not remember at what point the boost comes in and I will not have an answer for you until next spring when my hot rot will hopefully be on the road. It would be fair to say that the less throttle response the more lag so it would have to start boosting at a higher rpm-think of accelerating at a modest pace where the boost does not really come on.
Cheers
Uwon

Sorry for the double post. iPad had a seniors moment.

If I had my heads off i would have them drilled...........the rest of the equation can be dealt with at any time then