Twin Plug??

1972_911T · 11-24-2007, 03:36 AM

Im in the process of rebuilding my 3.0 engine, im ditching the CIS in favour of EFI and will be running 9.8:1 CR pistons probably with 964 cams. Should I twin plug the motor? If so is this just for safety or will it give me any extra HP from running a more suitable advance curve ?? Car will be run on 95RON fuel.

Steve

cstreit · cstreit's Garage

I think that's going to net out to about 89 octane US numbers? That's pretty close to the limit there. You'd be safe with conservative advance numbers and a richer mixture on 93 octane (US) but not so sure on your configuration. I'm sure Steve "octane" Weiner will chime in here...

BURN-BROS · 11-24-2007, 07:10 AM

9.3 is all I would go on single plug. 9.8 will not net you any power over 9.3 if you cannot run a healthy advance.

Henry Schmidt · Henry Schmidt's Garage

Higher cylinder pressures at all rpm ranges (torque), smoother running due to more complete fuel burn and a more aggressive advanced curves without detonation using lower quality fuels are the benefits of twin plugging the hemi head configuration used by the Porsche 911.

That was a mouthful!

hobieboy · 11-24-2007, 03:46 PM

Quote:

Originally Posted by Henry Schmidt

Higher cylinder pressures at all rpm ranges (torque), smoother running due to more complete fuel burn and a more aggressive advanced curves without detonation using lower quality fuels are the benefits of twin plugging the hemi head configuration used by the Porsche 911.

That was a mouthful!

Hi Henry,

I thought because twin plug produces more complete burn one should run less advance?

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by hobieboy

Hi Henry,

I thought because twin plug produces more complete burn one should run less advance?

With twin plug the net result is a more aggressive curve with less total advance.

Aggressive does not always equal more. Aggressive as I meant it = quickly accelerating, tending to move/change rapidly.

Aaron / Burn-Bros is the resident distributor expert, perhaps he's chime in.

hobieboy · 11-25-2007, 03:35 AM

Thanks Henry... got it now

1972_911T · 11-25-2007, 12:13 PM

Ok im sold on the twin plug just been and exchanged my heads for a set of ready twin plugged ones.

Now moving on to spark control one of the things that has worried me about running twin plug and hence a more risky configuration is what happens if you get a failure. Im planning on running a electronic ignition setup using wasted spark. From reading on the subject I know its recommended that one dual coil fires two opasite cylinders the theory being that the cylinder under load has the densist air and hence gets most of the spark energy, but wouldnt it be safer to run both plugs on one cylinder from the same coil then if there is a failure of the coil you will get no ignition rather than just one plug igniting?

or is there not enough energy to properly fire both the plugs?

Steve

Jeff Alton · 11-25-2007, 02:09 PM

You need to fire the top and bottom plugs from different coils, there is not enough energy to do it with one.

Search my user name and coils on the tech board and you will find a great thread about.

Cheers

safe · safe's Garage

Quote:

Originally Posted by 1972_911T

I'm ditching the CIS in favour of EFI Steve

What EFI-system will you be using?

1972_911T · 11-25-2007, 03:00 PM

Quote:

Originally Posted by safe

What EFI-system will you be using?

Im going to give MS a try, ive just bought a TBitz partial setup and considering ITB's, I like the look of the new PMO's. I was all geared up to build a 3.0 MFI engine but for various reasons gave up on that, this will be a nice alternative and if I do end up with ITB's it wont compromise the look of the MFI that was original to my car too much.

Steve

Jeff Alton · 11-25-2007, 07:46 PM

If you are thinking ITB's, I have the Jenveys and they are nice, but I will be back to back testing them with the new ones from Mark Hargett, and his look beautiful! I should have some results just after X-mas.......

Cheers

safe · safe's Garage

Quote:

Originally Posted by 1972_911T

Im going to give MS a try, ive just bought a TBitz partial setup and considering ITB's, I like the look of the new PMO's. I was all geared up to build a 3.0 MFI engine but for various reasons gave up on that, this will be a nice alternative and if I do end up with ITB's it wont compromise the look of the MFI that was original to my car too much.

Steve

I'm building an ITB setup on a 3.2 that I have. I thinking of using the Emerald system, have you considered that?
At £580+taxes its not very expensive and it will also control the ignition.

1972_911T · 11-26-2007, 01:25 AM

Quote:

Originally Posted by safe

I'm building an ITB setup on a 3.2 that I have. I thinking of using the Emerald system, have you considered that?
At £580+taxes its not very expensive and it will also control the ignition.

Just had a quick look at it and it only has 3 coil drivers so will only be able to fire 6 plugs in a wasted spark config so no good for a twin plug engine. Unless each coil driver could fire 2 simultaneous coils??

Steve

safe · safe's Garage

Quote:

Originally Posted by 1972_911T

Unless each coil driver could fire 2 simultaneous coils??
Steve

That can't be a problem, can it?
I would drop them a mail about it. I'm not buying anything just yet, but I would prefer a "proper" EFI system with support to a DIY Megasquirt.
I have talked to several shops and they all say that the 12x12 injection map of the Megasquirt is to small, at least for a high performance engine with high lift and overlap.
A system that some shop that you trust can map is also good. I don't think you can map it properly without a dyno.

1972_911T · 11-26-2007, 03:48 AM

Another option is the DTA systems there a little more expensive depending which model you go for, there based in the UK like the emerald. If the MS doesnt prove to be waht im looking for I think thats what I will go with. Probably the S80.

http://www.dtafast.co.uk/

Steve

Jeff Alton · 11-26-2007, 05:09 PM

I am pretty happy with my microtech and its iginition expander that allow me to fire 6 two pole coils. Software is pretty easy to use as well.

Cheers

TimT · 11-26-2007, 09:20 PM

Quote:

it only has 3 coil drivers so will only be able to fire 6 plugs in a wasted spark config so no good for a twin plug engine. Unless each coil driver could fire 2 simultaneous coils

With three ignition drivers you can easily control the ignition for a twin plugged six

you need two three channel ignitors, the output signal from the ECU's ignition drivers is split and feeds one each of the ignitors, each ignitors output goes to a twin tower coil.

This schematic from show how to wire it , you just use another whole set up like this fore the other set of plugs.

we use Bosch 0227 100 203 ignitors

CruiseControl · 11-26-2007, 09:28 PM

Steve, for wasted spark you only need three output drivers. Each output should be capable of triggering a pair of ignition modules. refer to the below wiring diagram which uses two Bosch 0 227 100 209 ignition modules which fires two 6 pack coils. The terminals A3, A4, A5 are the switch outputs of the ECU.

Paul

hobieboy · 11-27-2007, 05:28 AM

Quote:

Originally Posted by 1972_911T

Just had a quick look at it and it only has 3 coil drivers so will only be able to fire 6 plugs in a wasted spark config so no good for a twin plug engine. Unless each coil driver could fire 2 simultaneous coils??

Steve

Steve, as others have pointed out, with wasted spark you only need 3 outputs from the MS. This is the config that I'm running with MS right now. I also built the ignition drivers based on MS "recommendations" - way cheaper and allow me to "integrate" it directly to MS.

You do want to fire each cylinder from 2 different coils - though I'm still not 100% convinced its a must, but this is the "normal" way to set up wasted spark.