Ignition setup advice for a rebuilt hotrodded 3.0

[AndyLuft]

Hello,

I am in need of some advice to my engine project which is in reassembly phase these days.
I have a 930/09 3.0 engine that is completely rebuilt and most parts are set and ready, but I am unsure on which ignition system / components that would match my setup and ambition. I have an experienced engine builder doing the work for me, but we have not settled the ignition system yet other than keeping it single plug.

In order to receive some good advice, I'll try to explain my ambition and parts setup.
- The goal is to have a fun engine that lasts and is easy to use on the street. It needs some more "go" than original, but nothing over the top. Torque, drivability and response is more important than high rpm horsepower in my world. My thought is bringing the wife and kids on shorter and longer trips in this car. No track time.

The list of the larger parts that I have collected this far is:

1. Mahle motorsport 95mm P&S 10:3,1 comp (arp rodbolts, stock crank/rods/oilpump)
2. Lightned FW and sachs sport clutch
3. Ported and polished heads to 38mm (stock valves new guides and rockers)
4. Flow matched PMO manifolds and Weber 40 IDA's
5. Web Cam S/RS-profile cams (4 journals)
6. Schrick stiffer springs & titanium retainers
7. Dilavar cylinder bolts.
8. SSi heatexhanger and dansk sport muffler (ST style)
9. All new gaskets, washers, o-rings etc


Distributor - currently its the original 3.0 SC 6700rpm which I have. Its tired and in need for an overhaul. Has vacuum clock. I am in need for advice on this subject.

CDI - Currently original, and I am in need for advice on this subject.
I have seen the offerings of classic retrofit CDI boxes, but am unsure of their performance.

Coil - Currently original, and I am in need for advice on this subject.

Sparkwires - Currently original, and I am in need for advice on this subject.

Alternator - Currently a core exchange 70A with internal regulator that needs to be overhauled. Is 70A or 90A the way to go?

Fuel - I was thinking either the Malpassi FPR or the PMO FPR. I liked the PMO one as it has dual outlet for the Weber's. Fuel pump is new but regulated by the FPR. 8mm hoses in between. Will be using 98 RON European fuel.

The engine is going into a 71 T with an RS touring theme along with an overhauled 915 gearbox.

I'm open to suggestions and good advices from those that have BTDT before, but main thought of now is to avoid dual plug. If there is something I forgot, then please be kind and remind me.

thanks in advance,
Andy

[Geneulm]

10.3:1 compression. Those heads need to be twin - plugged, extra holes in the valve covers and replace that distribute with a twin plug variety. Multiple versions available (others can chime in here along w advance curve).

[snbush67]

Yep, at 10:3 all the advice you will get is that you’ll need to twin plug it.

My advice is if you want to stay single plug sell the 95’s P&C’s and get 98’s at 9:8 compression for more displacement.

Saying all of that, until you build your motor and measure the piston height, squish, deck height, etc. you won’t really know what your CR is going to be. You might get lucky and be under 9:8 even with the 10:3 pistons. Also you can add spacers to increase deck height and lower CR but it isn’t recommended.

[Mark Henry]

I have a very similar 3.0 engine right down to the P&C's, you have to twinplug it.

[trond]

10.3 is twin plug territory. Not that I can see your pistons shapes, but even if they are designed for single plug you would need to plan for octane booster. At least here where I live. So twin spark most likely. Cheapest and easiest would be EDIS maybe. At least I found that to be both easy and affordable. You could run it with a cheap and cheerful Megajolt box, completely standalone, or maybe later move on to running it by a Megasquirt CPU. Or source a 12 point distributor with built in advance regulator and two CDI boxes&coils. I tried EDIS first because it was cheap and easy, then after 10 years moved on to big distributor and CDIs that cost 10 times more and is more fiddly to set up. Looks cool though. Try EDIS first ?

[mikedsilva]

If he is using S style cams, would that lower his dynamic compression enough to be able to safely run the 10.3 with single plug so long as he uses high octane fuel?

The reason I ask, is my 3.0 was specced to 10.2:1 compression and with Mod S cams and on 98 fuel (here in Australia) I had no issues with detonation.

[Geneulm]

98 RON = 93.5 octane. Def twin plug... you may never hear the damage being done without.

[trond]

yes, you may be right Mike. How important is the shape of the piston dome ? It has been my understanding that at least with a split chamber type twin spark should be used. what shape or form the Ops pistons are, or yours I don't know. Also I assumed that yes more overlap and duration will give less dynamic compression. But at peak efficiency I think cylinder pressure will still be high (to make power)

[Mark Henry]

Originally Posted by Geneulm

98 RON = 93.5 octane. Def twin plug... you may never hear the damage being done without.

I was told long ago that if you can hear ping it was close to hitting the piston with a hammer.

[Jeff Alton]

Originally Posted by mikedsilva

If he is using S style cams, would that lower his dynamic compression enough to be able to safely run the 10.3 with single plug so long as he uses high octane fuel?

The reason I ask, is my 3.0 was specced to 10.2:1 compression and with Mod S cams and on 98 fuel (here in Australia) I had no issues with detonation.

Mike is on the right track here...

Did the actual CR get measured, or just relying on advertised CR? IF relying on advertised the CR is likely .5 lower that stated, give or take.

The S "ish" cam will reduce the dynamic compression. The motor may well be just fine with good fuel.

Forever that has been this internet "RULE" that 9.5 is fine single plug and 10.5 requires twin plug. Ok, what about this motor? We have run measure 9.8 single plug no problem with our terrible BC gas, the worst in North America...

Food for thought.

Cheers

[Peter M]

Why spend all that money on hotrodding an engine and then hobble it with single plugs?!?

The extra cost is well worth it.

[Richey]

i'm with Jeff , the only way to really know the CR is to partially assemble and measure the deck hight . Then measure the dome volume and combustion chamber volume and do the math , and yes 10.3 to 1 is too high for single plug . You could have a machinist cut the piston domes as necessary .

[buster73]

Just breaking-in a 930/09 engine after full rebuild. Not as highly tuned as your nice example but with some similarities.

1. Mahle 95mm 9.8:1 C/R
2. Big port heads, single-plug
3. Flow matched PMO manifolds and Weber 40 IDA's
4. Stock SC Cams
5. Early style SSI heat exhanger with stock Dansk muffler

Regarding ignition I opted for a programmable 123 Ignition distributor (USB) in combination with Bosch 3-pin CDI, black Bosch CDI coil and Clewett Engineering ignition leads (from our host). For the break-in I started with an ignition curve similar to a Euro 930/10 204 hp engine. Fuel is 98 RON European fuel. So far engine runs well and ignition seems fully adequate to do the job.

[Dpmulvan]

Why spend all that cash and go with 95mm pistons and cylinders? A bump in compression compared to cost is not worth it in a street car. Just my opinion.

[Jeff Alton]

^^^ Maybe his P/C set was not in spec and needed attention anyways? That said, we would have recommended 98mm if purchasing new parts.

Cheers

[AndyLuft]

Hey guys,

Thanks for all the feedback.
Im sticking with my builders recommendation with single plug, and adjust (if necessary) after it had some time on the dyno. The deck height and all other procedures was done and measured to spec, but I don't have those numbers on me.

Everything is flow matched and the Weber's are about to be done and set up to match the rest of the engine setup. It should be lots of fun.

I got lots of great help from this forum on parts that is not that easy to get hold of. Many thanks to those of you that contributes and sorry for my late response.


Here's some up to date pictures:

[mikedsilva]

Originally Posted by AndyLuft

Hey guys,

Thanks for all the feedback.
Im sticking with my builders recommendation with single plug, and adjust (if necessary) after it had some time on the dyno. The deck height and all other procedures was done and measured to spec, but I don't have those numbers on me.

Everything is flow matched and the Weber's are about to be done and set up to match the rest of the engine setup. It should be lots of fun.

I got lots of great help from this forum on parts that is not that easy to get hold of. Many thanks to those of you that contributes and sorry for my late response.

Andy
the motor looks fantastic. I love the fibreglass engine "tins".
I am pretty certain you will have no issues at all regarding detonation with this setup. Keep us posted.
Mike

[Neil Harvey]

Seems your well on your way to having this completed.

Something that caught my eye was reading your engine performance needs. Torque over high end RPM. I think your words were high RPM horsepower. Nothing wrong there, a perfect set up for street driving.

Contrary to your performance requirements are, stiffer Valve springs and Titanium Retainers. Too late now, but Titanium Retainers are more about lightening up the valve train for higher RPM needs. They also need regular inspection, more so than steel ones. Stiffer springs seem to be the norm unfortunately. These engines get over sprung way too often all based upon some historic idea that the valves will float. When used unnecessarily, they rob a lot of HP, load up the valve train and things wear out sooner.

Just how stiffer were the springs. Stock springs at stock retainer heights usually net somewhere around 70 lbs on the seat. Nose pressures often vary with different lifts used.

To give some idea on how far valve train technology has come, we are down in the 50's for the Intake and in the mid 60's for Exhaust. Camshaft designs have come along way from all of the historically used old designs all originating from Harvey Crane's work.

Enjoy and happy motoring.

[AndrewCologne]

@AndyLuft

Twinplug in your case of 10.3:1 ist not obligatory, it depends on the Fuel youre running.

In your case the secret is a "rpm AND MAP-based ignition". Set up via a 1° precise map table like known from Megasquirt set ups or similair.
The regular dizzy is very unprecise and so it comes with a huge risk of detonation if you don't count in at least 5° safe distance to the max angle possible. Not talking about that the the regular dizzy does not count in the actuall load present at a given rpm.

I know people here in germany running 10.5:1 on a 3.0 K-Jet set up with Super Plus fuel (98 Octane) and an optimized ignition with no problems resulting regarding detonation etc..

[PeteKz]

First, I don't think anyone else mentioned it: The Dilivar head studs are a bad idea. I've had a half dozen broken ones myself, and the pro engine builders here have seen hundreds. Since you already built the engine, you will have to decide whether to halfway disassemble it to replace with steel studs. You could just run it for awhile, and pull the engine and halfway disassemble to fix them when one breaks. Eventually, they will.

Second: Advertised CR's are usually optimistic. You can measure the Cr by setting one of the pistons at TDC with the valves closed, then use a graduated cylinder to pour a light oil into the spark plug hole until it is full to the bottom of the spark plug thread. You will have to tilt the engine so that the spark plug hole is at the highest point in the head, so you don't leave air pockets. Then you will have the combustion chamber volume as assembled. Calculate CR from that. It might be less than 10:1.

If you end up at 10:1 or less, stick to single plug, and stick to the original Bosch CDI system. Going to dual plug is expen$$ive. Not worth the price for a street car IMO. If you were a serious racer, you would need it to be competitive. The Bosch CDI works very well. After you get the engine running, then consider the A123 or other ignition systems. They have advantages, but they are easy to swap after you have the engine in the car. Get it running and driving first.

One other thing: Did you use base gaskets? If not, you can add one or two to decrease the CR slightly. Those copper base gaskets are about .004"/.1mm, if I recall correctly.