bosch twin plug rotor?

[jmz]

OK, guys lets just say I've got a Marelli twin plug distributor and I want to convert it to ignitor pointless ignition...is this sacrilage?

actually I've got a 2.8 w/ marelli twin plug dizzy in my garage waiting to either go into my 74 or for me to build a 2.8 RSR rep. I had spoke to Jerry Woods about convertiing the dizzy to ignitor points and it sounded like a pretty cool idea...but not real cheap. Anyone done this or have any thoughts on it.

[CamB]

I think the single dizzy is more elegent as well. If we can get a good signal to the second coil elegently.

But you still need a second distributor cap (ie 964 distributor) or the twin distributor to send the signal to the lower plugs.

One set of points (or optical or magetic) trigger is ok. One advance curve is ok. But you need 2 coils, 2 CDIs (possible exclusion being the MW ignitions high output CDI for twin plugs), two sets of plug leads and some sort of twin distributor, unfortunately.

The marelli distributor - if it were me I'd convert it to electronic in a flash.

[cstreit]

Right.... The Marelli diz had 12 plug points on it right? (So you wouldn't need a second cap) I wonder if you couldn't plug in a pertronix to it, but who knows if the Pertronix made of for Bosch would fit...

THe Marelli ones aren't made either though are they?

Were there any other cars with 6 cylinders and 2 sparks per cylinder? What about aircraft?

[TRE Cup]

We've had a few Magnetti twins modified for the Pertronix ignitors. They have worked very well
What Chris and the others here have discussed re: the cost of modifying a 964, even a used one, to a full twin (coils, gear, advance plates, inductive pickup, wires) makes for an expensive final outcome AND it is not 73-74 RSR "period correct" The plus side is the low future maintenance costs. 964 rotors and caps are far cheaper and more available than what I'm looking for.
Because of this Electramotive gets the nod (even with their sometimes troublesome pickup) more often than not in cases where performance is valued over the vintage look. It is just quicker to obtain and offers the plus of adjustable rev limit and advance curve for less money

[Chuck Moreland]

Originally posted by rs911t
What about a solenoid or relay? Doesn't a spinning rotor behave like 6 solenoids alternately closing a circuit?

Geez Cam. There you go trying to spoil Chris' beer-induced engineering mania with a out-of-the-box solution! THAT'S no fun!

I've got no beer in me, yet. But here is a idea that would let a regular distributor fire twin plugs -

Put the plugs in series, not parrallel. This would require the creation of a special plug that does not ground to the head. Instead it passes the pulse back out to a second high voltage lead that routes to the second plug. The second plug is one that grounds normally.

The plug gap would have to be a little less because the total gap is now the sum of the two. But with a high voltage system like MSD each plug could still be a respectable .025 or better.

Seems like it would work.

[cstreit]

A 12mm plug with some sort of high-heat electrical insulator around the threads with 14mm threads on the outside of it... Then a driver wire off it's ground to the other plug... COuld be done... Good one Chuck.

Still, Can it really be THAT hard to make a 12 plug cap and rotor?

[RPMClassic]

Chris -

One of my clients in Boston owns a restoration/race prep shop. He has looked into having these made on a few occassions over the last few years. For the CAD work and prototype of 1 cap - he has never gotten an estimate for less then $25K. Every unit after that was $250. Min run of 50 caps required.

$37,500 is alot of dough to tie up - only to break even by selling the finished caps at $ 750 a pop.

[Tim Walsh]

except once you've got the plans and done your initial run $500 a pop is reasonable and you're still making a $250 profit per cap. It all depends on what kind of demand there is out there.

[RPMClassic]

Well to steal the famous phrase of another Pelican poster, "candy store items like these, always look appealing to people when seen through the glass display case! Very few people will actually put their $$ where their mouth is." Sounds harsh...but the reality for the person who lays down with the initial $37k. It could take them 2 years to break even - then again it may not! Risk vs reward.

[Tim Walsh]

exactly.. what you would really have to do before you jump in is figure out what kind of demand there is. Do alot of people use them? IF so how often do they get changed? Of those people that use them who would stay with the twin plug dizzy instead of upgrading to electronic ignition.

[cstreit]

Exactly. I think a better approach would be to convince someone to make them. An e-mail campaign of support to their marketing and product development directors would probably help convince them that it's worth doing the development and production.

I've contacted a few manufacturers about this and will guage their response from there.

[finadict]

It seems to me that since both plugs fire at the same time in the twin plug set, and that plugs are a relative low current device. It would be easier to spec a higher output coil( more secondary turns) and a hot cdi box. Then Y the plug wires, that's probably the trickest part....

[cstreit]

Actually to a point made earlier you can't just Y off each lug wire from the distributor. Since the spark plug is just a short, it would short through the path of least resistance leaving the other plug high and sparkless...

[CamB]

We've had a few Magnetti twins modified for the Pertronix ignitors. They have worked very well
What Chris and the others here have discussed re: the cost of modifying a 964, even a used one, to a full twin (coils, gear, advance plates, inductive pickup, wires) makes for an expensive final outcome AND it is not 73-74 RSR "period correct" The plus side is the low future maintenance costs. 964 rotors and caps are far cheaper and more available than what I'm looking for.
Because of this Electramotive gets the nod (even with their sometimes troublesome pickup) more often than not in cases where performance is valued over the vintage look. It is just quicker to obtain and offers the plus of adjustable rev limit and advance curve for less money

I agree that if cost is an object then the Electromotive is better. However if deciding between modifying a 964 or buying a Bosch or Marelli twin plug, either way you need two coils, two CDIs and two sets of wires (as an aside, I have factory 964 wires). So the difference is in the distributor only. The 964 doesn't look factory correct, but I know which one I'd rather have in ten years...

[cstreit]

I'm looking for reliability over cost....

[jmz]

so how much power are you guys getting out of your 2.8 engines. how is the torque, drivability etc. I am running a pretty nice 3.0 and will eventually swap it for the 2.8 that I own. I used to run a 2.7 w/ solex cams and a little extra compression and it seemed "happier" than the 3.0 I run now.

[CamB]

What camshaft?

I have S cams in a 3.2 (3,164cc short stroke SC engine). I get ~85hp/litre (270hp) - approx the same as the early S cars, but with much higher (10.5:1) compression. I have slightly larger throttle bodies (40mm), midly ported heads and SSIs with a standard exhaust.

Driveability is fine, but I have EFI so it should be.

You might get 85hp/litre - 240hp.

[rs911t]

so how much power are you guys getting out of your 2.8 engines.

My 2.8 has Webers, S-cams, S-heads, 10.3:1 cr. I've not had it on a dyno, but the previous owners and mechanic in-the-know say 220-240hp. Drivability and low-end skoot are great.

[jmz]

CamB, What EFI are you running? I am not sure what is inside the 2.8 it was built years ago and probably has S cams. My 3.0 has GE60 or MOD s cams (same grind) It is fast but I remember my 2.7 would rev faster than the 3.0. It may have just been the tight power band that the solex cam created. It may also be that the 34mm venturis on my weber 40's are choking the 3.0 liter down. I may be happier w/ 36mm venturis...not really sure how much differnece this will make though

I have thought about changing the 3.0 to 3.2 and bumping up a point in compression currently at 9.3:1 but those 98mm p/c sets are pretty f*&in pricey!

[jmz]

rs911t, are you running 40's or 46 webers w/ your 2.8? the one I have has 46 webs on it...I guess w/ all that compression they might work OK but it seems you would have better drivabilty w/ 40s