Speaking of Twin Plugs How.....?

[deoxford]

I see alot of twin plug engines out there and I wonder how do they do that?
Is it a stock engine with new heads?
Is it just a type of head work?
Can I do It to a 2.4T , what engines can do it?
What are the HP gaines?
What does it do the the life of the engine?
What is the cost on such a project?
Is this a good way to hot rod my T
DO you have a pics and specs
Thanks
Derek

[JNadal]

With the 3.6L engines, twin plug is standard. Otherwise in an older engine, you need to have heads modified. The kits are very expensive and the headwork is too. Its cheaper to have a 3.6 installed.

Also it offers a little HP, but its mostly used to allow for a higher compression to be run.

You can search the forums for it, the topic has been beaten to death

[BURN-BROS]

Is it a stock engine with new heads?
1. Some are factory,some are done by a machinist on single plug head.

Is it just a type of head work?
2. Not only heads,but ignition system change as well.

Can I do It to a 2.4T , what engines can do it?
3. Yes, you will get a performance bump, but it allows for increased compression ratios above 10 to1 for even more performance.

What does it do the the life of the engine?
If you are experiencing detonation that is damaging you engine it will save it. If not then ther is no increase in engine life(of reduction)

What is the cost on such a project?
Some may argue but it starts around $3000.00 on up.

Is this a good way to hot rod my T
Not unless you were going to change engine internals(bump compression)

DO you have a pics and specs
Do a search, you should pull up some pics.

Steve at rennsports site
http://www.rennsportsystems.com/2a.html


Aaron

[JNadal]

I saw a NOS factory setup including heads going for 15,000.00 on ebay

[Wil Ferch]

I would question whether the cost to modify an early engine to twin-plug heads compares to a 3.6 engine swap, when all is said and done....
---Wil

[JNadal]

The only price I had ever seen for a twin plug setup was that $15000 setup on ebay. For $3000 a twin plug setup might seem doable in the future (after I add a 3.0SC with turbokit). Having twin plug alone on a 2.4 wont get much, and have to take the engine apart and buy new parts to upgrade the engine can be ÜBER costly. Its alot more bang for the buck to buy a 3.6. Besides, a chip and exhaust will put them at 290+ hp correct?

[Grady Clay]

As JNadal suggests, I wouldn’t be surprised if a NOS complete system went for $15K. That price reflects how few of these systems were built in the ’66-’71? era. For a perfect, show winning ’68 911R or ’71 911S-GT this might be the market.

What I was discussing was current manufacture, period looking, proper and reliable functioning (most important), twin plug systems with appropriate spare parts.

I won’t disagree with Aaron’s $3K+ estimate. My point is that it should be able to be properly done for less. Most, if not all, hotrod 911 engines should have twin plugs.

The only thing that will change the cost of machining the second spark plug hole (and exhaust valve covers, R chain housing, etc.) is more 911 owners using the machine shop services. This will allow the shops to invest in jigs and fixtures for better efficiency.


An electronic twin plug system that I don’t see on the market is one that simply slaves off the OE system. Why not have one that senses the coil wire and #1 plug wire (or #1,2,3) and three coils fire the exhaust set of plugs? The only other ignition change would be to restrict the mechanical advance range.

Best,
Grady

[thabaer]

My head work was $200 (admittedly 10 years ago) and was a good clean job. Using an updated 964 distrib is a good route, there are plenty of very good crankfire systems WELL below $15K (that's a high price for even a very tunable system). If you want gucci branding and gobs of extra features you can spend extra $$$.

The dual Marelli dist prices seem OK, but you get nailed when the time comes to buy a cap.

I pondered the slaving idea that Grady mentioned, but I dig symmetry and passed on that route.

[emcon5]

There are 3 basic ways of converting a single ignition 911 to twin ignition, with a distributor, with an electronic crank-fired setup, or a combination of both.

Distributor : There are 3 options,

1: Find a used twin plug distributor. These come for sale from time to time, but are very expensive. They come in both RSR and 935 versions, don't buy a 935 distributor, as they have no mechanical advance, and would only run well at high RPM. I saw a 935 distributor for sale at a recent swap meet for $2000 with cap/rotor/wires. The seller reported it had been installed on a N/A MFI 2.8L race engine, and it ran good, but was really hard to start.

2: Convert a single plug distributor to take a 12 point cap and rotor. Andial does this conversion, it is also expensive, and the Bosch cap and rotor are VERY expensive ($1000+).
2a: Convert to use a Jaguar cap and custom rotor. This is new, but looks very promising.

3: Convert a 964 dual distributor. Rennsport does this, as do a few others. I don't know about the others, but Steve Weiner at Rennsport installs the trigger from a SC distributor, and uses standard 964 tune-up parts. It will not fit on a turbo engine. I saw a 964 distributor with wires at a swap meet recently for $250, and the conversion is ~$400 IIRC.

All distributor options need a second CDI unit and coil, and the necessary wiring. Depending on which engine, and which distributor you are using, you may need to change the distributor drive gear on the crank, to make sure it spins the correct way.

Crank fired : Electronic twin plug solutions can be anything from full engine management systems, to the more economical Electromotive. There are a number of crank fired ignition systems from companies that have traditionally catered to the domestic Hot Rod market that can probably be adapted to a flat 6, like MSD, or Accel. There are also a number of crank fired ignitions on existing cars that may be adaptable by a resourceful do-it-yourselfer. An off-the-shelf electromotive unit costs ~$1600, Junkyard solutions will be less of course, but you will be on your own.

Combination units: This primarily applies to 84-89 3.2L engines, which use a electronic ignition with a distributor. On these engines, all the timing advance is controlled by the DME, rather than in the distributor. The 964 uses a similar system but with twin plugs. Andial makes a splitter to convert the stock DME output to drive 2 coils and a stock 964 distributor. It may also be possible to use a off the shelf timing control box, like the MSD Programmable Timing Computer to drive a 964 distributor on a non DME car, but like the junkyard crankfired solutions, you would be largely on your own.

In all cases, you will need to have the heads machined to add the lower spark plug holes. You will need to modify the lower valve covers to route the plug wires through, as well as the right side chain box to make room for the # 4 lower plug wire. This should add ~$400 to a standard top-end job machine work.

You will need to modify the engine tin to route plug wires. You will need to change one head nut on the bottom of each cylinder, the barrel nuts are too fat and prevent the plug wrench from fitting over the plug. You may need to modify the heater ducting on the left side to clear the new fatter distributor.

For My engine, I went with the Rennsport conversion.

Head machine work: ~$400, (above and beyond regular top end valve work)
Used 964 Distributor, with wires: ~$400
Rennsport conversion to 964 distributor: ~$400
Used Bosch CDI and coil: ~$150
Distributor drive gear for crank: $60 (only needed for 911SC)
Other small misc crap* <$150

*wires, connectors, lower plug retainers, shipping, tune up parts, heat shrink, etc.

Tom

[Grady Clay]

Tom,

Thank you for a great post!

For your twin plug mod it took not much over $1.5K additional. Good deal.

Many moons ago I used pairs of semi-custom Delta Mk-10 CDI on all the 4-cam Carreras. They allowed both CDs to operate from a single set of points. I think the “custom” part was a diode and two resistors. The CDIs were $35 each into the early ‘80s. My point is this isn’t rocket science.

There is no reason to be so expensive. Yes, the cap and rotor are unique parts. Aaron and others are addressing those issues.

For twin plug machine work, I first used Competition Engineering (then in Pasadena, CA) in the late ‘60s http://www.competitioneng.com/Welcome.htm .
My point; Ray Litz was doing this 40+ years ago.

Best,
Grady

[89911]

Twin plugging cost for my car (3.4L):
964 Distributer: $850
Signal splitter: $600
Modified stock sparkplug wires $250
Machining: $1000

[emcon5]

Originally posted by Grady Clay
Tom,

Thank you for a great post!

For your twin plug mod it took not much over $1.5K additional. Good deal

Thanks Grady, I am pretty happy with how the car turned out. Steve does good work.

Originally posted by 89911
Machining: $1000

Was that $1K just for the twin plug mod, or did you have other stuff done?

Tom

[Randy Webb]

Can I do It to a 2.4T , what engines can do it?

- Any engine - but the 2.4 is so small a dia. comustion chamber that I don't see the benefit.

A signal splitter is not needed - you can drive twin coils from a single MSD unit.

As usual, a cheap way to do things (jag. dist. caps mods) or a nice explanation (Waynes books & the new susp. wizard) comes along just aafter I finish a project....

[84toy]

Back 15 years ago I had a 914-6 that I hopped up. I used Elgin custom grind cams and 2.7RSR piston \cyl set and I machined the heads myself for the second set of plugs. They were 2.0 heads! I made a jig for my mill and made some custom tool bits and the job turned out great. For the distributor I used a Maserati distributor cap and rotor and machined an adapter that pressed over the outside of my distributer to mount the cap (machined the O.D. of the distributor first) The distributor had points so it was quite easy to trip another CDI unit for the other set of plugs by just attaching the other CDI to the points. Actually it was all quite easy. One thing I remember was that the performance increase was shocking and rates as one of the most fun and rewarding projects I have ever done. I got out of Porsches for 14 years but I would love to do this to my 84.

[89911]

Originally posted by emcon5
Thanks Grady, I am pretty happy with how the car turned out. Steve does good work.

Was that $1K just for the twin plug mod, or did you have other stuff done?

Tom

It was part of a large bill from Ollies for valve guide replacements, rod balancing, and such. I don't have the specifics so it might be lower. My mechanic handled this stuffl.