Twin plug and plug the holes or not...

euro911sc · euro911sc's Garage

I dropped my heads off at Xtreme Cylinder Heads this morning. VERY nice place and they had some amazing stuff going on (They have cast their own beefed up 911 heads for racers).

Anyway, I'm doing an OEM build 3.0l SC. It was suggested that I might consider putting the 2nd plug hole in and just plugging it until I move to a twin plug setup. That way I do not have to take it all apart again...

Thoughts?

best regards,

Michael

Candelaria · 05-01-2007, 01:55 PM

Do you have a phone # to contact them???, I'm in need of serious head work, let me know, Candy.

304065 · 05-01-2007, 02:00 PM

Grady says you can:

Hi-comp 2.4S or 3.x????

eapcpa · 05-01-2007, 07:00 PM

Michael,

I am unfamiliar with the thread about twin plug mod and plugging the holes until you are ready. When the time comes, you will need to pull the heads and raise compression or twin plugs will not give much benefit? I don't understand the logic. If you have high compression you need twin plugs now. If you are running 9.8:1 or less why would you go to all of the expense to twin plug. And I can tell you for a fact that it ain't cheap. Just wondwering.

Jeff Alton · 05-01-2007, 08:31 PM

Twin pluging adds around 250-300 to a complete head rebuild, at least where I shop. So, if you need guides or valves now, and in the future have more money to tear into the motor and up the CR, it may not be a bad idea. You just need to make sure you will do the other mods while the guides and valves are still in good condition.

If not, when you tear into it again, even if the guides are toast again, at least the work is already done.

Cheers

Henry Schmidt · Henry Schmidt's Garage

I would have to agree with Ed. I would rarely consider twin plugging heads as a "While you're in there" option.
Twin plug engines, like most engine formulas should be built with a specific intent.
Twin plugging is a 10 tenth modification. When your looking for the last horse power in a high end rebuild.
I believe that a plugged twin plug head offers unnecessary challenges that should be avoided unless twin plugging is mandatory (it rarely is).

Jeff Alton · 05-01-2007, 09:38 PM

What are the unnecessay challenges that should be avoided? What CR and cylinder bore can one get away with while not twin plugging? Or, what would you say the safe thresh hold is for not twin plugging when running pump gas?

Is there a rule of thumb for cam/cr/bore that can be applied to avoid the cost of going twin plug?

I always assumed (and quite probably incorrectly) that if the bore was 95 or above, one would be "pushing it" with a higher than 10.3 "euro" CR. (on pump gas) And even that may be pushing it. I realize running a bigger cam can help get away from detonation issues, but how big?

Anyone out there know of PROVEN high performance combos that work with out twin plugging that are not "mild" motors?

I know, a bit of topic of the thread, but it would still be good info to have.

Cheers

Jeff Alton · 05-01-2007, 09:41 PM

Quote:

Originally posted by Candelaria
Do you have a phone # to contact them???, I'm in need of serious head work, let me know, Candy.

If you don't mind shipping them up here, my machinest does fantastic work. Folks from all over North American ship him their heads. The local Porsche dealer and all of the local Porche independants use him too.

Contact me offline if you need any contact info.

cheers

euro911sc · euro911sc's Garage

Lots of good stuff here!

Candelaria: Call Bill @ 772-215-2773 He may not answer, but he will get back to you as soon as he can. His shop is in Stuart/Palm City FL so if you find quality shops closer to you it may save you some shipping $

The argument was simply to save $ on the heads if/when I choose to go bigger on the motor. $ saved is basically dis-assembly/re-assembly & set up time. Theory being I'm already doing a complete rebuild with all new parts so the heads are apart and set up anyway.

Don't get me wrong here, it was not a hard sell or anything like that. Just a suggestive thought if I am planning on something in the future.

I was simply considering it as the ultimate reason why I am rebuilding was detonation issues, though no one was truly sure. I'm running 9.8:1 OEM for ROW '82 SC and have read here much on how I'm probably at the limit for pump gas single plug.

However, if I ever want to go into F Stock I can't twin plug, but I figured it might be an easy swap back if I could simply plug the holes... I'm leaning on the 'No' side at the moment.

Best regards,

Michael

Henry Schmidt · Henry Schmidt's Garage

Answers in red.

Quote:

Originally posted by Jeff Alton
What are the unnecessay challenges that should be avoided? Hot spots, carbon deposits, lower compression from machine work, plugs notorious for falling out. What CR and cylinder bore can one get away with while not twin plugging? Or, what would you say the safe thresh hold is for not twin plugging when running pump gas? There are too many variables to define a specific c/r that works in every instance

Is there a rule of thumb for cam/cr/bore that can be applied to avoid the cost of going twin plug? same answer

I always assumed (and quite probably incorrectly) that if the bore was 95 or above, one would be "pushing it" with a higher than 10.3 "euro" CR. (on pump gas) And even that may be pushing it. I realize running a bigger cam can help get away from detonation issues, but how big? Static compression is only part of the equation. Dynamic compression is varied by cam configuration. Overlap is the key. More overlap = less compression.

Anyone out there know of PROVEN high performance combos that work with out twin plugging that are not "mild" motors? There are literally 100s. A thread all it's own. Compression, ignition timing, mixture, fuel octane, chamber shape and dome configuration all need to be considered to prevent detonation.

I know, a bit of topic of the thread, but it would still be good info to have.

Cheers

Jeff Alton · 05-02-2007, 06:51 AM

Thanks

kenikh · 05-02-2007, 02:26 PM

Quote:

Originally posted by eapcpa
Michael,

I am unfamiliar with the thread about twin plug mod and plugging the holes until you are ready. When the time comes, you will need to pull the heads and raise compression or twin plugs will not give much benefit? I don't understand the logic. If you have high compression you need twin plugs now. If you are running 9.8:1 or less why would you go to all of the expense to twin plug. And I can tell you for a fact that it ain't cheap. Just wondwering.

I disagree, at least on 2 liter heads. You can add the extra hole and go twin plug later with noticable performance effect. The key is dyno tuning the ignition curve after going from single to twin plugs. You can get much more aggressive with the ignition curve on twin plugs, extracting extra performance, even on a motor that is 9.5:1. Just ask Fritz Ficke, who went from single to twin plugs on his stock '67S; he says the difference is night and day. Whenever you increase combustive efficiency there is a gain to be had by (afterward) safely adjusting your curve.

eapcpa · 09:32 AM

Kenikh
I mean no disrespect but do you have dyno figures to support night and day. The engine in question is an "OEM 3.0SC". I can put fresh plugs in my 2.2S and set dwell and timing and get what I would consider night and day improvements. The other part of the discussion, cost, Jeff said it adds 250-300 to a complete head rebuild? That is just the machine work, then you have the ignition system and wires. I went with a 12 pin dizzy $1500, Wires, I am making mine using magnecor ends $235 plus the wire another $150, two coils $50 each +10 each brackets, twin MSD boxes $235 each. I am sure I have missed something including the pistons that required the twin plugs to start with and some odds and ends. My point is, 250-300 is like pissin in the wind compared to the overall cost of twin plugging. Are you machining the lower covers now also? The logic just doesn't seem to be there because you are going to do a teardown again when the time comes. Use the 250-300 and take your wife out to a few nice restaurants. Do the twin plugs when you need it. You guys need to understand that I am a CPA. In some circles that means a bean counter and in others that means Constant Pain in the A$$.

Jeff Alton · 05-03-2007, 06:03 PM

You are right, 250-300 for machine work. As a recent twin plugger (that doesn't sound right

) it gets expensive to finish the system off....

Cheers

euro911sc · euro911sc's Garage

It would be an extra $300 to put the 12mm plug holes in all 6 heads. That's it. All the other things needed to do twin plug are not included.

My answer was 'not at this time'. I think I'm just going to keep this engine as stock. I'll build a monster twin plugged beast on something else

Thanks for the comments all!

-Michael

KTL · 05-05-2007, 07:13 AM

Plugs notorious for falling out? With the plugs properly torqued, lower covers machined and plug wire ends in place with hold down tabs to hold the plug wire ends in place, the plugs seem like they should stay intact, no? Well, we'll find out. I just did the same thing.

Just trying to spread out the costs to reduce the kick in the junk caused by all the work needed to build a bigger engine.

Henry Schmidt · Henry Schmidt's Garage

If they did not fall out there would be no need for a connector holder.
When the spark plug is used as a dummy plug not intended to fire, there is rarely a plug wire attached and connector holders will not work without a connector..

And yes even properly torqued plugs fall out more often than you might expect.

cgarr · cgarr's Garage

I would be interested to hear how others tap the plug hole? With a standard tap I guess it could work loose but with the process I use the plug is snug. Do the plug wires hold the plugs in place?