Doing "twin plug" in stages: does it make sense?
 

Does it make sense to do a twin plug conversion in stages? My engine is now apart and would be a good - and relatively inexpensive - time to get the head machining done... but since I'm old, retired, and count my pennies more carefully than I used to (!) I don't want to have the distributor expense at this time.

Good idea or not to have the head work done, screw some plugs in the holes, and do the rest when it is a better time for me?

Thanks!

Rob

ABSOLUTELY YES !
Thats the way i did mine whilst I sorted the options out. ( money, and type of ignition )
Running a set of spare dummy plugs will hurt nothing. BTD
So do it. Have the heads drilled and tapped by a "knowledgeable shop"

I'm not sure I understand. You go to a twin plug set up by functional necessity. Why would you increase your compression to the range where twin plug is necessary, drill the heads, but not add the ignition? You would damage your engine.

perhaps he has a turbo coming in the future.

Let me try to 'splain... My engine is apart in San Clemente right now. For whatever reason, I am considering a twin plug conversion. It seems to me (and apparently there is at least some agreement) that now is the time to do the head work. One the car is in Texas, further work to the car will be done by Ed Mayo Mayo Performance)... friend of over 30-years.

Rob

you can do it in stages, but the question remains why? if the pistons and stroke result in less than abt 10.5:1 compression, you dont need it. if compression is higher, then you do. its kind of binary. if you are going to change your compression later then everything will be apart again anyway so id leave it to later.

if you are going to boost later then your compression now likely needs to be so low that it will be a dog but you wont need the second plugs and you can do it in stages.

Good points, John... Thanks!

Rob

No fun allowed around here anymore.
If the heads are at a place you trust to drill them, then maybe you should let them drill them.

I would !
one less trip back to the machine shop
simple

They are at Bill Brewster's shop in San Clemente... I wonder if they are any fum? :D

R

just about everything I do is in stages, I just don't have the money to match my goals....

OK, AB, here's another question for you... If I have the heads done but stop short of going "all the way" to twin plugs (operating, that is!), I have the choice of having the engine reassembled with either 9.5:1 CR or 10:1 CR... would I be safe with 10:1 CR for limited driving until I ponied up for the full twin plug job?

R

Think you're asking for trouble going that route. You can destroy those nice high compression pistons pretty quickly from detonation. That's what the twin plug helps prevent.

Here's another option:
Build the engine as a twin plug 9.5:1. Add the distributor, wires and ignition box later.
You might even consider Electromotive for cost savings.
We do it all the time. We build a 2450 (70.4x86) that is 9.5:1 with twin plug, 40mm Webers, 36 mm ports and Mod "S" cams that makes 180 RWHP @ 6400. They are a hoot to drive.
It makes for a plethora of timing options, the engine runs smoother, burn fuel more efficiently and you never have to worry about fuel quality.

12 mm plugs?

Rob

If the guy doing it has no idea of the size of lugs you must fire him !
If I remember correct, yes a smaller size on bottom.

Oh, I'm sure they know... they've done it a zillion times. I'm just trying to gather up enough knowledge so as to not appear the total ignoramus that I am!

12mm plugs will allow you to use the stock barrel nuts without issues.

No worries about Bill, he's been at this quite awhile and knows what he's doing.

When converting production heads, we always add a 14mm plug, but then again, we always Supertec head studs, so there's never an issue with clearance.

Studs
 

Speaking of your studs Henry can you send me a set please ? 3.0 based 911
Thanks, Mike Bruns
Sorry for the Hijack