TheSamba.com :: View topic - vintage 1990 twin plug engine build

Sat Jul 12, 2014 10:46 am

I thought you guys might like to read about this holstic experience in twin plug VW heads. I owned a 69-1/2 karmann Ghia convertible back in 1990 that I built a twin plug 1915cc turbo motor for. I really enjoyed that car. 120 honest hp at the rear wheels. I sold the car in 2007 to a guy in California. The next year, I called a VW shop in CA about a totally unrelated issue. I mentioned my company and he says " hey, I got your 041 twin plug heads" - I'm like, what? He goes on to say that the fellow ran the oil out of the engine and seized it up tight. He put in a different engine and kept the heads. He asked if I wanted them back. I said heck yes I want them back! He said they were buried on his work bench and he would contact me when he got to them. ,,, tick, tick, tick, 7 years go by and a couple of weeks ago he emails me, "you still want theses?" Yep I say. I bought my own heads back. I just got them and cleaned them up with a wire wheel. They look really good considering. I guess his work bench was REALLY messy if it took 7 years to clear it off. Note that the spark plugs are side-by-side, not on opposite sides. I had this done by an experimental aircraft place. I did not ask for that layout, that was just how they did them. dual 10mm plugs. Also note that they milled a bunch of the fins off the top side. I have no idea why they did that. I did not have overheating issues, so it must not be the end of the world. I have used 3 different twin plug distributors, 1st was a HASSAD dual 009 unit with toothed belt drive, 2nd was a 009 with a Datsun Z22 cap and rotor with 2 ignition moduals, 3rd was a Pertronix with the Z22 cap and rotor with 2 ignition moduals. Now I guess I need to build another twin plug engine with these heads! I wonder what a 2110 or 2332 would be like to drive?

Sat Jul 12, 2014 12:03 pm

I would imagine that in an Airplane engine it is done for redundancy, but in a VW engine probably your after better ignition. I have heard that the flame front progresses during a time when the piston is still compressing the air fuel mixture and that is why the ignition timing on an engine is advanced to about 30' or 40' at higher rpms. Is there less advance used on twin plug heads? I was looking for a 550 head picture but could only find these.

930 Head with twin Plugs:

911:

VW:

Sat Jul 12, 2014 12:35 pm

I've got no desire to hijack Clark's thread, but I thought I'd give him some props. I'm putting my own twin-plug engine together right now, and he's a big part of it. I started planning this over a year ago, and it's nearing the point of being ready to rock.

After a complete fiasco with a machinist who assured me he could drill a set of CB Super-Pros (and then proceeded to make a set of $1000 door-stops) for me, I purchased a set of 049 heads, CNC ported and twin-plugged by Revmaster.

The longblock is together-- it's a 2276-- .040 deck, 52.25cc chambers= 10.6:1. I'm using an FK8. I'd already's dry-sumped the engine a couple of years ago, and have 911 oil-squirters to cool the piston crowns. I'm using Cima/Mahle pistons/cylinders after a fiasco with Chinese nickies a back in '08. This is a street-only engine in my Intermeccanica speedster replica.

As difficult as the heads were to find, the ignition gave me a headache as well. Mario Vellota from the Dub Shop in Washington state could've set me up with a megajolt setup that would've been the cat's meow, but I really wanted an old-school bundle o' snakes twin-plug distributor.

Clark is doing a twin-plug conversion on an old .009 using an old twin-plug Datsun cap/rotor adapted to my distributor. I'm using one Pertronix pick-up. The mechanical in the distributor will be locked out, and advacnce handled by a modified CB Performance "Black Box"-- I had Mario tear it apart and add a second coil driver to the circuitry.

Doing this stuff means going where nobody else goes, or wants to go. It's expensive and time-consuming. You've got to really want to do it.

I've found a kindred spirit in Clark, and I can hardly wait to see the completed distributor.

Sat Jul 12, 2014 12:53 pm

Danwvw wrote: Is there less advance used on twin plug heads?

That's the whole idea, Dan. Two flame-fronts requires less advance, and allows higher compression (by one full point, according to Len Hoffman of HAM) than a standard set-up.

You are correct-- in an aviation application, the idea is redundancy, so there's two of everything.

Sun Jul 13, 2014 5:15 am

There is a guy in Australia named Stan Pobjoy, very well known and credible engine builder here, who swears by the twin plug setup. You could find lots of info if you google him. A mate of mine has one and loves it. Supposed to give loads of torque. Pretty sure he runs a Nissan bluebird dizzy. They had a 4 cylinder 2 litre twin sparkplug setup here in OZ. Check out AUSSIEVEEDUBBERS website.

Sun Jan 25, 2015 6:57 pm

Is a a big deal on the Remaster heads that the lower plugs have one angled to the exhaust valve and one to the intake? I know this is done to clear the pushrod tubes. I am wondering if flame travel will be different in the two cylinders.

Sun Jan 25, 2015 10:52 pm

In Aviation twin plugs are only to create a redundant ignition system. The engines are low CR and don't benefit from two flame fronts, like a high speed automobile engine would.

I have used twin plugs in both manners, and have found that the two flame fronts with high cylinder pressures, short cams and the largest bore you can fit will benefit the most from twin plugs. In the first decade of this Millennium every engine that I personally built was twin plugged. Once you create the combos, there's nothing like it.

Mon Jan 26, 2015 12:59 pm

Does the angle of the lower plugs matter?

Mon Jan 26, 2015 1:02 pm

Everything matters

Mon Sep 26, 2016 9:09 pm

i realize that i am dredging up an old thread, but i have a question about this type of head arrangement.

i have seen aero engines with two different styles of dual plugs. THIS style is the jabiru engine style. the opposed spark plug setup is the lycoming/continental style of cylinder head. i do not know if it matters either way, but i thought i would ask. i prefer the style as seen in the OP as it certainly looks easier to deal with.

sorry for the necro thread reanimation and the hijack. hey, at least im searching!

Sat Apr 15, 2017 12:03 pm

I just realized i never asked a question in my last post.

Who does this particular type of dual plug mod?

Sat Apr 15, 2017 9:37 pm

flyguyeddy wrote: I just realized i never asked a question in my last post.

Who does this particular type of dual plug mod?

Off the top of my head I know Mofoco does, but I'm sure there are others-

http://www.mofoco.com/item/Mofoco_040_Dual_Port_New_Cast_Stock_Cylinder_Head_SCORE_APPROVED_/237

Sat Sep 16, 2023 8:34 am

Reviving an old thread for interest.
I would think if you were to run dual plugs for the purpose of dual flame front that OP’s set up being so close together would be a little pointless?

Sat Sep 16, 2023 9:52 am

OP's configuration would be for aircraft redundancy. For a performance application, you would want a small lower plug, pointing toward the exhaust valve.
.

Sat Sep 16, 2023 10:12 am

Agree. But even the "redundancy" location improves the burn significantly.