I got rid of my Moto Guzzi habit a few years ago ('76 850 Lemans I),

'76 850 Lemans I

but some of the power fiends in the Guzzi worlds had worked out how to twin plug the heads for high compression fun. It's pretty common to do it to those old engines. A very small Chain saw spark plug is used for the confined spaces.


For those of you not familiar, the Moto Guzzi engines are very similar in design to the BMW flat twin (old one) exept the cylinders are pulled up into a 90 V to gain ground clearance. Otherwise, its a 2 valve, pushrod, aircooled engine. (Heads are much better than the Type IVs though since they are basically Hemi's)



Has anyone had any luck with the TypeIV in applying twin plugs?

a thread started by me


and a picture.....I put the sockets in there to measure the angles.....another one of those projects for a rainy day

Type I, but close enough



with crankfire ignitions, it would be easier..........

Find a copy of the June 2001 VW Trends for a story on one arrangement I did.

We have seen gains, but they are heavily dependant upon chamber shapes and piston designs used in conjunction with the mods.

The Mighty Spyder will have them as well as another Super Hero coming up in the line up soon.

I already have the dual plug direct fire ignition arrangement that works very sweet.. It bolts right onto a TIV with upright cooling or with mods to a stock cooled engine. it took me months to work that part of the dual plug heads out.

On a hemi with a relatively wide included angle between the valves (like the Guzzi, or a 911, or the Alfa twincam four), you usually have to run a pretty tall central dome on the piston to get sufficient compression for really high performance, simply because the chamber in the head itself is so tall. On those engines, having only one plug is a real problem, as the flame path has to go up and over that dome. Having two plugs will make a big difference, and that's one reason the later 911s were all twin-plugged.

On the Type IV, however, with a relatively flat combustion chamber, and the stock pistons are dished or flat. Any dome for adding compression can be offset to one side a bit to make a wedge that forces mixture closer to the one plug. Thus, twin-plugging isn't going to be nearly so beneficial. I suppose if you're running really high compression, having a second plug simply because the chamber ends up being long and thin might help.

yes, but it's been done primarily for redundancy (aircraft...).
hemi heads (like 911's ...) are rather easier to do, and need it more, with high-compression domed pistons. there are a few people who've done it to 356 heads, which are more like T-IV's than 911 hemi heads, and those people have reported good results.

the T-IV combustion chamber doesn't really lend itself to it -- but of course that's changeable. the valve position kinda sucks for that. Chrysler has managed pushrod hemi's, but they have a bit more design flexibility.

If you want twin plug so bad, get a 964 motor?

QUOTE (Brando @ Aug 19 2005, 08:04 PM)

If you want twin plug so bad, get a 964 motor?

or a 547. bring money...