Anybody runnin this type of motor have any input?
Just in process of assembly and want to know if I want it set up as
A twin plug. Please help with your experience.

Like a pair of HD heads you can do it at home with a hand drill,carefully.
You can run a leaner mixture,Webers I presume.

https://www.youtube.com/watch?v=DTfwwbsRopM

How much does a FAT 2.6 run? What's your plan for an exhaust system?

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http://cylinderheadshop.com/services/harle...lug-conversion/
all kidding aside,twin plug set-ups have been used on a/c engines for redundant ignition safety(magnetos have failed)since forever.High crowned pistons like the HD and Porsche(and Chrysler/DesSoto Hemis) physically inhibit the flamefront of the mixture burn.Placing an extra plug opposite the first allows the burn to start in 2 places,a more complete,leaner mixture.
More power,so all good,other than the hassle of machining the heads the correct way.
And yes,it has been done by hand,really.
Bring your heads to a flat6 machine shop,race shop to ensure it's done right and check the guides and seat retention.Overheated heads can and will drop the seats,they're aircooled afterall and exhibit a thermal momentum(hysteresis).
Drilling,clearancing and tapping for a set of smaller plugs has been done too.
Running separate advance curves on each set has worked as well.
Yes 2 distributors or a crank triggered ecu.

The rule of thumb I have heard for 911 engines is that it allows a full point more compression on the same fuel. Your mileage may vary.

--DD

Heads are set up already, distributor is set up for 8 plugs, just want to
Know if this is a good combination to run on the street?
Any potential problems that can be avoided like overheating?

May be some confusion, this a type 4, 4 cylinder 2.6 with twin
plug heads. Exhaust will be built to suit space

I suppose the extra plug on a "wedge" head does no harm other than a hot spot.
The same 2 points of ignition holds true,although to a smaller effect,if any.
Back to back testing to determine advantage would show degree.
The squish is what you want to maximize(minimal piston/head clearance).It's a big 4,it will run hot when under load,keep it cool,control mixture,add more oil+cooling capacity.

If you think outside the box and are willing to go the extra mile, there are no cons to a twin plug T4.

All the standard ignition and tuning specifications you'll run across are out the window once the second plug adds another flame front. This can be a con, if you like things that are straight forward and "normal".

All of my engines that use a 100mm or larger bore get twin plugs (below this bore size efficiency from two flame fronts wasn't beneficial enough). I've never experienced a twin plug T4 that optimized with more than 22* full advance and often they'll like to run fully retarded initially with a very slow advance curve.

The engines will set up much leaner than most, most of mine run 11.5:1 or as much as 12.3:1 CR on pump gas and love it. Instead of a 12.5:1 Air/ fuel ratio being optimum, I usually find that twin plugs with my combinations will like 13.3-13.7:1 AFR to make peak BSFC and power/ cooling.

With all the details and variables mattering so much, I'd pick up the phone and call FAT and ask them. I have never seen a FAT twin plug engine, so I don't know what theory they build them from.

The twin plugs and two flame fronts change everything, in every way. My record is 284HP from a 2.9L T4 on 93 octane pump gas using twin plugs. That engine took 3 days on the dyno to optimize, because it had to tell me what it wanted and I had to listen. That one wanted less than 20* of full advance, which is less than I have ever experienced before.

Also, the ignition system matters a lot. I have staggered the advance/ retard between the upper and lower plugs and that makes a difference just like firing the plugs simultaneously sometimes matters. The real differences from this stand point comes from camber shape and volume, especially toward the bottom of the chamber where things are more inefficient by design.

What ignition system does it run? These are fun to tune, fun to own and are few and far between :-)
The gains in efficiency can be huge, once you acquire the magical tune and internal combinations.

3 liter twin plug street engine in the back of my Wife's 79 beetle cabriolet back in 2006. Made 249HP @ 5,500 RPM and 255 lb/ft of torque @ 3,000 RPM. Averaged 32 MPG (even with 51.5mm IDA carbs!) with head temps less than 300 degrees.

Aside from FAT, there is also Willhoit in California that builds twin plug 356 motors who may have shard some of his knowledge online in the 356 registry forum...

Just another place to search for the theories....

I've built about 15 356 based twin plug engines over the years. The combustion chambers being a compact wedge Vs hemi really change the characteristics and the tuning between the two engines.

Several of the 356 engines I built with twin plugs liked cylinder pressures so high that the head studs would stretch and the engine would keep making power. Thats not the case with the T4, I hit a max cylinder pressure much lower and ended up needing to run much more cam to bleed it away, or at least seriously opening up the lobe separation. Doing this really unlocked the doors to efficiency, though... I tried the same thing with a twin plug T1 and it wouldn't work.

The first T4 twin plug I built was a huge disappointment because I tried to build it in the same manner than I had designed a twin plug 356 engine from successfully.

One of my 356 twin plug engines holds several Land Speed Records, its only 1500cc and made just under 200HP, turning over 9,000 RPM. It only took a month on the dyno to optimize it, so many pulls that I had to freshen it up before I shipped it out.

Wow,that's a tremendous achievement.
Years of experimentation.