Engine math: I6 + I6 = V12?

I know that various people have created V motors simply by merging two inline motors. Two I4s bolted together make a flat-plane V8, and two I6s make a V12. If I remember correctly, the TVR Speed 12's powerplant is basically two Speed 6 engines. Sounds like simple math, but here's my question: how do you go about designing a double engine like that? How much of the design can actually remain unchanged? It is really advantageous to do this rather than starting from scratch?

BTW, what would you guys think about combining two RB26DETTs into a 5.2 liter V12? Personally, I like the idea of a perfectly balanced twin-turbo (quad is just crazy) monster that puts around 2000 hp to the wheels. You would need a clutch from hell, though...

probably need a driveshaft out of a bus, too.

There have been many examples of this kind of engineering in the past. The advantage is that the cylinder head, valve gear, pistons, rings, bearings would remain the same. A new crankcase must be made, where they share the same crankshaft.
While it would be a new design, the advantage is in manufacturing, If its based on combining two inline engines to make a V, then all the same in line machine tools can be used. As it costs many millions to design and set up all the manufacturing tooling, the savings are considerable.

yea i'v seen a Twin V8 in parallel where one engine would operate in reverse so the crankshaft gears would mesh together and that would be output to a transmission. Very awesome appearence with 16 headers pointing everywhere :)

I'v had this idea for a 12 cylinder engine not a V-12 or a L12, 2 L6 side by side with the flywheels that transfer power to a central fly to send power to the transmission, something you could also do is chance the ratios on the fly wheel for torque or top speed. so mabey top speed for the transmission and tortue for the acessories (ALT, AC, power steering, what ever).

Some benifits. shorter crankshafts, smaller diameter flywheels, mabey half engine operation if electric clutches where use on the flywheels.:uhoh:

A 750il is precisely that, two six cylinder engines connected to get a 12 cyl engine. It has two of everything, including two engine controllers, imagine the expense of replacing both at the same time.

I think the 750 was 2 V-6 engines connect in series through a unified crankshaft, what i was thinking of is a parallel design unified through a fly wheel connection.

Also how difficult would it be to get 1200 HP from 366ci 12 cylinder engine, on say pump gas?

A double inline 6 configuraton sounds much harder than two V6's. Just Turbo it and you can do any HP you want.