I've thought about this approach in the past only to of course find out others have already done this to a degree.
I think your configuration as explained, in my mind, would be you would have a multi-engine car. Now if you made a common crankcase, machined one up, that held the 4 cranks and the 4 barrells and they were tied together within the common crankcase, via a chain primary drive or a gear primary drive, similiar to an Aerial Square Four with an output shaft you would have built a single engine. I considered this for two 750's for the 1500 class or say two 'busas for the 3 liter class, but determined it was probably way past my machining skills
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The common approach as been to use the cylinders, heads off of say two 'busas (this has been done and there is a link on one of the other threads) and make a new crank and crankshaft and end up with a V-8. This I would for sure qualify as a single motor and is way, way past my machining skills.
The simple approach to your problem is called a turbo, but of course that moves you to a different class
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c ya,
Sum