Too bad about the budget, or you could do what I saw in Car and Driver a few (or ten or fifteen) years ago: They tested a Civic that somebody added another engine to the rear. Actually it was the front of another Civic grafted to the rear, so it had double the HP and 4 wheel drive. They said there was no interconnection other than the gas pedal worked both engines. You just put them both in drive and they shifted and downshifted at the same time. I guess it wasn't super fast because of the weight.