OK so im a little late at this thread.. seems an interesting project.
Let me share my few bits of knowledge... so u have mentioned that u want to instal a heavy bike engine... dear that won't b a wise thing to do!
You have to understand difference between torque and horse power...
Or in simple terms power and speed respectively.... the heavy bikes engines, no matter u put a inline 4, or a single cylinder are made for producing more speed or break horse powers....
They produce power, but at a very high rpm...
However you don't exactly need a speedy engine for ur poor buggy! The poor thing would disintegrate into piece if u take it to top speeds...
Hence what you need to look for is a torque-y engine! That is an engine which produced lots of power at low rpms...
A high newton meter of torque producing engine... that is more likely to come off a cruiser bike, a chopper bike or a dirt bike...
With 4 people on a buggy, even ur 400cc heavy bike engine would struggle as it produces too low torque at low rpms...
I guess I've explained it adequately, hope u get it.... u dont need speed, u need power. A 250cc 4stroke dirt bike engine would be the best fit.
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