Here is a pic of the custom header I made myself, by modifying the golf cart header, just shorted it up, welded it all back up and using the same cheapy muffler, still loud as heck though. Debating a bigger quiet muffler. Quite a challenge basically doubling the power output in these buggies and the tuning needed to make it work, about the same as any other rig. If I had more time for it, I would put larger disc brakes and a power steering rack in it, with better shocks. But it does what we need it to, a little too fast at times, if the trails are a bit bumpy. Not as smooth as the Gator we goof around race with, but it has no problem passing an 800D on the straight and leaving them in our dust Always a riot in our pasture on burn nights lol
Just to note, we noticed an oil leak on the 670 on the flywheel side, the frame would get wet with oil. Upon inspection it was just the oil vapor breather tube came loose and was weeping oil. I thought maybe it blew a seal out since we run it around 4000-4500 rpm most of the time. That's the only issue I have had with the new engine.
It's doing great, far better than I expected even. I haven't really done anything to it for the past three months, except drive it. I was worried we would break the Predator engine, but it takes everything we can throw at it. The engine I replaced was a Robin/Subaru EH63. I am running the same CVTech powerbloc clutch, just with a slightly lighter spring , I believe it is the 400/700 spring. Had to go with a lighter spring as the extra torque of the 670 engine over revved (was annoying) a bit at wide open throttle, the lighter spring holds it around 4000-4500, vs 5000-5500 with the original spring. I put new plugs in it around 40 hours ago, and just change the oil. It runs really well now that the jetting is dialed in. I had to install a wide band O2 sensor to fine tune the Mikuni, but it's about as perfect as I can get it, running around 14.5:1 at cruise, and around 13.2:1 at full power. I have not put any other money into it, aside from a set of LED lights. The Kevlar drive belt has held up extremely well, even after attempting to smoke it by climbing some very steep terrain fully loaded on a 100+ degree day. If it has a weak link, I haven't found it yet lol