I Have a 16hp SC longtail with a 8x4 fairly new prop on it. Its on 1436 hull and will do 16 with two people in it. However my tiny tach says I only turn 3300 rpm at WOT. I realize this is close to 3600 and I get fairly decent speeds with a longtail, but any more speed I could get would be great. So if I were to add an aftermarket air filter or exhaust would this help up my rpms? BTW I hooked the throttle to the governor arm so thats not an issue......

IF you tweaked the throttle you should have been able to get it closer to 4000-4200 rpm out of the water. That might translate into another 2 mph...as you know with these longtails and no gear reduction, you get to a point of diminishing returns no matter how many rpms you spin. Those after market exhausts are a lot of money for only incremental gains. Don't know what kind of hull you hav, but I invested in some steelflex (fasco) for the bottom and though that did not get me any speed gains, it did reduce friction considerably for runnning thorugh mud and veggies, as well made it way easier to trailer/untrailer the boat- make sure to keep it hooked when easing back or it will slide off! If you don't have a backup prop, that would be a good investment and a different pitched/cupped prop (a matter of trial and error since we don't all live in the same elevation and run in the same aquaterrain) might get you that extra 1-2 mph for less than $200. Good scouting!

Yeah I have coated the bottom of the boat with steelflex when I rebuilt the boat. But I can turn 4600+ RPMs out of the water I Just cant seem to get the prop up past 3300 rpms

My first mud rig was a 1436 jon with an 18 HP GD longtail. I toyed around with a 3 bladed prop that GD had at the time which was fine in open water but really bogged down in the weeds. I did not have a GPS then, it was important to have the weight/load balanced and the cavitation plate adjusted. Is the 3300 rpm with two hunters in the boat? Since you stated the prop is fairly new, the type of pitch and cup on it could be a factor, don't know what the mfg. offers. You might contact them and get some input.

The problem is the cylinder..... its too small!

Stock you more than likley can't squeeze any more out of it.
I know I can run like hell in shorts and runnin shoes... but with waders, a gun, a few decoys, and a blind bag I can't run as fast. Thats just my anology on oow vs in water.

23 hp briggs new online is 1300. should bolt up.

problem solved.

$1300?!? Hell.. I could build another 16hp longtail and rig up duals for less lol