I have a 1999 28' Checkmate Convincor with twin 454 EFI Mags. Engines are currently getting checked out and dyno-tuned and I'm considering bolting on some black EMI Thunder exhaust manifolds and risers (I have Corsa Quick-n-Quiet switchable exhaust and it has to be compatible). I don't want to mod the engines much if at all, but a little more bolt-on power and less weight would be nice as the boat is obviously a little stern-heavy with this set-up.

Just wondering what gains I can expect in power and speed with this set-up. If anyone has any experience or knowledge, I'd appreciate it.

Thanks!

The most you will see is maybe 1-2 mph and that is probably more due to the weight savings.

I agree, maybe a 20hp increase if anything at all.

However, the dry joint is piece of mind over the stock wet joint you have now, plus the water dump will occur futher away from your engine which is also a plus.

Future mods with any kind of performance cam will not be possible with your stock exhaust.

The after market exhaust also has a decent resale value, you can pull it off before you sell your boat, re-sell or use on your next ride

I installed a set of EMI Thunder exhaust on a Nordic Viking with a 330HP 454. The gain was 1-2 MPH. I installed the same exhaust on a Nordic Rage with a 454 MPI 385HP and saw no gain without a computer re-calibration.