2 identical boats one with twin 496 ho's one with 500efi's the 496 boat does 75mph gps and the 500 efi does 80mph gps . with the new cmi exhaust for the 496 engines claiming 55hp per side , would it be possible to hit the 80 mph mark with exhaust and proping ? seems like the formula is 20hp per 1 mile per hr ?

You can try it but I don't buy the 55hp increase i the sport tubes. Maybe about 12hp increase, but they sound allot better.

WILL

Try the Sport Tubes on the 500 efi's.

An increase?
likely some increase.
5 MPH Increase?
NO WAY!!!!

No 5mph, but yes about 1 mph per 20HP.

Somebody will chime in but there are poeple claiming some pretty substantial gains from the sport tubes. It's pretty incredible that the hp500 is rated for 475 hp and the 496 with the sport tubes will have as much if not more hp. Sounds like a great porduct if it performs up to those claims.

Depends on the size, weight and efficiency of the hull. I picked up 1mph per 10 hp on my last boat. I have found this to be pretty accurate:

Speed Calculator

A 500efi is rated at 470 pshp.

A 496 HO is rated at 425 pshp. If claims are true, the sport tubes add 55hp, bringing the the 496 HO to 480 hp.

I don't see any reason that the 496 Ho with sport tubes shouldn't perform equally as strong as the 500efi if CMI stands behind their claims.

So to answer the original question, yes it should add at least 5 mph by adding the sport tubes. I would hope so for $7200 plus installation.

Agreed!

I added 300 hp and got 10mph.....