Carder

My boat has 496 HO's...using log-style manifolds mated to beautiful CMI custom exhaust that turns down at the water line. I have to believe the log manifolds are restricting exhaust flow, and with CMI boasting hp and performance gains, I am considering adding E tops in place of stock.
Hoping for: approx. 50 hp per engine, better crusing mileage, possibly more top end, but I am already on the rev limiters (5000) at 62 mph, with light fuel...
Has anybody did this upgrade? Is the boat too big to render any differences? Please let me know what you think...
Carder

38fountainecman

change drives to bravo 1's with four or five blade props and pick up 3-5 mph. I did.

pookie

I thought it came with Bravos.

TampaBeach

Most came with Bravo III counter rotating. Trust me you will not gain any performace by just changing the exhaust manifolds on a 496 HO, it will sound meaner, but that is eliminated because your exhaust is turned down out the back. Many OSO'ers have purchased headers for 496's and NONE were happy with their performance gains, a stock 496 just does not benefit form more exhaust flow.

fountain1fan

bravo 3 not bravo 1

mikebrls

save the money .. it's not a race boat it's a cruiser . but if spending around 10 k for 3 or 4 mph and now your at a wopping 65 mph if it's worth it to you then do it .

just do some research becuase the e.c. has down turn pipe's that sit under the water line at slow speed it may suck up water into the motor with header's on it " not sure "
i know the stock pipe have riser's that bring the angle of the pipes up wich i thought help's prevent reversion .

just my thought's not sure if im rite or not but it's worth checking into before you do any mod's

now if you realy wannt to gain some speed throw some whipple's and some xr's on the boat and i would bet you would be very close to 80mph top speed and cruise at 60

mike

Carder

Actually, its not the speed I'm concerned with, or I would have kept my Lightning... It's making the engine more efficient that I am focused on. If the risers are the restricting part in my othewise fuel-sipping set up, I want them out.
Carder
PS: have a friend with this boat and blowers and he has gone 83 to 85 with them.

38fountainecman

I think you are on to something. With better exhuast flow, increase pitch in props and gain mph at lower rpm? I seam to get 1.3 mph in the mid ranges with the stock set-up using my system view guages.

TampaBeach

Anything you do to a 496 other than keep off the throttle is not going to make any noticable difference in fuel consumption. I mean really were youthinking of spending 7-8K to try and get .001 of a mpg increase??????