glen george

iTrader: (1)

Has anyone had any problems not getting enough air into the engine compartment over 5000 rpm? I have the aftermarket vents on the side of my 253 and the openings besides the rear seats. I plan to run the boat at WOT this spring with the engine lid rasied up a few inches to see if any rpm/mph changes. I have been running around 5300 rpm at 75 mph a thinking something has been holding my boat back over these years with many major changes have seen little improvement.

Commander112

It looks like you may not be getting a whole lot of air with those vents. You may want to consider changing them to ones that would direct airflow into engine compartment. They're not pretty, but something like this http://www.cpperformance.com/detail.aspx?ID=5975 You could always get them powder coated to match the boat.

Additionally, do you have vents above the transom? I can't tell in your pic b/c cover is hanging down over back. Obviously airflow will drastically increase if you can get it to flow in and out.

glen george

iTrader: (1)

No other vents except the ones besides the rear seats, i have never been able to hit close to 6000 rpm no matter which prop, heads, cam, OVERTRIMED, After another oso member wondered about my air flow and i got to THINKING. I used to get a black transom on my holley 800 and the BG 850, no im running a hp1000 alot cleaner rear transom but my speeds never increased much, now im thinking that may be why it was running rich at wot with a dirty transom, when i installed the -2 imco shorty i was hoping to pick up the speed but was also disapionted. I know on race cars at speed some engine comparts suck out air rather that increasing it if not set up right. I was just looking at a few billet vent covers to add behind the rear grab handles that i have seen on other boats. My wonderful wife will not approve of another boat so i will keep updating thi$ one. I need to see 80 mph gps.

HiPerf2000

iTrader: (2)

I had a 97 253 with a 575hp b&m setup. I tested running with the hatch opened up a couple inches and saw no noticable gain on the tack or gps. The only think I noticed was the stress cracks it cause around the hinges from running with the hatch up.

I would try a couple vents above the transom. maybe they will fit under your 2 grab rails.

Vinny P

I too have messed around with leaving the hatch open a bit. I noticed no change in speed or rpm. I feel the concern is not that the engine compartment is restrictive to air flow, but rather all the heat, the engine generates, is heating up the air the engine breathes. In my opinion, the best solution to controlling the heat and air flow is the addition of a scoop. I thought about it for a while, but decided against it. I didnt want to mess up my upholstery on the hatch.

RJBBC

I agree transom vents are a good idea. We just purchased some a few months ago from Eddie Marine. The have transom vents that mount underneath your grab handles. The mounting bolts screw into your handles for a nice clean look. I will post some pictures as soon when we get the boat back.

glen george

iTrader: (1)

I just bought a used 1 1/2 bravo spacer to test from another oso member and a 26p hydromotive without the defuser ring . I ran 76 right befor i installed the -2 imco lower but the whole boat ride and tracking improved, but i never gained the 2-3 mph i was expecting. I will install grab handel vents and maybey different side vents in the spring. I have a hp 1000 carb might be a little big, but my transom is alot cleaner than before with the 800 holley or the 850 BG. I may look for another holly to try this spring. Speed is and on going improvement thing. I was thinking about lighting up the interior, removing the cabinets ect, redoing it with new vinyl just the basics. I see for sale a 01 pantera 28 with 650 hp only seeing 72 gps, I wonder sometimes if 80 is out of reach with my hull. I keep looking at used 28-32 ft boats, cig bullet, 28 pantera, 283 with the race faring and 29-32 fountains. Buying a boat is alot easier that selling one. I have so much invested in this one, I tryed to sell last year when i had (sucessful) colon cancer sugery for aroung $30,000 with only a few intrested emails.

RJBBC

I am fairly confident I know how to get your setup to 80mph plus. 5 pounds of forced air induction! Put a Blowershop 250 between your 1000 carb and new intake manifold set at 5 pounds of boost and 80mph is yours. If I had the cojones that is what I would do with ours.
Merry Christmas

glen george

iTrader: (1)

If fuel will stay at below $2 i would install a whipple+ XR upper. I order last night new exhaust tips. I plan to run with out the IMCO mufflers this spring. I needed a set with the 12 degree flange, were on sale on OSO vender x-mas special, $119. I bought this boat for $28,000 with the factroy windshild in 2004, I have replaced updated or changed everything from the key switch to the race faring. Lucky me.

Commander112

Glen,

RJBBC may have your answer. I owned a 1996 Checkmate Convincor 242 with a 454/350hp Bravo I set up. I went thru several engine mods during the course of ownership, but the very first one started with nothing more than some minor head work, cam, a weiland 177 supercharger and single Holley 950hp carb. If you ran only 5lbs of boost you wouldn't have to do any engine mods to your current set up (though inconel exhaust valves would be a good idea). My motor dyno'd right at 580hp and the boat ran 79.8 mph on the gps (probably could have broke the 80mph bearer with prop testing). And remember mine was only a 454. The torque of a blower motor really makes a big difference over carb'd. And the best part was that I actually got better fuel mileage b/c the motor was more efficient. Just a thought......