hi guys ive posted before about my 2007 27 with 496 mag ho ive fitted cmi sport tubes and they seem to have made no diference in performance just improve mid range still only once with very low fuel on my own 71 on gps l/h 26 bravo 1 that was before sport tubes now it will only doo 69 50lts fuel 2 people at 5300 tried 28 l/h b1 and 69 at 5000 5o lts and 2 people please has any body got any ideas wipple charger or sell it and buy my mates 29 with 600 sci or cam it or what realy like the boat but want it a litle faster

You might be limited with the 496 HO as it is not prepped for a blower with out replacing with forged internals. The most econimical route may be to put a Raylar BCK-103 kit on it and combined with the CMI's you should be somewhere around 550HP. That should be good for 8-12MPH with some prop testing. Don't quote me on the price but I think the kit is around $6K and with install and prop it should be around $8K.

Humm,, Headers are nice and sound great, but by themselves they don't really increase HP. To my understanding, they help cool and increase air flow, but if the motor doesn't need it (in the case of a 496) you will not see any real gains.

Imagine a 750hp Blower motor, not havine headers, and then putting them on, that is where you see a big difference, that motor benefits greatly, because it needs the extra cooling and air flow.

My suggestion to you would be to either go with Raylar 550 kit, or Whipple. Actually depending on your budget, if you have the money I would pull the 496 (store it) and put a motor like this in
http://www.offshoreonly.com/classifi...o27558-en.html

That 27 will be SCREAMING

Well as long as your gonna go all the way... Why not this motor?


http://stlouis.craigslist.org/pts/1020772332.html

Better plan on another 10K or so for a drive and gimbal, too. The 496HO package has a standard gimbal and standard B1 drive. Also, you would probably want to install a Gill or some other race mount for the engine, while its out because the 496HO package also uses the standard individual Mercury rubber pedestal mounts.

If you end up with a 76-78 mph boat, I think you will be really disappointed because that is the speed range where the 27 seems to want to chine walk pretty hard. You either need enough power to get beyond that, or just leave it alone and keep it in the low 70's, from what I have seen. I had a 27 with a stock Merc 500HP, and it was fun, but top speed was 76 mph, and the boat was just starting to be a handful at that speed - you had to back out of it, or drag the tabs a little and scrub some speed. A couple of other friends had the same boats with B&M 250's on top of HP 500's with mild boost, and theirs were really a handful, as they topped out around 78-79 mph. Another friend has one running 9 lbs of boost, and that boat runs 82-83 mph, and is rather stable, at that speed. You could see in Jim V's video, that he posted on here, that he went through a range where the boat chine walked, too, on its way to ~100 mph. Just my opinion, for whatever its worth.

I have a '97 with 454 mag. and vortech charger (3# boost) EMI thunder exhaust runs solid 75 seen 78 and yes that is as fast as that boat really needs to go.

OBTW that boat is for sale look in the classifieds.

thanks very much 4 the info guys i may be tempted to leave her alone have never liked chine walk and if i was to spend a load of money and it made it hard work to go quickly ide be realy pissed but thanks again

BTW, you mention your friend has a 29 w 600sci, that is a BAD AZZ set up, you could easily up the boost and get more performance with that set up.

WILL