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shockwaveharry
10-24-2001, 01:10 PM
I can't decide between building a roots blown 509 or a an unblown 540. On paper, with what I already have, there is no real cost difference between the two (if no intercooler for the blown motor). I'm targeting 600-650 HP. It'll be going in a 21' v-bottom in front of a Bravo 1. Any advice?

rivercrazy
10-24-2001, 01:26 PM
If it was me, I'd go with the 540. Less chances for problems. The wrong fuel, fuel pressure, timing, etc will increase the chances for a blower motor melt down. A blower motor will also necessitate some changes to your boats interior. The 540 will probably fit without too much fanfare.
Better upgrade that Bravo 1 or you might turn the insides to bits.
Is that 21 the step skier? A stock 502 mag 415hp turns it close to 80 already. Hang on tight with that much HP.

superdave013
10-24-2001, 02:14 PM
My Valasco stroker crank cost more than a new 8-71. I bet you could get a used blower, intake and pullies for less than a new stroker crank and rods.

shockwaveharry
10-24-2001, 03:18 PM
It's the 21 Lexis, no step on the bottom. With the 496 MAG HO I regularly see 76 on the GPS. I'm looking for for a real 90 MPH without being too loose. I think another 200 HP will get me there. Since I'm only looking for short bursts of speed on the River (no poker run shit) I wont be buying a $2500 crankshaft. I'll deal with the drive when it breaks.

rivercrazy
10-24-2001, 03:48 PM
Sounds like a real thrill ride. I always liked the euro look of the Lexis. That's a nice boat.

boatnam2
10-24-2001, 04:37 PM
go with the 540 for sure if your only looking at 600hp.im getting a 509 unblown it dyno's at 620hp.

shockwaveharry
10-24-2001, 04:46 PM
At what RPM are you making that number? I'm looking for max power at no more than 5500 RPM. If I can do it with a 509 I'll be VERY happy. http://free.***boat.net/ubb/biggrin.gif
[This message has been edited by shockwaveharry (edited October 24, 2001).]

boatnam2
10-24-2001, 05:01 PM
shockwaveharry,i dont know all the numbers yet.the motor is not in the boat yet.it is the teague 620 hp mated to a imco extreme drive.if your going to be happy with 600 hp leave the blower alone, but if your going to want more power later then the blower is the way to go.blower's are hard on the parts.plus in a 21 ft boat like your's the blower will have to stick thru the hatch,and i dont think a scoop looks good on a 21ft'r so you will have to be really careful as not to get water in the carb's.

BLOWNDRAGBOAT
10-31-2001, 08:47 AM
Sounds like your trying to get off as cheap as possible. Most of the people here that no me are gonna faint when I say this but, if all your looking for is 600-650hp, stick with a natuarlly apsirated motor. A 540 is pretty easy to build on pump gas and get where you need to be. Don't get me wrong, I LOVE blower motors but they aren't for everyone. Also, your getting right on the verge of what a bravo can handle in stock form. Keep it simple and as hastle free as possible. A 9.5:1 540 should get you high 80's to low 90's and run on pump gas. If you want that occational kick in the ass, a small shot(150-200) of nitrous will be all you need. Use the nitrous when your running a guy thats pretty even of slightly better(faster than you) and it won't be to much for the drive to handle if you use it on the top end. You will also need to increase your prop size and possibly change your gear ratio to take full advantage of the additional torque. I think you SHOULD be able to turn a 28-30 pitch prop with that much motor and a 1:50 ratio.

rivercrazy
10-31-2001, 09:23 AM
When its done, I wanna ride! That will be one heck of a v bottom rocket!

shockwaveharry
11-01-2001, 10:40 AM
Me? Cheap? OK, you got me. I'm gunna build the 540. I think in the end it's the best decision. Keeping it simple, keeping it real (you out there Daytonajeff?). Winter is short around here so I'm getting to work on it right away. Rivercrazy gets first ride. Thanks for the advise BDB.