B&m 250 or alum heads?
 

I'm almost done with ordering all my parts for my 509 build. Only thing left is a single plane intake and cam/springs from marine kinetics. The goal was 600hp or as close as I could get. My build is as follows:

Starting with gen 6 block (came in the boat 98' model)
4.500 wiseco 3.8cc small dome pistons
Gm steel crank
Dimple rods with arp bolts
Link bar roller lifters for custom cam
Chromoly pushrods
Roller rockers
088 heads - about to install 2.25 intake valves, blown blending, gasket matching and short radius work
Holley 850 carb

Planning on a dart single plane intake and getting bob to do a custom cam.

Sitting here I'm thinking I may add one more wrench into the mix, but would like opinions.

I have been considering a set of afr heads to go with my build, but I can also pickup a b&m 250 for similar money.

If I were to add one which one would you guys recommend.

The boat is a 98 280 velocity. I have a 1/2 fuel system so the fuel issue should be ok. I have a problem with always wanting more and I haven't even driven the boat since I bought it.


Thanks

I love AFR's, I have 2 sets but your not going tp buy them for what you can buy a 250 blower for. Trust me on thaT.

Tough call. Id get the alum AFR heads, then add the blower later, if you get the itch for more. When and if you do, skip the 250 and go with at least a 420, or 871. Really not much more money. See how you like it N/A though first. You might be happy with it.

I agree the afr's would be more expensive. I've always wanted a blown bbc, but never had one in all the cars I've built. Only thing that worries me is reliability. Apparently, it can be done as this site has shown me many people running them for hundreds of hours. I don't feel I'm hard on my last boat, mainly fast cruising with some 30 second to a minute or two wot bursts. What kind of power could be had with 5 psi? If I get 575-600 n/a out of this build I would assume 650ish with the afr heads.

My motors have pretty much the same bottom ends yours has and stock 500HP heads with roller rockers. With 250 blowers I got 689 and 678 on the dyno at 5 psi. I think it's always better to be blown. :lolhit:

Stroked , injected and blown , it don't git no better than that . :evilb: :lolhit: :thankyouthankyou:

How is the reliability with a blower? Would my 850 Holley work with the setup?

Ive been running various blowers for about 6 seasons now. I haven't had one issue blower related. The engines, start great, idle great, power is awesome.

Reason people are leary of blowers is because they always heard thru a friend about meltdowns. The 100% most important thing with any supercharger, is the tune. If the tune is off, yes, it will destroy parts.

As for your 850 carb, it will be enough if you purchase one more to put next to it. 700HP is a stretch with a single 850 on top of a roots.

Heres a link to my budget builds. 800HP 468's.

http://www.offshoreonly.com/forums/d...oed-today.html

I haven't had any reliabilty problems but then I don't have a lot of time on them yet either, so I can't really comment on that. My carbs are 850's but they have to be set up properly for blower use since you are sucking air through them.
Oh and don't forget about blower whine!! There's nothing like the sound of a blown motor. The 250's won't lope like the 6-71's but the whine is still there!! Ear candy!!

Last year my father and I built a 509 from a gen 6 block we decided to go with the Dart 308cc Iron Eagle heads, with the SRP mini dome pistons, a quick fuel 950, and the dart single plane intake. We made 601 horsepower on the dyno. It made 601 @ 5600 rpm. The motor went in a 1989 Sea Ray Pachanga 22 and we ran 85.6mph and was not satisfied... so we have replaced the dart single plane intake with a Pro-filer Sniper Jr. Intake and have switched heads to Edelbrock Performer Marine aluminum heads. The motor is going on the dyno this week I hope, but if your interested i'll share the new dyno numbers to give you and idea on what you want to do. If you want to know more deals about my motor since its similar to your feel free to ask.