that second graph was misleading as it was showing the victor jr making more hp from 3900 and took a while for the air gap to catch up....I think they crossed the intakes there..made no sense...any way my basicly stock 509 with the factory alum intake, wonder what i would see by changing the intake ?? thansk Rob

Nthing more than likey are you running a stock carb if so that's the frist thing I would change.

no, actually running a 750 DP, have a flowed 850 that I'm going to try next season...just put this engine in at the very end of the season, only have about 2-3 hours on it...have few things to try next season, just wondering about the intake so I could look over the winter...Rob

what I seen in other threads.... I seen guys have good luck with the stock merc alum high rise manifold that's why... I think you will not see much if you change out to the air gap think the only things you might see is a cooler air charge due to the runners are out of the oil maybe some hp possible it's like fliping a coin is worth 10 hp for 265 dollars for a new intake what are you running for a flame arrestor I'm running a 14" dia 4" height filter from k&n it is a marine flame arrestor if you are running the small merc arrestor that is a big problem. Have you tuned the carb to the engine can you read air fuel ratio or a exhaust temp. what camshaft are you running are you running the stock exhaust manifolds ?Tell me more about your engine spec's

http://www.knfilters.com/marine/boats.htm

running the tall K&N velocity stack w/5" filter on top, breathing thru a open scoop(am going to seal that off so breathes only outside air) engine is a fresh 509 stock roller cam w/1.7 roller rockers, full custom marine headers, just got the boat running after pulling my bower motor, boat ran over 80 with no tune time and handling was a big issue(no ext steering) so I pulled that engine, also running a 1" spacer under the carb, Thanks Rob

That's kinda a small filter element you might be a the max air flow the best gain for you at this point in time would be to replace the camshaft and springs and a good set of 10 degree locks and retainers I'm running a ultradyne bullet racing cams 228/236 @ 50 .601 int/exh lift 280/288 with the stock rollers lifers and gm roller rockers and eddie marine exhaust with stainless risers with my setup is a good 580 hp + 5000 rpm

thats 5" tall, it's the biggest velocity stack one that K&N makes, I could use it because I already had the room from the blower that I ran before... not looking at changing the cam anytime soon, just tuning on what I have...thanks for all the help..Rob

The stock cam is like a broom stick that's where you would gain alot of good power if changed it..

I would change the flame arrestor to a gaffrig,, the K&N are not made for a boat ,,,because they actually cloog up ,,,there is no dust on the water,,,they will take all the grease ,oil and belt wear and cloog the airflow.
tests proof that they are better then stock for about an hour of running time then they are worse then stock.
The only thing the flame arrestor should do is keep little kids out and keep the flames in when backfire.

Gaffrig gives u alot more airflow.

Thanks for the input on the flame arrester, but I don't think so...when I had the blower motor in this year, I had a eddie marine unit on, would not make any boost..none at all...called weiand and they told me to pull off the arrester, I was not believing but ?? removed it, made 4 psi no problem, took my 10+ year old K&N's off my gibson, have not been cleaned in years..still looked ok...tried one of them..3.5 psi boost, so not believing they are that bad...sorry..just what I found in my own testing...Rob