Kaama,
i think we we are comparing apples to oranges. your motor and DanB's are really different. if you take the same motor with everything being the same including the lift/ duration and only changing the LSA of the cam, the engine breathing, idle, and power range will be different. plus your talking about, crank stroke, rod ratios, different piston pin heights, pistons, head gaskets, heads, ported and unported, runner volume, chamber volume, quench area, valve sizes, heads, intake manifolds, compression and carbs. then the variables that you didn't mention were valve lift, lifter type (bleed rates?), air cleaner, and the size and length primary and runner of the exhaust used on the dyno. they weren't even the same dyno.
years ago, a dual plane was much better for low end and a single plane was much better for top end. modern intake designs have bridged the gap slightly with better flowing high rpm dual planes and single planes with better low torque. if you get a chance to change intakes alone on a motor on a dyno, you may be surprised at 3500 rpm's. my own feeling is a dual plane with a notched divider is the best of both worlds for almost any marine engine for pleasure use.

Excal, does the stock mercruiser alum dual plane intake fit your description of a notched divider intake? If not, what is that?

BT

BT,
the notched divider starts life as regular old dual plane intake but it's modified with a die grinder to notch out the divider under the carb a little. notching the divider helps the higher RPM breathing for more HP and won't hurt the very low end torque as much as an open plenum would.

excaleagle, Sure, all parts make a contribution to the power of an engine and I think most will agree that the heads and cam of an engine pretty much determine the major power source of an engine. The cam comparisons are practically identical---mine were Ultradyne Cams which even have more aggresive ramp speeds, my heads even flow better than his. The comparison of our engine components are pretty close and yet his engine wasn't built up as much as mine and he STILL beat me in the mid range torque curve area! The point I am trying to make is, a 540 should probably make more torque over a 509 around 3500rpm---right? I mean, lets face it; with NEAR COMPARABLE PARTS a 540 should beat a 509 down low.---and I am sure I would have if I was using a dual plane intake! I thought it was pretty much common knowlege that bigger cubed engines make more power down low, and with my 540 vs his 509 I should have had the advantage over him with bigger cubes and better flowing heads---but I didn't! I really believe it is because of his dual plane intake vs my Dart single plane. On the dyno, both engines used tubular dyno headers. Do you not think my 540 should have had MORE torque at 3500rpm than his 509? But instead it's just the opposite---not even close! BUT, if I had a dual plane intake on my 540 vs the Dart single plane, I am quite sure I would have at least turned that 37ft pound figure around to my advantage at 3500rpm or there about.

With all components remaining the same, let's say (for arguement) my 540 and his 509 make the same amount of torque at 3500rpm. And if I removed the Dart single plane intake from my 540 and swapped it with a dual plane intake you don't think I would see much more than 5ftlbs of torque difference @3500rpm? Well, I guess I am truely getting older and getting BEHIND the times or something. Perhaps the dyno comparison with my 540 vs his 509 isn't a fair one. I don't have a dyno, but boy I would sincerely like to see a back to back comparison on a dyno with an intake manifold swap from a single to a dual plane!

My boat is a 32'A/T with the 540's in it. Because my HP to weight ratio, I can get away with a single plane because torque isn't quite as crittical for me. I guess I was just really impressed with his 620ftlbs figure @3400rpm vs my 625ftlbs @4500rpm. And I know there are a lot of other variables that you have mentioned, but SOMETHING in his 509 was making a lot more torque than my 540, but perhaps you are correct.

Excal, that divider notching sounds good. I haven't installed my intakes yet and am looking for jobs this weekend. My intakes are stock alum dual planes off 502s. Can you describe how to make this change? I'm getting good on the die grinder as I just finished up the bore notching last weekend.

BT

BT,
just grind out one inch down along the entire divider that separates the odd bank of cylinders to the even bank.

.

Thanks excal, sounds simple enough. I'll give it a try.

BT

bt, sounds like you're begining to like anything with the word "notch" or "notched" in it.

he can add another NOTCH to his belt.

Yes, notching is good. I believe I am running out of things to notch though. Really I am turning into a die grinder junky. Ain't much you can't do with one of those little buggers.

BT