ask mike

511" 550 hp ????
 

I have 2 502's i'm building to 550 or so h.p.
a few things come to mind that i cant decide on.
1, rect or oval port heads ? everything i've ever learned about engines says oval port, i only plan on spinning it 5400,
but i have both oval and rect port so if rect why ?
2, single or dual plane intake ? again not turning a ton of rpm so why a large plenum single plane ? i see the 500hp's with them just cant understand why?
3, small carb just a bit more than the engine will need so it gets a good signal or go big as in use a 700 or a 1050 ?
700 would be more responsive with higher air speed through the venturis, i would think anything bigger the air would just stall in the intake due to a weak vacuum signal across the boosters.
again i'll use the 500 hp as an example an 800cfm holley with a 30 and 50 cc accelerator pump seem a bit excessive for that size engine but someone way smarter than me designed those beasts
Thanks in advance

mike who ? sick stinger ?

What are the oval ports your planning on using? If there 049's or 781's your most likely going to have to port them to get the power your after. When you figure that cost involved with that your most likely going to be better off buying a set of aftermarket heads. Or have Jim V put wedges in your rectangular ports to pick up velocity.

Intake I would run a good dual plane, either a Edelbrock RPM or Weiand Stealth.

Carb I hate to say it but there is no way your going to be able to use a 700 cfm carb just way to small. I'd do with a properly designed 800 or 850 holley.

781 heads, i've seen a few dyno sheets from 485 hp 468s that were only using 5?? change cfm as measured by the dyno datalogger. nascar engines make 800 on 500 cfm 2barrels, not arguing just points i've been taking into consideration. and i agree with the dual plane but why does merc use that big azz dart on 500s ?

You plan on spinning that bbc at 8000 rpm? NASCAR is not a good analogy :)

Take any info you've read in car magazines, throw it in the trash and burn it. Marine engines are a totally different animal. Just trying to help!

and i do appreciate any info, but horsepower is horsepower and cfm is cfm you need a certain amount of fuel and air to make a certain amount of horsepower. nascar motors make power at 8000 because there limited to 358 c.i., 511" will make same power at a lower rpm still need same air and fuel to make the power

Ok, go ahead with the 500CFM nascar carb. Will you be running a restrictor plate on long poker runs?

In all seriousness. Get a 750CFM, 830, 850, even a 1050 Dom. Do some dyno time at the same AFR and let us know what you find. Maybe the marine world has been doing wrong all along?

found my answer to the intake and carb question, cooler dense air is heavier than hot air, = more air in less space (space in this case would be carb venturi and intake plenum)
so in order to make that much power in a hot low airflow engine compartment/bilge of a boat you need a greater volume of air available into the engine.