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.

550 HP should be easy. Just went through the same thing.

- Stainless Marine Manifolds (these were already on the boat)
- Rectangle heads with stock valve size and a valve job (matched to intake NOT ported) with Performer RPM intake and 850 Holley 80330 vacuum secondaries, one jet size down on secondaries
- Converted Gen V 502 Block to roller, honed only not bored -- Bob Madera (RMBuilder) Custom Cam
- Stock JE700 pistons with new rings, stock rods.
- 9.25:1 compression up from 8.75 (.010 off the block and .010 off the heads)
- 1.7:1 Scorpion Roller Rockers

539HP and 562TQ full dress with wet exhaust. Peak power was ~5100

I am sure I left some power on the table -- I specifically told Bob this was a family boat and drive-ability and good idle characteristics were the priority -- he is the man and should be your FIRST phone call, he was EXTREMELY willing to work with me to get the RIGHT combination. He is the cam guru but will help you through the whole process.

I fought this a bit when I almost went with a stock hydraulic flat tappet and I am SOOOoooo glad I talked to him. If you already have a roller motor it won't even be that much more expensive.

http://www.marinekineticsonline.com/

yes my motors are rollers

They know something about carburetors:

http://www.holley.com/applications/C...bSelection.asp

wow crazy according to there calculator an 8200 rpm 358 and a 5400 rpm 511 both require an 850.......... must be something to that air/fuel/hp relation.
brivander thank you for the info on your motor, that is the type of helpful info i was looking for

With premium gas, you have a little hotter cam and a little more compression, 575+ horsepower should be a no-brainer.
Good Luck!

thanks! let ya know how it makes out gonna be a little while prob wont finish them until march or april

Bob designed my 439 C.I. BBC and I would strongly urge you to use him for your cam set up at the minimum, you will learn a lot from him. My little engine made 525 hp and he had ProSystems design the carb for it. It was a holley HP 950 with a 750 base plate. Flowed at 830 CFM. If I were you and if your going to buy a new carb have Patrick at Pro Systems build your carb. It will be built for your engine and its roughly the same price as a carb from Summit. Good luck with your build!

Sounds like a pretty cool package, post some specs, I'm curious. Compression etc.?

I can idle at 675rpm, IN gear...but like I said, I use this boat for a LOT of family activities so I needed something a little tamer, just a glance at the specs and you wouldn't believe the amount of lift he uses and have it run so tame. He knows his stuff. Bob is no joke, he's the man.

According to that Holley link, a mildly modified 454 (mild perf cam, stock heads, etc) turning 5100 rpm max (ie, a 454 MAG) should have a 650 cfm carb. Even Merc didn't go that small, the stocker was rated 750 cfm.

I ran my 590HP 468's through Holley's calculator and it said anywhere from their 850cfm to a 1050cfm Dominator. That narrowed it down. LOL

Guys this isn't rocket science, all they are doing is comparing the CFM flowing through the motor @ a specific RPM and suggesting a carb that get's close. It will recommend a couple sizes if you are close to the edge of a range (and what they have available) and we all know how sizes will affect different parts of the power curve.

A mild 454 @ 4500 RPM would be just fine with a 650. Much like my stock 420 horse 502 which came stock with an 850 didn't need it.

EDIT: And also they aren't going to recommend someone else's carb, they will recommend what they have, even if it isn't otiimal for your set-up.

Anyway this has been beat to death, I'm going to go piss into a hurricane, much like a carb :)

what was the cfm rating of the quadrajet on the 454 mag?

[QUOTE=brivander;3540180]
A mild 454 @ 4500 RPM would be just fine with a 650. Much like my stock 420 horse 502 which came stock with an 850 didn't need it.
QUOTE]
It didn't recommend it for 4500 - it recommended it for 5100 rpm. At 4500 rpm 650 might be OK, but then you don't need a mildly modified 454 - a 454 truck engine will work.

Books I've seen listed 750 for the stock quadrajet. The Weber was 725 or 750, depending on source.

While a 650 would work, it's clear that a 750 will provide less restriction and more power - and having a 7.4L 300 hp merc with a weber, it doesn't hurt low speed at all.

Either that, or all the high dollar builders and thier dynos are wrong.