Thanks for the help guys. After this season (if not earlier) Ill get a good set of heads and cam.
If im reading this right..I can make the motor about 575hp with a good set of oval heads,cam,intake, and exhaust right?? Ill probably run that set up for a season then go with a new drive and procharger and freshen up the bottom end. Im thinking my goal would be about 800 reliable hp. If the 454 mpi has a steel crank I should be ok..I think. but the b3 would be on e-bay.
575 HP for a set of oval's should be no problem, but if you want to get to 800 with those oval port heads I don't think it will happen, it might, but I think you'll be really pushin things to get that power from a set of oval heads, do you paln on buying 2 different sets? I guess if I were doing a 2 step upgrade I'd buy the bigger heads now for the planned usage later.
I know rectangle port heads are for higher rpm's, but believe they come standard on all the magnum engines, both 454/350hs and the 505/415. Remember how much harder a boat engine works than automotive and the amount of air it moves! On my street motor I have a set of the big port ovals that have had a lot of work done. Boat motor is a 502/450 longblock that came with the "square ports" Oval ports such as Edelbroch's or others are a far cry from GMs
Agreed, boat engines work harder! But it doesn't matter what the engine is in for air flow, a car or boat, the air needs of the engine at a given RPM are no different, 3000 is 3000 & 5000 is 5000, its just an air pump! But not knowing something has provoked a thought. IF GM only provides 2 choices in heads on its base gen V & VI marine engines then what do you get or do when buying factory iron? The small port heads aren't enough after 4500 RPM so maybe the only alternative from the factory is the square port head which out flows the smaller oval port heads & let the motors run past 5K. It would be interesting to see flow specs on the factory square port heads as compared to real good ovals & real good square ports.
gnarly, thats kind of what i was wondering, i thought all gm 91 and up 502bbc heads were rec port.
Why would they do that if the oval port worked better on those motors? My stock 500hp heads were good for 634hp at 5900 rpm's on a 540 i had so they are capable of making good hp. I obviously had a diff. Cam, roller rockers and lifters, ECT. I do not have the torque numbers in front of me but i will post the dyno sheet when i dig it up. Why does gm not use oval port heads? Just wondering.
Maybe the 502's only get the square ports? Do they on the truck line? It would be nice if a GM tech would enter here & straighten this out.
Newer Big blocks- 502's come with square ports, Mercs 454 come with Oval ports on base motor and Square ports on the magnums. The oval ports have "nail head" valves (tiny) and smaller runners and ports. Some of the oval ports can be made to run like a bat out of hell. In my Chevelle I have a pair off a 454/360hs that have been ported and larger valves put in, that motor spins at 6500 without any problems. My old boat motor was a base 454 with Ovals (stock) and if it turned over 4500 rpm I would run out and buy lotto tickets. I know nothing about the dart/world etc.. but if Merc uses the square ports on all the performance motors it can't be a bad start. Also have heard the Edelbrock ovals work pretty well. But then again I'm not one of the boys that can afford a big hp motor frown
Think Gnarley has the best idea- play wiht different combos on a dyno program then go to a recommended engine builder and run it buy him. What part of the country are you in? You also need to think about operating range of your drive, you don't want to run a Bravo at 7k rpm
[QUOTE]Originally posted by powerplay230:
you don't want to run a Bravo at 7k rpm
Thats kind of my point. How many of us have all the hardware & money to build then operate at those RPM's frequently? I want to have fun & not work on the boat all summer long, I only have so much time to work on my fleet & don't want to break the bank or myself. It just seems that pushing over the 5500-RPM boundary starts to encourage wear & tear on something. Building it to run 6500+ RPM's is just like pouring money into the water since those RPM's are rarely seen unless racing. Bullet proof is one thing but over built for the wrong operating range is another. We all have our own desired operating ranges, so for me as much power as I can build on a budget up to 5500 is good. Maybe this would be a good survey; What RPM do you run at most times and how often do you run 5000, 6000, 7000 RPMs?
http://forums.***boat.net/ubb/ultima...c;f=1;t=005102
[ April 01, 2003, 07:59 PM: Message edited by: gnarley ]
If anyone has money to pur into the water I have a better place. At least better for me!
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