454 MAG - MORE POWER !!

[gnarley]

[QUOTE]Originally posted by 502procharger:
I was under the impression that the 500hp was made to run a 5400 or so top end rpm, why then would these heads be best at 6500-7000rpms? I thought these heads would be great for anyone looking to boost hp on a 454 or 502 BBC with smaller heads. Please correct me if i am wrong.
Just my opinion, & from past experience with motors in general. The big square port heads flow fairly well, especially at mid-high RPM for stock heads but not low to mid. For low RPM the very small oval port/valve heads keep the velocity of the air/fuel charge flowing well at low RPM but just can't do it at high RPM. Other oval port heads have larger ports/volumes & valves that make them a better choice for low to mid range RPM’s up to 5500-6000. Best choice for 5500 & up are the big square port heads, it's all about air flow. Your new ones should be nice but myself I would be concerned about what RPM they are best suited at.
Back to your old heads, what cam was in that & matched to your heads & comp? Just remember Mercury isn’t in the business to build custom engines they make a few flavors that are supposed to cover all bases, they don’t. And what they sell they must warranty if you break it so they build them without combinations that might break something & limit how many RPM’s they turn. Built the right way a 454 can easily push 600 HP & 600 lbs ft torque, but you knew that right and a 502 even a bit more. So what are you trying to do with your new combo & what RPM’s will you run it at?

[502procharger]

Gnarly
Thanks for the info. I do not have my old cam spec's here but i will get them. Why does no company have a variable port head? You could get the benefit of the best of both worlds. I know many 2 stroke motors have variable exhaust ports for that reason. I would think someone could design a head that would give you a small port for low-end power and torque and open as rpm increase or something like that.
As for my new motor, i am just building a stout motor for one of my boats. It is a 25' Switzer with an xr drive. Should run about 900hp at 9lbs of boost. Give or take a little. All good stuff in the lower end also. I built it to last. I like the procharger because the build very little boost low end and are much easier on the drive, but give you a kick ass midrange and good top end. Should be a good setup. Not really sure how fast a 3600lb v bottom will be with 900hp, but should rum well.

[gnarley]

[QUOTE]Originally posted by 502procharger:
Gnarly
Why does no company have a variable port head?
Actually a few have played with them if I remember right, like in the 4 valve per cyl engines. They leave 1 port closed off & it opens at a given rpm for the mid range-topend. I think the new corvette does that, I think the Misubishi VR 3000 twin turbo did it as well as the stealth with the same engine & maybe the SHO Taurus

[502procharger]

ironicly i have a 3000gt vr4 it is 4 valves per cyl. twin turbo, awd, aws, but i knew nothing of variable valves.

[OC-PARTYCAT]

so do I need rectangualar or oval ports for my application. I dont think the motor is going to turn more than 5.5k. The boat weights in at about 4500#. Its got a bravo III hooked up. Im not sure but doesnt the engine (99 454 mpi) have a roller cam set up already.

[502procharger]

I guess it is really your choice, the oval ports are going to give you good low end and mid range and not be as good on top, the rec port heads will give you less low end but still have good mid and high end. I went through this on a 454 I had but it was a carb motor and i do not know if it makes a difference. I went with rec port Merlin heads and dart intake, in my boat it really woke it up.

[OC-PARTYCAT]

If mid range is 3k, and top end is 5.5K I think I would prefer the rectanular. I dont care if the boat doesnt jump out of the hole as long as it gets up on a plane like it does now, I would be happy

[gnarley]

[QUOTE]Originally posted by OC-PARTYCAT:
so do I need rectangualar or oval ports for my application. I dont think the motor is going to turn more than 5.5k. The boat weights in at about 4500#. Its got a bravo III hooked up. I’m not sure but doesn’t the engine (99 454 mpi) have a roller cam set up already.
I think I'd go with a nice set of oval port heads matched to a cam that makes power in the range you need it. Not the little oval port heads.
It's funny, as I'm going through this myself right now & I only want to twist it up to 5500. My engine needed to come out for some drive repair, so I thought GREAT I can finally see what’s in it. I found a tag & found the engine was a Merc & not an OMC. I called Merc & got the numbers & that made me sick! Then pulled it down & got the cam #'s that was better but didn't work well with my heads! So I'm installing a larger set of oval's that seem to work better with my cam based on the Dyno 2000. Again as I have said it's no substitute for real Dyno testing if you can, but it will point you in the right direction. Changing heads netted about 175 HP increase & 70 for torque so said the software. What I saw from the software was even with blower cam the heads were too restrictive, so change the heads & more airflow! That sounds almost like what you want. If the numbers are even close it will be a mid range torque monster & make good top end HP to the range I want! But a warning that the BIII might not take it!
[QUOTE]Originally posted by OC-PARTYCAT:
If mid range is 3k, and top end is 5.5K I think I would prefer the rectanular. I dont care if the boat doesnt jump out of the hole as long as it gets up on a plane like it does now, I would be happy
5000 on up is just the beginning of top end. Ask others what they think & would be the best choice of heads for your needs. I think the Rectangles are to big.
JMHO
WHats your email?
[ March 28, 2003, 04:10 PM: Message edited by: gnarley ]

[502procharger]

Gnarly knows his stuff, but i went with the rec port merlins and the motor was very strong. I guess there are many other variables that fit into the equation like cam, mpi or carb, ECT. I am just going from my experience. I think you will get some good hp gains with either.

[gnarley]

502pro I think you'll still be happy & will see good increases but think your giving up to much mid range & moving it up the scale where you rarely will use it & may not see what those heads are really capable of doing. Torque gets things moving & HP keeps them moving, having all the HP in the world doesn't do much if you rarely or never use it. I liken it to soo many guys I’ve seen build street engines & put way to big cams in, bigger isn't always better. I hope it works for you, let us know how it works.