Cam change
 

OK, I know I've asked this one before, but there's gotta be somebody that's done this. I've got a carbed MARK VI 454 300hp version. Has anyone swapped this cam for just the mercruiser magnum cam out of the 385hp 454? Just wondering if it's worth the trouble. Maybe someone can plug the cam #'s into a hp calculator and tell me the difference.

Cam specs for original cam (i think) are:

204 duration intake
208 duration exhaust

.480 intake
.483 exhaust

118 centerline ???

Magnum cam:

224 duration intake
224 exhaust

.483 intake
.483 exhaust

115.5 centerline

any help? anyone???? am i the only person in the world contemplating this??? :confused:

Changing cams without changing out the low flow peanut port heads will result in a very small power increase. When my motor was a 300 hp I put on an old set of chev "049" large oval port heads with 2.19 int. and 1.88 exh. valves. I added an oval port holley strip dominator intake, holley 750 double pumper carb, and a set of rewarder through transom headers. I then made a cam change to an Erson hydraulic with specs of 228/235 at .050" on a 112+4 installation with .540" lift. Performance went from turning a 26" spinelli 3 blade 4600 rpm to turning it 5400 rpm. Speed went from 65 to 75 and the low end and mid range were awsome. The cool thing is these parts are around and are pretty cheap.
Good Luck.

Guess I should have elaborated on my settup. It's got late model vortec heads which are a large oval port design, and also increased compression to approx 9.25:1. It also has a Edelbrock performer RPM intake, and K&N 14X3 flame arrestor. Carb is jetted to 454 Magnum specs. Otherwise stock. Any clues now if it will help? I've got the magnum cam laying around, but I hate to tear into it again for no gain. Thanks again.! If no one can tell me i may just sell this cam and get something 'REAL'.....ahahaha

If you have stock exhaust, use the mag. cam.
If you have exhaust that gets the water further away, the cam I suggested would probably make more power with your set up.

I have to agree with "Wette Vette" on his combination...he has pretty much hit the nail on the head! The old oval port "049" GM casting is a very good head or...buy a set of Merlin oval ports with the larger valves already installed and hardended seats. Although the "049" is a good head it still takes a lot of machining to bring it to a Merlin oval port head that pretty much comes with all the machining done to it. With 049 castings you will have to: machine for larger valves, machine for hardend exhaust seats, machine for larger spring seats, machine valve guides for valve spring retainer clearance (this may have to be done for the higher lift of the cam). By the time you're done with all the machining process steps on the 049 castings it may be wiser to just buy the Merlins.

Both the GM 049 and/or the Merlin heads will need to be pocket/bowl ported along with a 3-angle valve job. Another good item to add are bronze wall valve guides...I'm not sure if you can get them already installed on the Merlins from the factory or not but it's still a good thing to have done by a competent machine shop set up for those kind of machining processes.

Wette Vette was also right about the GM "peanut port" oval port heads that come on the those 300-330hp engines. You can modify them like the 049's, but because of the small size of the casting they just don't flow like an 049 or a Merlin oval port head. The cam he suggested is right in the ball park of what you should use. If not using a dual plane intake and you want to use a single plane be sure to add at least a 1" or better yet a 2" 4-hole spacer between the intake and carb...this is what definately helped us when using a single plane intake manifold on the 454. Without it we have noticed a loss in torque. There are a lot of different variables for what works for differing applications...however that is what worked for our combination of go fast parts. If you're running a single engine boat I would probably go with a dual plane intake manifold like the "air-gap" by Wieand(or whoever makes it). The correct amount of air flow while maintaining good torque is where it's at!

Vortec heads are pretty good heads from what I hear. They already have the hardend seats in them if I'm not mistaken. Then have them machined for the larger valves as Wette Vette has suggested on his original post and them have them pocket/bowl ported. You may need to have those Vortech heads machined for screw in rocker arm studs so that you can add roller rocker arms. I guess some of them have pressed in rocker arm studs vs. the screw in studs. I believe you'll need the roller rocker arms for the higher lift of the cam....the slots on the stock stamped steel rocker arms I don't think are adequate engough for the higher lift of the cam. I hope everything works out for you...just make sure you have a COMPETENT machine shop help engineer your set up so you don't miss anything.

Madmax,
No time to get together and talk shop!!! I guess I know why now. Hope the house is coming together for you. If you have a free w/e night coming up we should try and get together. BTW, my engine should be coming out next week. I sold it and decided to go bigger!

ttt

Sean,
If you are going to buy this cam, get it from Competition Products in Oshkosh, WI. They buy all off the take out cams, lifters, rockers, valves, springs, and pushrods from Mercury Racing when they build HP 500's and up. I guess the engines come from GM complete as stock 502 HO 450 HP versions. They list the cam you are looking at as GM PN# 12551622 for $39.95 and you get 16 pushrods for free. New lifters will cost you additional money if you need them. I doubt you can beat this deal. Call them @1-800-233-0199 to order or 1-920-23-2023 for a catalog. www.competitionproducts.com Good luck, I think that cam will give you a great increase with those heads.

Damn Voodoo.......that's cheap. Unfortunately i already have the cam, but i definately payed more than it for that........bummer....

house is coming along. Got most of the stuff moved yesterday. Was doin good until she decided to do a 'no look' back with her explorer into the side of my Suburban.......DOH! needless to say her bumper faired better than my quarter panel....

funny part is that i didn't even know she hit me, i thought i drove over the curb with the trailer.....

NEXT TIME I WILL HIRE MOVERS. WITH GOD AS MY WITNESS!.......ahahaha

we'll hafta get together this summer.......no time for any fun right now, unless ya consider playing bumper cars fun.....ahaha

so what motor are ya goin with? where's the Mag motor you pulled out? Did you ever buy those headers?