Pat McPherson

Zup, I am going to disagree and then agree with you...
Razor listed the following:
-New Edelbrock marine heads $1500
-Add springs, retainers, and locks $250
-New Intake $250
-Carb $600
-Ignition mods? New DUI or MSD $300-$600
Total around $3,000.

Now, add to that:
-Rebuild (rings, bearings, oil pump) and Balance short block $1500
-Full roller valve-train $1,000
Yup, you might sell your 600 for $5,500...

RazorsEdge

Thanks for the responses: I still have a few questions though.
The parts I am/was looking at come to around 3,200 with the roller rockers, complete heads, carb, intake, and all the gaskets. This is what I could do myself without pulling the engine. Does anybody know the flow numbers on the stock heads? If my peak horsepower is 350/365, what is the peak torque? And what is the curve like? I would love to see a dyno sheet of this engine stock if anyone out there has one. I'm not a big horsepower guy, the parts I listed should get around 500 ft/lbs at the crank and stay over 400 through out the curve (1500 to 5000). I am also not looking to push much past 5000 with a rev limiter set at around 5200. I do not want to get to the point that I am worried every time I go out that I may blow out the lower half or the outdrive. I just figured that a 454 mag with forged internals should be running more than the 365 HP that it currently has. I am not looking to pull the motor just yet, when I do I would likely switch to a 502 shortblock. I figured this upper half would work nicely with the new 502 shortblock once it is needed. Am I wrong in thinking that higher flowing heads with the stock cam (I believe 224/224) would give me a substantially more low-end torque? I just really like strong running engines. How much power should this lower half be able to hold at 5000 rpm’s with 200 hundred hours on it? I was hoping for an additional 75 to 100 hours. If the lower half cannot hold the power, I will wait to do anything. Ok, one last question. If I make the engine change later, will my drive with 10 years on it need to be replaced?

Thanks again for all the info,

z.zuperboat

200 hrs is about 1/2 the life of the motor. 365 is a good start, has all the good internals. If you have good semi dry exhaust I have a hydrolic crane cam that I loved. Its the merc 575 cam I will have to try to get the numbers. Probably $200 for cam and lifters.Ask Pat if you can do a cam change in the boat. A cam will wake up the motor. You will probably get more from a cam than a head with this setup.If your buying heads dont buy a large intake port size stay under 310. Works better for lower rpm and will make more torque. Best heads out there are the AFR but pricey.How big is the carb. A holley 800-850 will work. Any way best of luck. MIKE

Pat McPherson

Razor,
Highperformance Chevy magazine has the flow test numbers for your rectangular port heads. You can find them on-line...
I'm not sure if you have a Gen V or Gen VI engine; 1995 is the transition year. Either way, peak torque is about 450ftlbs. The 365HP @ 5000rpm rating is at the prop shaft. You have a bit more than that with the better Stainless Marine exhaust. On a dyno, max HP would be 400-420 @ 5000-5200rpm...
The components used in your short block are good for about 550HP @ 6000rpm if checked and balance properly.
Yes, if you bolt on a set of large oval Edelbrock heads, your engine will make more low end torque. But, I'm going to repeat myself, without a cam change, your waisting your time and $$. A Gen V 454Mag/OH cam is 220°/220°, .500/.500 lift and a Gen VI is 224°/224°, .480/.480; vary mild.
If you want your engine to make 500ftlbs and peak HP at 5200rpm, rebuild to something similar to the Merc 425. The cam in that engine was something like 230/236, .550/.560.
A 425 would push a 24' Super 76mph, 77tops...

RazorsEdge

Ok, Now I understand that the Head's are not the weak point. I will change my search to a cam, intake and carb. Will I have to have the engine pulled to change the cam? If I am not able to pull the engine at this time, would changing the intake and carb make any difference (positive benefits) at all?

I really do appreciate all the info.
Thanks,

Pat McPherson

I did change the cam in my boat last year but it's not easy.
You have to drop the oil pan. With a cam change comes new valve springs and a valve job so you'll be pulling the heads too.
If your 750 cfm Carter carb is working well leave it unless you change the cam. If you are having problems with starting, some people do with them, buy a 800cfm double pumper that will work with mods up to 500HP down the road.
The intake you have is a good one, so don't change it unless your going to build a 5600rpm screamer. In that case you will need a single plan...
Have Fun!

Dave M

Hey! wait a minute!

Pat McPherson

Yes Dave, your 1998 stepped pad hull is 1-2mph faster than my 97 or Razors 95 straight V...

RazorsEdge

The cam in that engine was something like 230/236, .550/.560.

OK, 425/500 is a lot beter than where I am. Who sells the cam and what valve springs to go with. Why the valve job? Should I look for a set of reworked heads already done?

Pat McPherson

Razor,
The Merc 420HP/454 was a Gen IV engine and the 425HP/454 was a Gen V version of the same engine. These engines were basically 454mags with a hotter cam, roller rockers, single plane intake, 750cfm Holley double pumper, and Gil exhaust. The cam was a hydraulic flat tappet made by Crane. You can find it easily on their web sight. Merc also used this same cam in the 525SC.
First you need to figure out if you have a Gen V or Gen VI engine. Gen IV and V engines have a sheet metal timing chain cover with 10 bolts. Gen VI engines have a cast aluminum cover with 6 bolts.
If you have a Gen V engine, the Merc/Crane 425 cam with roller rockers would be a great upgrade. The Gen VI engines have a roller cam so I would not suggest stepping back in time to a flat tappet cam. Merc never built a high HP Gen VI 454, they offered a 502 instead. However there are lots of good choices for roller cam upgrades.
Why a valve job you ask, well IMO it makes good sense with a cam change on a 200 hour engine. Just like I suggested that you do rings, bearings, and an oil pump in the lower if your boosting the overall power. Don't buy another set of heads, yours can be gone through for a few hundred $. They have good valves already so just have them clean up and install new springs, retainers, locks, and seals. Hell, I had mine bowl ported for an extra $200 last year.
Razor, I understand that you want to just bolt on a few new parts and go a little faster, but it's not going to happen. The only bolt on goody, other than a supercharger, that really helps is a better flowing exhaust. And you already have that.
Pull the engine out and do the job right or just leave it alone and enjoy.