Whether you upgrade or go new you will need a new oil cooler the stock 300 hp one just isn't big enuff for a 450 hp engine.

All the rest of the accessories can be transfered to a 502.

However if your 300 hp is a mark IV and you buy a new Gen VI then the following exceptions occurr:

Alternator bracket will need mounting holes to be drilled out to 7/16 .

The pully for the sea water pump will need to be shimmed to align properly. Shim the mounting bracket not the pulley itself.

Fuel filter/seperator bracket will need bolt holes drilled out to 7/16 if it is the type that mounts on the heads.

You will need the gen VI remote oil adapter plate and may need some custom oil lines depending on what combination of remote oil filter/exhaust risers and where you mount the new cooler. You may also need new water hoses if you mount the new larger oil cooler in the dif location. depends whether you use an after mkt combo unit or seperate oil and pwr steering coolers from merc.

The starter motor if it is the big one will need a custom mounting bracket at the front as the Gen VI block has no bolt hole to accomodate the stock bracket.

Well, if your looking for 70, the same combo I did should work for you, altho I have to admit, yours is a lil slower than mine was stock (mine ran 62mph). Mine is a Mark VI with the roller cam, so if yours isn't, none of this applies.

L-29 Vortec heads from 99-up 454 mpi motors ($400 used)
Edelbrock Performer RPM intake ($100 used)
Ugraded to GM L88 valve springs and 3/8 pushrods (60 bucks from e-bay)
GM 454HO crate motor roller cam ($125 new from internet)
K&N 14X4 flame arrestor ($75 from Summit Racing)
Gil/Mercruiser manifolds and risers ($900 used from local marina)
Mercruiser 454Mag Thunderbolt V module for 5050 rev limit ($100 used)
Lab finish 25p Mirage plus prop ($175 Bronson Hill)
Rejet stock Weber carb ($25 worth of stuff from Summit Racing)
Gaskets (???)

That's all..... nothing fancy, stock bottom end with 190+ hours. All GM or mercruiser parts except the intake manifold. Best of all is this stuff is all easy to find on the internet or e-bay. You could actually scrap the lab finished prop and just turn the motor higher, but I decided to go with the 25p prop and turn right around 4800 with it. I felt better not turning 2 many rpm's with the stock nonadjustable valve train.

Happy boating.!

Ursus, thats exatly the type information I was looking for. nothing you mentioned seems to difficult to overcome.

Max, I have the plain old 454, There isn't a roller anything in there, its not the 330hp its 300.

considering the boat does almost 60 now, doing almost 70 would be fine, and max, if I add up your parts, your at about 2,000 which sounds very good to my wallet.

boy, I hope this doesn't sound to ignorant, but where the heck is my current oil cooler ??

P.S. I checked on the boat performance analyzer web site and if I plug in all my numbers 23p mirage, spinning 4,400 and a 1.5 gear ratio, it comes out to 58.5 mph and a prop slip of 8%, i'm thinking if I bump up the hp and valve train, and run my current setup at 5,000 rpm, I would get just over 68 mph.. which would be o.k.

If your engine is a 96 or newer, it's got a roller cam. I.E., all the upgrades i listed apply. Mine was listed as a 300hp also. I can't comment on the oil cooler upgrade, but i'm sure it's a good idea. I didn't do it, cause i'm a cheap a$$........

o yeah, 5000 rpm isn't possible if it's a 97. Your rev limiter will kick in at 4750 rpm. My friend has a 96 and he turns 5000 rpm all the time on the stock engine with a 21p prop, so the engine should hold together. Plus if ya blow it up, your not out anything, you can transfer most of the parts (intake, exhaust, flame arrester, etc.) to the new motor.!

O yeah, 1 more thing, buy Dennis Moore's book on 'How to Upgrade your Marine Big Block Chevy' or something like that. It's the best $$ you will spend on your boat. Lists all the upgrades I did in there. I'm not smart or anything, just copy what works for other people....

big block marine performance... should have it in 3-5 days..

on older engines the cooler will be a combo oil/pwr steerin and will be on the lower port side of the engine under the exhaust manifold down by the engine mounts.

newer engines will have a seperate power steering cooler in the above location and a seperate oil cooler mounted vertically at the front port side of the engine under the pully's

http://www.mercruiserparts.com/selec....asp?type_id=8

a great site for parts diagrams of coolers/plumbing etc etc

454 mag head cracks.......

According to my engine builder, the merc exhaust is too restrictive for constant high speed operation (who would do that?).

the space between the int and ex valves is VERY small so all heat related problems tend to show up here in the form of very small cracks. He claims to see this on hard run 454 mags regularly.

When mine was torn down at about 500 hrs, both heads had this problem although I would have never known, I had no issues as a result. I wanted the merlin heads anyway, they made the biggest diff during my upgrades.

my 454 is a 96 and when I went to the merc web-page that happens to be the year they changed from the mark IV to the V, how can I tell which block I have and what my rev-limiter is set at ??


If I buy a new (some used) cam, heads, intake, exhaust (maybe), what internals will need upgrading ??, I know forged rods and pistons but what else ?

again, thanks for all the help everybody..