HI ok im tryin to figure out what to do to my 1991 454 mag (GEN 4 think) Im taking it in to get refreshed and i would like to upgrade the cam, carb, intake, ect. Look for some advice on what company to use. Estamated hp part#s or what maby someone else has done. I have a guy that will put it all together for me so i should be good on that end.
Thanks

There are about 1000 threads in the Technical general Q & A section about just what you want to do.

Griff was right regarding all the threads regarding the upgrades. There are numerous tips you will get on this board and you will spend hours reading them. Most are pretty informative.

Quick info from my experiences.

For starters I'm not sure if you have the 365 HP mag or the 330 Hp. If you have the peanut port heads or or the rectangular ports???

I have built many 330's and used the stock bottom end with the cast crank and 3/8's rods. Many will tell you these bottom ends are not good to use with upgrades over 400 HP however I have done so with no problems. It's pretty common to be able to get 460 - 480 HP at 5500 RPM. If you have a machine shop I advise to have your rotating assm. balanced. This is important especially with the cast crank and 3/8 rods. If not just be certain your builder knows what he is doing.

If you are replacing your pistons be sure and get enough dome to get you near 9.4 to 1 comp. (cast or forged) Your builder should know this if he CC's your heads and calculates your bore size.

I would probably stay with a hydrolic cam something like the crane #134561 (502 465 HP cam) or like the Comp cam # XM278H. Use std. 1.7 roller rockers - look on Ebay. Use the 3/8 pushrods if you don't have already. Stay with a dual plane alum. intake. 750 cfm - 800 carb. If your in a crunch use your Qjet for the time being.

This type of a set up especially with the hyd. flat tappet cam will give you an easy 450 HP and plenty of more torque than stock and very reliable. For marine use at the operating RPM you will be at the oval port heads are a plus. Check your casting numbers to id your heads. This will be a very reliable inexpensive package for you. With this package Exhaust will be a plus but not a demand. Put the extra dollars into your engine and replace your Exhaust later with some gils or emi's etc. Keep your total timing at near 32 deg. total advance.

If you use the crane cam I suggested just watch the water reversion. I have used this cam with no problems however I had lightening headers. Some on this board have had reversion issues with this cam. Maybe use the Comp one I suggested. This is the one I am going to use for my upgrades soon.

Also if you have the 3/8 rods it is always a good idea to use arp rod bolts but no absolutely mandatory. Just a little insurance and they are cheap.

On the intake I am searching right now to dind what is the best dual plane that is out there. Looks like maybe the Edelbrock rpm airgap. Single plane manifolds are used frequently however they are used most often with the bigger CI engines.

I am not an expert by any means although I have done my share of work on Marine engines / dyno and understand them pretty well. I continue to learn myself and enjoy the hobby very much.

Good luck and have fun...

John

PS also if you don't have bore notches in your blk it's not a bad idea to have those ground. Your engine builder can do this easily and it does make some power.

Everything he said is just about right...good luck with your motor. I'm in the process of turning up the wick on my 502 mag a little. Hoping to make an honest 500 hp...or real close to it.

Had the numbers ran and i have a mark 4 block 454mag forged internals short block and rec heads 4 bolt main. So that doesnt sound to bad 480 to 500 hp is what im looking for so thanks for the info thats a start. o also have imco thumper series manifolds and risers