1993 502 Mag?? What would you do?
 

I bought a Repo 1993 Baja 38 Special that (shows) it has about 280 hours on it. The motor's look to be the orginal 502 mag's (carb.) 390hp?? My question is over this winter I plan on replacing the Stock (Rusted)Exhaust with a better flowing Exhaust (I'm thinking Revolution Marine) And since I have all winter and I have to space and way to do it, I think I'll just pull the motor's to make things easier!! Plus that way I can inspect all the rigging and thoughly clean everything to get rid of all the salt water it came from!!

But, like all of you guy's I want a little more performance. Heck on it's maiden voyage it only showed 57.8 on my GPS!! I have got to get into the 60's at least!!!

Of corse a pair of 250 blowers would work! But that isn't in my budget. Plus I don't have hydrolic Steering so I don't need to get to crazy!!

A buddy said since I have them out I might as well re Ring them and put new berrings in them. That makes sense!?!?!

I've seen that a lot of people with the 454 (carb.) mag's do a head and cam change and pick up quite a bit.

How are the heads on these motor's?? Do they flow good?

Should I change the Cam's? Intakes?? Carb's??

I guess what I'm asking is what is the best bang for the buck with these motor's?? Or what should I look out for??

Dennis are you out there????

IMHO, Heavy boats, big hp, and bravos dont mix. But if you're going to go through the motors and upgrade the exhaust, it doesnt cost much more to change a cam, intake, and carb for a few extra hp. Dennis is probably the expert there.
Just wanted to reccomend going through the gimbals as long as the motor is out. At that age, they may have been fixed once. Check for the "famous" gimbal housing plugs at the top.
Gary

I found someone with a flow bench in the KC area if you want to do something with the heads.

If you budget is tight, don't waste your money on exhaust!!! Stock Merc exhaust is good to about 600 hp. I had a procharged 454 and stock exhaust. It ran great. I switched to Imco Powerflow and still ran great. Absolutely no gain anywhere! Others may disagree, but your $3000+ could be better spent.

Gary, Yea I was thinking the same thing, It's a heavy boat for sure!! But, I would still like to get into the 60's!! If not I might as well put a SeaRay Sticker on it!!

Rich, We need to hook up for a beer, I have this Powerboat mag. for you and we can swap stories like we usually do!! Who has a flow bench??

Pure Energy, Since it came from Salt Water the stock exhaust is pretty well gone and it's leaking a little bit. I want to change it before something really bad happens!!

Great engine, I wouldn't bother re-ringing it unless you know there's a problem.

Install a Comp Cams Xtreme Energy XE268H and you won't have to change to adjustable rocker arms. The camshaft and some Gill exhaust manifolds will give you a big performance increase.

Keep the stock heads and intake manifold for now (they're good) but when you can afford it, upgrade to large oval port Merlin heads and the Edelbrock Performer RPM oval port intake manifold.

Keep the stock 750 CFM Weber carb and add a K+N flame arrestor. Retain the Thunderbolt IV ignition but install a different ignition module, Merc #805361T2. Use Champion RV15YC4 spark plugs gapped at .045 inches.

This should get you pretty close to the power output of the 500 HP engine (especially if you use the oval port heads).

You can always by my book too!

Dennis Moore
www.mooreperformance.org

Buy the book! You won't regret it.
I am with Pure Energy on the exhaust. If you have to replace, go with the Moore Performance Exhaust. Click on the URL above and read why they are better than stock. Makes sense.
Save your money on the exhaust. You're gonna need it.

Dennis, what about the Edelbrock Oval Port Marine Heads?

Stock Merc exhaust is NOT good for up to 600 HP if you are naturally asperated.

RLW

I really like the Edelbrock marine heads. I wrote a magazine article about them and did the research. The inconnel exhaust valves are great. Probably the best heads for a 500 horsepower naturally aspirated engine (they are the same as the 502/502 horsepower GM crate engine heads except hard anodized and inconnel exhaust valves).
Dennis Moore

I wouldn't bother changeing the heads the gains will be insignifigant unless you really step up to like some canfields. The edelbrook and merlins are both great heads if you are starting from scratch but not much bang the $ if replaceing the original GM rectangular ports IMO.

If you have the budjet I would go with the XM270-HR and get the kit with lifters/springs etc to retrofit to hydralic roller lifters, it is 218/224 .51/.51 on 112

This slightly milder roller will make as much power as the XE 268H more mid range torque and has less overlap than the 224/230 on 110 and so you won't be in a borderline reversion condition.

Remember Merc had some reversion problems with the HP500 cam and had to go to taller risers on GILs and it was only 222/230 on 110

Either cam with decent exhaust should get you about 450-460 hp at the prop if you want to compare #'s to the 390hp you have currently which is rated at the prop

As for re-ringing 280 hours is kinda in the middle not really hi hours but not low either so do a leak down before you pull it apart to decide if thay are good/marginable / bad