502 engine build
 

Looking for some recommendations on my engine rebuild project, The engines are 502 mag mpi, Due to some wear they are at the machine shop being bored to 509s right now. I have been here searching and reading about cams and 502 builds for weeks, but it seems most are looking for more power than I am. The boat is a Formula 400ss that will mostly just be used for cruising, but, while i have the engines apart... :) So I am just looking for suggestions,
-What cam could I use? Currently have stock exhaust manifolds with silent choice.
-One of the engines has been apart before and has the better, H-beam rods (weird,that seems to be the only upgrade) should I get a set for the other motor?
-Use the JE forged replacement pistons, or is there a better choice? I don't want to be stuck using premium fuel, I plan on burning a lot of it, compression ratio suggestions?
-I'm told that these heads flow pretty good for this level and to leave them alone, true or? What about better valves, anything to gain there? I would use the springs that go with the cam.
Any other suggestions? I am trying to keep cost down as much as possible for now, might do more later (exhaust, intake work ecm...) I can do that in the boat.
Thanks!

Honestly I'd just be more concerned with rebuilding them correctly and not look for much extra power unless your going to change the exhaust. That cast or Gil's. Have the heads properly gone through and replace the exh valves with inconels and severe duty stainless intakes. Have springs checked or replaced. Depending on what exhaust you have you could maybe up the cams a bit but with limited budget and do mostly cruising you'd have to make some major changes to see any noticeable gains on that 40'. The H beams aren't necessarily better by any means. Stock 7/16 i beam are plenty strong and a great rod.

Post what exh you have. I have a feeling their the cast manifolds. That will dictatate what your limitations are on cams. Btw what castings are those GM heads. Just do a good job on rebuild and I'd keep comp 9.0:1 or less.

^^^^^i agree,the 502 mpi came with merc cast iron exhaust manifolds and they really limit cam choice.i think for your boat rebuilding to stock is the best route to take.i would for sure mark the injector location,then remove them and send them out for flow testing&cleaning.as part of the rebuild.

u might lo0ok at a simple upgrade to the( crane 731 I think) cam that was used in the 500 efi engines. and yes the h beam rods and je pistons stainless manifolds or emi manifolds are good choices for the money and ofcourse an ecm reflash

the 500efi engine did not use a crane 731 cam and they did not come with merc center rise cast iron manifolds.a 731 with stock manifolds will no doubt have a reversion problem.

I know there is a roller cam upgrade out there that does not require a reflash, although I dont know the number. I believe those black motors came with flat tappet which todays oils do not work overly well with.

the 502 mpi engine comes with a hyd roller cam but it is very mild.

As a note: Gen VI had the roller cam. Not the others.

good catch sb,i am so used to gen6 stuff that i forgot about the gen5 having a flat tappet cam but the last gen5 was made in 1995.

Personally I'd get away from the JE piston and the metric ring pac, maybe take a look at Wiesco pistons, the dimple rods in the other rotating assembly are fine, no need to get H beam, unless you want it all to match

My buds 94 is getting rebuilt as we speak, could have swore he said it had flat tappet!

Yup, 94 should be Gen V. Flat Tappet.

...

yep,91 through 95 were gen5.

The Gen V 502 Mag, had a 220/220 115 LSA flat tappet. The Gen 6, had a 224/224 115 roller tappet.

As far as I know, the MPI 502 MAG, whether it had either cam, was rated at 415HP.

Joe not related to this thread but which 502 used that small roller like .463 lift and real short duration. I'm just curious.

That was the gen 6 502/415hp mag. 224/224 , 483 lift i believe.

Motors are '99 gen. 6 with roller cam. The head's part number is 12562934. everything appears stock. The exhaust manifolds are stock cast iron mercury. They have a 4 inch spacer between the manifold and the riser that my other boat does not have.
I bought this boat as a non running project, so I don't know all the history of it. One of the motors got water in the oil and was left for a while, the cam and lifters have rust pitting and need to be replaced anyway, so i figured I would upgrade both while I am in there. If anyone knows of a bigger cam i can use with the stock exhaust that is what I would use. However It sounds like the consensus is an exhaust upgrade is where I would have to start. I probably will, but wanted to kick that can down the road and get it running for now.
Why would the H-beam rods not be better? Having two different rods in my engines would cause my ocd to kick in a little, but sounds like the oe ones are good and money would be better spent elsewhere.
Someone mentioned Wisco pistons, Are they better? and why?
Looking at valves, I noticed there are larger ones than what I have, would there be any benefit of going bigger at this level?

Thanks for all the replies, this is just the kind of info I was looking for.

The reason one engine probably has H beam rods, is its usually a wise investment, to replace the original rods when rebuilding the engine. Not that the OE dimple rods are bad, but by the time you pay to have them rebuilt, you're almost at the price of a set of new H beams, that are a bushed floating design, and overall better rod.

Would you notice any performance difference with one engine having H beams, and the other I beams? No. But, I also have ocd when it comes to that, my engines have to match in every way.

First thing I would do with those engines, rebuild them to stock specs, and simply put a better exhaust on. Unless you want to get into a different cam, custom ECM tuning, converting to an adjustable valvetrain, and so on.

It's kinda funny when you guys mention the OCD and exact matching parts etc. It's easy to sit back and say no biggy run what you have but when's it comes right down to it in my world it's kinda like wearing two different brand of white socks. Even though no body would know but myself it would still bug the chit out of me. MT U pretty much nailed it. I always felt good using my own reconditioned rods only cause I knew what I had and that it was worthy of the process. That was back before the H beams have become pretty affordable. I just wouldn't use any H beam as all.

Any brands to recommend on the rods? I have heard good things about Eagle products for the price.(from car guys)

When you say rebuild to stock specs, are you referring to my valve size question?

Eagles are a good rod. More than likely that's what's in the other one now. Or scats. There all very similar just go with the arp 2000 rod bolts which many come with. Up many with the 8740 which would probably be fine also but I'd get the 2000 just for future get ants in your pants and want more power. I think joes post regarding stock specs meaning merc specs. Correct springs, bearing clearances, valve guides, just in general copy cat the original build. Specs are easy for any engine builder to get.

just curious why you would keep the comp. 9.0:1 or less I'm rebuilding a 468 and was thinking of going to 10.0:1

Alot of guys want to run 87 octane.

ok i run 93 octane would the higher comp cause water reversion

No. Like MT said also most out on the water and considering your boat I assumed you were limited to what the marinas had octane and also with a heavier boat like that under a constant load I'd tend to keep the comp 9:1 or what ever the engine come with originally. Tell us a little more about the boat. For an addditional half point of comp with near stock cam or even perf your looking at min hp gains and not worth it. Detonation causes many problems. You have twins or trips in the boat. I get the part you like to cruise. If you like to cruise keep it as close to stock as possible.

Never mind the twin or trip question. If you had trips you might have aluminum rods in the third. Just kidding but anyway good luck am keep us posted. Even is you added another 50 hp a side what would you really see in mph gain. 2-3 maybe. Not worth it with a top speed of ? Just trying to safe you frustration and down time.

I definatily want to keep the compression down to where I can use cheaper gas. My boats aren't harbor queens, usually only parked during normal working hours lol. I think I will go with the H-beam rods in the other one. Would give me a good lower end if (when)I get the itch for more power later. Good news is the machine shop just called and said the block that had water in the oil is all ok, had some worries. Will see if I can post some pics of the boat tonight.

I would choose SCAT over eagle, I ran some scat H-beams in a 540

i have used both,imo they are equil,both use arp bolts and the big end size is spot on all the ones i have used.the pricing is also about the same.when it comes to crankshaft,s i would go with the scat,for some reason the eagle cranks i have used had journal dias all over the place.the scats were right on size.

I used SCAT cranks also

Good call on this, I disassembled the heads last night and found a lot of unevenness between cylinders on how clean the intake runners are, and how heavy the deposits were on valves. Who does this?

Also, someone mentioned stainless and inconel valves. Since these motors have been apart before how could I identify what kind of valves are in there now? I ask because I noticed a magnet does not stick to the bottom (valve) half of the exhaust valves, it will stick to the stem, and all over the intake.

Member ArticFriends, in Michigan, is close to you. He can do your injectors. He's quite intimate with the 502MPI system. LOl.

http://www.offshoreonly.com/forums/g...injectors.html

that's an understatement......................probably done more work on them than Mercury

Also, someone mentioned stainless and inconel valves. Since these motors have been apart before how could I identify what kind of valves are in there now? I ask because I noticed a magnet does not stick to the bottom (valve) half of the exhaust valves, it will stick to the stem, and all over the intake.[/QUOTE]

That can be a hard thing to determine. Manley put a code on the stem, usually a letter and number. I have not seen a code chart to figure it out, but you can call maley to find out. That is if they are manley valves. I personally feel better changing valves if I am not sure of what they are. Nothing worse than dropping a head of a valve on a nice engine. Good insurance.

http://i176.photobucket.com/albums/w...psbbijdmhe.jpg

Its not supposed to look like this? LOL, that is not from a boat, A customers car at work a few years ago. (I'm a tech at a GM dealership)