Stock 502 Mods for efficiancy
 

Hello my gear head friends!
First I am not a teckie just and engineer (not mechanical) to let you know where I am comming from.
I would like to make my stock 502 more efficient but remain stock as possible, my first thought is to make them breath better. Would I accomplish anything by bolting a 500EFI plenum (and if nessary manifold) to my stockers? Or would I be better off just changing to a K&N Breather?
Also would a change in exaust manifolds help to say CMI casties or somthing that will work with my captian call?

I assume you are taking about a 502MagMPI.
Yes, a better flowing exhaust will help. I put Stainless Marine manifolds on my engine.
The AZ Speed/500EFI intake does flow better than the Stock Merc but not worth the $$ and effort on this engine without other mods.
I don't know if a K&N arrestor flows better than a stock unit but they sure look better...:cool:

Efficiancy Mods for a 502 MPI
 

Thanks for your reply.
You are correct in assuming that these are MPI's. I need to change my exaust anyway because they are salted and making my starboard engine steam. I have Corsica captians call and will have to bolt up to that. I will look at Stainless Marine to see what they have.
Thanks again!

The Corsa diverters won't work with headers.

Headers
 

Thanks for your input.
I was not planning on going to headers, just a better flowing aftermarket system like mabe cast lowers with a close elbow upper to mate with the Corsica diverter.
I think a lot of companies make them, EMI, Stainless Marine, ect. I don't have a clue who's is the best choice for improving efficiency.

Moondance, If you are interested, I have a Rex Marine K&N adapter and filter for the 502 Mag that has very little use and will sell for $75.00 + shipping (new from Rex is $180.00) . call me Mike (909)576-4337

K&n
 

Thanks Michael,
I'll keep that in mind. If you look at the adaptor it closes down to a 3 or 4 inch round hole which would limit the CFM. This may not matter much but that is the question I am asking everyone. If you look at a 500EFI plenum, the K&N mounts to a larger opening (unless I am mistaken).
Thank you for your input.

Moondance, I have done quite a few of mods like you want. I would put on IMCO Thumper series manifold headers, that will work with your captians call. They can also be polished for not much more money-around $1200. I would then install some 1.8 roller rockers that would make your cam a little larger and a sharper ramp on opening and closing(more efficient). These two should take you up about 400-600 rpm, Which is at least one prop size up, If not two sizes. Please PM me for a more extensive list and prices. Good Luck, Rob

Do you have 2 of them???????

How many hrs would you have to put on the boat in order to recoupe the cost of installing exhaust from any gains in efficiency? Providing efficiency is the only goal here.

Good morning Speedreeder,
Thank you for your response. I wanted to share an example; One of my boating friends and I were talking last night about this. His boat is an 07 42 Fountain with Merc 700's and #6's, holds 220 gal of fuel. He can run 4 days (avg time on H2O/day ?) hard and still have fuel. Mine 31 Sunseeker Hawk twin 502 MPI's over B1's, 120 gal of fuel running moderate might make it a day....maybe. Granted Reggie has developed an efficient hull, but something needs attention. These engines had 270 hours of salt before I purchased the boat, only 5 hours in the last 5 years from the previous owner. They now have just under 500hrs the balance in fresh water.
I did commit to purchase 3 set of reworked 502 heads last night that have 10 hours on them (I'm not sure but I think Joey Griffin did the rework) and I will sell one set off.
With what you are talking about roller rockers are in the heads right?(showing my hand a little) Did I jump too quick at these heads for what you are proposing?

US1 Fountain
 

Hello my boating friend,
Efficiency is my real goal. I love gen6 502's (something nasty-n-gnarly about them for me, like an old shovelhead) but I prefer stone stock if possible for the reliability side. My hull is not very fast it's a Sportcruiser after all. When I feel the need for speed I ride with friends.

I failed to mention that I run with my through hulls closed a lot but try to keep them open above 3K RPM.

Moondance, I think it will be very hard for you to get any efficiency with the weight and design of your boat. I'm talking about any that you can feel. Do you have a flowscan or something equivalent to that (fuel flow). That would be a meter that you could look at and see SOME difference. Then I think you should try some 4 or 5 blade props for the way that you want to run your boat (not for top speed). Speed and fuel savings will not ever go hand in hand on a boat of that weight. I do think that you are past do on hours to change or rebuild your heads. You need the casting number from your heads to see if they are right for your setup. What kind of work (porting) has been done to the heads that you bought. I do feel you would get power and economy if you would port match the intakes to the heads with gaskets and also match them to some aluminum header manifolds. The guy on swap shop or ads that is selling the MARINEPOWER manifolds are very good and they are exact castings of IMCO thumper series. Good luck and ask anything else. Thanks

I think adding a decent set of the better breathing aftermarket exhaust manifolds is a good place to start without having to make computer mod adjustments---as I have always heard the 502mpi's run on the rich side from Merc anyway. Not sure if a computer mod would be required with adding 1.8 rocker arms though---although I think adding roller rocker arms would be a good upgrade----and the better K&N breather especially if it is true that you can get 400-600rpm increase without having to make cam mods and other internal stuff.

Years ago in Hot Boat Magazine, Tyler Crocket did a tech article on upgrading/mods of the Merc 502mpi engine. If I remember correctly he made these changes....

-surface cut the heads .020" (increasing the comp ratio)
-competition valve job (3-angle???)
-added a 2.25" intake valve (vs the stock 2.19" valve)
-upgraded to some CMI elbowed exhaust header system
-replaced the stock breather with a better breathing breather
-added a slightly larger cam profile
-replaced stock steel stamped rocker arms with ROLLER rocker arms (I think they were Crane Golds)
-remap of the computer
In his article I think he said these mods were good for about 100hp from the 502mpi.

I think I remember Crocket mentioning in the article that he had found that porting the heads to any extent did not really bennefit in boosting the power in the upgrading the 502mpi. I think all he did was clean up the bowls and remove any of the sharp edges on the short side radius.

Many Thanks
 

Thank you so much for your input! I, like you pointed out am looking for lowering my fuel consumption. My boat is possibly around 10.5 or 11k wet weight. It runs around 57 mph wfo which is fine with me. It has mph robbing bottom paint now but I am changing to white Interlux VC teflon paint this winter (mainly for the look instead of blue bottom paint). I will look at the mods that you have suggested. I assumed that I should look at prop changes but wanted to correct any mechanical issues first. I am lucky to have access to various sizes of props after I solidify the mechanical.
I deduct from your input that I am past due on a refresh which the heads may be a large part of fuel consumption then props the other part. I had a good mechanic evaluate these engines at the beginning of this season. All but one cylinder was within a pound of each other. His conclusion was time to freshen them both but he doesn't want to do the job. He wants me to repower with 496 HO's. Not going to happen, I love 502's. If I was planning to repower, it will be back to Diesels as this boat was built.
I may have three set of heads to sell.
Last, Where is your shop located?

Any input Tyler
 

I realize that stockers is not "your Bag" though.

Kaama
 

Thank you for your input. I may see if I can pull that piece from the internet. But I don't want more horses just less juice. Of all things to say; I want them to suck less not sux.

But after any mods this winter and no improvement, I will still LOVE my boat, shut the F... up and just feed it fuel.

Kaama by your name am I to assume that you also own a Kaama/Formula? One of my boating buddies has one.

Thanks everyone for your input it helps me a lot.
Moondance

No, but I once owned a KAAMA SE 38' Wellcraft w/TRS drives. I now own a 32' Active Thunder w/Bravo One's.

If you're trying to get better performance and efficiency with the gas the engine is already using, then I would install the better breathing exhaust, better breathing air breather, install roller designed rocker arms, and if you take the engines apart I would also clean up the rough edges and short side radius within the bowl/pockets on the heads. A little clean up porting and good breathing exhaust system is usually refered to as "free horsepower"----but then, we all know nothing is really for free---especially these days and in the marine world! Just have fun while you doing it. :)

Thanks that's exactly the information I was looking for. I assume the SUCK/BANG/BLOW theory would apply. "SUCK" in more air, "BANG" fire the gas right, and "BLOW" out more air.
Next question; Who's intake and who's exaust would work best for me?
Thanks Kaama

Moondance---

Well usually, when you suck a little more air it requires a little more fuel so you don't burn the engines down. But as I have said, Merc usually runs their engines more on the rich side vs lean. So, those mods MAY not require adding more fuel....or a fuel map change, but perhaps you can have it checked after the mods are completed just to make sure---you dont need to be burning the engines down.

As far as an exhaust system goes I would consider Stainless Marine, but someone else (Speedreeder) mentioned Marinepower manifolds that are supposedly the same exact casting as the IMCO "Thumper Series", but I do not know how accurate that is so I would continue to dig a little deeper. If speedreeder has done several of these mods then perhaps then he would know much more than I would. You can call him and ask LOTS of questions about his claims and experience with the 502mpi and the mods he has done to them. Also, I my friend "Articfriends" is a good guy to ask---he knows quite a bit about the 502mpi and he has a good reputation here on OSO and will tell you straight!

You mentioned the word "intake"....I do not believe you have mentioned that before. I would just leave the intake alone. Just put the better breathing aftermarket breather on it.

Thanks Again Kaama
 

So you think the 500 intake and plenum are wasted $, for little improvement. I will look for the best breather to satisfy that part, say the K&N units I believe they bolt right on.
You mentioned port matching the heads to the engine, I did commit to purchase three set of (I believe they are Joey Griffin) heads. If they don't match I can sell them for what I got in them. And I'll purchase the best exaust units I can find for my application. Then I'll re-prop next spring.
As I mentioned before these are salties and they just need some TLC.
Thanks for your input to my forum it help me stay on the right track instead of chasing ideas.

I did NOT mention anything about port matching the heads to the intake---although that would be a good thing to do. What I DID say was to CLEAN UP THE BOWLS within the heads and remove any sharp edges and casting marks/flaws especially on the short side radius----nothing major at all.

Also, you are asking the wrong guy about the 500 intakes. I do not know what if any gains you will make with them. Some things I know well, but if I don't know I am not going to pretend that I do. That's why I said that you might try calling "speedreeder" as he claims to know much about the 502mpi engine and mods---BUT I would ASK LOTS OF QUESTIONS about his claims and do your diligence and homework before you make any decisions.

Perhaps others who really know the 502mpi well and can chime in on the type of mods you are seeking and interested in. Speedreeder has already made some interesting suggestions, but I do not know him well. I hope I have helped you to some degree so far.

Also, I don't know where you're located, but if you're looking for a good shop with an awesome reputation to rebuild your engines without any "hype" you may want to consider WESCO Racing Engines in Jenison, Michigan. Dave Wesseldyke is the owner and 98% of the engines he builds are marine hi-perf offshore engines. His number is 616-662-2250.

Thank you Kaama
 

I have gotten a lot out of your input.
I am located in S.C. just an hour out of Atlanta. We have a few shops close but all the engine builders that I have been exposed to are all "Hot Power" guys. Scotty Cannon is a friend and a local, but he's doing 700's to 2200's and up with big $. Jerry Grimes is just down the road in Alt. but same...big horsepower. Joey Griffin in Washington, N.C. does mainly race boats for Fountain, and poker runners in the off season, he may entertain my stockers if he has a hole in his schedule. I have been to Joey's shop several times with friends and their Hot Boats and he absolutely positively knows what's going on.
Thank you for you "engine Guy" reference. I have drugg boats up there before for the "Silver Cup Series", so it's not out of the question.

Well, if you have someone who is local that has an excellent reputation with marine hi-perf offshore engines then I would use them.

My builder told me he treats each engine with the same respect as his high dollar stuff. It does not matter whether it is a bone stocker or an all out high pressure thumper race engine. There is a given number of point checks he does on each engine that he believes is paramount in how an engine survives.

Anyway, whatever you decide to do I hope it all goes well for you.

If your talking vehicle fuel efficiency vs BSFC (amt of fuel per horsepower) then:

If the engines are in perfect working order including tune, then your fuel mileage is almost solely dependant on the boat, it's set up, and it's driver.

If your boat takes 500hp to cruise at 50mph and your friends boat takes 300hp to cruise at 50mph, well, he's using a ton less fuel then you are at that speed.

HP=fuel !

Weight and hull design are 'way numero uno' in regards to fuel mileage. Propping/drive placement follows.

BTW: Idling = 0 mpg.

Thanks SB,
I think that through this blog I have determined that my engines are due a top end job. That may be the only real issue that I have other than some reversion on my starboard engine which I think replacing exhaust manifolds will correct that.