502 efi upgrade
 

IM upgrading my 454 330 hp engines in my 30 scarab panther to a pair of 1998 502 Mag 415 hp efi's.
I bought a pair of them and one has a broken rod and crank .After dissassembling the damaged one i decided to get a new rotating assembly (Scat) with all forged parts as that is stock in these.(Yes i knew one engine needed repairs before buying,lol)
My question is if im replacing the rotating assembly what can i do for mild power improvements without going crazy on the other engine too.
My thoughts were a camshaft upgrade maybe just to gain a few ponies, without the extreme expense(both engines of course)
If i upgrade the cams how does it affect the efi system?
Does the efi system need to be recalibrated , and how can that be done ?
Also what Pitch props would i expect to use?
With the 330 hp engines im running 60MPH @ 4850 RPM with 21 Mirage plus's which is higher than the 4600 Rpm i should have.
I figure a set of 25P mirage + props would be best but im not sure?
Thanx Ralph:ernaehrung004:

Did one. Scarab Panther, bravo drives, 502 MPI turned into 500HP MPI. ended up I think with 25 hydromotive QIV @ 81 MPH. Not too hard to change engine. Yes you have to remap the computer.

If you put bigger cams in,exhaust etc you might want to bore out the throttle bodys,its worth about 10 hp. I have a source for having it done,pm me if interested,Smitty

If anyone is looking a 502 to play with I got one that needs a home. 502 carb 123 hours. PM me you are interested.

jimg
Where did you get the computer remapped and what is it worth?Any idea what cam you used?What exhaust ?Thinking about Emi Thunders due to cost since true headers are extremely expensive for two engines.Are Emi's good enough?
Looking at Comp cams 01-419-8 / 114 lobe sep , 224/236 .510/.520 lift since they say no computer remapping required.
Thanx Ralph

Smitty,

When you bore the throttle body, do you change the flaps that in it??? where do you find these??

Harry

The butterflys are custom made in a larger diameter to match the bored out throttle body,it was worth about 10 hp/ft lbs of tq acrossed the board running my 540 N/A on the dyno,Smitty

If you change cams and exhaust, you MUST get the ecm remapped. It controls the fuel curve. Witout a remap, you will most likely lean out and burn holes in pistons. If you change to cam that says no remap is needed, then it is unlikely it give any more hp.

I have the EMI thunder exhaust on my 502 & I think that they would be fine for your modification plans. They will flow alittle better & are way lighter than the stock exhaust.

If you are doing so little in mods that it doesn't require an ECM remap, then why spend the $$$ for such a small gain????

Exhaust is a good purchase if you are going to do future HP mods, but it does little by itself.

Smitty,

Can I buy a throttle body which is ready bored and with the bigger butterflys.
You can e-mail on [email protected]

Harry

I have to find the sheet. there is a whole recipe for doing the engine. will basically be a 500efi when you are done. runs real well and dependable. don't ever let anybody tell you that you can put a bigger cam in & not remap. maybe you can but I don't think it is wise. the remap costs about $400 last time I did it.

WHo are the better names in remapping. I'm going to use a "731" cam.

cam I used was 169621.
Use Mark at Precision Marine for programming your efi. He is as good as they get. If you want to remap I would suggest a tried formula unless you want to send your engine out for dyno time & custom tuning.

That cam is very similar to my 168731

So who do i contact for a remap?What would be a good cam without having to change whole drivetrain on both engines?Exhaust Manifolds are first on my list and mirage plus 25p props.Sill dont know if Gil is much better than Emi Thunders?I can get a good deal on Emi's.

FYI...I have had my stainless marine exhaust for 6 years. Still like new.

I also like the stainless marine. I have it on my own boat & alot of others I know of. Nobody has leaks. just make sure you get longer tailpipes than the stock-like short ones for any type of high performance engine. I can also get the remap, machining, or any other parts or services for you for the upgrade.

Jim

So far Stainless Marine seems to be a favourite in this thread although from research on the internet it seems like Gil is most popular.Their runners are supposed to go all the way down the tailpipe from what i understand.I cant seem to find any info on the EMI thunders as to what they are built like on the inside.Are they just an open chamber Manifold or do they have internal runners?I hve decided to stick with stock 502 mags but im gonna get manifolds and risers this year.Next year i can still do some performance work once i get some more cash

If you buying rotating assembly you could make it a 540. You bore the block .030 over and make it a 4.500" bore with a 4.250 stroke. Use the Crane 168741 cam. I did this and used the stock fuel injection and the motor made around 600hp.

NoisePollution
would that not affect the fuel system?More CID - more fuel required?I couldnt imagine just putting a stroker crank without EFI remapping.
Ralph

Yep, there is more to it. There's a kit to make the fuel regulator adjustable. The Ecu has to be reprogramed. Mark at Precision Marine is good for that. $350 to reprogram. I used Dart Iron Eagle heads. While mine did run good, the biggest draw back is the 502 intake. Its restictive. The HP 500 EFI fuel injection flows better.
I'm looking for power so I'm changing over to a Dart or a Merilin single plane intake and a 850 Mighty Marine Deamon carb.The plus, I can tune it myself. Threre's a lot of Pro and con's here, but the carb wil make it simple.

Decided to stay stock for now since im rebuilding both engine and cash is getting low, but im preparing for the HP increase next year or so by installing New Forged pistons and Eagle H-Beam Rods And Manley Exhaust Valves now. he only thing im still wantingto do this year yet is Props and better Exhaust Manifolds. Any suggestions for these?
Thanx Ralph

Everything you might do for your motors is not always purely for more performance. Many things you can do are more for reliability than performance. Changing from stock exhaust is a great start. The difference in horsepower is not that great, but you add much greater reliability with regards to water problems in your boat and or motor. Personally I like the long, through transom risers from Stainless Marine with no hose and tips. And, If you opt for bigger cams later on reversion is virtually eliminated altogether. If you plan on cruising at 3500 RPM or above you might want to change the rockers as well. I've not seen too much written about replacing the stock air filter/flame arrestor on the 502 EFI's. You might consider adding a RACOR fuel filter if you have VST engines. The VST screen can really get fouled quite easily with dirty fuel stops and when fouled that motor is not going to run. I personally would add oil change lines to the oil pans to facilitate quick and easy oil changes. If it's easy it's likely you'll change more often.

Like I said, many changes are for reliability and not just performance.

I dont have a VST system on my 98 MPI's and im not too sure ill ever go all that radical on the cams.I'd be happy with 500 hp pr engine in the next few years.For this year 415 HP is gonna have to do

Thanx Ralph

The stock 502 MPI is a great engine package I believe. You have lot's of options and one option is to remain stock.

There's no bad options for your package.

Enjoy !

JIMG recipe
 

JIMG did you ever find that recipe...I need to freshen up my 502MAG and would like it to become a 500efi.:drink:




JIMG wrote....
I have to find the sheet. there is a whole recipe for doing the engine. will basically be a 500efi when you are done. runs real well and dependable

Tyler Crocket has a kit for the 502MPI engine that he claims is good for another additional 100hp. There was an article on it in Hot Boat Mag several years ago. I am going strictly by memory....

1) 2.25" stainless intake valves, and stainless exhausts
2) cut the decks of the heads about .020"
3) larger hydraulic roller cam
4) remap computer
5) larger throttle body and aftermarket airfilter (K&N?)
6) CMI elbow exhausts/headers

If I remember correctly Tyler didn't mention anything about any porting of the heads, so I would think just some minor clean-up in the bowl areas would be sufficient. Of course, I would always be tempted do some shortside radius work on the exhaust side. Also, I cannot remember if he brought up the cam specs, but I remember it being a pretty mild cam so that it works well with the MPI system. Last I knew computerized fuel injection systems do not like a big, choppy rough idling cam. If you buy the kit from Crocket you should probably expect to pay premium pricing.

With a little research and help from others on here you can probably piece it out part by part if you want to save a few bucks.

Also, you can call RMBuilder/Bob Madara of Marine Kinetics....he has been involved with some 502MPI cam upgrade projects as well. Bob's number is 585-654-8583.

You're most likely going to need an aftermarket exhaust system upgrade first if you expect to see any real power gains/differences. Have fun.

Already looking for cmi exhaust.Decided to rebuild motors and using eagle h beam rods and manley stainless exhaust valves and forged pistons/cranks.Getting both balanced so later all i need to upgrade is heads and injection/induction system

Thanx Ralph