Looking for info tech on the 525 EFI
 

Hey guys;

Looking for some info on the 525 EFI engines. I'm putting a 525 EFI system on a 502 Mag shortblock. I'm on a tight budget and am doing all the work myself. Looking to copy mercury's top end. Mercury racing won't give me any info without a serial number (understandable, but it still sucks), so any info, links to info, or even a serial number for a 525 would be great.

I've found plenty on the cam, including the crane part#, its the same besides the 114 L.C. Close enough?, or should I pay for the custom grind? Also what is the rocker ratio on the 525's.

Exhaust, I was looking at the lightning marine steel headers, the cost savings seem to come from the steel construction, not lack in performance, any thoughts?

Heads are totally up in the air, any info on the 525 heads? Intake/Exhaust runner size, combustion chamber volume, valve size, or any recommendations on a suitable aftermarket head. I was looking at the merlin marine prepped heads in the classifieds, as I said I'm on a budget.

I know this alot to ask, but if I can pull it off I'll list the whole setup I used in the spring, any input is greatly appreciated.

Thanks in advance

I'm no builder but if you intend for this motor to run for very long I REALLY hope you have the computer dyno/tuned once the build is finished. Last winter we built a pair of motors and thought we did everything right...(even put one on the dyno). 2 hours later we lost one! :(

Also; why is it that some posts can get dozens of responses in minutes and others (like mine) an lucky to get 5 in a week? Seriously, I'm not bitter, just curious.

The rocker ratio is 1.7.
I'm not sure on the exact spec on the heads, but if you are using a 525 ecm with it's program, you need to have the EXACT cylinder head for the program to be right. No one can get into that computer to tune it. Your other option is to use a MEFI 4 computer and harness and start over on the program. If the heads and cam are not exact, the motor will run like crap, if it runs at all.
I had a proven engine that I did several dozens of with Dart Pro 1 heads. I did a pair of engines and re-used the customers aluminum Merlin heads with the same size runner, combustion chamber, valves, springs etc as the Dart's and the engine would not start. The difference in shape and flow of the heads runners was that big of a deal.
As far as headers, I have had NO luck with the lightnings, but I came from salt water. Can't go wrong with CMI e-top headers or IMCO's powerflow manifolds. Hope this helps, Eddie.

Check Out

I have found a lot of info on mercruiserpartsonline.com without a serial number. I will also go through some customers files and see if anybody has a 525 EFI and get you a serial number if the previous does not work.

As far as responses to your posts, It depends on the question and how many people can help you. I am sure that the people do not know you personally and will not answer your questions out of spite!

I'm pretty sure they use a version of the edlebrock aluminum heads. I don't know any specifics though.

I'm with you Griff. I thought it was some kind of Edelbrock head, just don't know exactly which one.

edelbrock marine alum. head, its square port and the water jackets are coated, they also use a arizona speed and marine mono blade throttle body on the intake

go to the bottom heads 454-R marine is whats on the 525. the 741 cam is pretty big for wet exhaust, has a lot of overlap, thats why merc spread the seperation to 114 degrees from the 741's spread of 112,

If you are trying to make a copy of the 525EFI and using the computer, then use the custom grind 741 on a 114 lob sep.

The computer program is pretty unforgiving. If you really want a 525 you need to match the engine as close as possible if not exact. The cam must be exact as the sensors read vacumn to control idle. Controling idle is the hard part of a EFI. I would only do this with a marine stock 502 bottom end, the 525 cam which as stated is the 741 on a 114 lobe, Elderbrok aluminum heads, and CMI long sweep exhaust. Good luck & I hope it works.

Thanks for the info so far, I'm kinda wary but think I'll go for it, hell worst case I slap a carb and intake on and I've still got a big cam and bad ass exhaust.

Just wanted to say great sugestion, I even found serial numbers on there.

Does the 525 use the stock dog bone roller lifters with the "741" cam?

No. They use the style with the tie bar.

CHEKT OUT,

In case you are interested, I have many extra parts from two 525EFI after converting my engines to Whipple Blowers. They include heads, computers, wire harness, fuel injectors, manifolds, fuel pumps, Plenums and more. Will offer at a good price. Tell me what you need.

Ray

what kind of cyl. heads did you install to replace the edelbrock's with?

Do yourself a favor and get a wide band O2 sensor and weld a bung in your exhaust. Just my .02 reasons.
1. Use to test initail tune before you hurt parts.
2. Can be used for set up with new ECM program fien tuning.
3. Use it to set up your carb fine tune.