obnoxus

A couple questions for the experts. I am rebuilding a 1995 502 MPI I recently bought. While flipping through the manual I noticed the 95 has a different plug gap as 96 and newer,,,, anyone know why?

Also, would it be worth it to switch to roller cam and lifters, any large hurdles on a 95 motor?
I had planned on switching to roller rockers.

next,,,,,, cam selection,,, I put over 100 hours a year on my boat between april and oct and dont want any tempermental problem downtime I see others go through after trying to go faster.
That said, I am between a rock and a hard place ( I want to go fsater !!! ) of picking a stock cam and being safe, or going to something larger and having my ECU remapped,,, opinions,,,,suggestions?

Lastly,,, heads,,,,stock rebuild ( I will switch to inconel just becouse ) or larger valves, port work bowl port etc.


Thanks in advance,
Dennis

deboatmon

Obnoxus

I had great luck with Rod Dash at Fox River Performance Marine in Oshkosh, WI ( 920/236-4220 ) with a pair of 502EFI's. He added moderately agressive Crane roller cams/lifters and Crane roller rockers, modified the ECM's, did a little head work, added INCONEL and Manley stainless valves, tweaked the motors on a dyno to perfection and added long through transom Stainless Marine risers that dump water right at the end. He has built lots of these and knows what works as well as pretty much anyone going. He knows what works as well as what doesn't work. He will not sell you something that doesn't make good, reliable power. He's also not too far from you. My motors have 250hrs and have been absolutely trouble free. I am just now this winter freshening up the top end ( springs, lifters, etc. ) after two long seasons of long distance cruising and reasonably hard running.

Rod is not cheap, but good work is not cheap and cheap work is not usually good. He's reasonable and usually has lots of good motors around and might be able to do a swap with you.

As far as I am concerned, there's no room to experiment with EFI motors. Minor mistakes are usually costly. Use someone with a good track record. I'm sure there are others that offer good service, I'm just commenting on where I got mine.

obnoxus

I know Rod well,, just getting some ideas and input on a do it yourself project,,, stock rebuild will probably be the end result.

Thanks Ken,,, hope ya get another 250 out of them !!!!!!!!!

maverick1

Rebuild ideas

502 will accept a roller cam - roller rockers - you just need the right parts --- crane cam's hot line will give you ideas on retro-fitting also they will give you ideas on cam lift and duration- but you get different advice from different techs on different days. ECU - work by my recommendation goes to MARK BOOZ - he's out of louisiana & I have used him and others speek highly of his work also. iconnel valves seem to be used by those who are building big motors around here but stock 502 valves are pretty hard already.

Flame arrestor on 502 delivers nothing ( contrary to adds). Headers seem to deliver some speed-- IF you also put more fuel into the motor.

I've spent a lot of $ over the last few years and gained a little. Also, I lost speed when I paid a local shop to install a Hydrodyne cam -- the following year I took the motor down myself and discovered the cam to be an off the shelf crane cam with street spec.s lower than I started with. (lost performance was then no surprise)

For specs on the 502 -- look up the old Hot Boat series of artilcles on Hot Roding the 502. Good article and good specs - one of the series of articles was on headers, another on cam choice.

Anyone with a Merc service manual can get you the 502 magnum cam specs for your cam and the later 502s which DO run a roller cam. The advantage of the roller cam is that at the same cam spec - the roller is open higher / longer.

Good Luck

MAV

Raypanic

Check this article out this setup is good for about 500 Hp: http://www.azspeed-marine.com/articles-1.html

obnoxus

Thanks Ray,,, I have been looking for that article !!!!!!!!

JJONES

WHILE YOU HAVE THAT THING OPEN,PERFORM COMPLETE SURGERY,NO SENSE IN DOING SOMTHING THAT YOU WISH YOU WOULD HAVE DONE MORE LATER.AFTER ALL,ITS ONLY NUTS AND BOLTS!!!!