obnoxus

Not to beat a dead horse, but I have the motor apart and have a few questions,,,,, the heads I have down,, bronze guides and teflon seals seems to be the answer there.

It is a 95 MPI NON roller motor,,, is it worth switching over to roller cam/lifters? what cam can I use,,, roller and flat tappet specs. will the stock ECM support roller cam gains?

What rings are everyone using?

Also, I remeber a thread about grooving the heads for a special type head gasket,,, is it a good choice for a non blower motor?

Also,, has anyone used "coated " bearings,,, my motor guy recomended them. They had a grey coating on them,

CANT WAIT FOR SUMMER !!!!!!!!!!!!

KCHOTBOAT

Build a 540 motor out of it. I ran JE pistons and rings.

blown1500

obnoxus, if you can, make it a 540. The roller cam will outrun a flat tapped to death, but if you do ANYTHING to help performance much, you better have someone modify the computer!
I would talk to Jim at Arizona Speed and Marine.
I have tried many different rings, na and forced induction.
I do not like zero gap rings on the second ring. Zero gap top rings are the ticket, but you must follow dorections to the letter-which stone, load, number of strokes, etc. If you don't, you may have trouble. We use Speed Pro file fit most of the time. I have used several brands and had some success with them as long as you get the performance set recommended by the manufacturere. If you use JE pistons, they will sell you rings with them at a very good price and are excellent rings.
I had the thread about head gaskets and I would NOT use the receiver groove head gaskets on anything but all out engines. Fel Pro and Cometic are my choices, but there are many other good ones available.
I like to use coated bearings. Calico Coatings in NC can fix you up at a good price and recommend the proper coating for your application. Their number is1-888-236-6079. There are lots of others who can supply quality parts also. Any more help I can be, just post or pm

obnoxus

Remember,,,,, MPI !!!!!! Stock rebuild,,,, the only thing I am considering is roller valve train to bring it to gen6 specs,,, wondering if its worth it !!!!!

I have 2 people interested in the boat,,, I just want to give them the best and most reliable engine I can.

In the can thread there was 2 specs that were posted as stock for the MPI motor,,, a 483, and a 511,,, which is it?

If I was keeping it the 540 route sounds sweet !!!!!!!!

excaleagle42

a roller cam can pick you up to as much as 50hp with the same grind as a flat by parasitic friction reduction and increased valve speed. that means the fuel curve will need to be remapped slightly.
a roller cam is also not a straight swap. different lifter companies have diffent height lifters, you may need custom pushrods after checking the valvetrain geometry. the cost of a roller cam without the lifters is more than the cost of a flat cam with lifters in most cases.
i am of the opinion, if your selling the boat, keep it stock, save your money. with the money you saved you can start building those 540's. better yet, a 4.25" crank and a 4.50" stroke crank cost the same so build a 572 instead.

obnoxus

Thats part of the reason I have to question Mercruisers ratings,,,, The motor is a 95 MPI rated at 415 prop hp,,, but a 97 502 MPI roller valvertrain is also 415 prop HP,,, WHAT GIVES !!!!???

obnoxus

Yep,, according to my service manual both are rated at 415 prop hp,,, HOW CAN THAT BE !!!!????

obnoxus

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ANYONE !!!???

maverick1

I run a 502 EFI (manu - 1995 - no manual fuel pump on block - no port for one). Had #8 exhaust fail in the third year. After trusting a "local shop", the second year following "I" pulled the motor and did the work myself --- up graded to a crane roller cam and roller lifters, push rods and springs and 10 deg. titanium keepers-- all crane stuff. Per Merc's specs, I dropped a little duration and picked up some lift. What everybody tells you the valve speed in faster with the "roller" so even with the same specs the "roller" cam gives you a fatter opening period.

Unfortunately, I didn't see an increase in speed and had some hesitation with heavy throttle from idle. Booze out of LA., did some reprograming for me, and only then did I see an increase in speed. (Very happy with Booz - did what I asked, and good follow up customer service)

Yes, it will work. Is it worth it???? I'm not unhappy with the move, and am stepping up to CMI exhaust this year and am hoping for more speed.

Crane Cam's tech line will help you a lot, but different technicians will give you DRAMATICALLY different advice.

If I had it to do over again, I would have taken more duration and more lift. ( Maybe next year...... LOL.)

MAV

blown1500

MAV! I need to talk to BOOZE out of LA, please. Also, the Crane 741 works miracles in a 502!! Oh yea, you will need exhaust.