blown formula

I have discovered my new/old Sonic (88-31SS) has a Gen V & Gen IV 454's. One of them is labeled as a 420. Exactly what does the 420 designate?The other engine has no visible tag on the valve covers. Both engines have roller rockers and appear to be factory stock (sealed). According to the boat survey, both engines were replaced in '97-98. Is it likely that both engines are 420's? Were 420's made in both Gen IV & V versions? One electric fuel pump/no boss & one mechanical !! Both engines also have the Merc aluminum high rise intakes.......???
If they are 420's what are the specs and do they have "all the goodies" -forged crank, rods & pistons, roller lifters & rockers???
A search on 420's revealed some info but the links put up by
NW JIM in March are no longer any good. Help!!

I am considering a "freshening" & cam change if the internals are the good stuff.... always, the need for speed...... I'm just getting started finishing Too Old's project and already I'm going for the engine mods....
Help me please!!

formula31

Geez That deal is getting better and better. If I knew it had 420's I might have looked at it a little harder. I believe 420's were Mark 4's. Not sure but I dont think they ever made a Mark 5 420. The 420 has all the goddies, 8.8-1 compression,Rect port heads, 4 bolt main, forged rods pistons and steel crank, roller rockers and aluminum high rise intake. A ittle head work and a better cam and exhaust and its good to go. I dont know what to make of the one with no fuel pump boss. It has to be a mark 5 or 6. Post the serial numbers.

blown formula

I'll check the numbers next week end. My engine guy was the one who spotted the different Gen configurations and plainly the starboard engine has no mechanical pump, electric only. Thanks for that other info though. I have a two set of Stainless Marine exhaust on the way now.....just gettin' started!!

mcollinstn

420 is horsepower. Is a 454. Hydraulic flat tappet cam. Crane gold roller rockers. Only made them in MkIV's. Thru 1989 or 1990.

Dennis Moore

I have had a little experience with the 420's and have found that they are poor running engines because they are WAY overcammed. If I remember correctly they have Crane cams with 240 - 250 degrees of duration @ .050 lift.
Whomever (at Merc High Performance) chose these cams was stupid, plain and simple!
They also have the worlds worst ignition system the Mercruiser CD (not the Thunderbolt IV or V).
Changing these two things would turn the 420's into respectable performers.
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

blown formula

So, Dennis (or others) what cam should be used? Should I go to a roller lifters & cam? I would like to get about 450hp out of these engines..... with maybe a little head work...

Gary Anderson

The 420s were only Mark IV bocks. A 425 hp Gen V motor was made in 93. My guess is that they blew a motor and replaced the Mark IV with whatever was available, a Gen V motor. Since some parts are not interchangable between the 2 motors, I would have them checked out VERY carefully. Be sure it's actually a marine engine and the specs match the other motor. Keep in mind that they rigged it with an electric (marine?) fuel pump. A Merc Gen V motor runs the fuel pump off the water pump. There may be a lot of other things that were put together as a matter of convenience.
Also be sure the Mark IV engine was actually rebuilt. You may have one motor with A LOT more hrs than the other.
Gary

blown formula

According to the survey, BOTH engines were replaced, but I don't see how I could have different Gen blocks if they did. You may be correct. It is for that very reason, I am going to go thru them both...... still looking for help on cam selection

formula31

If 450 hp is all you want I wouldnt go the extra expense (lots)and less reliability of a roller cam. The flat tappet cam should be around 224, 232 duration at .050 with .525 to .550 lift. I use the Edelbrock torker cam because I am using silent choice with short risers. It has a 114 degree seperation with hurts its power some. You could go to 112 or even 110 degree seperation if your risers are long enough. If you have the money, the roller cam with give you more horepower but on a mark 4 I think you need to have the lifter holes bored true and bushed to use a roller lifter. There are special roller lifters made for these older engines. You may have a roller cam in the mark 5 engine.

Dennis Moore

If you really want maximum power and fuel economy (you should use Formula 31's cam specs but) use a hydraulic roller camshaft.

The engine will idle smoother and make more HP with a roller camshaft than a flat based camshaft with similar specs.

Remember that all new engines come from the factory with roller cams (even stock automotive and truck engines) and durability is not a problem for them!

The use of synthetic oil on a roller lifter camshaft is NOT a problem. If it were then we would have thousands of cars and trucks (with roller lifters that are using synthetic oil) failing every day. The synthetic oil manufacturers would be buried in lawsuits!

Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE