I have a 27/29 1988 fountain fever. The boat come stock with 330's and bravo's. I was looking to up the motors by about 100 a side. I found a set of 420 trs's and was curious how good they are.

Could I just take the flywheel off of the 330's and swap with the 420's or are the also used for balancing? (I know the ring gear is different)

Are they as reliable as the 330's?

My motors were rebuilt in 05 and have been perfect in terms of reliability. Or... should I just upgrade the 330's?

Sorry for the ramble.. Thanks in advance.

They are great bullet proof engines. They have all the good forged internals and I believe the base platform for the 525sc. Just add blowers.

Do a quick search in the Tech Forum and you will have a ton of reading.

From the way I understand it, you'll need the flywheels from a set of MAGS, the internals on your 330's are totally different (cast crank and pistons for one).

I am essentially re-creating a set of 420's this winter, except I'm using RMP performer intakes and a different set of roller rockers.

Put it this way, they are every bit as reliable as the 330's and then some.

I have a set I would sell cheap.
Pm me if anyone is interested.

Similar to Merc 525SC internals but not the same. 525SC's were assembled at Merc Racing. Not sure about 420's. The 525SC's had 7.5 comp ratio. the 420's were 8.75 CR. They do use the same crane cam, 454block, and GM crank and rods.

I believe the Hawk 525SC's were 420's with a 174 blower.

they were basiclly the 454 magnums ( rect port alum intake better cam) for the day good engines, the flywheels from your 330 will work fine, there is no diff in a magnum vs std flywheel, unless the 420's have the starter mounted high and reversed those will work as well, they are just 168 tooth ext manual trans flywheels...I bought one a while back that had the ring gear groove on both sides, and you can swap the ring gear by heating it...Rob

The Merc 420hp has an ALL FORGED rotating assemly and also comes with Crane Gold roller rocker arms, flat tappet hydraulic cam/lifters, cast aluminum valve covers and (if I remember correctly) a Holley carb.

The only thing I don't really like are the GM rectangle port heads which are a little too large for a N/A 454cid marine engine and also have a tendency to crack between the seats,....but even so, it is still a good/strong overall base engine.

Very good motors, good power. I've worked on quite a few. The only thing I would suggest, depending the hours the motors have, is to freshen up the valve-train. I've dealt with a couple broken rockers on friiends boats before. The only other thing I would mention is DON'T shorten the stainless stacks on the exhaust. There was a guy around here that put a 420 in a bravo application and cut the stacks down to about 3" long. The motor wound up suffering from reversion.

The 420's were originally assembled by Merc Racing. They are the same as the 525SC's except the SC's had 7.5 compression pistons in them.

Until I could afford it, couldn't I just use my basic merc exhaust from the 330's? They are 2 years old (4" center dump iron)