1stINSTIGATOR

I've got a 41' SONIC and it's time to freshen the motors. I currently have 454/420 Merc's with over 1000 hours. I'm debating whether to freshen these, build new or buy new. Cost IS a factor! I also need to pull the motors from the boat while on the trailer in my driveway, any suggestions?

Panther

From the looks of it, you got plenty of use out of those 454's. Is the boat fresh water cooled? My guess is that they are raw water cooled. If this is the case, the heads are probably junk, and the block probably has significant water passage wear. It may save you time and headaches to go out and buy two 502 crate motors. You can probably get the crate motor at close to the same price as someone will charge you for new heads, and rebuild etc.

Just my opinion!

blown formula

I concur about the 502.....go new/crate. You will have the engines in a week!!

1stINSTIGATOR

I've already redone the heads on my Port motor last fall. The cam had failed, so I redid the top end. The motor came apart on me again a couple weeks ago. Same problem. Sounds like the cam bearings are shot! SO, I've got at least 2 new heads already! Where would be a good source for new blocks?
THANKS!

Dennis Moore

Thats a lot of money that you will spend for new blocks. I doubt that you need new blocks but I would have them inspected closely by a very knowlegdable guy who understands the history of them.

Install better camshafts in those 420's. Mercruiser High Performance did a lousy job with cam selections back then.

I don't recall if the 420's had the Merc CD ignition (I am not talking about the Thunderbolt IV). If they did, get rid of them and install the Thunderbolt IV. Much more spark duration!
Usually you can not see a performance improvement with ignition mods but you will in this case.
The TB IV ignition with good spark plug wires and Champion RV15 YC4 plugs gapped at .045 will see a noticable improvement.

1000 hours, that is great!

Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE

Pure Energy

For the cost of rebuild look into the crate motors. Would be close in cost, but you get a warrenty with the crates. I got my 502 crates from www.1800runsnew.com I am very pleased with them. I put prochargers on mine and after 180 hrs. no problems! They also have 540's with somewhere around 550-575 HP.

XCAV8

540 (8.7L) 550 hp "Attack Dog"
$7,600.00
Picture coming soon
The Recon Engine builders start from scratch with a remanufactured GM 502 GEN VI block. A stroker forged nitrited steel crank is used with Eagle H-Beam connecting rods and J&E flat top pistons with Speed Pro plasma moly rings. World Products Merlin rectangular port heads with Manley stainless steel valves are used with Crane roller rocker valve train and Crane roller cam. Clevite "77" are the bearings of choice.
Every engine is dyno tested and shipped with its own dyno sheet.
The "Attack Dog" produces 565 hp @ 5400 rpm and a whopping 638 ft/lbs @ 3600 rpm
This Baby will run all day on Pump Gas

For situations where 93 octane gas is available we can increase compression at no extra charge.
This will increase horse power to 601 hp @ 5600 rpm and torque to 663 ft/lbs @ 3700 rpm.
This engine is also available with a Merlin block - call for price

cdscarab

Dennis Moore,
I am rebuilding a Hawk 525SC, which, I am told, is a 420 Merc with a B&M 174 blower added. What would you suggest for a cam? I was considering going with a hydr. roller, specs. undecided. I would consider a flat tappet as well, but motor must run on 89 oct.. Also this motor has the TBIV ignition, installed at the factory by the looks of it. Would the RV15YC4 plugs work in this motor as well? Have had much success with them in my other motors.

Also, thanks for writing two very comprehensive and informative books on the marine sbc & bbc. I have used both to build and tune both types of motors. They have been invaluable, surely saving me from much grey hair!!
Chuck

Dennis Moore

Because a supercharged engine doesn't really respond from high lift as much as a NA engine you can use a lower lift camshaft and save on the stiff valve spring problems. Use a hyd. roller camshaft with about 224/230 degrees intake/exhaust duration (a little more can't hurt) with a 114 degree lobe separation angle. No more than 6 degrees extra exhaust duration than the intake duration. You don't want to blow the fresh air/fuel mixture out the exhaust with the boost (because of too much exhaust duration and overlap).

I think I would go a little colder on the plugs, RV12YC maybe (just to be careful). Gap them at .035

The stock 525 SC cam is a flat lifter hydraulic with 228/236 with .530/.531 lift with 114 LSA. A Comp Cams roller camshaft will have a good increase in power over the flat camshaft with the same specs.

Dennis Moore