That is not a Merc 420

That's what mine have had done. Punched to 468, Comp 292H cam, Merlin Intakes, I'm not sure of the size Holleys on the engine, but it runs like a skeered haint!

it was a GM crate motor, now I am curious as to what I have...... ummmmm........

454 4 bolt truck block, Gen VI, JE Pistons, roller cam, no specs on it, and the 502 marine heads.....

Casting numbers check out....

Btw, mine came stock with Gil exhaust. That may have been part of the Kaama package.

i have a 454-HO crate motor from GM. I believe this is the same block that the merc 420 is. GM rates it at 425 hp. Mine has roller lifters but not rockers. All parts have Gm performance parts stamped on them. Big rectangle port heads. Beefy 4- bolt mains and aluminum intake. 7/16 pushrods, etc. Bullet proof motors. I know a lot of guys down here run them in work airboats. 5000 rpm all day long every day with no problems.

happy to hear that, I'm a GM dealer ! But, I'm surprised since every body says a marine engine is not a car engine... the eternal question...

Camshaft (hydraulic flat tappet) for:

Merc 400 / 420 / 425 / 525SC

Crane Part#132561 Grind # H-228/312-2S-14 T1.2
Duration at .004” : 298, 296
Duration at .050”: 228, 236
Lift with 1.7 rocker: .530”, .551”
LSA 114LSA
ICL 109 ATDC , ECL 119 BTDC

Part Number: 132561 Grind Number: H-228/312-2S-14 T1.2
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1967 Up CHEVROLET 8 FAIR IDLE, STANDARD CAMSHAFT FOR MERCRUISER 400, 405, 420, 425 HP AND 525SC-454 CU. IN. ENGINES, APPLICABLE TO 350, 365, 370 HP MILDLY MODIFIED ENGINES WITH FREE-FLOWING ABOVE WATER EXHAUST SYSTEMS FOR PERFORMANCE APPLICATIONS, 9.5 TO 11.5 COMPRESSION RATIO ADVISED. BASIC RPM 2800-5800
Engine Size Configuration
396-454 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 312 @Valve 530 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 324 @Valve 551
Rocker Arm Ratio 1.7

Cam Timing: TAPPET @.005
Lift: Opens Closes ADV Duration
Intake 35 BTDC 83 ABDC 298 °
Exhaust 87 BBDC 39 ATDC 306 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99893
Loads Closed 130 LBS @ 1.850 or 1 27/32
Open 330 LBS @ 1.320
Recommended RPM range with matching components
Minimum RPM 2800
Maximum RPM 6600
Valve Float 7200

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 5 BTDC 43 ABDC 109 228 °
Exhaust 57 BBDC (1) BTDC 119 236 °

Man!SB! You're an engine Bible!

SB,
How would you compare the 241 cam to the 561
Total lift is 0nly .004 more intake and .002 exhaust,but I believe slightly less in the middle. The 241 is what I put in my 454 mags. What would be the difference in how they run?
Holley 800s
Wieand Excelerator intakes
Gil exhaust water mixing 3" before transome.
Crane Gold rollers

Payton, to not sidetrack this thread I started one about your question on:
http://www.offshoreonly.com/forums/s...65#post1848165