Re: Mild SBC Upgrades
 

SB: I took a quick look at some Crane roller cam specs during lunch. Crane #109811 appears to be almost the same as stock merc. #104225 (2031) just a hair more lift than stock and 6 degress of additional intake duration. #104224 (2032) .452/.465 lift, 270/276 dur. Probably don't want to go any bigger than that. I'd still would want to make sure it would not impact idle and takeoff acceleration. I think the powerband didn't start until 2K rpms.

Re: Mild SBC Upgrades
 

Part Number: 104224 Grind Number: POWERMAX 2032 (FORMERLY COM
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1987 1989 CHEVROLET 8 FOR 87-89 CORVETTES, CAMAROS AND FIREBIRDS FACTORY EQUIPPED W/350 TPI ENGINES. ADJ. FUEL PRESSURE REGULATOR (99470-1) IS RECOMMENDED FOR MAXIMUM PERFORMANCE. (50 STATE LEGAL FOR LISTED APPLICATIONS, C.A.R.B. E.O. D-225-22). BASIC RPM 2000-5500
Engine Size Configuration
305 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 301 @Valve 452 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 310 @Valve 465
Rocker Arm Ratio 1.50

Cam Timing: -- @---
Lift: Opens Closes ADV Duration
Intake --- --- 270 °
Exhaust --- --- 276 °

Spring Requirements: Triple Dual Outer Inner
Part Number 96802
Loads Closed 107 LBS @ 1.800 or 1 13/16
Open 276 LBS @ 1.360
Recommended RPM range with matching components
Minimum RPM 1800
Maximum RPM 5800
Valve Float 6400

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 0.0 BTDC 34.0 ABDC 107 214 °
Exhaust 47.0 BBDC (7.0) BTDC 117 220 °

===================================

Part Number: 104225 Grind Number: POWERMAX 2031 (FORMERLY COM
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1987 1989 CHEVROLET 8 FOR MID AND UPPER RPM PERFORMANCE IN 88-89 305 ENGINES W/5-SPEED AND 3.45 OR NUMERICALLY HIGHER REAR GEAR RATIOS. ADJ. FUEL PRESSURE REGULATOR (99470-1) IS RECOMMENDED FOR MAX. PERFORMANCE (50 STATE LEGAL FOR LISTED APPS, C.A.R.B. E.O. D-225-22) BASIC RPM 1500-5000
Engine Size Configuration
305 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 292 @Valve 438 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 301 @Valve 452
Rocker Arm Ratio 1.50

Cam Timing: -- @---
Lift: Opens Closes ADV Duration
Intake --- --- 264 °
Exhaust --- --- 270 °

Spring Requirements: Triple Dual Outer Inner
Part Number 96802
Loads Closed 107 LBS @ 1.800 or 1 13/16
Open 271 LBS @ 1.370
Recommended RPM range with matching components
Minimum RPM 1400
Maximum RPM 5400
Valve Float 6000

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake (3)ATDC 31 ABDC 107 208 °
Exhaust 44 BBDC (10)BTDC 117 214 °

I am new to the site but not to boating. I have owned 3 inboard boats including a 1959 Chris Craft Capri (woody) and a 1988 Ski Centurion w/351W Indmar. My current boat is a
'95 Malibu Echelon w/Mercruiser 350 Magnum Skier engine. This fall I had planned to do some mods on this engine. My parts list include a set of RHS Vortec heads, a Weiand 8121 dual plane intake with a Holley 4160 marine carb and a Comp Cams Extreme Marine 264HR cam. The specs on the cam are: In/Ex - 212/218; lift - .488/.495 112 deg LSA.

So here are my questions: What are the concerns with this cam being over the .460 in lift limit? This is designed to be a marine cam. Is it with the valve springs? If so I already have the specified springs installed in my new heads.

My second question is about static compression. What type pistons does the Merc '95 350 Mag Skier come with? Do they not have valve reliefs? What size is the combustion chamber of my current heads? My owners manual says that my current compression is 9.3:1. I calculated my compression with the vortec heads to be approximately 9.6. That's assuming a combustion chamber volume of 64cc and a flat top piston with a head gasket that has a bore diameter of 4.2 and a compressed thickness of .039. Does this sound reasonable?

And finally....about the ignition. My engine came with the Thunderbolt V system. It has a knock sensor and module that controls spark advance. Is there any need to try to re-curve the advance? Will this system pull enough advance from the curve to compensate for the vortec heads?

Please give it to me straight. I want to gain performance without sacrificing too much on the reliability or economy. Thanks! Brian