Thread: New 496 build

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This is the first project I am attempting for use in my boat. What I am looking for is feedback on this project. Estimated HP and CR and suggested boost. Any pointers on the best combo for reliability and performance. (I know, some say bigger is better, but it’s not always true ) but since this is going into my boat there aren’t too many gas stations between buoys. What are the pro’s and con’s between the 177 with a single carb vs. the 6-71 with dual carbs? Will the 177 with a 850 be a better choice over the 6-71 with the 650’s?

I started with my 1991 Bravo Mag. 454 4 bolt main block going .060 over. The casting number is 10069286

PARTS 496 FORGED ROTATING ASSEMBLY
FORGED STEEL NITRIDED CRANKSHAFT STROKER 4.250"
4340 H-BEAM ROD SET BBC 6.385
KB PREM FORGED PISTON BBC 489 3CC FLAT
AKERLY & CHILDS EXTREME PISTON RING SET 1/16 1/16
3/16 4.310
CLEVITE PERF ROD BEARING, NEW MAIN BEARING SET
Melling M77HV BBC Oil Pump

COMP Cams #2110Big Block Chevy Magnum Timing Set
COMP CAMS XEM 234-244 @ .050 110LC 1 165.00 165.00T
HYD LIFTER SET

PRO-COMP ALUMINUM CYLINDER HEADS
320CC INTAKE RUNNERS, 115CC COMBUSTION CHAMBERS, 2.25 INTAKES
AND 1.880 EXHAUST STAINLESS SWIRL POLISHED VALVES. 1.460 DUAL
VALVE SPRING ASSEMBLY. 1.460" Dual Spring Assembly. Suitable for Mechanical Flat Tappet or Hydraulic Roller Cams up to .650 Lift 140 PSI Closed / 360 PSI @ .500 lift. .400 THICK DECK.

FLOW DATA @ 28" H20
PC3021 .100 .200 .300 .400 .500 .600
INTAKE 74 166 245 308 340 360
EXHAUST 62 118 160 195 229 248


I have a choice of superchargers and carbs.
B&B 177 or 6-71 BDS/GMC BLOWER BIG BLOCK CHEVY with either combination of 2-850 CFM Holley, 2-650 CFM Holley, 1-750 CFM Holley.

Originally Posted by Cisco398

This is the first project I am attempting for use in my boat. What I am looking for is feedback on this project. Estimated HP and CR and suggested boost. Any pointers on the best combo for reliability and performance. (I know, some say bigger is better, but it’s not always true ) but since this is going into my boat there aren’t too many gas stations between buoys. What are the pro’s and con’s between the 177 with a single carb vs. the 6-71 with dual carbs? Will the 177 with a 850 be a better choice over the 6-71 with the 650’s?

I started with my 1991 Bravo Mag. 454 4 bolt main block going .060 over. The casting number is 10069286

PARTS 496 FORGED ROTATING ASSEMBLY
FORGED STEEL NITRIDED CRANKSHAFT STROKER 4.250"
4340 H-BEAM ROD SET BBC 6.385
KB PREM FORGED PISTON BBC 489 3CC FLAT
AKERLY & CHILDS EXTREME PISTON RING SET 1/16 1/16
3/16 4.310
CLEVITE PERF ROD BEARING, NEW MAIN BEARING SET
Melling M77HV BBC Oil Pump

COMP Cams #2110Big Block Chevy Magnum Timing Set
COMP CAMS XEM 234-244 @ .050 110LC 1 165.00 165.00T
HYD LIFTER SET

PRO-COMP ALUMINUM CYLINDER HEADS
320CC INTAKE RUNNERS, 115CC COMBUSTION CHAMBERS, 2.25 INTAKES
AND 1.880 EXHAUST STAINLESS SWIRL POLISHED VALVES. 1.460 DUAL
VALVE SPRING ASSEMBLY. 1.460" Dual Spring Assembly. Suitable for Mechanical Flat Tappet or Hydraulic Roller Cams up to .650 Lift 140 PSI Closed / 360 PSI @ .500 lift. .400 THICK DECK.

FLOW DATA @ 28" H20
PC3021 .100 .200 .300 .400 .500 .600
INTAKE 74 166 245 308 340 360
EXHAUST 62 118 160 195 229 248


I have a choice of superchargers and carbs.
B&B 177 or 6-71 BDS/GMC BLOWER BIG BLOCK CHEVY with either combination of 2-850 CFM Holley, 2-650 CFM Holley, 1-750 CFM Holley.

Welcome,I would run a 8-71 on an engine this size along with 750 carbs.
I would also look into a smaller mech. roller cam something like a street roller cut on a 114 l/s.
The biggest problem in a boat is the chance of over-revving the engine to easily with a hyd. cam or a hyd. roller cam.

Hey Eric, Thanks !!! Now the trick is to get the 4th supercharger (forgot to mention the Procharger for my C5) and not have to live in my shed lol. Do you have any idea on the HP, CR, boost, etc? If I can't move up to the 8-71 what issues will the 6-71 cause? The 177 fits great under the sundeck and I was hoping not to have to cut a hole for the carbs... As for the cam and
over-revving have a suggestion? I usually am good at keeping the boat in the water. Its 6500lbs and ride very well in rough water. I have seen a few posts mentioning a desktop dyno. Are they failry accurate and if so, anyone have it that can plug in my info to determine the HP? I can then start looking at prop pitch. Again, thanks for your reply... I hope more info comes along soon... the block will be back in a few weeks.

On the Clevite bearing I would get the one ended with a V instead of H. The H brearing surface is too hard and will break down if it get any water or air bubble in the oil.

Originally Posted by Cisco398

Hey Eric, Thanks !!! Now the trick is to get the 4th supercharger (forgot to mention the Procharger for my C5) and not have to live in my shed lol. Do you have any idea on the HP, CR, boost, etc? If I can't move up to the 8-71 what issues will the 6-71 cause? The 177 fits great under the sundeck and I was hoping not to have to cut a hole for the carbs... As for the cam and
over-revving have a suggestion? I usually am good at keeping the boat in the water. Its 6500lbs and ride very well in rough water. I have seen a few posts mentioning a desktop dyno. Are they failry accurate and if so, anyone have it that can plug in my info to determine the HP? I can then start looking at prop pitch. Again, thanks for your reply... I hope more info comes along soon... the block will be back in a few weeks.

The biggest problem with the 6-71 on an engine your size is you have to spin the blower faster than the 8-71 causing the air to be more heated.
The desk top dyno is O.K. but there are better sims out there.
You can always run a chip in the MSD 6 box to try and control the rpm's.

Eric, I spoke with the machine shop and they haven't bored the block yet. Would going .030 giving me a 489 and a milder cam enable me to use the
6-71? (whan I brought up the 8-71 at dinner tonight the wife never said a word... but I will most likely head to the ER after this post to have her fork removed from my hand ). I am still wondering about how much HP and Torque I will end up with. Once I have that I can drill down the correct size and pitch prop and see where my est performance will fall.
I read some threads from camaro_fever68 and will look into his ignition box, boost retard, rev limiter package. Anyone have this installed that can shed some light?

Originally Posted by Cisco398

Eric, I spoke with the machine shop and they haven't bored the block yet. Would going .030 giving me a 489 and a milder cam enable me to use the
6-71? (whan I brought up the 8-71 at dinner tonight the wife never said a word... but I will most likely head to the ER after this post to have her fork removed from my hand ). I am still wondering about how much HP and Torque I will end up with. Once I have that I can drill down the correct size and pitch prop and see where my est performance will fall.
I read some threads from camaro_fever68 and will look into his ignition box, boost retard, rev limiter package. Anyone have this installed that can shed some light?

Yes,by lowering the rpm's you could make the the 6-71 work.
In fact the cam you picked out should work fine with a 6-71.
Always remember with a blown application the cam will seem larger.

Cool. I may have to take this route. I also have another identical engine I plan on rebuilding at a later date if I need to go bigger. I also may go with the MSD solution. Thanks Eric.

Originally Posted by Cisco398

Cool. I may have to take this route. I also have another identical engine I plan on rebuilding at a later date if I need to go bigger. I also may go with the MSD solution. Thanks Eric.

No problem .
I hope I was a little help.

I have had alot of conflicting info about the Pro Comp heads. Some very good, some not. I may have to rethink them. Would the best choice be Dart, Merlin or AFR? Anyone have experience with either of them? Would either of these heads require me to rethink the cam? I know its alopt of broad questions... but I am hoping to learn a few things before I had the engine together. Also I was looking into an intercooler but for the price maybe I should opt for an 8-71 or even a 10-71. I was hoping to keep the carbs under the engine hatch and sunpad. Anyone know where I can get some "Do not sit here" stickers?

Originally Posted by Cisco398

I have had alot of conflicting info about the Pro Comp heads. Some very good, some not. I may have to rethink them. Would the best choice be Dart, Merlin or AFR? Anyone have experience with either of them? Would either of these heads require me to rethink the cam? I know its alopt of broad questions... but I am hoping to learn a few things before I had the engine together. Also I was looking into an intercooler but for the price maybe I should opt for an 8-71 or even a 10-71. I was hoping to keep the carbs under the engine hatch and sunpad. Anyone know where I can get some "Do not sit here" stickers?

On a 496 I really like the AFR 305 cc heads.

I was able to get different heads for my build. What I am looking for is feedback on this project. Estimated HP and CR and suggested boost. Any pointers on the best combo for reliability and performance. (I know, some say bigger is better, but it’s not always true ) but since this is going into my boat there aren’t too many gas stations between buoys. What are the pro’s and con’s between the 177 with a single carb vs. the 6-71 with dual carbs? Will the 177 with a 850 be a better choice over the 6-71 with the 650’s? Also I would like to get max HP at 6000 RPM, any suggestions on that?
I started with my 1991 Bravo Mag. 454 4 bolt main block going .030 over for a 489 (maybe .060 for a 496... decisions, decisions!!!). The casting number is 10069286

PARTS 489/496 FORGED ROTATING ASSEMBLY
FORGED STEEL NITRIDED CRANKSHAFT STROKER 4.250"
4340 H-BEAM ROD SET BBC 6.385
KB PREM FORGED PISTON BBC 489 3CC FLAT
AKERLY & CHILDS EXTREME PISTON RING SET 1/16 1/16
3/16 4.310
CLEVITE PERF ROD BEARING, NEW MAIN BEARING SET
Melling M77HV BBC Oil Pump

COMP Cams #2110Big Block Chevy Magnum Timing Set
COMP CAMS XEM 234-244 @ .050 110LC 1 165.00 165.00T
HYD LIFTER SET

AFR 305cc Aluminum Cylinder Heads for Big Block Chevy
305cc Intake Runners
119cc Combustion Chambers
Premium quality stainless steel valves - 2.250" Intake/1.880" Exhaust
Heads feature a stout .750" deck thickness
New Comp Cams Beehive springs (PN 26120) and titanium retainers (PN 788)

FLOW DATA @ 28" H20
PC3021 .100 .200 .300 .400 .500 .600
INTAKE 74 166 245 308 340 360
EXHAUST 62 118 160 195 229 248

I have a choice of superchargers and carbs. Weiand 177 or 6-71 BDS/GMC BLOWER BIG BLOCK CHEVY with either combination of 2-850 CFM Holley, 2-650 CFM Holley, 1-750 CFM Holley.

I am also planning on the MSD Boost timing master with rev limiter. Anyone use this before that can advise?

Originally Posted by Cisco398

I was able to get different heads for my build. What I am looking for is feedback on this project. Estimated HP and CR and suggested boost. Any pointers on the best combo for reliability and performance. (I know, some say bigger is better, but it’s not always true ) but since this is going into my boat there aren’t too many gas stations between buoys. What are the pro’s and con’s between the 177 with a single carb vs. the 6-71 with dual carbs? Will the 177 with a 850 be a better choice over the 6-71 with the 650’s? Also I would like to get max HP at 6000 RPM, any suggestions on that?
I started with my 1991 Bravo Mag. 454 4 bolt main block going .030 over for a 489 (maybe .060 for a 496... decisions, decisions!!!). The casting number is 10069286

PARTS 489/496 FORGED ROTATING ASSEMBLY
FORGED STEEL NITRIDED CRANKSHAFT STROKER 4.250"
4340 H-BEAM ROD SET BBC 6.385
KB PREM FORGED PISTON BBC 489 3CC FLAT
AKERLY & CHILDS EXTREME PISTON RING SET 1/16 1/16
3/16 4.310
CLEVITE PERF ROD BEARING, NEW MAIN BEARING SET
Melling M77HV BBC Oil Pump

COMP Cams #2110Big Block Chevy Magnum Timing Set
COMP CAMS XEM 234-244 @ .050 110LC 1 165.00 165.00T
HYD LIFTER SET

AFR 305cc Aluminum Cylinder Heads for Big Block Chevy
305cc Intake Runners
119cc Combustion Chambers
Premium quality stainless steel valves - 2.250" Intake/1.880" Exhaust
Heads feature a stout .750" deck thickness
New Comp Cams Beehive springs (PN 26120) and titanium retainers (PN 788)

FLOW DATA @ 28" H20
PC3021 .100 .200 .300 .400 .500 .600
INTAKE 74 166 245 308 340 360
EXHAUST 62 118 160 195 229 248

I have a choice of superchargers and carbs. Weiand 177 or 6-71 BDS/GMC BLOWER BIG BLOCK CHEVY with either combination of 2-850 CFM Holley, 2-650 CFM Holley, 1-750 CFM Holley.

I am also planning on the MSD Boost timing master with rev limiter. Anyone use this before that can advise?

To take advantage of those great flowing AFR heads I would run a hyd. roller cam or a smaller mech. roller.