Twin 454's
10-18-2005, 12:37 AM
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Twin 454's
Hey Guys
I just bought a Wellcraft Scarab Panther 30' with twin bravo setup.The engines are missing, so i am looking to rebuild two engines as economical as possible.I am familiar with rebuilding engines but i would like to get 375-400 hp out of each 454 that i hope to find soon as a winter project.The hard part for me is cam and head selection since i am not familiar with performance modifications.As far as i know oval port heads are good enough but im not sure about valve size requirements or cam duration/lift requirement.If i use an automotive block i understand that i will need forged pistons,but are hypereutectic pistons also acceptable? Do i need dome pistons to get to 375-400 hp? I was hoping to go with a non rollerized block if possible to keep the cost down.What size carbs would i need 750CFM or 850CFM?
Does anyone out there have one of these boats?just wondering what kind of speed to expect to get? Not to sure how heavy the boat is?Also if anyone has a used complete drop in motor i might be interested in bying one since i will need all the accessories for these motors i.e. intake/flywheel,brackets,balancers,carbs and water pumps.
I just found a 4 bolt main with heads (head casting # 14092360 - 2.07 intake 1.70 ) Would these oval port heads be acceptableto stay in the hp range without major modifications?
Thanx
Ralph
I just bought a Wellcraft Scarab Panther 30' with twin bravo setup.The engines are missing, so i am looking to rebuild two engines as economical as possible.I am familiar with rebuilding engines but i would like to get 375-400 hp out of each 454 that i hope to find soon as a winter project.The hard part for me is cam and head selection since i am not familiar with performance modifications.As far as i know oval port heads are good enough but im not sure about valve size requirements or cam duration/lift requirement.If i use an automotive block i understand that i will need forged pistons,but are hypereutectic pistons also acceptable? Do i need dome pistons to get to 375-400 hp? I was hoping to go with a non rollerized block if possible to keep the cost down.What size carbs would i need 750CFM or 850CFM?
Does anyone out there have one of these boats?just wondering what kind of speed to expect to get? Not to sure how heavy the boat is?Also if anyone has a used complete drop in motor i might be interested in bying one since i will need all the accessories for these motors i.e. intake/flywheel,brackets,balancers,carbs and water pumps.
I just found a 4 bolt main with heads (head casting # 14092360 - 2.07 intake 1.70 ) Would these oval port heads be acceptableto stay in the hp range without major modifications?
Thanx
Ralph
10-18-2005, 08:22 AM
#3
Re: Twin 454's
ralphspa,
You can get 400hp out of a 454cid marine engine these days with GM oval port heads, but the heads may still require some mods/upgrades. A 2.19" intake valve and at least a 1.85" to 1.88" exhaust valve would be a nice modification for more HP, but if you're on a really tight budget, keep the same valve size on the heads, but you will still need good stainless steel valves like Ferrea. So, if you are going to retain the stock valve size of 2.07" and 1.72" you will need to have the heads bowl/pocket ported and with the new stainless valves you will need to have hardend valve seats installed on the exhaust side---you may need new hardend seats on the intake side as well, but I cannot remember. Someone else may have to chime in here. A flat tappet hydraulic cam of about 224*/230* .515"/.515" lift on 110* lobes would be a good cam. All you would need for your power is a Holley 750cfm carb. If you can find someone to do it and do it properly, I would also do what is called a "bore notch" job on the cylinder bores---it will give you an additional 30hp/torque or so. It's easy, cheap HP! A good aftermarket dual plane intake manifold like Edlebrock's "Air-Gap" or even their cheaper "RPM" intake manifold would be good. You should be fine with hyperutectic pistons under 5500rpm. As far as exhaust systems go it would help the engine breath much better if you replaced the stock Merc exhaust system and used an aftermarket exhaust manifold system like Stainless Marine, GIL or something comparable. Just remember, accurate , precision machine work, and how the crank sits/spins in the main saddles is where it all begins. Clearances/tolerances are different in an engine destined for the marine enviroment than it is for a car or the street.
Here's something I wrote in another thread concerning a 454cid marine engine with some cheap upgrades that you might want to consider....
Therefore, if you are looking for a BUDGET/low dollar set of 454's here's something that might interest you. A couple of years ago my cousin had his stock Merc 330's 454's with some very inexpensive upgrade/mods and then had them dyno tested on Earhart's dyno, with flat tappet hyd cams (.515"/.515" lift with 218*/226* duration at .050" on 110* lobes), dual plane intakes, stock Merc Thunderbolt ignition, 8.6 comp ratio, 830 Holley carb, with a turned 10/10 cast crank, 3/8" rods, cast pistons (although I would prefer at least forged pistons), and 2-bolt main blocks, some junk old GM, semi open chambered, oval port heads that he added some 2.19" stainless intake valves and 1.85" exhaust valves to. JimV did the port work, and originally tried using a 1.88" exhaust valve on that particular head, but he said the smaller valve actually flowed better (on the flow bench) than the larger exhaust valve. This is true even with the porting, and valve un-shrouding work the smaller exhaust valve still out-flowed the larger 1.88" valve. He was definately on a BUDGET, but he still had good, accurate machine work done. I call these the "poor mans hi-performance 330's". Or you can get real elaborate with your $$$ if you want as you are making parts choices.
On Earhart's dyno he made 461hp (with dyno headers) @ 5100rpm, and 510 lbs of torque @3600rpm and stayed very flat up to 5000rpm.
He runs the engines in a 1988 32' Baja' with GIL exhaust manifolds, and dry pipes. He was originally turning 3-bladed 21" prop with the stock engines, and with a GPS it is showing he has picked up 10mph at cruising speed of about 3500-4000rpm with a 3-bladed 25" prop with a top speed of 69.7mph @5000rpm with the old Bravo One gear case. He still needs to play with props a bit and he doesn't know what the boat did with the stock Merc 330's as he didn't have a GPS back then, but he said he can feel a BIG difference and is very happy.
You can get 400hp out of a 454cid marine engine these days with GM oval port heads, but the heads may still require some mods/upgrades. A 2.19" intake valve and at least a 1.85" to 1.88" exhaust valve would be a nice modification for more HP, but if you're on a really tight budget, keep the same valve size on the heads, but you will still need good stainless steel valves like Ferrea. So, if you are going to retain the stock valve size of 2.07" and 1.72" you will need to have the heads bowl/pocket ported and with the new stainless valves you will need to have hardend valve seats installed on the exhaust side---you may need new hardend seats on the intake side as well, but I cannot remember. Someone else may have to chime in here. A flat tappet hydraulic cam of about 224*/230* .515"/.515" lift on 110* lobes would be a good cam. All you would need for your power is a Holley 750cfm carb. If you can find someone to do it and do it properly, I would also do what is called a "bore notch" job on the cylinder bores---it will give you an additional 30hp/torque or so. It's easy, cheap HP! A good aftermarket dual plane intake manifold like Edlebrock's "Air-Gap" or even their cheaper "RPM" intake manifold would be good. You should be fine with hyperutectic pistons under 5500rpm. As far as exhaust systems go it would help the engine breath much better if you replaced the stock Merc exhaust system and used an aftermarket exhaust manifold system like Stainless Marine, GIL or something comparable. Just remember, accurate , precision machine work, and how the crank sits/spins in the main saddles is where it all begins. Clearances/tolerances are different in an engine destined for the marine enviroment than it is for a car or the street.
Here's something I wrote in another thread concerning a 454cid marine engine with some cheap upgrades that you might want to consider....
Therefore, if you are looking for a BUDGET/low dollar set of 454's here's something that might interest you. A couple of years ago my cousin had his stock Merc 330's 454's with some very inexpensive upgrade/mods and then had them dyno tested on Earhart's dyno, with flat tappet hyd cams (.515"/.515" lift with 218*/226* duration at .050" on 110* lobes), dual plane intakes, stock Merc Thunderbolt ignition, 8.6 comp ratio, 830 Holley carb, with a turned 10/10 cast crank, 3/8" rods, cast pistons (although I would prefer at least forged pistons), and 2-bolt main blocks, some junk old GM, semi open chambered, oval port heads that he added some 2.19" stainless intake valves and 1.85" exhaust valves to. JimV did the port work, and originally tried using a 1.88" exhaust valve on that particular head, but he said the smaller valve actually flowed better (on the flow bench) than the larger exhaust valve. This is true even with the porting, and valve un-shrouding work the smaller exhaust valve still out-flowed the larger 1.88" valve. He was definately on a BUDGET, but he still had good, accurate machine work done. I call these the "poor mans hi-performance 330's". Or you can get real elaborate with your $$$ if you want as you are making parts choices.
On Earhart's dyno he made 461hp (with dyno headers) @ 5100rpm, and 510 lbs of torque @3600rpm and stayed very flat up to 5000rpm.
He runs the engines in a 1988 32' Baja' with GIL exhaust manifolds, and dry pipes. He was originally turning 3-bladed 21" prop with the stock engines, and with a GPS it is showing he has picked up 10mph at cruising speed of about 3500-4000rpm with a 3-bladed 25" prop with a top speed of 69.7mph @5000rpm with the old Bravo One gear case. He still needs to play with props a bit and he doesn't know what the boat did with the stock Merc 330's as he didn't have a GPS back then, but he said he can feel a BIG difference and is very happy.
