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Mystery BBC please help
Recently Purchased a 1992 IMP Europa 240 that had a BBC and Bravo 1 swapped into it sometime around 2006. I am trying to get an idea of what kind of horsepower numbers I should expect from the engine. This is what I know about the engine:
Block Casting number #10114182, 1991 and up gen V 454 CI 4 bolt main standard deck block. Mercruiser 454 Magnum Long block, Forged pistons, rods, and crankshaft. Early 90's 454 mag pistons. Gm std. # 14097021. 13.8cc dome 8.8:1 Compression ratio.Cylinder Head Casting #14097088, cast iron 118cc open chamber rectangular port heads. Largest as cast GM production iron head ports (325CC intake runners). Retrofit hydraulic roller camshaft (unknown cam specs) with Crane Gold roller rockers. Weiand Single plane aluminum intake manifold (port matched to heads). Holley #9022 4150 style 800CFM double pumper w/ mechanical secondaries. What kind of HP numbers should I be expecting out of this set up? |
401.6 ?
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That’s an oddly specific number. Not sure I understand your response.
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I would agree 400 is in the neighborhood.
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Originally Posted by SecondWind
(Post 4926009)
I would agree 400 is in the neighborhood.
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The limiter in your setup is the 088 heads.
The 365 mag hp rating I believe is at the prop. The GM marine forged BBC offerings were pretty much identical. They were rared at 390hp @5200 at the flywheel. Important to compare the apples to apples. This would have been with cast exh manifolds. Manifold upgrade would likely net some better peak tq and HP #s. As mentioned, the 088 heads have maybe the worst exh port GM made. Flows 165cfm at 0.400" lift. That is SBC territory. Intake ports are not bad for flow at 240cfm ish at 0.400" intake lift. That is great for a SBC with a 195cc port. Prett lazy on a 320cc port. These heads were on the 800SC 420 blown engines, so they can make power, but that exh port is requiring a lot of gross energy to pump out. My 088 heads have been machine in from the factory so there is very little to no venturi taper underneath the seat. The only real way to fox that is to put larger valves in and rework the seat, so the valve port diameter is 90% of the valve size. These engines cam with a single pattern cam 224/224 @ 0.510" lift. Hyd FT. 115.5° LSA. The L29 BBC Vortec heads flow better for a 450hp marine application. Without knowing what cam you have in the engine, difficult to determine where you are HP wise. Single plane intakes here are not as efficient as a good dual plane. You don't get as good of a signal to your carb, and you're likey not turning enough rpm to benefit from them. A good dual plane rec port style intake and a good flowing exh. system, would wake it up. If you prop for higher rpm 5500 to 6000, with proper cam and springs, the heads will flow, and you'll make more HP. 088 heads are great for what they are, but not worth putting any paid port work into them etc. |
Originally Posted by Tartilla
(Post 4926023)
The limiter in your setup is the 088 heads.
The 365 mag hp rating I believe is at the prop. The GM marine forged BBC offerings were pretty much identical. They were rared at 390hp @5200 at the flywheel. Important to compare the apples to apples. This would have been with cast exh manifolds. Manifold upgrade would likely net some better peak tq and HP #s. As mentioned, the 088 heads have maybe the worst exh port GM made. Flows 165cfm at 0.400" lift. That is SBC territory. Intake ports are not bad for flow at 240cfm ish at 0.400" intake lift. That is great for a SBC with a 195cc port. Prett lazy on a 320cc port. These heads were on the 800SC 420 blown engines, so they can make power, but that exh port is requiring a lot of gross energy to pump out. My 088 heads have been machine in from the factory so there is very little to no venturi taper underneath the seat. The only real way to fox that is to put larger valves in and rework the seat, so the valve port diameter is 90% of the valve size. These engines cam with a single pattern cam 224/224 @ 0.510" lift. Hyd FT. 115.5° LSA. The L29 BBC Vortec heads flow better for a 450hp marine application. Without knowing what cam you have in the engine, difficult to determine where you are HP wise. Single plane intakes here are not as efficient as a good dual plane. You don't get as good of a signal to your carb, and you're likey not turning enough rpm to benefit from them. A good dual plane rec port style intake and a good flowing exh. system, would wake it up. If you prop for higher rpm 5500 to 6000, with proper cam and springs, the heads will flow, and you'll make more HP. 088 heads are great for what they are, but not worth putting any paid port work into them etc. |
Originally Posted by Capt.Jack
(Post 4926031)
boat weights about 4200lbs with gear and fuel, I’ve got a 24p bravo 1 prop. Hoping for mid 60s. Is this too optimistic?
You don't know if the cam's been done, or what valve springs you have in there. What exhaust have you got? Post some photos. 4200 lbs isn't super heavy, but getting to 60mph is your first goal. What drive do you have? Assuming you have a 1.5 drive reduction. 24p prop 5000rpm 12%slip ish Gives you 67mph. Depending how it runs with the 24p, dropping down a bit may be beneficial, if you can't hit at least 5000rpm. |
Originally Posted by Tartilla
(Post 4926037)
Hard to say. If the cam has been done, it's going to want to breathe above 5000, vs the 4600-5000rpm suggested by Merc. Something like that.
You don't know if the cam's been done, or what valve springs you have in there. What exhaust have you got? Post some photos. 4200 lbs isn't super heavy, but getting to 60mph is your first goal. What drive do you have? Assuming you have a 1.5 drive reduction. 24p prop 5000rpm 12%slip ish Gives you 67mph. Depending how it runs with the 24p, dropping down a bit may be beneficial, if you can't hit at least 5000rpm. |
Here is a short video of the idle
https://youtube.com/shorts/cVviyM_rl3g?si=cVD-HiOijsyPdTgu |
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