HangerWide
Member
BLOWN BAHA BOAT BUILD
Project description:
Repower a 1997 Baha 290 Mach 1 Open Bow that was purchased at a discounted price due to loss of short block integrity. The original block suffered interior expansion cracks to both cylinder banks just above the lifter bores from freeze damage.
Project Goals:
Focus points of engine components:
Selected Components
- Performer RPM 2.O
- Holley / Quick Fuel M-850
- Baker engineering / ProCam Marine Mechanical Fuel Pump
- Kenne Bell / AutoRotor 1.5L Twin Screw SuperCharger
-Ignition
- Davis Unified Ignition Marine HEI with Custom Advance Curve
* (14 degrees / all in @ 2800)
- Talylor Cable 8mm Spark Plug wires
Project Details:
The 1997 Baha Cruiser 290 Mach 1 Originally came equipped with a Mercruiser 7.4L Bravo III engine and drive package. In Brief detail this package consist of a GEN VI 7.5L cast block with small oval port cast heads with open chambers and a volume listed as 118cc, a cast 4bbl intake manifold supported by a Weber/Carter AFB with mechanical secondaries rated at 750CFM. The Short block is a 2 bolt main with cast steel 4.00” stroke crank, 6.135” forged press pin rods and cast pistons supporting 5/16 top and second rings and 3/16 oil rings. The Cast Pistons are flat with a slight dish but i was not able to find the exact volume of the pistons. The heads are 156 casting small oval ports with non adjusting stamped rockers and guide plates listed as 118cc and having Valve size 2.06 intake, 1.72 exhaust. The head gaskets are mercruiser MLS gaskets. The camshaft is a Mercruiser Marine roller cam with 215/217 duration@.05 the centerline is 110 and a lobe seperation of 115.4 The engine is listed to have 8.1:1 Static Compression and with and intake close time listed at 69 the dynamic compression is roughly 6.5 assuming 118cc heads and a 3cc dish. The engine is rated at 330HP.
Detailed Specifications Link:
https://www.perfprotech.com/blog/tech-specs/mercruiser-bigv8-marine-engines-specifications
To replace the engine I chose a Mark IV block that i pulled from a 76 motorhome with roughly 86000 miles on it. The owner stated that he had the engine rebuilt years ago from a spun bearing and the crank has been turned on the main journals. After breaking the engine down I confirmed bore size as 4.25” and the cylinder walls were in very good condition. The crank was as stated with 1 size under on the mains. I ditched the flat tappet cam, lifters and all the bearings then delivered the bare block, crankshaft and heads to the machine shop for inspection. The shop reported that all components passed magnaflux inspection and were usable components. After discussing the build project and my desired goals we chose an approach for required machine work. I had the block cleaned including oil plugs pulled and galleries brushed, hot tank treatment and a jet wash cycle then the cylinders were honed for use with moly rings. The crank was turned and polished with a final measurement of 10 under on the rods and 20 on the mains. I had the heads resurfaced and the valves cut and seated, the guides were inspected and noted well within tolerance. The springs and retainers were replaced with the springs from the mercruiser engine head seeing as i intended to use the mercruiser cam from the damaged engine. We discussed oversize valves and extensive head work but the machinist felt the money would be best spent elsewhere as the marine exhaust manifolds are rather restrictive to benefit from larger valves. On the way home i stopped by the car wash and pressure washed all the parts using a degreaser and a few brushes. At home i prepped the block and heads for paint. After painting and a quick recleaning I treated the parts with wd4 and covered the engine with plastic wrap and spent a week or so researching and ordering parts.
Everything went together rather well. I chased all threaded holes and cleaned all hardware with parts cleaner and a wire wheel. The main caps and heads received stud fasteners and all valve train components were coated in assembly lube and sprayed with dry moly film. I followed many threads and instruction from this site in regards to clearances while putting everything together and feel rather confident in the build and was rather proud of myself.
Once assembled I Ran the engine naturally aspirated for break-in and confirmed timing. I had good oil pressure at 60 psi above 2000 rpm and no noted temperature issues. SOOOOO i took her to the lake. It started good and ran without issue while in the no wake zone but once i tried to plan off i could get to about 2800 and that all she had. I checked timing it was good so, checked fuel supply and pressure and volume were good. Then i noticed my oil pressure had dropped and there was oil noted in the builg. I wasn’t far from the loading ramp so i returned at just above idle throttle, at idle my oil pressure was near zero and just off idle I had almost 20lbs. Back home I found that the issue began when the secondarys would open then the engine would flood, severely flood, I checked the plugs and they were black and fouled. I checked compression and THIS is where the trouble was found. 80 on all cylinders.
It took several days to find the issue but the low compression comes from a miscalculation on deck height where i ordered pistons that do not have the accurate compression height. I ordered 1.27 pistons and needed 1.52 pistons. My current configuration deck height is .395 in the hole so my compression is hammered. I suspect that with the low compression i was way over jetted and flooded the cylinders causing the rings not to seat and push excess crankcase pressure to the pan pushing oil out the rear main. I intended to bump my static compression slightly by using flat top pistons in place on the cast pistons in the factory block as i needed a higher static ratio to achieve the desired dynamic ratio with the cam i have, but now i'm at a critical turning point in my build. The cost of piston and rings is far more than replacing the rods or crank so I would like to keep the pistons. I am sure the crank will need turned again and all the bearings replaced as well as the whole engine cleaned, im sure I ate the bearings, I cut the filter and there was metal in the element.
As i assess myself over this build I can account for many mistakes, such as failure to check deck clearance after installing the rotating assembly, or checking the measurements of the rod and pistons together. Hell i didn't even check the length of the rods when i got them to make sure they were the correct length that i intended at the time. I did clean all the parts as instructed from several of grumpy's threads. I spent lots of time and money on the proper tools for checking clearances i just missed it. I don't feel i rushed the build… maybe i was just overwhelmed or over my head but one thing's for sure. I was real proud of my self as i thought I had done well with my project. Setting goals, researching all the options and parts, reading reviews and setting realistic performance goals (i hope). I know its no 1000hp cannon, but i thought it was a modest build with a little flare and would be a great engine from my boat… im not all that confident in it anymore. Embarrassing
All that aside this thing needs to come apart. So im looking at my options, i have spent a lot on rods and pistons and they are forged components. The crank is stock so to me the best results for the money would be to replace the crank with a stroker crank and take advantage of the added performance, BUT there is no way to make up the distance with crank stoke alone. So Im buying rods either way. Now Its not much more expensive to just replace the crank with a 4.25 stroke and run 6.385 rods to put me at .020 deck height and a .020 gasket to achieve .040 quench and adequate compression. If i do not replace the crank i can run 6.535 rods and that puts me -.005 out the deck. I can make that up with a gasket to get somewhere between .035 and .038 but to get to .045+ from a gasket that will match well with boost I would have to go to copper head gaskets which are awesome but expensive. About the same cost as buying a crank, either way i need to balance the rotating assembly So in the end I’m about to spend 1000$ on the bottom end and would like some opinions and suggestions on where to go with the engine at this point. I am not worried about the expense as much as i am worried about reliability and cost vs gains. Seeing as it’s coming back apart this is a good time to review the all of the parts and see if i am even close to what i intended to build (obviously not in the compression area) is there alternative cam specs that would be better suited for this engines intent? Are there other obvious issues that i am missing? Any suggestions and PRO TIPS are welcome and wanted. Im open to changing anything that needs to be corrected either for better performance or especially for reliability. I have other specific information if needed, I know I left a lot out in terms of specific details that i can provide if needed.
Project description:
Repower a 1997 Baha 290 Mach 1 Open Bow that was purchased at a discounted price due to loss of short block integrity. The original block suffered interior expansion cracks to both cylinder banks just above the lifter bores from freeze damage.
Project Goals:
- Determine a realistic budget
- Prioritize decisions and expenditures as 1: reliability 2: efficiency 3: performance gaines
- Appropriate & Realistic power for application. (500HP/ 1800-5400rpm range)
- Improved overall performance from factory power package.
- Overall build to create strength and durability in a engine that produces a minimum of oem power then apply low boost for reliable power gaines and performance increase
Focus points of engine components:
- Estimated Build Cost = $5200.00 - $5700.00 / Max out of Pocket $7000.00 Allowed
- Initial Machine Work for surfaces, cleaning, and inspections.
- 454Ci cast block W/ Increased rotating assy strength and main studs
- Large Oval cast heads W/ increased valve train strength and head studs
- Intake - Forced injection W/ aluminum aftermarket dual plane, single carburetor, manifold
- Fule - high output mechanical with ⅜ minimum supply lines
- Carburetor - Holley marine grade blower carb with mechanical secondaries 850cfm
- Replace Stock ThunderBolt V ignition with more reliable setup.
- Oil Supply - High Volume Pump
Selected Components
- MKIV 454CI Short Deck
- Standard Bore
- Stock Crank
- Scat I-Beam Forged Cap Screw Rods
- Icon Forged Flat top pistons, Fee floating pin
- Speed Pro Tri-metal Performance Bearings
- Standard Bore
- Mercruiser OEM Roller Cam
- Lunati Retrofit Hydraulic Lifters
- ⅜ Push Rods
- Comp Cams Stainless Steel Roller Rockers (standard ratio)
- Comp Cams Adjustable Guides Plates
- Mercruiser OEM Roller Cam
- Performer RPM 2.O
- Holley / Quick Fuel M-850
- Baker engineering / ProCam Marine Mechanical Fuel Pump
- Kenne Bell / AutoRotor 1.5L Twin Screw SuperCharger
-Ignition
- Davis Unified Ignition Marine HEI with Custom Advance Curve
* (14 degrees / all in @ 2800)
- Talylor Cable 8mm Spark Plug wires
Project Details:
The 1997 Baha Cruiser 290 Mach 1 Originally came equipped with a Mercruiser 7.4L Bravo III engine and drive package. In Brief detail this package consist of a GEN VI 7.5L cast block with small oval port cast heads with open chambers and a volume listed as 118cc, a cast 4bbl intake manifold supported by a Weber/Carter AFB with mechanical secondaries rated at 750CFM. The Short block is a 2 bolt main with cast steel 4.00” stroke crank, 6.135” forged press pin rods and cast pistons supporting 5/16 top and second rings and 3/16 oil rings. The Cast Pistons are flat with a slight dish but i was not able to find the exact volume of the pistons. The heads are 156 casting small oval ports with non adjusting stamped rockers and guide plates listed as 118cc and having Valve size 2.06 intake, 1.72 exhaust. The head gaskets are mercruiser MLS gaskets. The camshaft is a Mercruiser Marine roller cam with 215/217 duration@.05 the centerline is 110 and a lobe seperation of 115.4 The engine is listed to have 8.1:1 Static Compression and with and intake close time listed at 69 the dynamic compression is roughly 6.5 assuming 118cc heads and a 3cc dish. The engine is rated at 330HP.
Detailed Specifications Link:
https://www.perfprotech.com/blog/tech-specs/mercruiser-bigv8-marine-engines-specifications
To replace the engine I chose a Mark IV block that i pulled from a 76 motorhome with roughly 86000 miles on it. The owner stated that he had the engine rebuilt years ago from a spun bearing and the crank has been turned on the main journals. After breaking the engine down I confirmed bore size as 4.25” and the cylinder walls were in very good condition. The crank was as stated with 1 size under on the mains. I ditched the flat tappet cam, lifters and all the bearings then delivered the bare block, crankshaft and heads to the machine shop for inspection. The shop reported that all components passed magnaflux inspection and were usable components. After discussing the build project and my desired goals we chose an approach for required machine work. I had the block cleaned including oil plugs pulled and galleries brushed, hot tank treatment and a jet wash cycle then the cylinders were honed for use with moly rings. The crank was turned and polished with a final measurement of 10 under on the rods and 20 on the mains. I had the heads resurfaced and the valves cut and seated, the guides were inspected and noted well within tolerance. The springs and retainers were replaced with the springs from the mercruiser engine head seeing as i intended to use the mercruiser cam from the damaged engine. We discussed oversize valves and extensive head work but the machinist felt the money would be best spent elsewhere as the marine exhaust manifolds are rather restrictive to benefit from larger valves. On the way home i stopped by the car wash and pressure washed all the parts using a degreaser and a few brushes. At home i prepped the block and heads for paint. After painting and a quick recleaning I treated the parts with wd4 and covered the engine with plastic wrap and spent a week or so researching and ordering parts.
Everything went together rather well. I chased all threaded holes and cleaned all hardware with parts cleaner and a wire wheel. The main caps and heads received stud fasteners and all valve train components were coated in assembly lube and sprayed with dry moly film. I followed many threads and instruction from this site in regards to clearances while putting everything together and feel rather confident in the build and was rather proud of myself.
Once assembled I Ran the engine naturally aspirated for break-in and confirmed timing. I had good oil pressure at 60 psi above 2000 rpm and no noted temperature issues. SOOOOO i took her to the lake. It started good and ran without issue while in the no wake zone but once i tried to plan off i could get to about 2800 and that all she had. I checked timing it was good so, checked fuel supply and pressure and volume were good. Then i noticed my oil pressure had dropped and there was oil noted in the builg. I wasn’t far from the loading ramp so i returned at just above idle throttle, at idle my oil pressure was near zero and just off idle I had almost 20lbs. Back home I found that the issue began when the secondarys would open then the engine would flood, severely flood, I checked the plugs and they were black and fouled. I checked compression and THIS is where the trouble was found. 80 on all cylinders.
It took several days to find the issue but the low compression comes from a miscalculation on deck height where i ordered pistons that do not have the accurate compression height. I ordered 1.27 pistons and needed 1.52 pistons. My current configuration deck height is .395 in the hole so my compression is hammered. I suspect that with the low compression i was way over jetted and flooded the cylinders causing the rings not to seat and push excess crankcase pressure to the pan pushing oil out the rear main. I intended to bump my static compression slightly by using flat top pistons in place on the cast pistons in the factory block as i needed a higher static ratio to achieve the desired dynamic ratio with the cam i have, but now i'm at a critical turning point in my build. The cost of piston and rings is far more than replacing the rods or crank so I would like to keep the pistons. I am sure the crank will need turned again and all the bearings replaced as well as the whole engine cleaned, im sure I ate the bearings, I cut the filter and there was metal in the element.
As i assess myself over this build I can account for many mistakes, such as failure to check deck clearance after installing the rotating assembly, or checking the measurements of the rod and pistons together. Hell i didn't even check the length of the rods when i got them to make sure they were the correct length that i intended at the time. I did clean all the parts as instructed from several of grumpy's threads. I spent lots of time and money on the proper tools for checking clearances i just missed it. I don't feel i rushed the build… maybe i was just overwhelmed or over my head but one thing's for sure. I was real proud of my self as i thought I had done well with my project. Setting goals, researching all the options and parts, reading reviews and setting realistic performance goals (i hope). I know its no 1000hp cannon, but i thought it was a modest build with a little flare and would be a great engine from my boat… im not all that confident in it anymore. Embarrassing
All that aside this thing needs to come apart. So im looking at my options, i have spent a lot on rods and pistons and they are forged components. The crank is stock so to me the best results for the money would be to replace the crank with a stroker crank and take advantage of the added performance, BUT there is no way to make up the distance with crank stoke alone. So Im buying rods either way. Now Its not much more expensive to just replace the crank with a 4.25 stroke and run 6.385 rods to put me at .020 deck height and a .020 gasket to achieve .040 quench and adequate compression. If i do not replace the crank i can run 6.535 rods and that puts me -.005 out the deck. I can make that up with a gasket to get somewhere between .035 and .038 but to get to .045+ from a gasket that will match well with boost I would have to go to copper head gaskets which are awesome but expensive. About the same cost as buying a crank, either way i need to balance the rotating assembly So in the end I’m about to spend 1000$ on the bottom end and would like some opinions and suggestions on where to go with the engine at this point. I am not worried about the expense as much as i am worried about reliability and cost vs gains. Seeing as it’s coming back apart this is a good time to review the all of the parts and see if i am even close to what i intended to build (obviously not in the compression area) is there alternative cam specs that would be better suited for this engines intent? Are there other obvious issues that i am missing? Any suggestions and PRO TIPS are welcome and wanted. Im open to changing anything that needs to be corrected either for better performance or especially for reliability. I have other specific information if needed, I know I left a lot out in terms of specific details that i can provide if needed.