1st post. Have done lots of reading here. I'm looking to build a high torque low RPM motor for a boat mud motor.
I have a stock non-hemi on the boat right now and it bogs pretty bad and will only run 2000-2300 rpm with a full load. I need more torque to get it up on plane so the motor can wind up. Prop is 7x4", so can't go smaller there (American prop, not Thai).
I bought a new hemi from HF today to build, so I can keep using the mud motor in the meantime. From my research here and elsewhere I plan the following:
Remove governor / billet flywheel / Billet rod (+.0xx to get deck to zero)/ Black Mamba Jr cam / 26# springs / header with RLV / mikuni VM22 / mill head / full port
Questions...
Flywheel timing: for lower RPM (sub 5k) do I need spark advance? PVL flywheel is stock at 28°, ARC is 32°. Is it better for lower RPM to NOT have greater than stock advance? Or does advance help at lower RPM on these motors?
Cam: The Black Mamba Jr. vs. NR 280-0211? BMJ gets great reviews. Have not read anything about the NR 280. Thoughts? NR 280-0211 is advertised as the ultimate 2k-5k torque cam.
Rocker Arm Ratio: Will I see any benefit in lower RPM torque from going to a 1.1, 1.2, or 1.3 ratio arm?
Compression ratio: I can mill the head easily (have bridgeport mill) and found the tables of height vs CR. What CR should I target? I'd like to stay on pump gas 93 or below.
Thanks. This site rocks. I love reading about your builds.
Sandor27
I have a stock non-hemi on the boat right now and it bogs pretty bad and will only run 2000-2300 rpm with a full load. I need more torque to get it up on plane so the motor can wind up. Prop is 7x4", so can't go smaller there (American prop, not Thai).
I bought a new hemi from HF today to build, so I can keep using the mud motor in the meantime. From my research here and elsewhere I plan the following:
Remove governor / billet flywheel / Billet rod (+.0xx to get deck to zero)/ Black Mamba Jr cam / 26# springs / header with RLV / mikuni VM22 / mill head / full port
Questions...
Flywheel timing: for lower RPM (sub 5k) do I need spark advance? PVL flywheel is stock at 28°, ARC is 32°. Is it better for lower RPM to NOT have greater than stock advance? Or does advance help at lower RPM on these motors?
Cam: The Black Mamba Jr. vs. NR 280-0211? BMJ gets great reviews. Have not read anything about the NR 280. Thoughts? NR 280-0211 is advertised as the ultimate 2k-5k torque cam.
Rocker Arm Ratio: Will I see any benefit in lower RPM torque from going to a 1.1, 1.2, or 1.3 ratio arm?
Compression ratio: I can mill the head easily (have bridgeport mill) and found the tables of height vs CR. What CR should I target? I'd like to stay on pump gas 93 or below.
Thanks. This site rocks. I love reading about your builds.
Sandor27