Hi all,
I realize this site is dedicated to mini bikes, but it is by far the best resource for modifying Predator engines. I'm a motorcycle mechanic and fabricator and will use a 212 Predator Hemi to build a longtail boat mud motor.
It's nice to see how affordable these race parts are compared to motorcycle engines, however the limiting factor for this build is not exceeding around 4,000 rpm at the propeller with direct drive. Eventually I will build a short tail, surface drive type motor, which utilizes a belt drive for gear reduction and will allow modifications to support higher RPM's.
In the meantime, I'm looking for "bang for the buck" mods that will deliver increases within the stock RPM range. So far it seems to be:
1. K&N style pod filter and carb adapter.
2. Header. Robertson claims their 33" long stepped H-loop gives the the best power, I will fab something similar that runs straight out the back and down to the water.
3. Jetting. Am I correct in assuming there is nothing to be gained at low RPM's from a bored/modified carb, and re-jetting is all that is required?
4. Compression. Using a 0.010" head gasket will provide minimal gains, but for $7 it seems worth it. It appears the budget 14cc heads will not fit the Hemi engine, but GX160's will so long as the Honda valves and springs are used? Are there higher compression pistons available, or is decking the factory Hemi head worth it?
5. Governor. I've seen the factory governor can be adjusted to 4,000 RPM, and the stock flywheel and rod should remain "safe." I've also read that the governor can fail and it is better to remove it. Is there a simple way to limit it to 4,000 RPM's with the governor removed, or is it reliable enough to leave alone?
6. Timing. I'm unclear whether advancing the timing 4 or 8 degrees will help or hurt the power curve at this rev range?
7. Valve springs. I understand how they prevent valve float at higher RPM's, but stiffer valve springs also rob more power compressing them if they aren't required.
The NR Racing stage 1 kit looks like a good buy for $50, then add a 0.010" head gasket and fab a header.
They are claiming around 10 hp with those mods, does that seem accurate or are they assuming the engine will be turning 6,000+ RPM's? Any input would be greatly appreciated, I've really enjoyed what I've been able to find on here so far.
I realize this site is dedicated to mini bikes, but it is by far the best resource for modifying Predator engines. I'm a motorcycle mechanic and fabricator and will use a 212 Predator Hemi to build a longtail boat mud motor.
It's nice to see how affordable these race parts are compared to motorcycle engines, however the limiting factor for this build is not exceeding around 4,000 rpm at the propeller with direct drive. Eventually I will build a short tail, surface drive type motor, which utilizes a belt drive for gear reduction and will allow modifications to support higher RPM's.
In the meantime, I'm looking for "bang for the buck" mods that will deliver increases within the stock RPM range. So far it seems to be:
1. K&N style pod filter and carb adapter.
2. Header. Robertson claims their 33" long stepped H-loop gives the the best power, I will fab something similar that runs straight out the back and down to the water.
3. Jetting. Am I correct in assuming there is nothing to be gained at low RPM's from a bored/modified carb, and re-jetting is all that is required?
4. Compression. Using a 0.010" head gasket will provide minimal gains, but for $7 it seems worth it. It appears the budget 14cc heads will not fit the Hemi engine, but GX160's will so long as the Honda valves and springs are used? Are there higher compression pistons available, or is decking the factory Hemi head worth it?
5. Governor. I've seen the factory governor can be adjusted to 4,000 RPM, and the stock flywheel and rod should remain "safe." I've also read that the governor can fail and it is better to remove it. Is there a simple way to limit it to 4,000 RPM's with the governor removed, or is it reliable enough to leave alone?
6. Timing. I'm unclear whether advancing the timing 4 or 8 degrees will help or hurt the power curve at this rev range?
7. Valve springs. I understand how they prevent valve float at higher RPM's, but stiffer valve springs also rob more power compressing them if they aren't required.
The NR Racing stage 1 kit looks like a good buy for $50, then add a 0.010" head gasket and fab a header.
They are claiming around 10 hp with those mods, does that seem accurate or are they assuming the engine will be turning 6,000+ RPM's? Any input would be greatly appreciated, I've really enjoyed what I've been able to find on here so far.