Perkins 4-108 Power Curve

[CSY Man]

Originally Posted by Cheechako

Hard to remember now, but I think I was propped for 3000 max rpm or less. Seems like I thought at the time the engine was rated much lower than 4000....

The 4-108 is rated for Max continuous operation @ 3000 RPM.
Not sure how many HP that is, 37 perhaps.
4000 RPM is for "emergency" power, or "war power" for you military folks

That being said, I had to use 4000 RPM several times, mostly for going under bridges about to clip my mast, or maneuvering in strong currents.

The power is there and thank God for it.
If folks over-prop their boats, the Horse Power is not available and they complain that the Perkins 4-108 does not deliver the goods.
For normal cruise I used 2100 RPM, probably 15-18 HP or so.

Compare it with a car, say you buy a Corvette with 400 HP: The muscle is not meant to be used all the time, or continuously, but for "fun", for bragging rights or to be safe when overtaking and passing a truck on a 2 lane road.
It probably takes only 10% of the 400 HP to go down the road at cruise.

[Cheechako]

Originally Posted by CSY Man

The 4-108 is rated for Max continuous operation @ 3000 RPM.
Not sure how many HP that is, 37 perhaps.
4000 RPM is for "emergency" power, or "war power" for you military folks

That being said, I had to use 4000 RPM several times, mostly for going under bridges about to clip my mast, or maneuvering in strong currents.

The power is there and thank God for it.
If folks over-prop their boats, the Horse Power is not available and they complain that the Perkins 4-108 does not deliver the goods.
For normal cruise I used 2100 RPM, probably 15-18 HP or so.

Compare it with a car, say you buy a Corvette with 400 HP: The muscle is not meant to be used all the time, or continuously, but for "fun", for bragging rights or to be safe when overtaking and passing a truck on a 2 lane road.
It probably takes only 10% of the 400 HP to go down the road at cruise.

That makes sense, I havent looked at the curve, but Torque is higher at a bit lower RPM usually ... right? I had no problem with less than 3k rpm in my medium heavy 44 footer, even in the high current situations in the PNW. But I had a long waterline and Maxprop