Perkins 4-108 Power Curve

[zeehag]

if the alleged 54 hp machine can move my formosa in a reasonable manner it WILL move your boat appropriately.
keep your perkie--they rock. repairable everywhere and work forever.
mine was rebuilt in 2014 and is perfect...love ka lunk.

[CSY Man]

Originally Posted by Trekka

I'm wondering if I am under propped...

I have a 4-108 in my CSY 33. I often run at 3000rpm for cruise, 1-3 hrs at a time before dropping back a tad for a bit. I have run at 3500 when powering off a bar. Have a 16 R10 3 blade prop.

Wonder if I should add some pitch?

Btw, no overheating problems after taking apart the cooling system and degunkifying the coolant passageways of slime, and cleaning the heat exchanger. The slimy, waxish buildup was apparently from the PO using different coolants that were incompatible with each other. (I documented my cleaning in posts and pictures here).

I usually ran the 4-108 in my CSY33 @ 2100 RPM, 70 % of Max continuous as recommended by some Diesel guys.
I had the prop pitched to turn 4000 RPM at full throttle.
If running for extended time above 2600 RPM it would slowly but surely overheat.
Not because of overpropping but probably because the heat exchanger was a size too small.

[Cheechako]

My 44 ft Cutter had the 4-108 in it. Surprisingly it was plenty of engine for that boat. Max Prop and I was set about 2800 rpm max IIRC, normally I cruised at about 2400 rpm which was smooth and sweet. No problem going 8 knots and pushed a bit more would do 8.5. About a 39 foot waterline on that boat and it went thru current and chop very well. I believe I had the later bigger heat exchanger, never had any overheating at all. Bowman exchanger IIRC.
The boat was a CT44/Tanton 44. Heavy, but not heavy as many Formosa or CSY would be. (Avatar picture)
That boat resold a couple years ago, about 20+ years after I had it .... 4-108 still going strong.

[CSY Man]

. The boat was a CT44/Tanton 44. Heavy, but not heavy as many Formosa or CSY would be. (Avatar picture

A CSY 44 would displace about 37,000 lbs from the factory, but none of them had the 4-108. They came stock with a 62HP Perkins, but many owners later upgraded to 75 or 85 HP power plants.

Some CSY 33s and CSY 37s had the 4-108.

[Cheechako]

Originally Posted by CSY Man

A CSY 44 would displace about 37,000 lbs from the factory, but none of them had the 4-108. They came stock with a 62HP Perkins, but many owners later upgraded to 75 or 85 HP power plants.

Some CSY 33s and CSY 37s had the 4-108.

Yeah, was referring to the earlier CSY mentioned

[CSY Man]

Originally Posted by Cheechako

Yeah, was referring to the earlier CSY mentioned

I had a CSY 33 with the 4-108, quite enough power for a small but heavy boat.
Only 25' waterline so hull speed was not great, but the 4-108 at 4000 RPM
Would almost punch beyond hull speed leaving a large wake behind and making noise, smoke and some vibration.
At 2100 RPM however it was smooth as silk and burned about 0.65 gallons per hour @ 5.3 knots.
Those claiming it did not deliver 51 HP may be the same folks who over-propped it badly so it could never reach the rated RPM, or the rated HP?

[Cheechako]

Yeah, my guess is the 51 hp was a very conservative rating maybe. As mentioned, it pushed my 44 ft at 8 knots readily. The fuel burn over the lifetime of that boat was .65 gal per hour too! The boat was heavy but also a bit of a canoe shape underwater!

[CSY Man]

Originally Posted by Cheechako

Yeah, my guess is the 51 hp was a very conservative rating maybe. As mentioned, it pushed my 44 ft at 8 knots readily. The fuel burn over the lifetime of that boat was .65 gal per hour too! The boat was heavy but also a bit of a canoe shape underwater!

I had 2 props and kept adjusting the pitch on both (as well as the balance)
find the "optimum" solution.
Did over-pitch on purpose for a Bahamas cruise, just to try. Sure enough, more speed for same RPM but also limited high-end RPM.
I kept hearing how over-propping was bad for the engine so I went back to a pitch that would give me 4000 RPM when running free and 90% of max when tied to the dock. (Forgot where I got that from, but it and the 70% of max for best cruise worked really well for me)

Did a total of 27 Bahamas cruises and with all the Gulf Stream and Bank crossings under power, I had plenty of opportunity to compare fuel burn, speed, etc.,etc.

[Lepke]

From another direction...
I got a 1972 4108 running a 14kw generator @ 1800rpm with the current boat. It put a oil sheen on the water so I overhauled it. Talking to previous owners, it had never been overhauled in 40+ years. The only internal problems were glazed sleeve walls from running too many hours on light loads and the usual rear main seal leak. Pretty good for unknown thousands of hours and no warmup. Crank was still stock, no head cracks, etc. I could have got by with honing, new rings, valves and gasket/seal set.

[Davey1000]

Only ten years late but better late than never! The Perkins 4.108 maximum power is 51 horsepower at 4000 rpm. Of course in a hot climate the air will be less dense so some power loss will occur. (At one place where I worked a diesel generator set never produced its rated output but the engine was breathing hot air from the engine room! The "experts" tore down the engine and fitted new piston rings but after this the generator output was less than it was before!)

A big problem with the 4.108 is overheating in waters that are like a sauna bath and it would appear that the OEM heat exchanger is only suitable for temperate climates. Possibly the best solution is to fit a Perkins 4.236 heat exchanger.

Good luck!

[Cheechako]

Originally Posted by CSY Man

I had 2 props and kept adjusting the pitch on both (as well as the balance)
find the "optimum" solution.
Did over-pitch on purpose for a Bahamas cruise, just to try. Sure enough, more speed for same RPM but also limited high-end RPM.
I kept hearing how over-propping was bad for the engine so I went back to a pitch that would give me 4000 RPM when running free and 90% of max when tied to the dock. (Forgot where I got that from, but it and the 70% of max for best cruise worked really well for me)

Did a total of 27 Bahamas cruises and with all the Gulf Stream and Bank crossings under power, I had plenty of opportunity to compare fuel burn, speed, etc.,etc.

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....

[Cheechako]

Originally Posted by Davey1000

Only ten years late but better late than never! The Perkins 4.108 maximum power is 51 horsepower at 4000 rpm. Of course in a hot climate the air will be less dense so some power loss will occur. (At one place where I worked a diesel generator set never produced its rated output but the engine was breathing hot air from the engine room! The "experts" tore down the engine and fitted new piston rings but after this the generator output was less than it was before!)

A big problem with the 4.108 is overheating in waters that are like a sauna bath and it would appear that the OEM heat exchanger is only suitable for temperate climates. Possibly the best solution is to fit a Perkins 4.236 heat exchanger.

Good luck!

The 4-108 came with two different heat exchanger systems that I know of. One side mounted and one front mounted. My side mounted unit (Bowman name cast into the housing) never had a cooling issue.

[robertsquire]

thanks for the reply.I have it in a 43ft BENETEAU and I run it at around 2,5-2,8 rpm I'm a little hesitant because I don't know the history.I have noticed that if you are looking from the front towards the back the left rear mounting is broken .any further thoughts.

[Cheechako]

The motor mount is broken?

[donradcliffe]

I had a love/hate relationship with my 4108, and swapped it out for a Beta 50 at 4000 hours. I loved the 4108's reliability, but hated its noise and oil leaks. The boat was a Bene First 456, which had a design weight of 26,000 lbs, but a cruising weight of 33,000.

If I ran the 4108 at over 2500 rpm, it used a lot more oil and made a lot more noise and fumes. So I repitched the max prop to cruise at 2400 with a max of 3000. In flat water the boat would cruise at 6 knots and max out at 7.5, which was enough for me. If I had to beat against heavy wind and seas like going up the Red Sea, I just used the sails, because that was faster and nicer than using the engine. My limit on oil leaks was half a liter every 100 hours, so I ended up replacing the front/rear seals and oil pan gasket twice in 4500 hours.

After going RTW with the 4108, I put the Beta in. The Beta sales people recommended their 37, but I went with the 50 to get a little more reserve power. The Beta pushed the boat at over 8 knots, but the fuel burn at 6 knots was about the same. The main improvement was in the noise and oil leaks/fumes. The cruise RPM of the Beta was about 1800, and it was much smoother and quieter. Repowering with a Yanmar would have meant changing the exhaust system--all I had to do was put blocks on the motor mounts.

The 4108 ended up in a forum member's Westsail 32.