4 stroke Engine Revs

[CB77]

Hi,

I am interested to hear what revs 4 stroke owners cruise at?

My 140 Suzuki runs sweet at 3800-4100 RPM doing about 30km/hr.

Guy told me the other day that he runs every where almost flat stick.

Obviosly there are a lot of differences ie hull, engine, set up etc.

[Mr__Bean]

Craig,

I reckon this is a damn good question, and one that I have often wondered about but haven't yet got a conclusive answer to.

I have a 225 Yammy four stroke and a rather heavy boat, the WOT max RPM is stated as 6100 for this motor, but does that mean that it can run up around this all day without harm? I doubt it.

But what I don't fully understand is whether the motor is similar to a production car 4 stroke engine whereby it can rev to that level without throwing itself apart but really would prefer that you kept it around 4500 max.

Or, is it a highly refined 4 stroke like in many motorbikes etc that are built to rev sweetly to around 10000 rpm and running at or around 5500 rpm for extended periods is what it is actually designed for.

Me not sure??????

- Darren

[DAZMC1]

My 140 suzuki usually sits on around 50kmh at 5000rpm and stays there for an hour or more each time. I get about 1.7kml @5000 but if i drop back to 4500rpm-45kmph I get 2.0kmpl and thats on an EDENCRAFT 565 SPORTS with standard 14x19 prop.

[Fish Guts]

have a pair of 250 zuks. 3900 seems to be the best for us.

[CB77]

Craig,

I reckon this is a damn good question, and one that I have often wondered about but haven't yet got a conclusive answer to.

I have a 225 Yammy four stroke and a rather heavy boat, the WOT max RPM is stated as 6100 for this motor, but does that mean that it can run up around this all day without harm? I doubt it.

But what I don't fully understand is whether the motor is similar to a production car 4 stroke engine whereby it can rev to that level without throwing itself apart but really would prefer that you kept it around 4500 max.

Or, is it a highly refined 4 stroke like in many motorbikes etc that are built to rev sweetly to around 10000 rpm and running at or around 5500 rpm for extended periods is what it is actually designed for.

Me not sure??????

- Darren
Hi Darren,
Thanks thats exactly what I was trying to get at, are these engines capable of longer running periods at higher RPM without flying to bits or wearing out quicker?

If I push mine upto 4500 - 4800 she really flies but I havent been game to keep her up there for long distances and I havent yet taken it out to WOT so I dont know what it goes up to.

I never like flogging the arse out of my gear but i would like to know if I am being to conservative running at around 4000rpm.

[culbara]

If yo drive a boat at the compfortable speed you will get good fuel economy but when you raise the reves above it comfortable crusing speed you cheww a hell of alot more fuel also once you get abouve this cruising speed yo dont seem to get a lot of extra speed for the extra revs perhaps it over revs prop and is not as efficient above certain revs and given the cost of fuel these days is wise to conserve and if yo have a motor under warranty remember these days they put a laptop on your motor and they can download exactly what revs it has been doing and for how long

[CB77]

My 140 suzuki usually sits on around 50kmh at 5000rpm and stays there for an hour or more each time. I get about 1.7kml @5000 but if i drop back to 4500rpm-45kmph I get 2.0kmpl and thats on an EDENCRAFT 565 SPORTS with standard 14x19 prop.

Thanks for that maybe I am being to conservative at 4000rpm? My 140 is on the 550c Signature so it is probably comparable to yours only mine is running a solas stainless prop.

I havent had the boat long enough to have checked mileage yet.

[Luke G]

If im on night shift my 115 Suzuki would sit on 6000 for 20 miles till I was out on the grounds, then troll till about 10.30 then come home at WOT again to maximise fishing time. I never had any problems with that motor. For a normal day I would sit on 4000-4500. Same for my new 150.

Cheers

[CB77]

If im on night shift my 115 Suzuki would sit on 6000 for 20 miles till I was out on the grounds, then troll till about 10.30 then come home at WOT again to maximise fishing time. I never had any problems with that motor. For a normal day I would sit on 4000-4500. Same for my new 150.

Cheers

Thanks,

Thats pretty much what another guy I was talking to was saying, it was not unusual for him to run it at WOT or close to it for duration of the trip.

How many hrs did you run up on the 115 before you sold it?

I am not sure if that is a good strategy for the longetivity of the engine?

[TimiBoy]

The V-Rod purrs wherever you set it. I usually cruise at about 4200, getting near 1.2km/l.

I have no troubles with going flat stick (6200), except for the fuel usage at .7km/l.

Cheers,

Tim

[Scott nthQld]

Mine sits on cruise at about 4000rpm and about 24knts, WOT is only 29knts loaded doing about 5000rpm. Wouldn't have a clue on fuel usage, but an avergae day, seeing lots of trolling, WOTting around the place will see it burn about 1L per 3km (4.8m tinnie with a 60 4str yam pushing her along)

[Luke G]

370 hours - 270 of those was in 8 months.

Cheers

[foxx510]

I feel quite comfortable running our little 25 Honda four stroke at WOT for extended periods, you can "feel" when a motor doesn't like reving, this just feels smooth as at 5500 rpm. There is nothing in the handbook to suggest that you shouldn't run them at WOT for extended periods either. It's all about how well balanced the motor is, and the Japanese do it well.

[PADDLES]

our 140 sooz purrs away in the same rev range as yours craig, 3800-4100rpm pushes our 6.2m freedom along around the high thirties to low fourties or so km/h with the stock 14x19 prop

[Spaniard_King]

Guys, IMO its not the rpm on an engine that will do the damage.. its the combination of load and rpm that will do the damage.

If you have your boat correctly propped it should be able to run at high rpm for extended periods but if you are running it overloaded which will create more heat than normal.. things will not be runing at there correct tollerance.

Much better to have an engine free rev to its WOT than to not quite acheive maximum rpm.. no big deal to run at 4400 for 25knots than 4100 and loading the engine for 25knots.

I have spent a lot of time maintaining water taxis and this is definately the case.