Suggested Prop size for a DR 490

[two stroke mick]

Hi

I am running a Valiant DR 490 with an 60 Hp ETEC. The engine will rev past 6000 RPMif I let it (Max recommended 5750 -6000 RPM). I suspect that the engine would rev to 7000 RPM but I dont want to exceed Max Revs.

Is there a rev limiter on ETEC's ?


The current prop is a Ali 13.25 * 17. Max speed at 6000 RPM 32 knots

TSM

[rib-x450]

I bought gadget for go kart engine as I had a similar problem, it wrap around the HT wire and counts the sparks, but best off all it gived the highest RPM reading when you oush a button, really useful to get the right prop etc. I bought mine on ebay for about 40 pounds secondhand.

Look under rev counter Go Kart..........

Hope this is useful...........

Can remember the make of mine but it has lasted really well in the wet no problem.

wellhttp://www.minimotoclub.co.uk/vb/showthread.php?t=12890

See the web page for a similar one.

Chris

[ian parkes]

Mick although my 490 had a suzook 70 it had the same size prop that you are running. That 17" prop was ok for heavy loads ie 4 people plus or towing .
I found a 19" was best for cruising and general use .
I ended up getting a prop re pitched to 18 for all round use as i always had 3 or more aboard plus a fair bit of kit and my suzuki was a lot heavier than your motor

[Downhilldai]

Originally Posted by ian parkes

Mick although my 490 had a suzook 70 it had the same size prop that you are running. That 17" prop was ok for heavy loads ie 4 people plus or towing .
I found a 19" was best for cruising and general use .
I ended up getting a prop re pitched to 18 for all round use as i always had 3 or more aboard plus a fair bit of kit and my suzuki was a lot heavier than your motor

DF 70 has a different gear ratio to the etec 60, so prop pitch shouldn't be compared 'like for like'

[ian parkes]

Originally Posted by Downhilldai

DF 70 has a different gear ratio to the etec 60, so prop pitch shouldn't be compared 'like for like'

True but i was trying not to complicate things . the etec is higher geared and over 50 kg lighter so given my experience I would have thought try a 19 was a good starting point . to get an 18 you would have to get a prop re pitched and as we know thats another saga

[two stroke mick]

Hi Ian Got a 19" pitch prop last night. I never did let the engine go all the way to WOT with the 17" as it would rev past 6500. The 19" prop is good for 33-34 knots one up at 6400 revs (wot). 1 person, 53lt of petrol. I have 10 lt of petrol and a small anchor in the bow locker. I think I need more weight in it when facing a headwind?

TSM

[ian parkes]

Originally Posted by two stroke mick

Hi Ian Got a 19" pitch prop last night. I never did let the engine go all the way to WOT with the 17" as it would rev past 6500. The 19" prop is good for 33-34 knots one up at 6400 revs (wot). 1 person, 53lt of petrol. I have 10 lt of petrol and a small anchor in the bow locker. I think I need more weight in it when facing a headwind?

TSM

They do feel a bit flighty without any load don't they . sounds like your much lighter wieght engine is making all the difference , I expect the tubes are completely clear of the water when you are on the plane . The etec is higher geared and you are still getting more revs than i did with a 19 pitch .
From memory unloaded mine would do 40mph at about 5800 rpm . i guess you could work out the differences there for the different rpm and gear ratios , but sounds liike you could pull an even higher pitch maybe

[two stroke mick]

I usually have one other person in the boat with me I suspect that the weight of the extra person will bring the revs down to approx 6000 RPM. I also intend to use the boat for diving from time to time (4 divers) This I expect will greatly reduce the revs. So I think I wll stay with the 19" for the moment. Thanks for the advice.

I have added 11kg of lead to the bow locker along with the 10lt of pertrol 3kg anchor and 2lt of water. (26kg -27kg approx) I used to keep 25lt of pertrol in the bow but then I bought a smaller anchor that would fit into it. The boat behaved much better with the 25lt of petrol up front.

TSM