Couple of questions

[smax]

I have a 1989 Force 85hp on a 1977 16' basscat bass boat. Currently I have a baddly beaten 21p aluminum prop and I am getting 35mph(gps), but I don't have a tach so I don't with the RPM is. I have an inductive pick up tach and I am wondering if this will work on the Force since the 20 pole tachs are hard to find? I also found a descent deal on a 19p stainless prop, but I was wondering if stainless would be too much for the 85hp?

 

[steveclv]

Re: Couple of questions

Yes an inductive tach will work as long as you can find somewhere on the flywheel to mount the sensor (probably a hall effect magnet).

Stainless is fine for the prop - just be aware that if you are likely to anywhere near to where you may prop hit, then SS will break/shatter whereas aluminum just bends - thus SS is way more expensive to repair.

Until you know your revs it's pointless experimenting with props - you need to know your revs at WOT with the 21p - if they are close to max then you are risking it by decreasing to a 19p. 2 strokes will rev and rev beyond their 'max revs' but you are then outside of the power band and it does nothing for your fuel consumption!

 

[smax]

Re: Couple of questions

I think the 21p is bogging the engine. The tach I have actually has a sensor that clamps on a plug wire. I will go ahead and test it and see what I get. The tach is just sitting in the garage anyway.

 

[steveclv]

Re: Couple of questions

OK, it should work as I don't think the Force works on a lost spark ignition system so as long as the tach can be set for 2 stroke and not 4 stroke you should be good to go. Let us know how you get on.

 

[smax]

Re: Couple of questions

Well with the beat up 21p I'm get 35mph at 4500 rpm's. Should I get the 19 stainless or get a 17 aluminum?

 

[Frank Acampora]

Re: Couple of questions

I don't use anything but stainless--but, of course, I don't make it a practice to go banging them into rocks. The one time I did, it cost me 90 bucks to repair the prop and I was also left with half a skeg.

That said, Force engines like stainless and generally do much better with them. If the prop you are looking at is NOT cupped, then you can expect about 600-800 RPM more from the 19 pitch and probably a couple of MPH more. 17 pitch aluminum will raise RPM about the same but I suspect you will find a drop in top speed.

While the 21 pitch is not bogging your engine--operating range at WOT is 4500-5500-- you are at the bottom of the range. These engines run better at or near the top of the range.

 

[smax]

Re: Couple of questions

Ok, sorry it took so long to get back. I got the tach working and got the new 19p ss prop on the boat. I am now running 40-41(gps) at 5100 rpms. The boat has a much better hole shot and pulls pretty good from part throttle cruise to wot.

 

[Frank Acampora]

Re: Couple of questions

I told you that you would be happy with it.