View Full Version : rpm@36 mph,1;1 vs 1.5:1
10-14-2007, 11:07 PM
two identical boats,1998 PS190s one has a powerslot 1.5:1 and the other has a 1:1 tranny.these boats have factory running gear and LT1 engines.What will the differnce at 36mph be in engine rpms????will the powerslot be running a higher rpm(aprox.4300)as compared to the 1:1 which is (aprox)3600rpm.Just trying to understand the differance and which will burn more gas and if there is any top end differnce?
thanks in advance,any input will be helpful
10-14-2007, 11:34 PM
I am not sure about the newer and heavier boats, but the older and lighter boats like my 82, both boats ran about the same top speed (45) at the same RPM (4500).
If you calculate it out on paper and not account prop slippage the Powerslot should have a top speed of about 50 miles per hour @4500 rpm and a 18 pitch prop. The 1:1 drive would have a top speed of about 55 miles per hour @4500 rpm.
Since the bigger pitch prop of the power slot is more efficent, it slips less and provides a stronger pull.
Now with the bigger and heavier newer boats with more drag............someone else can speak to that.
In my experience with the earlier boats, they both ran about 3600 rpm at 36 mph.
10-14-2007, 11:49 PM
I would agree with Ski King. They seem to run the same rpm/mph unloaded. The difference comes when you load the boat with weight or pulling and the slippage is not as great and the fall off is less with the slot. As far as the gas usage I would think it would be the same unloaded and have no idea loaded. That being said my ski buddy has the same engine and year boat that I have with a 1:1 and I have seen that boat pull 6 deep water starts at the same time.
10-16-2007, 08:17 AM
so all boats with similar powerplants will run the same engine rpms,regardless if equipt with powerslot or a 1:1 setupfor a given speed?????guess thats what I am trying to answer.Thanks in advance
On my 84 powerslot the RPM's vary according to the load. If someone wakeboards at say 23mph/2600rpm with just a driver and spotter they might then ride at 23mph/3000rpm with driver/spotter and a 1000lbs of ballast.
The rpms for slalom speeds seem to be pretty similar to speed ie. 32mph is about 3200rpm and 36mph is 3600rpm.
10-16-2007, 11:02 AM
water is not like pavement.
When you look at a prop it has a pitch. That is when it rotates the surface pushes rewards at that point. Say the pitch gives you 3" of travel. If the water didn't allow slip then you wouldn't get that amount of forwards movement out of the boat. But in reality if the prop is spinning it is moving the water in that zone faster than the water around it. Or rather the prop is slipping always.
When you look at the 1.5 drive you are turning a larger prop that should slip less. and is very good at accelerating the boat because it slips less. but at 36 mph in an unlaiden boat you are getting past the slip and reaching more of an equal slip condition.
as for 3600 36 correlation the 100 rpm to 1 mph does not always hold. Would be nice if it did right.
east tx skier
10-16-2007, 11:38 AM
The way it was explained to me, since the powerslot is turning a bigger prop with greater pitch, it all ends up being about the same from a speed versus rpm standpoint.
Our 92 190 w/ slot turns 34rpms at 34mph and just under 36rpms at 36mph w/ an OJ 454 XMP 4 blade. This is down about 75 - 100 rpms (depending on the skier load) from the original prop OJ 14x18 3 blade.