It takes a certain amount of fuel to make a certain amount of horsepower. It doesn't matter if you're making that power at 3,000RPMs, 4,000RPMs, 5,000RPMs, etc etc. If the same amount of power is being made at 4,000RPMs as is being made at 5,000RPMs, the engine will require the same amount of fuel regardless of the RPM.

The engine has to make a certain amount of power to generate a certain amount of thrust. In regards to fuel consumtion, it doesn't matter at what RPM it makes it at. The engine will still consume the same amount of fuel to make that certain amount of power. Engine vaccuum controls how much fuel is consumed, and the load placed on the engine controls how much vaccuum you have. More load = less vaccuum = more air = more fuel. RPM has nothing to do with it.

As far as the "more thrust at lower RPM with a bigger impeller", actually you get the same thrust at lower RPM. And yes your RPM may be lower, but if you're making the same amount of thrust at a lower RPM, the pump is requiring the same amount of horsepower as it would at a higher RPM with a smaller impeller to move the same amount of water to create the same amount of thrust.

That was an INCREDIBLY "LOGICAL" post..... You should put some more thought into what you just said.

I think you're misunderstanding what I'm saying.

Let's take your boat for example. At 5200 RPM you would go through 6 gallons of gas around the BV loop. Then when you drop the RPM to 4800 it only uses 4 going the same distance. All you did was change the throttle position to drop the RPM, which will in fact decrease fuel consumption. This is because with the same impeller the engine will see less of a load at the lower RPM.

However, let's say that with an A impeller your max RPM is 5200. Then you swap it to an AA impeller and your max RPM drops to 4800. And let's say that at 4800RPM the AA impeller places the same load on the engine as the A impeller spinning at 5200. Even though your max RPM dropped, your fuel consumption will be the same as with the A impeller spinning at 5200RPM. This is because the same exact load is being placed on the engine, which will require the same amount of fuel to make the same power it made at 5200RPM with the A impeller.

I misunderstood. Now it's all making sense to me... Based solely on what your post was claiming, can you see how I could be confused?

I do see where you could be confused. The whole point of this post was because Jim Rich claimed that with a bigger impeller you could get the same thrust at a lower RPM and not use as much fuel, and I was merely trying to correct this.

To answer your question...fuel is an energy source. It takes X amount of energy to perform X amount of work. This basically means that an engine requires X amount of fuel to produce X amount of power. Remember, energy can neither be created or destroyed...it can only change form. In the case of an internal combustion engine, you convert combustion energy into reciprocating energy (the up and down movement of the pistons). You then convert reciprocating energy into rotary energy (the rotation of the crank). Having said that, there is no way that you can make the same amount of power with less fuel just because of RPM. You get what you put in.

AT's semi-sad attempt at a built in bowl stuffer... cutesie shit right there. They try too hard to buy out smaller companies and don't spend enough time actually researching...

AT's semi-sad attempt at a built in bowl stuffer... cutesie shit right there. They try too hard to buy out smaller companies and don't spend enough time actually researching...

Well Dave and I talked a bit today, he is not back yet but is returning a few calls.

The AT deal is very effective but the impeller itself does not lend a very good helpful hand in thrust.  That must be the why they are working on the new Hihelix design impellers.  But Aggressor has a new design too and it should be even more efficient then their other impellers.  Dave stated today that their A impeller will spin 400 rpm less than a Berk A and create more thrust, higher speed.  I am pretty sure that being the Aggressor impeller is made in 4 parts which is a much better and aggresive design than the 1 step AT.  But the AT stuffer is still much better in my eyes.  But this season I will be running Aggressor impellers in my CJ boat exclusively.  Now the tin boat will run a 10" AT with lip, it is not a high speed boat so low rpm efficiency is most important and the AT 10" gives that.

well put Josh. It is semi sad because they had a good idea and never fully developed it, they started then kinda let off. Dave's new impeller is worth the wait. You guys are gonna like it.