For Any Cruisers contemplating switching over to Hill Marine 4 Blade props....

Dream_Inn

Handymans342 said:

Dream_Inn said:

On my B-2 drives, I went from 23p to 22p.  The diameter is also 3/4" larger for me, so it equaled out.  Loving my new marine hill bug cow props!  Best one out there for B-2 drives!!

Never heard of "bug cow props" RLMAO

I've been sitting in spring cove marina all weekend drinking Mai tais. But I'll still blame auto correct.

Black_Diamond

Pondering the 4x4 props. Hill recommended 20P, a drop from 22P currently. WOT is 4800 rpm now. A 20P should take it to 5200 rpm. 

Carsnmorellc

I just bought my 22p 4 by 4 props today. 2k.... they better do the trick! haha

jmichels

what boat, current props etc. versus now Carsnmorellc

Carsnmorellc

@jmichels I have a 2001 340.  Right now I have the stock 3 blade 24p

Handymans342

Carsnmorellc said:

@jmichels I have a 2001 340.  Right now I have the stock 2 blade 24p

2 blade???

Carsnmorellc

3**** @jmichels  Sorry must have hit the wrong key

jmichels

let us know how you make out

J3ff

Black_Diamond said:

Pondering the 4x4 props. Hill recommended 20P, a drop from 22P currently. WOT is 4800 rpm now. A 20P should take it to 5200 rpm. 

I know you aren't a 270, but just to add to this thread, here's what I can say about the 20p's


https://rinkerboats.vanillaforums.com/discussion/7574/put-new-20p-4x4-hill-marine-props-on-this-morning-2004-fiesta-vee-270-w-383#latest

Black_Diamond

Good info. Thanks!  Pondering the spend here. Plus haul costs. Hmmmmm

J3ff

Black_Diamond said:

Good info. Thanks!  Pondering the spend here. Plus haul costs. Hmmmmm

so here's a question. I'm a shade tree mechanic, don't really know the answer.  If a motor is turning at 4000 rpms but working HARD to turn at 4000 rpms, does it burn the same amount of fuel as a motor that's really not having to work hard to maintain 4000 rpms? I can tell you that I burned more fuel then estimated.. 

randy56

If your running 4000 rmp to stay on plane or if your running 3600 rmp to stay on plane. It would be interesting to see how much, but you have to be using less fuel.

J3ff

Yeah, I know that less rpm = less fuel.. according to this chart:

(boattest.com)

Of course this wasn't generated from 270.  I can tell you that I did not get anywhere near 2.28 MPG and I was around 4000ish the whole time here. I used the 4500 number to do my estimates and I used even more than that!!  So when an engine works HARD to maintain 4000 rpms, does it use more fuel than an engine that isn't working hard at all to maintain 4000 rpms is the real question. 

Handymans342

Yes it does

Handymans342

For example, when you have an empty truck going 60mph at 2500rpm vs a truck pulling a boat at the same speed and rpm it will use more fuel

J3ff

Handymans342 said:

For example, when you have an empty truck going 60mph at 2500rpm vs a truck pulling a boat at the same speed and rpm it will use more fuel

that's what makes sense, so by switching to a 20p, the engine is not as "loaded" to run the same speed, lets hope that improves the MPG.  

Not to go too far off topic, why does a loaded down engine/truck/boat use more gas to maintain? Is it a function of the computer just dumping more fuel into the cylinders because it knows you're demanding more power than it is providing?

Black_Diamond

The air/fuel mixture for a gas engine does not change from light to heavy loads on normally asperated engines.  Generally 16:1 air to fuel. (Not so for diesels). What does change is the throttle position to maintain the desired power/speed output. 

2.28 mpg would be impressive in a boat!  Most are in the 1.0+/- mpg range. GPH is a better rating though. 

J3ff

Right, so I estimated 17.50 gallons per hour even though I was running at about 4000 Rpm's it my actual numbers were closer to 20. 

Handymans342

J3ff said:

Right, so I estimated 17.50 gallons per hour even though I was running at about 4000 Rpm's it my actual numbers were closer to 20. 

What are you trying to accomplish?

reneechris14

Most based of throttle position and vacuum so computer opens the gate(time injector opens)there for uses more fuel. Its just to bad the boat can't Coast down hill. You can do some drafting like Nascar but that just having some else breaking the waves. You will notice a different position of the throttle to keep the 4k rpm.

jmichels

Wow just jumping back into this now and a bit has transpired since I left!

So yes a computer determines the amount of load on a motor based on throttle position and other variables and then applies certain timing, fueling etc. 

In the computer there are maps of timing, fueling, air/fuel mixture etc , coolant temp versus timing etc etc . Each box on the table correlates to another variable which is what the computer used to determine fueling , timing etc. 

The optimum Stoichiometric Ration for a gasoline engine naturally aspirated is 14.7:1
In the boat word 95% of engines are not monitoring the Air fuel ratio to adjust fueling to those finite amounts. They do not have wide band air fuel monitors to be able to accurately read that field. 

Basically drive it and let the computer do the rest.