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steve hale

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"On my 29 phoenix, straight sh

"On my 29 phoenix, straight shaft inboards, crusader 5.7's, one engineruns WOT at 4600 and one at 5000. Does this mean that I am underpropped? Can I have a different pitch on one motor than the other to even out the RPM's. I am still struggling to get 1 mpg at any speed. I've got plenty of power."
 
"..."I am still struggling

"..."I am still struggling to get 1 mpg at any speed. I've got plenty of power."

Then do what I did: deliberately over prop. My 32 footer gets 1.2 to 1.3 mpg and, if you're not holding on, will toss you on your stern at half throttle while planing off. RPM at WOT is less than 3,900--perfect!

The rpm difference is probably a better tune/ more compression/ etc. Both are running way too high for proper gas mileage, as you've seen.

Jeff

PS: The "experts" will insist that your motor "must" top out at such ridiculous rpms or the motors will be damaged. BS! At 2,500 rpms cruise speed on mine, you couldn't slip a pencil between the butterflies and the carb throat, so little is the throttle open. Kinda like yours, I'll bet."
 
"jeff,
Can i just increase th

"jeff,
Can i just increase the pitch considerably on my 18's or do I need bigger diameter props. Will prop shops give you loaners to try until you get it right?"
 
"That's the cheapest way,

"That's the cheapest way, unless you can find some used replacements on eBay cheap. A good prop shop can bang another 2 inches of pitch on yours easily.

Jeff"
 
"I have a Carver Santego 380 @

"I have a Carver Santego 380 @19.000lbs give or take. Crusader 454xl's recently rebuilt from 320 hp to 385 apiece as per dyno test w/new intake manifolds, cam, one over, forged pistons and multi angle grind on the valve seats (reduced carb jets two sizes) Is the max rpm allowed of 4400 changed as a result of this? Turning bronze,Mich 20X20 props. WOT gives me about 3800 rpm. The engine rebuilder sez I'm not overstressing and doing no harm. Lots of info out there to the contrary. I run about 3200 at 20mph when cruising which is not often (usually around 1200 - 1400 ) Looking for best possible fuel burn economy with no damage. I'm not a mechanic and know only enough to be potentially very dangerous changing things around without good counsel."
 
"Jay:

Your setup mirrors mi

"Jay:

Your setup mirrors mine, and it works fine. Ignore those who insist a marine engine must ALWAYS turn max rpms at wot, for they don't know what they're talking about. Lightly loaded boats can safely be way "over-propped" without damge (and get better gas mileage).

Jeff"
 
"Jeff,

Does the engine

"Jeff,

Does the engine "beef-up" change any of the RPM limits or is that a design feature from initial engine build-up. My re-builder does race car engines and is quick to say "you can't hurt it" (within' reason) All this wot stuff is a moot point 'cause the only time I ever do that is a quick "blow-out" which has been recommended in the past. I'm looking for best fuel consumption at "cruise" where ever that turns out to be. and considering the "FastRail" lifting strakes system for that as well. It may be that FloScan is in my future also. Thanks for your input Jeff.

Jay"
 
"Jay:

My old Bayliner had t

"Jay:

My old Bayliner had the usual 260 hp engine. Replaced it with a 315 high performance, but it liked the same old prop!

Jeff"
 
"Not to hi-jack anything here

"Not to hi-jack anything here Jay BUT..This season I have fuel flow meters on our boat. Been out many times last year where we just pushed the throttles up and ran out to places without even thinking.

THIS YEAR, every creak of the throttle sends that 30 to 40 gal / hr visual up on the screen and we just ease it all back to 7-8 knots, not even up on plane. Nice to know fuel flow but a pain to live with.... I feal like a sissy"
 
"Fuel flow meters are a great

"Fuel flow meters are a great reality check!

If you want to see something really interesting, do an RPM vs. fuel flow study in neutral. Note how much gas it takes to merely rev the motor and trans to higher rpms! That's why deliberate overpropping--assuming the boat is NOT underpowered--pays off in better fuel mileage.

Jeff

PS: That's why modern cars and trucks use overdrive trannies."
 
"I'm feeling better about

"I'm feeling better about my somewhat overpropped set-up. At the end of the day as long as I'm not doing damage to the engines, I'm happy with some liveable fuel flow at a comfortable planing speed. I do a Ton of 1200 rpm, relaxing, no stress "rides". Those of us in the non "highroller" status will just have to be happy with that for the duration, I 'spose. I do hate it when the gas truck comes!"
 
"You'll feel even better w

"You'll feel even better with your set up if you do this little experiment:

While at cruising speed, on plane, carefully mark the position of your throttles. Later, engines off, pull the flame arrestors. Place the throttles where you marked them and note how little the butterflies are open!

Jeff"
 
"Thanks Jeff,
I noted that

"Thanks Jeff,
I noted that tip on an earlier post of yours and am going to do just that. Now the question is "how much better does it make you feel?" HA

Jay"
 
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