Am I over pitched?

[Hitchcrack]

All right I have been reading messages on this board for about a week trying to figure out the prop stuff. I have a 1978 Galaxie tri-hull with a 1982 Evinrude 150. When I bought the boat about 2 months ago it came with a precision SS turbo 3blade prop. The prop is a 14 1/4" X 24. At Wot I am turning 4k rpm. From what I have been reading I am way over pitched. I need to go down to like a 20 or a 19. I do plan on sking behind this boat so I would like some power to pull people out of the water but still have some top end to get me where I want to go when I am fishing. I am also consuming lots of fuel and I am wondering if this is due to the pitch of the prop. I am just looking for an idea of where to start with my prop I am going to start looking for a prop shop that will let me try before I buy. I am asking you guys because you seem to know your props and I am afaid the guys at the prop shop might try and sell me something I don't need. I appreciate any help you guys provide.<br /><br />Thanks,<br /><br />Ryan

 

[Silvertip]

Re: Am I over pitched?

The best prop is one that allows the engine to run at the manufacturers maximum recommended wide open throttle RPM. For your engine thats probably 5500. Assuming your test was with normal load and the engine trimmed properly, you need to pick up 1500 RPM. Since one-inch of pitch change changes rpm by 150 - 200 rpm, you would need roughly 7 inches less pitch. That puts you with a 17. Maybe a 19. That said, make sure you are trimming properly, the engine height (X-dimention) is correct, the tach is accurate and the engine is properly tuned before spending money on props. Check with a local dealer -- they may let you test a few props (new or used) with a small down payment.

 

[walleyehed]

Re: Am I over pitched?

The HP on that engine was taken at 5000RPM, so in this case, we will need to throw the 200 per inch out the window. It may gain 700-800RPM with 2" decrease in pitch when near 5000RPM.<br />I feel a 21 would be a good place to start.<br />That engine likes to run at around 5700RPM for a WOT.

 

[Hitchcrack]

Re: Am I over pitched?

Well see the wierd thing is that when I purchased the boat I replaced the guages and the tach that was in the boat was set for a 8 pole stator. Everything that I have read says that that motor has a 12 pole. with the original tach hooked up it says that I am 6K a wot but it also says I am idling at around 1100 rpm. When I adjusted the new tach for a 12 pole it now says i am idling around 700 rpm and 4k at wot. From the sound of the motor I believe the 12 pole to be correct. Would the pitch have an effect on fuel consumtion.

 

[walleyehed]

Re: Am I over pitched?

Heck yea pitch has an effect on fuel consumption...especially if you are at a true 4000RPM WOT...loads of fuel and extremely high combustion temps are present at that RPM when that's all it will turn, in fact, 4000RPM WOT will destroy that engine.<br />Need to get your hands on a 21 or a 19 pitch and test-run to get a base-line with a ballpark prop, and we can go from there.<br />That engine might turn 6000RPM with a 24 Turbo if it was mounted on a 14ft aluminum boat, but not on that Galaxie.<br />700 Idle sounds close, 600 would be better but we can figure that out later.<br />If we know the tach is set correct...it's not a XP150 is it?????? We need to get that 19 or something close and go get some numbers.

 

[Hitchcrack]

Re: Am I over pitched?

Well I got a 14 1/2" X 19 and HOLLY COW is there a big difference. I come out of the hole shot so much faster and plane up instanly when trimed down. I am now at Wot 5400 rpm trimed up about as far as i feel comfortable. I think I will stay with the 19 for now and maybe look for a 17 next summer when I start kneeboarding again. Thanks guys for all of your help now hopefully I will save some gas and some money at 2.80 gallon.<br /><br /><br />Sincerley, Ryan Hitchcock

 

[walleyehed]

Re: Am I over pitched?

Might want to consider lifting the engine a hole and testing...you'll gain 75-100RPM per hole up.<br />It usually ends up running best in the 3rd hole from the top with no set-back.