Freestyle Cutback - what difference does it make to engine load?

[Superjetjim]

I've got a 155 Mag pump and I needed a 10/16 thin blade 3mm cutback prop, but ended up with a 10/18 5mm cutback on because it was the closest they had in stock (and I was foolish/impatient), figured I'd try it and repitch if it's to steep... Guess what - it feels to tall.. My question is, does the 5mm cutback load the engine more than the 3mm cutback, if it does I might try a 2mm washer behind the pump first before repitching?

Is the repitching fairly easy if you have the pitch chart?

Thanks

Jim

 

[Matt_E]

Yes, it loads it more. The distance between blades and stator acts as sort of a clutch. The smaller that gap is, the sooner the engine is loaded. You want the engine to have a chance to spool up a bit before the impeller 'bites'.
You should be able to use spacer washers.

 

[Superjetjim]

Yes, it loads it more. The distance between blades and stator acts as sort of a clutch. The smaller that gap is, the sooner the engine is loaded. You want the engine to have a chance to spool up a bit before the impeller 'bites'.
You should be able to use spacer washers.

Nice one Matt, will give it a try..

Jim

 

[orangefinger]

what do the spacer washer exactly do..??

 

[Superjetjim]

what do the spacer washer exactly do..??

In my instance 5mm has been removed from the inside rear hub of the prop where it meets the shaft bearing so it sits 5mm closer to the pump viens that stock - I need 3mm in reality so adding a 2mm spacer moves it back forward towards the stock location and gets me to where I need to be.

Jim

 

[orangefinger]

but moving it forward has which effect ??

 

[Scraggly]

but moving it forward has which effect ??

loose

 

[masterblaster]

Ive talked to the Tech guy at Scat about using certain cutback props in mag pumps,He reinforced my findings,IF you get to tight within certain tolerance with the prop to the stator,performance suffers with low end response and even mid and top end hookup in chop when the pump is unloading out of the water a bit. I have it written down somewhere on the measurement they tested it within.
Ive found that hooker props with the big cutbacks on them suck in mag pumps compared to skat mag swirls.The diff you have to use in pitch to get a hooker to work in a mag is crazy. They are made to make stock pumps hook being cut back 7mm or more