Z7 Prop

[Mike Wagner]

To those of you running a Z7 with a 150 Pro XS, what prop do you have? I would be interested in hearing what your WOT RPM's and GPS speed are.



Also, if any of you made the switch from a Tempest 24 to 23, what was the increase in RPM's, and what effect did it have on top speed?



I still have the factory installed Tempest 24, and my max RPM's vary from 5200-5300 depending on load and conditions. I am happy with both the hole shot and top speed (58-61 depending on conditions), but think it might be better for the long term life of the motor to be turning more RPM's.



Thanks.



Mike

 

[Mike Fischer]

I'm in about the same range. Can hit 62/63 with nothing on board except basic gear and myself, 5250/5300 RPM. Factory 24p prop. I have no problem with holeshot even with three big passengers and a full livewell so the only reason I'd switch is the reason you say, longevity of the motor, but I don't run mine a ton so I'm not that concerned, yet.

 

[Kevin Dumser]

I've got the same factory prop as you. Right now, running 5200 RPM and 57 is top speed I'm hitting going down current on the river. I hit 53 - 55 running up current, but the water is still high.



That's with 2 people 3/4 tank and full gear. I am either going to get a different prop or alter this one to up the RPM to 5400 - 5500.



I'll be curious as to what others say.

 

[Mike Orth]

Curious to know what the suggested WOT RPM limit is for that motor? It should say on the SN# tag or in the manual.



Prop the boat to hit that number and not go over. If you are short of it the engine is not fully unloading. If you are right on it already then I would not mess around with it.



Mike

 

[Mike Wagner]

Thanks to everyone that replied. It seems that I am not the only one right at the bottom of the recommended RPM range. It does make me wonder why they are putting 24p's on at the factory.



The WOT RPM range for the motor is 5250-5750 according to the manual. I am not even close to the limit. To get 500 more RPM's than I have now, I would probably need to drop to a 22p or maybe even a 21p, and I would be afraid of losing a lot of speed by doing so. I have never heard of anyone running a 21p or 22p on a Z7. I'm thinking that a 23p would at least put me in the middle of the range.



Mike

 

[Mike Orth]

Here is a link to a prop 101 from a prop shop near me. It has some great insight.



I agree with you concern over a loss of top end by going to a 22p, but perhaps the increase in RPM will actually cause it to increase. The 22p will travel through the water at 22 inches per revolution and will be turning at a higher rate due to the increased RPM... perhaps increasing your speed...



I am not sure how to calculate engine RPM into Prop RPM. If you can determine that you can calculate the amount of distance the prop travels at various engine rpm. This will tell you if the 22p at 5700 will be faster or slower than the 24p at 5300.



If top end is about the same... the 22p will increase your hole shot.



A quality prop shop will allow you to demo a prop so your can see how it performs prior to dropping $$$'s.



http://www.formulapropeller.com/propellers.html

 

[Mike Orth]

I found the gear ratio for your lower unit. I found 1.87:1. That means the engine needs to turn 1.87 times to equal one revolution of prop shaft.



Based on that ratio your 24p turning at 5300 engine RPM should have a top speed of 64.4 mph (this does not take into effect prop slip, cavitation loss, etc.)



The 22p turning at 5700 engine RPM should have a top speed of 63.5 mph (again assuming no loss due to cavitation etc)



Again I would talk to a prop shop, but this math would indicate a minimal top end loss but gain you hole shot...

 

[Mike Wagner]

Mike, thanks for the advice and the link. I will check it out.



Mike