Yet another prop question, scarab sprint 3.0

[chevyracer5613]

Hey there, I am sure yall get these kind of question alot but that just means yall are good at what you do

Anyhow, I am trying to help my buddy out on his boat, it is a early 90's scarab sprint with the 3.0 4 cylinder. Assuming the gages are accurate the boat is allegedly running about 50 at around 5000 rpms with one person in the boat (the speed/rpms seem to be almost 1:1). The "problem" is he is wanting more top end speed and more bottom end power......however as I have learned from one of my other topics this is not a easy or cheap thing to accomplish haha. So ideally i'd like to perhaps find a prop/other items that will help his bottom end power without hurting the top speed much/at all.

The boat right now has a 3 blade SS rapture prop stamped 9513 and 1425r23. I think if I read correctly on a few different forums these boats weigh around 1800 lbs and have about 140 hp? This boat will be used to occasionally pull a tuber/skier but mostly for fun filled lake runs.

Suggestions I have had:
1. SS 4 blade prop
2. Variable pitch prop (however that might be a touch out of budget)

Thanks ahead of time for your time/help!
David

 

[steelespike]

Re: Yet another prop question, scarab sprint 3.0

I can't be too specific I'll leave that to those more experienced.
If the Scarab speedo is right it must be a pretty speedy hull.You seldom see a 3.0 approaching 50.especially if its 18 ft.Your not likely to see much more speed and getting close to 50 and strong hole shot are nearly impossible.
I'm pretty sure the 3.0 is rated at about 4,800 you need to confirm that.
You also may want to varify the tach is accurate.
A 4 blade will help the hole shot but will almost surely cost a couple of mph.
If the rapture is tuned for bow lift that will slow hole shot but without bow lift the boat will likely slow a bit.
Being at 5,000rpm(probably allready too high)you can't really drop down in pitch unless specifically when towing and then you would have to watch the rpm.

 

[chevyracer5613]

Re: Yet another prop question, scarab sprint 3.0

Steelspike- Aside from swapping tachs (which is planned in the future anyhow) I am not sure of how else to easily test the current tach.....however it seems like it might be accurate as it shows a idle of a little under 1000 rpms which seems reasonable. I should be getting the manuals for that boat shortly, I am sure it will mention max recommended RPM in there? I had planned on adding the smart tabs to the boat as they allegedly help acceleration a little bit but from what it sounds like the only other way to get better acceleration would be to take a small hit up top and put a 4 blade prop.

 

[steelespike]

Re: Yet another prop question, scarab sprint 3.0

I like the smart tabs but with any tabs you need to try not to be too agressive with them or they will steal speed as well.
Trim tabs are more expensive and difficult to imstall but if your in a hurry you can lift them and be sure your getting top speed.
I wonder what the actual gps speed is?What size is the boat?

 

[chevyracer5613]

Re: Yet another prop question, scarab sprint 3.0

steelespike- I plan to put a gps on it next time I go out on that boat to find out its true speed as i'd be surprised if its actually running that fast. I think it is 18 or 19'

 

[steelespike]

Re: Yet another prop question, scarab sprint 3.0

steelespike- I plan to put a gps on it next time I go out on that boat to find out its true speed as i'd be surprised if its actually running that fast. I think it is 18 or 19'

That will be interesting.As far as varifying the tach you might be able to borrow shop tach,dwell meters have a tach,as I understand it some timing lights have a tach setup.
I'm curious because you allready appear to be near or over max rpm.Doesn,t leave much room for prop diddling for hole shot.

 

[45Auto]

Re: Yet another prop question, scarab sprint 3.0

No big deal to prop it for more of a holeshot (if that's what he wants). Just be aware that it will over-rev if you go for a WOT top end run.

Just hold it at whatever RPM you choose as max with the throttle and accept whatever the top speed is at that point.