1994 scarab sprint rpms and prop

[kenny_1234]

i have a 1994 scarab sprint i was woundring what rps i should be geting out of it with a 3.0lx alpha 1 drive iam only about 3800 rpms full throttle. but it bogs down when I hit the throttle and iam not sure if I have the right prop on it I can still get it around 40mph but iam not at the rpms I think I should be able to get if anyone could please help????? thanks

 

[junior1113]

Re: 1994 scarab sprint rpms and prop

recommended wot rpms for that motor is 4200-4600.

what size prop is on it? hole shot must suck huh?

if it were mine id run it at 4400-4600 to maximize engine life.

right now you are lugging your motor and not getting all the horseys.

bogging down when throttling explain this more.

what is your current max speed?

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

i think its a 21 pitch but ya the hole shot sucks

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

3800 rpms at full throttle

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

40 to 45 mph max right now

 

[junior1113]

Re: 1994 scarab sprint rpms and prop

i'd look for an 18 pitch if a 21 is indeed what you have. that will get you in the 4400 ball park. first explain this bogging? what is top speed mph?

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

well when i put the throttle all the way down rpms drop for a sec and the slowly go u till a tirm it out and them iam only hittin 3800 rpms full throttle and about 40 to 45 mph

 

[hwsiii]

Re: 1994 scarab sprint rpms and prop

Kenny, I have not run any numbers on your boat yet, but I believe you need to be looking for a tach problem before you buy anything. If you will give me all the information on the boat I will run some numbers and see what they show.
We will try to help you as much as we can, but there is certain information that is needed in order to help you. The following form has all of the information that is needed to help you with your problems in finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planing hull boat that needs this information, and most other people who are trying to help you will need the same information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the exact prop you need for your particular uses, and this information is required to do that.
It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed and RPM.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
8. Manufacturer?s recommended WOT range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from prop, how much gas and how many people in boat for test data

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

1994 wellcaraft scarab sprint , 18foot , 1800 lbs , 2 to 4 people 16 gallons of fuel, deep v sits 3 foot in water, 1994 3.0 mercruiser lx alpha 1 2 Barrel mercarb , 135 hp, not quit sure on the gear ratio , hydrafoil,i know it is a ss prop i think a 15inch 21 pitch prop , i dont know the Manufacturer?s recommended WOT i have hade it at full throttle and its at 3800 and doing 40 to 45 mph but slow to get there

 

[junior1113]

Re: 1994 scarab sprint rpms and prop

recomended wot rpm for that motor is 4200-4600 i would shoot for 4400-4600ss 18 will put you close to 4500 if that is a 21". i agree with hwsii though i would check tack for accuracy and do comp test. confirm motor didnt lose power some how to make this prop too big. has this prop always been on there? has rpm always been 3800?

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

i just bought the boat 2 weeks ago and i rebuilt the carb got it idling good..the guy befor me had a 17 pitch prop but he said it to small and wouldnt do anything with it and put the one thats on it now i still have the 17 pitch prop as well

 

[hwsiii]

Re: 1994 scarab sprint rpms and prop

Kenny, there is a problem I don't know what it is but I am showing your motor to have a gear ratio of 1.94:1, and if that is correct and your tach is showing 3,800 RPM and you said your speed was between 40 and 45( I used 40) and the prop is a 21" pitch I am showing a negative prop slip of -3%, and that is impossible. Do me a favor and take the boat this weekend and run it with the 17" pitch, but don't run it over 4,600 RPM and if the engine sounds like it is overrevving before it gets to 4,600 don't run it over 4000. But I need to know how fast your going at 3,500 RPM, 3,800 RPM and 4,600 RPM (GPS speed). I think the 1.94:1 gear ratio is right but I am not positive. Also find out what pitch prop that is you are running now, look on the sides, in the back and also under where the prop nut goes on and check the one that is supposedly a 17" pitch as well.
If I am right about the gear ratio then I would bet your tach is wrong, I just dont know that is why I need those RPM and speeds, so I can see if I can figure it out.

Real Prop Slip

H

 

[junior1113]

Re: 1994 scarab sprint rpms and prop

how are we achieving mph? speedo? has to be off. gps should be used to obtain true speed. nedd model # off of out drive ratio should be 1:1.94.

 

[kenny_1234]

Re: 1994 scarab sprint rpms and prop

ill take it out this weekend get my buddys gps and try that 17 pitch and let u know what its running at and also get the gear ratio on that for and let u know. now what would happen if the gear ratio is not the 1:1.94 would that do0 any damage to the eng or anything?

 

[hwsiii]

Re: 1994 scarab sprint rpms and prop

Just don't run it over 4,600 RPM.

H