what prop for my omc 4.3 cobra

[bigbo27]

just got a 1989 harris float dek with a 4.3 cobra was wandering what would be the best prop for tubing & to get fast plane.I am new to the boating world for the most part could someone plz tellme where to start on this

 

[jestor68]

Re: what prop for my omc 4.3 cobra

Does it have prop on it now?

Need to know what size prop is on it now and what rpm the motor turns running wide open in order to tell if it's the best choice.

You "prop" the boat to run within the motor's WOT rpm range (4400-4800 rpm) at full throttle.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

I not sure what prop is on it now but I'll do some checking.as far as the rpm only had it out twice 7 did'nt pay that much attention I will try & take it out sunday & pay attention.

 

[Scott Danforth]

Re: what prop for my omc 4.3 cobra

right from the sticky at top of the forum titled "Read this first"

ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

Very sorry like i said i am new to the boating world & to this forum .I did although find out what prop i have now it is a 14 1/2 x 19

 

[jestor68]

Re: what prop for my omc 4.3 cobra

Very sorry like i said i am new to the boating world & to this forum .I did although find out what prop i have now it is a 14 1/2 x 19

OK; that's good. Now all you need to do is see if you are turning the proper rpm. Ideally you want to get on the high side of 4400-4800 rpm with a light load in the (pontoon) boat.

Does your pontoon boat have two or three logs(or tubes)?

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

well its more of a tri hull.So ideally 4400-4800 rpm at wot?

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

my wot was 3000-3300 seems a little low but im used to my car which has a 2500 stall. So tell me if im wrong but with these #'s i should beable to go with about a 14 1/2 x 15 correct.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

Do i need more info or will this be enough it was at 36mph plz need your input

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

In need of advice, it was quick to get a response when first posted thread but what happen.

 

[Scott Danforth]

Re: what prop for my omc 4.3 cobra

are you sure your getting WOT? 3300 RPM is really low, I would suspect you have something awry preventing the motor from reaching full RPM.

would you have the drive ratio?

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

As far as i could tell thats was at wot but my prop is a little chipped up lake was really reall y choppy .the engine is running great purrs like a kitten had my son check timing & comprssion he said every thing was fine. It will be aleast a week before i can get back out & recheck the rpm anything else i need to be awarte of. thanks for the quick reply hope this gets figured out like to put a new prop on but not sure if i should change I could possibly get a 15 x 17 but i was'nt for sure if it would work since the one now is a 14.5 sorry but the gear ratio is 1.68

 

[Scott Danforth]

Re: what prop for my omc 4.3 cobra

you will need to put the controls full forward and inspect the carb to see if it truly is open full

how chipped is your current prop?

 

[john cole]

Re: what prop for my omc 4.3 cobra

i would check with a couple of you local marina's and see if they have one you can "borrow" to see how it works before dumping a ton of money on something your not sure if is right for you application. you will be suprised at what you find. I had to prop my down a pitch and it made a ton of difference in my engine performance. last thing you want to do is lug you engine.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

ITS PRETTY BAD figured that would have something to do with it. like i stated before this is the start of my boating since i was a kid i'll check the carb to see when i get off work or first thing in morn. these thing always take some figureing out when you start a new hobby im use to gassers with 4 wheels and alot more rpms

 

[Scott Danforth]

Re: what prop for my omc 4.3 cobra

if your prop is "PRETTY BAD" where its beating the water vs cutting thru it, its like driving your "gassers with 4 wheels" where the wheels have 10' 2x4's bolted to them. I would recommend taking the existing prop and having it repaired as a starting point.

I also recommend borrowing a prop from your local marina to see if you need to change it.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

I will check the carb and hook up my own tach some people have talked about an app on there phone to get the mph do u happen to know that app. I can get the prop I was asking about dirt cheap just wandering if i should put it on to see what kind of differnce it makes up for all kinds of suggestions. iw ill talk to my marina to see about repairing my prop

 

[john cole]

Re: what prop for my omc 4.3 cobra

most any of the gps apps will have a speed indicator on it. just have to look thru them

 

[Scott Danforth]

Re: what prop for my omc 4.3 cobra

if you can get the prop dirt cheap, then get it. worse case you hit max RPM way too early and you sell it. however I think your best prop will be a 17p or 19p (with straight teeth)

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

chaecked the carb this morning & yes with the controler in full throttle the carb is at full throttle so every thing is good there. So you are saying it won't hurt to go with the bigger diameter 14.5 to 15