Porting a prop on smaller fourstrokes

[jrdonicht]

Is there any advantage to porting a prop on the fourstrokes 115 and under to achieve a better hole shot? Has anybody experimented with it just on the fourstrokes? Pros cons? I heard with the exhaust gasses of a fourstroke it is not all that beneficial to hole shot like a two stroke?

[REW]

JR,
Porting a prop for hole shot works for all motors.

But, generally speaking, I think you are just better off in running a prop with a lower pitch and forget about the porting.

Porting works as long as you run two speeds. Idle and wide open.

The issue with porting is that whenever you are in the 3000 rpm range, you are at the rpm range of porting, not porting, porting, not porting.

So, any time that you have your engine running at this critical range, you will find that you get both uneven boat speed, as well as uneven engine speed. With a constant throttle setting, the engine will port and speed up, then the boat will speed up, and the engine will not port Then the engine will slow down and the engine will port etc. etc. etc.

This is particularly troubling if you are trying to just stay on plane when working big waves. It is also a problem when you are working the throttle when working big waves. It is also a problem when you are trying to run at speeds at about planing speed for long distance cruising.

In past years, I had several props that I used, particularly when doing water sports. But always a problem for fishing and big wave work.

So, eventually all of the props had plugs placed in them and I now no longer use any ported props. Now, the engine is always running nice and smooth, and the boat is always running at a constant rpm and the engine and boat work well together working at both just planing speed, as well as working big waves.

Your choice. But just be aware that if you port a prop, you will have engine and hull issues when the engine is trying to run long term at the critical port - no port rpm of somewhere around 3000 rpm depending on hull and engine.

Good luck
REW

[propmann]

We typically port them 1/4" or 5/16" for the smaller motors and it does work well start out small you can always drill bigger, alot more work to weld up holes if you get to big.

[jrdonicht]

Thanks guys. I know years ago I had a 150hp 2 stroke out board with a ported prop. I did not have the issues that you have had REW. It may have been the perfect size holes I do not know. I had great hole shot also[but alot more hp]. Now I am running a F90 on different boat and never tried a ported prop. I am always looking for a better hole shot but do not want to have to much slippage as you can have with too big of holes. I know I can achieve a better hole shot with a smaller pitch prop but right now I am at perfect max rpms. Thanks propman -I know also you probably have done allot of experimenting with hole sizes. Yes definitely do not want to go to big. Thanks for the hole sizes!!

[sjfishon]

i have a 9.9 4 stroke, i do need to go down a pitch, it is now 8.5 will go to a 7, i have never heard of porting, it makes sense, how do you do it and where do you put the holes, how big? thanks

[MarkG]

In regards to the first question...as REW said,it should not make any difference whether 2 or 4 stroke.

In regards to engine rpm and speed, years ago I did it to one of my props ( a prop shop did it for me) for my 40hp Evinrude with great results and no issues of trying to stay on plane or rpm surging at the lower speeds. However the vent holes were not very large,probably in the range of where propmann suggested. Improved my holeshot as expected,with no ill effects at any other rpm range.

I also had a Quicksilver Lazer on a 90HP Merc and always had the ports open, and that also had no ill effects from them being open.

It always seemed to me that if the boat was moving forward at all, the ports would seal. These days I just used a lower pitch to improve my holeshot,because it gave overall better performance especially over differences of how heavily the boat is loaded, (fishing by myself, compared to with several people in the boat)