Prop Sizing

[welshman]

hi all im new here and need your help i have a 1994 maxum 27 it has a 5,8 v8 alpha one can anyone till me the size prop i need for it it has a 17 inch on it but i cant get up on the plane very good and its using a lot of fuel also got over heating problem i have changed the impeller and that was ok the risers seem ok but i don't no what im looking for and don't no if the manifolds are ok one side of the risers gets very hot and the other side not so hot can anyone hep meeeeeeeeeeeeeeeeeeeeeeeeeee

[mmwjr]

Welshman welcome aboard

First this is a 3 year old thread you should have started a new one.

Before doing anything with the prop lets get the engine running properly.

I recommend you get a handheld IR thermal sensor and take temp readings of the exhaust elbows, manifolds, and a few spots on the engine including the t-stat housing.

I think it may be time to replace the exhaust if it is as hot as you say.

The engine is a 5.7 not 5.8, GM small block. How many hours are on it?

A compression test will give you an idea on its health.

What is the WOT rpm?

[shrew]

Welcome aboard Welshman!!!

hijacking a 4 year old thread is somewhat frowned upon. I've moved this to a new thread of your very own.

Prop Size has nothing to do with heat. If it's hot on one side, it is constricted and the entire system is going to be impacted. As MMWJR stated, it's time to replace the manifolds and risers.

As for the prop, it is a combination of size and pitch.

1) Get the boat up to Wide Open Throttle (WOT). Make sure its properly trimmed and tabbed, and relatively smooth water.

2) Verify whether the rpm's are within the max range for the engine. (typically around 4400-04800). If your rpms are over, then you are under propped. If the are under, then you are over propped. This is usually dictated by Pitch.

Use the Mercury Prop Selector on their website.

Finally, use the SEARCH feature on this site. You will find hundreds of threads on the re-propping topic. Read through them and you'll find links, good advice and a common thread in all of them.

Best of luck.