308 conversion to 253 in Jet boat

[conrad f]

hi there Motoman,that sounds fairly minimal wear which would trans late to less than 10 thou side play on the impellor.The berno marine jet impellor you have fitted are excellent and will give a 5 to 10 mph increase over the original impellor .Ih ave fitted about 4 of these impellors and the performance gain was impressive.Another area to pay attension to is the intake entry under the hull. Sometimes the aluminium casting hangs down past the hull surface creating drag and disturbing the flow of water up the intake.If you have any sharp angles or edges grind and fill them so you have a smooth radiused entry into your intake.Also when reversing your boat never do it off the bank .With the reverse bucket pointing down you will blast sand ,rocks ,mud, through your jet and quickly wearing out your impellor clearence resulting in loss of performance and the boat struggling to get on the plane which I think you have experienced.Alway push your boat away well clear of the bank before reverseing.How did you go with your motor options.Regards Conrad.

[Motoman76]

hi there Motoman,that sounds fairly minimal wear which would trans late to less than 10 thou side play on the impellor.The berno marine jet impellor you have fitted are excellent and will give a 5 to 10 mph increase over the original impellor .Ih ave fitted about 4 of these impellors and the performance gain was impressive.Another area to pay attension to is the intake entry under the hull. Sometimes the aluminium casting hangs down past the hull surface creating drag and disturbing the flow of water up the intake.If you have any sharp angles or edges grind and fill them so you have a smooth radiused entry into your intake.Also when reversing your boat never do it off the bank .With the reverse bucket pointing down you will blast sand ,rocks ,mud, through your jet and quickly wearing out your impellor clearence resulting in loss of performance and the boat struggling to get on the plane which I think you have experienced.Alway push your boat away well clear of the bank before reverseing.How did you go with your motor options.Regards Conrad.

I put a stock 308 in, she's pretty good but I am in the process of rebuilding the 355 stroker . Will certainly have a look at the grate bit though because I had to make one to replace the original because it was broken and I know the fins are sticking below the level of the hull aprox 3mm. Thanks heaps for advice though. Its hard to get here in Canberra.

[conrad f]

Hi there Motoman,I have some worn out jaccuzzis under the house so i have some spares, shafts, grates etc.The 355 sounds good.What type of hull do you have, do you know the manufacturer,may be put up a pic or two.Regards Conrad.

[Motoman76]

Hi there Motoman,I have some worn out jaccuzzis under the house so i have some spares, shafts, grates etc.The 355 sounds good.What type of hull do you have, do you know the manufacturer,may be put up a pic or two.Regards Conrad.

Are you in Australia? The hull is called a shadow 1 . dont think its a mass producted boat. Ill get some photos of it and email them to you if you like.

[conrad f]

Hi there motoman , Im in Melbourne ,my email address is jfi19826@bigpond.net.au ,the name of your hull doesnt ring a bell so I will wait for the pics.Regards Conrad