SBC rpms and impeller

[banson1]

I just installed a 355 425 hp sbc in my 1972 searay pachanga.I am turning 4800 rpms.I have a berceley 12jg pump I think the boat came with a 455 olds at one time.Could any body tell me what the rpms should be and what impeller should i have.

[Jetmugg]

You need to know the torque vs rpm curve for your engine. Using this curve, you can match it to the curve of various impeller cuts. A handy tip is to plot all the curves on the same graph. Then you can see where your engine power intersects the impeller curves. This will lead to a real understanding of how the jet pump power requirements match up with your engine's power output. A good way to achieve maximum speed for your application is to find the engine's HP peak, and then size your impeller to allow the engine to hit that rpm level.
SteveM.

[banson1]

Thanks for the info jetmugg. Is there a way to determin the correct impeller without a dyno?

[77charger]

What impeller is in there now? if it is an a cut a b will be better siuted this should raise your rpm by around 250-300 i believe.I f you are turning an a at 4800 and the pump is in good shape that is not bad for a small block.

[banson1]

77charger Im not sure I am pulling the pump apart next weekent Putt I think because the boat had a BBO 455 from the factory im might have an a impeller and I picked up an ab impeller to put in if I do have an A. do you think the 4800 rps aree good for a mouse or the 5100 range?

[77charger]

Likei said those rpms are verygood for a smallblock in my opinion.But your not even in your max hp range and have more to gain.