488 powered boat question

I have a 1983 boat with a 488 engine. I recently talked to someone with the same boat and motor (century 5 meter) they said their boat did 53 and had a ticket to prove it. My boat will only do 47. I have changed plugs, done a compression test everythings fine. My boat runs good and hits the top of the rpm range even full of people. It runs really good no antifreeze cam seal leaks all plugs come out the same greyish light brown. I dont think the temp has ever even hit 160 f. Just can't think of anything else that would cause my boat to be that much slower than the same model. Would a stainless prop or ingitor halls effect ignition make that much of a difference? I have even weighed my boat to see if it was heavier than advertised weight which it is not. It seems like something stupid to worry about but makes me think there is something wrong. I don't know the prop setup used to hit 53

Re: 488 powered boat question

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Re: 488 powered boat question

You'll have to help me with the specs of your 488. Would be nice to have the gear ratio,may be on the outdrive.
Need your wot rpm and speed.
also need prop size, brand/model,condition? Other boats prop size,make and model.
Things to check: Timing ; if it is set right and advances as it should?Does the throttle open all the way.
Is the bottom clean and smooth. Is your bottom painted,antifouling?paint smooth? not peeling?Other boats bottom?
Were the boats exact same year and model,weight? Same bottom configuration?

Re: 488 powered boat question

I have a 21 pitch turning point aluminum 3 blade. With that prop I get 47 mph at 4800 rpms. 4800 is the top of the rpm range. The outdrive is a 1.84. The 488 is a 4 barreled carb 470 motor and the data plate says 188hp. I don't know the setup of the other boats prop just that its the same year and motor. Both boats weigh about 1650 lbs dry. I have a mercury aluminum 21 pitch with a smaller diameter and less cup than the turning point that over revs to 5100 and 44 45 mph so its not used. I will be checking timing today and the advance today. The boat runs great and has good acceleration. I had a whale tail hydrofoil but took it off and didnt really notice any changes.

Re: 488 powered boat question

My boats hull is clean and smooth not painted. The props paint is missing from sand but it is smooth without dents or deformation. Will double check the throtle rigging.

Re: 488 powered boat question

Your setup is working pretty well. 47 at 4800 indicates about 9% slip to me this is very good for an aluminum prop.
For his boat to make 53 at 4800 he would have to run a 23 -24" prop.I don't think the 488 could twist a 24 to that rpm.
Some history of the motor; the block is a Mercury design aluminum block with a cast iron head and used a ford 460 head.
I do believe the motor can be hot rodded with a special intake and probably other goodies.I wouldn't be surprised if he was running more than 4800. The guys were talking about land use for the motor.Something like adapting easily to Chevy components.
In researching the 488 I think there was some discussion about the 4 barrel carb needing to be setup right.
They also mentioned that that the speed of the 190hp was only about 1 mph faster than the 170.You would need about
a 45 hp difference to really notice anything.
2 weaknesses water pump seals letting coolant into the oil and the alternator over heating and needing to be upgraded with a heavier one. Pump seals need replacing before they fail.
Unless you find something wrong with your setup/motor I don't think your going to make up 6 mph.
If you do a little research you may find what the typical speed of the 488 is on a little boat like yours.
It's possible a 21" ss prop could get you a little more speed. I think you would be lucky to see a couple of mph.