regal prop question

maineslr

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Aug 24, 2015
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I have just purchased a 98 regal slr 21 with the 4.3 motor and merc alpha1 outdrive. I was wondering what prop ot wld take. I believe it has the original on there now which works very well...quick to plane and decent speed. Any prop suggestions? is the size stamped on the current one?
 

steelespike

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Apr 26, 2002
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Your prop number may be near the base of the blades or under the prop nut.
The size would depend on the typical activities and load. 17,19 and 21 are common pitch sizes
though many other sizes are available depending on the setup and activities.
If you do a lightly loaded test run and get us your prop size,wot rpm and gps speed we can tell you about your setup.
 
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maineslr

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Aug 24, 2015
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I will check for ptop numbers, the 8nterior of my new boat is mint, it has a brand new 4.3 motor I'm breaking in, unfortunately the tach and depth finder don't work. It planes in u.der 4 sec and will hit 48 mph with 3 ppl and full tank of gas
 

steelespike

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Apr 26, 2002
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What hp is the 4.3? Do you know the gear ratio?Is the speed by gps?
You can't properly setup your boat without a working tach. Tachs are always suspect when numbers don't make sense.
A gps is the only for sure accurate speed.Your 48 is a reasonable number.The prop calculator is only as accurate as the numbers we put in.
Numbers we can usually be sure of are the gear ratio, prop size ,assuming we find yours,speed by gps rpm by an accurate tach.these can usually help us solve
for slip which will help us evaluate your numbers.
 

maineslr

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Aug 24, 2015
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190 hp, the speed was with odometer but can verify this weekend when I get back out. I knew the tach woukd make it hard to get correct info but was hoping someone with a similar set up wld know what worked for there's , but all boats are different. Like I said I really like the way the stock prop planes and takes off maybe I'll just get another but was considering going SS. Thanks for your reply wish I knew what my tach wasn't working. The just rebuilt the motor and the guy said it's connected on that end fine. Hard to tell with a 16 yo boat lol
 

steelespike

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Some tachs have a selector switch on the back. Sometimes if you note the position and operate the switch a few times it may help.
It is very critical for the health of your motor that we have a working tach.Hopefully you can find the prop numbers.
Your hole shot indicates you may have too light a prop.
If the old motor was tired they may have had a prop that masked the problem something like as 17".This would no doubt deliver a strong hole shot but over rev with the new motor.
 
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maineslr

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Aug 24, 2015
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A8 78 20 A4 19P is the current prop number on there now. Only measures 13"in diameter and that seams small. I looked online and can't match that number
 

steelespike

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Apr 26, 2002
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Typically the smalllest diameter is 14 for a Mercruioser. The 13 may be intended for an outboard.
As you may have figured your pitch is 19"That little prop 13" might let the motor rev easier for hole shot,
But I think a 21 footer would do better overall with at least a 14".
I think a 4.3 would over rev with a 19" pitch,Especially with a 13" diameter.
 
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maineslr

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Aug 24, 2015
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I don't dought that and the boat is new so I ha e nothing to compare to. I was hoping to look up that prop number and get more info but can't seem to find any info
 

Rick Stephens

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Aug 13, 2013
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You can attach a decent digital timing light with a built in tachometer and use that in testing your rpm and speeds. You MUST determine your wide open throttle (WOT) rpm to make certain you aren't overrevving your motor. You must have GPS speed, rpm, gear ratio and prop pitch to have any chance of choosing a proper replacement prop.

Rick
 
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