23 pitch prop for rebuit Mercruiser 4.3

[dlogvine]

I rebuilt 1993 Mercruiser 4.3 v6 engine on Bayliner Capri 1850. It was bored to .30 over, so it definitely added some HPs. Original prop was 19 pitch which is consistent with prop recommendations for this engine. However the fellow I sold the boat to said that it was getting rpms too high even on the half open throttle and the sales guy at the marina store told him to buy a 23 pitch prop. I looked up at the prop Wizzard https://turningpointpropellers.com/PROPWIZARD/ to see if 23 pitch prop could be used on this boat and it does not show so. Recommended props are 19 pitch for towing, water skiing and such, 21 pitch is for speed. The prop my buddy bought was aluminum and cost him according to his words $300 or so. My guess is that he was sold an expensive prop possibly overpriced since decent aluminum props go for about $200-250 new. But my main concern is that 23 pitch prop can overload the engine and damage it. Am i correct?

 

[Scott Danforth]

what RPM is he getting at WOT? verified with a shop tach?

when you had the motor rebuilt, did you have the rotating assembly balanced?

 

[dlogvine]

He said he was getting in the range of 5000rpms with the throttle half opened (according to him). And the reading he got from the dashboard tachometer. Rotating assembly was not balanced, I did the engine assembly myself so had to do it without shop tools.

 

[Sea Rider]

Seems tach is way off...

Happy Boating

 

[Scott Danforth]

the $5 tach in the dash can be significantly off. hence the comment to verify the tach with a known good shop tach.

a simple 0.030" bore isnt going to add any significant hp.

 

[dlogvine]

Is there another way to check the real tach reading, besides the indash tachometer? Ive heard there are laser tachs available for this. Or should i buy a better tachometer from the store and hook it to the engine

 

[Lightwin 3]

Many multi meters for automotive use have an inductive tach built in. That is an inductive lead you clamp on the plug wire.

A useful tool to have around and not expensive.

I suspect the dash tach is off or set on the wrong pole. There is a rotating dial on the back with various settings.

 

[Maclin]

Just curious as to what MPH they are seeing at the half-throttle 5k rpm's...

 

[Chris1956]

A 21P prop is a common prop for that setup, and is what I had on my SeaRay 18' bowrider w/ 4.3LX motor. My neighbor had a slightly smaller and newer BR with a 4.3 engine. I think the gear ratio was lower than mine. He used the 23P prop.

However, like the others, I suspect the tach is way off.

 

[dlogvine]

Would this tachometer work?
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/282489404379

 

[Lightwin 3]

Would this tachometer work?
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/282489404379

Yes.

 

[Scott Danforth]

so would this one https://www.amazon.com/AGPtek%C2%AE-...oto+tach&psc=1

i would probably get a loaner tach from your Friendly Local Auto Parts Store (FLAPS)

 

[dlogvine]

The problem with the boat tachometer is that it is almost unreachable, Bayliners dashboard design and the carpeted shelf right underneath make it virtually impossible to reach the rear side of the gauges, unless you sport a 4ft hands or are a really small child or a dwarf

 

[dlogvine]

[No message]

 

[porscheguy]

1. Your friend got ripped off on his prop. No aluminum prop (especially one for an alpha 1) should ever cost more than $150. $300 is what you pay for new entry level stainless, or immaculate used high quality stainless.

2. A 4.3 in a 18/19’ bayliner has a 99% chance of having a 1.81 gear ratio (especially if it can turn a 23p at all).

3. I can turn a 23p laser2 up to redline with my 4.3/1.84 alpha gen 1, in my 19’ Wellcraft. I get 4700rpm with a 23p mirage+. Both props have far less slip than an aluminum. (My 4.3 is an ‘02 2barrel.)

4. It really depends on what rpm and speed he’s getting with the prop. If he’s getting 4600rpm he’s fine. The low limit is 4400, but if you’re that low, you’re losing performance.

 

[dlogvine]

He got a ss prop, so it was not such a bad deal. But I told him to check his rpms with the better tachometer

 

[jkust]

Just to toss this out there but a 1993 4.3 is already low on HP because it is the pre vortec design which came about in 96. Did the rebuild get a vortec head and intake upgrade or is it still the old school version?
Thinking your friend has to be mistaken on the cost of his aluminum prop. That number doesn't compute with the real world as aluminum props are cheap.
Something you have going for you however is that bayliners of that era are built extremely light weight which equates ultimately to the possibility of higher speeds. Light weight in the pedestrian sense here means a lesser build not that it is made of carbon fiber (ha ha).
The comment of over revving at half throttle tells me there is a need to verify the RPM's with a separate tach.

 

[Jgcrock99]

Since you guys are talking props on a similar setup I would like to ask for recommendations. I have the 205 hp 4.3lx mercruiser on a 19' chaparral. I bought the boat used with a 14.25 x 21p aluminum prop and I believe it is a mercury. I can turn 4900 rpms (dash tach) and with just my wife and I it does great. It is in need of replacing because of some nicks I inherited from the first owner. I have been doing a great deal of research but it is a bit overwhelming. I like it's current performance but we never do anything but cruise. We are about to start tubing, skiing, etc and just having larger loads in the boat. I bought a turning point 4-blade hustler 19p but it dropped my revs to around 4500 on smooth water. I'm trying to stick with aluminum for cost concerns but also because of varying depths and the occasional submerged tree tops.

 

[dlogvine]

Just to toss this out there but a 1993 4.3 is already low on HP because it is the pre vortec design which came about in 96. Did the rebuild get a vortec head and intake upgrade or is it still the old school version?
Thinking your friend has to be mistaken on the cost of his aluminum prop. That number doesn't compute with the real world as aluminum props are cheap.
Something you have going for you however is that bayliners of that era are built extremely light weight which equates ultimately to the possibility of higher speeds. Light weight in the pedestrian sense here means a lesser build not that it is made of carbon fiber (ha ha).
The comment of over revving at half throttle tells me there is a need to verify the RPM's with a separate tach.

He actually bought a stainless steel prop so the price is not too bad. As for the RPMs and his speed on WOT, I told him to check it with the proper tachometer, not a 25 year old cheap dashboard version. And the best part, he bought the boat, even though I reduced the price significantly for the repairs he had to do himself.
The engine is a prevortec, I believe first Vortec 4.3 engines came in 96 (at least Chevy started making these blocks). It has 4 barrel rochester carb and old intake. I decided not to upgrade it to vortec since I did not want to spend any more money on this boat. Just the machine work cost me about $1500, considering that I did all the assembly myself + upholstery and plywood for the seats and panels and carpeting + storage costs, I am glad to finally get sell this boat.

 

[dlogvine]

Since you guys are talking props on a similar setup I would like to ask for recommendations. I have the 205 hp 4.3lx mercruiser on a 19' chaparral. I bought the boat used with a 14.25 x 21p aluminum prop and I believe it is a mercury. I can turn 4900 rpms (dash tach) and with just my wife and I it does great. It is in need of replacing because of some nicks I inherited from the first owner. I have been doing a great deal of research but it is a bit overwhelming. I like it's current performance but we never do anything but cruise. We are about to start tubing, skiing, etc and just having larger loads in the boat. I bought a turning point 4-blade hustler 19p but it dropped my revs to around 4500 on smooth water. I'm trying to stick with aluminum for cost concerns but also because of varying depths and the occasional submerged tree tops.

Looks like your prop is right in the parameters for the engine. You can check recommended propellers at the Prop Wizzard
https://turningpointpropellers.com/PROPWIZARD/ (working link below), but for this engine and similar boat it recommends either 19 pitch or 21 pitch with the right diameter. As for the nicks on the blades, if they are not too deep and the blades are not deformed, just use the file and take the nicks out, that is what the shops do.