Prop questions on a 16' 1976 StarCraft Montego (Merc 888)

ratdude747

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Reposting something from my ongoing build thread that probably should be a post in this subforum. The boat is a 16' Starcraft Montego with a Mercruiser 888 (302).

I've edited the wording a bit for clarity.

Different subject while it's on my mind: props.

The outdrive currently has a 4-blade composite on it. Here's the remains of the box: (edit: this is to provide the specs on the current prop)

img_20240209_173140__01-jpg.394239


Also included was an aluminum prop. Has a ding in it:

17075184302628372397218292456716-jpg.394240


The damping rubber is cracked too... Probably junk? FWIW it's part number 48-74888-21, also marked with other things:

1707518626222116966315589326314-jpg.394241


Might be original; the PO was very fond of the plastic props (based on how many bladeless (crashed) cores were in the garage).

Thoughts?

Supposedly they were hitting 60mph in this thing before it was out of service; it had been (badly) upgraded to a 4 barrel carb. It still has a 4 barrel in my setup, but I've swapped the carb out to a marine rated unit (among other upgrades, fixes, and redos). They liked the plastic prop for the flexibility helping with hole shots (and getting on-plane faster). I saw no fewer than three sheared prop cores in the garage/barn I pulled it from.

Am I correct that the aluminum prop is junk? My current plan is to stick with the plastic unit, but I'd like a second opinion before I spend any money on it.
 

Scott06

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Reposting something from my ongoing build thread that probably should be a post in this subforum. The boat is a 16' Starcraft Montego with a Mercruiser 888 (302).

I've edited the wording a bit for clarity.



Supposedly they were hitting 60mph in this thing before it was out of service; it had been (badly) upgraded to a 4 barrel carb. It still has a 4 barrel in my setup, but I've swapped the carb out to a marine rated unit (among other upgrades, fixes, and redos). They liked the plastic prop for the flexibility helping with hole shots (and getting on-plane faster). I saw no fewer than three sheared prop cores in the garage/barn I pulled it from.

Am I correct that the aluminum prop is junk? My current plan is to stick with the plastic unit, but I'd like a second opinion before I spend any money on it.
The aluminum could be rehubbed by a prop shop or just by a new black max or similar in same pitch. By the stamping on it it has been repaired already which is no big deal but sounds like PO liked the bottom of the lake too much

I doubt he was hitting 60 unless he was towing it down the highway. With a 4 bbl is probably around 200-205 hp. The boat is light but it takes some power to get to 60, especially if the carb install is scabby ....
 

ratdude747

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The aluminum could be rehubbed by a prop shop or just by a new black max or similar in same pitch. By the stamping on it it has been repaired already which is no big deal but sounds like PO liked the bottom of the lake too much

I doubt he was hitting 60 unless he was towing it down the highway. With a 4 bbl is probably around 200-205 hp. The boat is light but it takes some power to get to 60, especially if the carb install is scabby ....
They slapped a 4 barrel Holley off a 1970's Ford super duty on it (along with an Edelbrock intake off one of their cars). I swapped in a 4 barrel marine Holley made for a 5.0 that I got used on eBay (flame arrestor included, which was also missing on the old setup). Otherwise it was stock... I've upgraded to a pertronix ignitor solid state ignition (stock prestolite marine distributor) because I can't be bothered messing with points and condensers.

Per the marketing materials the stock 188hp was good for "over 50 mph" ... 60 might have been possible. The pitot tube/hose was in pieces so who knows (I am swapping in a gps speedometer, so when the time comes I'll know more).

Yes they did hit the bottom a lot... But since I'm a boat noob, I'm not going to point a finger.

Didn't think the aluminum prop was rebuildable or worth rebuilding. The part number did come back as a standard mercruiser prop... If I ditch plastic I'll probably get another one new or used.
 

Scott06

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They slapped a 4 barrel Holley off a 1970's Ford super duty on it (along with an Edelbrock intake off one of their cars). I swapped in a 4 barrel marine Holley made for a 5.0 that I got used on eBay (flame arrestor included, which was also missing on the old setup). Otherwise it was stock... I've upgraded to a pertronix ignitor solid state ignition (stock prestolite marine distributor) because I can't be bothered messing with points and condensers.

Per the marketing materials the stock 188hp was good for "over 50 mph" ... 60 might have been possible. The pitot tube/hose was in pieces so who knows (I am swapping in a gps speedometer, so when the time comes I'll know more).

Yes they did hit the bottom a lot... But since I'm a boat noob, I'm not going to point a finger.

Didn't think the aluminum prop was rebuildable or worth rebuilding. The part number did come back as a standard mercruiser prop... If I ditch plastic I'll probably get another one new or used.
Any of the entry level Merc/Quicksilver Black Max, Michigan Vortex or Match series props will work. Since the original was a pressed hub you may need different thrust washer vs the newer style replaceable hubs

If it has an automotive intake just watch for corrosion in the water cross over. I assume you are in fresh so probably wont be an issue but normally marine intakes have brass lined water passages.

If you swapped out to pertronix I think you need to bypass the resistor to supply full 12 v to the coil. You see some folks swear by the Pertronix and some folks swear at them. Seem to see a lot of failures of their system both here and on the muscle car forums. While no one likes points might be worth keeping them in the boat in case the pertronix fails
 

ratdude747

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Any of the entry level Merc/Quicksilver Black Max, Michigan Vortex or Match series props will work. Since the original was a pressed hub you may need different thrust washer vs the newer style replaceable hubs
Noted. Any "good" reason to swap instead of sticking with plastic, since plastic was working? Other than that it seems that Comprop is no longer in business (DOH!). Piranha props any good?

If it has an automotive intake just watch for corrosion in the water cross over. I assume you are in fresh so probably wont be an issue but normally marine intakes have brass lined water passages.
Yes, fresh water only (they used on a couple of northwestern IN lakes, I'd be using on a lake near me and possibly the ohio river. It's a cast aluminum manifold. Likely nasty inside but I'm sure the exhaust manifold I had to take apart for a helicoil repair was way worse (tons of rust and scale, raw cast iron from the looks of things). The stock threads were completely gone (bolt slid out); it was one of the bolts holding on the fuel filter/water separator body to the manifold, which is how I discovered the issue.
If you swapped out to pertronix I think you need to bypass the resistor to supply full 12 v to the coil. You see some folks swear by the Pertronix and some folks swear at them. Seem to see a lot of failures of their system both here and on the muscle car forums. While no one likes points might be worth keeping them in the boat in case the pertronix fails

The ballast wire is chopped and out of the circuit... I connected ignition power straight to the RUN wire that goes to the choke heater (and where one end of the ballast wire used to be).

I've read the Ignitor is solid... Ignitor II and III are less reliable. I got lucky and found an open box (installed but never used) one made for marine prestolite distributors on eBay for a good price. Fit perfectly. Paired it with an epoxy Flamethrower coil.

An ignition issue is what got the boat parked in the first place (died on the water)... they suspected the "ballast resistor" was the culprit (which they never found, since in this case it's a ballast wire embedded in the wire harness). Another issue potentially responsible for the original fault (or at least why it couldn't be recovered) is that the START ballast bypass wire was non-functional (per the other thread, they disused the original starter relay when upgrading to a PMGR starter), but that issue is also solved by the Pertronix with no resistor. I also suspect the coil was bad; it was an oil filled stock unit. Said coil worked OK (wouldn't idle) with the ignitor during a test start while I was waiting on the new coil but was noticeably warm after testing (in any case, not happy with the Pertronix ignitor).

I haven't had the muffs on it since installing the new coil so I can't say how much better it is since the swap. Likewise, the no idle condition may have been caused by other factors such as a vacuum leak (bad carb and carb spacer gaskets since fixed), a badly rust plugged and rotten fuel filter/water separator (since been replaced, the fact that cheap butt here never did the spark plugs, plug wires, cap, or rotor (but the latter 3 weren't in bad shape despite being very old), or that the fuel in the tank is 10 years old (but doesn't smell like "bad" fuel, surprisingly). There were other issues too, mainly that it wasn't exhausting water; water was making it to the block and manifolds at least, and upon outdrive disassembly the impeller was a bit soft (but not in pieces at least). Depending on weather I'll be putting the muffs back on pretty soon and will try again at running it, now that all of the above issues have been addressed to the best of my knowledge.
 

Scott06

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Noted. Any "good" reason to swap instead of sticking with plastic, since plastic was working? Other than that it seems that Comprop is no longer in business (DOH!). Piranha props any good?


Yes, fresh water only (they used on a couple of northwestern IN lakes, I'd be using on a lake near me and possibly the ohio river. It's a cast aluminum manifold. Likely nasty inside but I'm sure the exhaust manifold I had to take apart for a helicoil repair was way worse (tons of rust and scale, raw cast iron from the looks of things). The stock threads were completely gone (bolt slid out); it was one of the bolts holding on the fuel filter/water separator body to the manifold, which is how I discovered the issue.


The ballast wire is chopped and out of the circuit... I connected ignition power straight to the RUN wire that goes to the choke heater (and where one end of the ballast wire used to be).

I've read the Ignitor is solid... Ignitor II and III are less reliable. I got lucky and found an open box (installed but never used) one made for marine prestolite distributors on eBay for a good price. Fit perfectly. Paired it with an epoxy Flamethrower coil.

An ignition issue is what got the boat parked in the first place (died on the water)... they suspected the "ballast resistor" was the culprit (which they never found, since in this case it's a ballast wire embedded in the wire harness). Another issue potentially responsible for the original fault (or at least why it couldn't be recovered) is that the START ballast bypass wire was non-functional (per the other thread, they disused the original starter relay when upgrading to a PMGR starter), but that issue is also solved by the Pertronix with no resistor. I also suspect the coil was bad; it was an oil filled stock unit. Said coil worked OK (wouldn't idle) with the ignitor during a test start while I was waiting on the new coil but was noticeably warm after testing (in any case, not happy with the Pertronix ignitor).

I haven't had the muffs on it since installing the new coil so I can't say how much better it is since the swap. Likewise, the no idle condition may have been caused by other factors such as a vacuum leak (bad carb and carb spacer gaskets since fixed), a badly rust plugged and rotten fuel filter/water separator (since been replaced, the fact that cheap butt here never did the spark plugs, plug wires, cap, or rotor (but the latter 3 weren't in bad shape despite being very old), or that the fuel in the tank is 10 years old (but doesn't smell like "bad" fuel, surprisingly). There were other issues too, mainly that it wasn't exhausting water; water was making it to the block and manifolds at least, and upon outdrive disassembly the impeller was a bit soft (but not in pieces at least). Depending on weather I'll be putting the muffs back on pretty soon and will try again at running it, now that all of the above issues have been addressed to the best of my knowledge.
Never used any of the composite props. If you have one sure why not use it. I suspect if they were better you would see more of them around.

Sounds like you are up to speed on the other issues and possible pertronix stuff.
 

ratdude747

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Reviving this thread since I've had a few outings under my belt and on the last one (3rd), I did find some prop damage:

1720320563922.png

There had been an undocking incident where my wife backed into deadwood (mostly wrecked the stern light, but that's another story). Not sure if that's what broke it or what.

Performance wise it's ran excellently. Nothing to complain about that's prop related.

I'm thinking of staying composite, so that would mean moving to a Piranha prop. Anybody have experience with them? Should I go for A-series or B-series?
 

ratdude747

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Figured it out... yeah, I want A-series since that's all they make in my size. LH rotation too.

Found a deal on an NOS hub (MA4) and 5 blades (1418A-4LH). Saved a fair bit compared to factory direct... ;)

Will try... it's a hair larger (14" vs 13.7") but everything else matches.
 

ratdude747

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Figured it out... yeah, I want A-series since that's all they make in my size. LH rotation too.

Found a deal on an NOS hub (MA4) and 5 blades (1418A-4LH). Saved a fair bit compared to factory direct... ;)

Will try... it's a hair larger (14" vs 13.7") but everything else matches.
Wrong blades... forgot that despite the comprop box having an "L" in the part number, it's actually an RH prop. I actually need RH blades. Working on getting that straightened out (the seller has 8 RH 1418A-4 blades for sale, so I'll buy all of them so I have a complete spare set).
 

ratdude747

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I am assuming that we're talking actual WOT RPM and not "designed" RPM. The latter is hard to say since the engine isn't 100% stock (likely putting out over 200HP, but I don't have dyno data on such) ; the redline is at 5000RPM per the original tachometer. As for the former:

If I had a prop I felt I could safely run hard and water I could safely/legally run WOT on I'd find out. My existing prop is failing (see prior post) and the only other one I have is the messed up aluminum one. And the water on the Ohio river is a bit choppy to go super fast one without loosing kidneys and fillings. Maybe I'll get a better answer on the next outing (which is on a lake that should be calm enough to actually get speed on.

I have to have something to run... hence why I elected to match what was already there and working well the best I could with what is still made today.

Per a chat with one of the prior operators, switching from the 14.5x21 3-bladed stock aluminum to the 13.7x18 4-bladed composite cut top speed a bit (which per above, isn't a huge issue) but the improved acceleration made getting on plane a bit easier (which was/is further boosted by the hydrofoil they added later).

We shall see how the new prop reacts...
 

jimmbo

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"Hopped Up", 188hp, to 200hp would be about 2 mph more top speed, and likely a slightly slower Holeshot. What exactly was done to Hop it up?
 

ratdude747

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"Hopped Up", 188hp, to 200hp would be about 2 mph more top speed, and likely a slightly slower Holeshot. What exactly was done to Hop it up?
Carb/Intake upgrade: Edelbrock Performer 289 intake (it's freshwater only, so no worries), 1" carb spacer/PCV hookup, and a Holley Marine 4160 carb, factory tuned for a Mercruiser 5.0 (Chevy 305?). Previous owners had the same setup other than running a non-marine 4160 off a 1970's ford superduty v8 (trash truck).
 

jimmbo

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A 302 spinning 5000 rpm isn't going to Need more than 370 CFM@1.4" Pressure Drop. The Marine Holley, if Factory Calibrated properly, will certainly have a Fuel Delivery Curve far more Appropriate for a Marine Application, than an Auto/Truck Carb, and be USCG Compliant, reducing the Chance of the Boat blowing up...
I wonder if the Previous Owner, replaced any Electrical Components(Distributor/Alternator/Starter) with Non USCG versions... If they do one item, they usually continue, on Others.
As I stated, you would get about 2 more Mph over a Stock 188
 

ratdude747

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A 302 spinning 5000 rpm isn't going to Need more than 370 CFM@1.4" Pressure Drop. The Marine Holley, if Factory Calibrated properly, will certainly have a Fuel Delivery Curve far more Appropriate for a Marine Application, than an Auto/Truck Carb, and be USCG Compliant, reducing the Chance of the Boat blowing up...
I wonder if the Previous Owner, replaced any Electrical Components(Distributor/Alternator/Starter) with Non USCG versions... If they do one item, they usually continue, on Others.
As I stated, you would get about 2 more Mph over a Stock 188
I've been through the rest of it. Ignition was stock and why it was marooned in the first place; I upgraded from points to Pertronix Ignitor/Flamethower (still using the stock Prestolite marine distributor) per a prior post. Starter is a newer PMGR-type but is in fact marine rated (I did redo the control circuit using a marine-rated Mallory starter relay). Alternator is stock but it did need a rebuild.

The carb/intake swap was a "hey we have some extra 302 parts sitting around" project... the intake came off the PO's mustang I'm told. The carb install was pretty hacked in other ways too: used automotive fuel hose, wired-open choke, throttle springs tied to metal fuel lines, and no flame arrestor due to the stud threads being stripped. Was one of the first things I redid as I didn't want the boat blowing up... the carb and flame arrestor was a lightly used set I found for "cheap"- I'm told it came off an engine that spun bearings twice before getting replaced. I did have to rebuild said carb to get everything working right. And all fuel hoses were replaced with USCG A1-15 (only "old" line kept is the factory steel line between the fuel pump and the water separator).

Keep in mind that while the bottom end of an 888 is a 302, the top end is actually a 351W, specifically the cam and heads, the latter under-drilled to accept 302 head bolts) which may change things (it's high enough compression to have a minimum octane of 88). Such heads and cam are stock.

I was told that the carb/intake/spacer swap did wake the engine up a bit. I will say that other than being a bonehead at idle, I haven't had any issues with it bogging down... does run well.
 

jimmbo

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351 Heads on a 302 actually raising Compression sounds like a long shot, the Combustion Chamber is Larger and will drop the Compression from 8:1 to less than 7:1, unless some Machining and/or Parts changes also happened. As for the Cam, is it a Marine Grind, or some Street Auto/Truck Grind?
 

ratdude747

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351 Heads on a 302 actually raising Compression sounds like a long shot, the Combustion Chamber is Larger and will drop the Compression from 8:1 to less than 7:1, unless some Machining and/or Parts changes also happened. As for the Cam, is it a Marine Grind, or some Street Auto/Truck Grind?
Didn't know the combustion chamber size was different, I was thinking more along the lines of bigger valves flowing more/better. Duh.

Cam is the stock one Mercruiser installed. 351W firing order.

Here are the supposed specs on the 888 in stock form (225 supposedly is the stock 4-barrel version, likely a close match to what I actually have?):

1720721051103.png 1720721148207.png

(Shamelessly pulled from another forum...)
 

jimmbo

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With a Recommended Top Rpm of 4200, a 302 is not going to need much for Carburation, a very small 4bbl, like a 390 cfm would be overkill
302 cu in at 4200 rpm can inhale 367 CFM, at 100% Volumetric Efficiency, However an engine from that Era, would at best have, 75% VE, so it would inhale 275 CFM.
 

ratdude747

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Prop came in.

IMG_20240712_180804.jpg

Will need to swap anode to clear...

IMG_20240712_180238.jpg

But that and a fresh tab washer are on order. For now, I tried trimming with my oscillatory saw:

IMG_20240712_184109.jpg

Kinda rough, so for now it's a placeholder.

The new anode is an offset variety:

Screenshot_20240712-195727~2.jpg
 
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