94 chaparral 1930 ss with 4.3 prop help

[Lt1z350]

Ok so this prop seems very well made didn’t see anything I saw complained about in some older threads. It’s powder coated not painted so that’s nice and it rings like a forged materials not the dull thud of cast aluminum like the 3 blade does. So some nice quality there for a 100 dollar prop.
Performance wise incredible hole shot vrs 3 blade or the 13.25 24p 4 blade stainless. About 3 seconds max from wot to on plane. It comes up so easy now. I can also get on plane and back it down to around 15 mph and not fall off plane. I think it’s coming out around 17-19 mph I didn’t pay too much attention to that as was so excited it had punch out of the hole.
Now the bad I guess as I think the 19 is too much and I almost got a 21. It’s only getting to 4200 rpm which is 43 mph so almost the same mph as the 3 blade but a lot lower rpm. The 24p was 42 mph but 4500 rpm. It was pretty rough out also constant chop vrs almost glass for the testing of the other props those days. So there might be a little more in day it’s smooth.
Now the question is will a 17 letting it reach more rpm go faster? I can’t see hole shot being better but might be I have zero complaints about that.
It also might be the motor just isn’t making enough hp or the power it should I need to put a timing light on it for sure as could be some power on the table.
I had tools with me so on our last cove stop to hang and swim I said what the hell grabbed the 9/16 and advanced the timing 1/4 inch nothing much. Said it will like it or it will ping as I needed to check it anyway after what I found in the lower.
So on the last trip back after advancing the timing a little took off even stronger and hit 45 almost and maybe 4400 still choppy though. And didn’t ping at all. I do a lot of ecm tuning on line sort of my current job custom tuning so do know a lot can be gained with engine timing and what the engine can stand on the current fuel. I also had 87 in it so maybe even more to be found on 93 I’ll have to play with this before I say this prop is too much pitch. But at first test I’m still weary 17 would have been better. I just do not know if more rpm can equal more mph if not adding any power. So this is where someone with experience can help me decide. Or just keep trying to add a little more power with this 19 on it. A 21 would have killed it maybe this boats weight or engine is a little tired it doesn’t smoke any at all wot from the breathers so I’ll have to do a compression test just to feel better. It’s super clean under the valve covers zero build up I know the last owner babied it a lot.
I’m also going to reach out to edelbrock see if that boat intake has a specific hp number they know it can gain before spending that money on these old heads.

I ran around for 3 hours or so and used 10 gallons or about that with a lot of time at 38/39 mph just shy of 4K so that seems like a lot to me so not sure if it’s the engine is struggling so much or that’s just normal which seems like a lot to travel around the lake here if trying to get there in decent time. I guess that is where a good hp v8 will shine being able to run 45/50 and still not be at wot.
I kept trying to pull throttle back so not in the 4 barrel but still was a pig I’m really hoping the timing is still too low and not efficient. Seems like a boat this size and weight can use more hp at least 250. I see why so many complain with the 4 cylinders on all sizes of boats.

 

[harringtondav]

Ok so this prop seems very well made didn’t see anything I saw complained about in some older threads. About 3 seconds max from wot to on plane. It comes up so easy now. I can also get on plane and back it down to around 15 mph and not fall off plane. I think it’s coming out around 17-19 mph I didn’t pay too much attention to that as was so excited it had punch out of the hole.

I missed the details on the prop you mention above. What pitch and diameter? 3 seconds from idle to plane is very, very good. What was your max speed and WOT rpm with this prop?

Now the question is will a 17 letting it reach more rpm go faster? I can’t see hole shot being better but might be I have zero complaints about that.

Maybe, but probably no. At zero slip a 17" prop pushes you 17" per prop rev. 19", 19" per prop rev. At 4800 rpm WOT limit the higher pitch gives more speed. Remember, low pitch gives hole shot at the cost of lower WOT speed. Higher pitch gives higher WOT speed (limited by HP) slower time to plane. Your boating style determines where you want to be pitch wise. A single prop rarely gives you both. On my 4.3 180 hp LX I used a 21P for play, 23P for high speed cruising. 21P was on the boat most of the time.

I had tools with me so on our last cove stop to hang and swim I said what the hell grabbed the 9/16 and advanced the timing 1/4 inch nothing much.

Be careful here. Your Thunderbolt 4's timing curve has an aggressive advance. Tinkering with more advance has resulted in many pistons with holes burnt clear through them. Merc and GM knew what they were doing when they set the specs. later model 4.3's had the TB-5 ignition with even more aggressive timing advance. But this included a knock detector to back things off if predetonation was risking piston hole burning.
I'd get that timing light, and set it back to base timing. I'm away from my manual, so I don't recall the spec. But I believe the procedure calls for pulling one ignition module wire for setting base timing. ...the Mercruiser group here can steer you.

I just do not know if more rpm can equal more mph if not adding any power. So this is where someone with experience can help me decide.

Per above. Not likely

I’m also going to reach out to edelbrock see if that boat intake has a specific hp number they know it can gain before spending that money on these old heads.

My 180 hp 4.3 had a Weber (Edelbrock) 4bbl. It was jetted for the CFM that a 4.3 can swallow. My pal's 350 mag has the same carb body with different, larger jets since it can inhale 25% more air/cfm. Tweaking jets will likely only get you an over rich mixture, smudge on your tansom and very poor fuel economy. I don't know much about the Vortec head 4.3s. My in laws had one. It had a Merc 2BBL carb that likely provided the extra air/fuel.

I ran around for 3 hours or so and used 10 gallons or about that with a lot of time at 38/39 mph just shy of 4K so that seems like a lot to me so not sure if it’s the engine is struggling so much or that’s just normal which seems like a lot to travel around the lake here if trying to get there in decent time.

My past little Larson 4.3 got 4 mpg/8.75 gal per hr on a long three day Mississippi cruise. 35 mph, probably about 3700 rpm. You're not too bad with a heavier boat. Boats are fuel guzzlers.

 

[Lt1z350]

Thats correct on my boat the carbed 4.3 came with a 1.81 drive, the mpi 4.3 which is 220 hp came with 1.62 drive as did the 5.0/220 hp carb and 5.0 mpi/ 260 hp.

the drive ratio diff between a 1.81 and 1.62 is similar to about 2” in prop pitch . I repowered my boat from a 4.3 to a 5.0 with a edlebrock 4 bbl and intake, kept the 1.81 drive just proped up from a 19” to 21” pitch prop.

Cool that’s good to know so thank you. So if I do a 350 hp ls 5.3 down the road I can go out to a 24 and be covered most likely.

 

[Scott06]

Cool that’s good to know so thank you. So if I do a 350 hp ls 5.3 down the road I can go out to a 24 and be covered most likely.

No you were complaining about 10 gal of gas on your current boat. I’d recommend a 3.0

Don’t just eyeball timing use a timing light. U may not hear detonation

 

[Lt1z350]

No you were complaining about 10 gal of gas on your current boat. I’d recommend a 3.0

Don’t just eyeball timing use a timing light. U may not hear detonation

I tune for a living I understand how all that works and how to read a spark plug after a wot pull and hot shut down so that’s all good. If people stuck. That is part of getting the most from something. I have found 25whp in 2 degrees of timing on a typical stock Camaro or corvette with an lt1 in it.
As for a 3.0 my buddy has one and has to drive everywhere with it pinned wot as it’s such a pig and under powered in a 17 foot sea ray. He hates it as it’s worse off then my boat on fuel.
When you over power something you can then run it in the efficient range of the engine and accomplish the same goal on speed. Point being 45 mph on this 4.3 is wot pushing motor hard. 45 mph on a v8 will be less then half the fuel need due to motor is in its efficient range of rpm. I have a 1000whp Camaro that still gets 28 mpg it’s all about how much throttle it takes to achieve the given mph and that’s running 80 mph in the Camaro. That’s better then when it was stock and had 650 engine hp it’s the supercharged model.
A 350 hp that weighs the same or maybe less then this 4.3 will be way better on cruise fuel but yes it will be worse on wot but not by much.
This 4.3 is like most marine engines and very old out dated engine technology. The new ls v8 engines can make a lot more hp on a lot leaner afr. We run naturally aspirated motors at 12.5 -12.7 vrs 11.2-11.7 as these older motors as the combustion chamber designs so much better. So much more efficient on how it’s using the available fuel and the power it can produce. I know a boat is different but if you dyno a motor get a rating on it and we’re to slap it in a boat nothing is changing. So the new design engine is going to make a lot more hp on the same exact fuel as per an 90s 5.0-5.7 motor. Also aluminum heads can take more timing I am in fresh water so not concerned with needing cast iron.
In 2005/2007 gm made the l33 a 5.3 h.o. Which is all aluminum and that’s what I will be using if do the swap. That with a proper marine cam and either the factory fuel injection and truck ecm ran in open loop so no oxygen sensors or go to a carb setup which has been proven in hot rods to make more hp but not as efficient as efi.
Can’t just be stuck on thinking boat tech when so much better is to be had that’s if got the knowledge to do the swap which I do.
Things I don’t know are ratios and props how to get this older 4.3 to run it’s best.
But I’ll keep posting my updates as I tweak this motor and keep trying to get more from it.
Going to take a little while To source all my parts as that engine is pretty limited and I found the exhaust for the ls motors can be hard to come by.
A friend in Texas has that Malibu with the corvette ls6 in it and says he fuel usage is way better then any 3.0 and that’s a 405 hp motor and that’s pushing it and wake boarding all the time.

 

[Lt1z350]

I missed the details on the prop you mention above. What pitch and diameter? 3 seconds from idle to plane is very, very good. What was your max speed and WOT rpm with this prop?

Maybe, but probably no. At zero slip a 17" prop pushes you 17" per prop rev. 19", 19" per prop rev. At 4800 rpm WOT limit the higher pitch gives more speed. Remember, low pitch gives hole shot at the cost of lower WOT speed. Higher pitch gives higher WOT speed (limited by HP) slower time to plane. Your boating style determines where you want to be pitch wise. A single prop rarely gives you both. On my 4.3 180 hp LX I used a 21P for play, 23P for high speed cruising. 21P was on the boat most of the time.

Be careful here. Your Thunderbolt 4's timing curve has an aggressive advance. Tinkering with more advance has resulted in many pistons with holes burnt clear through them. Merc and GM knew what they were doing when they set the specs. later model 4.3's had the TB-5 ignition with even more aggressive timing advance. But this included a knock detector to back things off if predetonation was risking piston hole burning.
I'd get that timing light, and set it back to base timing. I'm away from my manual, so I don't recall the spec. But I believe the procedure calls for pulling one ignition module wire for setting base timing. ...the Mercruiser group here can steer you.

Per above. Not likely

My 180 hp 4.3 had a Weber (Edelbrock) 4bbl. It was jetted for the CFM that a 4.3 can swallow. My pal's 350 mag has the same carb body with different, larger jets since it can inhale 25% more air/cfm. Tweaking jets will likely only get you an over rich mixture, smudge on your tansom and very poor fuel economy. I don't know much about the Vortec head 4.3s. My in laws had one. It had a Merc 2BBL carb that likely provided the extra air/fuel.


My past little Larson 4.3 got 4 mpg/8.75 gal per hr on a long three day Mississippi cruise. 35 mph, probably about 3700 rpm. You're not too bad with a heavier boat. Boats are fuel guzzlers.

I need to go weigh this as curious now the actual weight. I think when I first looked it up I did the 1995 which shows the v8 as the motor size and that was 2500 lbs.
This is a 1994 sst which I now see is a little different then 95 ss. Probably not a lot why worth going to the truck stop and seeing. I’ll just have to weigh trailer by it’s self to get the exact weight as I do think it’s got a tag with some weight info on it.
Boat rides so good even in chop so guess the only benefit to the heavy side of a 19 foot as I saw a 94 cobia 5.7 at 2100 but it had a Yamaha out drive and was told run like hell from that boat. Guy still can’t sell it probably the only nice boat I see listed local that’s been on 3 months and won’t sell even with him dropping the price 2k so far.

 

[Lt1z350]

I missed the details on the prop you mention above. What pitch and diameter? 3 seconds from idle to plane is very, very good. What was your max speed and WOT rpm with this prop?

Maybe, but probably no. At zero slip a 17" prop pushes you 17" per prop rev. 19", 19" per prop rev. At 4800 rpm WOT limit the higher pitch gives more speed. Remember, low pitch gives hole shot at the cost of lower WOT speed. Higher pitch gives higher WOT speed (limited by HP) slower time to plane. Your boating style determines where you want to be pitch wise. A single prop rarely gives you both. On my 4.3 180 hp LX I used a 21P for play, 23P for high speed cruising. 21P was on the boat most of the time.

Be careful here. Your Thunderbolt 4's timing curve has an aggressive advance. Tinkering with more advance has resulted in many pistons with holes burnt clear through them. Merc and GM knew what they were doing when they set the specs. later model 4.3's had the TB-5 ignition with even more aggressive timing advance. But this included a knock detector to back things off if predetonation was risking piston hole burning.
I'd get that timing light, and set it back to base timing. I'm away from my manual, so I don't recall the spec. But I believe the procedure calls for pulling one ignition module wire for setting base timing. ...the Mercruiser group here can steer you.

Per above. Not likely

My 180 hp 4.3 had a Weber (Edelbrock) 4bbl. It was jetted for the CFM that a 4.3 can swallow. My pal's 350 mag has the same carb body with different, larger jets since it can inhale 25% more air/cfm. Tweaking jets will likely only get you an over rich mixture, smudge on your tansom and very poor fuel economy. I don't know much about the Vortec head 4.3s. My in laws had one. It had a Merc 2BBL carb that likely provided the extra air/fuel.


My past little Larson 4.3 got 4 mpg/8.75 gal per hr on a long three day Mississippi cruise. 35 mph, probably about 3700 rpm. You're not too bad with a heavier boat. Boats are fuel guzzlers.

I need to get a manual and see where I’m at so far on it. Plugs looked good and my guess is the guy working on this boat for him re sealed this intake and didn’t set it up right as it felt so much better with just a tiny tweak. Even idle cleaned up like he had it too low. So I’m going to find the specs today and see where I’m at as of right now.

 

[Lt1z350]

Here is the other thing I’m thinking on so many hp versions of the 4.3. Some better heads I know that but anything from 170 to 230 mpi. I know that in the past manufactures change to engine timing was how they got certain ratings. They do this on small engines all the time like atv/ lawn mowers / even out boards in the past. A different timing curve and fueling to move a hp rating around.
So the thought of the manufacture having pushed the engine timing so far is on a ragged edge is very unlikely unless it’s the hottest version of the motor which mine is far from that at 180 I’m told. Edelbrock shows this engine at 202 with their manifold on it and 1409 and you know they screwed with the timing until it got to that 202. Just thinking out loud I guess I think differently as everything I do is around performance it’s how I make my living.
This all works out I might add boats to my list of vehicles I work on. Lol

 

[Scott06]

Here is the other thing I’m thinking on so many hp versions of the 4.3. Some better heads I know that but anything from 170 to 230 mpi. I know that in the past manufactures change to engine timing was how they got certain ratings. They do this on small engines all the time like atv/ lawn mowers / even out boards in the past. A different timing curve and fueling to move a hp rating around.
So the thought of the manufacture having pushed the engine timing so far is on a ragged edge is very unlikely unless it’s the hottest version of the motor which mine is far from that at 180 I’m told. Edelbrock shows this engine at 202 with their manifold on it and 1409 and you know they screwed with the timing until it got to that 202. Just thinking out loud I guess I think differently as everything I do is around performance it’s how I make my living.
This all works out I might add boats to my list of vehicles I work on. Lol

Its good you have that back ground- you can install a fuel air ratio meter, but I believe due to load on engine marine engines tend to have a higher detonation potential and I believe historically more conservative timing. Certainly MPI and electronic controls can push this as well as aluminum heads

I tune for a living I understand how all that works and how to read a spark plug after a wot pull and hot shut down so that’s all good. If people stuck. That is part of getting the most from something. I have found 25whp in 2 degrees of timing on a typical stock Camaro or corvette with an lt1 in it.
As for a 3.0 my buddy has one and has to drive everywhere with it pinned wot as it’s such a pig and under powered in a 17 foot sea ray. He hates it as it’s worse off then my boat on fuel.
When you over power something you can then run it in the efficient range of the engine and accomplish the same goal on speed. Point being 45 mph on this 4.3 is wot pushing motor hard. 45 mph on a v8 will be less then half the fuel need due to motor is in its efficient range of rpm. I have a 1000whp Camaro that still gets 28 mpg it’s all about how much throttle it takes to achieve the given mph and that’s running 80 mph in the Camaro. That’s better then when it was stock and had 650 engine hp it’s the supercharged model.
A 350 hp that weighs the same or maybe less then this 4.3 will be way better on cruise fuel but yes it will be worse on wot but not by much.
This 4.3 is like most marine engines and very old out dated engine technology. The new ls v8 engines can make a lot more hp on a lot leaner afr. We run naturally aspirated motors at 12.5 -12.7 vrs 11.2-11.7 as these older motors as the combustion chamber designs so much better. So much more efficient on how it’s using the available fuel and the power it can produce. I know a boat is different but if you dyno a motor get a rating on it and we’re to slap it in a boat nothing is changing. So the new design engine is going to make a lot more hp on the same exact fuel as per an 90s 5.0-5.7 motor. Also aluminum heads can take more timing I am in fresh water so not concerned with needing cast iron.
In 2005/2007 gm made the l33 a 5.3 h.o. Which is all aluminum and that’s what I will be using if do the swap. That with a proper marine cam and either the factory fuel injection and truck ecm ran in open loop so no oxygen sensors or go to a carb setup which has been proven in hot rods to make more hp but not as efficient as efi.
Can’t just be stuck on thinking boat tech when so much better is to be had that’s if got the knowledge to do the swap which I do.
Things I don’t know are ratios and props how to get this older 4.3 to run it’s best.
But I’ll keep posting my updates as I tweak this motor and keep trying to get more from it.
Going to take a little while To source all my parts as that engine is pretty limited and I found the exhaust for the ls motors can be hard to come by.
A friend in Texas has that Malibu with the corvette ls6 in it and says he fuel usage is way better then any 3.0 and that’s a 405 hp motor and that’s pushing it and wake boarding all the time.

Some of what is seen on auto tuning doesn't carry over, you may want to look at offshore only or scream and fly that are more performance oriented sites than this one.

The comment on the 3.0 was more of a joke than a serious suggestion. I'm sure an LS can be reasonably swapped, even with a more efficient engine that can run leaner mixtures I suspect you will not find that great of a fuel efficiency improvement. If it takes 10 gph down to 8 gph that's a huge % but won't translate into much savings unless you go great distances.

 

[velociraptorfarmer]

Most of what others have said lines up with my experience as well.

99 Sea Ray 185BR w/ a 4.3L Merc Alpha One Gen II, 1.81 gears. Run a 14x19 4 blade Hustler on it. 4600rpm at 44mph wide open in a relatively heavy (2700lbs dry) boat for the motor. Gets on plane effortlessly, turns on a dime, and can fully trim out at just about any speed for fuel efficiency.

I had a Vengeance 3 blade stainless 21p on it, but it took forever to plane with more than 2 people in the boat, plus I still cruise at the same speed and rpm with the 4 blade since it slips less and gets the boat out of the water further. WOT on that prop was 4700rpm at 46 mph.

 

[briangcc]

Just to comment on your go-fast approach....you are aware that a small bump in power isn't going to translate to a large bump in speed correct? Cause that doesn't translate from the car world to the boat world.

My FourWinns in my sig ran 55mph and that was a 5.0mpi pushing 270HP. Very similar boat to my current one.