Lightened boat, same speed?

[Scott Danforth]

ok, Folks, lets re-set with the same information

if you read all the threads

OP just bought the boat - OP lives in Florida
Boat is a restored 1977 Aquasport 222 (quality of restoration unknown)
the motor will go to 4800 RPM at WOT (speed at WOT RPM unknown)
OP is obsessed with 3800 RPM/18mph point (reason not given)
Motor is a remaned 350 running a DUI ignition and Holley carb (650 CFM 4175 spreadbore)
Base Timing of 10 degrees BTDC and a 25 degree advance
Idle set at 600 RPM
drive ratio unknown
drive type unknown (assuming inboard gear)
prop unknown
tach unverified (need to compare to known good tach)
speed unverified (need GPS speed)

My guess is that this is the boat https://www.popyachts.com/center-co...sale/aquasport-222-in-lakeland-florida-140750

if that is indeed the boat, it is an inboard
Cruise speed listed in the ad at 18mph

that speed at that RPM is a function of the hull, prop, gear ratio and RPM and has absolutely nothing to do with weight (until you add so much weight the boat sinks). So the OP removing the tower, etc. would do absolutely nothing to the speed at that point.

In order to determine if the correct prop is on the boat, a WOT RPM run needs to be taken

 

[jimmbo]

I saw pics of that model as either an Outboard, or something with an inboard engine at the stern. However I wasn't able to see if it was sterndrive, or a Vee Drive...
18mph as a cruise speed sounds awfully low, not even on plane. If so, a 350 is way overkill for power.

 

[Faztbullet]

Semi planning hull with V drive....high drag due to running gear and wetted hull surface..

 

[scoflaw]

Semi planning hull with V drive....high drag due to running gear and wetted hull surface..

This ^^^ That boat wasn't designed for that motor.

Good looking boat, too bad it doesn't have an outboard. That SBC looks like no joke to work on either.

 

[dingbat]

This ^^^ That boat wasn't designed for that motor..

The velvet drive was a factory option. Competing with Shamrock of the same design

 

[Scott Danforth]

And trying to compete with the SeaVees

 

[Silvertip]

Look at this another way. Whatever prop you have now provides the numbers you stated (18 MPH @ 3800 rpm). So you increase the pitch which "theoretically" would increase speed at the same 3800 rpm. There is an IF in that theory. More pitch means more power must be delivered to the prop to achieve that 3800 rpm and resultant speed increase. In practice, that can't happen without an accompanying increase in throttle position. The IF in this situation is IF the boat is severely under propped (too little pitch). I doubt that's the case. But another physics lesson here is that if your boat is propped incorrectly for WOT it will be propped incorrectly across the entire rpm range. Run the boat wot with what you consider an average load and then prop to get the engine at or very near the top end of the rpm band. What you get is what you get unless you want to fine tune for another 1 mph at the expense of running a bunch of different props.

 

[LAWRENCE Owen]

Every angle you guys are proposing makes good sense. I'm a hot car aficionado and even though I've owned a ton of boats during my 77 years in FL ( sail and power), I'm obviously no where near being a marine engineer. When you lighten a race car you go faster with the same HP. That was my thinking.

Here's the odd story: Since I started this thread, I believe I bent some valves and/or push rods. I was installing a new distributor and to get on TDC and I used the starter (slightly) to bump the #1 cyl toward TDC. (I know, I know). Turned out just by chance it was already at TDC, so I snapped off the piston stop and the piece went into the cylinder. I couldn't get to it with a magnet or my bore scope; the piston had gone up a little too far.

I then tried to back off counterclockwise to bring the cyl down a bit and found that the engine was locked up; wouldn't budge by hand (wrench), and when more pressure was applied, the 16mm crank pulley nut started to back out. So I removed the pulley and screwed 3 G8 14mm bolts into the balancer and using huge leverage with a breaker bar I was able to turn it a tiny fraction and the stop piece became visible and was sitting just inside the spark plug hole!

Still couldn't turn the pulley by hand, but it would turn with the starter (?) Worried I had damaged something in Cyl, 1, I attempted to do a compression test and it looks like the engine timing was way off. Compression on the 2 cylinders tested was a weak 80 psi (needle didn't even bounce with each power stroke). My theory is at that time the pistons hit the valves.

This has never happened to me before, and I have no explanation beyond what you've heard here. Please tell me what I'm missing .... I can't be more appreciative.
Larry

 

[LAWRENCE Owen]

Actually, with a race car, it goes fast quicker. Not necessarily faster at a given RPM. This is where my thinking could be off.

 

[Scott Danforth]

Think of a boat engine as a dump truck engine. a dump truck loaded with sand, driving up-hill in sand and only has one gear.

your marine gear ratio will determine your speed

in your other post, you still need to determine what is wrong with the motor, which means the motor most likely will need to come out.

 

[Maclin]

Taking off in a boat is kinda like a truck-pull but in reverse, where the weights start out full then get lighter as it comes up on plane, then you gotta keep it there.

 

[Faztbullet]

Distributor timing wont cause pistons to hit valves...timing chain will. Piston stop broken can damage that cylinder but not the other. Sounds like a bad engine conversion.

 

[LAWRENCE Owen]

The mammoth console has been made ready to come off; screws and bolts removed, all wires, cables and lines are disconnected and marked. I'll inspect the timing chain, and remove the starter, carb and distributor today to get it ready to take the boat to a marina on Monday, where they'll pull the console and engine with a forklift. I decided against using a huge block and tackle hung from an oak tree branch in my back yard ;-)

The engine will come home in the pickup so I can pull the heads and go from there. But no matter what I find, I've decided to buy a new long block with new heads. The engine is old (casting #0010) and has a lot of hours on it -- the boat has fished the Florida west coast for years and the Keys was a favorite destination.

I will research this more, but with more HP turning a bigger prop and pitch I should get the speed I want, even if I go from only 18 mph to, say, 25-30 mph. There's enough room for a larger prop. The current prop is 13" x 9p, which is pretty puny, don't you think? The marina guys -- who have a good deal of experience with smaller inboard boats -- feel the construction and condition of the hull can stand more HP and the weight would be about the same. And one seasoned old timer (like me) suggested I remove the humongous 3+ inch wide keel and if the boat 'walks' a bit, install a fin. He says that keel is costing a few MPH.

By the way, this 1977 Aquasport 22-2 originally came with a Crusader 5.7 350 which I have learned has from 270 HP up to 300 HP. The current Chevy 5.7 350 in the boat now has from 260 HP up to 325 HP. The blue engine color suggests a 4-bold main.

 

[Scott Danforth]

paint color doesnt mean anyting. truth is most SBCs in boats are 2-bolt mains

motor will weigh the same if you build a 261 cubic inch or a 396 cubic inch small block (3/8" stroke). it will weigh about 5# more if you go to a tall deck block, then you can build up to about 427 cubic inches of small block.

 

[Scott Danforth]

I would start by finding out the HP rating or your transmission. then decide on a motor

 

[LAWRENCE Owen]

Hi Scott, about the engine, I stated it is a "marineized" 350 cu.in (read GM car engine). It is covered with a black waterproof coating/paint everywhere; block, intake, valve covers, oil pan, and all bolts and nuts are stainless and brass freeze plugs). However, in a couple of places some blue surface is showing through. I read that a blue engine of the 1969-80 era denoted a 4-bolt main (in most cases, the article said). This engine could be as low as 195 HP or up to 260 HP, I don't know. I could not locate the VIN#, only the casting #3970010..

About the Borge-Warner Velvet Drive (In-line 1:1 ratio), and here is what I found on two websites:
Model 71C rated capacity is 360 HP @ 4800 RPMs
Model 72C has 3 groups:
Group A is 550 HP @ 5000 RPMs / 500 HP @ 4500 RPMs
Group B is 460 HP @ 5000 RPMs / 400 HP @ 4000 RPMs
Group C is 420 HP @ 5000 RPMs / 400 HP @ 4800 RPMs

I have the 72C model, but I'll have to look at the plate again to see which group.
Man, these gears are tough ... and expensive!

I am going to decide on a 345 HP or so long block and with a dual plane intake manifold all of my high-per bolt-ons it should live up to it's rating. We have a very professional prop shop in my town, General Propeller, and they will help me with the prop.

I'm excited about this, but sooo much work before getting the new engine in place.
I'll keep you up to date if you'd like. Larry

 

[Scott Danforth]

dont count on the motor being a 4-bolt.

Plus, I would not consider repowering unless it was a roller cam, 1-piece RMS block and vortec heads. no reason not to. in fact, you can get a running motor from LKQ in either Tampa or Bradenton for $250, change cam, core plugs and head gaskets, bolt on an edelbrock marine intake and have an honest 330hp at the prop for under $1000

the guys at General Propeller know the wife and I on a first name basis :facepalm:

three kinds of boaters on the ICW....those that have run aground, and those that will run aground - the third category is those that lie about running aground.

 

[LAWRENCE Owen]

"Group B is 460 HP @ 5000 RPMs / 400 HP @ 4000 RPMs" It should have said, 400 HP @ 4400 RPMs.

 

[LAWRENCE Owen]

Scott, you sure know the Sarasota-Bradenton area! If I can't order a long block with the roller cam and RMS block (Vortec heads is a given), then I'll do something else. There are at least three reputable engine/ head machine shops here which I've learned about. I'm going to choose one and see if they'll put together an engine with the specs you recommend. I'm not talented enough to do it, nor do I have some of the right tools. I can find the native engine at LKQ (delt with them a number of times), and also get the cam. The shop could create the heads, etc.

I'm no longer a man of means (by any means) so I'll have to stick to a stingy budget ... but it seems that the custom built engine could end up being affordable even with the machine shop work -- and I'd know what I have. Thanks.

 

[LAWRENCE Owen]

Go to SummitRacing.com and plug in the part # MLL-BP3503CT1. It seems to have everything plus the 1-piece main seal. I've heard good things about BluePrint engines, and they have very good rewiews.