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Guesstimating the expected longevity of my 91 454bs

S

slauder

Regular Contributor
"I bought them 3 years ago wit

"I bought them 3 years ago with 850hrs. I had boat survey which also included compression testing. All were +-5 from each other and dont remember the extact numbers, but recall them as good numbers (130?). I did 100 hours a year, so they are at 1150 now.

They run well and have no complaints (neither do I). Elbos changed, half dozen oil changes and raw water impellers is the extent of my service record.

I just did a WOT at 4300 and 30 knots. One of the carbs is dumping too much unburn gas out the exhaust. I have little to complain about.

So I have to decide how to spend money now. For instance, do I replace the Qjets with Edbrocks or keep money on the side for engine rebuilds (I'm liking carb swap project as I can DIY and payoff of ~20 less gas?)

I think I need a power system game plan (or do I?) I like the boat and will keep her no matter what I have to do (91 Tiara). I just want to make sense in what I spend and what projects I do.

Also just met someone that took there 97 Tiara and put in new yanmars, trannys and generator. I think he did nothing himself and paid 100k after all was done (100k not in my cards).

I was always heard if you want a boat with diesel, then buy a boat with diesel (never cost effective to switch a gas to a diesel)."
 
"Of the 100 hours a year, how

"Of the 100 hours a year, how much is fast cruise? If your going to do a diesel/gas financial analysis, your current gas $/year could be as high as $10k per year, or as little as $4k, depending on your speed/GPH. $100k cost sounds high to me, since your 31 should already have 1 1/2" shafts, good enough for a 240hp, maybe even a 300hp diesel. I'd have guessed closer to $60k for diesel equipment, plus labor, depending on power, keeping the same tanks, which may be arguable."
 
Get that errant Q-Jet rebuilt

Get that errant Q-Jet rebuilt by someone with a reputation (and a warranty) and you'll be all set.

Jeff
 
"Keep the gas stuff running -

"Keep the gas stuff running - it will be cheaper in the long run. Ask your new friend how much he can get for his $100K investment, especially in today's environment.

Get your rochester rebuilt and then 'tuned' for those engines in that hull. If you can make 30kt at WOT, that hull has to be 'light' and I'll bet you can economizer the A/F curve a good bit.

Those engines should go to 1000 hours before the heads may need to come off. 2000+/- hours is the nominal life span for the bottoom end. I got over 3000 hours on mine before major overhaul and never had any issues."
 
"Mark,
I'm at 1100 hours

"Mark,
I'm at 1100 hours now. What am I to do to the heads now? I dont want to neglect her at this point.

Also, who to send the q-jet to for a good rebuild? Can we keep this rebuild in this new family? And 'tune' is what I need to do at the boat in spring.

Dave,
I have a very strange rpm to fuel curve (maybe you guys can suggest why)...
I do almost all 100 hours at 2900-3200 because:

I seem to get .6-.7 mpg lower at around 1100-1700.

I seem to get .8-.95 at 2900-3200.

She screems above 3200 (4brls) and I hate to see the twin flowscan pointing both above 18 gph (or is that when I stop looking), not to think what a needless beating I am doing to her.

I only WOT with new oil and for short intervals of minutes, because I heard thats good to bottom half?"
 
"if you have a good maintenanc

"if you have a good maintenance schedule, you might not have to do anything to the heads. The 1000 hours for an overhaul on the heads was the 'average' from the shop where I worked, mostly I/o's, but a few inboards. If your compression is up, you like where your leakdown rate is, and there is no oil going thru the guides, you don't have to do anything except keep up the good work.

A few gents on here have used Cliff Ruggles. His ovoerhaul kits are top notch and thorough. He can also do flow testing if desired. I'm a bit beat after days of snow shoveling - i don't get the "new family" Q.

Yoou can also work the linkage to delay the 4 barrel open though the air valve is usually easier to adjust.

What GPH do you run at cruise and do you know your vacuum vs rpm info?"
 
"Mark,
1. Another good tool a

"Mark,
1. Another good tool and some schooling:
"A leak-down tester is a measuring instrument used to determine the condition of internal combustion engines by introducing compressed air into the cylinder and measuring the rate at which it leaks out. Compression testing is a crude form of leak-down testing which also includes effects due to compression ratio, starter/battery condition and other factors."

Due I need to do compression if I'm going to do this test?

2. How do I check oil going thru guides?

3. Can someone email Cliff Ruggles contact info to [email protected] or alternte way to contact him.

4. GPH at 3150 is the best (other then running at hull speed 6 kts). Flow scan reads ~12 each and I'm doing ~21 kts.

22 Nautical Miles/Hour / 24 Gals/Hour = .91666 Nautical Miles / Gal

I cannot seem to do better with my setup. slower with tabs just takes longer to get to places and may even burn more gas.

10500 pounds is the weight of my 31 Tiara.

5. How to measure "vacuum vs rpm info"?"
 
"Don,
Thanks. Just ordered hi

"Don,
Thanks. Just ordered his book. Too bad I didnt have it on the xmas list.

PS He is taking work for August carbs so it looks like it will be me with his kit this winter."
 
"Mark,
I think i just answere

"Mark,
I think i just answered my own question... found this for vacuum testing. Oil leaking thru guide is Worn Guide?

WORN VALVE GUIDES: If the needle fluctuates with jerky motions somewhere in the 14 to 21 inch range at idle but steadies as speed in increased the valve guides are worn.

Looks like Santa is still working dads list...

1. parts to build leakdown tester (http://www.motorcycleproject.com/motorcycle/text/leakdown.html)
2. Vacuum Gauge

http://www.theautoist.com/vacuum_guage.htm"
 
"Scott; If you don't need

"Scott; If you don't need to add any oil between 50 hours changes, I would not consider rebuild work on the head or bottom end, assuming no crazy noise. One early indicator is blow by out the cover vents, these will show some smoke, increasing with age."
 
"Scott:

Good research!

"Scott:

Good research!

The vac vs rpm is something you create. With it, you can determine where the carb transitions between systems and adjust their operating points.

Cliff also has the www site - cliffshighperformance.com.

With a boat that light, you should be able to cruise with the power piston down. You may also be able to lean the mixture at cruise if you can find the larger primamry rods. Read the book thru a few times and then develop your plan of attach. The only bad part is the time it takes.

On the compression vs leakdown - both have their place. I'd say if compression is fine and no other performance issues are noted, you are probably OK. Leakdown will show things the compression test won't, as noted by the example in the link you posted."
 
"One can spend a fortune getti

"One can spend a fortune getting everything "just right", or use the money saved to buy a bit more oil and gas. The later is better on one's digestive system, and it provides getting enjoyment of one's hobby.

To butcher a biblical saying, "Blessed are those who can ignore minor difficulties to enjoy life instead."


Jeff"
 
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