454/7.4 PCM or Mercruiser

[88Supra]

Re: 454/7.4 PCM or Mercruiser

Powerslot Rocks! ..the Best performance so far that I know of, the only Boat that can Drop the rear most corner of the Boat in a turn, correct back to a level plane and still be turning a sharp turn. Try that Stern Drives?!!
Yes, I think we have a match!
Except, I'll check my Compression again, I'm sure it was 140
but, I didn't write it down specifically (Mine has 170 hours).

Please Note: From here in when I say Performance I mean speed and since I'm talking about Competition BBC
I think that Speed and excelleration (can) go hand in hand.


Don't worry about a thing, I've done the Prop Swap$. You just sit back, relax, read along and answer questions occassionally

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

Pssst, Hot Rod! ...Really just wanna improve efficiency to it's fullest but, Don't tell anyone, lets make this fun

 

[QC]

Re: 454/7.4 PCM or Mercruiser

If you want flat turns AND top speed, get a tunnel. I think I am lost as to what you are trying to do . . .

 

[Tail_Gunner]

Re: 454/7.4 PCM or Mercruiser

Here have a read your fighting both drive drag and wetted hull surface: http://www.google.com/#hl=en&sclien...ddaee4ee84f1b4&bpcl=35466521&biw=1366&bih=673

Due to the enormous cost and competition perhaps some day a hull and drive will be developed that will allow one to have the best of both world's. But the boat's today are designed to drag and in very spefic way's. Now if youy could find a prop that would provide very high lift at the cost or thrust that might provide a bit of releif but is counter intuitive.

http://gavlab.auburn.edu/uploads/r daily thesis.pdf

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

Now if youy could find a prop that would provide very high lift at the cost or thrust that might provide a bit of releif but is counter intuitive.

http://gavlab.auburn.edu/uploads/r daily thesis.pdf

Yeah. Google is definitely your friend here.

The PDF above reminded me of how much I hated Calculus, Differential Equations and the Fourier Transform!

That paper was quite interesting in that the wave analysis outlined there is exactly the same analysis used in Electrical Engineering. (EM [radio] waves behave like sound and light "waves........ and waves in other mediums like liquids and solids etc.....)

I sort of question the term described as "lift" from a propeller. They do not produce "lift" by themselves.............. They produce Thrust along the rotational axis...... (the "x" axis..... no force is produced in the "y" axis [or any other axis] that is not equal in all directions....)

There is "resultant" lift from a propeller that loses some of the total thrust by forcing it up through the surface of the water (the thrust fans out in a wide "fan" but because it's near the surface of the water, some of the thrust breaks through the surface causing a "rooster-tail") the side and lower thrust is not lost so there's a resultant lift............ loss of thrust will reduce your hole shot (another reason the dual propeller/contra-rotating props produce far more focused thrust than single props.


Any force in the vertical ("y") axis is simply a component of thrust if that thrust is not exactly parallel to the hull centerline....... like in a inboard boat! OR a sterndrive that is trimmed to an angle that is not parallel.

This is the disadvantage of inboards (vs outboards or sterndrives) because it's not adjustable. But for ski and wakeboard type boats that are only really designed for approx 40mph or less, the "disadvantage" is negligible.

:facepalm::facepalm: I can't believe we're talking about this bs........but I suppose it does answer the OP's original question.... You ain't going more than about 45 mph with that boat unless you cram a LOT of HP into your V-drive!!

 

[Tail_Gunner]

Re: 454/7.4 PCM or Mercruiser

I can't believe we're talking about this bs........but I suppose it does answer the OP's original question.... You ain't going more than about 45 mph with that boat unless you cram a LOT of HP into your V-drive!!

 

[QC]

Re: 454/7.4 PCM or Mercruiser

And since he has a direct drive, he's basically effed . . .

 

[Bondo]

Re: 454/7.4 PCM or Mercruiser

And since he has a direct drive, he's basically effed . . .

Ayuh,.... Quite true,....

The Op is only considerin' Horsepower, 'n is ignorin' the fact that the hull bottom is Not built for speed...

A BaZillion horsepower, won't make a barge, a speedboat....

 

[wca_tim]

Re: 454/7.4 PCM or Mercruiser

but it WILL make it a GREAT ski boat that holds consistent speed pass after pass, consistent wake, easily pulls a couple out on slalom skis, etc... there's a reason that good ski boats are not cheap - they put a lot into designing them for optimum performance in their purpose.

We do a lot of skiing behind our little i/o and it is NOT optimal, but it works OK, nothing like some friends' ski or wakeboard boats do...

of course when we're moving to different water, I can take a nap waiting for them to get there... ;-)

 

[Tail_Gunner]

Re: 454/7.4 PCM or Mercruiser

I am going to tinker with the boat's look again this winter...So i stopped into a dealer here in town to look at the new toys color scheme's etc etc. I was not to impressed on the styling but how there built is amazing and cost....i looked at 24' i believe at 100 grand. How they can justify that i dunno... However i really like this seadeck imatation teak stuff they use..

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

...Really just wanna improve efficiency to it's fullest (Like I said in the Previous post) and what is the Speed one can expect
from the Subject; 454/7.4L if common inefficiencies are corrected ...in this case Non-regulation size 22 foot, Competion Boat, Low Compression, Small port head, Approximate 454/330hp, Truck Engine, Stainless Steel prop (Supra Bravura) With all that said; I'm sure we can all agree the target and reasonable top speed is 44 +/- 2 mph @3800 +/- 100rpm? Correct? Anything after that, the design limitation is pretty much unrelenting. <--Period Ok, I get that! Nope, not gonna get another boat!
But, for cases related to the Thread -Not limited to Competition Boat; we have talked about a case of WOT BBC @70mph with a IO?
Given the same parameters for engine; What is the most speed for the Subject, not limited to boat size but, cats and tunnel type Boats excluded.

 

[QC]

Re: 454/7.4 PCM or Mercruiser

Huh?

You want to know how fast a older, carbed, 454 will push a boat, any mono hull. A small flatty or a small I/O could easily hit 70. Is that all you wanted to know?

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

But, for cases related to the Thread -Not limited to Competition Boat; we have talked about a case of WOT BBC @70mph with a IO?
Given the same parameters for engine; What is the most speed for the Subject, not limited to boat size but, cats and tunnel type Boats excluded.

Not sure what you're asking.

Different hull designs and adjustable thrust angle (TRIM) will allow much higher speeds on the same HP.

Over on the Offshoreonly.com forum site, there is a guy that has/had a FourWinns 211 Liberator (21' 3000lb boat minus the engine and drive) ....like mine below, that still had the 460 King Cobra inside. He stroked, bored and tricked the engine such that it would "bury the speedometer at 80 mph" (it had a 0-80 mph speedo)

 

[Tail_Gunner]

Re: 454/7.4 PCM or Mercruiser

Well both engine's do not suffer from low end tourqe but run out of steam on the top end....so anything you do to improve induction will help the engine to perform. In marine the most common approach is super charging and i assume that's due to cost yeilds vs performance. The hulls are the hold back here due to the drag.... as they were designed to do and what it takes to overcome that drag at high speed is incredible...

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

Well both engine's do not suffer from low end tourqe but run out of steam on the top end....so anything you do to improve induction will help the engine to perform. In marine the most common approach is super charging and i assume that's due to cost yeilds vs performance. The hulls are the hold back here due to the drag.... as they were designed to do and what it takes to overcome that drag at high speed is incredible...

Agreed and thank you for the most up to date and intelligible input yet, put to this Thread! ...and I'm sure you all agree!
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We've pounded through best Prop; Approximate 14X16 (Bronze) for Given 1988 Supra Bravura Stock Boat Straight drive, 454/330hp, 750cfm Carb, fully advanced ignition adjusted at WOT for best speed (approximately 30-36 degrees before top dead center),
yielding Approximately 44 mph +/- 2 mph at 3700 rpm +/- 100 rpm loaded with four people.
Please note: These are extremely advanced ignition and low rpm engine lugging conditions -Do not try this at home- unless you know what you're doing!
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Moving on Forward:
To all: Please, do continue conversations; [Bolt on performance enhancements; Best horse power for the dollar?!!]
How many Horse power would it take to break 46 mph to make 50mph (Same subject Boat)?
I guess; Not +100hp +/- 30hp to Break 46 and 200hp just short of 50mph but, 550-600 foot pounds tork @optimum rpm to get just short of 50mph. ...Comments?

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

"Huh?

You want to know how fast a older, carbed, 454 will push a boat, any mono hull. A small flatty or a small I/O could easily hit 70. Is that all you wanted to know? "

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Ahem ...Gasp!

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Thank you! ...I will consider purchasing another Boat ☺
However, we're stuck with this one for...?

 

[QC]

Re: 454/7.4 PCM or Mercruiser

But, for cases related to the Thread -Not limited to Competition Boat; we have talked about a case of WOT BBC @70mph with a IO?
Given the same parameters for engine; What is the most speed for the Subject, not limited to boat size but, cats and tunnel type Boats excluded.

I was responding to this. Why don't you, one more time, tell us what this thread is about I still don't know.

Oh, and if you are suggesting that an increase in torque, at the right RPM, will make a boat go faster, you are correct. The reason? More horsepower. HP = Torque x RPM/5252

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

I was responding to this. Why don't you, one more time, tell us what this thread is about I still don't know.

Oh, and if you are suggesting that an increase in torque, at the right RPM, will make a boat go faster, you are correct. The reason? More horsepower. HP = Torque x RPM/5252

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Few old School (80s) Big Block Chevy 454 (Not limited to Competiton Unorthodox Boat) owners; know how to set up their Boat for optimum performance... as designed. There's a lot of us out there (including myself) but, very little information and way too many questions. Seems to me, correct set up is a very very fine line, at least for a BBC Comp Boat ☺

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

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Few old School (80s) Big Block Chevy 454 (Not limited to Competiton Unorthodox Boat) owners; know how to set up their Boat for optimum performance... as designed. There's a lot of us out there (including myself) but, very little information and way too many questions. Seems to me, correct set up is a very very fine line, at least for a BBC Comp Boat ☺

Understand that you have OTHER limitations on performance with ANY boat. For example, your particular set up has a fixed "trim" (propeller shaft angle) ..........Forgive me if I repeat myself....:facepalm:

If I remember correctly, you also have a direct (1:1) drive setup (instead of a reduction drive?) This will also give you an upper limit on engine RPM because propellers are VERY limited in the upper range of RPM. (too high an RPM for most pleasure craft propellers will cause severe blade cavitation, especially LARGE diameter props......)

(Racing props excepted......you have a ski boat not a racing boat)

 

[QC]

Re: 454/7.4 PCM or Mercruiser

88Supra,

Are you trying to tell us how to set up an "old school BBC" for marine performance? Or are you trying to setup a Comp boat for top speed? I can't believe I am still asking these questions. I am certainly capable of being the dense one. Just take a look at Dockside Chat; I couldn't understand a simple request regarding an address change :facepalm: Butttt, If you want to go 50, you need another boat. If you want more horsepower for whatever reason, then good on ya. Or, if you want to find the best combination of power, hole shot, speed etc with prop changes, then I can kind of understand that. I'd drop pitch and get this thing wound up a little more. Why you think 3800 RPM is a good WOT target is odd to me too.

With all that said, it's just not clear (to me) what it is you want.