454/7.4 PCM or Mercruiser

[88Supra]

Hi Everybody!
Whats the next step to get more speed?
I have a 1988 Supra Bravura (Non-Regulation Size) 22' Competiton Ski Boat
Looks like this if the link is still there http://cgi.ebay.com/ebaymotors/1988-Supra-Bravura-wakeboard-boat-sale-NO-RESERVE-/200817677522 ...for those who don't know.
Has a Chevy, 454ci/330hp, PCM (Pleasure Craft Marine), Original cast iron (truck) manifold, Smallest round intake ports you ever saw "Peanut plug heads" on a big block, 8.13:1 low Compression engine, straight shaft 1:1 Velvet drive.
New Carb, New Fuel Pump, New Cap-Rotor-Wires, Replaced points for Inductive pickup kit in Mallory Distributor and Runs Perfect and even on all cyclinders 140! Tried a New Edelbrock 600cfm Item 1406 and Currently Running a New Edelbrock 750cfm Item 1411

Currenlty advanced timing at full throttle WOT (Couldn't get to ping) to get best speed &
RPM of 42 mph on GPS and 3700 RPM, running New 3 blade bronz 14 diameter 16 inch pitch prop and 750carb 42 mph on GPS @3700rpm and 4 people.

Tried these;
New 3 blade bronz 14 diameter 16 inch pitch prop and 600carb 40 mph on GPS @3600rpm and 4 people
New 3 blade bronz 14 diameter 18 inch pitch prop and 600carb 35 mph on GPS @2900rpm and 4 people
New 3 blade bronz 14 diameter 14 inch pitch prop 41 mph on GPS @4200rpm and driver only


I have the original Holly ...I'll rebuild and try that but,
What$ the next step to get more speed? Help!!!
...Different kind-a Prop? Retangle port Heads? Tighter Combuster Chamber? RV Cam? Dual plan intake Manifold? Headers or Super Charger? Who makes a good Marine 454 Super Charger?!!

What$ the next step to get more tork and or speed? Help!!!

 

[FuelishBehavior]

Re: 454/7.4 PCM or Mercruiser

I'm not sure how much your boat hull or drive unit is made for speed and their limitations respectively. However, I do know that you should be getting close to 4600 RPMs from your engine. 4200-4600 I believe. So I think you're close with the 14 prop. I have a 7.4L/Bravo 1 in my 1993 Crownline 225CCR, a 4000 lb. boat, and I'm getting about 55-60 mph with a 21 pitch. So at 4200 RPMs and 41 mph, you're probably gettin' about what she's got. I would be curious to know what kind of ignition system you have? I would say more torque and speed, stroke that 454 to a 496! That's what I'm doing! That big block should easily push an 18 or 19 pitch prop I would think.... There are some really smart people on here, you should get some better answers than mine soon.

 

[tpenfield]

Re: 454/7.4 PCM or Mercruiser

You could go rectangular port intake and heads . . .

. . . How fast is that boat designed to go . . . being an inboard, etc. ???

 

[Bamaman1]

Re: 454/7.4 PCM or Mercruiser

I hate to tell you, but specialized ski boats are displacement hulls--not planing hulls. They plow through the water instead of getting "on top" of the water like an inboard-outboard. They are designed for a specific use, and getting an inboard ski boat into the 60's would be doubtful.

Your boat is like owning a 3/4 ton diesel supercab diesel pickup truck. You could pull a house down or tow a 13,000 lb. 5th wheel trailer. A Corvette will run 170 mph, but it won't even tow a bass boat to the lake. Life is just one big compromise.

You may could get a little more speed out of your boat, but increased speed requires much, much more horsepower--a very expensive proposition.

Sometimes you've just got to accept your boat's limitations and enjoy doing your water sports.

 

[westportfish]

Re: 454/7.4 PCM or Mercruiser

Whipple charger makes a supercharger for a 454. I run one on my tow vehicle. They work well on stock engines and lower compression engines.

 

[Lyle29464]

Re: 454/7.4 PCM or Mercruiser

I think the 14X14 is your all around prop.

 

[Bondo]

Re: 454/7.4 PCM or Mercruiser

Hi Everybody!
Whats the next step to get more speed?
I have a 1988 Supra Bravura (Non-Regulation Size) 22' Competiton Ski Boat
Looks like this if the link is still there http://cgi.ebay.com/ebaymotors/1988-Supra-Bravura-wakeboard-boat-sale-NO-RESERVE-/200817677522 ...for those who don't know.
Has a Chevy, 454ci/330hp, PCM (Pleasure Craft Marine), Original cast iron (truck) manifold, Smallest round intake ports you ever saw "Peanut plug heads" on a big block, 8.13:1 low Compression engine, straight shaft 1:1 Velvet drive.
New Carb, New Fuel Pump, New Cap-Rotor-Wires, Replaced points for Inductive pickup kit in Mallory Distributor and Runs Perfect and even on all cyclinders 140! Tried a New Edelbrock 600cfm Item 1406 and Currently Running a New Edelbrock 750cfm Item 1411

Currenlty advanced timing at full throttle WOT (Couldn't get to ping) to get best speed &
RPM of 42 mph on GPS and 3700 RPM, running New 3 blade bronz 14 diameter 16 inch pitch prop and 750carb 42 mph on GPS @3700rpm and 4 people.

Tried these;
New 3 blade bronz 14 diameter 16 inch pitch prop and 600carb 40 mph on GPS @3600rpm and 4 people
New 3 blade bronz 14 diameter 18 inch pitch prop and 600carb 35 mph on GPS @2900rpm and 4 people
New 3 blade bronz 14 diameter 14 inch pitch prop 41 mph on GPS @4200rpm and driver only


I have the original Holly ...I'll rebuild and try that but,
What$ the next step to get more speed? Help!!!
...Different kind-a Prop? Retangle port Heads? Tighter Combuster Chamber? RV Cam? Dual plan intake Manifold? Headers or Super Charger? Who makes a good Marine 454 Super Charger?!!

What$ the next step to get more tork and or speed? Help!!!

Ayuh,.... Welcome Aboard,.... A Different boat....

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

I hate to tell you, but specialized ski boats are displacement hulls--not planing hulls. They plow through the water instead of getting "on top" of the water like an inboard-outboard. They are designed for a specific use, and getting an inboard ski boat into the 60's would be doubtful.

Um.. Not true. That boat is absolutely a planing type hull. It doesn't have much (or any) dead-rise, but it still "planes".

Ski boats have little or NO "deadrise" (which is why they're called "flat-bottom" boats........this reduces the wake size.... but they "plane" quickly and ride terribly in rough water........AND is also why no one usually wants to drive them at very high speeds in rough water!

Below is a 1988 Supra Bravura. That doesn't look like a "displacement" hull to me!

Currenlty advanced timing at full throttle WOT (Couldn't get to ping) to get best speed &
RPM of 42 mph on GPS and 3700 RPM, running New 3 blade bronz 14 diameter 16 inch pitch prop and 750carb 42 mph on GPS @3700rpm and 4 people.

Tried these;
New 3 blade bronz 14 diameter 16 inch pitch prop and 600carb 40 mph on GPS @3600rpm and 4 people
New 3 blade bronz 14 diameter 18 inch pitch prop and 600carb 35 mph on GPS @2900rpm and 4 people
New 3 blade bronz 14 diameter 14 inch pitch prop 41 mph on GPS @4200rpm and driver only

You might notice above, that as you lowered your prop pitch, your speed was increasing as was your RPM (AND HP)!

Using a prop pitch calculator, and your 18 pitch prop, (AND 1.0 ratio, AND 15% slip as is common) I get 69 MPH!
That boat is probably NOT going to go 69 MPH! But it should easily do 45-50MPH!

http://www.go-fast.com/Prop_Slip_Calculator.htm

You were getting close. IF the engine is running correctly, try a 13p 3 blade or a 12p 3 blade prop and see what happens. You WANT the engine turning 4600 at WOT with the boat loaded where you'll normally operate (4 people etc)



Using your numbers above for the 14P prop and 4200 RPM (which is getting close to where you want to be) I calculated 25% slip. That is WAY too high! Meaning: your tach is OFF or your Speedometer AND/OR Tach is WAY off.


If your tach and speedo are correct (use GPS for speed and get another tach) and you're engine is otherwise running correctly and you have good compression, timing is correct etc, THEN, YOU ARE still SERIOUSLY OVER PROPPED!

By comparison, my 454/Bravo III pushed my 21' Four Winns 211 Liberator to about 57 MPH at 4600 RPM with 26p props! (But I have a gear reduction of 1.81:1 vs your "direct-drive" 1.0:1)



Cheers,
Rick

 

[Lyle29464]

Re: 454/7.4 PCM or Mercruiser

You can only compare your boat to an inboard. The shaft angle and the BB inboard setup in the middle of the boat wipe out the really go fast capabilities. Cheer up you can out run all of mine.

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

You can only compare your boat to an inboard. The shaft angle and the BB inboard setup in the middle of the boat wipe out the really go fast capabilities. Cheer up you can out run all of mine.

The shaft angle would absolutely contribute to a higher slip and would certainly increase stern lift during hole-shot (which you want in a ski-boat)

Maybe some others can post their performance numbers for similar boats.

I spoke to my brother today about his Ski Centurion (which he bought before he sold me my Four Winns Liberator)

We did some "racing" and he was doing 44mph (along side me measured with my GPS) at 5000 RPM, direct drive and a 14p 4 blade.

I was turning about 3800 cruising easily, he was flat out getting beat up on the relatively light chop..

For the original poster, I would still suggest verifying the tach and speedo.

If you're still only turning 4200 at WOT, you need to select a lower pitch prop......You're "lugging" the engine.

 

[johnmogs]

Re: 454/7.4 PCM or Mercruiser

I just picked up a 1986 Mastercraft Tristar 22' with stock 454 and 1:1 with a 14x14 stock prop, having just sold a 1980 MC SS 351w with powerslot 1.52:1, 14x18 prop, the hole shot on my newer MC is disappointing compared to the powerslot. They are different boats but I miss the power.

I'm running the 14x14 stock prop and got up to 40mph @ 4000 rpm. Looking for minimally invasive options to improve hole shot, and top end slightly. I would like to avoid the cost of trial and error of multiple props, but prop sounds like the place to start, also read about advancing timing 5 deg, and will upgrade ign to electronic conversion. I'm going to avoid the More expensive options like Roller cam, upgraded heads & intake, at some point I'm going to save the cash for other toys.

Forgot to mention that my 454 only has 220 hours on the engine, measured compression at 120psi in each cylinder but engine was cold.

 

[86 century]

Re: 454/7.4 PCM or Mercruiser

I have a 90 bravura with the 351w(240hp)1.23-1 trany with a 14x14 bronze prop.
I get 43mph gps at 4300rpm.

Proping an inboard is more art than sterndrives or out board where there is a bit of science.

Check out the supra forum there are some prop gurus that hang out there.
Upgrading to a newer design cnc machined prop will make a huge difference(almost to the point of unbelievable).

 

[QC]

Re: 454/7.4 PCM or Mercruiser

All you need to do is go to BoatTest.com and compare other tournament boats. Especially true inboards just like yours. Horsepower makes very little difference. None of them break 50, and most barely make 45. You're just not going to get there with a ski hull and a straight inboard. As Bondo-o posted "Different boat'.

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

Essentially, the same "rule" is still going to apply when "propping" any recreational boat................ for hole shot and medium speeds.....
(it's more "black" science for racing boats and there's other more important rules that don't really apply here..........i.e stuff that makes a boat go 2 mph faster at 150 mph will not be significant at 40 mph))

Propping for MAX RPM (or in the mfr rec range) will still likely give give best all around performance (especially hole-shot).

Propping for a low RPM (outside the recommended range) will likely cause "lugging"

Inboard boats are like a stern-drive boat with the drive-trim fixed at not very efficient DOWN angle.

That angle is "OK" for hole shot and low (skiing) speeds but not at all efficient for higher speeds. (It's a SKI BOAT! duh!) Ski speeds are generally well below 40 mph.


The boat is still only going to go "so" fast with the available thrust (and thrust angle) because of the amount of hull contact with the water at higher than skiing speeds.


If you notice the way ski boat hulls sit in the water on plane, and much faster boats (with much higher deadrise), the ski boats plane with the bow lower, and more hull surface contacting the water where a V-bottom boat has much less contact (read less drag) with the surface.

Part of the reason is the increased deadrise AND the thrust angle because sterndrive and outboard boats have adjustable thrust angle capability [TRIM] AND nowadays, outboard boats have adjustable elevation.

BUT the MAIN reason is LESS DRAG. Hydrodynamic drag increases as the square of the velocity. So if you have less hull surface AND less drive components contacting the viscous liquid [water], you can go faster on the same HP.

This isn't rocket science... (it IS Physics though!.....and it STILL gives me a headache!)

 

[QC]

Re: 454/7.4 PCM or Mercruiser

BoatTest.com Even with 400 hp these things rarely hit 45!!! I'll NEVER understand big block power in these things. IT DOESN'T DO ANYTHING!

 

[HT32BSX115]

Re: 454/7.4 PCM or Mercruiser

BoatTest.com Even with 400 hp these things rarely hit 45!!! I'll NEVER understand big block power in these things. IT DOESN'T DO ANYTHING!

Yeah. when you reach terminal velocity, additional thrust doesn't do much!

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

I have a 90 bravura with the 351w(240hp)1.23-1 trany with a 14x14 bronze prop.
I get 43mph gps at 4300rpm.

Proping an inboard is more art than sterndrives or out board where there is a bit of science.

Check out the supra forum there are some prop gurus that hang out there.
Upgrading to a newer design cnc machined prop will make a huge difference(almost to the point of unbelievable).

Way Cool Reply! ...and to everyone else as well but, of course apples to apples ☺
All Competiton Boats; 351 Ford prefered cause, smallest intake Ports (Makes the very best low end tork).
I'd verture to say; you're making more Tork on the Prop with "1.23-1 trany" than I'am! Put a 14X16 on it and See!
I had a 1995 Matercraft Pro Star, 1999 350 vortec, Qaudrajet, No Name Dual plan Manifold, 14X18, 1.5:1 trany - 46mph GPS & 5500 +/- 200?rpm (Fastest I've ever seen) Beat everything to 35mph (A few Seadoo xp Jet skis, a 200hp Merc Bare foot Warrior, dusted all other Comp Boats while over Loaded 8 people...). Point is; (I've found) The Transmission Reduction helps tork alot and that's what makes a Boat (Comp Boat) go forward but, lets try a Big block this time!

Yup, "14X14" barely 41 mph on the GPS @ 4200 rpm, 600cfm Edel 1406 with just me in it.
Best performance so far IS 14X16 42 mph on the GPS @3700 rpm, 750cfm Edelbrock 1411 Carb, four people,
advanced Timing at this speed (to get this speed) and this is where it stays for now. Yes, Mallary Electronic Ignition.
Tork curve says 3600 RPM is top Tork rating and I'm a believer but, lets dig deeper!
!Low 8.1 Compression; Not specifically caring if "lugging" when performance is at it's Zeneth!
Please also note worse speed thus far was with 14X12 @35 mph GPS RPM unknow but, Viberating/screeming "slow down"
Please note the best speed thus far 14X16 @42 mph GPS, (Tach says) 3700 RPM, Edelbrock 1411 (750cfm) & FOUR PEOPLE while I was only WOT for a few seconds, felt smooth and like I could stay at WOT all day.

I mean speed and Performance is ability to carry a big load at high speed! Sure, the hull is all the way in the Water
but, it's flat and so is a 160mph K-Boat (V-drive of course is not all the way in the water).

I know a Competion ski Boat is a weird Duck but, the conversation is missing from Iboats and I'm gonna say;

My opinion; The Higher pitched props have NOT slowed excelleration but, increased excelleration, increased speed, increased my ability to carry more people as I lower or rather close the RPM gap to 3600 and prop slip or flex is massive.
...Yes, 1 Ton Diesel, Baby Also, just tweeking per reading your replies I've been able to increase speed with full load Seven Miles an hour! But, those replies were for inboard/outboards.
Lets get a straight inboard what to do thing going here?!!

Dreaming about Tork in this game, Baby, I'm aiming for the 50mph Barrier ...496 4.40inch Stroker (as opposed to 4.0inch) IS the key or Maybe just bolt on a Super Charger and let it blow! ...I hope not up ☺

Update:
Showed a Prop Guy my Favorite Propeller and he says the blades drop off in pitch from leading edge to trailing edge and "this is a waste of Tork". Said he'd fix it $110, "These Competiton Props don't flex much at all, don't mess with the engine yet" ...and we'll be back for another update. Stay tuned...!




For those following along; !SAFETY FIRST! While trying cool props !Use Caution!
Competiton Boats vs IOs The Prop is Keyd where outboards are Splined
So, don't forget to tork your Prop nut/lock nut and check your Cotter key each time you're outta the water!
I've dropped one Prop to the Bottem but, it wasn't very far to paddle back to the Boat Ramp.
Careful of sharp Balde edges!

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

You can only compare your boat to an inboard. The shaft angle and the BB inboard setup in the middle of the boat wipe out the really go fast capabilities. Cheer up you can out run all of mine.

******

So, far you're RIGHT! ...I hope !OMG! in the after math, your not! ...Thank you for your Reply☺

 

[88Supra]

Re: 454/7.4 PCM or Mercruiser

To the Gentalmen whom offered up Boatest.com;

That information is MIA (missing in Action)

 

[QC]

Re: 454/7.4 PCM or Mercruiser

Add another T Boat Test.com

Edit: If all you want is quicker hole shot, then go bigger power and play with props. But take a look at the 400 hp examples on boattest.com. None reach 50. And most are V-drives, and as you have noted, have more potential speed. I honestly think you are nuts to chase this. If you wanna go fast you need a different boat. Yes, Flatty V-drive drag boats are fast, but you don't have that either.