I just cant leave anything alone !!!
 

Wife and I came home with this gorgeous 2007 Chaparral 256ssx a few weeks ago. It came with a 375hp Volvo Penta 8.1 Gi and DPS-A duoprop outdrive.
Finally got in on the water two Fridays ago and it runs great. Managed 55.4mph on the GPS pretty effortlessly. Might have hit 56 or 57 if I really played with the trim... but wife was already annoyed with the wind in her face.

Any normal, sane or rational person would be tickled to have a 55mph 26ft bowrider... but coming from 30 years of hotrodding cars, building big blocks and drag racing on the 1/4 mile... I want faster than 55mph.

Unfortunately I didnt do enough homework before buying the boat. Originally wanted this same hull but with Mercruiser 496HO power. Unfortunately Mercruiser power in this model is rare... and the HO version even more rare... so I compromised and at least still got the big block... but it is Volvo Penta... which means almost ZERO aftermarket support.

I am in talks with Larry Hofer at Raylar Engineering and he tells me I need to find a GXi ECM for the easiest way to make his stage1 525hp top end work... so that hunt is currently ongoing.

Other thoughts are...
I currently have F6 props (24pitch) on the boat. It jumps on plane and powers to 55mph without a struggle at all.
I am wondering if I can just do a simple jump to the F7 props (26pitch) and pick up a few more MPH since the 8.1 is a torque monster... or if this will just load the engine more and hold same speed at lower RPM.
I already have a pair on order (found them cheap @ $750)... so either way... maybe they will work better with the Raylar 525hp upgrades.


Any thoughts on this ?
And please dont say... "Leave it alone"... because I CAN'T leave it alone. Not even possible. :angry-smiley-044:

Sorry to say this even though you said don't say this.... I would completely leave it alone or replace it with a 502 based engine. The 8.1 platform is not a very cheap build and I have seen way to many builds go wrong on the 8.1's.

Duly noted.
I can always just build a 572/598 combo on a MKIV platform. Might be cheaper in the long run.
:ernaehrung004:

You can throw a bunch of money and power at this hull but in the end you won`t be happy.
Anything power wise that will make a difference will blow your outdrive so then you go down that rabbit hole. It`s a deep and expensive one.
Basically you have a 10 bolt and you`re trying to throw a bunch of power at it , Its not going to last and upgrades are $$$$.
That hull is not made for speed either.
Either enjoy what you have or get a different hull.


not on this site :D

That motor will have a hard time spinning an F7 prop set. You RPM at WOT will be greatly affected. That boat is setup perfectly as it...don't spend a dime on chasing speed with it...it ain't gonna happen without a motor transplant and your "gorgeous" bowrider will be a lab experiment that no one will ever touch down the road.

Sorry, just not the platform for speed.

And that's what brought me here. :D

..........

Techman and Icdedppl got it right.

Only thing is, is to check that your WOT rpm is near the top end of your recommended rpm for that motor. Otherwise it will feel more sluggish than it should. Very simple idea, but so many dont understand that concept, or have never even checked it. But chances are what you have is correct.

It is approx 4500-4600 @ 55mph... so yeah it is spot-on and does run like a beast for a 5500lb boat. Last boat was a 5.7 merc and was all done @ 42mph. Nothing I did to it made it any faster. Tried a set of Stainless Marine manifolds/risers, Holley carb, new DUI HEI distributor, etc... and it still only went 42mph.
The new 350 I built for it never made it into the boat... as I sold everything and got back into a big block platform. That got me out of an underpowered smallblock boat and into a strong running big block boat.
My problem is... I like to make everything better/faster... hence the reason I am here.
I gave up on the F7 props. The ebay seller flaked on me and now i am doing battle trying to recover $850.
I will likely just build a whole 'nuther engine for the boat and prop it accordingly.
Wife and I really like this hull layout. We shopped several months for the right deal and paid $45k for a $60k boat.
I would be happy if I could squeeze another 10mph out of it with a healthy big cube combo.

You will be farther ahead selling a stock 55mph Chappy as a 55 mph day cruiser and just buying an 80mph performance boat - less money/ headaches and you know what you have under you without settling for 65 or 70mph steps each time you want to go faster.

I second this motion.
By the time it's said and done you'll have a ton of money into it, (comparable to just buying a performance boat) and probably hard to resell boat.
Get you a west coast open bow style performance boat if you need the open bow.

This comes to mind with trying to make a Chaparral fast, even more so with Volvo Penta stuff.
https://cimg0.ibsrv.net/gimg/www.off...d6bd02b2f.jpeg

I'm one of the oddball guys that is into these 8.1s and modifying them for more HP. I can tell you it's difficult, as there aren't many parts options out there, and I'm working with the more common Mercury platform. It sounds like your drive might be a weak link too. Are you sure you want to go down this path? The boat you purchased looks like a great sporty comfortable cruiser as it sits.

And I can't leave anything alone either so I get it, but again are you sure with the boat you have you should mess with it?

yeah at that wot rpm, you couldn't swing a larger prop. It MAYBE would not loose much or any top end, but would feel like a dog. And that would load the heck out of the motor. Don't even think about it.

Something else to consider and I don't know the answer..........some hulls just don't respond to extra HP. That boat was made to run comfortably and an extra 100-200 hp might not make it any faster. Even if that is not the case, 200 extra hp is needed to get roughly 10mph and the drive might not be able to handle that.

Fair enough. I will leave it alone and maybe shop for a 2nd boat instead. :D

Well I do know this hull goes alot slower with the 5.7 in it... like 8-10mph less than this big block. This is why I would not buy another underpowered boat. Already been down that road with previous boat.
Not even sure why Chaparral offered a 5.7 in this thing. I think anything 24+ft should have a big block in it.
That said... I think a Raylar 525hp kit will be more fun to drive than the current 375hp... even if it only gives me another 5mph... its still a gain.

Yep, this is how the disease starts...........:bunnydance: My disease metastasized in the form of a FourWinns 210 Horizon open bow family boat. A 383ci stroker making around 471hp, reglassed transom and raised x dimension 1 7/8, CMI headers and dry to the tip tails, nose cone on the OMC King Cobra lower...........boat ran 68mph radar on pretty nasty water. You see, just about all of us here have had the disease for some time. There is no cure.........................:boat:

Put a procharger on it with 3-5 psi of boost,, throw stock ecm in trash, retrofit a holley ecm and harness. Drive it till you break the drive, bux a imco SCX and hyd steering. I just dynoed a 540 with modded mpi intake that went in a 23 foot bravo 3 bow rider boat, made 710 ft lbs of tq and 655 hp, runs 67 with bravo 3 and 72 with bravo one xr (from what I was told)(guy switches them back and forth depending weather hes towing tubers or hauling ass). Build a 540 while the 496 is being beat up on for that day it pops, BTW, my friends wives call me MR B.I.G. (Bad influence guy).

lol... Im that guy also. Always had one of the fastest cars or biggest engines. Been doing this stuff almost 40 years now. God only knows how much hard earned cash ive tossed into making horsepower for whatever I was building over the years. Last big dollar toy was a 70 Camaro with a Big Chief headed 632.
The boat will get more power eventually. Just havent decided how deep into it I want to go.
Safest route will be to just build a whole spare engine from scratch.
Since these 496's are already tall deck motors, it only makes sense to build a 572 or 598. Tons of off the shelf stuff available and easy combo to slap together. Also never had one before... so thats reason enough. Ive done 496's, a 511, 540, 565, 615 and last was the 632.
I also know enough to not hack up the boat to do this. I can/will transplant a very neat and clean OEM looking build.
I will obviously update with progress as it unfolds. Still in the permit process of getting a 30x40 2-story shop built. Once that is done, i can focus more on the next engine build.

Yeah this boat is a keeper and probably the last one I will buy. It checks all our boxes and is why we drove from Atlanta to LOTO to buy it.
I will be "messing" with it for sure.

Do it :)


https://cimg6.ibsrv.net/gimg/www.off...dde2ce94e4.gif

Might as well start here and sell the current unit before it grenades'.

https://www.diamondperformanceparts..../products/1100

I stand corrected on the bravo 3 boat I mentioned, has ran 66, not 67, with bravo 3 and 71 with bravo 1, not 72

18k with no warranty 😕

Yep crazy I know but also proven to be reliable.

Would the lower really be necessary for boats sub 80 MPH?

Thats my thought as well.
I understand that even the B3 to B1 comparison is a moot point when dealing with speeds to 65mph.
Ive also read (and please correct me if im wrong) that the VP Duoprop drives are stronger than its Mercury Bravo3 equivalent.

And for the record... I am not here as a cheerleader for VP. I actually was shopping for a Merc 496ho package in this hull but they are rare as hens teeth.
I settled on the VP drivetrain because the rest of the boat warranted it and because it was still a Chevy big block.
It was only after getting the boat home in my driveway that I learned almost NOBODY has aftermarket support/upgrades available.
Sofar all I have found is Larry Hofer at Raylar offering the Gen7 BBC upgrade packages... and Hardin Marine sells Stainless Marine exhaust manifolds/risers for my VP combo... to which I am seriously considering. They are approx $3500 vs CMI stuff @ $8k+.
I still havent found a simple solution to the untouchable drive-by-wire Volvo Penta ECM.
Best option presented by Larry Hofer was to source a 420hp GXi ECM to swap with my 375hp Gi ECM. Still havent found one yet.

The performance increase that Im looking for is not unrealistic. The boat already runs an honest by GPS 55mph in bone stock trim.
I see no reason this thing cant hit 65mph with proper and realistic upgrades. Thats not asking alot honestly.

I have a new set of Gil manifolds with used dry pipes with mufflers in them that should fit that motor for $2500. I am only about 30 minutes from you if you want to look at them. for the record on the VP duo prop, I used to maintain an eliminator that had a 750hp Procharged 509 in it with a duo prop and it never had a drive issue in the 10 years he owned it. he was not abusive on it but did run it pretty hard at times so they are tougher than the merc b3 IMO.

The VP risers are pretty tall and have 6" spacers under them. I would definitely be interested in having a look at yours.

And yeah... im not abusive on stuff anyway. I drive very conservatively and safe... but do occasionally like to go hammer-down from a roll. I never vo to WOT from a dig. Always ease into it until im up out of the water and pull throttle back to maintain happy speed.
My full throttle blasts are typically initiated at 30mph+.
I expect this VP Duoprop to last me awhile.
https://cimg6.ibsrv.net/gimg/www.off...0b6d4ab611.jpg

And now that ive managed 10 posts i can toss a pic of the boat up. lol
https://cimg8.ibsrv.net/gimg/www.off...a062078bd1.jpg

Good point. I threw a nose cone on my old OMC lower because it had the leading edge of a 2x4. lol I bet Art will not stay satisfied @65 for long. First boat that goes out around him will trigger the disease. :angry-smiley-038: $$$$$$$$$$$$$$$$$$

Pics of pics that didn't turn out too good but you get it I'm sure. :whistle: Hotrodded family boat.

https://cimg6.ibsrv.net/gimg/www.off...6f1bde2252.jpg
https://cimg7.ibsrv.net/gimg/www.off...3d83b4f216.jpg
https://cimg8.ibsrv.net/gimg/www.off...371c6b773a.jpg

Speaking of the outdrive .. I've got a DPS/a as well but it's on a stock 5.7G something , and I've got a B3 on another boat .
The hydrodynamics of the DPS/a unit make the regular B1 look like a 22 cubic foot upright Amana refrigerator . So you know it's better in that aspect than a B3 and the Volvo F series props look like racing props compared to the Merc B3 version so I don't think there's anything to worry about in the old argument about B3 speeds vers B1 and subsequently Volvo DP .
A member who shall remain nameless and is no longer here was a Volvo guy as well as Merc and he said that the internals of the Volvo unit were vastly superior to the Merc stuff the main difference in build was that the gearcase casting was thinner .

A couple of months back a guy was on here building a monster motor for his boat , that if memory serves me was very similar to yours , I can't remember his HP number but it was over 600hp and I asked him to keep us up to date with how things went and ran in the end.
I was thinking in terms of the driveshaft safety coupler failing with that much power.

HONESTLY the physics are the limiting factor, and the physics cannot be reasoned with or negotiated with. Period.

IF your hull was "40 hp shy" of lifting up onto one more strake or chine, then it would be worth pursuing that increase. Increments like that deliver results because you have several points in the hull's operational range where pushing just a little harder will get you up over another hump. We're all familiar with the spot where you're transitioning from "pushing water" to "planing" on top if it. That's a huge hurdle that delivers in spades. If you ever lose an engine in a twin while running 35mph you might be able to maintain that 35mph (or more) on the remaining engine. But if you stop to figure out what broke, and you're 20 miles from the nearest launch ramp you will be very sad to discover that your single engine will not be enough to plane the boat and you'll have to heas towards the ramp at 6mph.

Well, your hull has several lifting strakes thar represent smaller increments of reducing the wetted surface and friction as speeds increase.

Once your hull is running on the last set of strakes that will support it at speed, the only thing that reduces hull friction at that point is riding higher which lessens the effective frictional length of the wetted surface. These inscreases come with a parabolic relationship beyween added power and additional speed.

You can WANT more, but just because you feel your desired outcome is totally reasonable, the physics dont give a damn about what you think.

So HERE is a suggestion for you.
Remove everything from the boat that can be lifted out or uncoated. All the seat bases, hatches, doors, accessories, potty, tools, spare clothes, dock lines, anchors, etc. If you have a freshwater system, drain it. Bimini top? Take it off the boat. Two batteries? Leave one in the garage. Run the fuel level down below 1/4 tank.
Take the windshields off. You should have a pile of stuff weighing about 400 pounds or more.

Go run the boat on a clear day with very light chop. Run upwind and turn around. Run wide open WITH the wind wide open and toy with trim to find best GPS mph. Record the speed, the rpm, and the trim angle. As long as your engine rpm was not above 4900rpm, this test just showed you what your boat will do with 100 more hp with those things installed.

If you end up revving over 4,900 then you will need to increase prop pitch to see legitimate results.

This is the best, most accurate, FREE and totally reversible merhod of determining if you really want to add power to your hull.

Sounds like a great idea Mcollinstn. We've all "unloaded" the boats somewhat, but not to that extent. Sounds like a good way to tell for sure before adding the power.

I would love to have the time, energy, and ability to turn the boat over and play with different hull surface stuff. I've heard sanding at 45 deg angle, sharpening the strakes to a very sharp edge, even putting a tiny wedge across the back edge of the hull where the transom is(say 3/6" or so ) to help lift the boat, etc, etc,

One thing i experienced many years ago.... We had a "performance" knee board that had had half moon indentions all over the bottom every 3 to 4 inches. Like if you took a tennis ball and cut off 1/5 of it. Say 3/8" deep x about 1 1/2" diameter. That board glided FOREVER. We stopped using it because it was so slippery you couldn't hardly turn it. So it would be interesting to know if this would work on a v hull. Just on the back running surface when running fairly hard, say the back 5 or 6 ft just between the strakes.

Anybody have actual experience sanding or trying anything on the hull??

if you want to look at the exhaust or see if there is any thing else in the pile of parts you may need feel free to give me a call on my cell during the day (no cell service at home) 954-270-2628 (still have a fla cell). parts are at the shop I work at in Clermont between Gainesville and Cleveland on hwy 129.
thanks
steve

I had the boat that the 256 replaced for 15 years. 2004 260 SSi with a 496 MAG/Bravo III. Best it saw GPS was 53 MPH. Nicknamed it the Fat Ba$tard as my 6K LB Poly Lift would sink if the boat was full of gas and I stepped onto the boat. Had to get an 8K lift for it eventually. Here are a couple pics to show what he's up against hull-wise that will limit gains from tossing a bunch of HP at it. The two boats share the same hull design. There is a whole bunch of rounded surface area with a lack of lifting strakes on these hulls.

https://cimg6.ibsrv.net/gimg/www.off...5c67f7ab1a.jpg
https://cimg7.ibsrv.net/gimg/www.off...0512bb61d5.jpg

I've spoken my peace about modifying this boat, which is a good looking Chap, by the way.

I've had Volvo's and DP's in my previous two boats which were Cobalt's. I can attest that the DP's are tough! I was enjoying a WOT blast down the local river when I t-boned a submerged log at top speed. The boat made a slight jolt but kept on going. Back to the ramp quickly to see what happened. The Skeg was gone and the prop set was mangled to the point where I had no idea how it was producing thrust or wasn't shaking itself to death. Repaired the prop set, new skeg welded on, and some paint and it looked brand new. That drive never gave me an ounce of trouble. No leaks, smooth shifts, etc. The VP motors are pretty much pulled off of the GM assembly line painted orange and given a marine ECM more or less. So they aren't fussy and have some nice features like the sea pump and fresh water flushing. Easy access to just about all service points.

Good luck finding more speed. I like the idea of ditching as much weight as you can.

Your reply triggered a distant memory from a time when I had a Corvette. This was about 10 years ago... bone stock 2005 Corvette with the 400hp LS2 in it. It had a tune and mild mods done to it and made 396rwhp.

I had a guy roll up behind me one time in a 4dr Honda Accord. As we approached a traffic light (just the two of us) he ducked over into the lane next to me and lined-up at the red light. I thought this was suspect and immediately figured "game-on" this dude wants a piece of my Vette...
Light turns green and this SOB in the Accord took off like a bullet. I reeled him in and drove past him... but not without sweating it a bit. The little Honda must have been a turbo car because I barely caught and passed him.

Anyway... that night the search for a supercharger began.
I ended up with an A&A supercharger @ 12psi, Alkycontrol Meth injection kit, Fast LS2 intake, Stainless Works 1-7/8" headers, cat deletes, 3" dual exhaust and Flowmaster mufflers.

On the chassis dyno at Race Proven Motorsports it made 636rwhp.

All because I almost lost to a Honda.

True story.

Yes... that looks like the same hull underneath...