Why so slow?

[d1mbu1b]

I hit a wall and I am breaking the boat back down.
Please let me know what you think might be causing the poor performance

It runs 68 mph gps at 4800 rpm
I expect to see around 75 mph @ 5200-5500

I figure you need about 375 HP to do 68 in a 22c
I should have about 475

I dont know if its a fine tuning issue or a major flaw somewhere.

here are the specs:
22c
sbc 385c.i. (383 040 over)
750 holley
edel air gap rpm intake
AFR heads, 10.7:1 CR
comp Xr270HR straight up
always > 6 lbs fuel pressure
15 inches at idle
0 inches WOT
curently at 30 degrees timing
volvo DP 1.68:1 wf8 props
motor should be at the very least least 450 hp, AFR advertises copmperable dyno sheet at 500hp



possible problems
. driver
. motor HP estimate
. motor problem
. outdrive swap
. outdrive


here is a pic of the outdrive in the merc hole

[VetteLT193]

What is your prop selection? (wf8 doesn't mean anything to me, but it might to others here)

[d1mbu1b]

What is your prop selection?
they are F8 props
volvo dp props dont go by pitch, dont know why

my guess would be it is probably comperable to a 25-27 in a 1.5:1 drive

[VetteLT193]

they are F8 props
volvo dp props dont go by pitch, dont know why
my guess would be it is probably comperable to a 25-27 in a 1.5:1 drive

If it's like a 'big eared' (Mirage style) Bravo 27P, it's too much. If it's like a big eared Bravo 25p, it's probably ok... if it's like a 27P Bravo Cleaver, probably also ok...

Anyone have a good 'translator' for duoprops?


Also, what's your exhaust?

[d1mbu1b]

Also, what's your exhaust?
gil offshore headers

[The Hedgehog]

Well the drag of the duo prop is not helping. They are typically several mph slower than singles at top end. It would be good to know how much slip you are getting but that setup is way out of my league.

[BUIZILLA]

my opinion is.... thats not too damn bad... pretty good actually... if you can drop to the next prop size or take the larger diameter one and drop it one size, you'll be doing all it can... I don't like the 10.7 CR with pump gas though, even at 30*... I wouldn't be so hard on yourself

[VetteLT193]

I agree with Buizilla...

AFR is in the business to sell a product. the setup they list as having 500 HP is probably on an engine dyno, running straight headers and no accessories. It was probably run and tuned for hours on end to squeeze the most out of it...

You have a good setup, probably spinning too much wheel... with a prop change I think you can get it into the low 70's.

[blackhawk]

Well the drag of the duo prop is not helping. They are typically several mph slower than singles at top end. It would be good to know how much slip you are getting but that setup is way out of my league.

Volvo duoprops are not any slower than a single prop.

I remember seeing a link to a nice chart that had the pitches of the props. I can't remember where it was though.

F9s are the highest pitch so you are one step below. My buddy runs 67-68mph with his F9s and he has a 1.95 drive. So that makes them about a 30 pitch. F8s are a little less. How much I don't know.

If they were 28s or so I would think you should be running faster IF the power is there.

[blackhawk]

Here you go. Some conflicting info but should get you in the ball park.

Looks like F8s are about 28-29 pitch which would put you in the 75mph range.

http://www.volvo.com/NR/rdonlyres/2D2F5550-D247-4F3D-BE18-B8D3E71BEAA6/0/Prop_guide_2005_2006.pdf

[blackhawk]

here is a pic of the outdrive in the merc hole

Just caught that part. Maybe the Volvo needs to have a higher/lower X?

Although the slip numbers seem to be decent.

I'm guessing the power isn't there.

[mrfixxall]

I hit a wall and I am breaking the boat back down.
Please let me know what you think might be causing the poor performance
It runs 68 mph gps at 4800 rpm
I expect to see around 75 mph @ 5200-5500
I figure you need about 375 HP to do 68 in a 22c
I should have about 475
I dont know if its a fine tuning issue or a major flaw somewhere.
here are the specs:
22c
sbc 385c.i. (383 040 over)
750 holley
edel air gap rpm intake
AFR heads, 10.7:1 CR
comp Xr270HR straight up
always > 6 lbs fuel pressure
15 inches at idle
0 inches WOT
curently at 30 degrees timing
volvo DP 1.68:1 wf8 props
motor should be at the very least least 450 hp, AFR advertises copmperable dyno sheet at 500hp
possible problems
. driver
. motor HP estimate
. motor problem
. outdrive swap
. outdrive
here is a pic of the outdrive in the merc hole


put the timing at 34 deg,,you loose a point of comperssion with alunimum heads because they dont hold the heat like cast iron heads do...it will be safe..ive been running mine at 34 with 10.2 compression....

also the cavation plate looks a little to high,,i believe it should be even with the bottom of the boat:confused:

[d1mbu1b]

If they were 28s or so I would think you should be running faster IF the power is there.

The big IF is right.

I think the motor is a creampuff.

I am going to pull the motor
make sure it has the parts I bought in it
and have it tested on the dyno.

Anybody know of a good dyno shop in Orlando/Daytona?

[d1mbu1b]

also the cavation plate looks a little to high,,i believe it should be even with the bottom of the boat:confused:

I thought that was odd too.
I researched the volvo and found it was designed with the same dimension
from the crank to the prop as the merc but who knows?
I measured 8.5 inches from the plate to the center of the prop and 6" from the bottom of the hull to the center of the prop.
Is 6" to small? (insert joke here)

What are the side effects when its too high?

The boat handles great in all respects.
way better than the alpha I replaced.
I would think it would start slipping or launching a rooster
but it does neither

when trimmed up enough to launch water it'll loose 5-10 mph

[blackhawk]

I thought that was odd too.
I researched the volvo and found it was designed with the same dimension
from the crank to the prop as the merc but who knows?
I measured 8.5 inches from the plate to the center of the prop and 6" from the bottom of the hull to the center of the prop.
Is 6" to small? (insert joke here)
What are the side effects when its too high?
The boat handles great in all respects.
way better than the alpha I replaced.
I would think it would start slipping or launching a rooster
but it does neither
when trimmed up enough to launch water it'll loose 5-10 mph

My X is 17" and my measurements are about the same as yours. My anti-ventilation plate is about 2-2.5" above the bottom of the boat and the propshaft about 6" below.

[The Hedgehog]

Volvo duoprops are not any slower than a single prop.
I remember seeing a link to a nice chart that had the pitches of the props. I can't remember where it was though.
F9s are the highest pitch so you are one step below. My buddy runs 67-68mph with his F9s and he has a 1.95 drive. So that makes them about a 30 pitch. F8s are a little less. How much I don't know.
If they were 28s or so I would think you should be running faster IF the power is there.

You sure about that? I think it all depends on the x-dim, prop depth, hull weight etc. Lots of blade=lots of drag. At least for the top end. Seen many cases where more blade = less slip at a cruise speed. But at high end not so much. That is why BIII's and Duo's are used on cruisers but seldomly on sport boats. That's why a 22 classic with a standard x likes a 3 blade. Throw a 5 blade on there and see what happens. It will kill it. Now put on a shorty, you will have less drag but will need a 4 blade. Sure I have heard about Duo's reaching into the seventies but you don't really hear about them hitting 80's and 90's (unless maybe a Blackhawk but that gets back to the surface piercing situation).

[blackhawk]

You sure about that? I think it all depends on the x-dim, prop depth, hull weight etc. Lots of blade=lots of drag. At least for the top end. Seen many cases where more blade = less slip at a cruise speed. But at high end not so much. That is why BIII's and Duo's are used on cruisers but seldomly on sport boats. That's why a 22 classic with a standard x likes a 3 blade. Throw a 5 blade on there and see what happens. It will kill it. Now put on a shorty, you will have less drag but will need a 4 blade. Sure I have heard about Duo's reaching into the seventies but you don't really hear about them hitting 80's and 90's (unless maybe a Blackhawk but that gets back to the surface piercing situation).

Positive. Bravo 3s and the Volvo Duoprops are two totally different animals.

All things being equal(same hull, X, etc) I have seen first hand a Duoprop with F-series props be just as fast as a single prop. If there is more drag it is offset by more efficiency.

There are a lot of fast Batboats out there running the DPX drive.

[BigGrizzly]

I re3member Trailer boat did an artical years ago using sam boats same power one with a merc bravo, one with a duo prop and merc with 2 props not a blackhawk. the twin props were within 1mph of each other but the standard drive was 3 mph faster. Last week a pontoon boat with a hp500 was tested on this lake it was suppose to do 60 according to paperwork, guess what 52 was all she wrote, The original Black hawk brochure said it would 85mph not true either so don't believe everything you read.

[MOP]

I think what you are running into is the cubic inch wall, I run a 383 it is real good low to mid then starts to peter out up top. It had decent torque figures but the little inches just can't pull the torque up high. With the cam you are running I would try to spin it up to around 5200 that should give you some, also bump the timing up to 34 like MFA says.

[The Hedgehog]

Positive. Bravo 3s and the Volvo Duoprops are two totally different animals.
All things being equal(same hull, X, etc) I have seen first hand a Duoprop with F-series props be just as fast as a single prop. If there is more drag it is offset by more efficiency.
There are a lot of fast Batboats out there running the DPX drive.

What makes them so different? The hydrodynamics look basically the same.

I was aware that Batboats (with the Ocke Mannerfelt hull) ran them. I was not aware that there were a bunch of them even out there.

It may be just as fast in an application or two but overall I think not. I can tell you it is about 4 mph slower on a 27ZX.

More surface = more drag. Period. It also applies to the air. As a matter of fact some air force studies show that a single blade prop is the most efficient. It was odd and had some weird characteristics but was the most efficient.

Yes, I do think that Volvo makes a fine product, just not faster.

[MOP]

Ruling out the parasitic drag thing it takes more HP to turn the drive its self, I think Mr.X said 30 to turn a Bravo good chance a dou takes closer to 40.

[Last Real Texan]

Somebody get me some popcorn...


Bryan

[mrfixxall]

Correct me if im wrong but dont you want your boat to ride on the cavatation plate of the drive? If the x factor is to high wont the boat ride lower in the water which will slow you down?(plowing effect) if the drive is deeper in the water wont it bring the boat out of the water (higher)
ask the professionals ( volvo penta ) also see if they have a 2'' drive spacer and the coupler..

l r t popcorn on the way:wink:

[gcarter]

[QUOTE=Big Green ZX;420296
More surface = more drag. Period. It also applies to the air. As a matter of fact some air force studies show that a single blade prop is the most efficient. It was odd and had some weird characteristics but was the most efficient.
Yes, I do think that Volvo makes a fine product, just not faster.[/QUOTE]

Interesting observation about the single blade prop....but it doesn't necessarily transfer to boat propellors. Granted submarines use long thin curved blades (similar to some super efficient aircraft propellors) but they operate at essentially "0" slip and at only 5 knots or so.
According to Dave Gerr N.A., on a boat the prop w/the most metal that comes nearest to filling in the circle and with the fewest blades will be the most efficient. I don't know much about DuoProp drives and Volvo's props, but I too find the historic performance of the DPX drives very interesting. Every time I see one for sale on eBay, I get the itchy finger.

[The Hedgehog]

Interesting observation about the single blade prop....but it doesn't necessarily transfer to boat propellors. Granted submarines use long thin curved blades (similar to some super efficient aircraft propellors) but they operate at essentially "0" slip and at only 5 knots or so.
According to Dave Gerr N.A., on a boat the prop w/the most metal that comes nearest to filling in the circle and with the fewest blades will be the most efficient. I don't know much about DuoProp drives and Volvo's props, but I too find the historic performance of the DPX drives very interesting. Every time I see one for sale on eBay, I get the itchy finger.

I will agree with you that there is a big difference between hydrodynamics and aerodynamics. My point was really addressing parasitic drag. This is one of the principals of the surface piercing prop or a surface drive- to have less blade and less drag in the water. Having less lower unit in the water helps as well.

Alright, I will get off the prop drag soapbox. Wrong, right I don't care. I will say that this discussion is much more fun than the interest risk management report that I am trying to write!:eek!:

[blackhawk]

I'm not going to get into a technical discussion because I don't know the answers! :D I do know that generally the Bravo 3 is mounted lower and does not have performance type props.

I agree that 2 props SHOULD equal more drag and SHOULD equal less speed. All I know is real world results. 2 identical boats, one with a duoprop and one with a single prop and identical top-speeds.

And maybe in some situations a duo-prop is slower. But I would say 1-2 mph TOPS. Just my $.02.

Bottom line, in this thread, the power isn't there.

[blackhawk]

Correct me if im wrong but dont you want your boat to ride on the cavatation plate of the drive? If the x factor is to high wont the boat ride lower in the water which will slow you down?(plowing effect) if the drive is deeper in the water wont it bring the boat out of the water (higher)
ask the professionals ( volvo penta ) also see if they have a 2'' drive spacer and the coupler..
l r t popcorn on the way:wink:

It's my understanding that you want the anti-ventalation plate out of the water at speed. If it's in the water it's creating drag and slowing you down. The plate is there to keep air away from the propeller so it doesn't ventilate in slower turns and when getting on plane.

[blackhawk]

Correct me if im wrong but dont you want your boat to ride on the cavatation plate of the drive? If the x factor is to high wont the boat ride lower in the water which will slow you down?(plowing effect) if the drive is deeper in the water wont it bring the boat out of the water (higher)
ask the professionals ( volvo penta ) also see if they have a 2'' drive spacer and the coupler..
l r t popcorn on the way:wink:

It's my understanding that you want the anti-ventalation plate out of the water at speed. If it's in the water it's creating drag and slowing you down. The plate is there to keep air away from the propeller so it doesn't ventilate in slower turns and when getting on plane.

Some Cats and newer stepped hull boats have the propshaft even with the bottom of the boat. Putting the anti-ventilation plate 8-9" above the bottom of the boat!

[The Hedgehog]

I'm not going to get into a technical discussion because I don't know the answers! :D I do know that generally the Bravo 3 is mounted lower and does not have performance type props.
I agree that 2 props SHOULD equal more drag and SHOULD equal less speed. All I know is real world results. 2 identical boats, one with a duoprop and one with a single prop and identical top-speeds.
And maybe in some situations a duo-prop is slower. But I would say 1-2 mph TOPS. Just my $.02.
Bottom line, in this thread, the power isn't there.

Whether it is 2 or 5 mph I do agree that the power is not there. I agree that 450hp in a small block should push a Classic 22 nicely above 70 whether it has one or two props.

I also agree that talking about this is way more fun than the report I just finished!

[oldandtired]

You are definitely over propped. The pitch has to come down to get your engine into its power band. Check your speed versus the hp that engine makes at 4800 and see if that's in the ballpark. That will give you a better idea if your setup is in the ballpark. I would guess that if that engine makes 450 hp at 5400, it probably makes less than 400 at 4800. The hp numbers are at the crank which means that you are going to have somewhere around a 10% driveline and accessory loss as well. I think that your timing is conservative, but that's safe, not necessarily fast, but safe.

Rene

[blackhawk]

You are definitely over propped. The pitch has to come down to get your engine into its power band. Check your speed versus the hp that engine makes at 4800 and see if that's in the ballpark. That will give you a better idea if your setup is in the ballpark. I would guess that if that engine makes 450 hp at 5400, it probably makes less than 400 at 4800. The hp numbers are at the crank which means that you are going to have somewhere around a 10% driveline and accessory loss as well. I think that your timing is conservative, but that's safe, not necessarily fast, but safe.
Rene

IF the power is there he should be able to spool the F8s to 5100-5200. Now, if he needs more rpm then he will have to go down in pitch.

That being said if you have access to smaller props give them a try. What looks good on paper doesn't always work in the real world! :D

[BUIZILLA]

if it was me..... i'd find a F6 front prop and leave the rear as an F8, if that doesn't get you to 5300, then go to an F7 rear and leave the F6 front...

[blackhawk]

I'd REALLY like to know what props Tony Sporer is running...

Are you talking about Tony from Michigan that runs the 1996 22 Classic with the 454 and DPX drive? If so unfortunately the DPX runs different props than the DPS drive.

[VetteLT193]

I got a chance to look at the chart that Mrfixxall posted... I gotta ask a couple of dumb questions.

How many times did you test, how long were you at top speed for, and what were the conditions? What kind of GPS, and how old is it?

It seems, according to Volvo's chart anyway, that you should be running 70+ at 4800 RPM with those props.

If it is an old GPS, it could have not 'caught up' with you. Also, are you confident in your tach?

[oldandtired]

Regardless of what the actual peak horsepower number is, the engine needs to see peak hp rpm to achieve max power. Propping down or finding why the engine isn't making power are the only ways to do that. Also, exhaust seems to be soon on your shopping list.

Rene

[d1mbu1b]

Also, exhaust seems to be soon on your shopping list.
Rene
Yes I am waiting for a cheap set of used CMI's to present themselves.
The gil setup looks nice but the runners are very short.

[d1mbu1b]

thanks to everybody for there help,
I really appreciate all the ideas
keep them coming.
I will try to address all the questions.

I hope I am driving it wrong.
but I'm taking it to the dyno for sure.
I just have to find one near by.
any suggestions?

I am not confident on the tach at all.
Especially since it reads half RPM some times (very infrequent)
when it is reading correctly it sounds right.
1 grand sounds like one grand and 3 grand sounds like three grand
BUT the motor never came alive the way you would expect it to sound when you open it wide open, you know what I mean.


The speedo is a new marine auto meter in dash analog with the GPS receiver in the antenna.

more importantly the props are f8s but have been ruined by a local hacker and repaired by frank and jimmies prop shop.
I had an earlier thread where the big front prop actually warped on me and made the boat faster.
The guy that hacked the props up put cupping in them which frank and jimmie's says is a big no no for duo props.

I believe they may have had to decrease the diameter slightly to fix some of the bad cupping that were put in them.

I think this because the rpms came up more than the speed.
It went from 60 at 4000 to 68 at 4800, before and after prop repair

they told me they have to be a matched set and cannot interchange volvos like you can bravo IIIs

I have spent a lot of time tuning this thing and nothing seems to help
it always performs the same no matter what I do.
I changed timing, three different carbs, mixture, over and over and it always ran the same and hit the same wall.

I always ran the boat in calm to about 1.5 ft chop.
I stayed wide open for time on end playing with the trim.
one funny thing i found is that I had to trim past optimal and come back down to get faster. weird huh?
maybe it let the motor build more RPM


I am hoping a professional can dial it in for me on a dyno.

Does this make any sense:
One other thought I had was to retard the cam a couple degrees to sacrafice some low end power (which I have more than enough of) for top end power then this will allow me to run more timing safer since the IVC will be later and have less cyl pressure. It is supposed to be straight up now. That will have to be checked too

The cam comes with 4 degrees advance built in.
should I have left it at the 4 degrees advance and not installed straight up?
but like I said who knows where it is I did not double check the engine builders work.


One more... This motor never has any signs of detonation no matter what i did running lean rich advanced retarded.,.. this makes me think the engine is not built to spec too.

[blackhawk]

I would verify the tach asap. You may be running less rpms than you think. It's tough to "hear" the difference between 4200 and 4800.

After that try to find some similar unmolested props.

[BUIZILLA]

they told me they have to be a matched set and cannot interchange volvos like you can bravo IIIs I really don't think this is true, but I could be wrong.... we do work for a 6 boat Parasail operation on Paradise Island that runs Volvo TAMD42A diesels with duo props, another two boat Parasail operation in Islamorada, and also Holland America Cruise Line that owns Half Moon Cay island in the Berry islands uses them for passenger ferry's, and I know for a FACT they all swap props around like I stated before...

[mrfixxall]

Southern style racing,,talk to George pils he will treat you rite...around tampa area...727-546-7000

[d1mbu1b]

and I know for a FACT they all swap props around like I stated before...

I didn't mean to dimiss your suggestion.
Just a little overwhelmed at the moment.
When I get the chance, I will definitely give it a try.

the problem is that there so expensive.

[d1mbu1b]

Southern style racing,,talk to George pils he will treat you rite...around tampa area...727-546-7000
props or dyno?

[blackhawk]

I didn't mean to dimiss your suggestion.
Just a little overwhelmed at the moment.
When I get the chance, I will definitely give it a try.
the problem is that there so expensive.

I know you're overwhelmed with all this info but don't start mismatching props until you try a stock set.

You need to set a baseline with unmolested props and accurate tach readings.

Once you get a good baseline you can start making changes.

[Last Real Texan]

My popcorn now nees some butter......


Great debate on drives and such, good luck getting it sorted out.


LRT

[mrfixxall]

props or dyno?

engine dyno..

LRT butter on the way,,,HEs going to need it

[VetteLT193]

thanks to everybody for there help,
...
BUT the motor never came alive the way you would expect it to sound when you open it wide open, you know what I mean.
The speedo is a new marine auto meter in dash analog with the GPS receiver in the antenna.
more importantly the props are f8s but have been ruined by a local hacker and repaired by frank and jimmies prop shop.
I had an earlier thread where the big front prop actually warped on me and made the boat faster.
The guy that hacked the props up put cupping in them which frank and jimmie's says is a big no no for duo props.
I believe they may have had to decrease the diameter slightly to fix some of the bad cupping that were put in them.
I think this because the rpms came up more than the speed.
It went from 60 at 4000 to 68 at 4800, before and after prop repair
they told me they have to be a matched set and cannot interchange volvos like you can bravo IIIs
...

Have you checked to see if the throttle opens the carb all the way up:wink: (trying to add some humor here!)

You really need to look at what you have, and have realistic expectations. Companies advertise BS all the time about horsepower this, horsepower that... but they never seem to give you all the facts you need. You can't even tell if the engine even had a water pump hooked up to it during the dyno run. This can make huge real world differences in power Vs. what the company claims. You can definitely count on no extra accessories like alternator and power steering pump.

My opinion is 425HP is very realistic; 450 can be tweaked out of it.

The props you have need to go. Get a fresh set. I don't mean offense to the company, but I feel like frank and jimmies are more specialists in bigger wheels at lower speeds (big sport fishers come to mind in their area). I know they do a lot of work on smaller stuff too, but I don't know how much they do in the high performance category.

My prop is too big, and I know exactly what you are hearing/feeling. I have a 'big eared' mirage, and it's just too much for the engine... I am betting a size down in prop size will make a big difference.

BTW, I grew up in the Melbourne area (Sat. Beach) and know the waters there very well:cool:

[BigGrizzly]

This is pretty simple to make horsepower you either have more bangs or bigger bangs. Your horse power and where the torque is too high, and I really doubt if you have 450 hp. The mph numbers are typical 383 22 Donzi speed numbers.

[The Hedgehog]

Positive. Bravo 3s and the Volvo Duoprops are two totally different animals.
All things being equal(same hull, X, etc) I have seen first hand a Duoprop with F-series props be just as fast as a single prop. If there is more drag it is offset by more efficiency.
There are a lot of fast Batboats out there running the DPX drive.

You mean Batboats like this. I found this in front on my hotel tonight. I went looking for the ole Duo Prop but found this instead. True story!

Alright, I know that this is beating a dead horse and the comment is tacky. It was sort of funny to see an actual Batboat in front of your hotel after you get back from dinner and drinks. Especially in Jacksonville Il! It looks pretty fast

[BRIAN73]

Hi,

Definately get your engine dynoed, you will be quite surprised.

I built a 383 almost identical to yours with a 270 marine cam 10.1comp, sportsman 2 heads,holley double pumper,msd ignition, stainless marine exhaust and on the dyno with the marine exhaust and bravo style water pump , it came out at 364hp.

I changed the heads, cam, intake and carb and it dynoed out at 458hp with marine accesories on. And the engine idles at 650rpms

The dyno shop said that with a set of true headers, I would be right around 500hp.

I'm not trying to offend anyone, I have just been there and it is sucks.

Brian