AQ225D/280 More pitch?

[PatinIdaho]

Boat and prop combo just does not feel/seem right. Hard to explain i guess but here is the set up.

18F Trihull
3500 rpm,
32mph(boat Speed'o forgot to check gps but im pretty sure its close enough)
4400 rpm Speed'o said 40mph
Prop is brand new Solas Amita3 cup. 15.5X17P
GR 1.61:1

At 4400rpm (Max recommended rpm)boat seems to hit a wall. Boat pulls good from idle to 4400 with no flat spots with plenty of power through the entire range
I'm thinking i could go with more pitch maybe 21P.
I do not pull skiers or tubes.
I sometimes just cruse the lake but usually race from one fishing spot to the next.

Worth trying more pitch or just stick with what i have?

 

[SkiDad]

I wouldn't go any higher than 19p. Try to stay with similar brand/style prop for a predictable result.

 

[steelespike]

Volvo numbers are pretty much a mystery to me.
Your numbers look really good. 9% slip. at 4400 and 40 mph. I'm always suspicious about boat speedos and tachs, really prefer gps.
As it stands I feel an increase in pitch will slow hole shot, top end probably a wash,could make it more of a struggle to maintain the usual cruising speed.
The 21 will make the motor work harder through the entire range. While it might be faster at some intermediate speeds it probably would require more throttle.
Actually it just occurred to me that your probably running a 4.3 or or similar seems like on a 18' it should be running a 19 or 21" at speeds approaching 50.
at 4400.
I'm thinking the motor may be older, a little tired or out of tune.

 

[SkiDad]

i believe his engine is a 305 V8

 

[Bondo]

Boat and prop combo just does not feel/seem right. Hard to explain i guess but here is the set up.

18F Trihull
3500 rpm,
32mph(boat Speed'o forgot to check gps but im pretty sure its close enough)
4400 rpm Speed'o said 40mph
Prop is brand new Solas Amita3 cup. 15.5X17P
GR 1.61:1

At 4400rpm (Max recommended rpm)boat seems to hit a wall. Boat pulls good from idle to 4400 with no flat spots with plenty of power through the entire range
I'm thinking i could go with more pitch maybe 21P.
I do not pull skiers or tubes.
I sometimes just cruse the lake but usually race from one fishing spot to the next.

Worth trying more pitch or just stick with what i have?

Ayuh,.... If the motor can only pull 4400 rpms with the 17" prop, the Wot Rpms will go Down, if ya increase the pitch,....

That'll induce luggin', 'n detonation, leadin' to a motor melt-down,.....

The motor runs into a wall at 4400 rpms, 'cause that's where it runs outa Horsepower,.....

 

[PatinIdaho]

Yes it's a 305 V8. running last falls regular gas with stabilizer and about 10gal fresh regular gas. Maybe i should start filling with premium?
Actually when i bought it last fall it had a 14.1/4X17P no Cup prop. Was a little beat up so i bought a new one. Some how i messed up and ordered the larger diameter prop. I did not worry to much as i read that diameter is not that big a deal so i figure not a problem. Anyway can't return it now anyhow.
I did use a hand held tach to verify the new boat tach. So boat tach is right on.
I can not vouch for the speedo as i forgot to check gps but i sure will next time out! and the speedo is brand new also.
Oh well. You guys convinced me to just keep it and use it. THANKS!

 

[steelespike]

Pretty sure your motor is rated for 87 octane. If you run a higher octane it actually makes it harder for the motor to burn it.
The higher octane is designed to resist pre ignition with a motor with higher compression.

 

[PatinIdaho]

Na. it calls for 91 octane

 

[Maclin]

Gotta look at the Octane requirement from the manual closely, to see if it is the RON method or the R+M/2 method. RON is Europe and rest of the world, while R+M/2 is USA and some other spots. They are different Typically a RON of 91 is the same as 87 in R+M/2.

My VolvoPenta 570/DP (same as AQ271C)) which is the carbureted 4bbl GM 5.7 V8, shows an Octane RON requirement of 91 and R+M/2 octane of 87. If the AQ225D is the GM 305 V8 then I bet the 87 available in the US is the Octane specified..

 

[Maclin]

My opinion on the prop pitch, is that the numbers you posted for WOT RPM's achieved and MPH seem to be close to ideal for that engine in that boat with that drive ratio and prop.

 

[Maclin]

The AQ225D is indeed the GM 305 V8, and the Volvo manual shows 91 octane in RN (Or RON=Research Only Number). Equivalent in the US method of R+M/2 is 87.

If you do not have a VolvoPenta Owner Manual for that engine and drive, try the link below. The VolvoPenta.com website has publications available for almost all of the "older" setups available free of charge there. Choose the country, then go to Parts and Service, then Publication Search. the type in the AQ series in the Engine number.

Anyways, see if this link gets to your manual, if so then you can hover the cursor on the bottom right to get a window that will give you a Save option so you can plop it onto your PC...:

http://pie.volvopenta.com/ViewFileFr...936&lang=en-US

 

[Maclin]

I am commenting on this here as some may not be aware of the differences in fuel octane rating. Volvo being a European company published the European typical numbers for fuel octane rating requirements first, and sometimes only those, in their manuals for the "older" stuff. Again, including this here for future researchers.

Octane rating method for gasoline has 3 basic methods worldwide.

One is RN or RON, which is Research Number or Research Only Number, same thing.
One is M or Motor method.
The 3rd method is not really a method all to is' own but is an average of those 2 numbers.

RON or RN is chemical analysis with no real running in an engine. Just lab experiments on a sampled fuel.

The M method uses an engine with very specific and configurable characteristics that affect the Octane it needs for combustion in a lab. The detonation events from actually adjusting and running it using the sampled fuel are measured and converted into the M octane number.

The R+M/2 method is the average of these 2 methods from the sampled fuel, In the United States this is the number most widely used to show the Octane rating of the fuel at the delivery point. Europe typically uses the RN (same as RON) number

 

[PatinIdaho]

"Fuel Grade
Use only high-octane premium petrol (gasoline) with an octane rating of at least 91(Research Number).
The engine can run be run on petrol without lead additives."

I cant find the info in the Volvo Penta factory manual i have.
This info is from the Instruction Book down loaded from Volvo Penta #7733450

I guess " 91(Research Number)" is the key to this and what i would suspect alot of us find confusing.

(Edit) Thanks Maklin that is the link to what i described above.

 

[PatinIdaho]

Ok so just a update for any one who posted.
My outdrive was trimmed in the last hole down. I did not think much of it as it was used and i assumed set up fine. Boat had great hole shot and got on plain within 2ish seconds and seemed to ride just fine.
Had a friend with me who just mentioned how flat my boat would run across the water so then i noticed it also. Was probably dead level from just on plane to what i thought was 40mph(not gps) just boat speed o.
So got a gps app and actually checked it. Was only getting 32mph at full throttle!. Bow had to be actually plowing water.
Pulled boat to shore and got in the COLD water raised out drive to last hole out.
Bow now goes kinda high when getting on plain and takes maybe 10 seconds to get on plain, rides slightly bow high now and not plowing water
Checked gps and still 32mph 4400rpm but boat feels better but why the same speed?.
Read that a large prop will also make more drag?. 15.5X17 cup
So out of curiosity i borrowed a 15x19 volvo penta brand prop that is slightly nicked up but usable.
Boat still handels the same but now top speed 4400 rpm is 40 mph(gps) NICE!! and you can sure tell the difference!!
And now for the BUT
Now it will rev past 5000 rpm. I don't know how far past as i back out of it because i don't want to blow it up. It is still accelerating pretty hard though.

Leave well enough alone and just watch the rpm's or would you suggest a different prop now?

 

[Maclin]

If you were lightly loaded on that last test then I think this is good advice...."Leave well enough alone and just watch the rpm's ..."

You know you have some headroom in the RPM's for experimenting later

 

[Maclin]

BTW thanks for that update. For the non-Volvo initiated, trimming is not as obvious a factor on those drives as power trim was an option and not standard. When they do not have power trim then the drive is in a fixed position, and you can only move the drive manually up/down by adjusting that locating pin, much like an Outboard with no power trim. The 280's all had power tilt but trim was optional. The 270's did not always have power tilt, yikes.

 

[PatinIdaho]

The load was a normal one for me. 3/4 tank of gas two people and fishing gear. No clue what the boat actually weighs. Heavy im sure being a old(1979) Trihull
Anyway thanks for the reply!