warbled prop = +5 mph

[d1mbu1b]

here are the facts, as i see them:

. I have been stuck at 62 mph (GPS) at 4200 RPM with the new build for some time.
. Volvo DP 1.68:1 F8 props, SBC, 3.75x4.040~385, afr heads, comp 270, 10.5:1 cr
. no matter what I changed, timing, mixture, weight it always went to 62 with ease and stayed there
. the boat has great torque down low and rips right out of the water
. the motor is built for Torque peak ~4500 and HP peak @ ~6000

just the other night the boat started to come alive, it was calm and warm, which are sub optimal conditions for best speed.

it did 67 (gps) at 4500

when i put it back in the slip one blade on the prop was wiggly!


The props were cupped, the prop guy did them with out the use of a computer (prop MRI?). I am told now that it is not possible to work dou-props by hand.
Is this true?

Also the prop guy said he had to lift one blade considerably.
Can you weaken a blade by doing this?

Is it possible the props are fighting each other?
Is it posible one blade lost the fight?

Or did I just get stupid lucky and hit something making the boat go faster?
The prop damage is smooth and oscilating not dented???


In any event I plan on sending the props to Frank and Jimmies in Ft Lauderdale and bring them back to stock.
They seemed nice enough on the phone.

Any suggestions or theories?

[Johntrip]

I think most will tell ya that the cold weather is better conditions for engine performance. My best top end speed was in 60 degrees dry climate with a chop in the water....

[MOP]

My opinion you need a good prop shop that can lessen the pitch by about 2", you say your best torque is @4500 I would shoot for about 4800 as top rpm. I would not run those props until fixed.

Phil

[BigGrizzly]

If that prop did that and you did not feel it happen there is a problem. I would get them off before a blade comes off. Any way some guys are good enough to do props on single prop applications but duo prop I would be leery.

[oldandtired]

I think that your props are waayyy off. You need a lot less pitch. Since your hp peak is at 6000, I would shoot for a fully loaded rpm of 5800. That should take you up to about 6k running light. You will definitely pick up a significant gain in speed. Right now you are running at peak torque which has got to be harder than necessary on you drive. Some say that you should prop for peak torque + 1000 rpm. I think that peak hp is the fastest place to run. You will also benefit from the reduced pitch in holeshot and acceleration. It seems like you should reduce pitch by 4-6". The props in the pic definitely need some work. Cup was a bad idea. Cup will reduce your rpm even more even though you may need it for bow lift. You are probably better off getting a new pair of props that are closer to the correct pitch than reworking those. The general rule of thumb that I have heard is that you can change pitch by 2". RPM generally changes by 200rpm per inch of pitch. Therefore, you need about 1300 rpm which equals around 6.5" of pitch. I'ld try between 4 and 5 first.

Just my opinion,

Rene

[BUIZILLA]

just curious here...

are the AFR heads aluminum or steel?? with a 10.5 comp rate I would hope they are aluminum, using current 93 pump gas, if they are steel your in uncharted waters with that setup... 5800 is wayyyyy past what I would spin that 270H grind too....

:wink:

[d1mbu1b]

this whole effort is "uncharted waters"

thanks for your replies.
here is more info...

I planned on running about 5200 wide open thats why I chose the comp XR270HR I did not want to over rev the outdrive and did not want to loose bottom end torque
Yes the heads are alluminum, zero decked, 0.041 quench, no sign of detonation yet, still dialing in carb issues. I installed a A/F ratio gauge too along w/ fuel pressure, oil temp, press., and manifold vacuum in the dash.

desk top dyno puts the peak HP @ ~5750 rpm, so who knows, there are no dyno's in Melbourne florida. AFR advertises comperable baselines at any where from 460 hp to 500 hp at 9.5:1 CR, ( I am at 10.5:1)
but we all know manufactures will tweek numbers to suit there needs.
http://www.airflowresearch.com/chevy_dyno.php

the F8 props are pitched for 75 mph at 5000 rpm
http://www.volvo.com/NR/rdonlyres/2D2F5550-D247-4F3D-BE18-B8D3E71BEAA6/0/Prop_guide_2005_2006.pdf

the motor "should" have enough between the heads and the CR once I get everything dialed in. but its been a pain given that everything is suspect.

This is all besides the point the question is why are the "warbled" props faster than before "warbling"? 62@4200 vs 67@4500 mph


I agree I should test the setup with less prop and dial the motor in first, but the problem with that is they are hard to come by. Its not easy to find a set of volvo duo props.
BTW there about $1500 new. and they will still need to be labbed anyway.
Hopefully, by taking that cupping out it'll make a few hundreed rpm difference and get me closer to 5000.

If anyone knows of a set of F6's or f7's for cheap, or a loner please let me know.
If anyone knows of a dyno in melbourne that would be great too

Respectfully,
Jeff

[mrfixxall]

here are the facts, as i see them:
. I have been stuck at 62 mph (GPS) at 4200 RPM with the new build for some time.
. Volvo DP 1.68:1 F8 props, SBC, 3.75x4.040~385, afr heads, comp 270, 10.5:1 cr
. no matter what I changed, timing, mixture, weight it always went to 62 with ease and stayed there
. the boat has great torque down low and rips right out of the water
. the motor is built for Torque peak ~4500 and HP peak @ ~6000
just the other night the boat started to come alive, it was calm and warm, which are sub optimal conditions for best speed.
it did 67 (gps) at 4500
when i put it back in the slip one blade on the prop was wiggly!
The props were cupped, the prop guy did them with out the use of a computer (prop MRI?). I am told now that it is not possible to work dou-props by hand.
Is this true?
Also the prop guy said he had to lift one blade considerably.
Can you weaken a blade by doing this?
Is it possible the props are fighting each other?
Is it posible one blade lost the fight?
Or did I just get stupid lucky and hit something making the boat go faster?
The prop damage is smooth and oscilating not dented???
In any event I plan on sending the props to Frank and Jimmies in Ft Lauderdale and bring them back to stock.
They seemed nice enough on the phone.
Any suggestions or theories?


if you get those props reworked just make sure the prop shop has the correct pitch blocks for those props or they will never be correct...

Do a google.com search, i thought i say a set on their somware for 800.00.

theirs a guy in lake havasu az thats his specialty! volvo dual props..His name is jonny gibbs propellers,dont have his # tho and i heard it takes forever to get your stuff back..

BTW it sounds like your running out of fuel...wot for a 1/2 mile then turn the ignition off...pull a front sparkplug and read it,if its white fatten her up.

good luck.

[oldandtired]

This is all besides the point the question is why are the "warbled" props faster than before "warbling"? 62@4200 vs 67@4500 mph

It seems to me that you knocked some pitch out of it allowing the motor to spin faster and putting more horsepower to the water. Take what you can out of the props that you have and see where that puts you. I would have a tough time swallowing a $1500 prop pill myself. I didn't realize that you were shooting for 5200 rpm. My prop pitch comment was based on 6k rpm peak hp. It still does seem like you are going to have to bring your pitch down by about 4" at least.

Rene

[oldandtired]

I just took a quick glance at ebay and found a couple of different sets. I don't know anything about the volvo terminology for pitch, but I saw F9,F7,F6,F5 and and F4. That may get you where you are going for a lot less. I have bought all of my props through ebay with no problems. Good luck,

Rene

[tmdog]

here are the facts, as i see them:
. In any event I plan on sending the props to Frank and Jimmies in Ft Lauderdale and bring them back to stock.
They seemed nice enough on the phone.
Any suggestions or theories?


Frank & Jimmy's is a good shop to use. Living in S. Fl in the 70's 80's and 90's F&J did all my prop work . Very satisfied and guaranteed work. By all means it is not a small shop.
As mentioned, 5200 would be my goal with your cam choice.