Tahoe 2007 Q7i Prop Question

[On the water]

I have a Tahoe 2008 Q7i (22 feet in length and about 3500 pounds dry weight) and am looking to switch props in order to get a better hole shot for wakeboarding and skiing (our primary reason for having the boat). The current prop is a Tahoe OEM Mercury aluminum prop, which I believe it is a 21 pitch prop but I have been unable to verify this. I do have the serial number from the prop (832832A45P21) but a google search hasn't been very helpful - other than this where do I look (sorry, I don't have much experience with prop stuff)? The engine is a 2008 Mercruiser, 220HP (carb) connected to an alpha 1 outdrive.

I would appreciate any advice.

Thanks in advance!

 

[Bondo]

Re: Tahoe 2007 Q7i Prop Question

I have a Tahoe 2008 Q7i (22 feet in length and about 3500 pounds dry weight) and am looking to switch props in order to get a better hole shot for wakeboarding and skiing (our primary reason for having the boat). The current prop is a Tahoe OEM Mercury aluminum prop, which I believe it is a 21 pitch prop but I have been unable to verify this. I do have the serial number from the prop (832832A45P21) but a google search hasn't been very helpful - other than this where do I look (sorry, I don't have much experience with prop stuff)? The engine is a 2008 Mercruiser, 220HP (carb) connected to an alpha 1 outdrive.

I would appreciate any advice.

Thanks in advance!

Ayuh,.... Answer these questions, 'n We'll see what We can do...

 

[On the water]

Re: Tahoe 2007 Q7i Prop Question

Apologies, I tried to put the answers in the body of the paragraph, but here we go.

1) Performance issue you are trying to correct. - better hole shot for wakeboarding and skiing
2) Current prop manufacturer, model, aluminum or stainless as a minimum. - Mercury aluminum
3) Current prop diameter and pitch (required). - Not sure, I believe it is a 21 pitch prop but I have been unable to verify this. I do have the serial number from the prop (832832A45P21)
4) Wide open throttle RPM and speed with an average load (very helpful) WOT RPM 6500, speed 48 mph (on dash speedo)
5) Engine/drive make, model, year, and HP - 2008 Mercruiser 5.0L, 220HP (carb) connected to an alpha 1 outdrive
6) Boat make model, year, length and weight - 2008 Tahoe Q7i, 22 feet in length and dry weight of 3500 pounds


Thanks again for your help!

 

[jestor68]

Re: Tahoe 2007 Q7i Prop Question

Is that WOT rpm of 6500 a typo?

 

[On the water]

Re: Tahoe 2007 Q7i Prop Question

Yes, apologies. It should have been 5600, which is what reads on my tach.

 

[Bondo]

Re: Tahoe 2007 Q7i Prop Question

Yes, apologies. It should have been 5600, which is what reads on my tach.

The engine is a 2008 Mercruiser, 220HP (carb) connected to an alpha 1 outdrive.

Ayuh,... I'm thinkin' the Wot rpms for that motor is 4600/ 4800 rpms....

That far off, I'm guessin' the Tach is flaky...

 

[jestor68]

Re: Tahoe 2007 Q7i Prop Question

Your WOT rpm range is 4400-4800 for the base 2008 5.0(220hp) with a 1.62 gear ratio.

I too think that the motor shouldn't be capable of that much rpm swinging a 21" prop.

Try pulling the plug on the back of the tachometer and cleaning the (3?) pins on the connector.

 

[On the water]

Re: Tahoe 2007 Q7i Prop Question

Thank you each, I will clean the connector and let you know. Given the stock specs mentioned, is there a recommendation for a different prop for a better hole shot?

 

[saintv90]

Re: Tahoe 2007 Q7i Prop Question

wouldnt you just go down in prop pitch for more pop out of the water? Maybe a 19p or a 20p stainless.

 

[theBrownskull]

Re: Tahoe 2007 Q7i Prop Question

Try the 19 pitch and see how that goes.

 

[jestor68]

Re: Tahoe 2007 Q7i Prop Question

I will reserve a recommendation until we're confident the rpm reading is accurate. 5600 just doesn't sound right.

We may end up recommending a 17" 4 blade; who knows.

 

[spdracr39]

Re: Tahoe 2007 Q7i Prop Question

I had this same setup in my old 2001 model and I had a 21p stainless three blade but the rpms were a little low. I would go with a 19p stainless or 21p aluminum but you really need to fix your tach first because that reading can't be correct with that prop.

 

[Maclin]

Re: Tahoe 2007 Q7i Prop Question

If the tach is set for 6 cylinders then the reading will be high by a 6 to 8 ratio (ok, 3/4). A 5600 rpm reading would be more like 4200. Interesting number because using a prop calculator with 4200 rpm and a 1.62 drive ratio hitting ~48mph and assuming 10% slip calculates a 21 pitch prop in use. These calcs seem to point to the tach being set for a 6 cylinder. Again, I had to assume the 1.62 ratio is correct and estimate 10% slip.

 

[On the water]

Re: Tahoe 2007 Q7i Prop Question

Thanks to everyone for the insight and recommendations. We very rarely (i.e. never) reach WOT. It just isn't something we find ourselves doing on the inland waterways where we mostly boat (Severn river, Maryland). Either to waves are too rough (and chop too high) or we are pulling skiers at a speed far less. It just isn't our regular practice to drive it all out. We do make it out to a few lakes over the summer where i can comfortably get to WOT and will left you know.

Again, thanks for your help.

 

[jestor68]

Re: Tahoe 2007 Q7i Prop Question

Thanks to everyone for the insight and recommendations. We very rarely (i.e. never) reach WOT. It just isn't something we find ourselves doing on the inland waterways where we mostly boat (Severn river, Maryland). Either to waves are too rough (and chop too high) or we are pulling skiers at a speed far less. It just isn't our regular practice to drive it all out. We do make it out to a few lakes over the summer where i can comfortably get to WOT and will left you know.

Again, thanks for your help.

You may be missing the point of propping to achieve that WOT rpm range. It is insure good all around performance. It really doesn't have that much to do with running wide open all time. The engine must be propped to run within it's WOT rpm range to insure it's longevity.