Help!! 3,000 RMP @ 44MPH!! Please

[redducati]

I have a 2004 tahoe q7 with a 5.0 ,350 ,mercruiser alpha 1, 220HP with a mercury vengeance 19p prop. At full speed(cell gps) 44mph and the rmp are @ 3k. My lake Elevation is 6,600 feet. If I put a 17pitch will I get the RPM to 4,500?.Can I use it or this unsafe for the engine? On top of motor it says . WOT RPM Range 4400-4800. all cheack my gear ratio when I get home

 

[pauleqer]

Re: Help!! 3,000 RMP @ 44MPH!! Please

Not an expert but i would check out the tach or possible engine problem... A 19p prop should turn way more than 3000rpm, that is unless the outdrive has been replaced with odd gears.

 

[oops!]

Re: Help!! 3,000 RMP @ 44MPH!! Please

i am thinking that this is an out drive ratio issue....

44 mph at 3k is well......unusual for any boat.

is your wot 3k?

 

[Don S]

Re: Help!! 3,000 RMP @ 44MPH!! Please

Either the speed is wrong, or the RPM is wrong.
1" of pitch is going to get you a change of around 200 rpm + or - not the 1600 rpm you need.

 

[redducati]

Re: Help!! 3,000 RMP @ 44MPH!! Please

i am thinking that this is an out drive ratio issue....

44 mph at 3k is well......unusual for any boat.

is your wot 3k?

at full speed never gets passed 3k rmp,I think it needs to be regear for My Elevtion?? Can I wait till winter and use it the way it is?
On Airclear it says WOT RPM Range 4400-4800.The boat came from a Elevation of: 1,291 ft and I'm at 6,700 ft.

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

at full speed never gets passed 3k rmp,I think it needs to be regear for My Elevtion?? Can I wait till winter and use it the way it is?
On Airclear it says WOT RPM Range 4400-4800.The boat came from a Elevation of: 1,291 ft and I'm at 6,700 ft.

gearing has nothing to do with elevation. Some may have to retune(rejet, etc) their motors for elevation, but drive gears are not in any way affected by air density.

I would verify the tach first. You need to know for sure what rpm you are running, to be sure that you're not lugging your motor.

 

[redducati]

Re: Help!! 3,000 RMP @ 44MPH!! Please

FYI!! Gear is 1:62

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

http://www.rbbi.com/folders/prop/propcalc.htm

using your gearing and 19p prop (assuming 10% slip)....you would theoretically be running 30mph. Your tach is probably wrong(assuming you're positive about the gearing)

 

[redducati]

Re: Help!! 3,000 RMP @ 44MPH!! Please

gearing has nothing to do with elevation. Some may have to retune(rejet, etc) their motors for elevation, but drive gears are not in any way affected by air density.

I would verify the tach first. You need to know for sure what rpm you are running, to be sure that you're not lugging your motor.

When I called Lake Conroe Marine, LLC they said for high altitude I should run 1.81:1 gears and I have 1:62

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

I'm certainly no expert, so maybe the pros will chime in.

I'm curious as to hear why diff gearing would be suggested based on altitude.

From my limited knowledge, altitude should only affect the fuel mix being fed into the carb(or injectors etc). Computer controlled engines(automotive, marine, etc) would adjust the mix automatically. If a motor is carbureted....new jetting and adjustments would have to be done manually.


Regardless....using the gearing and prop pitch you provided....your tach is probably giving you a false reading of 3000rpm.

 

[steelespike]

Re: Help!! 3,000 RMP @ 44MPH!! Please

At 6600 I think your power is down 18-20% even if you have fuel injection or rejet.
So your down to about 175.
If your going to be there permanently a gear change will help make that up.
If not a prop will help
At 200 rpm per inch if you go down about 5" to a 14" prop. You should approach 4200.
Enough for a visit. Theres more choices in a 13".

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

At 6600 I think your power is down 18-20% even if you have fuel injection or rejet.
So your down to about 175.
If your going to be there permanently a gear change will help make that up.
If not a prop will help
At 200 rpm per inch if you go down about 5" to a 14" prop. You should approach 4200.
Enough for a visit. Theres more choices in a 13".

The OP's numbers are not computing using the prop calc. 44mph @claimed 3000rpm on a 19p prop. I wouldn't change a thing til speed/rpm are confirmed. A 13" prop seems awfully small for that motor.

 

[redducati]

Re: Help!! 3,000 RMP @ 44MPH!! Please

The OP's numbers are not computing using the prop calc. 44mph @claimed 3000rpm on a 19p prop. I wouldn't change a thing til speed/rpm are confirmed. A 13" prop seems awfully small for that motor.

I put a cheap auto meter gauge and the rpm are at 3,350 . So OEM gauge is around 300 off. I don't know what to do,guess get a estimate on new gears.f&ck

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

I'm at a loss.

According to the prop calc.....you CAN'T be reaching 44mph with the numbers you're giving.

 

[redducati]

Re: Help!! 3,000 RMP @ 44MPH!! Please

I'm at a loss.

According to the prop calc.....you CAN'T be reaching 44mph with the numbers you're giving.

Yea cell gps and mph show 44mph....going to get a 14Pitch Friday and see if it works

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

Yea cell gps and mph show 44mph....going to get a 14Pitch Friday and see if it works

Hopefully, there are some Tahoe owner's who will chime in with what props etc they are running to give you some better guidance.

JMO, but your impatience could end up costing you money on props(and hurting your motor-by over revving it).

A motor running 3350rpm pushing a 19p prop with 1.61 gearing cannot be going 44mph. It's physically impossible. Even with near zero prop slip...you would be running 37mph max.

Your rpm's are wrong or your gearing isn't what you think it is or both.

If you get a 14" prop and your rpm are really higher than you think(which I suspect).....you will be seriously over revving your motor.

JMO

 

[Maclin]

Re: Help!! 3,000 RMP @ 44MPH!! Please

Interesting that a tachometer when set for a V8 reads 3300 rpm when connected to a V6 and the actual rpm is 4400.

 

[BonairII]

Re: Help!! 3,000 RMP @ 44MPH!! Please

Interesting that a tachometer when set for a V8 reads 3300 rpm when connected to a V6 and the actual rpm is 4400.

Also interesting when putting 4400rpm/1.61 gears/10% slip/ and 19p prop into the calculator = 44mph

http://www.youtube.com/watch?v=R2sdGmbLNwY

 

[fishrdan]

Re: Help!! 3,000 RMP @ 44MPH!! Please

I have a 2004 tahoe q7 with a 5.0 ,350 ,mercruiser alpha 1, 220HP with a mercury vengeance 19p (stainless steel) prop.

At 200 rpm per inch

I'd try a 15P aluminum, that should give you about 1200 RPM over the 19P SS prop, maybe 4500RPM WOT.

I had similar issues going up in altitude, could only get around 3500RPM with a 19P aluminum, swapping to a 15P aluminum brought the RPM's up to the low side of my WOT range.