25p on my baja 208. 454efi/mp??

[butchmotors]

I have a 96 islander 208 with 454efi. currently Im running the stock 23p quicksilver. I was thinking the 25p would give me a higher cruising speed and maybe a little top end. Im not 100% sure where im running rpm wise due to a bad connection on the back of my tach. Does a 25p sound like to much? any advice would be appreciated before I purchase a prop that might suck..

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

Dude... the reality is that the RPM at wide open throttle is a MUST before the most seasoned expert can answer.

No way around it. Actually all the info posted in the 'sticky' at the top of the prop forum would be best.

On instinct alone: Not if she is stock from engine to the drive. You ain't got the HP or gearing to turn a 25p.

 

[Tail_Gunner]

Re: 25p on my baja 208. 454efi/mp??

Dude... the reality is that the RPM at wide open throttle is a MUST before the most seasoned expert can answer.

No way around it. Actually all the info posted in the 'sticky' at the top of the prop forum would be best.

On instinct alone: Not if she is stock from engine to the drive. You ain't got the HP or gearing to turn a 25p.

When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

Butch nice boat really nice boat..I know its annoying but as Phil said to get you smiling the info is needed. I know there are very inexpensive digital tach's some place...I believe you can reant one from Oriley's..I have a personal friend with a 26' Rinell for years he resisted doing the above...Finally got him on the water...That boat went from 54 to 62 and he still doesnt buy the beer..

But lets do this...25p @ 4800 with 1.50 gearing nets 76mph...@ 12% slip your at 67mph
And this...25p @ 4800 with 1.32 gearing nets 86mph...@ 12% slip your at 76mph

If thats aq Mag with a bravo drive your hunting...But there is know way of knowing if your combo can push that.

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

Butch nice boat really nice boat..I know its annoying but as Phil said to get you smiling the info is needed. I know there are very inexpensive digital tach's some place...I believe you can reant one from Oriley's..I have a personal friend with a 26' Rinell for years he resisted doing the above...Finally got him on the water...That boat went from 54 to 62 and he still doesnt buy the beer..

But lets do this...25p @ 4800 with 1.50 gearing nets 76mph...@ 12% slip your at 67mph
And this...25p @ 4800 with 1.32 gearing nets 86mph...@ 12% slip your at 76mph

If thats aq Mag with a bravo drive your hunting...But there is know way of knowing if your combo can push that.

Ok. Tomarow I will get a tach hooked up and see what Im running wot .I see your figuring 12% prop slip. Is that a good average amount of slip?

 

[Tail_Gunner]

Re: 25p on my baja 208. 454efi/mp??

One never know's until a solid aprroach is used...Other than that its a WAG

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

So I finally took my boat out yesterday but had four people on it. To my surprise It would only spin 4400rpm. I was doin 66mph.I previously gpsd this boat at 72mph with half the gas and people. I dont know when the efis make most power but 4400 sounds a little low. Hope this helps.

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

No way @ 4400 RPM and any gear ratio that I know of (within reason, such as a 1.5) will a 23P prop push a boat to 66.

@ 4900 RPM, you might sniff 63 on a 23p prop with a 1.5 ratio.


EDIT:

Well... if you run down river with a decent current, the GPS speed will be inflated by whatever the speed of the river current is. GPS runs require passes in multiple directions and averaging. If you were to turn against the current, I'd expect to see something like 54 MPH. 54+66 = 110 ; 110/2 = 60 MPH (and this sounds somewhat plausible).

@4400 RPM you were probably going less than 60, or just about 60, as speed over water, which is what matters.

Take a 60 MPH boat. Go down river @ 6 MPH current. GPS says 66.
Take a 60 MPH boat. Go up river against 6 MPH current. GPS says 54.

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

No way @ 4400 RPM and any gear ratio that I know of (within reason, such as a 1.5) will a 23P prop push a boat to 66.

@ 4900 RPM, you might sniff 63 on a 23p prop with a 1.5 ratio.


EDIT:

Well... if you run down river with a decent current, the GPS speed will be inflated by water the speed of the river current is. GPS runs require passes in multiple directions and averaging. If you were to turn against the current, I'd expect to see something like 54 MPH.

@4400 RPM you were probably going less than 60 as speed over water, which is what matters.

I was in lake ontario not the river and I took two passes .one each way.and no way 54 . I know the boat will do 70 no problem .I understand the speed over water is what im looking for but Ive never seen a very accurate speedo . The boat has a pretty flat bottom and only weighs 3500lbs

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

And it is a 23p prop with a 1.5 geared outdrive?

 

[Maclin]

Re: 25p on my baja 208. 454efi/mp??

Do we know the drive ratio? I think Merc put 1.32 ratios behind big blocks on Bravo I and II's ?

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

And it is a 23p prop with a 1.5 geared outdrive?

I have no clue ...boats sitting in the river

 

[Maclin]

Re: 25p on my baja 208. 454efi/mp??

Those last 2 posts were not in yet when I started mine, with a 1.32 then 70mph with a 23p at 4900 and 12% slip is possible.

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

Those last 2 posts were not in yet when I started mine, with a 1.32 then 70mph with a 23p at 4900 and 12% slip is possible.

I fixed the bad connection on the back of my tach. At idle it seems to be correct. It seems to act normal as rpms raise. Im pretty sure its dead on at 1000 rpms seeing this is the rpm Ive ben running for years for the 20mins it takes me to get out of the river. You think its possible the tachs just shot?

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

Those last 2 posts were not in yet when I started mine, with a 1.32 then 70mph with a 23p at 4900 and 12% slip is possible.

Yeah... I was hoping to hear the ratio, because I had it in my head it was 1.5, but I am jumping through too many threads and have a buddy on the side trying to prop his Nova.

1.32 would make sense. I like when it makes sense. lol

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

Yeah... I was hoping to hear the ratio, because I had it in my head it was 1.5, but I am jumping through too many threads and have a buddy on the side trying to prop his Nova.

1.32 would make sense. I like when it makes sense. lol

I also like when it makes sence . so I take it if I get a good gps speed over still water with a empty boat at 70. and reliable tach I can get an accurate prop slip % ?

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

yeah... with the gear ratio.

It's a must to do a calc, but we can determine the gear ratio (see Maclin) from all other info.

If your numbers are right, you cannot be running a 1.5 ratio, it has to be lower (Maclin).

There aren't infinite #'s of ratios. I had 1.5 on the brain. To run 70 with a 1.5, you have to turn a 25p prop. So... nevermind me. :redface:

 

[Tail_Gunner]

Re: 25p on my baja 208. 454efi/mp??

So I finally took my boat out yesterday but had four people on it. To my surprise It would only spin 4400rpm. I was doin 66mph.I previously gpsd this boat at 72mph with half the gas and people. I dont know when the efis make most power but 4400 sounds a little low. Hope this helps.

Time for a major tune up...Form 72 to 66 is quite a loss....While your at it id have the tach checked by a alternate source but the engine needs work...OK one last thing just how clean is the hull...A hull full of growth can make a huge difference...The gas is it high grade mpi engine can retard the timing if kocking occurs...And im sure you have 1.32 gearing when i stated 1.50 i ma just looking at all the possiblileties...A huge amount of poster's come in looking for new props when its somthing other causing the performance loss.

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

Time for a major tune up...Form 72 to 66 is quite a loss....While your at it id have the tach checked by a alternate source but the engine needs work...OK one last thing just how clean is the hull...A hull full of growth can make a huge difference...The gas is it high grade mpi engine can retard the timing if kocking occurs...And im sure you have 1.32 gearing when i stated 1.50 i ma just looking at all the possiblileties...A huge amount of poster's come in looking for new props when its somthing other causing the performance loss.

The moror runs fine . the only.reason for not hitting over 70 that day was because I had a full tank of gas ....four people on the boat ...coolers, grill,ect. I will pull the tach and have it checked out.

 

[Philster]

Re: 25p on my baja 208. 454efi/mp??

If the load changed drastically, then that would explain it. You sound propped right: with a good load, she drops to the bottom of the recommended RPM range, but within the recommended range. When light, she jumps to the top of the performance specs.

Most setups never work out this well.

 

[butchmotors]

Re: 25p on my baja 208. 454efi/mp??

Www

If the load changed drastically, then that would explain it. You sound propped right: with a good load, she drops to the bottom of the recommended RPM range, but within the recommended range. When light, she jumps to the top of the performance
Thanx Philster I figured it was decent .Didnt know if ther was room for improvment. I guess that explains why I get such awsome mpg. Thank again Philster and everyone else who took the time to help

Most setups never work out this well.