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View Full Version : little help please-low rpm/speed?


redmike
05-25-2005, 02:20 AM
Had the boat out for a quick spin today (finally quit raining) everything I got from skidim worked great (thanks for the tips guys), do have a question though, what do your boats top out at (speed/rpm) my 88 is about 42 (haven't calabrated speedo's left gps at home :( ) and 4200 rpm seems a little low to me. Engine runs great, can hear the secondaries opening, just wanted to know if i have an issue or not. Thanks in advance for the info.

BrianM
05-25-2005, 11:06 AM
That rpm and speed is a little low. You should be spinning around 4700 rpm and top out right about 45mph (Ford 351). What prop are you running?

6ballsisall
05-25-2005, 11:09 AM
Mike, tell us what prop you are running, I know with my Acme 541 I lost some top RPM due to the bite this prop has but the speed was equal to speed I got prior with higher RPM's.

east tx skier
05-25-2005, 11:40 AM
Last I checked (before the new intake) I was getting 4,600 rpms and 45.5 mph with an acme 541 (same top end as with the OJ 13x13).

redmike
05-25-2005, 04:13 PM
thanks for the help guys, will see if I can find info on prop when I get home tonight. just seemed like engine should spin a little faster :confused:

east tx skier
05-25-2005, 05:03 PM
thanks for the help guys, will see if I can find info on prop when I get home tonight. just seemed like engine should spin a little faster :confused:

The diameter x pitch will be printed on the rear of the prop hub.

redmike
05-25-2005, 05:57 PM
The diameter x pitch will be printed on the rear of the prop hub.
thanks east tex, didn't wan't to ask too many ???'s saves me some time

east tx skier
05-25-2005, 06:24 PM
Ask away. It doesn't hurt anything.

redmike
05-25-2005, 08:46 PM
OK, just looked again, 1:1 , 13x13 prop, prop has a few "scuffs" and 1 ding that I hadn't noticed before....any ideas, new prop??? :eek:

bobk
05-25-2005, 09:20 PM
I don't know anything about the rpms on a boat engine or any engine for that matter. However I do care that you get yours fixed. I will be checking in later to see if you fixed the problem


Now for a golf ball I could help you out. A driver with a club head speed of 105 should have 2500 to 3500 ball spin rpms Launch angle of 12 to 14 degrees.

SKI*MC
05-25-2005, 09:25 PM
If sounds like i have the same problem with my 83, maybe its just age, or the prop, otr maybe our ditributor (not getting a good spark in it) any info???

redmike
05-25-2005, 09:44 PM
bobk, thanks for the info on my golf game; but it is in far worse shape than my prop! I think of it as slash and find!!!

BrianM
05-26-2005, 09:26 AM
OK, just looked again, 1:1 , 13x13 prop, prop has a few "scuffs" and 1 ding that I hadn't noticed before....any ideas, new prop??? :eek:

The scuffs and ding is more than likely causing that prop to not work at its full potential. I would say to buy yourself a new CNCd prop either an ACME or OJ XMP.

I should have a full review of both of these props in the next week or so. I have been running an Acme #541 13 x 12 for a few months now and the performance difference is amazing. I also have an OJ XMP of the same pitch and am currently running it on a friends 205 with similar results.

As many here can testify the new props make a world of difference in your boats performance. Then have yours fixed for a spare.

redmike
05-26-2005, 09:50 AM
thanks for the reply Bob, once i really looked at the prop, I figured it was that, but didn't want to just assume.
Looking at either the oj or acme props, any input on the best one would be great!

PeteS
05-26-2005, 10:03 AM
I understand your concern, Redmike. I own an '88 Prostar (351) which I purchased last summer, and since then have tuned, cleaned, and replaced many general items relating the powerplant.

Unfortunately, I still only can turn about 4400 RPM's, with a top speed of around 42. I run an Acme #541, nick free, and the carb has recently been rebuilt. BrianM and I have the same boat, and the fact that he is getting 45 MPH and 4700 RPM's interests me as well.

I'm not sure if this could be the case, but the previous owner "slacked" on a few items related to the motor for quite some time, and although the boat only has 320 hours, I question what the performance results could have been from his lack of general maintanence.

east tx skier
05-26-2005, 11:24 AM
I should have a full review of both of these props in the next week or so. I have been running an Acme #541 13 x 12 for a few months now and the performance difference is amazing. I also have an OJ XMP of the same pitch and am currently running it on a friends 205 with similar results.

I'm going to the lake for a week in June. Should have a the review done by 6/15.

BrianM
05-26-2005, 01:07 PM
.
Unfortunately, I still only can turn about 4400 RPM's, with a top speed of around 42. I run an Acme #541, nick free, and the carb has recently been rebuilt. BrianM and I have the same boat, and the fact that he is getting 45 MPH and 4700 RPM's interests me as well.

I may have spoken out of line a bit. I know that my boat can run right at 44-45 mph but I am not exactly sure what rpm I am spinning at WOT. I took the 4700 number from my manuel. I rarely run WOT so I can't remember.

I highly reccomend the Acme #541 or according to EJ OJPROP on this board the XMP 13x11.5 is also a good option. PM EJ and he can give you some ideas. He will be glad to send you a prop to try out.

PeteS
05-26-2005, 02:02 PM
I may have spoken out of line a bit. I know that my boat can run right at 44-45 mph but I am not exactly sure what rpm I am spinning at WOT. I took the 4700 number from my manuel. I rarely run WOT so I can't remember.

I highly reccomend the Acme #541 or according to EJ OJPROP on this board the XMP 13x11.5 is also a good option. PM EJ and he can give you some ideas. He will be glad to send you a prop to try out.
No problem, Brian. I'm just concerened that my max boat speed is 3 MPH less than what it should be. Maybe the valve springs are just a bit weaker than yours, or maybe I have a little more carbon in the heads or something. Who knows.

BrianM
05-26-2005, 02:32 PM
Maybe the valve springs are just a bit weaker than yours, or maybe I have a little more carbon in the heads or something. Who knows.

Maybe it's the water. Who knows? There are a lot of factors that can effect top end. I can only run 44-45 with a very light load (the wife and I and a 1/4 of fuel). Add another person and a nearly full tank of gas and 42 is about it. My boat is VERY sensitive to weight.

Sledneck
05-26-2005, 02:43 PM
Similar results here too my '87 351 w/ 1300hrs runs 4,200rpm 41-42mph fully loaded (full tank of gas, 4 people + gear).. Pretty good for the old girl in my opinion..

-Sled

PeteS
05-26-2005, 02:44 PM
Maybe it's the water. Who knows? There are a lot of factors that can effect top end. I can only run 44-45 with a very light load (the wife and I and a 1/4 of fuel). Add another person and a nearly full tank of gas and 42 is about it. My boat is VERY sensitive to weight.
That's a good point, as I'm learning more and more about slow vs. fast water as it relates to skiing. I'm sure it applies to boat speed as well.

When you ski with just a driver, do you weight the port side to compensate for driver weight?

BrianM
05-26-2005, 03:07 PM
When you ski with just a driver, do you weight the port side to compensate for driver weight?

We ski with just a driver a lot and to this point I have not been weighting the boat on the observers side although making a couple of easily movable weights is on my to do list because it really needs it.

I have been planning on making a couple of 70lb cement blocks that will fit along the port side walkway. I am going to carpet them and put a carrying strap on them for easy in and out. I was thinking of building a custom MTS system but that was going to get expensive. The cement ought to cost me less than $10 and I have leftover carpet from when I redid my trailer bunks.

As I am sure you know the wake is very lopsided without some extra balast.

east tx skier
05-26-2005, 03:12 PM
Brian, have you considered using lead shot? It's a bit more expensive, but also less space consuming.

redmike
05-26-2005, 04:23 PM
thanks for all of the info, will pm ej later to see what he thinks, you guys are great :worthy:

BrianM
05-26-2005, 04:27 PM
Brian, have you considered using lead shot? It's a bit more expensive, but also less space consuming.

Yeah I considered the lead shot bags that someone around here posted. That would be a perfect solution but it would be very expensive to have shipped plus the 50lb bags were kind of expensive. I was not able to find a local supplier for something similar so I think I am just going to go the concrete route.

east tx skier
05-26-2005, 05:12 PM
You ought to be able to find it at a good gun store. They come in canvas bags, but you could go with a neo bag from a dive shop. You can also cook and mold tire weights into bricks.

Bear in mind I haven't tried any of this, but I'm starting to think about it again.