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View Full Version : What cup for OJ XMP 13.7 x 17.5?


Nvrgvup
05-20-2012, 09:27 PM
I have a 83' S&S 351W Powerslot. 575hrs.

Looking to get a new 4 blade.

Acme recommended a 13.5 x 17.5 w/ .080 cup due to the age of the boat.

OJ has the similar XMP 13.7 x 17.5 with a .090, .110 or .120 cup.

I would prefer to go with the OJ since the prices are better.

Any recommendations on the cup on the OJ for this engine and boat setup?

We mostly ski with some wakeboarding no ballast other than the kids.

Thanks!!

DooSPX
05-21-2012, 08:03 AM
Give Eric a call and ask him!

TRBenj
05-21-2012, 11:45 AM
If you go with OJ, I would go with the least amount of cup possible. My bet is that it would still turn more RPM than the comparable Acme. The 2 props vary significantly in their design, so do not expect identical performance from 2 props whose dimensions are the same.

What are you trying to do with the boat? Based on my experience, Acmes are generally better performers (holeshot and top end). The OJ's run a little mellower and may offer a slightly more bow-down running attitude, which combined with lower RPM's at skiing speed, may make the wake slightly smaller and the rooster tail slightly softer.

Nvrgvup
05-21-2012, 07:32 PM
I called Eric and he suggested the .110 cup on the XMP 13.7 x 17.5. To my surprize he actually suggested the Legend / 4Force hand finished 14 x 18 over the CNC to save some $$. Said I wouldn't be able to tell the difference and that is what he personally ran. He also told me that they both were made from the similar castings and same materials. The CNC version was just cast slightly larger to allow for machining.

We mostly ski and some wakeboarding no ballast other than the kids.

Nvrgvup
05-22-2012, 11:50 AM
Any experiences with the following 4 blades on a 351W Powerslot setup. What would be your pick?? I can find them all at about the same prices. Any suggestions would be appreciated.

OJ XMP 13.7 x 17.5 .110 Cup
Acme 275 13.5 x 17.5 .090 Cup
Acme 381 13.5 x 17.5 .105 Cup

Acme recommended the 275 with the .090 cup however it seems others are running the 381 as well on the same engine set-up with really good results.

Kyle
05-22-2012, 12:11 PM
Any experiences with the following 4 blades on a 351W Powerslot setup. What would be your pick?? I can find them all at about the same prices. Any suggestions would be appreciated.

OJ XMP 13.7 x 17.5 .110 Cup
Acme 275 13.5 x 17.5 .090 Cup
Acme 381 13.5 x 17.5 .105 Cup

Acme recommended the 275 with the .090 cup however it seems others are running the 381 as well on the same engine set-up with really good results.


Your boat has a 240-260 horse power engine. I would start out with a .090

The more cup you have the less rpm you have at wot.

I have owned 4 different OJ props and am looking for a different prop. I have a buddy that has the same engine as I do and we are trying props out. He ordered an ACME and it was by far the smoothest running prop I have ever used on a 190. We tried the 13.5x17.5 four blade 817 and the three blade 1749 and the 4 blade was by far smoother and better for our needs. We still could turn the 817 no problem but we are now going to try the 13.5x19 acme 907. We have 325 or more hp that our engines are producing so stay with the 17.5 pitch.


As far as me picking one......... Call ACME and order both the 275 and the 381 and try them out. They will take back the one you dont want and refund you your cost. All you will be out is the shipping for the prop to go back to acme.


Keep in mind that I like OJ and think that they make a good product. I personally felt a difference between the ACME and the OJ and I personally think the ACME suits my boat better.

TRBenj
05-22-2012, 12:55 PM
My experience has been the same as Kyle's with Acme vs. OJ. Eric Johnson is great to work with and OJ is a terrific company, but I just prefer the way Acmes run on my boats.

Acme is good to work with as well. However, I would not recommend buying a prop directly from them, as they have a policy to charge full retail on direct sales in order to protect their dealer network. Many of their dealers (like Delta Propeller) will allow you to demo a prop and return it for full credit towards another one if you didnt like the way it performed.

Start with the 275 though, as I doubt you'll be sending it back.

Regarding adding hp, I only know of one boat that had top end engine modifications (did not add cubic inches via stroker) that ran just as fast with a larger prop. It ran the same speed with a stock sized prop, but at a much elevated RPM. (Normally it takes a stroker to make a greater amount of power at a lower RPM). That boat was beyond the 1hp/ci level, and considering the other modifications to the engine, had a pretty undersized cam. Every other ski boat I can think of with top end mods has run its fastest with a stock-sized prop... usually the Acme equivalent, if we're talking modern ski boats. So that 275 will most likely be the hot prop, even if you add some heads or a cam later on down the line.

Kyle, Id be trying the 275 and 381 as well, if I were you. You may lose in the ballpark of 600rpm by going to a prop with 1.5" more pitch- thats an extreme change. It will move your WOT rpm's away from your hp peak (optimal performance) and towards your torque/pressure peak, which could have disastrous consequences with detonation (especially if your compression ratio is 10 or greater).

Kyle
05-22-2012, 01:43 PM
Kyle, Id be trying the 275 and 381 as well, if I were you. You may lose in the ballpark of 600rpm by going to a prop with 1.5" more pitch- thats an extreme change. It will move your WOT rpm's away from your hp peak (optimal performance) and towards your torque/pressure peak, which could have disastrous consequences with detonation (especially if your compression ratio is 10 or greater).

Still a 17.5 acme 817 .150 cup can turn 4760 rpm on phantoms boat and the factory oj 14x18 turned the same rpm.

I have a different cam and can turn 5050 to 5100 rpm. Jim at Acme told us to try the 907 19pitch out. we are playing ship props back and fourth right now.


keep in mind that at 4600rpm I hit top end speed but spin the prop another 500 rpm without going any faster.

TRBenj
05-22-2012, 01:50 PM
That different cam allows your engine to breathe better, and make more power... which will most likely occur at a higher RPM. So turning the same prop faster will net the best performance, more often than not.

It will be interesting to see how the bigger prop runs, report back with your results. The 1.5 slot ratio may have some effect, but on the 1.23, a change in pitch of 1/2" equates to ~200rpm. The 1:1 boats arent *too* far from that either. If your WOT RPM's go down to 4500, then it will probably be a few mph slower (since youre not allowing the engine to develop its full hp). It will also be doggier out of the hole, obviously. Just be careful not to run that prop at WOT for extended periods... loading an engine down with a big prop like that can be dangerous. Moreso on an engine with higher compression.

Kyle
05-22-2012, 01:57 PM
I am trying to achieve a 4800 to 4900 or so rpm but nothing less. I think the 17.5 pitch .150 cup was great but I think that I can run a bigger prop.

Obviously if the 19 pitch makes it a ragedy old dog out of the hole then it will go back but right now I have a monster out of the hole but loose top end speed but can turn the prop 500 rpm more for no reason.

TRBenj
05-22-2012, 02:03 PM
Do you make peak hp at 4800-4900? If so, then I agree that is a good goal.

Are you saying that you get the same top end speed at 4600rpm that you do at 5100rpm with the same (817 Acme) prop?

Kyle
05-22-2012, 02:45 PM
Do you make peak hp at 4800-4900? If so, then I agree that is a good goal.

Are you saying that you get the same top end speed at 4600rpm that you do at 5100rpm with the same (817 Acme) prop?

This is so confusing to explain.

Phntmski has the same engine but it turns 400rpm less. We have only tested props on his boat. Tonight I will have exact numbers on my boat because we are putting the 817 and the 1749 on my boat.


We do have issues with the 3 blade though. The trailing edge is close to the rudder and we are hearing a harmonic sound and a slight flutter from the turbulance on the rudder. Bill over at Acme said that it is just too close to the rudder. We plan on looking at the 2 different props tonight. I am taking my note pad with me to the lake and writing down every detail about both props on both boats.

I will have a way clearer picture tonight to discuss. Bill assures me that the loss in speed will not happen on the ACME and he thinks like you do that the 19 pitch will be too big to turn. The only reason we were considering the 19 pitch was because I am trying to bring down rpm and the 817 did not bring phntmski rpm down at all. I just fear that if I can spin a 817 5000rpm that I will need to bump to the 19 pitch.


We will know for sure what will need to be tried here in a few hours.

TRBenj
05-22-2012, 03:49 PM
Now Im following.

How much strut to prop clearance do the 2 boats have? (This wants to be as small as possible- just enough to get a puller on there.)

I have run Acmes with minimal clearance to the rudder... within ~1/4". Never noticed any weird noises or performance characteristics (the boat ran into the mid 50's). But every boat is different.

If your engine makes peak power at 4800-4900 (do you know this for sure?) then whats the problem if you spin the engine to 5000? I mean its not right on the money, but its close. Surely worlds better than it would be with something too big that dropped your revs to 4500. That will kill your performance everywhere AND be more dangerous to your motor.

If the 817 isnt quite enough prop, is the 2003 (14x17.75, .135 cup) an option? How much clearance do you have between the prop and hull with the 13.5" diam wheel?

Kyle
05-23-2012, 12:15 AM
Ok here are my results. Phntmski has very similar results but the rpm is lower due to a different cam.


OJ 13.7x17.5 four blade (refinished by local prop shop)
Distance from trailing edge of the prop to the rudder 1 5/8"
Max rpm 5050-5100
Max mph gps confirmed 44.5 ish
Decent hole shot and has very slight vibration in no wake speed to 15mph (no dings on the prop)

ACME 1749 3blade 13.5x17.5 .150 cup brand new
Distance from trailing edge of prop to rudder 1"
Max rpm 4840
Max mph 45.7
Slight vibe coming out of the hole and has a harmonic sound
Extremely strong out of the hole and more top end

ACME 817 13.5x17.5 4blade .150 cup brand new
Distance from trailing edge to rudder 1 1/4"
Max rpm 4850
Max mph 44.9
Very smooth in and out of gear. Very smooth in no wake speed.
Extremely strong hole shot
No vibe
Very quiet
Smoother than the 3 blade





After my research I have decided to buy the acme 4 blade 817. Now I need to place my order. Phntmski had ordered the 2 props and he too is keeping the 4 blade. The 3 blade needs to go back to acme. It was a real good prop but I don't foot that often and 44.9 is plenty fast enough. I'm over trying to hit 50. You guys were right, I was wrong. I need A LOT more power or a non slot boat. I do feel good though that I have a reduction gear 1.5:1 tranny pulling 45.7 mph. I feel that if I had a 1:1 it would be faster. My friends factory 285ho '93 205 goes 47 with a 3blade OJ legend 13x13. I would be very curious to see how an acme would do on his boat and if he had different heads and intake.

TRBenj
05-23-2012, 09:28 AM
Good data, but dont pull the trigger on that 817 just yet.

Have you tried the 381 or 275 on your boat? They look to be the same props, but with less cup (.105 and .080 vs. .150). I would guess that one of those would be the hot prop for your combo. I have never had much luck with adding extra cup to a prop to get the boat to speed up. Cup can control RPM pretty well, but it also makes the prop more inefficient. If you make peak power around 5k RPM, then let the motor turn that fast and overall performance will improve. I bet the boat would pick up another 1/2 mph or so with one of those other 4-blades.

On the rudder clearance, 1" is waaaaay more than you need- no issue there.

Im not so sure youre giving up much with the slot... variations from hull to hull, running surface, exact motor placement, etc can cause 2 boats that appear identical on a spec sheet to run quite differently (several mph). My uncle had a '96 Ski Nautique with a stock 310hp GT40 that would peg the speedos... that thing was a legit 48-50mph boat, no doubt about it. My '90 (same hull) with all sort of mods (~350hp) is only good for 46-47mph on a good day. I can think of many other examples. Also, several of the faster ski boats Ive spent some time in have reduction (1.23) transmissions. So I dont think theres anything inherently slower with the reduction gearbox. Certainly not a significant one (that would have more than 1-2mph effect, at most).

Kyle
05-23-2012, 09:59 AM
I just don't know where max rpm max HP meet. I wish I did.

TRBenj
05-23-2012, 10:05 AM
What are the specs on your cam? Which heads? Compression ratio? Intake manifold?

I could make an educated guess based on your parts.

Regardless, even if your peak power is at 4800, I would expect the boat to speed up slightly if allowed to turn 5k with a more efficient (less cup) prop (275/381), vs. the performance youre seeing with the 817.

Kyle
05-23-2012, 10:42 AM
Block .040 over, hypereutectic pistons, factory crank and rods, high vol oil pump

Cam
http://www.mastercraft.com/teamtalk/attachment.php?attachmentid=61379&d=1283370835

3 angle cut valves, factory valve springs, non roller rocker, non roller lifters

Heads gt40p

Intake Edlebrock performer performer with a weiand 1" spacer

Coil factory

Distributor (new) protonix electronic

Timing 10*~11*


I was shooting for 325~ HP

TRBenj
05-23-2012, 12:17 PM
That cam isnt much warmer than stock (.456/.457 lift at the valves). Do you know what the dome/dish on the pistons will give you for compression ratio with the 58cc GT40p head chambers?

With the smaller cam, I would expect peak power to be occurring around 4800. If you were to add 1.7 RR's, you'd net closer to .485 lift at the valves and that power peak would go up a bit and probably pull up to 5k or so. If youre not done tinkering, I think you'd appreciate the difference.

Nonetheless, I still think that a version of the same 817 with less cup will improve your performance. If you can still take advantage of a free trial or 2, Id take them up on that and see if Im right!

Kyle
05-23-2012, 01:09 PM
I dont know about the roller rockers.

http://www.summitracing.com/parts/PRO-66878/


Ok here is an example of pedestal mout RR set up.

For an extra $200 to $300 I really may consider it. All I would have to do is remove the valve covers and put the new RR in and torque them down to 50lbs I believe (will have to confirm torque) and it would be easy to do. I dont have to remove the exhaust or the intake. I would have to be careful to make sure the push rod stays in the lifter but that is not impossible.



Now with 1.7 RR I am concerned that the valve covers will rub or that everything will work.

1) So if I am able to spin another 200rpm out of her and the lift would move up to .485 will it sound any different

2) How much HP would be gained

3) Would it turn the 817 better

4) Why do you say going to a smaller cup would be better.

5) Will I have issues with the valve springs and compressing them too far



I want top end and a better fuel economy. LOL like that is possible.

Pistons are not domed they are pretty flat with valve relief

TRBenj
05-23-2012, 01:23 PM
No answer on the pistons/compression ratio?

Avoid cheap chinese (proform) rockers. The last thing you need is a poor quality rocker grenading and sending little pieces of bearings into your engine. Stick with Scorpion or Crane. Used is fine. Ford Motorsports are good as well, those are rebranded Cranes. I have Crane RR's in 2 boats, theyre nicely made. They are also pretty low profile, so theres a good chance they'll fit under your existing valve covers.

Just to clarify, by improving your engine's breathing in the manner we're describing, it will move the peak power up in the RPM range. It is unlikely to have a negative effect on power elsewhere- in fact, it may improve it. It will just keep the hp curve extending a little longer. It has no effect on your engine's ability to withstand spinning a certain speed... that all goes back to the strength of the components you chose (mostly the bottom end). A stock 351w bottom end is good for 6k rpm, so Im told... so no issues there. So when you say "I am able to spin another 200rpm", you really mean "I am able to make peak hp 200rpm higher". You will also not necessarily gain 200rpm of performance at WOT by going to 1.7rr's... it just means you will make hp a bit further up the band and can take advantage of a slightly shorter (less cup) prop.

1. No, you wont notice any difference in sound.
2. Tough to say exactly... ~15hp?
3. It would turn anything better, since it will make a bit more power, and extend the hp curve a little, including the 817.
4. Take a look at your prop. Cup is located at the trailing edge of the blades. Right there where it flares up about 1/8". The more cup, the larger the flare. Its easy to add and subtract, as youre not changing the blade shape (as with pitch)... its just that trailing edge. However, it should be really obvious that while the cup allows you to tweak your RPM's a bit, it also does not make the blade shape more efficient. It acts like a little paddle wheel at the end of the blade. So I am of the opinion that less is better. Give me .080" anyday... anything much beyond .110" is excessive. Rather than add extreme amounts of pitch (.150"), Id prefer to go with a prop with a bit more pitch (1/4" to 1/2") and keep the amount of cup down.

In your case, I think you'll win all around by going to a prop with less cup. Everything except maybe fuel economy... but the difference will be pretty darn small, if its measurable at all.

Kyle
05-23-2012, 01:37 PM
How do I know for sure that I do not need 1.5 or 1.6 or 1.7 ratio RR

Will I have clearence in the head where the pushrod goes through. Does that need to be ovaled?

I do not want to hit the valve on the pistons.

The cheap RR that I posted off of summit was an example of the pedestal style that I would need. I plan on running a good brand if I do this.


I dont know pistons or compression ratio. It is very close to factory


If I am doing this for top end Speed then I think it will not give me much. I have 100# or more of stereo crap and then more in gear under my bow. It is extremely hard for me to get the bow up and I have a wet hull. I would not expect 46 out of her. If it happened I would be shocked.

TRBenj
05-23-2012, 04:43 PM
The stock Ford Windsor rocker ratio is 1.6.

By stepping up the ratio, you get more lift at the valve. (.456 / 1.6) * 1.7 = .485

The holes in the heads for the pushrods are huge- no effect there.

Unless you have some crazy domed pistons, it is unlikely you will have any valve interference issues. Remember, we're only talking an increase of .03" of lift... while thats significant when talking cams, thats less than 1/16" in terms of piston/valve clearance.

Yes, most modern factory Ford Windsor heads used pedestal rockers. Check out corral.net and see if you can pick up a good used set of Cobra 1.7's or 1.72's for cheap (<$200). Those were made by Crane as well.

If you were to go with the 275 prop and some 1.7rr's, I would not be surprised if the boat ran 46mph. The prop is probably the bigger part of the equation though.

DooSPX
05-30-2012, 03:31 PM
I have no idea about the ACME props, but my OJ CNC 454 .110 cup lowered my skiing speed RPM's only, my max RPM is the same 4600 it was with the factory SS 3 blade 14x18. I love the lowered RPM at 32 and 34 mph though. It holds speed against the pull of the skier like a vice, yet feels like a soft pull vs. the train pull I was feeling with the factory prop.

Kyle, when you can, ski behind the boats with the ACME vs. the OJ and let us know how it feels to you and if the wake was different please. I bought the OJ because all I really cared about was the feel to the skier, better hole shot, and the wake. The OJ did seem to knock the rooster down a little as well as soften the wake a tad.

Kyle
05-30-2012, 05:13 PM
Jason

I got a PM from Eric about my 13.7x17.5 today about 10 minutes before you posted.

I am going to get with him and speak about an idea that he has. My acme should be here tomorrow and I should be able to pick it up from Phantom next wednesday. I want to speak with Eric about the OJ that I have too.

I think here in the next few weeks I will have an answer for you.


As far as the rooster tail and the hard wakes between the current OJ that I have and the Acme, it is really hard for me to answer the wake question. I am skiing infront of the rooster tail. If you would like I can try to run a -15 off pass to test it out for you guys, but do keep in mind that I have not been at -15 in years so everything will be tall and more of a bump. It is also hard to give a honest answer of how hard or soft or tall a wake is at -35. What I start to notice is a bigger dip down or a trough that I ski through, its not a bump or anything you go up and over.

DooSPX
05-30-2012, 06:52 PM
Gotcha, I forgot you are -32 and up. Sorry about that! Still would like to know the feel you have of the boat while behind it as well. Also, If you and Eric come up with something, and its not a secret, I would love to know what it is and how it works. You can PM me if need be.

Thanks Kyle

Kyle
05-31-2012, 04:11 PM
Ok back on props.

After speaking with Eric I will have more testing to do. I got a call from Phantom saying my 817 is in today. Although I am excited about a new toy, I am also excided for another specially "Tweaked" package to arive next week from Eric.


Here is what I am planning to do.

1) I plan on putting the OJ on my boat and getting some data and to speak with Eric about before posting OJ info. Eric has gone out of his way to "Tweak" and ship me a prop to have me post up numbers and opinions. I feel that it is fair to post info after speaking with him. Then I will spill some more information.

2) Since there is virtually no difference between the Acme prop 817 on my boat and Phantoms boat we will hold a challenge and put the Acme on one boat and the OJ on the other and run a Ski League at our club one night. We will probably have 10 skiers that will be skiing from -15@30mph to -32@34mph. We will not let people know who has what prop and get different opinions with two like boats with the difference being OJ vs ACME. I just dont know how else to get opinions from lots of different levels of skiers other than that. Round one of the ski league will be pulled with one brand and round two will be pulled with the other brand. Bacically 10 skiers will have 2 sets each and we can have the "SHOW DOWN"



Keep posted in the future weeks as this will take at least 2-3 weeks to cordinate and I do need to make a test run with the "Tweaked" prop and get some base line numbers to get back with Eric before the prop war begins.

DooSPX
05-31-2012, 04:39 PM
Such a great idea! I like the idea that the skiers will not know which boat has which prop, as personal opinion can cloud judgment. I look forward to the results!!! I will be watching this thread like a hawk for now.

Do yours and Phantoms boat perform equally per testing? I know that they have the same build, same trans, but everything is different a little bit?

PS,
I stand by my saying that Eric is the best CS of the prop companies I have ever seen. I have called just to BS a little about family and such, always taken time to speak with me.

Kyle
05-31-2012, 05:45 PM
Such a great idea! I like the idea that the skiers will not know which boat has which prop, as personal opinion can cloud judgment. I look forward to the results!!! I will be watching this thread like a hawk for now.

Do yours and Phantoms boat perform equally per testing? I know that they have the same build, same trans, but everything is different a little bit?

PS,
I stand by my saying that Eric is the best CS of the prop companies I have ever seen. I have called just to BS a little about family and such, always taken time to speak with me.

The difference between the boats will be the upholstery and color basically.

His cam is slightly different and I can out run him 0.5 mph on gps with identical set ups.

There is no difference as far as wake goes when it comes to 817 acme between his boat and mine.

I think this will be a very fair comparison as far as wake and performance of the boats.

DooSPX
05-31-2012, 06:39 PM
Are the hole shots the same on both boats Kyle?

Kyle
05-31-2012, 09:53 PM
Are the hole shots the same on both boats Kyle?

Extremely close if not the same. That's from dead stop to WOT. We drag raced in the ski course. Had the boat guides as the center lines and you drove between the outer guide bouy and turn bouy.

Do keep in mind we have not raced with each having 817's yet. I know I will have him by a 1/2 boat or less by the end of the course. We come out of the hole real strong but I know I will pull him by .5 mph.

His boat maxed out just pulls .5 less so knowing that we really don't need to have a race with the same props. We know the outcome already.

He pulled on me with the 3 blade and I was running the 817 by .5 or less. When I ran the 3 blade it was a win by 2 or 3 boats.

I just don't know how else to put it. If we both run 817's I have .5 on him but it is only after we hit WOT before I really pull on him. It's so darn slight I'm not going to worry about it and I'm sure not changing his cam to make the cams the same.

DooSPX
05-31-2012, 10:20 PM
Good enough for me! Look forward to testing!

Kyle
06-03-2012, 12:33 PM
So I went to the lake yesterday for a party at a buddies house. I pull up at the house and we have 18 people there and 1 other boat. I piled in 9 adults in my boat and headed for the island we park at to drink and float. One of my friends asked how fast does she run loaded down.


Well I got 43.7-44.1 out of her with my OJ 13.7x17.5 that I am replacing. I had to give it a lot of throttle to get on plane as the boat is not designed for that many people. My buddy who had the other boat ('98 air Nautique) was like I can't keep up. I shut the boat down and let him get infront of me so that I would not have to take the chop that we ran into.


So here is the weird part. I lost less than 1mph and I had 8 more people than when I ran her wot by myself.

There was also no hole shot with 8 other passengers but I expected that. 4 people on the back seat and 2 riding on the back sides is a lot of weight. It was a tight fit but the ride was only 5-10 minutes To the island.

DooSPX
06-08-2012, 04:35 PM
Kyle, not asking for a update per say, but have you heard from Eric about a prop that will compete with the other 4 blade hole shot???