Prop questions holeshot versus top-end

[areamike]

Looks like OJ will be sending me a couple props to try. After talking with them, they think that a 4 blade will be what I need. I don't know if they are correct, but they know more about this than I do and are willing to let me try more props, so why not?

My Sporty had a 13 X 14 4 Blade OJ Legend on it when I bought it. I was getting almost 53 mph out of it at 5000 rpm with my little 310 HP carbie. You have somewhere close to 100 more HP. Not sure how the XMP 4 blades compare to the Legend 4 blades. Like you said, try it, and record the data.

They are sending 2 - 4 blade props.

One is a 13x14 the other is a 13.5x15.5. I'll probably try the 13x14 first.

almost 53MPH @ 5000RPM? DANG!

[VinRLX]

With that being the case, aren't the new 383's 400HP? What prop do they run on the new responses these days with the 400 HP motors? Or maybe that would be comparing apples to oranges?

It is apples to oranges because the hulls are different. However, the WSM BBG showed the 2008 RLXi with HH using a 13x13 3 blade prop turning 5150 for 49 MPH. I just saw a 2008 RLXi with HH rigged out for barefooting--it had the 13x12.625. Don't have any numbers on it yet and probably won't in time to help you make a choice.

Have fun testing!

[BillFooter]

The prop that Malibu has used for several years for their barefoot boat is the Acme 3 blade 13 x 12.625 with .080 cup. Sanger uses the same prop with .090 cup.

I think you will surprised that 100 horsepower doesn't generate that much more top speed. A few years ago one of my buddies built an engine for his Supra that probably had 120 horse more than the factory PCM rated at 265. It only gained about 3 mph on top end. The hulls on our comp boats don't allow big speed gains. My Response only gains about 2 mph top speed with the Hammerhead 365 vs the Monsoon 325. The main difference is the ability to hold the speed at 45 or 46 with a barefooter in tow.

[Woodski]

Another effect on top speed will be a 4 v. 3 blade prop. The 4 blade will pretty much stall out and not pull any more than 5000 rpm. That will solve the over rev problem. It will also generate an awesome holeshot.

I added 100 hp and gained 10 mph but it is not totally apples to apples since the boat also ended up 300 # lighter and this has an effect also along with prop changes that are also significant. Key point, since these boats have lots of wetted surface, they generate a lot of drag, so it takes lots of power to gain more speed. Do it to a bass boat, and a totally different result and those boats will do over 60 with half the power.

Report on the testing if you don't mind, there are many interested minds on the board.

[areamike]

Well, now I am worrying more. My buddy tells me the LAST thing you want to do is put your engine under load at lower RPM(under-rev). He says you are better off over revving that engine than under revving. Regardless, he says when I try these new 4 blade props, be very very careful. If I feel the boat lag at all then the prop is not right.

In other words he says if you run WOT and are only pushing 500 RPM @ 53 maybe 54MPH, then that is bad. Not 1:1 ratio, under revving the engine and can cause more harm than over-revving. He's a motor guy, so I trust his opinion. Not to mention I have 4G's invested in this motor and the last thing I want to do is mess it up over a 400 dollar prop.

By the way, my wife said if I have to buy anything else for this boat, it will be a for sale sign.

[VinRLX]

Mike, your buddy is right, you don't want to lug the engine. If you could only turn 4,400 RPM @ WOT, you would need to step down in pitch. Also, no holeshot would = a prop that is too big for the engine to turn, particularly at low RPM while trying to throttle up.

Based on your 13x12.5 spinning 6000 RPM, you would have to go, theoretically, to a 3blade 13x15.5 to bring RPM to 5,200.

If you've mentioned this, I don't recall--when your engine was rebuilt did you make changes to the electronics? ECU/ECM, MEFI, etc? IOW, does your computer know that the engine is bored 30 over? Or is it still managing variables based on programming for the stock motor?

Is your tach accurate? Have you checked it against a shop tach?

[areamike]

Mike, your buddy is right, you don't want to lug the engine. If you could only turn 4,400 RPM @ WOT, you would need to step down in pitch. Also, no holeshot would = a prop that is too big for the engine to turn, particularly at low RPM while trying to throttle up.

Based on your 13x12.5 spinning 6000 RPM, you would have to go, theoretically, to a 3blade 13x15.5 to bring RPM to 5,200.

If you've mentioned this, I don't recall--when your engine was rebuilt did you make changes to the electronics? ECU/ECM, MEFI, etc? IOW, does your computer know that the engine is bored 30 over? Or is it still managing variables based on programming for the stock motor?

Is your tach accurate? Have you checked it against a shop tach?

There was no electronic changes made to the boat during rebuild. I talked to the Malibu Tech when he came by and hooked up his computer to diagnose some small issues we were having after rebuild. I asked that specific question. Do we need to have the ECM re-programmed for the rebuild and he said No. Whether he is correct or not, I can't tell you. I think the guy who rebuilt it put it on a tach at the shop and it checked out then As for comparing it to what the boat tach reads, have not done that. I'm fairly certain the tach is pretty accurate. When it got up to almost 6000RPM you could tell it was really over-revving. You just kinda "know your boat" sometimes if you know what I mean.

I agree, a 13x15.5 would probably be what I will end up needing in the end. I'm a little confused as to why OJ is sending me 2-4blade props. From everything I have read 4 blade prop is not the way to go with my boat. I am wondering if they are worrying more about getting the rev down but aren't considering that under revving will be worse. I have a strong feeling I will not be satisfied with either 4 blade. Makes me wonder if I will end up having to go with an ACME prop instead.

[VinRLX]

When I mentioned the 15.5, it was just based on prop theory. I'm not saying that is what you should have on the boat--it may in fact lug with a prop that tall. Because of that, a 4 blade would make sense to get the RPM down.

In addition to trying different props on the boat, I would check into the other possibilities. Get a shop tach on the thing while you are running it and check with a couple of different sources--including Indmar--about how a rebuild could be affected by ECM.

[areamike]

When I mentioned the 15.5, it was just based on prop theory. I'm not saying that is what you should have on the boat--it may in fact lug with a prop that tall. Because of that, a 4 blade would make sense to get the RPM down.

In addition to trying different props on the boat, I would check into the other possibilities. Get a shop tach on the thing while you are running it and check with a couple of different sources--including Indmar--about how a rebuild could be affected by ECM.

I found an email when I was talking to Larry at Indmar during our rebuild. He said he didn't think the ECM will need to be reprogrammed but I will need to run

premium fuel all the time.

Now that does not tell me for sure that it does not need re-programmed, but he did not "think" so.

[Woodski]

The ECU will control spark tables and air/fuel ratio. If you did not change the compression ratio, the combustion properties will be pretty much the same, the slight overbore will not make that much difference. No need to change fuel if the CR or spark map is not changed. If you did raise CR, then the spark table should probably change. Also, if you changed the cylinder heads or the shape of the piston top, that would also nessesitate a spark table change.

In my experience a 4 blade (correct pitch) won't necessarily lug the engine, but it will basically stall out at 5000 rpm and not pull past that point, so there are two different things happening there. I would recommend a 3 blade since the boat has the capability to easily pull over 50 mph assuming you don't spend the majority of your time using the boat at 10-20 mph for wakeboarding, etc.. Other considerations are wake properties that are affected by different props.

[areamike]

Pistons were originally cast cupped top. The new ones are forged flat top.

Is adjusting the spark table done easily? I'm clueless there

Edited March 28, 2008 by areamike

[Woodski]

That will raise the compression ratio unless a thicker head gasket was used. Probably a bit difficult to change the table, if you have a distributor you might be able to take some timing out. If not, run a higher grade fuel to keep from detonation. The engine will run better with higher CR.

[areamike]

That will raise the compression ratio unless a thicker head gasket was used. Probably a bit difficult to change the table, if you have a distributor you might be able to take some timing out. If not, run a higher grade fuel to keep from detonation. The engine will run better with higher CR.

That was pretty much the only instruction I got from both Indmar and the mechanic. I have to run 93 octane all the time.

BTW, I get the two new props today and will be testing both out this afternoon.

Edited April 3, 2008 by areamike

[edwin]

Fill us in this evening if you can...tnx

[Woodski]

If you can find someone that has a Tech 2 or the correct cal reader and programmer, the table can be changed. You would want to take a little spark out at WOT. I raised my compression ratio and did not need to take any spark out, the small block likes about 33 degrees advance at 5 to 6000 rpm. You might take a timing light and see what you have. The other thing to do is read you plugs, pay attention to how the engine is running and make sure it does not run hot.

[areamike]

If you can find someone that has a Tech 2 or the correct cal reader and programmer, the table can be changed. You would want to take a little spark out at WOT. I raised my compression ratio and did not need to take any spark out, the small block likes about 33 degrees advance at 5 to 6000 rpm. You might take a timing light and see what you have. The other thing to do is read you plugs, pay attention to how the engine is running and make sure it does not run hot.

Yup to all that. One thing I do is pay too much attention to the engine. After sinking 4g's into it, I can't afford not to.

We have timed it a couple times per Indmar's timing procedures and she is pretty dialed in. I'm thinking once I get my Prop woes figured out, and my little "impeller issue" then I should be all tuned in and ready to rock.

Yeah Edwin, I'll keep you guys posted on my prop results.

[Woodski]

I don't want to lead you astray, but with 10:1 compression (production is 9.4:1) I can still run 89 octane fuel. One difference is all the top end stuff on my engine is aluminum including the exhaust, so it dissipates heat quicker. But that CR and 33 degrees of advance at 5000 rpm, no detonation. Heads are the Fast Burn 385 heads, so quite the same as the Vortec heads.

[areamike]

Yeah, from what I understand about these motors they are a stock 350. Then they take and put in GM FastBurn high performance Vortec aluminum

heads and a new camshaft in it and call it a Hammerhead, but they don't touch the pistons or lower end at all.

The old compression was 9.4:1. After we added the new pistons and rods, the compression went to 10:1

I have to ask about your exhaust. I've read that is a great upgrade. You end up losing about 80-90lbs of dead weight and even get a performance boost. Is all that true?

Edited April 3, 2008 by areamike

[areamike]

Results:

13.5x15.5 - 4 blade = 43mph @ 4000rpm at WOT

13x14 - 4blade = 43.5mph @ 4400rpm at WOT

Oh well. I guess my instincts were correct in telling me that 4 blade is NOT the way to go for my boat. Oh, the 2-4blade props they sent me were both XMP's.

There has to be a prop that will work good with my boat. Back to square one, my current SS CVP 13x13 does 49.5 @ 5600Rpm at WOT. In a prefect world, I'd liek to see 51mph @ 5300 RPM. Or close to that.

[areamike]

OJ props are a no go.

I am trying ACME now. Bill from ACME wants to send me a 13x14 .80 3 blade.

[Woodski]

Mike,

You should be able to run 89 octane gas with that, sounds very much like what I did to my boat, fast burn heads (50#) and a ZZ4 cam, CR ends up at 10:1 with those heads. Additionally, I added Stainless Marine aluminum exhaust manifolds, they have runners in them so improves the exhaust flow and reduces weight by 45# per side and an aluminum intake manifold (25#). They flow great but are 4" tubes so I increased the exhaust size and added 4" stainless tips out the back. All that really picked up the performance of the boat, top end is 55 mph at 5600 rpm, up from 45 mph as original. Did take some prop tuning to get it there and I actually got it with an old CVP prop that has been worked over pretty good. BTW, you can't spend too much time on the engine, fine tuning makes it run to perfection. The end result is you can't snooze on the barefoot line on deep water starts, if you do, you'll be still on your butt at 42 mph! The 2k-5k accel is much better than standard issue. Bottom end on a SBC can handle 6000 rpm pretty well.

In addition, I have removed the water pump and gone with the stainless splitter tube, reducing another chunk of weight. Flows plenty of water, but you have to keep a good impeller in it. Total weight reduction is 250#, which really makes a difference in the wake.

What made the OJ's a no go, testing or did not get them? I have spoken with Bill at Acme about props and I am going to try one that has a lot of cup. That should keep the holeshot and then not overspeed at the top end. When you wound your engine up, does it feel like a rubber band, the engine revs up and the boat does not keep up, then slowly gains speed? That is what happened to me at the beginning until I tuned the prop, that is cavitation. The surface finish of the CNC props is one element that keeps them from cavitating. The Acme's have a lot of blade area and that also helps.

[areamike]

Mike,

You should be able to run 89 octane gas with that, sounds very much like what I did to my boat, fast burn heads (50#) and a ZZ4 cam, CR ends up at 10:1 with those heads. Additionally, I added Stainless Marine aluminum exhaust manifolds, they have runners in them so improves the exhaust flow and reduces weight by 45# per side and an aluminum intake manifold (25#). They flow great but are 4" tubes so I increased the exhaust size and added 4" stainless tips out the back. All that really picked up the performance of the boat, top end is 55 mph at 5600 rpm, up from 45 mph as original. Did take some prop tuning to get it there and I actually got it with an old CVP prop that has been worked over pretty good. BTW, you can't spend too much time on the engine, fine tuning makes it run to perfection. The end result is you can't snooze on the barefoot line on deep water starts, if you do, you'll be still on your butt at 42 mph! The 2k-5k accel is much better than standard issue. Bottom end on a SBC can handle 6000 rpm pretty well.

In addition, I have removed the water pump and gone with the stainless splitter tube, reducing another chunk of weight. Flows plenty of water, but you have to keep a good impeller in it. Total weight reduction is 250#, which really makes a difference in the wake.

What made the OJ's a no go, testing or did not get them? I have spoken with Bill at Acme about props and I am going to try one that has a lot of cup. That should keep the holeshot and then not overspeed at the top end. When you wound your engine up, does it feel like a rubber band, the engine revs up and the boat does not keep up, then slowly gains speed? That is what happened to me at the beginning until I tuned the prop, that is cavitation. The surface finish of the CNC props is one element that keeps them from cavitating. The Acme's have a lot of blade area and that also helps.

After testing the OJ props.

The 4 blade OJ props both cavitated badly when putting boat in reverse. Both felt very slow out of the hole and both trimmed my WOT mph down about 6 MPH.

The 3 blade I got from OJ just spun out of control. I hit about 6000 RPM and was not even at WOT. I about peed my pants. Although I know the motor can handle 6000RPM, I did not feel comfortable. The funny thing is at 6000 RPM the motor sounded very clean and smooth.

I feel with propper propping, I should be able to get 51 MPH @ 53-5400 RPM at WOT. The hull design may limit me any more top end speed. But I would rather run 49.5@ 5300 rather than 49.5 at almost 5700 at WOT like I do now. I've also read weather can alter performance results. It is still pretty cold here. Water temp was 42 the other day when I was testing.

I'd love to get the Stainless exhaust manifolds. Problem is my Wife said, if I have to buy anything else for this boat, it will be a For Sale Sign!

[Woodski]

Maybe Santa will be good to you this winter! Sounds like the 4 blades aren't the hot setup, a 6 mph loss is pretty dramatic. I think the Hammerhead has slightly less torque down low than the standard engine, so it the 4 blade makes the engine labor out of the hole. I have tried a couple of 4 blades and the boat just plane stops accelerating at 50 mph. IMO, especially for footing, the 3 blade is the way to go. You should easily be able to get to 1:1 on speed/rpm. You might also think about the Acme 515, with maybe a little more cup if is spins too fast. Weather and water temps do have an effect, colder weather will allow the engine to make more power and colder water should keep less hull in the water, similar to setting up a ski.

My buddy has a Cutter 4 blade and it does the same thing in reverse. Let us know how the Acme 13x14 prop works out.

[VinRLX]

Mike, I'm going to guesstimate that the ACME 13x14 will spin 5200-5400 RPM on your boat. Anyone else care to offer a prediction? Maybe we should have a pool or something!

[hotrodbowtie]

How about a acme 1257. Still a 13x14 3blade but with a lot of cup (.135) That might prevent the cavitation that you are seeing. If you get it to grip rpms should drop ~300 and speed should shoot up. With the huge blades, it should be very strong and stable.