The data is in
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=46763
Printed Date: March-10-2025 at 5:56am
Topic: The data is in
Posted By: AlfaDon
Subject: The data is in
Date Posted: August-31-2018 at 1:26am
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I finally got my 96 176 on the water after a long rebuild process. Stock Crank and rods with Forged pistons. Custom grind cam with .550 lift, 227/224 duration, 112 lobe centers Roller lifters and rockers 185cc heads with 58cc chamber 2.02In/1.60ex valves Edelbrock RPM intake manifold Quick Fuel 750 cfm with mechanical secondaries Redline Aluminum Exhaust manifolds At 5000’ with an Acme 422, up to about 3200rpm it was 1MPH/100 rpm, then the speed fell off a little in relation to rpm’s. Top speed was 51mph @5600rpm. I don’t know what it all means but it was fun to listen to it sing. I hooked up an AEM 02 sensor. It was running a little rich at 10.9-11.3, at 5600rpm it leaned out to 13.5. |
Replies:
Posted By: 63 Skier
Date Posted: August-31-2018 at 10:57am
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Congrats on the rebuild! Is it the roller assembly that makes it safe up to 5600? ------------- '63 American Skier - '98 Sport Nautique |
Posted By: stepper459
Date Posted: August-31-2018 at 11:30am
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Wow, that's fantastic. I bet it sounds amazing @ 5,000+ rpm. Is there still a muffler inline somewhere? Or is it just straight to the transom? |
Posted By: JoeinNY
Date Posted: August-31-2018 at 11:42am
Safe is relative - stock crank and rods are probably limiting factor but anything close to balanced they should be fine as long as they are getting oil.. Roller cam, intake, and heads will get you to the point where you are making max hp up around there. Prop slippage is a biatch on these larger boats at speeds 50+. Anything other than a pristine never been, scratched, never been reworked prop on my boat will completely fall apart above 51 - ie running 51 at 4900rpm and 53 at 5800 rpm. A pristine prop with the original machining lines intact would be closer to 57. In your case if its a good prop you would probably benefit from more diameter if you can fit it - something like a 224 or a 1490 might work. If you think you should be running lower rpm to hit your max hp you could consider a 1492 if it fits but its a full 1inch bigger in diameter along with the increased pitch. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
63 Skier wrote:Posted By: TRBenj
Date Posted: August-31-2018 at 1:56pm
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Hate to disagree with joe but I suspect the nature of the diminishing returns st higher speeds has a lot to do with the planted nature of the NWZ based hull (even moreso than the 2001). I’ve seen 1:1 tracking (speed vs rpm) up to about 40 and then a 500+ rpm differential at wot, even when topping out in the mid 40’s. All with perfectly tuned props. The faster you go, the smaller the speed returns for a given (additional) RPM. I also haven’t seen advantages of larger diameter props from a speed perspective... once you get into the 12.5” diameter range on these size boats, they all seem to push ok. Holeshot probably improves notionally with larger diam, though. There is a new Acme 3-blade option in the 13x16 range that would be fun to try if getting the revs down would be advantageous... all depends where that engine is making peak power. Those are good numbers for that hull at 5k’. Curious what type of “185cc” heads they are. |
Posted By: AlfaDon
Date Posted: August-31-2018 at 3:01pm
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63- I think what Joe said makes sense. From what I’ve read, lighter pistons help as well as the roller assembly . Stiffer valve springs are a necessity, otherwise the stock springs are just going to float. Stepper- I added a second exhaust tip much like Trbenj. Then I used Centek straight fiberglass mufflers. They have a small baffle at each end and I think they hold a little water to help with noise reduction. JoeinNy- I thought I’d try a bigger prop once I got back to sea level. Ive got an OJ 14x16 that was given to me, although I don’t know the condition. It was fun to see the difference in performance from stock. With the same prop at 5K’ on the stock motor, the Max speed was 38mph- 4800rpm at WOT. Tim- The heads are RHS 35011, although some time was spent porting the runners and valve pockets. They were tested to flow about 265cfm at .500 lift. Something that was interesting to see after reading about planted or slow hulls, as speed increased I could see and feel the nose drop a little. Something that confused me was there was a noticeable stumble about 4800 rpm as I was accelerating. I was increasing rpm slowly so I could watch the O2 sensor. I wonder if the mechanical secondaries wanted more of a “stomp on the gas” , than a gradual increase like vacuum secondaries Thanks for the responses. |
Posted By: JoeinNY
Date Posted: August-31-2018 at 4:05pm
There is all that 2 but I have seen 4-5 mph change on the same boat with the same prop at the same rpm just before and after being reconditioned (by acme)... no difference in performance upto about 50mph - only explanation that works for me on that case is that the prop is not holding shape as well as it did before they sanded off the lines or that they aren't getting the shape back perfect... but the latter explanation doesnt explain why the track the same until higher rpm. . What is known for sure is that it slips a whole lot more at 53mph than 57mph if they both occur at the same rpm. Yes the nose planting and general prop angle at high speeds causes the increased drag that is what is making the prop slip more at the higher speeds but if the engine can still increase rpm greater than its peak hp then you need to address that increasing rate of slippage if you want to go faster. It's the same reason you need more prop diameter or more props and not just more power to pull more skiers - if you cant use all your hp what good is it. We can't really add another prop here, so to address slip you are limited to a few options. For the same material/thickness/profile/rake - props will slip less with more diameter, more blades (to a point), and more pitch - More diameter gives you a bigger water column to push and will slip less for a given rpm and speed. Now it takes more energy to turn it through the water to begin with so maybe you cant get to the same rpm you could with a smaller diameter but either way you are better utilizing the hp available. Obviously you are going to reach a limit here quick but there are big changes in prop area to be had when you increase the diameter even .5-1" Props with more pitch hold their shape better under load, but also require more torque to turn through the water at a given rpm - so more is better until its too much and then its not good at all - but if you feel your peak hp is at less than 5700 rpm and diameter increases failed to get you there then a little pitch might be a win/win. 4 Blades is what you have now, so you are not going up there. I think less blades on a prop that is already being taken to the point where its rate of slippage is going up fast is probably not a top speed winner, although generally more efficient. If the boat was lighter or easier to move through the water then a 3 blade would likely be an improvement, but I think that's how you get a 48 mph flat bottom ski boat to 49.7 not how you get a 51-52mph boat to 54-55. For the same material/thickness/profile/rake props will slip less with more diameter, more blades (to a point), more pitch - ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: JoeinNY
Date Posted: August-31-2018 at 4:10pm
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And with all that being said something don't add up about 3200rpm it was 1MPH/100 rpm 38mph- 4800rpm at WOT. Top speed was 51mph @5600rpm. All out of the same prop/boat ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: 75 Tique
Date Posted: August-31-2018 at 4:42pm
Obviously I dont have the experience/smarts to comment on any of that, but I am enough of a geek that many years ago I put this spreadsheet together to play with prop slip, if anyone is interested and wants to play with it. Also, may not be right, if anyone finds a fault in my logic, let me know. ------------- _____________ “So, how was your weekend?” “Well, let me see…sun burn, stiff neck, screwed up back, assorted aches and pains….yup, my weekend was great, thanks for asking.” |