What are the max RPM's?
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Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=46810
Printed Date: April-29-2024 at 3:36am
Topic: What are the max RPM's?
Posted By: davidg
Subject: What are the max RPM's?
Date Posted: September-12-2018 at 3:02am
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I took the '87 Martinique (351W) out for a run this evening, and decided to run it up beyond the normal cruise/ski/tube speed, and see what the old girl would do. I have never given this boat full throttle since I have had it (bought late August 2018), but, what the heck....lets live on the edge! So, I gave her all she's got, to see what max RPMs would be, and hopin' she wouldn't blow. It has a Acme 542... that is a little nicked on the edges. Bottom line.....only got to 4000 rpm. I was expecting more like 4200-4400. Is 4000 correct for this boat/prop combo? What would hold it back from the higher range? I do question whether the 4 BBL is kicking in. Would that be a culprit? |
Replies:
Posted By: MrMcD
Date Posted: September-12-2018 at 4:08am
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I don't know your prop at all but I am familiar with the 351W. I believe the factory says max RPM should be 4400-4600 RPM. Ideally your prop should keep you in that range. Your engine may or may not be young enough internally to reach full power or your tune up could hold you back a little. Some Hulls are harder to move in the water than others. My 78 Nautique with a 351W would RPM up to 5,200 turning a 13x14 Prop and top speed was over 50 MPH. My brother with the same engine in a Supra TSM Comp turning a 13x13 prop could only hit 4,200 RPM and top speed was 42 MPH. I tuned it best I could, checked compression and it would not turn any higher. The Supra had a spare prop in the boat that was a 13x12 and I suspect the previous owner wanted more snap and RPM so purchased that prop. Maybe the Martinique Hull has more drag than the Ski Nautique hull? Our more experienced members will give you the prop specific information. ------------- |
Posted By: 8122pbrainard
Date Posted: September-12-2018 at 7:03am
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Dave, I'd double check the RPMs with a shop tach. Yes, I too would expect a few hundred more than the 4000. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Orlando76
Date Posted: September-12-2018 at 7:13am
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At 4000 I’m sure secondaries are kicking in. 87 Martinique is a BIG girl, I myself am a little a slow with a girl that big, don’t want to blow a gasket or break a rod. ------------- Please support The Cystic Fibrosis Foundation 1976 Ski Nautique 351 Escort 1993 Ski Nautique purple and black 351 HO PCM |
Posted By: KENO
Date Posted: September-12-2018 at 8:16am
If you want to check your secondaries you could do what the guy in the link did All it takes is a zip tie that can slide on the shaft that operates the secondaries and you have to drive it on the water under load because they won't ever open in neutral no matter how high you rev it. http://www.correctcraftfan.com/forum/forum_posts.asp?TID=41479&title=holley-secondaries-issues" rel="nofollow - link |
davidg wrote:Posted By: KENO
Date Posted: September-12-2018 at 8:21am
Well........this will keep me chuckling for a while We don't need any pictures of you in action with a big girl 
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Posted By: phatsat67
Date Posted: September-12-2018 at 1:09pm
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Dave, pick up an Inova timing light if you want to spend a few bucks. They are worth the money. The digital version just does timing and RPMS. The digital pro does timing/rpms/voltage/dwell. I opted for the standard digital because I own a dwell meter already. You can use this to check your timing specs and also verify your tachometer. I would fully expect a good running 351 in a MQ with a 542 to pull at least 4400. The last one of those I drove was surprisingly peppy and pulled the stock prop 4500. https://www.amazon.com/dp/B000EVU8J8/ref=twister_B00OLF5MGW?_encoding=UTF8&th=1" rel="nofollow - Timing Light |
Posted By: davidg
Date Posted: September-12-2018 at 3:43pm
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Thanks for all the responses guys. I do wonder if my tach is totally accurate. I have not done any tuning at all on the boat. If it ain't broke.......! Although, even if it isn't broke, I always manage to go in and break something try to make it ABSOLUTELY perfect! I do agree something is amiss. Tach may be off, engine not quite tuned to perfection, etc. I will have to put this on the long list of stuff that I need to fix. Always something! House, car, truck, kids house, kids car, kids truck....! 
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Posted By: JoeinNY
Date Posted: September-12-2018 at 4:15pm
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That prop if not terribly damaged should have you at all of 4400-4600 with that boat/engine, assuming your tach is right it would be worth popping the distributor cap off and making sure the advance weights are intact and free and maybe setting the points. ------------- 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: TRBenj
Date Posted: September-12-2018 at 4:32pm
| Agreed. I would assume that 4krpm with a 542 on that hull isn’t breaking the 40mph mark (this would be good to confirm). If so, it should have more in it than that. I’d expect closer to 42-43mph. Tune up time. |
Posted By: davidg
Date Posted: September-12-2018 at 7:35pm
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I agree. I think a tune up is in order. The boat actually runs pretty "good". But, more comes to light when you pour the coals to it. Tune up, check distributor, maybe even put a Pertronix in there. I know there is more performance to get out of it. Plus, it has been a bit temperamental to start at times, and will stall out when the unfamiliar drive the boat. You guys like Pertronix? I have had pretty good luck with it in my '68 Ford F250 (390). |
Posted By: TRBenj
Date Posted: September-12-2018 at 7:41pm
| No. Skip that. |
Posted By: phatsat67
Date Posted: September-12-2018 at 8:53pm
| Skip. If the points don’t look overly worn they likely have a good original set in there. Visual inspection and check the gap/dwell is all that’s needed. Verify though you’re ballast resistor is working and you’ll never have issues. |
Posted By: davidg
Date Posted: September-12-2018 at 10:32pm
Zach....Okay, that ballasty thing. Is that the ceramic block that has the two wires attached to it? I know I have seen it on my other boats. I don't know where its at on this one. So, if it is that ceramicy thing, how do you tell if it is good or bad? |
Posted By: phatsat67
Date Posted: September-13-2018 at 10:04am
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Dave, if you have a multimeter check the voltage while idling on the input side of the coil. It should be anywhere from 7-10 volts. If it is getting close to 11-12v then your ballast isn't doing its job. |