speed question

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speed question

Postby UT.EAR.DOC » Thu Jul 16, 2015 10:43 pm

Hi Everyone,

I am new to the forum. I have a 1997 Interceptor 212 with a Volvo Penta 5.7 engine. I got the boat 3 years ago with 230 hours on it. We have loved the boat but I have often thought the speed was low for this boat. At full throttle the RPM is 4200 and the max speed on the gauge is 37 mph. Recently, the max speed has decreased to 32 mph or so. I see posts here about boats going 50 mph or greater so I am concerned my boat is not performing correctly. I have 3 props but I don't know the pitch. We use the boat for cruising and rides, not tubing or skiing. Any advice would be great!
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Re: speed question

Postby AndrewT » Fri Jul 17, 2015 4:19 am

Hi UT.EAR.DOC
There should be a number stamped on the prop, with pitch and diameter etc. The factory prop on your set up should be 21P x 14.25" x 3 blade.
You should achieve mid 50s MPH at Wide Open Throttle at around 4800RPM,need to find out what prop you got on her.
Mine does 55MPH @5000RPM I've got a 270HP 5.0GXI with a 3 bladed 21P prop.That's by GPS, check your speedo against a GPS usually they read faster than a GPS.
Something does not add up.Is the motor running fine?
https://youtu.be/q2fZR3TXp9c
2005 Interceptor 212
Volvo 5.0 GXi 270hp
21P 14.5 3B SS prop and 19P 4B SS for wakeboarding and tubing.
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Re: speed question

Postby UT.EAR.DOC » Fri Jul 17, 2015 7:08 am

Yes it has always run just fine, but I've always felt like it wasn't reaching it's top speed. Being a new boater, it was "fast enough" as I was figuring things out :D Now I am eager to get more top end speed, especially if it is capable. It also seems to be bad on fuel consumption but we do take long boat trips. Thanks!
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Re: speed question

Postby m_snow » Fri Jul 17, 2015 4:17 pm

Just a guess, but I think you might be over propped. Too high a pitch makes engine lag and performance suffers. However, you're speedo may be off (obstructed.) Spiders love little holes to home in.
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Re: speed question

Postby iammarcuse » Sun Jul 19, 2015 6:36 pm

Your speedo is blocked. Check the speed on your cell phone. Lots of free download gps apps. You maybe want to drop 2 pitches on the prop and get your rpm to 4500-4600 for that motor.
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Re: speed question

Postby UT.EAR.DOC » Sun Jul 19, 2015 10:03 pm

Ok,
I checked the prop and it has 14 1/4 x 21+ stamped on it. The boat runs great, but at 4200 rpm at max throttle I am going 32-35 mph. So, I assume it isn't the prop and may be something else? It seems like 4200 rpm at max throttle is a bit low to me.
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Re: speed question

Postby AndrewT » Mon Jul 20, 2015 6:28 am

Right prop for this set up.Is your motor carb or fuel injected? GL or GX? 4200RPM is a bit low,is it running smooth?Not missing?
2005 Interceptor 212
Volvo 5.0 GXi 270hp
21P 14.5 3B SS prop and 19P 4B SS for wakeboarding and tubing.
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Re: speed question

Postby UT.EAR.DOC » Mon Jul 20, 2015 8:11 am

Pretty sure it isn't fuel injected but I am not a mechanic, by any stretch. It is a GL for sure. It runs just fine, just seems like it should be faster. This weekend, I pulled it out and pulled the drain plug to see if water was weighing it down. I gained a few mph but then it went back to the old ways later that day. It seems like the throttle tapers out, at 2/3 throttle it is still kicking but as I continue to push to full throttle the rpm goes up but not the speed. Thanks!
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Re: speed question

Postby iammarcuse » Mon Jul 20, 2015 9:50 am

There is really no where this discussion can go until you verify the actual speed with a gps. Speedos are hopelessly inaccurate and useless if the pitot is plugged. The GL is carbed and makes 260hp at 4200-4600 rpm. Your boat would be a good candidate for a 19p Enerta prop to get the most out of it. Should give you 4500 rpm and 50 mph GPS or somewhere between 0 and 60 with a water pitot speedo.
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Re: speed question

Postby UT.EAR.DOC » Mon Jul 20, 2015 9:57 am

Thanks iammarcuse. I tried using the GPS this weekend on my iPhone but couldn't get the mph on the app I used. I will try again next weekend but I have 'paced' the boat with our jet ski and with a friend's bass boat and it is consistent with the speedo on the boat. Thanks for the prop suggestion also.
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Re: speed question

Postby m_snow » Wed Jul 22, 2015 7:36 pm

You're prop may be spinning on the hub. Try tightening that sucker down.
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Re: speed question

Postby iammarcuse » Thu Jul 23, 2015 12:20 am

Yes, it definitely could be a spun hub but tightening it down won't help. It would need to be rehubbed. Assuming it is a pressed in rubber hub, a spun hub will allow the motor to rev up without going faster.
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Re: speed question

Postby buyfire » Thu Jul 23, 2015 10:30 am

m_snow wrote:You're prop may be spinning on the hub. Try tightening that sucker down.



If the hub were spun, his RPM would be high, not low.

Check the back of your tach & make sure it's set to V8, not 4 or 6. Would also be a good idea to have a mechanic put a timing light on it to verify RPM readings.

If all is correct on the tach and the prop is in fact a factory 21P ( not tweaked or re-pitched), and drive is a 1.50, there's either a mechanical or weight issue with the boat. You should be running about 4800 RPM and 50 MPH with your setup.
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Re: speed question

Postby UT.EAR.DOC » Thu Jul 23, 2015 1:42 pm

Thanks buyfire. Quick question, is it hard to check the back of the tach? Do I simply crawl under and look on the back of the gauge for this setting? Sorry if this is a stupid question. We usually pull the boat out after Labor Day for the off-season so I may have it checked by a mechanic at that point. I am glad I found this forum.
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Re: speed question

Postby buyfire » Fri Jul 24, 2015 10:16 am

I'm only familiar with the back side of the Faria tach. If it's the VDO setup, I cant be of much help. If you can crank your head around that far you should be able to see the switch from the back side. There's a small (black?) switch that is either set to V8 or 4/6. If it's set to 4/6 it will read incorrectly, but to be honest, I don't recall if it reads low or high. It's prob set correctly anyway, but it is the easiest thing to verify.
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