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21 SSI 2020 with 4.3 Volvo stern drive 240 hp


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The max RPM that I get with 1 or 2 passengers and half tank of gas is about 4400 RPMs. Manual says that with this aluminum block gen 5 that I should get 5600-5800 RPMs

Yes... I know that this is high for a 4.3 V6, but this is how the reworked gen 5 is rated (according to owner's manual)

I'm trying to figure out if I have a Tach problem (in wrong cylinder configuration etc.) or if I have a computer / fuel injection issue.

Top speed is around 48 MPH (about right). Acceleration seems okay

I run 89 octane marine grade  gas...elevation is 1670 MSL...Air temps around 78*F

The prop is what came on this boat... A 3 blade aluminum 14.5 X 19 pitch

Going to 17* pitch would add RPMs. But maybe all I have is an error (or switch position) in my TACH

 

Appreciate your feedback!

Thanks

Sandy

 sreinauer@hotmail.com

 

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Did not register that it was a 2020.  What will it do with a full load of people & equipment & gas ?  Dealer is putting on the cheapest prop he had in his shop.

Dealer IS SUPPOSED to size the prop correctly to the conditions you specify !!!!!!!!!  That is included in that many thousands of dollars  called Dealer Prep charges.

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6 hours ago, cyclops2 said:

Did not register that it was a 2020.  What will it do with a full load of people & equipment & gas ?  Dealer is putting on the cheapest prop he had in his shop.

Dealer IS SUPPOSED to size the prop correctly to the conditions you specify !!!!!!!!!  That is included in that many thousands of dollars  called Dealer Prep charges.

Dealer tells me that this is the prop that Chaparral Inc. put on the boat BEFORE they shipped it to Atlanta Marine (Lake Lanier, Georgia). So, top speed is usually around 46-48 mph (half tank gas). Acceleration is okay...even with 3 or 4 adults while pulling my 9 year old grand daughter up on water skis (she's not heavy). 

It's just that I don't get anywhere near the expected RPM that this 4.3 aluminum block gen 5 is supposed to get... Manual says up to MAX 5600-5800 RPMS... I'm getting 4450 RPM.

If I'm just cruising the lake around I usually set 3200 RPMs and trim for best speed. But if TACH is in error, I could be running a higher RPM.

For sure in the spring will take back to dealer to get a better sized prop or fix the tach.

I'll post the final fix later.

Thanks again,

Gordon

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Dealer is supposed to  ASK YOU  what & how the boat will be used .   ALL the props ARE KNOWN that would run your boat in a full load condition . I have always had 2 props for my 20 footish V 8 powered boats.  ALL are single prop drives. 

Me alone prop.... Go out racing around a bay doing floored from a dead stop doughnuts. Figuree 8s.  Then a WOT for several minutes.  Drink water do it till lunch.  Do it again after lunch.  I can burn up 28 gallons by sundown.

other prop is for great cruise with 6   ....over 210 pounders on a full plane.

I jump in the water with rops on the tools used to change props.  Takes 5 minute3s to change the props. Prop HAS A ROPE ON IT at all times.

Piece of cake to tow 2 BIG guys .

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I have suspected all along that my tach is set for a 8 cylinder engine thus giving me a low reading...Top speed (48 mph) and sound suggests that this boat is running properly. 

I have another engine analyzer that has a tach function. Will use this to cross check. In the spring, will return to the dealer ( 1.5 hours away) to get tach replaced if necessary.

I sure thank you all for your input...this forum has been very helpful!

When all is figured out, I plan to replace  OEM aluminum prop (19 pitch) with stainless steel prop... hoping to add a little more top end.

Thanks

Gordon "Sandy" Reinauer

 

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9 hours ago, Sandy Reinauer said:

Suspect that  NMEA2k gateway might be expensive...I'll try my engine analyzer first. If it is a tach error then I'll be taking it to my Chaparral dealer (in the spring).

All winterized for now so no rush.

Thanks

Nope, cost was about 175. Plus a few cables.

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  • 2 weeks later...

Think I found the problem...The TACH which is made by Teleflex (not Faria) was set for an 8 cylinder engine. Had to remove from dash which was easy to do ( 2 nuts)

Takes small bladed screwdriver to move selector to correct position (6 cylinder)  ... This TACH could work on a 4 or 6 or 8 cylinder engine (just adjust selector)

It was set WRONG from the factory...I'm the new  & only owner of this 2020  21SSI  (4.3 V-6 Volvo gen 5  240 hp)

Boat is now on trailer & winterized... so next spring I'll confirm the TACH is reporting correctly  (should be around 5600 - 5700 RPMs)

BTW...  I'm replacing the OEM prop alum 3 blade 19 pitch with new stainless 3 blade 19 pitch...I'll provide feedback in the spring about any performance changes.

Safe safe!!

Thanks all

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On 11/28/2020 at 7:29 AM, dan02gt said:

You’re tach is way off. The math indicates you are turning ~5500 RPMs at 48 MPH. I think dropping to a 17P would put you right in the middle of your recommended WOT range. 

The engine was running fine with 19 pitch prop...speed and sound confirm this. Just discovered that the TACH was set for 8 cylinder which gave false reading (too low).

Easy to remove TACH and move selector to 'correct' V-6 position (was set wrong by factory). Should be working fine now...Will check in the spring when I put her back in the lake.

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