want more top speed

[Horizon190/5.0GLI]

Re: want more top speed

Hello sparkinator

What ratio are you running on you Sx Drive?

 

[Sparkinator]

Re: want more top speed

1.60 : 1

My 19 pitch is really a much more versatile prop, but I can definitely get better top end with the 21. I can overrev the engine with the 19, but only if I trim it all the way up and the lake is smooth as glass. Thats the only time I really have to be careful with it.

 

[Tail_Gunner]

Re: want more top speed

http://www.rinda.com/marine/mtspec.htm

Im sure im off the beaten path here but mefi-1 has a rev limiter you cant go past 4900. 6000 is impossible

 

[QC]

Re: want more top speed

This thread is driving me nuts . . .

I still think the tach is wrong. 6000 RPM? Without the gear ratio this discussion is stupid, and I see a possibility of 1.41, 1.51 and for some reason we have somebody else's ratio stated as 1.6. I think that is mucking this up. No matter what ratio, 6000 RPM, 17 or 19 pitch, and 52 MPH does not add up. We have 20 - 30 % slip and I ain't buying any of it . . . maybe it is totally blowing out, but these are stupid numbers at this point.

And TG, do we know what type of controller is on a Volvo, Cobra 5.8? I am guessing it is not MEFI, but I can't confirm by my first look. No matter what, I believe there would be a rev limiter well below 6000 . . .

What I can confirm is that 5.8s were definitely used in Volvo SX's around that time. roknrollo, nobody else, what is your gear ratio? I am guessing 1.51 at this point and showing a 4200 - 4600 recommended WOT RPM.

 

[45Auto]

Re: want more top speed

LMAO, I know what you mean QC!

At 5800 RPM it's probably putting out about half the power it delivers at 4800 RPM. If it was really doing 52 MPH at 5800 RPM, then just think what it will do once it's propped into the correct RPM range! It'll easily be a 70 MPH boat!

 

[Sparkinator]

Re: want more top speed

This thread is driving me nuts . . .

I still think the tach is wrong. 6000 RPM? Without the gear ratio this discussion is stupid, and I see a possibility of 1.41, 1.51 and for some reason we have somebody else's ratio stated as 1.6. I think that is mucking this up.

Take some deep breaths. You'll be OK. That always helps me.

The guy asked me a question about my drive after I had given some usefull information to the OP. Did you look at the link I posted? It gave him MPH and RPM for a 21' 6" bowrider with a 5.8L Ford with an SX drive. Thats the best link I could find for MPH/RPM for his boat. I had already given him a link for the VP service manual.

Oh yeah, and I answered the ratio question 4 days after the OP quit responding in the thread.

 

[QC]

Re: want more top speed

I'm sorry to sound pizzy . . . Actually your link was one of the things I used for reference.

It does get messy though when we have specs from other combos. Considering we still don't know what his ratio is, I thought I'd bring it up again and see if we could make some sense out of it.

 

[Sparkinator]

Re: want more top speed

No problem QC.

I don't have my manual with me, but I'm pretty sure the 5.8 had a 1.50:1 gear ratio.

And I agree on the tach. I haven't been around them as much as the OP states, but those numbers he's turning don't sound right at all.

I'll hang up and listen now.

 

[Tail_Gunner]

Re: want more top speed

I went into Havasu today as it was blown out on the water, I found a 19 pitch prop I couldnt pass up for 80.00 brand new in the box (volvo penta), so I figured I'd give it a try, it will make a good spare anyways.

I did check the tach with another one I had in my garage and the tach on the boat is right on the money, for some reason this omc cobra 5.8 will rev up to 5500 and smack almost 6000 if I push it, I would think it would have a rev limiter on it, obviously I only did it for a couple seconds, from what I read max rpm is like 4400.

Ok ... your tach is off..The 5.8 ford with a cobra uses a 1.51 drive ratio.

1.51 @ 5600 yeilds 67 thero speed...Now 10% which is a robust number thats 60. (19p prop)

Now lets clean it up a bit...

19@ 5600
20@5400
21@5200
22@5000
23@4800........

Heres the yield.....69 mph thero...62 @ 10% slip. Thats a 260 hp boat..Older and a i/o...55mph would be a leap for that combo..Fresh and right out the box

Notice the 5600 and the 4800..then take a look at your final speeds. you can just keep propping up until you find the prop that slows you a bit..Then your over propped.



Chris Craft 21 Concept Bowrider Specifications

Monday, August 6th, 2007
Chris Craft 21 Concept Bowrider Specifications. The following specs for Chris Craft Boats are for informational purposes only, we do not guarantee their accuracy.
Length: 20′ 11″
Beam: 8′ 0″
Draft: 2′ 9″
Weight: 3375 lbs
Fuel tank size: 35 gallons
Water tank size: 8 gallons
Hull type: Modified V
Deadrise: 17 degs
Production year(s): 1994 - 1997
Engine options: Single Stern Drive Gas 250 hp 5.7L Volvo
Top Speed: 50+ mph


The ecu is probably a ford ec 4 ...delphi running a ford motor...

 

[Robbabob]

Re: want more top speed

Yes, things have gotten a litte confusing. Since the OP checked the RPM with another tach, could there be an issue with the wires going back to the engine?

I have an issue with my tach jumping 1000 to 1200 higher than actual, then it settles back again without any changes to throttle, trim or engine sounds. OP's 3500 rpm at 32 mph sound right, but then WOT readings muck things up.

Seems to me (and most everyone here), the readings are impossible. Can it be in the wiring or am I completely off base?

Mods should delete this comment if I am only confusing the solution further. Just want to add a brainstorming direction... if it helps.

 

[QC]

Re: want more top speed

No need to delete . . Most tach issues are with the switch in the back for 4, 6 or 8 cyl or OB . . .

With that said . . . we haven't seen the OP for over a week, so I think we'll just have to hope he chimes back in.