Max Speed Chap 265ssi

[TedSie]

This is a new to me boat. It pulls like a bull, planes quickly and runs out steady topping out at 4200 RPM @ 45 MPH. The thing that puzzles me is that on the web I've seen top speeds listed from 45 to 60mph for this model. I've checked for codes with a Tech Mate, no codes. I've done fuel pressure and cylinder drop tests and everything checked out fine.
The original owner changed the prop from an F7 to an F5 set because he ran at higher elevations.

My question:
Is my engine performance OK or should I keep looking for that last 200 to 400 rpm.
I would think I should be running at 4600 to 4800 with the F5s

Thanks in advance,

Ted

2002 Chaparral 265ssi
Motor: 8.1Gi-B 401205587
Drive: DP-SM 1.78 (M22) 4202041733
Prop F5
Fuel Pressure a WOT 44psi
RPM at 4200 at 571 above sea level
Full Fuel (75 gal) and Water (40 gal)
Published Dry WT 5850
Clean Bottom
Bimini Up

 

[1947dodge]

Re: Max Speed Chap 265ssi

Maybe check the speedometer cable to be sure thats working right.. Just a thought...

 

[Don S]

Re: Max Speed Chap 265ssi

Boats don't have speedometer cables.

 

[Don S]

Re: Max Speed Chap 265ssi

It pulls like a bull, planes quickly and runs out steady topping out at 4200 RPM @ 45 MPH.

You are right at the bare minimum on WOT rpm, try dropping down 1 size in props and get that rpm up closer to 4600 and you should see an increase in speed as well.

Are you using the trim at best angle (by feel, not by gauge alone).

 

[QC]

Re: Max Speed Chap 265ssi

I know a 255 Chap with the same power plant well. 50 MPH and it is lighter weight.

Can you verify how you're getting speed numbers? And can you confirm your RPM? Doesn't make a lot of sense to be so low in WOT RPM when the last guy was at higher elevation, and dropped pitch to get there. Also bottom condition?

 

[TedSie]

Re: Max Speed Chap 265ssi

Bottom clean
Speed by GPS
RPM using Techmate

Here's what Ive done since I posted last.
Checked throttle body linkage, opening 100%
Changed the plugs. 3 & 5 were a little dark all the rest were nice and tan.
Did a compression test, 150 on all cylinders.
Ran at max. She's surging at WOT.
Removed and checked the fuel cell screens all was clean, I changed the fuel filter at that time also,
Removed, checked and cleaned my anti-siphon valve, it had some junk in it.
Looked like plastic that got in the tank when they drilled and theaded for fittings.
Removed and had injectors cleaned and tested.
I did another cylinder drop test at 1500 rpm all eight dropped equally.
Ran at WOt with the TechMate and fuel pressure guage. Fuel was at 40 to 44 psi,
RPM at 4430.
Speed 42.8 -44
No more surging.

RPM and MPH seem to be tracking 3000 = 30, 3500 = 35, 4000 = 40 so on.
Ran the numbers through a prop calculator seems to make some sense.
6% slip
F5 = approx 19.5
F6 = approx 21
F7 = approx 22.5


Thanks for any insight.

Ted

 

[TedSie]

Re: Max Speed Chap 265ssi

Forgot to mention trim,
Raise the drive until RPM at max (4430)
MPH starts to drop and lower it back down a bit.
(I'm starting to think performance specs on the internet may be slightly exaggerated)

Thanks,

Ted