Reply With QuoteFirst thing is to verify that your tach is correct. You should pick up more that 100 rpm's with almost a 4000' elevation change.
Last year I dropped a new motor in my boat. Not my choice but it had to be done, long story so I won't go into it. Boat is a 2000 glastron/Carlson CSX21 it had a Volvo 350 280 HP with a SX outdrive 1.43 ratio and I had a carbureted ZZ383 425 hp and 450 Lb ft torque installed exhaust is thru motor not thru hull. This is where it gets interesting. currently have 19 pitch prop turn 4800-4900 RPM - 50 MPH at elevation 4900 ft (pineview reservoir Utah) at Lake Mead same prop 5000 RPM 60 MPH at elevation 1140 FT.
Shouldn't I be turning more RPM's at Lake Mead? Maybe my gauge is messed up.
Is the gear ratio the issue at higher elevation?
I should be running around 5500 RPM at WOT or more
Do I need to pitch down to 17?
Suggestions, input or ideas?
First thing is to verify that your tach is correct. You should pick up more that 100 rpm's with almost a 4000' elevation change.
Sorry I am not much of a motor guy, how do I verify my Tach?
Any idea what kind of RPM gain I should see.
Is the ZZ383 Gm's 383 crate motor? If so, I think you might be having problems with that eventually because thats a car motor and not marinized. Maybe BDMarine can clarify a little more...? As far as RPM, it would be better to run a 1.50 gear ratio but I don't know if that is a possibility with your drive. But do varify that your tach is correct and what kind of speedo do you have?
-Tom
on the other hand your gain is 10mph by going down in elevation with only 100 more rpm?? doesn't seem quite right. .02
Yes it is a zz383 crate motor. It is setup with partial closed cooling system to avoid some of the issues.
Yes I have heard that the 1.50 gear ratio would be better, what does it usually cost to change the gear ratio?
Cash would propbably be the issuewith the gear ratio change at this point.
It seems to me that I might have a tach issue or some rev limiter issue but I am not a expert in the motor department. I am network/computer geek as the wife would put it.
I would dare venture you have at least a rev limiter problem. What were you running for prop before the motor replacement? If a 1.43 was good for you before the swap you will be just fine after! I run up to Pine View from time to time, PM me if you need some help.
Clint
Runnin' Wild
Part of the problem is I picked the boat up from advantage and ran it once at leak mead when I was down there and then had to replace the motor before I could use it again in Utah. So I don't have a clue how it was running before.
The main issue is really what kind of RPM's should I be seeing on that type of motor?
The guy that built the motor suggested that around 5000 would probably be good for WOT.
Any other opinions?
Once I know the RPM range I should be in I can start playing around with a new prop or consider swapping gears.
Mercruiser has the 377 [ 6.2L] rev limiter set at 5150 . The ZZ383 can also be set at this rpm. My drive ratio is 1.65 , spinning Bravo1 26 P props at 5000
WOT . The Bravo1 26 P props measure 25P+1 with cup on a pitch gauge from the factory . I have my props tuned to true 26 , and they're labbed .
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