VP 5.7 GL low rpm/mph

[shabs1986]

new to the I/O world here so bare with me, I recently bought a 05 Glastron sx 195 that came stock with a 5.0Gl but the owner before last upgraded to the 5.7 after they failed to winterize properly. Anyways i've tried a few props
-18p x 14 3/8" 4 blade mich apollo averages 50mph@4800
-20p x14" 4 blade mich apollo 52mph@4600
-21p x14" mich apollo 3 blade 53-54mph@4600
My Question is are these normal numbers or should i start looking into tuneup items on the engine, I was kinda expected more from the 5.7. Seems to run good other than it's a little cold blooded in cooler temps. Suggestions welcome thanks

 

[Dave-R]

If the original engine was a MPI , and you just swapped all the parts. I think the ECM will need to reflashed to allow more fuel for the 5.7. If they are both carb engines, maybe nothing needs to changed. Are you hitting the rev limiter? Dave-R

 

[Scott Danforth]

welcome aboard

would need a bit more information

was the 5.7 a boat motor or a truck motor tossed into the boat?

if it was a GL, its a carbed motor. was the carb re-tuned for the larger motor?

if your looking for 60+ mph, you need more motor

 

[jimmbo]

deleted

 

[shabs1986]

Yes it's a GL carb version, by doing some research on here looks like only carb setting difference is a bigger power valve, otherwise both seem to be identical setups. Shouldn't be hitting the rev limiter operating range in manuals say 4600-5000rpm. I'm hoping it's not a truck 350, work was done at a marine shop not a back yard mechanic but the paper work details don't really specify just has product numbers. I will probably do compression checks and do complete tuneup this fall, regular engine and drive oil changes were done but doubt full tune up has been done regularly i'm pretty particular. Don't necessarily want a 60+ mph boat but don't want to leave anything on the table either, if it's tuned and proped correct i'm happy with what it is.

 

[QBhoy]

Sound reasonable to me...if they are GPS speeds.
Don't pay too much attention to folk with similar boats and engines who tell you their boat does 60/70mph.
Speedometers on boats are often also known as dreamometers!
The speedo on my boat has figures up to 65mph and increments up to 70+.....it will fill the clock easily, but in reality is only doing 63/64mph in most cases in general family use with the hood up.

 

[QBhoy]

Jeez...the jet ski I have speedo says it does 112kph (69 mph) but the GPs says 57/68 tops!

 

[alldodge]

Jeez...the jet ski I have speedo says it does 112kph (69 mph) but the GPs says 57/58 tops!

Not much difference between 68 and 69

Edit: Ok little difference between 57/58

 

[QBhoy]

Haha...you know what I meant to type AD.
57/58....obviously. It's late over here...cut me some slack !

 

[QBhoy]

I had a great example of speedo exaggeration syndrome tonight.
A fellow at the pub on the island was boasting that his ring 16 with the 90hp yam was doing 60mph easy...
Reckoned she was amongst the fastest boat on the lake....(and she may well be in the top 20, if she was)
Although the ring hulls are well known racing boats...they cannot be compared to their bigger siblings, the 18 and the 21, which both demand 200hp v6 upwards...and are famed for 70+mph.
Anyway, he had a wee run in against the campion tonight on the way home...the results were inevitable...in fact i even ran next to him and he was only doing 47mph real GPs speed. Impressive as that is for the moderate HP.....it ain't the 60mph his speedo or ego dictates !