2020 Glastron GT185 only 43 MPH top speed

Steph Tremblay

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Jun 28, 2022
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Hello Glastron GT185 fans, can you share your top speed (along with engine and prop combo) ?

Mine is a very disappointing 43 MPH. I am alone in the boat, speed has been verified with GPS and I have the stock 4.5L 200 HP Mercruiser. The prop is the stock 19 pitch.

My top speed is limited by RMP limiter that kicks in at only 4800 RPM.

Is it normal? The boat runs fine otherwise
 

jimmbo

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May 24, 2004
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Welcome to iboats

I would expect about 45- 46 out of that combo, so you're not too far off.
I doubt the Rev Limiter is set at the top of the recommended WOT Range which is 4400 - 4800. They usually don't kick in until a few hundred rpm above it.
Are you trimming the outdrive out for best speed, once on Plane?

A 19" sounds a bit low, but without knowing the Gear Ratio, I really can't speculate. What RPM are you getting?
Try a 20, or a 21, if the RPMs remain at 4800, then the 19 was too small of pitch. However the Holeshot will be much slower
 

Steph Tremblay

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Jun 28, 2022
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Welcome to iboats

I would expect about 45- 46 out of that combo, so you're not too far off.
I doubt the Rev Limiter is set at the top of the recommended WOT Range which is 4400 - 4800. They usually don't kick in until a few hundred rpm above it.
Are you trimming the outdrive out for best speed, once on Plane?

A 19" sounds a bit low, but without knowing the Gear Ratio, I really can't speculate. What RPM are you getting?
Try a 20, or a 21, if the RPMs remain at 4800, then the 19 was too small of pitch. However the Holeshot will be much slower
Yes, this is the problem, rev limiter is kicking way too early. The 4.5L 250HP is EXACTLY the same engine, only the PCM tune is different and Mercruiser limit the 250HP at 5200 RPM.
Will definitely prop it to 21 pitch but I find it ashamed that Glastron publish 49 MPH for the GT185 on this engine (page 8 of attached PDF)...
 

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jimmbo

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MC 4.5L 200/A 14 1/2 x 19 AL 48-51mph 77-82kmph Page 13

If Glastron is giving a range of 48 - 51 mph, with a 19 inch prop. I will assume the 48mph is at 4400 rpm and the 51 is at 4800 rpm. So something is not adding up. What is the gear Ratio on your outdrive?
 

Steph Tremblay

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Jun 28, 2022
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MC 4.5L 200/A 14 1/2 x 19 AL 48-51mph 77-82kmph Page 13

If Glastron is giving a range of 48 - 51 mph, with a 19 inch prop. I will assume the 48mph is at 4400 rpm and the 51 is at 4800 rpm. So something is not adding up. What is the gear Ratio on your outdrive?
I don't know about the gearbox, I am 99% sure the previous owner didn't change from stock.

Would really like other owners of GT185 with the 4.5l chime in and report their top speed too...
 
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