williamhay
New Member
I've had the boat for about two months. Still practicing with the trim tabs. How far down is too far down where I will start creating drag?
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Hello rknecht and masterfab. I would like to ask a question reference your comment below. I do have problems reaching my max speed. Not RPM's tho. I have an 06 340 with twin 8.1S v drives. I can hit 4900 RPM's according to my smart craft. But I start to fall off plane at 3800 RPM's and I can only top out at 30mph. The bottom is clean. Could this be related to exhaust issues?
William
These numbers seem way off to me. I have a 2002 340 with 8.1s and I cruise comfortably on plane at 26 to 27 miles an hour at 3200 RPM. My top end was 43 MPH at full throttle. You did mention the bottom was clean, which I have found to be the biggest contributor to poor performance. I had a Silverton last year that I spent thousands trying to diagnose why it wouldn't get on plane only to find the bottom needed cleaned!
Rob
I have a friend with an 01 340 and the 6.2l MPI motors. He's having problems with his port motor not achieving the desired rpms. Does anyone know what the compression should be on this motor?
My 5.7s on my 300 was 130-140 psi... It is important that there is consistancy in the numbers....
I think he said all cylinders were at 180 but one was at 145ish.
William
These numbers seem way off to me. I have a 2002 340 with 8.1s and I cruise comfortably on plane at 26 to 27 miles an hour at 3200 RPM. My top end was 43 MPH at full throttle. You did mention the bottom was clean, which I have found to be the biggest contributor to poor performance. I had a Silverton last year that I spent thousands trying to diagnose why it wouldn't get on plane only to find the bottom needed cleaned!
Rob
Rob, what is the pitch of your props?
Hi -
Maybe this can help with the RPM issue. I had problems with my '07 340 with 8.1's speed / RPM's when I moved from ~200' to ~6300' at Lake Tahoe. I never did push my top speed at 200', but I had a big problem when moving to altitude (80% air density of sea level). I could barely plane and the RPM's were 2800 / 3400 on my engines.
Here are some of my stats.
Pre-move (200' above sea level): As far as I could tell, normal performance to what has been reported here.
Post-move (6300', filled up with ethanol fuel after arrival, non-ethanol unavailable): Top speed was 23mph barely on plane with full throttle and my engines at 2800 and 3400 RPM, respectively.
Post-move (added ethanol buster to fuel, never had to worry about that): Top speed of 31mph with engines at 3650 and 3850 RPM, respectively.
Post-move (ethanol buster + repropped from 18 x 21.5" RH prop and a 18 x 22" LH prop to 18 x 19 for both props): Top speed of about 33mph with engines at ~4300 RPM. Both engines now in sync again. I run it at about 3800 / 27mph.
So, if you're not at any significant altitude, my thoughts would be to make sure you have non ethanol gas or an ethanol buster additive. I couldn't believe the difference.
-Gary
I'm fairly sure I have factory props (18x21.5) If I were to change to a higher pitch, would that increase my speed? What are the down sides to a higher pitch prop?