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Where’s my speed at?
I’ve got a 25’ 2’ 1990 Larson Senza Spectre with the 454 mag, bravo 1 with a 23pitch prop (365hp and 350hp at crankshaft). With 3 people (about 550lbs) and 3/4 tank (80 gallon tank) I run at 53mph (on GPS) @5500RPM... the RPMs seem a little high and speed seems low (even for an older boat). The 300hp test boat ran at 58mph on radar and the 230hp test boat ran at 41mph. This step hull runs 10mph faster than conventional hulls. Haven’t had a ton of time to mess with the boat and really play around so this is pretty much all of the info I have. What can I do to regain some speed? |
Originally Posted by Prestigeworldwideee
(Post 4673063)
I’ve got a 25’ 2’ 1990 Larson Senza Spectre with the 454 mag, bravo 1 with a 23pitch prop (365hp and 350hp at crankshaft). With 3 people (about 550lbs) and 3/4 tank (80 gallon tank) I run at 53mph (on GPS) @5500RPM... the RPMs seem a little high and speed seems low (even for an older boat). The 300hp test boat ran at 58mph on radar and the 230hp test boat ran at 41mph. This step hull runs 10mph faster than conventional hulls. Haven’t had a ton of time to mess with the boat and really play around so this is pretty much all of the info I have. What can I do to regain some speed? Propeller Calculator / Prop Calculator |
Have you checked gear ratio? It may be a 1.65
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53 at 5500rpm sounds like a ton of slip if you have a 1.5 ratio drive.....something doesn’t add up. I dont think the ECM will allow a 454mag to turn that fast unless it’s been reprogramed. Tach off? |
Scratch that last statement, just realized you have a carbed engine. |
Originally Posted by liberator221
(Post 4673080)
Scratch that last statement, just realized you have a carbed engine. |
compression test ?
condition of the props - any redone - Some prop shops do chitty repairs inreturn cost lower performance running condition. My area that is the norm - repaired props junk work Timing and advance ? Full Ignition tune up needed --- possible ? check tach rpms to compare how accurate they are. The tach possible set on the WRONG pole setting would be a good guess here. Or inaccurate Bottom of the hull spotless clean and do you have a painted bottom ? or a repair bottom. Check for hooks in the bottom of the hull. IMPORTANT -- holding extra weight ? water logged ? or bringing water into the boat - ? Rotted wood ? Is your Larson the one with the single Step hull bottom ( DDC) that Harry Schoell designed ?? If I recall correctly that hull bottom for Larson was in 1992 or 93 or 94 ? Forgot when that happened |
Assuming your numbers are correct and it’s a 1.5 drive that’s a crazy high slip. I’d want to borrow a box stock prop and go from there. |
I haven’t checked my gear ratio, I assume it’s 1.5 and it’s one step. The prop is the original 3-blade stainless steel quicksilver prop which seems to be flawless. I think everything is original on this boat, if it’s the 1.5 gear ratio, that’s means I’m getting like a 33% slip. I don’t know if the RPMs are right but that’s what I’m seeing. I can’t do anything right now as it’s winter here. |
Get a good timing light with a tach and you can check the accuracy when you get better weather. I would still try a box stock prop. Easiest thing to do. To see if the numbers change. The prop may look fine to your eyes but people knock and ding them a lot and get them repaired. Very easy to ruin a prop. Next I would go to a waterlogged type situation. |
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