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| Author: | Teacher Todd [ Sun May 17, 2009 7:59 pm ] |
| Post subject: | What effect will gearing have |
I am still working on diagnosing my tach problem. Last time out the tach read WOT at 3200 RPMS and 38 mph on the gauge. Some things I was wondering, the boat has been repowered. The previous owner cracked the block. It had a 5.0l in it and he put in a 5.7l. I am 99% sure he did not change the gearing so that means it has a 1.50 gear ratio instead of the what would have came with the 5.7l of 1.41. What will this do to performance and RPM's at WOT? Also notice the prop is scraped front in back on the exact same spot on the blades. Wondering what would have casued this and what damage that may be doing. The current prop is a 15X17 and I do have a spare the previouos owner gave me that is 15X15. From reading it seems this boat should have a 19p prop, is that correct? I am taking the boat in friday to have all the fluids changed, impeller, and the tach checked. I want to get it running perfect and then I will maintain it from here on it. The guy working on it have 30 years experience with OMC so that is good. Any thoughts on what the different gear ratios will do to me? Thanks in advance. |
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| Author: | Choices II [ Sun May 17, 2009 8:07 pm ] |
| Post subject: | Re: What effect will gearing have |
I would start with the prop. Seems to be the easiest and most appropriate place to begin. Might lose a little on the hole shot, but pick some up on the top end as well with the higher pitched prop. |
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| Author: | powellcrazy [ Mon May 18, 2009 6:55 am ] |
| Post subject: | Re: What effect will gearing have |
Changing the gear ratio is similar to changing prop pitches. I wouldn't want to change the gears unless you have found that to get proper RPM you are having to prop way up/down from where you want to be. Example: 15 to 21 pitch being the 'normal' pitch range to get the correct RPM at WOT. If you must install a prop with a pitch that would be out of this range to get RPM desired then consider regearing. But you need to know that the tach is reading correctly, they are off some. You really don't care what pitch prop your using vs. what is recommended from somewhere because most likely that was how to equip at sea level with a empty boat, no options, ect.... What you care about now, is getting the max rpm at WOT, with it today, loaded how you boat, where you boat. There are so many factors that effect performance; elevation, barometric pressure, humidity, weight in boat. |
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| Author: | Teacher Todd [ Mon May 18, 2009 8:01 am ] |
| Post subject: | Re: What effect will gearing have |
powellcrazy wrote: Changing the gear ratio is similar to changing prop pitches. I wouldn't want to change the gears unless you have found that to get proper RPM you are having to prop way up/down from where you want to be. Example: 15 to 21 pitch being the 'normal' pitch range to get the correct RPM at WOT. If you must install a prop with a pitch that would be out of this range to get RPM desired then consider regearing. But you need to know that the tach is reading correctly, they are off some. You really don't care what pitch prop your using vs. what is recommended from somewhere because most likely that was how to equip at sea level with a empty boat, no options, ect.... What you care about now, is getting the max rpm at WOT, with it today, loaded how you boat, where you boat. There are so many factors that effect performance; elevation, barometric pressure, humidity, weight in boat. So true. I am thinking that being that I boat at 3600 feet or higher the majority of the time the gear ratio of 1.5 to 1 might be perfect for me. As soon as I can find out what is up with the tach I will get some proper numbers for us to disect. |
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| Author: | Walt [ Mon May 18, 2009 6:05 pm ] |
| Post subject: | Re: What effect will gearing have |
I would also get a tune-up before getting carried away. You'd be amazed what replacing your fuel filter could do. Along the same lines, make sure you are running good gas, and not last years "left-overs". Changing gear ratio may be somewhat overboard, compared to doing the usual seasonal checks. After all that checks out, then try different props. |
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| Author: | powellcrazy [ Mon May 18, 2009 7:08 pm ] |
| Post subject: | Re: What effect will gearing have |
The lowest my boat ever see is 3700 ft., and upto 7000 ft. There sure is a huge difference between 4000 and 7000. Night and day! When I go to the higher lakes, I just live with poor performance. We don't go often to justify any corrections. |
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| Author: | Teacher Todd [ Mon May 18, 2009 7:29 pm ] |
| Post subject: | Re: What effect will gearing have |
Walt I agree about the tune up. The new gas made a noticable difference. I guess I should add that the boat runs great. Planes immediatley and seems to have plenty of power. I have not towed anyone or driven next to a comparable boat to verify the seat of the pants feel yet. Once I figure out if the tach is bad, I am pretty sure it is, I can determine how I am doing. I am not planning on changing the gears out I was more curious as to the effect with the engine chamge that was done. Boat is going in friday so that will tell me about the prop. Taking a camping trip in a week and will be towing people so that will confirm what I believe to be a strong running boat. Thanks for all the help and keep it coming if you think of something else. |
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| Author: | powellcrazy [ Mon May 18, 2009 8:05 pm ] |
| Post subject: | Re: What effect will gearing have |
The 1.5 ratio will let the motor rev higher vs the 1.41. this is a benefit for higher elevation. If you were running identical boats (motor wise), one with each of the ratios, you could run a higher pitch prop to get the same RPM at WOT with the 1.5 ratio. 1.5 ratio with 19 pitch prop could over rev, at sea level, would have to prop up to maybe a 21. Hope that may explain a little different than before??? |
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| Author: | 1NiceHarley [ Mon May 18, 2009 8:38 pm ] |
| Post subject: | Re: What effect will gearing have |
The guy I bought my boat from replaced the dash and when he did that, he didn't put the RPM gauge on the correct setting for a V8. Which gave me some weird RPM readings. Now that it is in the correct setting my RPM gauge works better and I am in the correct range for WOT, where as before I couldn't get to the correct range no matter what I propped it. Just another thing to consider, check your RPM gauge for the correct setting for your engine. |
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| Author: | Teacher Todd [ Mon May 18, 2009 11:50 pm ] |
| Post subject: | Re: What effect will gearing have |
Troy thanks for the tip on the gauge. It is set correctly. I was hoping it was off and the problem would be sloved.  Powellcrazy Thats what I was thinking, but needed to hear from someone else as well. First things first though I need to determine if my prop is working. Also i noticed that at times with the boat turned off and the isolator switch off the tach gauge would read 400 rpms. |
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| Author: | Teacher Todd [ Fri May 22, 2009 6:42 pm ] |
| Post subject: | Re: What effect will gearing have |
The boat is back from the shop. I had all the fluids changed. I also had the fuel filter changed. As for the tach it was reading 1000 RPMS low. THey were able to get it withing 300 RPMS of actual. I told them that the boat seemed to run great but surged a little at idle and would stumble. They checked and found the timing to be off. They fixed that and said it should be a lot stronger. I will now try to get a more accurate read on this prop, but I am thinking I may need to go to a 19p at the home lake and keep the 17p for the high lakes. Hope everyone has a safe Memorial day. |
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| Author: | LouC [ Sat May 23, 2009 5:21 am ] |
| Post subject: | Re: What effect will gearing have |
I was going to say that the drive ratio for the 5.0 should actually help you (kind of like going from a 3.73 to a 4.10 rear in a car), and that the tach had to be reading low. My boat came with a 19 originally, it was supposed to have a 17 on it, and with a 15x17 it performs great. The tune up and setting the dwell and timing exactly right also made a big difference. That boat should fly with a well tuned 5.7. |
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| Author: | Teacher Todd [ Sat May 23, 2009 9:54 am ] |
| Post subject: | Re: What effect will gearing have |
The wait to get it on the water is killing me. I decided to avoid the lake this weekend since we are going camping on Wednesday and will be on the lake for 5 days. The scary thing is I was perfectly happy with how it was running before I took it in. I just wanted to know what was going on with the tach and why I had some surging and stumbling at idle. When he said the timing was off and that I was way down on horse power I got a little excited to see what it will really do. 
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| Author: | captkevin [ Sat May 23, 2009 11:14 am ] |
| Post subject: | Re: What effect will gearing have |
Sounds like you should be in good shape |
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