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What limits the RPM and what is safe to Spin to? 7.4L

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Old 05-22-2009, 01:57 PM
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Originally Posted by boat teck View Post
I could be wrong here but I do not think merc was doing rev limits yet in 1986, Do you have a old manual of any kind laying around or do you still have the OEM flame arester on the carb or any old stickers on the engine that would say what max RPM you should be running at when it was still stock that will give you a starting point, To me 4300 just sounds a little to low of a RPM.
yep I figure 4300 is a bit low as well, I'm lookin for 4800 at WOT after props.. one can only hope
also I did not mention the exhaust internal flappers were all fouled and sticking closed, the new tips will have external flappers
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Old 05-22-2009, 03:19 PM
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What are low hour 7.4L EFI's going for these days
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Old 05-23-2009, 08:34 PM
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Well boy was I wrong, I watch the tach today while doing a full throttle run and it hit 5,500rpm's! Should I consider a prop change? I do have a 3 blade SS prop (not sure on the pitch but I can check) maybe a 4 blade prop??Sorry for stealing this thread but just a simple question.
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Old 05-23-2009, 09:03 PM
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Originally Posted by daredevil View Post
5500 is way to much for a stock 454 !!! 5000 @ the most !
And even that is pushing it !
If i where u i go 2 pitch sizes bigger ,or 4 blade and still 1 size in pitch higher.
I know it is for a stock junk 330 454, iam suprise it didnt throw a rod out the pan today!
Do you think I can benefit from changing my 3 blade SS prop to a 4 blade? What is the con's and pro's? I will get the pitch size tonight on my 3 bladed SS prop thats on it now.
Erik
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Old 05-23-2009, 09:06 PM
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Originally Posted by crapr6 View Post
Well boy was I wrong, I watch the tach today while doing a full throttle run and it hit 5,500rpm's! Should I consider a prop change? I do have a 3 blade SS prop (not sure on the pitch but I can check) maybe a 4 blade prop??Sorry for stealing this thread but just a simple question.
Thanks
Erik
Yes 5,500 would be a bit over the safty zone 4800 to 5000 is just a safer way to go.You should try to stay around 5000 when you run a lighter load in the boat [less gas and just you and the g/f or wife] That way you should steel be around the safe zone at 47/4800rpm when it time to take out all the g/f or wifes hot frinds
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Old 05-23-2009, 09:14 PM
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Its funny because when I had it out Wensday I thought I only seen 5,000 rpm's on the tach but today she spun up to 5,500rpm's. Now the only diffrence from Wensday to today is Iam running the fuel tank down to empty, but also I had my sister in the boat. So less fuel but an extra person.
Will prop change in pitch and going from 3 blade to 4 blade help mph?
Erik
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Old 08-31-2009, 10:39 PM
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What did u ever come up with...
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