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Props and rpm

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Old 08-05-2002, 12:31 PM
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Default Props and rpm

I picked up a real clean 1989 272. 7.4's what do others run as far as props on this setup. what kind of rpm as related to speed should I be seeing. I am running 25 pitch 3 blade mirage no prblem with the hole shot seems to be hooked up all the time as far as i can tell. When I give it the go it does not feel like it is slipping. What gets me is I am only seeing 55 mph at 4200 rpm 2/3 tank fuel 3 people. I would think 65+ whats up??

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Old 08-05-2002, 12:37 PM
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russ; you are running to much prop for this hull and motor combo!!most 272 with a 502 and 25 pitch mirage run 65 mph. drop down to a 23 pitch and your rpms will increase about 300 rpms. you will pick up some mph also,but not 65 mph. hope this helps you. bill
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Old 08-05-2002, 12:45 PM
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Thanks Bill but I think you are thinking this is a 271 single. It is a 272 with twin 454's. I would have a hard time believing 65 is not posible. I was told Formula stated 68 as top end.

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Old 08-05-2002, 01:43 PM
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HELP
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Old 08-05-2002, 04:35 PM
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Sombody got to have somthing to say.

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Old 08-05-2002, 06:23 PM
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Russ,calm down. I just tuned in. I too,have a 1989 272 sr1 twin 454/330's with 25" Mirages. I get 78mph...nah, just kidding . I do get better than you. I can run 66-67 most any time at 4600-4700 rpm. Best ever was 69 mph with 4 people and 3/4 tank of gas.BUT that was about 65 degrees , low humidity , with a nice chop and sea level here. This all makes a difference. The only thing different is I have Imco Powerflow headers. They gave me about 2 mph. Now don't be offended , but how about your trim do you know what you're doing with that? I can change my speed about 5 mph with the trim of the drives and/or K planes. When was the last tuneup? How about your timing? Just a few ideas off the top of my head. Hope it's a help. You should get a lot more than 55mph Also check throttle cable adjustment , are the carbs open all the way Just thought of that while proof reading my post
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Old 08-05-2002, 06:27 PM
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Hi Russ, me again. I also have a set of 23" Mirages ....Same speed ,just higher rpm's about 4900. Also lower cruising speed at 3000 rpm and less milage. The 25's are what you want
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Old 08-05-2002, 06:48 PM
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Thanks mopower

The boat is in great shape tuned this year although I have never checked if the throtles are wfo. As far as trim I do believe I have a handle on that. although one of my trim guages is acting up. Machanical indecators are going in next week. The hull is clean but the drives are starting to peel. the boat was in the water 4 seasons befor i got it. I have to check the throtles if you can turn that much rpm I should be close or A little less with stock exhaust.
I need to find out what other 272 are running. what is your cruse at 3000-3500

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Old 08-05-2002, 07:25 PM
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3000 RPM gets me about 40 mph. That's about where I nomally run (3000-3300) I think 3500 I'm doing about 46/47mph. My engines have 711 hours as of 6PM yesterday. Still run good and use about a quart of oil a season. I have stockpiled all the parts for a pair of nice 540's , including brand new Merlin blocks and heads. That will be this winters project
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Old 08-05-2002, 10:09 PM
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Russ --don't mean to tread on your thread, but I've got to do some prop swapping too. I'm running 25 3-blade mirage's, wot trimmed and detabbed is at 4250rpm top speed of 51mph. this is on a 40' scarab with 454's (475hp) and trs drives.
I was going to try some 15*23 pitch 3 blades. but i wondering if i should try some 4 blades, to try to get more stern lift, but might be too much again----maybe 21's?? The props are spinning out right now if I hammer it at just about any rpm- if i take it easy no problem. Any one have some ideas?
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