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What performance issues with 1 cyl down?

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Old 12-09-2011, 09:49 AM
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Default What performance issues with 1 cyl down?

On my formula 311 with 420's I had a cylinder completely down would that cause both motors to run poorly? Mechanic told me I would have lost 750rpms from one cylinder. I was running 25p plus mirages and at wot I only got 4k rpm out of both motors. Would it be worth running those props again with full power now?
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Old 12-09-2011, 10:44 AM
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Hey man -- I wouldn't change props until you know both motors are running correctly.. The other motor would not run incorrectly based on the opposite engine being bad, if that's what you are asking. However, it's effectively doing all the work, especially at higher rpm, and being "dragged" down my the low performer of the pair.

Don't change a thing until you get it fixed and back on the water to get a baseline of where you really are with both motors making full power. Buying anything until you get a good baseline is like throwing money into the fire. You may need different props, but you'll be able to figure that out pretty accurately once you get this baseline.

It's going to be a long winter, for both of us
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Old 12-09-2011, 11:26 AM
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I lost @ 400 RPM when I had a plug wire fall off.
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Old 12-09-2011, 11:34 AM
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Years ago I lost an injector and lost a cylinder.....motor lost about 500 rpms but the other motor lost rpms too. I'm guessing the added stress of trying to push that heavy azz boat was too much for the other motor (382)
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Old 12-09-2011, 11:51 AM
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What did you decide to do with the motor? Just the top end, top and bottom, crate motor?
How did the cylinder walls look?
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Old 12-09-2011, 08:22 PM
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Originally Posted by brivander View Post
Hey man -- I wouldn't change props until you know both motors are running correctly.. The other motor would not run incorrectly based on the opposite engine being bad, if that's what you are asking. However, it's effectively doing all the work, especially at higher rpm, and being "dragged" down my the low performer of the pair.

Don't change a thing until you get it fixed and back on the water to get a baseline of where you really are with both motors making full power. Buying anything until you get a good baseline is like throwing money into the fire. You may need different props, but you'll be able to figure that out pretty accurately once you get this baseline.

It's going to be a long winter, for both of us
Trust me I know, I'm just trying to get my ducks in row so that when I do get the boat in the water I know where to start and what to start with. I think I'm going to keep the 25+ mirages on there and see where I get my rpm's up to at wot. If there even and up to 5k rpms then I'll probably leave them and maybe borrow a set of 24p Bravo's off of Artie.

I got the boat back this week and put it away for the winter, I'm going to try to pull the bolsters out when I get some nicer weather and have some of the vinyl replaced.

As for the motor that was worked on I had the one head partialy rebuilt. They had to mill a tad to make it flush again but not a hole lot, valves were replaced, and springs where good. Apparently the heads have had work done before. The other side was left as is. The compression was down but he sprayed some carbon remover crap in it and left it over night and the next day the compression was back up. I didn't want to tear a whole bunch into the motor or just top end, I just wanted to fix what was broke and go from there. He warned me redoing all of the top end good put more strain on the bottom end do to the age of the motors.

I love the boat and will make a more drastic change on the motors when I have the money. The tranny job and the water cooling system issues from earlier this year has trained me.

Gonna def be a long winter...
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Old 12-09-2011, 09:03 PM
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Sounds like you will eventually need motors done but hopefully, you will be good for a year or two.

As for the prop, I bet my house those 25" miriages are too big. But I don't know what ratio you have so I can't say for sure. Get back on the water and do some testing. Maybe 22" 4 blades will be the ticket.
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Old 12-09-2011, 09:25 PM
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Originally Posted by In The Pink View Post
Sounds like you will eventually need motors done but hopefully, you will be good for a year or two.

As for the prop, I bet my house those 25" miriages are too big. But I don't know what ratio you have so I can't say for sure. Get back on the water and do some testing. Maybe 22" 4 blades will be the ticket.
I agree with both of you, sounds over propped, but if he's got a set of 24" props to try I'd start with what you have and then try those... Just don't get ahead of yourself with props until you verify the motors are running correctly -- the 420's are a 5000-5200rpm motor correct?
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Old 12-09-2011, 10:59 PM
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As for the motor that was worked on I had the one head partialy rebuilt. They had to mill a tad to make it flush again but not a hole lot, valves were replaced, and springs where good. Apparently the heads have had work done before.
So what was done to the heads before? Heads ported?

What kind of valve did you end up with and what size are they?
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Old 12-10-2011, 01:36 AM
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Drive's me up a freakin' wall when people are worried about their performance when their engines are not even running right. I am glad you got it fixed, most do not, but I would keep an eye on all of it. There are a lot of kids out there now a days that buy sports cars, boats, etc and are only worried about performance and forget that sometimes the biggest performance mod you can do on a single platform is to ensure the car, boat, etc is running correctly. Maintenance before modifications in my book (including props). But, not everyone is a super picky mechanic and worries about that sort of thing like me. I hope it all works out for you in the end.
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