Compression 454 MPI MAG
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Compression 454 MPI MAG

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    Member Mach80's Avatar
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    Default Compression 454 MPI MAG

    I have been trying to trace down low performance on my 2001 454 MPI MAG. I did a compression check today and they checked between a high of 120 PSI to a low of 80 PSI per cyllinder. I'm sure that I probably need at least a valve job. I'm planning to do a leakdown test on the low cyllinders tomorrow. What compression numbers have any of you seen on a bacically stock 454 Mag? Do any of you have any good head and cam reccomendations for a 454 MPI motor? It seems it may be time for some more power.

    Thanks,

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    New here Beer:30's Avatar
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    Tyler Crockett Marine has a "recipe" for 454/502 marine engines. It's a "top end" kit, with their-spec cam and a bunch of parts that you have your machine shop (of choice) put in. Or, you can send your heads to them.

    A guy here did this to his 502mag and was MORE than happy with the results. Easy 100hp just by "freshening" the top end of the motor.

    http://www.crockettmarineengines.com/products.html
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


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    Here is the latest. Tried to do a leakdown test and none of the cylinders would hold more than 10/15 lbs with 50 to 90 PSI on the input side. I could hear most of the air excaping from the intake / intake valves. This seems to me that I'm doing something wrong as I would not think the boat would run with this much leakage. It actually runs pretty good at WOT, but it idles roughly. I tried a standard compression tester and they actually tested 10 lbs higher than yesterday. They tested between 90 and 130 today. The engine was cold today. Any thoughts??

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    cfm
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    80/90 psi is enough reason to tear it down. IMHO no reason to do a leakdown test at that point unless wanting to hear if air is going thru to crankcase or going past a valve.

    Oh, make sure you are doing leakdown at compression TDC, not overlap TDC.

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    Member Mach80's Avatar
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    I rotated it all the way through to see if I was not a TDC. There was no position that raised the numbers. The weird thing is that I can get 5000 RPM at WOT and run 68 on GPS in a 25' Nordic Rage. I just have rough idling and a very poor holeshot.

    Thanks,

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    Well the engine is coming apart. I'm going to go with the Tyler Crockett MPI upgrade kit.

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    Quote Originally Posted by cfm View Post
    80/90 psi is enough reason to tear it down. IMHO no reason to do a leakdown test at that point unless wanting to hear if air is going thru to crankcase or going past a valve.

    Oh, make sure you are doing leakdown at compression TDC, not overlap TDC.
    Compression tests are a waste of time in my opinion. All it does is tell you to perform a leakdown test to find out what is really wrong. If the rings are fine and its the intake or exhaust valve you wont know that with a compression test.
    http://www.performanceboats.com//signaturepics/sigpic837_1.gif
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    gn7
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    Quote Originally Posted by Mach80 View Post
    Here is the latest. Tried to do a leakdown test and none of the cylinders would hold more than 10/15 lbs with 50 to 90 PSI on the input side. I could hear most of the air excaping from the intake / intake valves. This seems to me that I'm doing something wrong as I would not think the boat would run with this much leakage. It actually runs pretty good at WOT, but it idles roughly. I tried a standard compression tester and they actually tested 10 lbs higher than yesterday. They tested between 90 and 130 today. The engine was cold today. Any thoughts??
    I'd be asking if the valves are adjusted correctly.



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    Quote Originally Posted by gn7 View Post
    I'd be asking if the valves are adjusted correctly.
    DITTO!!! Or over tight! I would back them all off and redo the leak down test. Question =??? how many hours on the motor????

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    gn7
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    Quote Originally Posted by ol guy View Post
    DITTO!!! Or over tight! I would back them all off and redo the leak down test. Question =??? how many hours on the motor????
    Ah come Ol Guy, you know full well thats what I was aiming at



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    The motor only has 210 hours. I am under the impresion that the stock valves and rockers are non adjustable.

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    New here Beer:30's Avatar
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    You DID do the compression test with the throttle WIDE OPEN, right??
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    The throttle was wide open. There is a problem in the valvetrain or heads. I just ordered Tylers kit. This should take care of what ever I find as well as pumping up the engine some. I'll report back what I find when it comes apart next week. Thanks for the suggestions.

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    Quote Originally Posted by Mach80 View Post
    The throttle was wide open. There is a problem in the valvetrain or heads. I just ordered Tylers kit. This should take care of what ever I find as well as pumping up the engine some. I'll report back what I find when it comes apart next week. Thanks for the suggestions.
    Good. Just wanted to make sure you had done the test right. Good job.

    If done properly, you will be REAL happy with the Crockett kit. "Kevnmcd" on here did it to his 502. He was in the same sit as you and - from what I remember - was just going to freshen the motor up. I did the same thing and sent him the link for the engine kit. He got the kit, had all of the machine work done locally, put the motor back in and was real happy with it. The boat was (still is?) for sale now, as this was a couple of years ago. The cost of doing the kit as opposed to a stock rebuild would have to be fairly minimal and you get around 100hp boost.

    Keep us all posted, as there are several others who are - or will be - in the same situation as yourself.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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