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  1. #1
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    Question Mercruiser 5.7 intake manifold

    I need some help please;
    The intake manifold on my 1997 5.7 LX cracked and needs to be replaced. The engine serial # is OK 147937.
    The first question, is there a difference between an auto/truck intake manifold and a marine manifold ?
    next question , Do the exhaust risers have to be taken off to replace the intake manifold ? My engine is closed cooling.
    Thanks for any help !

  2. #2
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    Default Re: Mercruiser 5.7 intake manifold

    Check out Edelbrock's website. They offer marine applications.

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    Default Re: Mercruiser 5.7 intake manifold

    Did it crack from freezing? If so, other stuff usually cracks before an intake. So check other stuff! Hopefully that's not the case.
    + 1 on using an Edelbrock, Go with the "performer" or "performer rpm"

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    Default Re: Mercruiser 5.7 intake manifold

    First of all , the auto/ truck intake will work but needs some modifications to the 4 center bolt holes as they are at a 70 degree angle in your heads and automotive manifolds are all 90 degree. Aftermarket aluminum work fine with closed cooling. You shouldent have to pull the risers but you need to pull at least 1 valve cover to do the job. Just noticed the post above, do not usr the performer"RPM" it is designed for 3000 to 7000 rpm and you will loose bottom end power.
    Last edited by dan t.; April 16th, 2012 at 02:44 AM. Reason: More info
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    Default Re: Mercruiser 5.7 intake manifold

    Quote Originally Posted by dan t. View Post
    First of all , the auto/ truck intake will work but needs some modifications to the 4 center bolt holes as they are at a 70 degree angle in your heads and automotive manifolds are all 90 degree. Aftermarket aluminum work fine with closed cooling. You shouldent have to pull the risers but you need to pull at least 1 valve cover to do the job. Just noticed the post above, do not usr the performer"RPM" it is designed for 3000 to 7000 rpm and you will loose bottom end power.
    Ayuh,... A '97 oughta be vortec heads, so it Needs to use a Vortec cut, 'n drilled manifold, with only 8 retainin' bolts....

    'n I agree,... I'd Expect to find more freeze damage, down lower, like the heads, or more likely the block...
    Any Grease is Better,..... Than No Grease at All.......

  6. #6
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    Default Re: Mercruiser 5.7 intake manifold

    Thanks Guys for all the replys;
    The manifold did not crack from freezing, is seems to be rust. A small piece broke off by one of the hold down bolts while running and now its leaking.
    I have contacted Edelbrock with my info and am waiting for a reply.
    Thanks again everyone.

  7. #7
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    Default Re: Mercruiser 5.7 intake manifold

    Quote Originally Posted by dan t. View Post
    First of all , the auto/ truck intake will work but needs some modifications to the 4 center bolt holes as they are at a 70 degree angle in your heads and automotive manifolds are all 90 degree. Aftermarket aluminum work fine with closed cooling. You shouldent have to pull the risers but you need to pull at least 1 valve cover to do the job. Just noticed the post above, do not usr the performer"RPM" it is designed for 3000 to 7000 rpm and you will loose bottom end power.
    just to be clear...Edelbrock lists performer as " idle to 5,500 rpm" ... performer rpm as "1,500 to 6,500"

    as noted should be vortec 8 bolt style

  8. #8
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    Default Re: Mercruiser 5.7 intake manifold

    It looks to me, from the serial number that this is NOT a vortec head engine. (mercurypartsexpress.com) Looks like a 4brl carb on the same hi-rise intake as the non-vortec 350 MAG. If going edelbroock, you want the performer rpm. I don't believe merc made any 4brl vortecs in '97. They were all EFI and MPI.

  9. #9
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    Default Re: Mercruiser 5.7 intake manifold

    Well everyone is entitled to their opinion, first of all I dont think the motor will be turning over 5500 rpm for a start, second, why compromise your bottom end power by using an intake that is designed for top end.
    motorsport is the most efficient method known to man of turning money into noise

  10. #10
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    Default Re: Mercruiser 5.7 intake manifold

    Looks like john is correct, pre vortec if it is an untouched 1997 with a 4 barrel.
    Shows to be a 350 mag!

    http://www.perfprotech.com/store/Cat...nder,3172.aspx

    http://www.perfprotech.com/store/Cat...2097-1430.aspx

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    Default Re: Mercruiser 5.7 intake manifold

    Quote Originally Posted by dan t. View Post
    Well everyone is entitled to their opinion, first of all I dont think the motor will be turning over 5500 rpm for a start, second, why compromise your bottom end power by using an intake that is designed for top end.
    Edlebrock performer and performer rpm manifolds are extremely versatile and always do well in dyno test on stock type 250 hp all the way to 450 hp hopped up small blocks. All kinds of back to back dyno comparison videos on youtube. I have personally used both on several different engines, with good results.
    Generally gains on low end as well. The "RPM air gap" does so by having a small cut away in the top of the dividing wall of the plenum. Generally doesn't give away any bottom end and makes big gains from like 2,500 on. They are great intakes.

  12. #12
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    Default Re: Mercruiser 5.7 intake manifold

    Quote Originally Posted by dan t. View Post
    Well everyone is entitled to their opinion, first of all I dont think the motor will be turning over 5500 rpm for a start, second, why compromise your bottom end power by using an intake that is designed for top end.
    If the OP posts a picture of the intake and/or the casting numbers, can easily confirm the parts diagram is correct, ie it is the high-rise cast iron intake. You can still buy the earlier version of that intake, but the latter one with canted center bolts, is harder to find.

    The performer rpm is as close a match as they come. Going with a performer could mean some carb tuning and a slight loss of high rpm hp.

  13. #13
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    Question Intake manifold

    Installing a Edelbrock Performer intake manifold on my 5.7L vorteck 4BBL. Do you think I'll notice any difference over the stock manifold ?
    Thanks !

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    Default Re: Intake manifold

    Quote Originally Posted by GasCan II View Post
    Installing a Edelbrock Performer intake manifold on my 5.7L vorteck 4BBL. Do you think I'll notice any difference over the stock manifold ?
    Thanks !
    Update: How quickly I forget! http://forums.iboats.com/showthread....11#post3718511

    Anyway, from your other thread, you did not have a vortec head engine. From the parts listing, from looking up your serial number, you should have standard head, hi-rise, castiron intake. That intake produces more hp at higher rpms than a performer. You might also need to retune carb.

    Post a picture of your old intake to be sure.

    A vortec intake will not fit standard heads.

  15. #15
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    Default Re: Intake manifold

    I'm sorry I forgot to mention I had a new engine installed in 2010 and it does have the vortec heads. ( had to call the installer )
    Please forgive me , getting OLD.
    Thanks !

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    Default Re: Intake manifold

    Quote Originally Posted by GasCan II View Post
    I'm sorry I forgot to mention I had a new engine installed in 2010 and it does have the vortec heads. ( had to call the installer )
    Please forgive me , getting OLD.
    Thanks !
    With out an ID on the existing intake, can only offer a guess. My guess would be that whatever the installer used, it was at least the equivelent of a performer. With that short time on it, I'd be more interested in what caused the failure to make sure it wasn't repeated. You mentioned rust, but not aware of any iron 4brl vortec intakes. If if iron, that is quick to rust. Are you running in saltwater with raw water cooling? If so, and reg alluminum intake might not be the answer.

    OK, missed the closed cooling, but still would want to know what rusted out??? Pics would be great.

  17. #17
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    Default Re: Intake manifold

    here are several "marine" intakes for vortec heads.... some aluminum, some cast iron

    http://www.michiganmotorz.com/intake...32_37_133.html

  18. #18
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    Default Re: Intake manifold

    Quote Originally Posted by joewithaboat View Post
    here are several "marine" intakes for vortec heads.... some aluminum, some cast iron

    http://www.michiganmotorz.com/intake...32_37_133.html

    WOW, some good mark-up on those stock GM cast iron (non-vortec) ones! Interesting low profile intake. Looks like they took the old GM and machined and drilled it for vortec. Outside of that one, they look equivelent to performer or performer rpm.

  19. #19
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    Default Re: Intake manifold

    Quote Originally Posted by John_S View Post
    WOW, some good mark-up on those stock GM cast iron (non-vortec) ones! Interesting low profile intake. Looks like they took the old GM and machined and drilled it for vortec. Outside of that one, they look equivelent to performer or performer rpm.
    Yea, prices are crazy! How would you like to need an 87-95 4v high rise for everyday low price of $650.00. Ouch! Out of stock new, but they have used for $330.00 what a bargain.

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