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Author Topic: 425cui heads on a -75 500cui  (Read 1847 times)

Daniel

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425cui heads on a -75 500cui
« on: February 20, 2005, 02:38:10 PM »
I heard that i can change my 500 heads to 425 heads to get higher compression,how much vill i get? what i can see it aint much difference between them.is there anything else to think about? the engine is in a -75 calais coupe.
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Michael Stamps 19507

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Re: 425cui heads on a -75 500cui
« Reply #1 on: February 20, 2005, 05:09:34 PM »
From what Ive heard it will get around 9.0 CR and gain 30-40 hp depending on other performance parts on the engine.  If I remember correctly you will have to drill out some steam passages but looking at the blocks will show you which ones.

Stampie
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Daniel

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Re: 425cui heads on a -75 500cui
« Reply #2 on: February 20, 2005, 11:36:10 PM »
I`m planning to buy a new camshaft, edelbrock intake manifold and a new carbureator.
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Michael Stamps 19507

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Re: 425cui heads on a -75 500cui
« Reply #3 on: February 20, 2005, 11:50:36 PM »
A cam can be mild to wild.  What ones are you looking at?  The edelbrock intake is good for 99percent of the applications.  I would have the orginal carb rebuilt by a good shop before buying a new one.

Stampie
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Daniel

  • Guest
Re: 425cui heads on a -75 500cui
« Reply #4 on: February 21, 2005, 04:14:45 PM »
Something between mild and wild.some extra hp.its gonna be my daily driver not a dragracer.vill probably use a holley 780 vacum that i have in my garage,the original carb needs lot of work.
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Michael Stamps 19507

  • Guest
Re: 425cui heads on a -75 500cui
« Reply #5 on: February 21, 2005, 11:49:15 PM »
Daily driver ... assuming around an MT5 or MT10 cam.  The heads would be a decent swap for you.  That carb is going to cost you mpg vs. spending $200 to have the orginal rebuilt right.

Stampie

PS - Im building a 514, 10.2 CR plus, MT20, and Manual valve body for the trans to put in my 70 SDV as a daily driver.  Different strokes for different folks.
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Daniel

  • Guest
Re: 425cui heads on a -75 500cui
« Reply #6 on: February 22, 2005, 03:20:40 PM »
Dont know any around that repairs cadillac carbs(i`m from sweden)do you know where i can buy a new one or similar?MT cam is that maximum torque specialities? are they ok?
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Michael Stamps 19507

  • Guest
Re: 425cui heads on a -75 500cui
« Reply #7 on: February 22, 2005, 06:04:46 PM »
Your carb isnt all that special.  Its a QJet as used on many GM cars from that era.  Any good carb shop should be able to rebuild it.  I know that some of the bigger US shops will rebuild it for you.

Yes MTS ... I bought most of my parts from Al and he is a great guy to deal with.  Hes also a CLC member.  For a street car I would have to say that hes the best.

Stampie
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Steve Toth CLC 21939

  • Guest
Re: 425cui heads on a -75 500cui
« Reply #8 on: February 23, 2005, 03:34:06 PM »

Stampie,  hows it going.  Its nosgbody....=)

Daniel,  Mike is right about the Qjet. It you find a good rebuilder the qJet is great for the street..  IMHO a properly rebuild Qjet will performe just as well as a Holley on the street maybe even better.  you might want to hop over to www.cowboyseven.us and post a few questions there. Those guys only deal with the 472s and 500s
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