502 Chevrolet head swap.
+ Reply to Thread
Results 1 to 8 of 8

Thread:
502 Chevrolet head swap.

  1. #1
    Member
    Join Date
    Apr 2009
    Posts
    40

    Default 502 Chevrolet head swap.

    Got a stock Gen 6 420HP 502 Chev with 8.5:1 compression. Wondering if I could bolt on a set of Mark 4 closed chambered heads to bump up compression thus more horsepower. Got a set of Edelbrock AL open chambered but that won't help anything. I don't think a cam swap would help me either with stock engine. Looking for some cheap horsepower and need some help.

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member DuaneHTP's Avatar
    Join Date
    Dec 2007
    Location
    Shell Knob, MO
    Posts
    1,245

    Default

    Heads and cam swap will both help.

  4. #3
    UMPBA.ORG sleekcrafter's Avatar
    Join Date
    Dec 2007
    Location
    South Elgin, Il.
    Posts
    5,024

    Default

    Widow Maker was runing a stock bottom 502, making close to 750 HP
    Upper Midwest Power Boat Association
    DRAG BOAT RACING UMPBA #926


  5. #4
    Foxwell Motorsports
    Join Date
    Dec 2007
    Location
    N/E Tennessee
    Posts
    12,321

    Default

    Quote Originally Posted by DuaneHTP View Post
    Heads and cam swap will both help.
    Bolt the alum heads on with the right cam and you'll make plenty more power. You didn't mention this in the Dyno section. Even just a cam swap with your heads would make a big difference.
    FOXWELL MOTORSPORTS
    STRAUB TECHNOLOGIES
    Performance Cylinder Head Specialties
    Custom Cams
    Complete Engines
    Retail/Wholesale Parts sales




    In the madness of this world, know the Peace of God.

  6. #5
    Progressive Auto/Marine
    Join Date
    Apr 2009
    Location
    Pothole Haven..... Clinton, Ia. If your shocks dont bust your bladder will!
    Posts
    12

    Arrow Heads

    Oval or rect.port? If I remember correctly the 420's are rect. I have replaced them b4 with oval GM casting # 353049's which make awesome marine power. Pocket port them and gasket match for an extra 70 hp. The larger valves help out a bunch too. I went from rect. to oval due to the power characteristics. These heads are 113 cc. and came stock with 207, 172 valves.
    If you want to bump your compression a bit, you can straight mill these heads without any problems. What I did however was used a .020 shim gasket from Mr.Gasket and punched in additional cooling passenges to match the existing Mercruiser gaskets.
    The Comp Cams 11-236-4 cam set has awesome numbers and has a nice idle with noticable lope.
    This makes a nice combo.
    Do you know your existing head casting #'s?
    Go to www.compcams.com Download their Camquest 6 software.[Free] There you will be able to custom tailer your heads, compression, carb, intake and what have you to build the ultimate powerplant and the cam that works best for your needs. It will basically pick the correct cam for your application. Cool tool to keep in mind.
    Last edited by progressiveauto; 04-29-2009 at 07:48 PM. Reason: Added info

  7. #6
    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
    Join Date
    Dec 2007
    Location
    Newton Ks.
    Posts
    6,834

    Default

    Quote Originally Posted by progressiveauto View Post
    Oval or rect.port? If I remember correctly the 420's are rect. I have replaced them b4 with oval GM casting # 353049's which make awesome marine power. Pocket port them and gasket match for an extra 70 hp. The larger valves help out a bunch too. I went from rect. to oval due to the power characteristics. These heads are 113 cc. and came stock with 207, 172 valves.
    Did (had my stock '049 heads ported and the larger valves installed) that winter of '07-'08, and made a bunch more power, and great throttle response all over the rpm range.
    No money to hit a dyno (as always) but pulled 400RPM more against my Aggressor B, zero other engine changes (cam, intake and headers were not stock tho so the heads were the "choke point")
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

  8. #7
    Foxwell Motorsports
    Join Date
    Dec 2007
    Location
    N/E Tennessee
    Posts
    12,321

    Default

    Quote Originally Posted by SmokinLowriderSS View Post
    Did (had my stock '049 heads ported and the larger valves installed) that winter of '07-'08, and made a bunch more power, and great throttle response all over the rpm range.
    No money to hit a dyno (as always) but pulled 400RPM more against my Aggressor B, zero other engine changes (cam, intake and headers were not stock tho so the heads were the "choke point")
    I have another set of those done with big valves, bowl blend, and flow sheets...fuly assembled, if any one is interested.
    FOXWELL MOTORSPORTS
    STRAUB TECHNOLOGIES
    Performance Cylinder Head Specialties
    Custom Cams
    Complete Engines
    Retail/Wholesale Parts sales




    In the madness of this world, know the Peace of God.

  9. #8
    E-7 Sheepdog (ret) SmokinLowriderSS's Avatar
    Join Date
    Dec 2007
    Location
    Newton Ks.
    Posts
    6,834

    Default

    Quote Originally Posted by steelcomp View Post
    I have another set of those done with big valves, bowl blend, and flow sheets...fuly assembled, if any one is interested.
    If I needed another set, I'd be interested.
    "As democracy is perfected, the office of president represents, more and more closely, the inner soul of the people. On some great and glorious day the plain folks of the land will reach their heart's desire at last and the White House will be adorned by a downright moron."
    H.L. Mencken

    OBAMA: Some people deserve this.
    The rest of us are being dragged along kicking and screaming.

+ Reply to Thread

Quick Reply Quick Reply

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Tags for this Thread

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90