Intake Manifold Modification
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Page 1 of 2 1 2 LastLast
Results 1 to 15 of 26
500, 472, 425, 368 Discussion, Intake Manifold Modification in Cadillac Engine Technical Discussion; Who's got the skiny on modding the 472/500 intake?...
  1. #1
    kiowamec is offline Banned
    Automobile(s): None
    Join Date
    Jun 2007
    Location
    Arkansas
    Posts
    99

    Intake Manifold Modification

    Who's got the skiny on modding the 472/500 intake?

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    drmenard is offline Cadillac Owners Connoisseur
    Automobile(s): 95 fleetwood 81 deville
    Join Date
    May 2003
    Location
    Massachusetts
    Posts
    1,004

    Re: Intake Manifold Modification

    Here some pictures...I hope this works...
    Attached Images

  4. #3
    74eldog is offline Cadillac Owners Fanatic
    Automobile(s): 74 Eldorado
    Join Date
    May 2005
    Location
    Columbus, Ohio
    Posts
    149

    Re: Intake Manifold Modification

    I always thought the idea was to cut the plenum out all together?

  5. #4
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
    Automobile(s): Unicycle
    Join Date
    Mar 2003
    Location
    Where I park it
    Posts
    11,009

    Re: Intake Manifold Modification

    I still have my '68 472 intake manifold, and yes, the entire center plenum is cut out.

    That, along with about 2/3" carb spacer, a rebuilt factory Q-jet and my 14" open element air filter (not so sure how much it really helped though).... made for some very nice improvements to the otherwise stock 425... could really feel it, and that was with the stock restrictive exhaust too... some free flowing exhaust and I bet it would really do wonders for a stock engine.

  6. #5
    kiowamec is offline Banned
    Automobile(s): None
    Join Date
    Jun 2007
    Location
    Arkansas
    Posts
    99
    Thread Starter

    Re: Intake Manifold Modification

    I have researched plenty and that seems to be the most popular answer. I believe because these engines have such a large amount of available vacuum at idle they do not notice the open plenum or loss of signal as it does not go below a decent level. Just a guess though.

  7. #6
    Night Wolf's Avatar
    Night Wolf is offline Cadillac Owners 10000+ Posts
    Automobile(s): Unicycle
    Join Date
    Mar 2003
    Location
    Where I park it
    Posts
    11,009

    Re: Intake Manifold Modification

    Some said I would loose off-idle torque.... but with the thing (even a 425) a torque monster the way it is, I did not notice any loss at all.

    I'll also note that the '68 intake dosn't have EGR, so had to drop that.... kinda stinks but ah well... Before the modded intake and rebuilt carb the 425 performed well, but didn't really do much to show it was a big block.... afterwords though... man, floor it at 25-30 when it was loafing along in 3rd, and it downshifted into 1st, it would really push you in the seat and yank the front end of the car up.... spin the tires more easily too.

    a better exhaust and a slightly bigger cam with the intake mods would really wake the 425 up.

  8. #7
    bicentennialcadillac is offline Cadillac Owners Enthusiast
    Automobile(s): '76 Fleetwood Brougham, '79 Sedan deVille
    Join Date
    Aug 2004
    Age
    37
    Posts
    635

    Re: Intake Manifold Modification

    Here's what mine looks like. Just got it back today.


  9. #8
    kiowamec is offline Banned
    Automobile(s): None
    Join Date
    Jun 2007
    Location
    Arkansas
    Posts
    99
    Thread Starter

    Re: Intake Manifold Modification

    Why did you not cut the holes out of the right side? The thin piece thats left looks a little dangerous in the picture?

  10. #9
    bicentennialcadillac is offline Cadillac Owners Enthusiast
    Automobile(s): '76 Fleetwood Brougham, '79 Sedan deVille
    Join Date
    Aug 2004
    Age
    37
    Posts
    635

    Re: Intake Manifold Modification

    It's not as thin as it looks in the picture - it ain't going nowhere.

    Still, do you think I should have it taken on down? The gentleman at the machine shop thought it was right, and me, having never done this before, didn't know any better.

  11. #10
    SupRNatural's Avatar
    SupRNatural is offline Cadillac Owners Fanatic
    Automobile(s): 1996 Montana Blue Eldorado,1982 Eldorado Biarritz Diesel
    Join Date
    Nov 2007
    Location
    USA
    Age
    49
    Posts
    148

    Re: Intake Manifold Modification

    Quote Originally Posted by bicentennialcadillac View Post
    Here's what mine looks like. Just got it back today.

    Dual Planes=Mucho Torque. The only way to fly on the street in a 4000lb + caddy. A little material smoothing around the intake ports, matched to the cylinder heads,with higher flowing exhaust manifolds/camshaft/headers will wake any sleeping giant in to a monster

  12. #11
    bicentennialcadillac is offline Cadillac Owners Enthusiast
    Automobile(s): '76 Fleetwood Brougham, '79 Sedan deVille
    Join Date
    Aug 2004
    Age
    37
    Posts
    635

    Re: Intake Manifold Modification

    Anyone know exactly how to reroute the EGR stuff so that no new vacuum problems are introduced? I'd like to keep cruise/etc. in a workable state.

  13. #12
    kiowamec is offline Banned
    Automobile(s): None
    Join Date
    Jun 2007
    Location
    Arkansas
    Posts
    99
    Thread Starter

    Re: Intake Manifold Modification

    You can simply plug the line running to it. If you do delete the EGR with out re-tuning the carburetor you will hurt performance and possibly the engine. If you are not comfortable with rebuilding a carburetor its best to keep it working the way it was designed.

    Back to the manifold…
    Why were the holes left on the right side? That small bit of metal in-between seems like it could break out and fall into the engine.

  14. #13
    bicentennialcadillac is offline Cadillac Owners Enthusiast
    Automobile(s): '76 Fleetwood Brougham, '79 Sedan deVille
    Join Date
    Aug 2004
    Age
    37
    Posts
    635

    Re: Intake Manifold Modification

    Neither the shop nor I knew any better. I'm gonna take it back and have the remainder machined out - I'm doing this for better flow, might as well get the max.

    What carb adjustments should I pull w/o EGR? I'm putting in a rebuilt unit and a spacer with the "new" intake.

  15. #14
    kiowamec is offline Banned
    Automobile(s): None
    Join Date
    Jun 2007
    Location
    Arkansas
    Posts
    99
    Thread Starter

    Re: Intake Manifold Modification

    I intend to retune mine using this setup. http://toax.free-bsd.org/vm/air&fuel...%20Monitor.htm

    There are several sources for quadrajet info on the net. One is old car manual.

  16. #15
    SupRNatural's Avatar
    SupRNatural is offline Cadillac Owners Fanatic
    Automobile(s): 1996 Montana Blue Eldorado,1982 Eldorado Biarritz Diesel
    Join Date
    Nov 2007
    Location
    USA
    Age
    49
    Posts
    148

    Re:

    A Roch. Q-jet is a finnicky sob when modifying an engine, some idle/air circuitry mods are needed to make it run well on the street. FWIW I would install a Demon, or Barry Grant or Holly for optimum performance. An adapter may be necessary, but the performance gains would be off the hook. Standard Q-jets were 800 cfms. I would go no larger than that,850 cfms on a modified 472/500 if you were going to drive it/race it.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

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

Please enter a valid email address for yourself.

Log-in

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.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting