cheap power improvements to the 425...
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500, 472, 425, 368 Discussion, cheap power improvements to the 425... in Cadillac Engine Technical Discussion; Since I decided to push the build up on the 425 out of line for this winter project (NorthStar took ...
  1. #1
    Night Wolf's Avatar
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    cheap power improvements to the 425...

    Since I decided to push the build up on the 425 out of line for this winter project (NorthStar took it's place) I was thinking what I could do to get a little more power from the beast....

    my first thoguht is the cat... it's gotta go... my father mentioend something about thee first gen cats having a "drain plug" that you can take out, and the beads inside fall out, kinda like gutting the cat? On his '79 Coupe, he had a test pipe on it.. but I can't seem to find them anymore.... I don't think I could take it to a shop , even though it is now over 25 years old, and there is no emmisions testing... so what would the best thing seem to be?

    While under the car, the whole exhuast system seems to be restriced... especailly all the bends going over the rear axel... what is this, 2.5" piping (my 4.9 has 2.5") but I am not messing with the exhaust system now... I was thinking maybe a cheap after market muffler... might flow better? something like $40 or something? also give it a nice tone... but not too loud... would I even benifit form that? or just keep what it has.... Also the resonator... from what i coudl find out, they don't seem to restric the flow of exhaust at all.. do they?

    Then it would be some sort of an intake... I bought, and tired to fit a 14" open element on it, but it hit the AC compressor... somebody menitoend about a 1" spacer? should I do that or see if a 9" kit will work (but probably look bad)... also would I gain anything from the open element over the factory air cleaner assembly?

    the tune-up I first did on it consisted of:

    new air filter
    new fuel filter
    new spark plugs
    oil change

    I suppose I should rrepalce the cap&rotor and wires also... just for the extra touch, and maybe even the plugs, although they are new... they are basic AC Delco, $2/each... nothing special (platnium, double tipped etc...) do you think they are ok to keep in there? should I replace the cap/rotor and wires, or leave them? the wires are 8mm Whitiker....

    What else can I do for a tune up? I know my carb needs to be rebuilt as it acts funny when the enigne is cold... anything to restore some power?

    I do need to change the coolant, as it is really ugly... but that really isn't anything for performance...

    my AC dosn't work (leak in the lines) no big deal, but should i remove the AC belt... less rotating mass?

    Abotut he carb... here are the problems... when the enigne is cold.. after I first started it, if in park I put my foot to the floor for a second.. it'll sputter, run rough and want t quit... if i drive it.. there is an off-idel dead spot where it'll shutter and have a hard time accelerating, and if the engine is cold enough.... stall out... also until the engine has fully warmed up, if I try to floor it... well, to the point where the secondaires would normally start to open... when it gets to that point, the enigne looses alot of power, the car shakes and shutters, engine RPM really dosn't build, it may back fire, then depenging on how warm the enigne is, either rev up in RPM like normal, or just keep doing that.... maybe a problem witht he secondaires?

    Everythign else with the carb is fine, when the engine warms up, there is no delay or anything, runs great... if it hasn't been ran for a day or 2, a cold start can be hard.. I heard all Q-jets have a drip down problem? I pump the gas 3 times, crank it, stop, pump twice then crnak and it'll start... although when warm, it'll start up within a split second of turning the key...

    Maybe if the carb is out of adjustment, and I fix it, that coudl improve power and gas millage.... IIRC my father said the caps on the adjustments have been removed, so it is adjustable now...

    I am just looking for some cheap ways to tya nd improve the power a little... I know the enigne isn't running how it hould be (well, have the power it should... she runs nice) so maybe I can get some help from the crew

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    mastertech is offline Cadillac Owners Fanatic
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    Re: cheap power improvements to the 425...

    I had a similar problem with my 425... The carb probably does need an overhaul, not very much trouble if you are mechanically inclined...the accelerator pump seal you will probably find dry rotted, causing that hesitation, and these fuel pumps have a problem with a check ball to return excess fuel at idle... you should probably throw one of those on, too...they run about $35...also be sure to clean the secondary rods when you have it apart! Let us know how it goes!

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    Re: cheap power improvements to the 425...

    anything?

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    Re: cheap power improvements to the 425...

    Quote Originally Posted by Night Wolf
    my first thoguht is the cat... it's gotta go... my father mentioend something about thee first gen cats having a "drain plug" that you can take out, and the beads inside fall out, kinda like gutting the cat? On his '79 Coupe, he had a test pipe on it.. but I can't seem to find them anymore.... I don't think I could take it to a shop , even though it is now over 25 years old, and there is no emmisions testing... so what would the best thing seem to be?
    There's about a 2" plug on the bottom of the cat. It's a pain in the ass to get it out, and if you can get it out there's a good chance you'll have deformed it so it won't go back in there. If you know someone with a welder you can just weld some sheet metal over the hole. I did this a few weeks ago and it did seem to make a good differance. I left the hole open for awhile and it was pretty loud...

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    Re: cheap power improvements to the 425...

    I was thinking about going ot the local Midas, and saying that the car is over 25 years old, no emmissions testing etc... if they can cut the cat out and put a stright pipe in it.... if he says no, I'll ask about slipping him a $20...

    Did it make a nice difference? I would imagine it helping, as the whole exhaust system seems to be restrictive...

    ... what about using JB Weld to keep a piece of aluminam over the hole?

    Also, when you pulled the plug, did the beads just drain, did you have to shake it etc....?

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    lux hauler is offline Cadillac Owners Connoisseur
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    Re: cheap power improvements to the 425...

    Chances are, a "chain-type" muffler shop isn't going to touch it. I've heard there are big fines if they're caught. Best bet would be to find a small local shop or just buy the stuff and do it your self.

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    Re: cheap power improvements to the 425...

    Quote Originally Posted by lux hauler
    Chances are, a "chain-type" muffler shop isn't going to touch it. I've heard there are big fines if they're caught. Best bet would be to find a small local shop or just buy the stuff and do it your self.
    most will make you sign and offroad use only waiver

    but agree start with exhaust make it flow then intake make it flow. the easier you can make air move in an engine the more power you can make

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    Re: cheap power improvements to the 425...

    Quote Originally Posted by Night Wolf
    Did it make a nice difference? I would imagine it helping, as the whole exhaust system seems to be restrictive...

    ... what about using JB Weld to keep a piece of aluminam over the hole?

    Also, when you pulled the plug, did the beads just drain, did you have to shake it etc....?
    It did for me - but then again my FW was in pretty bad shape and had run real rich for awhile, so the beads were fairly clogged with carbon. Cats get pretty hot, I'm not sure how well JB weld would hold up under several hundred degrees. I put a paper bag under the hole, the beads took their time to come out, I used a rubber mallet to help them along.

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    Re: cheap power improvements to the 425...

    well, I am not looking to spend alot of money for this.. but besides dumping the cat, what else could I do to free up the exhaust? the piping dosn't look too big, but I am not replacing it, as mine is fine... that leaves the muffel and the resonator...

    ..for intake, maybe I'll try the spacer and get the 14" open element again... I really don't want to spend *alot* of money into the 425 (yet) but just something to make it a little more snappy....

    that is true with the chain stores.. there is a local private shop that does exhaust work,t he kid goes ot my school... the only thing i owrry aobut is, they beat the hell out of cars.. customers cars, cars they sell on the lot etc... so I suppose I could just wait there and make sure thing bad happens... I know they woudl do it too...

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    Re: cheap power improvements to the 425...

    I notice sometimes after running the enigne, or is I stand outside the car while it is running, the exhaust will smell like rotten eggs.... mixture too rich?

    Should I bother to replace the cap+rotor, and wires, or no... also are the basic AD Delco plugs good enough for the job for now? they are practically brand new...

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    Re: cheap power improvements to the 425...

    The rotten egg smell may be indicative of a cat that's already going bad. It might go away after the catalyst beads are gone.

    My friend had some exhaust tubing and a perfectly good chrome tip so we cut off the resonator and replaced it with that. It didn't change the sound at all but I never took it on the freeway to see if it increased the drone.

    Take a look at the cap and rotor and if any contacts don't look good replace. The plugs should be OK, I mean it won't hurt to change them but it won't do much good. At least visually inspect the wires for cracks, and take a look at them in the dark with it running, if you see any electricity 'leaking' from them it's time for some new wires.

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    Re: cheap power improvements to the 425...

    hmm, maybe the cat is starting to go... only (almost) 86k, but it is 25 years old....

    ... the only wear point on the cap was where the finger touches the metal plate.. my father said it is in pretty good shape... no cracks on the wires, nothing strange at night either.... I never heard of the brand... Whitiker (sp?)they are orane and 8mm....

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    Re: cheap power improvements to the 425...

    if you wanted to remove the cat you could try getting a couple of 2 and1/2 to 3" clamps along with about 18" peice of pipe and cut that cat off and clamp the pipe on tighten it down should work fine also I replaced my muffler a while ago as the weld had totaly rusted away with a turbo muffler from dynomax but its 3" very open almost straight through sounds excelent with a good low rumble until the secondarys open then it gets loud very loud muffler was only round 40 to 50$ definitly improved the acceleration also replace that cap and ignition coil in there I replaced my cap with one from acdelco along with a ignition coil form acdelco with 8mm wires and plantnum bosch plugs all for under about 60 or 70$ the plugs i think were the most expensive plus get that 14" air cleaner you'll need to get some eltra spacer peices and longer stud but that stock air cleaner has an opening of about 4" whereas the edelbrock is 14" round and 3"high and will definitly let her breath in a lot better also look in to replaceing that carb ABC gets a performance rebuild
    Q-jet from a place in california cost around 250$ but works wonders over the factory carb

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    7.0,hellyeah is offline Cadillac Owners Fanatic
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    Re: cheap power improvements to the 425...

    As far as all of this exhaust talk goes, it gave me loads of powr just ripping everything off after the cat. It keeps it quiet enough that police won't immedietly cry no exhaust but it gives the car more snap. The 14"X3" will only take in loads of hot air. Get a later models fuel injection air intake assembly. That will be able to handle a 14X3 K&N and it will get you cold air from the front of the car. No riser is needed either. If you do use the 14X3 assemply and riser make sure to plug the vacuum tube coming out of the original assembly. That caused me really bad timing problems later on. Dist. coils give good power too.

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    abcdefg is offline Cadillac Owners Member
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    Re: cheap power improvements to the 425...

    My cadillacs 1977 425 is a gutless wonder. Im amazed at how i "cruise" up hills in this thing. With the gas pedal about 3/4 on the floor (in 2nd gear going 20mph) it barely holds its speed, and this is a fairly new engine.

    When i put it in Low and "floor it" its pretty good untill about 25-30 then its like im towing a school bus behind me, it accelerates faster in 2nd after that than it does in 1st. I busted out my cadillacs service manual, and looking at a cutaway view doesnt give me a suprise as to why this engine is neutered on the top end.

    The intake manifold looks like a snake, you can even see the tight bends just by popping your hood.

    I do have a muffler and exhaust tip off a 12 liter kennworth diesel, but i think the caddy would drag bottom with either thing. Plus i dont want it to look like a "ricer" (5" 4.5 foot long chromed pipe hanging out)

    The easiest route to go would have been to buy that 500 cid on ebay. It had a blower, 8 port nitrous fogger, heavy duty performace connecting rods pistons and all, hot valve cam... but i dont want to blow up my THM400...


    Is the 425 cid really this wimpy?


    If im lucky enough to find a 425cid or 500cid caddy with fuel injection, and figured out how to hotwire it into my carbureted wiring, would this give it more balls at the top end (past 2000rpm)? I see the fuel injected deville is rated at 190hp, versus the carbureted 180hp. I suppose a die grinder and carefull planning would give the fuel injected manifold more oomph?

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