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500, 472, 425, 368 Discussion, cheap power improvements to the 425... in Cadillac Engine Technical Discussion; Guys, I'm helping my uncle get his 77 Eldorado (D'elegance Package w/425) up and running. He has determined the issue ...
  1. #76
    m1gunr is offline Cadillac Owners Member
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    Exclamation Re: cheap power improvements to the 425...

    Guys,
    I'm helping my uncle get his 77 Eldorado (D'elegance Package w/425) up and running. He has determined the issue to the ECM needs replacing. His problem is locating the thing. Since I am new Cadillacs I have no idea where to start looking for the thing. I am 1/2 the state away from him and will visit mid October any help is greatly appreciated.

    Bill
    Driver Move Out, Gunner Take Over....

  2. #77
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    Re: cheap power improvements to the 425...

    well, I did the modified 472 intake manifold swap... but I am 1,500 miles from the car to see what kind of a difference it makes carb is awaiting to be rebuilt.

  3. #78
    bigblockcaddy is offline Cadillac Owners Member
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    Re: cheap power improvements to the 425...

    i know a couple cheap improvements that work excellent for my 425 but everybody knows this..a brand new air filter,oil change,belts,oil filter,i know this works great for a fact cause i live in phoenix and i go up north quite a bit and one time a drove up north without no oil change,new airfilter,oil filter and i top'd my car off and when i got to my destination(1hour 45 min away) my caddy was already out off gas ...just on the way up their...then this christmas i went up north again got everything done and i still had 3/4 tank their and back...treat your car good and it will treat you good..thats for sure

  4. #79
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    Re: cheap power improvements to the 425...

    Well... no more 425 for me.... damnit I miss that car so much now... never realize what ya have....until its gone...

    Anyway, my list of, well, cheap power improvements to the 425...

    - full tune up. This includes fluids changed, plugs, wires, cap and rotor, air filter, fuel filter, PCV valve etc....

    - 14" open element air cleaner. Mine was made by Edelbrock, it looks really nice. Free flowing, and sounded sweet, especially when the secondaires opened . It also greatly helped to clean the engine bay up.

    - drain cat. conv. If your car still has the origanal cat... its plugged. Pry out the drain cap on the bottom and drain the beads... make sure they all come out... then take it to a shop that has those plugs... when I got an inspection on the car, the guy had a bunch of them laying around (old GM part) and charged me $5.... it was loud, but got annoying fast with the plug missing.

    - rebuild carburator. The Qudra-Jet is a sweet carb, don't let anyone tell you otherwise... but obvisouly a ~30 year old carburater is going to have problems. Rebuild it, and if you know about carbs, or a shop does, then dump the emmisons settings from factory and go for a little performance, a stock Q-jet can be worked over to squeeze more out of it. Keep in mind this is an 800CFM beast that fits the engine perfectally, keep it. A good book for the Q-jet is Doug Roe - Rochester Carburators.

    - find a 1968 472 intake manifold. This intake manifold, stock, flows alot better then the 425 intake. The '68 dosn't have EGR either, so the 425 now dumps EGR. While I don't mind EGR, with an old valve and lines, it is more of a problem then anything. Then, take the manifold to a machine shop and have them totally cut the center section under the carb out, so it is 1 big opening. You now have an intake manifold that flows 95%+ of the Edelbrock intake, for a whole lot cheaper. Sure it still weighs 45lbs, but it looks stock. This intake manifold will flow just as well as the Edelbrock until around 5,500RPM.... seeing as how these big blocks don't rev past 4,000RPM stock, you have to do alot to really get out of the effective range of it. It is also a low-riser intake, no more hood clearance problems. Perhaps the biggest thing is, you can still use the factory AC, not so with the Edelbrock. The A-4 from the 425 has a different mounting bracket, so to correctly mount the compressor, you need the 472 AC compressor bracket. Swap that over and she bolts right in. Revs smoother, sounds more healthy at WOT and noticeable power boost. The BB Cads are so cool, there is no coolant to mess with .

    Another non-engine related performance boost that really helped the car in handling and overall driving, was installing a factory rear sway bar. Mine was from a '79 Fleetwood, but I have been told 70's G-bodys use the same bar. Very nice mod.

    The stock '79 DeVille with out 472 intake or rebuilt carb ran a 17.5@78mph. She was noticeably faster after words. I gotta say, the car was actually fast by the time I was done with these minor things. Floor it at 30 and she'll downshift into 1st, put you in the seat and you see the nose of the car jump up.

    Other cheap things I had in mind was a shift kit for the trans... that would really help since the trans is calibrated for excessive slipping for smooth shifts.

    Another thing that was going to be sweet, since the factory 2.28 gears don't offer much for performance, I was going to swap a cam in... not a hot cam, but a cam that brought the power band lower then stock... an RV cam. More low end torque at the expensive of high RPM HP. The neat thing is, the cams power band is idle-4,000RPM... well, it would shift at 3,900RPM going in to 2nd and 3,400RPM when going into 3rd, when in drive. It was perfect. The cam is the MTS #3, stock valve train is fine. It is also the gas saver cam and is very possible to get 20mpg+ on the open road... that was going to be the project. I wasn't ready to swap the rear end just yet, and so being stuck with the 2.28 gears, I was going to make a torque beast, a whole lot meaner.

    Also, find the cross member from a Caprice 9C1, that way you can easily run true duals. True dual 2.25" exahust on a near stock 425 would be sweet, unleash a few ponies too, and with the MTS #3 cam, really open it up...

    while on the exhaust note, the 425 manifolds are junk. Find a set of 472/500 manifolds, while not the best, they flow alot better, direct swap in for the 425, that and the true dual exhaust would be sweet.

    There are all the basic plans I had for my '79... I had lots of plans. Hopefully this will help anyone else that just got a 425 and wants to bring the life back. Mileage dosn't effect the BB Cads much at all... meaning a 425/472/500 with 100k, if mainted thru its life, will show minimal wear and be ready for any plans you may have. Same goes for the Turbo 400.

    - BTW from an appearance standpoint, something that REALLY helps the '77-'79 DeVille is to run a 2nd pin striping down from the fender and follow the body line that ends at the door. That right there is the missing link, without it, the car looked bland and missing something... I added that and DAMN those 2 pin stripes really set the car off like nothing else, it looked soo nice.

    She will be missed....

    Roflow75 likes this.

  5. #80
    burnrubber is offline Banned
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    Re: cheap power improvements to the 425...

    One other performance mod, if you have your engine out for a refresh or rebuild is to have the block decked. As I understand it - at top dead center - the pistons are down in the holes a bit which could cause detonation. Besides preventing that - it should give a slight bump in compression which would be good for power.

  6. #81
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    Re: cheap power improvements to the 425...

    Decking the block is usually done to get a good quench distance (piston to head dist.) Depending on the crushed thickness of your headgasket, you'll usually want around zero deck for a tight quench. Or you'd want to run the pistons way down in the hole, like .120, for a very loose quench. In between has a tendency to see detonation problems.

    If you want a bit more compression have the heads milled. .040" which is about all I'd be comfortable doing, should get it to about 8.75:1 by calculations (which might be wrong since it's 1am and I should get some sleep.) Still would do well on regular gas, and might net you a dozen ponies or so.

  7. #82
    bicentennialcadillac is offline Cadillac Owners Enthusiast
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    Re: cheap power improvements to the 425...

    Well, the '68 intake and '78 sway bar are lying in my office floor, and a crossmember from a '96 Impala SS is on the way.

    I'm gonna put Night Wolf's plan to work.

  8. #83
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    Re: cheap power improvements to the 425...

    Sorry, somehow I missed this question. I posted a writeup on it in the tech section. Basically it uses the EMR module to pull out 10 degrees timing by grounding a wire, unground it and it goes back to base timing again. So you can have an easy starting high compression engine and have a flatter timing curve and one that is ultimately more controllable and desirable.

    It also helps you make a smogger distributor with limited mechanical advance a performance one, as the old performance distributors of yesteryear had lots of mech advance and little vacuum adv. You will likely need to watch your vacuum adv can usage, an adjustable is recommended. As the smogger ones are often 20-25 degrees, if not 30. So if you had a 25 degree initial advance, ground the wire and 15 degrees is your starting timing or nitrous timing, or turbo, etc, then when vacuum adv comes in, adding 25 to it would be too much and hitting upwards 50 degrees. I recommend not to exceed 45 degrees.

    You can hook the terminal to a vacuum port with a switch, or a pressure port for boost, or even a line on a nitrous nozzle to automagically ground the distributor before pinging even starts to be an issue.

    Really can be a handy dandy addition to a high compression engine or other performance uses.

    Quote Originally Posted by Chrome View Post
    I haven't seen anybody ask yet, so what is this trick?

    Thanks

  9. #84
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    Re: cheap power improvements to the 425...

    Quote Originally Posted by bicentennialcadillac View Post
    Well, the '68 intake and '78 sway bar are lying in my office floor, and a crossmember from a '96 Impala SS is on the way.

    I'm gonna put Night Wolf's plan to work.


    That is awesome... I still have my '68 intake manifold... I pulled it when the car was wrecked. You'll need to dump the EGR system though, normally I woudln't do that, but ah well.

    '78 rear sway bar? you'll notice a big difference.... very good difference too, that was a really nice addition to my car.

    And... cross member from the '96.... the double hump? I was looking for one of those... thats the only thing that kept me from getting a nice, new dual exhaust... the stock exhaust system is pretty bad.... some nice headers and dual 2.5" exhaust the whole way back would really wake it up too.

  10. #85
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    Re: cheap power improvements to the 425...

    I have a 77-96 B/D Body rear bar that will be up for sale soon if anyone is looking. Should work in the 73-77 A/G body cars too. It is the large 9C1/F41/Impala SS/FE2 Fleetwood bar.

    Yes, all 94-96 (all LT1) cars are double hump.

  11. #86
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    UPDATE to Re: cheap power improvements to the 425...

    Quote Originally Posted by djcwardog View Post
    Anyway, for your question, I think I am with you on this. I would want to tweak out the stock 425 first for not alot of money just to see what it will do. Then if I decide it doesn't do enough, I can go ahead with the 500 option. So - to optimize beathing, first you need to at least port match your intake manifold. If you swap in a 472/500 one check its ports as well. You will not be creating extra work in doing this because you are going to have to remove the manifold anyway to do the one thing that is mandatory for you...

    Pitch out that stock cam and put in something like the MTS 3 (for great torque and better mpg) or their MTS-5 or MTS-10, or even a just a stock spec 1973 cam, for better power over what you are getting now. Your stock smogger cam is retarded by design and not at all optimized for much of anything! A new cam with lifters is maybe $200. If you can use your stock rockers and valve springs then you are doing OK.

    I would also recommend a true dual exhaust system custom bent at your local muffler shop. I like Dynomax Super Turbo mufflers but pick what you want.

    Bottom line: short duration/high lift cam, port-matched intake, dual exhaust, and a proper carb setup to go with these mods and you will be at a point where you know whether or not the 425 will do it for you in the long run. If not, pull it and sell on ebay - someone else will want such a carefully prepped motor for their MPG king Caddy! You can then put in a 500.
    UPDATE - I bought a 1977 CDV just a few weeks ago. I had true duals bent and installed - which required me to jet the stock Rochester carb up two sizes - from 72 mains to 74 main jets. I cleaned up the primary (seem to read as "62b" rods... and appear to be the newer style) and secondary metering rods and replaced both the choke pull-offs (primary and secondary). Already the car is faster than it was when I got it. I put on the offset MTS chrome 14" air cleaner to clear the stock a/c compressor. On hand is a pair of 500 exhaust manifolds and a 472/500 intake (with EGR - which I will not use). I also have the MTS-3 cam and lifters ready to go. I plan to remove the valve from inside the RHS exhaust manifiold and seal the holes so the gases flow better - no need for the heat riser/EFE warm-up here! Marty at MTS is sending me the 500 a/c brackets I need to go with the 500 intake. I'll post up results as I progress in this build-up. Maybe the 425 will do all I need until the block lets go. Of course, now I have all the parts needed to adapt a 500 short block (with the 425 heads and holes drilled in the 500 block for steam), or a 500 long block if I use the 500 heads... I know a guy who said his 77 CDV went 425,000 miles on the stock motor and ran fine when he sold it!

  12. #87
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    Re: cheap power improvements to the 425...

    Post pictures of the '77 somewhere!

    About the 425,000 mi Deville, that's nothing. The world record for the car going the most miles without an overhaul was held until very recently by a 1979 Sedan DeVille with just over 650,000 on the clock.

  13. #88
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    Re: cheap power improvements to the 425...

    Hello i have rebuild my 425 i have put a 472 intake on it from 1976
    , but i have a carb thats belong too the intake can i used that or must to buy a original 425 carb, mayby the 472 carb its too big

    thanks for your opinion.

    the carb its a rochester quadrayet 17056230.

    I have not 425 carb but it was earlyer a injected.

    thanks sleutelgek from the netherlands (europe)

  14. #89
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    Re: cheap power improvements to the 425...

    Quote Originally Posted by Benzilla View Post
    Post pictures of the '77 somewhere!
    I just posted up a few pics on this site under Previous models - Deville. Not much to look at (yet) but it is a fun project.

  15. #90
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    Re: cheap power improvements to the 425...

    Quote Originally Posted by sleutelgek View Post
    must to buy a original 425 carb, mayby the 472 carb its too big...the carb its a rochester quadrayet 17056230.
    Your 472 carb should work just fine. Be sure to use the correct ports and plug any ports not used so you don't have vacuum leaks. You may end up rejetting a bit but this is a good start.

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