Boosting HT4100 Performance
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HT4100 4.1, 4.5, 4.9 Discussion, Boosting HT4100 Performance in Cadillac Engine Technical Discussion; To get the best possible performance out of your HT4100: 1. CHANGE THE CATALYTIC CONVERTER. Makes a HUGE difference on ...
  1. #1
    DrDave is offline Cadillac Owners Fanatic
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    Boosting Ht4100 Performance !!!

    To get the best possible performance out of your
    HT4100:

    1. CHANGE THE CATALYTIC CONVERTER. Makes a HUGE
    difference on throttle response, and also acceleration,
    clogged or not. Meineke is a good place to
    get it done, or any place that does it cheaper.
    Magnaflow seems to be a good brand. If the
    original converter is left on, it can rob the car of
    30-40 precious horsepower as well as throttle
    response. If it has the original converter and over
    80-90,000 miles, you almost certainly don't need it
    tested--just replace it. Complain of low throttle
    response, and difficulty attaining high speeds even
    though the engine revs at high rpms. Can also cause
    rough idle and difficulty starting, if the rest of the
    ignition system is in decent working order.

    2. Make sure your oxygen sensor is working (can make
    a low growling sound when accelerating and cruising
    over 30). This can affect idle, minor surging, and
    cruising speeds. You can also check this with onboard
    diagnostics (make sure it reads rich/lean at fast
    increments.)

    3. Using performance ignition components can make a
    BIG difference on responsiveness, horsepower, and EASE
    OF STARTING. After significant and extensive
    research, I've singled out Denso Iridium spark plugs
    (other Iridiums plugs may also be good), Magnecor
    spark plug wires (www.magnecor.com), and Accel
    performance components (ignition coil, ignition
    module, distributor cap, and rotor--all available
    through kragen, and sometimes autozone.) The ignition
    module and coil together, both from Accel, can make
    your HT4100 start in half a crank. No kidding.

    4. Have a good air filter in there -- the best one
    I've found for performance and good filtration is
    Amsoil, available at www.amsoil.com. I wouldn't use
    K&N paper filters since they can lose efficiency over
    time and aren't as good for the engine.

    5. Advance the timing 2 or so degrees if you want to
    squeak out a few more horses. I haven't done it yet,
    but it can make a pretty decent difference.

    I've had this setup for two years and 15,000 miles,
    and have been extremely pleased with the performance
    of this HT4100. It may not necessarily be the
    swiftest car on the road, but it has certainly made
    this beauty an even greater pleasure to drive.

    If one performs all these modifications (listed in
    order of significance above), it will probably feel
    like a hotrod compared to stock. Although, it may not
    quite be ready for a drag race. Now mind you it'll
    finish the race easy enough, just not ahead of any
    other cars--unless, of course, there's another HT4100
    on the track. In this setup, the components seem to
    hold up very well, though if there's any ignition
    symptoms in the future, check the coil--as it's
    usually the first culprit to go out (coils can cause
    varied ignition symptoms like rough idle, no start,
    and even backfiring through the throttle body--similar
    to a clogged catalytic conveter.)

    Hope these comments help, and if anyone's tried these
    modifications, please post and let us know your
    results! My experience with my '82 Eldorado has been excellent.
    As a luxury car, it's comfort and elegance is to be enjoyed
    the most. But if you want a 'few' extra horses, these
    mods will get them.


    -Dave

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  3. #2
    _slash_'s Avatar
    _slash_ is offline Cadillac Owners Member
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    Re: Boosting HT4100 Performance

    dude, you are my hero.

    origional cat converter is going bye bye asap. and im ordering new ignition components anyways.

    then maybe my eldo will be able to safely merge onto a highway

  4. #3
    DrDave is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    cool! glad I could be of help. When I started these mods a couple years ago, I had really wished someone posted stuff like this.. would have saved a lot of research and wondering what this baby wanted!

    Let us know your results and if it made as big a difference for your HT as it did for mine!! BTW, I also use amsoil synthetic oil and have been happy with the results so far.

    But if your engine already has higher mileage on it (>70-80k) you *may* want to stick with good quality petroleum or blends, since the synthetic cleans everything out so well it can cause minor leaks. If you don't mind changing some gaskets or using 'stop leak', good quality synthetics might work well. But if you don't want to deal with the leaks on a higher mileage engine, you can add GM EOS (Engine Oil Supplement--$8) to your usual oil, and it will add much of the concetrated ZDP anti-wear additive that makes higher quality synthetics such good quality. And with the camshafts on these engines, they need all the anti-wear protection they can get. I'd shy away from other engine oil additives though, since they rarely offer any real benefit and can sometimes be harmful.

    Also remember to add the coolant pellet supplements to the cooling system (available at GM dealer). Very necessary on this car (not using them caused my original motor to go out at 122,000 miles--I'm making sure to use them every year with annual coolant changes on the new one)!

    Hope this helps!! Looking forward to hearing the results!!!

    -Dave

    If anyone has any questions feel free to email me.

  5. #4
    D'Elegance is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    on my HT4100 i put a Holley Fre Flo air cleaner with the washable foam element, $19.95 at Advanced Auto, its the one in the shape of a triangle all open all around, little to no restriction, I got a little more zip on mine, I also put a glass pack, purrs like kitten yet roars like a beast

  6. #5
    godown is offline Cadillac Owners Member
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    Re: Boosting HT4100 Performance

    I just made a new 4" intake for mine today. I also put on a Dunomax Super Turbo muffler yesterday and advanced my timing. I can't believe how much extra power I got. I still need to hack out the cat converter. Thanks for all the tips everybody. I love this place!!! Here's my intake. (just wanted an excuse to post it )


  7. #6
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    Re: Boosting HT4100 Performance

    yeah, i am thinking about doing some of these mods, i need a new cat anyway cause mine has holes in it. maybe thats a good thing, lol. but thanks for the help dr. dave. the a 4.1 seems a little undersized for a 2 ton car, but these tips might help it not quite feel so bad.

  8. #7
    D'Elegance is offline Cadillac Owners Fanatic
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    Question Re: Boosting HT4100 Performance

    I would like to remove the cat on my car soon too. However I noticed the tube comming out. The one I would like to replace this cat with does not have the tube. So can I just leave the tube open when I take of the cat? Will It do anything different or effect anything?

  9. #8
    DrDave is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    The 'tube' coming out of your current converter helps combust the unburned fuel by giving it O2 from the air pump. If the tube is disconnected or the air pump isn't working, the cat won't get the added O2 and the emissions will probably go up. You'll probably notice more of a fuel smell in the exhaust, and it may cause (I believe) the HC/Hydrocarbon count on the smog test to go up.

    My air/smog pump was going out, and the max ppm (parts per MILLION) allowed for HC in the exhaust was 122 ppm to pass the smog test. The results were 121 ppm out of my exhaust. This is the second time in a row my '82 Eldo has 'beat out' the smog test by 1 ppm. Whether you want to try your luck by disconnecting the tube is your call esp. if you're in CA, but otherwise you can get a goodd Magnaflow cat off ebay for around $50 shipped.

  10. #9
    D'Elegance is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    Thanks for the info, might be able to get a converter with the tube comming out of it, I have seen these. The only thing is how do you reconnect a metal tube like that, mine looks fragile if it hasnt broken off already.

  11. #10
    D'Elegance is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    They got rid of the emissions testing in my state but now they're bringing it back. That is also another reason why I would like to change my cat, Im pretty darn sure that if I try to go through emissions with the cat that is on there now, theres no way the car will pass. The exhaust smells pretty bad on my car too, especially when is cold.

  12. #11
    Edahall's Avatar
    Edahall is offline Cadillac Owners Enthusiast
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    Re: Boosting HT4100 Performance

    The air/smog pump only pumps air into the catalytic converter when the engine is warming up. It should have no effect on emissions when at the smog station.

    You can make the numbers much lower at a smog station by retarding the timing as much as possible. Then once you pass, just set it back.

  13. #12
    D'Elegance is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    Thanks for the tip, bye bye original cat, lol, Yeah I know theres no way in hell Im passing emissions with this car, a new cat and a little retardation of the timing will hopefully help. And hey, if all else fails i'll just set up a fake exhaust for the guys to stick there little tester into. LOL

  14. #13
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    shredder130 is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    mines seems to do this and runs rich

    2. Make sure your oxygen sensor is working (can make
    a low growling sound when accelerating and cruising
    over 30). This can affect idle, minor surging, and
    cruising speeds. You can also check this with onboard
    diagnostics (make sure it reads rich/lean at fast
    increments.)

  15. #14
    DrDave is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    Does anyone have 0-60 specs on their HT4100's? I'm curious to see the range on the early Eldos etc. They're probably somewhere in a magazine, but I'm wondering what the best-case scenario for one would be and how big of a difference mods can make Mind you, don't go racing around your HT if it's on it's last leg or anything, but for curiousity's sake if anyone happens to already know theirs, it'd just be interesting to know

  16. #15
    henrydean40 is offline Cadillac Owners Member
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    Re: Boosting HT4100 Performance

    Dr Dave (and others)
    Thank you very much for the info you provided (like 6 years ago). You're a good man...it was extremely helpful information for me and others I'm sure.
    I'm trying like heck to make my 84 Deville HT4100 run in peak condition. I'm going to replace the Catalytic Converter soon (planning to replace it myself). However, a couple of quick questions in regards to converter swap:
    1. Do you believe it is something I should try to take on myself? I'm very mechanically enclined, and I'd really like to not have to spend the money for a mechanic...
    More importantly,
    2. What model catalytic converter will provide the improved performance? You mention Magnaflow, but is there additional model/part info that I'll need in order to get the right one??

    Anyone's help would be greatly appreciated.

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