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HT4100 4.1, 4.5, 4.9 Discussion, Boosting HT4100 Performance in Cadillac Engine Technical Discussion; Alright everyone, I thought I should post an update since I followed a lot of the advice posted on this ...
  1. #16
    henrydean40 is offline Cadillac Owners Member
    Automobile(s): 1984 Cadillac Sedan Deville - ht4100
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    Re: Boosting HT4100 Performance

    Alright everyone, I thought I should post an update since I followed a lot of the advice posted on this form. I wanted to make my 84 Deville with ht4100 ride in top condition, or at least have some decent power and throttle response.
    Starting with Dave's original posting:
    1. I Changed the Catalytic Converter → It was a bit of a headache job, but only because I didn't have all the right tools/parts. Once I had everything I needed, it was pretty darn easy. The result from this was fantastic.
    2. O2 sensor was replaced, but due to error code.
    3. I replaced the air filter with hi-performance from Baxter.
    4. I advanced the timing to 13 BTDC
    5. I also replaced the spark plug wires, distributor cap, rotor and PVC valve - the dist. cap & rotor made a HUGE improvement to the throttle response and overall operation.

    Together, all of the changes have made the car run MUCH better and the hesitation I felt while first accelerating is nearly completely gone. I plan to replace the spark plugs with a brand called Pulstar (at $13 each, that,s a $104!!) but they claim to garauntee a "livelier throttle response and 12% increase in horsepower. " Now that's what I'm talking about!!

  2. #17
    Stingroo's Avatar
    Stingroo is offline Wagon/Audio Enthusiast
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    Re: Boosting HT4100 Performance

    That sounds like total bull to me.

    Want performance? Get that 4100 nightmare out and find a 350.

  3. #18
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: Boosting HT4100 Performance

    Sounds like you did everything that can be done to these engines. I would avoid those spark plugs though, nothing works better than plain old AC Delco RapidFire

  4. #19
    DouglasJRizzo is offline Cadillac Owners Enthusiast
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    Re: Boosting HT4100 Performance

    This is an interesting thread. The 4100 has always gotten short shrift because of cooling system problems and it was rather soft in the power department. Too bad GM didn't put more development into it. I had always wondered if anyone has ever tried to coax more power out of it.

  5. #20
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
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    Re: Boosting HT4100 Performance

    Quote Originally Posted by DouglasJRizzo View Post
    Too bad GM didn't put more development into it.

    They did - the 4.5 and 4.9. The engine series ended up performing well for it's day, while building the stellar reputation for reliability that we see today.

  6. #21
    ponchoman49 is offline Cadillac Owners Member
    Automobile(s): 1990 Fleetwood Brougham
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    Re: Boosting HT4100 Performance

    The first year 1982 HT 4100 engines were rated for only 125 HP and 190 torque which curiously was the same HP and 20 less torque than Buicks carbed 4.1 liter V6 of the same vintage. 1983-1985 full size plus Eldo and Seville saw a 10 gain on both figures or 135/200. The FWD 1985 Deville/Fleetwood curiously dropped back to the 1982 power and torque figures and then in 1986 went up to 130 HP and 200 torque which leads me to believe more power in hiding in these engines than what was advertised at the time. The pellet converters which were on 82 and 83 cars were terrible on flow and the 84 on up change over to monolithic helped a little. A change to the mentioned high flow cat will net a 5-8 HP increase on these engine from the stock factory pellet design and improve power, response and mileage some. The increase in timing and change over to premium ignition parts would probably be worth another 5-8 HP. Stock 1982 0-60 times given for the Eldo with 4100 V8 were 14.5 seconds when new. With the changes above I have seen a drop of over a second or around 13 seconds to 60. the 83-85 models with the extra factory power and torque may be a tad quicker still. Would be interesting to see everyone post there 0-60 times on fortified HT 4100 cars.

  7. #22
    KINGUYOM is offline Cadillac Owners Member
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    Re: Boosting HT4100 Performance

    thank's Dr dave !


  8. #23
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: Boosting HT4100 Performance

    Awesome information, I didn’t know that about the original pellet cat converter.

  9. #24
    MisterDeville is offline Cadillac Owners Member
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    Re: Boosting HT4100 Performance

    Hey guys i too am tryin to squeak a little more oomph out of my '84 deville (which according to production numbers was one of the absolute last RWD devilles ever produced, w 33000 miles on it!) Any ideas would be appreciated, but, on a side note im having a problem w my cruise control not working. It lights up when flipping the switch to on but thats all. Having trouble w diagnosis, control switch or vacuum leak maybe, but there does not seem to be a vacuum pro
    blem. Ideas anyone?

  10. #25
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: Boosting HT4100 Performance

    Yeah, but that might help mpg! I would look at a 4.8L or 5.3L Gen III truck engine. Weight is close, and would more than DOUBLE hp and torque! And cheapest mod you can probably do to get that much more power.

    Quote Originally Posted by Stingroo View Post
    That sounds like total bull to me.

    Want performance? Get that 4100 nightmare out and find a 350.

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