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Registered
1990 Fleetwood Brougham
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15 Posts
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.
 

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Registered
Sedan Deville 1984,92,99
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1 Posts
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?
 

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Registered
94 Fleetwood Brougham
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7,534 Posts
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.

That sounds like total bull to me.

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

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Registered
1985 Cadillac Seville
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5 Posts
I know this is an old thread but I found it VERY Useful. I always wanted an 80-85 Seville, but stayed away from them over the years because of the potential headaches with the electrical system and general HT4100 issues. I finally made the decision to find one in good shape and drive the wheels off of it. 3 weeks ago I picked up a 1985 Seville with 103K miles in very good condition. It had been dealer reconditioned 3 years ago and aside from a few minor things like an exhaust leak, it runs great.

However, when I bought it and drove it home (over 100 miles), it was sluggish...more so than I remember these cars to be. I found this thread and so far have replaced only the plugs, coil, rotor, and PCV valve, and let me tell you it runs 200% better than when I bought it, is averaging 17-19 mpg, and has a LOT more pickup and power than it did when I bought it. The cat converter will be replaced next when the exhaust is fixed. These suggestions made a HUGE improvement on the overall power and feel, and makes the car better, safer and more fun to drive.
-CP
 

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Registered
94 Fleetwood Brougham
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7,534 Posts
I still find it amazing that the HT4100 only made 140 hp in the 80's, and my Lexus with a 4.0L V8 makes 300. Even the 4.0 Aurora 4.0L only made 250 hp.

I wish I had $$ to take a HT4100 and see what made it so poor on power. See how much power can be made from it. Considering these cars already had 3.42 gears factory, and high alt got 3.73, there is potential with a looser converter and custom cam grind and a LOT of headwork and a modern PCM to run it.

But alas, the $$ would be about fruitless if the bottom end can't handle it or the head gaskets can't take it.

Maybe when I get my billions... :)....
 

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Registered
1986 Coupe Deville
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138 Posts
Standard timing on my 86 4.1L is 8 degress TDC however it loves it at 10 degress TDC.

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check the actuator on the cruise system near the throttle body
 

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Registered
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12 Posts
I took off the stock cat. Ran 2.5" from y pipe back and out in front of RR wheel. She's loud works better on top end, slow to get there. She's loud but goes good.
Swapping to duals this weekend with mufflers, no cats. Putting in NGK Iridium plugs( have had great experience with these in all my cars) making up a set of 8.8 plug wires purchased a MSD coil. Doing a tranny flush this weekend too. Not sure if it's ever been changed. Got rid of alot of unneeded vacuum hoses kept the important ones.
Running straight pipe gave me better mileage but too loud to sneak around late at night with! Lol
I'm going full out with what I can get here locally. But I'm searching for a 472/500. None around here unless you want to pay damn near 10k for one that needs rebuilt. I'll probably wait until I get back to the western US to get that.
Love my car. She's a 1983 Fleetwood Bd'E.
She looks rough paint wise but she's solid!
Looking into another one to buy already!
First caddy ever, definitely not my last.
I'm in the automotive industry, certified tech for 25 years, now into the after market parts end of it, and body end too.
Can't find much into performance for 4.1. all geared toward the 5.0 and the 5.7. even the 472/500 has more add ones than can find for the 4.1.
I'm in NB Canada there is barely any Caddys here of the generation I have. So I get alot of attention.....some unwanted!
 

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Registered
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24 Posts
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?
Swap an 88 4.5 in- it’s a direct bolt-on and go.
 

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2000 Deville
1985 Cadillac Eldorado, 22k mikes
Joined
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16 Posts
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
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
Dr. Dave, are you still on here? I would like to learn from your experience 🙂. Thanks!
 
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