Video: Building the new HT4100

[Big Apple Caddy]

I remember shopping for my first Cadillac in the late 80's,   I was mostly looking at the early 80's.    I had it in my head that diesel was bad but didn't know there was anything wrong with the 4100.   4100 sounded pretty powerful and was a much bigger number than the 3.8, 4.1, 4.3, 4.9's I was looking at in other cars.  I was most worried about the 'metric' transmission which did fail in the 83 Fleetwood I ended up buying.   I had friends with early 70's Cads but I didn't like the style as much and those just seemed old at the time.   I liked all the fancy electronics that the 83 had.

Issues with the HT4100 would've been fairly known by the late '80s.  Of course, there was no Internet or social media like today to as easily and rapidly share or search for information.  There was even a "sudden acceleration" investigation on HT4100 equipped cars just a few years after the Audi 5000 case but it never amounted to anything.

The HT4100 still didn't affect resale values like the diesels.  Some used diesel equipped GM cars were practically selling for half what equivalent gas engine (which included HT4100) models went for.

[76eldo]

They were big sellers because of the styling.
It's a shame that they did not use an engine based on the olds 350.
The HT4100 is only 252 cubic inches.
If they had taken an olds 350 and made it more economical hey would have been better off.
I know that they had received a lot of flack for the 76 Seville because Cadillac buyers didn't want to pay Cadillac prices for a car with an Olds 350 in it.

[Eric DeVirgilis CLC# 8621]

I absolutely agree: In terms of styling, ride, comfort, quietness the full size Cadillacs of the early '80s were great cars. I never found the 4100's performance overly objectionable, which was still miles better than the later 307 Olds and diesel, IMO. You just had drive with its power limitations in mind. I once let a friend take the wheel of my '83 FB but I soon stopped him when it became obvious he was trying to make the car do what it couldn't. 

[bcroe]

They were big sellers because of the styling.
It's a shame that they did not use an engine based on the olds 350.
The HT4100 is only 252 cubic inches.
If they had taken an olds 350 and made it more economical hey would have been better off.
I know that they had received a lot of flack for the 76 Seville because Cadillac buyers didn't want to pay Cadillac prices for a car with an Olds 350 in it.   

The Olds is a bit dated, back to 1948.  But the small block version has proved
to be an extremely durable engine under maximum stress (3/4 million miles at
the Roe testing facility).  I wonder if the Cad can match it?  Bruce Roe

[Scot Minesinger]

Eric,

I just drove an Olds 307 V-8 a few months back and six months before that a Cadillac 4100.  No way is the 4100 comparable to the superior 307 Olds V-8 in power.  The 307 is no power house, but the 4100 is by far the weakest V-8 I have ever driven in my entire life.


Bruce,

The Cadillac 4100 has no chance of matching the longevity of your Olds V-8 under current test.  If it could, 4100 engines may be replacing Olds 307 engines (only if they were more powerful) instead of the other way around.


All,

The 4100 is terrible, except being all aluminum block scrap value may be higher than a normal engine of the era.

[Eric DeVirgilis CLC# 8621]

I guess we have differing opinions is all I can say. 

[g27g28]

My parents had an 83 Eldo and I had a diesel 81 Eldo at the same time.  Mine needed an injector pump and had the head gaskets done twice before the engine exploded at 88 k.  Theirs made it to 115 k  before it needed an engine.  They then drove it to 140 k and I talked them into trading for a 91 sedan.  They both had no acceleration but even full of people they were both easily able to make the digital dash flash 85 mph all day long.  For those that don't know the digital dash's at the time only went to 85 and then started flashing.  I had both of them that fast many times.  I changed the water pump on an HT once, won't ever do that again.  I also later had an 84 Coupe that already had the engine replaced.  My experience with being around 2 HT's wasn't that bad, the diesel was a nightmare.

[TJ Hopland]

I think if you do the math on the 4100 it comes out to 249.something cubic inches.   The 4.1 Buick I think is the one that comes out to 252.   The Buick had that extra 2 inches and the 4bbl.  I thought they felt like they had more power but that could be because the carb was what more people were used to.

[BigBlock83]

I'm in the process of having the 4100 in my 83 Coupe Deville replaced with a 425 as I type this. It soldiered on for 116k. The last few years were pretty bad though, it developed bearing knock, vacuum issues and toward the very end started burning oil. I should add it was meticulously maintained and still couldn't last. But when it was right it was very smooth and quiet, thats about the only good I can say about it.

I wish a GM/Cadillac executive from the early 80s would come forward and do a sort of AMA. I imagine a FI 368 with the THM200 R4 would have gotten decent mileage. Why not make a Caddy exclusive FI Olds 350 or 307? Pretty much any drivetrain scenario would have been better than the basically a prototype HT4100.

[TJ Hopland]

If you can start a new thread and share any details you have on the swap process.    The subject comes up a lot and a lot of the info out there is outdated or kinda thin.  I'm sure people considering this would appreciate anything you can share about the process.   

[BigBlock83]

I'll be glad to when its all done. Hopefully soon. The project just hit a small snag because the 425 flex plate won't work with the Turbo 200 torque converter. I'm waiting on a universal flex plate from 500cid.com and then the 425 is going to its new home. The only significant issues I see on the horizon is figuring out fuel delivery and the A/C system. But we'll get it there.

[TJ Hopland]

Fee free to start the conversion thread now.   We may have some ideas to share that will help. 

[bcroe]

The project just hit a small snag because the 425 flex plate won't work with the Turbo 200 torque converter. I'm waiting on a universal flex plate from 500cid.com and then the 425 is going to its new home. The only significant issues I see on the horizon is figuring out fuel delivery and the A/C system. But we'll get it there. 

I suppose, the 425 flex plate was drilled for a 13" converter, but the TH200 has a
12"?  Might be possible to just drill another set of holes where nothing interferes;
lots of engines had both sets. 

Things should bolt up OK; the electronics and fuel delivery will be the challenge.
Cars I have converted had frame holes for about any engine the General made. 

Bruce Roe

[BigBlock83]

I've read that drilling new holes in the flex plate is very labor intensive and if not done properly can lead to it shattering. I'm happy to just buy the new one with the universal bolt pattern.

I'll start a new topic I promise, don't let this drift away from the awfulness of the 4100!!!

[Bill Young]

In My opinion the best all around Cadillac's I ever owned both gas mileage and reliability were the 3- 1990 Cadillac Fleetwood Brougham's I owned . The first I bought in September 1991 with 23.000 miles on it in triple Autumn Maple Firemist with leather and drove it to 200,000 miles , the second I bought in Summer 1996 with 18,000 miles on it in Academy gray with gray roof and dark carmine leather and drove it to 200,000 miles and the third was a sunroof car in medium blue with dk. blue leather , all three were 5.7 litre TBI cars and got 19 around town and 21 on the road religiously . None of them EVER gave me a problem. If Cadillac made them today I would buy one hands down. They were true Cadillac's in the grand term . 6 seat belts and a large trunk and they would tow my boat no problem. The stuff they make today gets good mileage , woop di doo , they can't hold six people have no trunk room and can't tow anything and look like an Audi . One Mans Opinion

[cadillacmike68]

In My opinion the best all around Cadillac's I ever owned both gas mileage and reliability were the 3- 1990 Cadillac Fleetwood Brougham's I owned . The first I bought in September 1991 with 23.000 miles on it in triple Autumn Maple Firemist with leather and drove it to 200,000 miles , the second I bought in Summer 1996 with 18,000 miles on it in Academy gray with gray roof and dark carmine leather and drove it to 200,000 miles and the third was a sunroof car in medium blue with dk. blue leather , all three were 5.7 litre TBI cars and got 19 around town and 21 on the road religiously . None of them EVER gave me a problem. If Cadillac made them today I would buy one hands down. They were true Cadillac's in the grand term . 6 seat belts and a large trunk and they would tow my boat no problem. The stuff they make today gets good mileage , woop di doo , they can't hold six people have no trunk room and can't tow anything and look like an Audi . One Mans Opinion

Bill, you must have been very gentle with the gas pedal. I can't get any better than 16 or 17MPG combined in my 1996 Fleetwood. Sure on the interstate, I can get 22-24MPG, but as soon as I hit the off ramp, down it goes.

Are you in FL? That avatar of yours looks familiar.

[Scot Minesinger]

Big Block 83,

That is a great project to be doing, switching a 4.1 for a 425 V-8 Cadillac engine.  My question would be the 4.1 transmission and rear diff., are they strong enough to manage the increased power and torque?  The TH400 was a very durable trans.  Not familiar with TH200.  Please definitely post all your work thru results in this conversion, as it comes up all the time.

Bill,

Agree my 1995 Cadillac RWD Fleetwood Brougham in triple black was the best car ever.  I got same mileage as Mike.  Sold the car with 254k trouble free miles only because it was ten years old and had a quarter million miles, looked perfect and ran well.  I remember driving it 25mph one time and had some reason to floor it, then it downshifted to first and spun the wheels - this car was unstoppable with gobs of power.  I think the HP rating was lower than reality.

The best thing that came out of this post is we may learn how to switch a 4.1 for a 425 engine in a RWD 1983 Cadillac.

[bcroe]

The best thing that came out of this post is we may learn how to switch a 4.1 for a 425 engine in a RWD 1983 Cadillac.   

With the BOP pattern just about any of the Generals engines and transmissions
could be bolted together.  The trans front surface is always in the same place. 
And frames have been configured with universal sets of engine mount holes. 

The new, electronic problems started with fuel injection.  They carry on into
gauges and transmission control.  Now that these systems all interact, the
problem gets much, MUCH more complex.  Mix and match, port injection, carb,
throttle body injection, different displacements, coil pack or on plug ignition.  Of
course such creations have no chance with a strict emissions testing program. 

I have managed to "pass" a fuel injected 403, because I could tune the ECU and
it looked like a 350 (there never was a production injected 403).  Its going to be
a lot more difficult with 80s stuff.  good luck, Bruce Roe

[35-709]

I don't think a TH200 will stand up to that engine, a TH200-4R, maybe.  TH200's even had a hard time behind GM straight 6.

[TJ Hopland]

The 200 did evolve over time and got a little better.   When it first came out in what 75? they did appear to not quite do enough testing with some of the new concepts and maybe took the value engineering a little too far.   The late 70's they did apply some updates to them which really seemed to help.  The updates first appeared in the E body version the 325 so maybe it was Olds or Cadillac that pushed to improve the design that was then applied to the RWD versions.   What seemed odd about the whole era was the OD's came out in 81 so why did they even bother with the FWD version and improved RWD version in 79?   You would think they would have just gone for the OD right away.   I wonder what the hold up was?   It didn't seem like the OD or locking versions had any real special or unique technology.  To me it all looked like concepts that had been around and used before they just needed to put them together.