1987 Deville 4.1 to 4.9 Conversion

[Ed Hall]

This car was the last year that the infamous HT4100 was used. It's got 270k miles on the clock and everything on the car (paint, interior, transmission) is still in good condition except the engine. The engine has had a noisy valve train for a long time but lately, it has been getting progressively worse to the point that everybody could hear it coming from several blocks away. Also, the rated 125 hp was more like 50 hp. The engine would struggle in 2nd gear with the pedal through the metal going up Snoqualmie pass and passed by semi's that were carrying a full load. By the time you got to the top of the hill, 25 mph was as fast as she would go. We did open up the valve covers to inspect the rocker arm support fixtures for cracks and they were fine. So most likely, the camshaft and cams were wiped out.

Anyways, long story short, we were given a 4.9 out of a 1992 Seville with 80k miles on it. The decision has been made to put this engine in place of the 4.1. The plan of action is the following:

1. Block off all the injector ports on the 4.9.

2. Bolt down the 4.1 throttle body to the 4.9 intake manifold

3. Transfer all the accessories over to the 4.9

4. Use 350 Chevy injectors

5. Bolt the stainless steel 4.1 exhaust manifold onto the 4.9

6. Use the 4.1 distributor

7. Modify exhaust system to have 2 glass packs in series and replace the back muffler with a chambered muffler.

Replace this

With this 4.9

[Ed Hall]

I forgot to mention that average fuel economy on the HT4100 had dropped down to 12 mpg. This is worse than my 1990 3/4 ton Suburban.

Edited August 13, 2012 by Ed Hall

[Texas Jim]

Isn't the injectors on the 88 in the middle of the throttle body ??

They were on my '84...

[Ed Hall]

Isn't the injectors on the 88 in the middle of the throttle body ??

They were on my '84...

Yes, the injectors on the 87 are in the middle of the throttle body. The intake manifold on the 4.9 have 8 injector holes which will be covered shut and the throttle body with the injectors from the 87 will be bolted onto the 4.9 intake manifold. Basically, I'll be changing it from Port Fuel Injection (PFI) to Throttle Body Injection (TBI).

[Texas Jim]

OK... understand now...

What threw me off was you mentioned using 350 Chevy injectors...

I was thinking you meant 350 PORT injectors and I was wondering how you were going to use port injectors and TBI all at the same time...

I am now assuming that you are going to use 350 Chevy TB injectors in the 4.1 throttle body.

That should work pretty well.

[Ed Hall]

OK... understand now...

What threw me off was you mentioned using 350 Chevy injectors...

I was thinking you meant 350 PORT injectors and I was wondering how you were going to use port injectors and TBI all at the same time...

I am now assuming that you are going to use 350 Chevy TB injectors in the 4.1 throttle body.

That should work pretty well.

Exactly, 350 Chevy TBI injectors into the 4.1 throttle body.

[Cadillac Jim]

I would suggest turbo mufflers instead of glasspacks. You can get the turbo mufflers in stainless steel.

[Ed Hall]

I would suggest turbo mufflers instead of glasspacks. You can get the turbo mufflers in stainless steel.

I'm hoping the following setup won't be too loud. But if it's too loud, I'll have to do as you suggest.

Here's the setup

2 glasspacks in line

Plus Flowmaster chambered muffler in the rear.

[Cadillac Jim]

I was thinking future maintenance rather than noise. If you are thinking Flowmaster chambered mufflers in the rear, you probably don't need the glasspacks at all. That's assuming that your exhaust system is similar to mine, a Y-pipe as close to the manifolds as possible, followed by a cat, a long and large tube down the center, then a Y-piple two two mufflers, which have the tips very close to their outputs.

[Ed Hall]

The 2 glasspacks will be installed in place of that long large tube down the center. The idea is have a quiet but free flowing exhaust. The glasspacks (absorptive muffler) take out the high frequency noise while the Flowmaster (reactive chambered muffler) cancel out the low frequency noise netting as much sound reduction as possible without causing much restriction.

Engine yanked out! Bye Bye HT4100. Anyone want it? Might be good for a riding lawn mower.

Edited August 13, 2012 by Ed Hall

[Cadillac Jim]

The high-pitched sounds won't make it through two Y-pipes, a long center tube, and baffled mufflers, and possibly yet another Y-pipe as part of the tips. I know this is true for my 4.6 because I lost my mufflers to a rear-end glancing blow a few years ago while Borla and Cadillac were both out-of-stock and I ended up with straight-through mufflers, and my car sounds like a vintage Chris Craft with a big V8, all soft bass rumble. Even my wife likes it, and we are old enough to be retired.

The big tube down the center serves as a volume resonance that helps provide the bottom-end torque for get-off-the-line agility, which the 4.9 is really good at. If you use a smaller tube and/or break it up with a glasspack, you can expect to do strange things to the bottom end torque curve. At least that is the way that I read my exhaust system.

One thing that you might think about is to leave the glasspack out in favor of the production tube as a first cut, and, if you don't like the exhaust sound, add the glasspack.

[Ed Hall]

I've heard that too little back pressure could kill low rpm torque. When I replaced the muffler on my 1988 Eldorado, I drove it around the block without the rear muffler and it sounded exactly like you described. It was noticeable, but not objectionably loud. However, I think the catalytic converter also cut down a lot of volume as well. My guess is that it would have been pretty loud without the catalytic converter in place.

I got the engine bay pressure washed. It was a terrible mess from all the oil that the HT4100 leaked out.

Instead of switching distributors, I took some of the guts from the 4.1 distributor and put it into the 4.9 distributor. I left those 2 connectors (at the bottom of the picture) disconnected because the 4.1 doesn't use those. I hope it works.

[Texas Jim]

About exhaust systems...

I have had two different vehicles in which I had exhaust systems put on them that had too little back pressure.

They lost almost all low end torque...

They would scream at high RPM, but at low RPM they would barely pull your hat off of your head.

They were SLUGS at low RPM.

I had to have a resonator put on one of them to eliminate drone and to increase back pressure.

Had to put different mufflers on the other one to increase back pressure a little.

Both of them ran OK after that...

[Ed Hall]

Here's what was partly responsible for the terribly low power. Hint... Take a look at what has come out of the end of the pipe.

Plugged up all the injector holes on the 4.9 with some bolts and RTV. Those injector holes don't need to be used since I've converted it over to TBI.

The distributors are different between the 2 engines but wanted to avoid swapping them. So I swapped the innards instead. I hope it will work.

4.9 engine ready to be installed.

Edited August 14, 2012 by Ed Hall

[Ed Hall]

Got it running. I'm currently working out some of the kinks. The exhaust was a major success. It sounds very good and produces just the right level of noise.

Edited August 15, 2012 by Ed Hall

[Ed Hall]

Here's how the 4.9 engine sits in the car. It runs very smoothly and has tons more power than the HT4100. So far, I'm very pleased with the results and I'm glad that I saved this very well built car from being sent to the crushers and recycled into a Smart car. With only 80k miles on the heart transplant, it should last for a very long time. Also, my homemade exhaust fits like a glove and sounds like some of the more expensive exhaust systems out there. It was easy to do with the engine out.

I don't know if anyone else is interested in saving an old car like this but if someone is, I would be willing to write something up on how to do this. The job was not difficult but there was someone planning and homework that went into this to make the conversion successful.

Edited August 16, 2012 by Ed Hall

[Cadillac Jim]

I think that we could use a set of "how-to" pages on Caddyinfo. But, that's up to Bruce and Texas Jim. It's easy to write a post like this, another to maintain a web site.

[Texas Jim]

Ed,

I think a detailed write up would be really useful for some of our other readers.

It could very possibly save a few nice cars from going to the wrecking yard.

Bruce can then decide exactly where to put it.

[Cadillac Jim]

Congratulations to Ed Hall, for his successful transplant of the fine 4.9 into his 1988 Eldorado.

[Ed Hall]

To set things straight, the car that the work was performed on was my parents 1987 Cadillac Sedan DeVille. It had 270k miles on the 4.1 and was running pretty shabby. Other than that, the rest of the car was in good shape.

The 1988 Eldorado still runs very good. The Cadillacs built from 1988 and up had much improved 4.5 engines compared to the earlier 4.1. The major improvement was roller cams and much more power. Also, the intake manifold gaskets were much improved which decreased the likelihood of coolant getting into the oil and wiping out crankshaft bearings.

The Cadillacs that could benefit a lot from the conversion would be FWD Cadillac's with the transversely mounted 4.1 built from 1985-1987.

Edited August 16, 2012 by Ed Hall

[Ed Hall]

So far, all is well with the 4.1 to 4.9 conversion. It just needs a little tweaking with the tuning. I'm currently using 350 injectors but it's causes it to run a little bit too rich. So I'm looking for a set of 305 injectors.

[CadillacDeville]

On 8/25/2012 at 1:23 AM, Ed Hall said:

So far, all is well with the 4.1 to 4.9 conversion. It just needs a little tweaking with the tuning. I'm currently using 350 injectors but it's causes it to run a little bit too rich. So I'm looking for a set of 305 injectors.

If I use 350 injectors for my conversion because I’m doing a 4.5 to 4.9 engine swap on my 1988 Cadillac Deville would it turn on the engine 

Edited April 19, 2019 by CadillacDeville

[BodybyFisher]

Ed Hall used the 350 injectors in the 4.9 and it ran rich, and was planning on going to the 305 injector here. I am going to ask Ed here >>>   @Ed Hall <  How did this turn out?, its been a while, I hope all is fine with you, Mike  <<<

So you would also get a rich mixture using the 350 injectors on the 4.9.   Does that help?

[bil.dun]

Hey guys, interesting topic....I wondered if you guys could give some input on a 1984 Seville, in near mint condition, but in need of an engine upgrade. What, if anything, can be done to boost the power of the old 4.1l, or can it be replaced with a much better 4.5l, 4.9l, or a 307 Olds engine?   Any input would be helpful, if this needs to be reposted somewhere else, great, but I'd like some help!    Thanks       Bill in VT

[Cadillac Jim]

The car is old enough to be exempt from emissions rules that require exact OEM powertrain and emissions components, so you have a clean slate.  The best pushrod replacement is the later 4.9 liter V8, but the 4.5 liter V8 may be simpler because of motor mount and accessory mounts; others will have experience with swapping the aluminum pushrod V8s.  The 1991 STS was offered with the L26 4.0 liter V8 so that might be the best option.  Be sure and get the transmission, wiring harness, and PCM with it.

The Olds engine and the bowtie 350 that were used in some larger sedans may be an option, for a total conversion project.  For a daily driver, I would recommend a bowttie 350 because of parts availability and such for simpler maintenance over the long haul, but an iron engine will require suspension changes because it weighs over 200 lb more than the smaller aluminum V8s.  Even a Cadillac 425 weighs less than an iron bowtie engine, because Cadillac uses stronger alloys for its blocks and thus can cast them thinner and still be stronger.

If a Northstar falls into your lap, you will be looking at a full conversion project as thorough as a switch to the Olds or bowtie V8s, except that added weight will be less of a problem.  Just make sure that you get one of the transverse mounted FWD models and get the transmission, wiring harness, and PCM with it.

For a full replacement project, the ECM might be simpler if you use a Holley fuel injector and ECM.  The TCM is up to you, though.

For a good time, look at a GM Performance E-Rod engine.  They offer everything you need for a street-legal powertrain including engine, transmission, ECM, and PCM.  The price may seem higher than for other alternatives but I think you may find that by the time you look at all the extras you need for other total replacements you will find this option a bargain.  Weight is similar to that of the HT engines/transmissions..  Here's one:

https://www.gmperformancemotor.com/parts/CPSLS3EROD4L65E.html

Note that at 430 hp you may need to upgrade brakes, suspension, wheels and tires before you let your wife drive it.