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Discussion Starter #1
Here we go I'm now really considering doing a modern Ls swap vs just a 80s 350 set up in my 80s Fleetwood my 4100 is very tired, has anyone in this group actually done it? Just a few questions I want to know like can I use the Ls stick headers or do I need shorty headers? do I need to swap out the truck intake for a car one since it sits lower and hopes to not hit the hood,do I need to change the oil pan to a car one? What are some good mounts? And could I use a 700r4? I won't take a chance with my stock 200r4
 

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1980 FBC
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It isn't cheap but LS engine/transmission setups including wiring are available on epay.

No way would I recommend screwing around with a 2004R or a 700R4. Those are antiques that were weak when new.

Back and current issues of Hotrod magazine are good resources for information.

IF I needed a drivetrain for an early 80s Fleetwood Coupe I would do this myself.
 

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A 6L80 would be a really good choice IMO but it is not my dollar : )

A 4L60 is basically an electronic 700R4 which was the Achilles Heal of many an otherwise good GM product over the years.
 

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1998 Deville Concours
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Swaps and parts chosen for same are always open for debate.
Short answer on the transmission is that a STOCK 200-4R or 700-R4/4L60 (or “E”) probably won’t hold up behind a reasonably souped up 6 litre LS type engine.

However, a properly MODIFIED one WILL hold up to quite a bit of power & torque.
(I am running a 200-4r behind 475 hp 350 Chev in an ‘84 Rx7 bracket car. Not even a hint of a problem in over 3 years of passes. Best pass: 10.94/124mph. [Yes, its 3 tenths soft...] )

Swapping in a different transmission will mean a bunch of extra work, like having to relocate the rear transmission mount and deal with new linkage, driveshaft length, etc..
Doing a performance build on your 200-4R will sidestep all that, and depending exactly how much power you want, can be built to work up to 650 hp.

The more modern transmissions, like 4L80E, 4L85E, 6L80E, are available, but you can spend more money up front on the modern transmissions. And the 4L80/85 series should get a couple of performance upgrades as well, though not as much as the 200.
Electronic controller is needed for the ‘E’ versions, fairly expensive as well.
(There is no point considering a 4L60E if you don’t want to use the 200.)

BTW, the 60 or the 80 is the torque rating that the factory gives each transmission.
It’s not a directly readable value, but the higher number is rated for higher torque.

I don’t have experience trying to match ECM/TCM’s which is why I mentioned the stand alone type transmission controller.

As for using a truck LS, all I can say is, ‘try it’. If you run into issues, you’ll know soon enough and can source any needed parts like oil pan, alternator mount, or intake manifold.

There is always a bunch of stuff that comes up when trying to mix and match engines to cars, but a lot of the fun and satisfaction comes from solving those things.

Have fun, and keep us posted please.

Bjc789
 

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Discussion Starter #9
Oh ok I see I guess I would have to make that decision with transmissions and rear end gears thanks for that input. Seems like truck Ls motors are cheaper so just finding a decent milage one,someone told me I could use my stock radiator and just ad dual electric fans,I need to figure out to on what electric fuel pump to run etc
 

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A lot of 6 litre trucks already have the 4L80E, so that might be the best way to go.
Then it is a matter of integrating the electronics from the truck to operate the engine and transmission. Mid to late 2000’s the cpu’s are all tuneable.

Usual swap stuff like engine / frame mounts, trans mount, driveshaft mods. (4L80E has larger output shaft) There is a bunch of LS swap stuff on the old interwebs. Try and read some of it to decide how to approach this swap.

Getting a complete truck may be the best bet so that you have various parts handy in case they will work. Saves buying aftermarket, unless you want something specific.

Yes APEMAN 525+ ft.lbs. of torque will turn a lot of transmissions into junk. I’ve seen a t-400 give up behind one, but it didn’t start out the most healthy.
My trans only has to deal with around 425, and it was built to ‘known good’ at 500 specs. It also doesn’t shift super hard, but is still quick shifting, which keeps the impact forces down while minimizing heat build-up. This was one of the many items my trans builder and I talked about. I give the credit to a very knowledgeable trans builder.

As an aside, I am actually still running the stock Mazda rear end. I’m getting a 9” together, but in the meantime it just keeps on keepin’ on. Sometimes I feel ‘lucky’ it hasn’t broken, but then again I put it together ‘just so’ and purposely kept the trans shift a tiny bit softer. 4100 stall converter doesn’t hurt either.
If there is a point to the above, it is possible to do a lot with a little less by paying attention to the details. Hopefully 84 Fleetwood coupe can do something similar, and not break the bank doing it.

Bjc789
 

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Discussion Starter #12
i been seeing them cheaper out the trucks so trying to definently staying low cost as possible and will try to find a trans complete with it to keep headaches down,yea know about moving the trans bar and driveshaft more conserned about motor mounts,fuel pump and regulator if needed,and most important the oil pan and headers
 

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We've got a truck 5.3 on a stand at work, and are just about to pull a 4.8 and trans out of van. Not sure if it's a 4 or 6L80, I'll have to check. Eight lugger, though.
 

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I have a 83 Fleetwood. was looking for a BBC but Im thinking Ill go with the LS. I have an avalanche and a silverado at my disposal for engines and such. is it a real bitch to get the wiring done?
 

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Wiring is either a couple of clicks on the internet and a charge of a few hundred on your Visa, or, a few hours with the truck harness stretched out on a piece of plywood and the wiring diagram as you trace wires and remove circuits that you don't need on the new install. You'll then need to have the PCM reprogrammed. And, integrate the new harness to the Cadillac body so everything operates (AC/fuel/ignition/etc). Difficult? Not really. Looking at pictures, then matching to connectors and wiring colours. Time consuming? You bet.

There are many really good step by step youtube vids on doing the harness.
 

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1996 Fleetwood hearse
1996 Cadillac Fleetwood Superior Coach Hearse Conversion
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You might be better off using a stock engine without a computer, then install a MSD ignition and a Holley Sniper EFI.
 

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I have a 83 Fleetwood. was looking for a BBC but Im thinking Ill go with the LS. I have an avalanche and a silverado at my disposal for engines and such. is it a real bitch to get the wiring done?
Tons of LS swap info in the Conversions forum over on LS1tech.com.

Older thread that didn't really go anywhere, but has some good info about what other GM platforms (built on the same RWD chassis) to look at to help you with doing the swap. Thinking About it. 1978 Cadillac Coupe Deville 425 to 6.0 LQ9 swap. - LS1TECH - Camaro and Firebird Forum Discussion . Search that Conversions forum for some of the other models listed in the 2nd post of that thread and you'll find some good swap threads to help you see what's involved.


You might be better off using a stock engine without a computer, then install a MSD ignition and a Holley Sniper EFI.
Seems like a step backwards to have to install a carb-style intake manifold and the carb-style throttle body. I would suggest the Terminator X or X Max instead - Terminator X and X Max LS Kits - Holley Performance Products.
 
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