Piston Slap: The perfect candidate for an LT1 swap?


Woody writes:


I was reading an old post of yours regarding doing an LS or an LT1 engine swap in a Cadillac Brougham. I have a great example from 1989 with a weak, 307-cubic-inch small-block. I like your idea of an LT1 [engine] and 4L60E [transmission], but would really like to do a five-speed. Ideas?

I was also thinking to swap out the rear end with one from a period Olds Delta 88 with 3.73 gears. I was thinking the 3.73:1 would give a better holeshot. Any thoughts on this—or if you can point me in the right direction—would be greatly appreciated.

Sajeev answers: 

A restomod Cadillac Bro-ham? Sign me up for this! Let’s start from the easiest part of the operation and go upstream from there.

Rear axle: While it won’t get you a better holeshot (talk to Circle D, they’ll have what you need for that) a quicker axle ratio is always on the table. Provided the car is in good shape and you’d be throwing out a perfectly good axle, don’t swap out the entire rear end; just switch the gears and add positraction. You can get 3.73s for either the GM ten-bolt or the twelve-bolt axle that some Bro-hams had as an option. This isn’t an Oldsmobile thing; it’s a standard GM off-the-shelf part thing.

Unless you’re certain you’re getting high-quality used parts, buy new gears/posi and have a professional install them into your existing differential. If you don’t drive much on the highway, go nuts with 4.10 gears because you should never fear the gear!

Transmission: As a Ford guy, I am kinda surprised at how hard it is to find a Camaro five-speed (T-5) manual transmission for a small-block Chevy. (Well, for a reasonable price.) You can broaden your search to include Chevy S-10 gearboxes, but those can’t handle as much torque and have wider gear ratios.

If I were to manual-swap a Bro-ham, I’d get a six-speed (T-56) from an LT1 fourth-generation Camaro or C4 Corvette. These six-speeds do not easily interchange with those intended for the LS, making them dirt-cheap to acquire. They install behind a traditional small-block Chevy V-8, and their stupid-tall, double-overdrive gearing ensures effortless highway cruising and insane fuel economy. But when it comes to Cadillacs, I generally prefer column-shifted automatics. They just cruise better with a torque convertor, and make properly smooth moves to feed my luxurious soul.

Engine: No matter which transmission you choose, an LT1 swap is so much cheaper than an LS, and is far from inferior considering the improvement relative to a carbureted 307 Oldsmobile. Sure, those needing maximum performance will (rightly) choose an LS, but the LT1 can easily make over 300 horses and still be perfectly tractable in a big ol’ Bro-ham. Just get a tired 1992–96 Corvette with an automatic ($2000–$5000, and less if you look hard enough), as you get the best of everything with that singular donor-car purchase. Easily fixable warts aside, the LT1 is the most bang for your buck.

Yes, you can do an LS-swap plus whatever transmission you choose. That said, it is still a metric ton of labor to get any EFI Chevy into a carbureted Caddy. And good labor ain’t free, if you’re pickin’ up what I’m puttin’ down.

So instead consider swapping to a Chevy 350 (or a 383 stroker?) with an RV cam and a modest four-barrel carburetor, shorty headers, and a higher-flow exhaust. You’ll get similar levels of performance with a little decrease in drivability, but the labor cost will be a fraction of that for any other motor swap.

Facebook Marketplace

Not gonna lie, if I found a nice 350 with Vortec heads on Facebook Marketplace right now, I’d refresh it as needed, source an RV cam, install a low-rise intake manifold for a four-barrel carburetor, and drop that bad boy into the big Bro-ham for basic bucks.

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    I have a bit of experience with LT1 engines.

    If you get one from a 94-96 Caprice, all the engine and computer wiring will easily separate from the rest of the Caprice wiring and transplant with the engine into a new home. These engines are rated at 265 HP, but are underrated. They are also torque monsters, which is just what you need in a Cadillac. They are paired, in the Caprice, with a 4L60E transmission, which is a really good fit for a big heavy car. The computer that controls the engine and transmission lives under the hood with the engine, which also makes swapping easy.

    Engine mount placement is different than an older Chevy V8, but it is easy to make offsetting plates.

    The flaws of the LT center around the ignition. The optispark distributer is sensitive to water ingestion. There are minute difference over the years, but none of them seem to work well. The kiss of death for many of these cars, though, is the module that runs the coil. These fail, or partially fail. Replacements are hard to find, and are often defective right out of the box. I’ve seen decent Caprices in junkyards that are there, I’m cetain, because of multiple module failures, and the difficulty to diagnose.

    The aftermarket makes new ignition systems for these engines. Most use 8 individual coils from an LS engine. You need to make brackets to mount he coils on the valve covers, but otherwise it is a simple modification.

    There arere many aftermarket, and GM, options to increase horsepower. The aluminum heads from a Corvette will also add power. Edelbrock even makes an intake manifold that allows the use of an old style distributer and a carburetor.

    After you finish te engine swap, consider installing the sway bars from a Caprice cop car. That will make a huge difference in handling. A cop car steering box will improve the steering feel, as will replacing the rag joint in the steering column with joint from Borgeson. Both easy swaps. Rplacing the upper control arm bushings with harder ones from Moog, or urethane ones from other companies, will also sharpen up the steering at no ride penalty. The original ones are probalby shot by now anyhow.

    It is easy to add disc brakes to the rear. Later cop cars, and the Impala SS had factory rear discs, as did some of the other B body cars. You will need a new master cylinder and proportioning valve as well.

    Good luck.

    The author must be a ford guy as he knows little about GM or Cadillac. The 89 Caddy is the same car as the same 90s models that came out with the Chevy LT1. It is an easy swap. Upgrading motor and tranny with bolt in parts.

    I just noticed that this car has a 307 CID engne. I think thatis an Oldsmobile engine. The easiest swap, i that is the case, is a 455 CID Olds engine. Almost nothing has tobe changed. The increase in displacement, and torque, will make a shocking change to the performance.

    Great article Sajeev!
    Bob also has some excellent ideas. I do like the idea of going completely old style with the 455. Love that too!

    Bob nailed it. After my own experiences, the ignition problems are what keeps me away from LT1s. Especially when the car in question is something you want to be reliable- long trips where the comfort would be appreciated or infrequent driving where you just want it start each time you do go for a drive.

    I’ll also vouch for upgrading the brakes and suspension with cop car or Impalla parts!

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