Piston Slap: The perfect candidate for an LT1 swap?
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.
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.
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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