You already know we’ve chosen the powerful and compact LS3 for this build, but which LS3?

We went right to the top and got the LS376/525 crate engine. It’s the most powerful production-based crate engine in the Chevrolet Performance portfolio: 6.2 liters, 525 horsepower at 6,300 rpm and 489 ft.-lbs. of torque at 4,400 rpm. It’s just over the top enough to be perfect.

After admiring this amazing piece of engineering, we brought out the cutting tools and got right to work making the engine bay and interior modifications needed to make it fit.  After many hours of cutting and pounding, we’re well on our way to making a home for this aluminum monster.

Coming up in the next installment of Project Thunderbolt: assembly begins!

ls376 525 cubic inch crate ls engine on a pallet in a shop
ls3 engine next to mazda miata size comparison for swap project
empty mazda miata engine bay
modifying miata interior tunnel and floor pans for ls engine swap
engine cradles for an ls engine miata swap project
man pushing ls engine on a cart under a miata
ls engine test fit in a mazda miata swap project

The Chevrolet Performance LS376/525: 6.2 liters, 525 horsepower at 6,300 rpm and 489 ft-lbs. of torque at 4,400 rpm. Just the right amount of power for our lightweight Miata!

This photo illustrates the genius of the LS3 engine. Its footprint is only slightly larger than the stock Miata 1.8 liter four cylinder engine on the left, and the low profile allows it to fit under the stock hood with plenty of ground clearance.

Here’s a look at the engine bay modifications in process. The bulk of the work is focused on the rear frame rail area and where the firewall meets the transmission tunnel.

There’s also work to be done on the interior. Here, I’m drilling spot welds out of the factory firewall supports so the supports can be removed. That is required so we can cut and widen the transmission tunnel. The supports will be welded back in place later on.

This is the LSX engine and transmission mounting kit from V8 Roadsters. It is a key ingredient in this drivetrain conversion by providing a strong, reliable, and hassle-free installation.

We removed the cast iron exhaust manifolds from the LS3 (they won’t fit) and bolted on the V8 motor mounts and subframe. Placing the engine and subframe assembly on a sturdy moving dolly allows for easy positioning for our first test fit.

Looks like it belongs in there, doesn’t it? This is a very encouraging step, but there is still a ton of work to be done.


Author: Alan Rebescher

Editor, author, PR man—Alan Rebescher has done it all in a 25 year career in the high performance industry. He has written and photographed many feature stories and tech articles for Summit Racing and various magazines including Hot Rod, Car Craft, and Popular Hot Rodding, and edited Summit Racing’s Street & Strip magazine in the 1990s. His garage is currently occupied by a a 1996 Mustang GT ragtop.