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LS Engine Swap - Modern Muscle

An LS Swap can Infuse New Life into Classic Muscle

1303 Chpp 01 O LS Engine Swap Chevy 2/30

In the hot rod world engine swaps are a big part of what we do. It can be a small-block V-8 to replace a straight six-banger, a big-block in place of a small-block, or any number of "this for that" combinations. These days one of the more popular gyrations is to drop a modern EFI-fed, computer-controlled mill underhood, and the most popular choice is GM's line of LS engines. After all, what's not to love? Great street manners, lightweight aluminum goodness, killer gas mileage, and a rock-solid EFI system wrapped up in an arguably affordable package.

But, swapping in an LS engine isn't exactly a straightforward endeavor. The LS mill has needs that differ from a carburetor-fed Gen-I small-block. There are also mounting details that need to be addressed. The early swaps were pretty challenging, especially when it came to dealing with wiring harnesses and computer programming. Today these challenges are easily overcome by a host of companies churning out parts to make swapping in an LS engine nearly painless. And while this install deals with a Chevelle, the principles apply to any Chevy you might feel needs a little mechanical modernization.

A great way to shave a few pounds and add a bunch of reliable power is to drop in a 6.2L (that’s 376 ci for those who shun the metric system) LS3. A typical LS3 is rated at 430 hp, but this example is an LS376 engine from Chevrolet Performance. With its more aggressive bumpstick it churns out 480 hp. At a street price of just over $6,500 it’s not cheap, but, when you consider it's an all-aluminum EFI small-block then it's certainly a great bang-for-the-buck.

 Chpp 02 O LS Engine Swap LS3 3/30

Backing up our LS376 is a Tremec T56 Magnum from Hurst Driveline Conversions (HDC). With triple-cone synchronizers on gears one through four and doubles on the rest, including reverse, it shifts like butter. The Magnums can be ordered in different ratios and we chose the version with a 2.66 First gear and 0.63 Sixth gear. All Magnums share a 26-spline input and stout 31-spline output shaft. HDC offers basic kits starting at $2,995, but we opted for their Elite Kit, which was $4,295. Hey, what’s cooler than a wagon with a manual transmission? The answer is, "not much".

 Chpp 03 O LS Engine Swap Tremec T56 Magnum 4/30

The Best of Show crew then lowered the LS376 crate engine into the Chevelle’s cavernous engine bay.

 Chpp 10 O LS Engine Swap Best Of Show 5/30

Getting an LS engine into a classic Chevy, or any car for that matter, requires the right oil pan. This task is even more challenging on a Chevelle due to interference with the steering linkage at full lock. One of the most compact oil pans out there is this steel 5.5-quart oil pan from Autokraft ($400). It features a four-corner trap-door baffling system and a thick steel flange that’s less likely to warp and leak. It came to us with a billet oil filter adapter, which we used to make life easier, but they also offer an adapter if you want to run a remote oil filter and cooler arrangement.

 Chpp 04 O LS Engine Swap Autokraft Oil 6/30

To accommodate the large T56 Magnum six-speed trans, it was necessary to enlarge the trans tunnel quite a bit.

 Chpp 11 O LS Engine Swap Trans 7/30

Mating the new-school engine to the old-school frame mounts used to be a pain, but today it's as easy as calling up Holley and ordering up a set of their billet engine plates. This let us bolt on a urethane motor mount kit from Energy Suspension (PN 31114.G, $40) that would work with the factory frame mounts. Keep in mind that engine plates from different companies place the engine in slightly different locations, which can effect transmission placement and header fitment. So do your homework before ordering.

 Chpp 05 O LS Engine Swap Holley Engine 8/30

Here you can see the Magnum installed under the Chevelle. The Hooker headers hugged the floor nicely for added ground clearance.

 Chpp 12 O LS Engine Swap T56 Magnum 9/30

The clutch actuation parts aren't included in the Elite kit since one can either go mechanical or hydraulic. The mechanical kit runs $350 and the hydraulic kit is a bit more, at $595. Because it's easy to install, compact, and, in our opinion, simpler to deal with, we went hydraulic. The kit came with a GM throw-out bearing, “short”-style Tilton master, billet firewall mounting bracket, remote reservoirs, and a bunch of fittings. The firewall bracket is especially nice since it seals the required hole in the firewall and is much stronger than the angled steel plate brackets we've used in the past. The kit also included all the various bits needed for installation. Having these parts, especially the electrical pigtails, included sure beats running around town trying to source them.

 Chpp 06 O LS Engine Swap Clutch Actuation 10/30

You can spend as much or as little on pulleys as you want. In this case we just wanted something functional and reliable and this kit from Chevrolet Performance fit the bill perfectly. The kit (PN 19155067, $800) included a 150-amp alternator, power steering pump, V-7 variable displacement A/C compressor along with all the brackets, tensioners, and belts needed. Since we’re not running A/C we went with a kit that omits this (PN 19155167, $699). We should note that the low mounting of the A/C compressor wouldn’t work in most applications without frame modifications and the GM compressor isn’t compatible with most aftermarket A/C systems.

 Chpp 13 O LS Engine Swap Chevrolet Performance Pulley 11/30

The Hurst Driveline Conversions installation kit included this Luk HD Pro Gold clutch kit (PN 04-905). It's pretty much a factory replacement for the LS7 Z06 Corvette, so it should serve the wagon well.

 Chpp 07 O LS Engine Swap Luk HD Pro Gold Clutch 12/30

To prep the Magnum for installation we bolted on the GM clutch master supplied in the kit. As a bonus, it came pre-bled.

 Chpp 08 O LS Engine Swap GM Clutch 13/30

We splurged a bit and went with a Quick Time SFI-certified spun-steel bellhousing (PN 8020), which came in at a relatively svelte 20 pounds. In addition to being super strong we’ve found them to very accurate dimensionally. Trust us that an out-of-shape bell is nothing but headaches down the line. If you want to save some cash then HDC also offers an aluminum GM bellhousing.

 Chpp 09 O LS Engine Swap Quick Time 14/30

And here's our pulley system all installed and looking good. If you're on a super-tight budget you could source something like this from a bone yard, but we feel the convenience of having all the bolts, nuts, and widgets along with the sparkly new parts is worth the asking price.

 Chpp 14 O LS Engine Swap Chevrolet Performance Pulley 15/30

It’s easy to overcomplicate a fuel system, but this one is simple. Fuel from the tank enters the 10-micron filter (PN 162-554, $74) on the left and is pulled through the pump before going to the bypass regulator (PN 12-846, $145). The return off the bottom of the regulator sends the unneeded fuel back to the gas tank. The pump (PN 12-700, $259) is Holley’s new high-volume billet in-line deal, which is rated up to 700 hp in EFI applications.

 Chpp 20 O LS Engine Swap Holley Fuel 16/30

Going to an LS means you also need to run a cooling system with electric fans. Again, you can spend a little or a lot on this, but we found a great bargain to be the aluminum radiators offered by Summit Racing. The dual-row, crossflow radiator (PN SUM-380457, $300) fit the Chevelle perfectly and the dual 12-inch fans (PN SUM-G4850, $210) move 2,600 cfm to keep our LS376 running cool.

 Chpp 24 O LS Engine Swap Summit Racing 17/30

Even the once complex task of wiring up an LS engine is now a plug-and-play deal, especially if you're using a Chevrolet Performance crate engine. This kit (PN 19258267, $1,080) includes the controller, engine harness, mass airflow meter, fuse box, throttle-by-wire pedal assembly, oxygen sensors, and sensor mounting bosses. The computer came pre-programmed to run the LS376.

 Chpp 15 O LS Engine Swap Chevrolet Performance Wiring 18/30

We used this trick Aeromotive fitting (PN 15118, $38) to change our factory quick-connect fitting into an easier to integrate -AN style. In this case, it was from 3/8-inch quick connect to AN-08. Our fuel line is AN-06 so we used some fittings from Earl’s Performance Plumbing to connect it to the black braided fuel line coming from our regulator. We were also careful to route the fuel line away from heat sources, like the headers and exhaust.

 Chpp 21 O LS Engine Swap Aeromotive 19/30

Of course you’re not going to be able go down to the local auto parts store and ask for ’71 Chevelle LS1 radiator hoses, but the good news is that if you dig around long enough you’ll find something close enough. In this case NAPA had upper (PN 8919) and lower (PN 708) hoses that fit perfectly. For an air induction system, Spectre Performance sent us an LS air intake kit made for our Chevelle (PN 901208K, $200).

 Chpp 25 O LS Engine Swap Radiator 20/30

It’s the simple things that typically end up being the most difficult to address. In this case it’s trying to get the wiring harness from the engine bay into the car’s interior. We found the best grommet for doing this over at Speartech Performance where in addition to making killer wiring harnesses they also offer specialized LS swap widgets.

 Chpp 16 O LS Engine Swap Wiring 21/30

After pulling the power brake booster, which wasn’t working anyway, we installed the billet clutch master bracket from HDC. With this in place, we were able to mark the firewall and make the hole for the Tilton clutch master.

 Chpp 22 O LS Engine Swap Clutch Master 22/30

Headers are another area that used to be a pain, but are now relatively simple. Quite a few companies bend up pipes for various Chevys, but we thought we would try out the new ceramic-coated Super Comp headers from Hooker. These 1.75-inch mandrel-bent conversion long-tube headers (PN 2289-1HKR, $680) have 5/16-inch flanges for a better seal, and long-transition collectors to decrease backpressure. Best of all they are designed to fit when used with Holley LS engine mount adapter plates. The GM plug wires that came with the crate engine wouldn’t clear the headers, so we installed some MSD wires (PN 32813, $66) with angled boots.

 Chpp 26 O LS Engine Swap Super Comp 23/30

Installing the wiring harness was a snap due to all the connectors being clearly labeled. We then continued plugging in all the various wires to the throttle body, MAP sensor, fuel injectors, and coils. It really couldn’t be any easier. We did find that the wiring kit called for a different oil pressure sensor (PN 12616646, $73), so we had to buy one at the local GM dealership.

 Chpp 17 O LS Engine Swap Wiring Harness 24/30

After installing the clutch master, and attaching it to the new clutch pedal, we installed a new power brake booster from Classic Performance Products (CPP). You can see the clutch reservoir mounted to the firewall behind the booster.

 Chpp 23 O LS Engine Swap Classic Performance Products Power Brake 25/30

Once we had the engine and transmission installed we could measure back from the tip of the T56’s output shaft to the middle of the U-joint on the Currie Enterprises 9-inch rearend. Hurst Driveline Conversions was then able to send us the appropriate driveshaft. You can also see where we mounted the Holley fuel system.

 Chpp 27 O LS Engine Swap Output 26/30

Included with the harness is an OE-style fuse box and all the fuses and relays needed to fire up the LS3. Even more importantly, there was a detailed instruction manual for those of us who are electrically challenged. The fuse box can be mounted in the engine bay or, as we chose, under the dash.

 Chpp 18 O LS Engine Swap Fuse 27/30

The cool thing about a wagon is that it’s not very common. The pain about owning a wagon is that it’s not very common. To complete the exhaust system, we picked up a Flowmaster stainless Chevelle kit (PN 817409, $543) and let the guys at Warner’s Muffler in Oceanside, California, custom tweak it under our wagon. The system is centered around a pair of sweet-sounding Super 40 stainless mufflers.

 Chpp 28 O LS Engine Swap Chevelle 28/30

Moving into the interior we mounted the throttle-by-wire gas pedal (PN 10379038). To get the placement just right we welded a panel to the firewall and then mounted the pedal in just the right spot to make heel-toe shifting easy. We also swapped in the new brake and clutch pedal assembly from Ground Up (PN FC-682, $100).

 Chpp 19 O LS Engine Swap Throttle By Wire Gas 29/30

And with that, our swap was done. In fact when we turned the key it fired up on the first try! Since the hood was off we added a pair of Eddie Motorsports billet hood hinges (PN EMS149-57M, $550). The old battery wasn’t holding a charge, so we installed an Optima Yellowtop battery. The only thing left to do now is hit the road in our LS-powered Chevelle.

 Chpp 29 O LS Engine Swap LS3 30/30


Summit Racing
Akron, OH
Lenexa, KS 66214
Eddie Motorsports
Rancho Cucamonga, CA 91730
Warner's Muffler
n/a, CA
Spectre Performance
Ontario, CA 90761
Chevrolet Performance
Ground Up
Quick Time
Optima Batteries
Milwaukee, WI 53209



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