Ask Away! with Jeff Smith: Advice on Swapping a 4.8L LR4 LS Engine & 4L60E Trans into a 1969 Firebird

I have a 1969 Firebird that I’m swapping in a 2002 LR4 4.8L LS engine from a GMC Sierra pickup. I have the mechanical swap parts for mounting the engine but I’m looking for a budget way to control the spark and fuel. I also need some way to control the 4L60E truck trans that came with the engine. Plus, I would like to run an LS6 intake. What’s the best way to do all this?

D.M.

The most obvious approach would be to re-use the existing ECU and wiring harness. You didn’t mention whether these parts came with the engine. Unfortunately, it’s a bit of a risk purchasing a used harness and ECU with no guarantee that these pieces will work. And if you decide to change some parts (like upgrading to a performance LS camshaft), this will require the expense of a custom tuner to use software like HP Tuners to make the necessary idle and part-throttle changes to help the engine run its best.

Find the Right Engine Control System

This leads us to an alternative path to get where you want to go. That would be a Holley Terminator-X Max EFI system for your 24x LS engine. The Terminator-X Max will control both spark and fuel and also includes transmission control. The Terminator-X kit comes with a complete ECU, wiring harness, and a hand-held screen that allows the user to input all the data and do simple tuning without the need for a laptop. It’s a simple conversion and you only need the handheld instead of a laptop although you can use a laptop if you so desire. The injector harness may need wiring harness adapters to connect to the stock LR4 truck injectors.

This allows you to use a factory passenger car manifold like the LS6 intake because that truck manifold probably is too tall to clear the stock hood, although that will require a different passenger car accessory drive since the LS6 throttle body will hit the truck water pump upper radiator hose connection.

At the time of this post, the Terminator-X Max is a little less than $1,500 which sounds like a lot of money but when you consider that this will plug right into the existing engine (including the electronic drive-by-wire throttle), all you would have to do is add an electronic throttle pedal to your 1969 Firebird and plug in the harness. The Terminator-X Max also uses a wideband oxygen sensor for feedback air-fuel ratio control that you set with the handheld tuner. Placing the O2 sensor in the exhaust will require some custom welding but any muffler shop can do that for you.  

Updating the Fuel System for EFI

You will also have to spend a little bit more money to convert to a return style fuel delivery system. We’ve had really good success using Holley’s Sniper tank and pump assembly and they offer one specifically for the early F-body. The kit is easy to assemble and replaces your existing tank with a brand new stamping that has been powder coated. The only other thing you would have to do is add an electronic throttle pedal but perhaps you can pull that from the truck that donated the engine.

The switch to a passenger car style manifold is a good idea since, as we mentioned, it’s likely the truck manifold will not fit under the flat hood of a ’69 Firebird. The LS6 intake is becoming difficult to find but similar performance can be had with an LS2 intake for a cathedral port engine. There is an AC Delco passenger car replacement manifold for cathedral port heads that is affordable. We’ve listed its part number in the following chart. This will require injectors, a throttle body, fuel rails, and bolts to complete the installation but at least the basic manifold is affordable at under $150.

Consider the Carbureted Route

Because the 4.8L engine is a little short on displacement, we’d recommend a dual plane intake. In the parts list we’ve included all the major parts you’ll need to install the intake, carburetor, and an MSD spark controller. This will take care of the fuel and spark requirements but you will still need a separate box to control the 4L60E transmission. We’ve had real good luck with the Compu-Shift Pro controller. We’ve also listed other controller options such as the MSD Atomic for the 4L60E but there are other companies including Edelbrock, Painless, TCI and others you might investigate.

One advantage of the carbureted system is that you will not be required to completely convert the fuel delivery system but you will need to add an electric fuel pump to feed the 4.8L engine since LS engines offer no provision for a mechanical fuel pump.

We totaled the prices of the complete carbureted fuel system and compared that to the cost of a complete Terminator-X Max and we found that the two are somewhat similar—although the EFI version will be slightly higher if you include a replacement intake manifold. Of course there may be some money to save on the carbureted side if you already have a carburetor, which will save about $500.

However, with the carburetor you give up feedback control of the air/fuel ratio, so that you will have to tune the air/fuel ratio manually in the old school tradition of changing jets and probably the idle circuit since that little motor will need less fuel at idle.

We would tend to side on the EFI side of this equation but there are certainly advantages in terms of simplicity with the carburetor. The best part of all this is the variety of options.

LS-Swap 1969 Firebird Parts List

• Holley Terminator-X Max, 24x, 4L60E control – HLY-550-916
• ACDelco GM Genuine Parts EFI Intake Manifold – ADO-89018187
• Holley LS Mid-Rise Carbureted Intake Manifold – HLY-300-130
• Holley 4160 750 cfm Carburetor – HLY-0-3310C
• Edelbrock TC Transmission Controller – EDL-36212
• MSD 6LS Ignition Control Unit – MSD-6014
• MSD Atomic 4L60E Transmission Control Module – MSD-2760