Iron Eagle: Building an Iron-Block LS2
Whether you are a Chevy fan or not, there is no denying the performance potential of the LS-series engine. With the legendary LS1 back in 1997 to the LS9 powering the ZR1 Corvette and ZL1 Camaro, the Gen III/IV engine platform has massive potential. These engines share most of the internal and external components with each other and are darn near a drop-in install in place of any gen I Chevy small-block. It just makes sense that these engines have become the go-to power plant for practically every application out there.
Building an LS-series engine is a bit different from what you might expect. It is a standard pushrod-type design, so you don’t have overhead cams and 4-mile long timing chains to deal with, but there are some unique differences that you need to be aware of when putting one of these beasts together. We set out to assemble a 500-ish horsepower hi-torque LS engine for one of our projects, and found a few interesting issues along the way.
We had several qualifications for this build which led us down the path we took. We wanted cubic inches, minimum 6.0 liters (366 ci), an iron block for strength, everything else was up for grabs. There are several iron-block 6.0 liter engines from the factory, these were used in the 1500 and 2500HD trucks, most notably the LQ4 and LQ9. The LQ4 is a low-compression engine, 9.4:1, and the LQ9 is hi-compression at 10.0:1. We know that we might eventually add boost to the engine, so we went looking for an LQ4. Most of the salvage yards get these motors in regularly, typically with 150-200k miles on them. While a maintained LS-series engine can last 300k miles, there would likely be some issues that would need to be addressed. The cost of a 6.0 liter Vortec (Gen III/IV truck engines are all Vortec) has remained high because these are sought-after engines; we could not find one with under 200k miles for less than $1500 locally. That is when we started looking at rebuilt short blocks. Summit Racing offers an ATK LQ4 6.0L short-block for right at $2000, considering that we will be upgrading the heads, cam, intake and all the rest, this is about as perfect of a deal as they come. We snatched one up and started working on the rest.
For heads, we opted for a set of Trick-Flow LS2 Fast As Cast heads. These heads feature 220 CC runners, 65cc CNC chambers, 2.055 intake 1.57 exhaust valves, and are fully assembled, ready to run. Less than $900 got these to the door. The flow chart on these heads impressive. Without any porting, these bad boys flow 306 cfm at .550” of lift, but the real story is the mid-lift numbers, from 133 cfm at .200” to 297 at .500” of lift, considerably more than the stock LS2 heads (142 @ .2”, 236 @.5”, 240 @.6”). The camshaft selection was kept conservative because we are looking for bottom-end torque as opposed to top-end horsepower. A Comp Cams XR265HR cam was selected for its street performance, with duration @.050” of 212, .558” valve lift on a 115 lobe separation. We can always swap in a bigger cam, but this gets us the power level that we are looking for.
We also selected a FAST LSXR composite intake and a massive 104mm throttle body to finish off the top end of the motor. The 6.0 liter is going into a ‘71 Buick GS, so we picked up a Holley Performance LS-swap oil pan, specifically the F-body pan which provides some extra clearance on the crossmember. Rounding out the build are a mix of Summit Racing and Chevrolet OEM items, all bolted together with ARP stainless steel fasteners.
One of the biggest lessons we learned from this build is that there are a bajillion little sensors, special bolts and covers that you need in order to complete an LS build. We highly suggest picking up a high-mileage core from a salvage yard if you plan on building your own. The couple of hundred dollars you spend on a core could easily save you a few hundred more in the small parts.
In preparation for installation in the Buick, we put together the engine in the Red Dirt Rodz shop. The little parts are what kill progress on projects like this. Waiting for bits and pieces that you didn’t realize you needed have a tendency to stop all progress for a few days. When that happens several times, you can find yourself several weeks or even months delayed. With this article as a guide, you can get all the little pieces in hand before you start putting things together, so that it won’t take more than a weekend to wrap it all up.
1. Our build starts with a freshly-built GM LQ4 short block from Summit Racing. This ATK short block takes the hassle out of building the bottom end.
2. We slipped the crank gear and oil pump ring onto the crank snout.
3. Unlike an SBC, there are a bunch of little parts that you might not think of, like the rear cover shown here. We ordered this from Summit as well. Don’t forget the bolts.
4. The Comp Cams roller was lubed up and slipped into the journals. Royal Purple Max-Tuff assembly lube is our go-to oil for assembly.
5. To secure the cam, LS engines use a retainer plate. There is an o-ring that seals the oil galleys, do not forget it. The bolts are not supplied, you have to source them. This one is from Comp Cams.
6. Each retainer bolt got a dab of medium threadlocker and torqued to spec.
7. Comp Cams has this trick little eccentric for adjusting cam timing.
8. The comp cams timing set was then installed and bolted to the cam.
The LS-type oil pump bolts on after the timing chain is installed. You will need these bolts as well.
9. There are two timing covers for LS-series engines; one for a front cam sensor, one for a rear sensor. We have a front sensor cover, which has a hole in it. The gaskets on LS engines are almost all reusable o-ring-type, even the timing cover gasket. We used Fel-Pro gaskets on this build.
10. Securing the timing cover is a set of ARP stainless-steel bolt. No silicone necessary.
11. We flipped the motor over on the stand and prepped the top end. If you don’t have a donor motor, you need to purchase a set of lifter holders. These hold the lifters in the block. We got ours from Summit Racing. The Comp Cams roller lifters were slipped into the holders and lubed up.
12. The lifter blocks drop into the block in 4 locations.
13. LS engine use MLS (Multi-Layered Steel) head gaskets, which are reusable. These new Fel-Pro gaskets will handle high boost too.
14. We dropped the Trick Flow LS2 heads onto the block over the factory-installed locating rings. These heads are high-flow out of the box, and with the 64cc chambers, the compression will get a bump too.
15. All of the ARP head bolts get a liberal coating of ARP assembly lube, which allows the bolt to spin and yields an accurate torque rating.
16. The head bolts were then installed with a washer into each hole and threaded until snug.
17. Following the proper sequence, the heads were torqued down in three equal steps.
18. There are two different socket sizes for the head bolts with different specs, so pay attention to the specs for your bolts. ARP bolts have torque specs, while the GM bolts are torque-to-yield bolts and are not reusable.
19. The rocker studs go through the intake runners, as you can see here in this pic. If you want to use stock-type rockers, you will need a rocker support base. We are using Comp Cams roller rockers with individual studs, so the base is not required.
20. We sealed the studs by rolling the threads in silicone. This will ensure that there are no leaks.
21. Next, the Comp Cams pushrods are loaded into the heads.
22. We used a set of Comp Cams roller rockers on the Trick Flow Heads. The rockers were tightened with the supplied locks and preloaded with ½-turn past contact.
23. A set of Summit Racing aluminum valve covers were bolted on along with a stock valley cover that we sourced locally. We planned on using a billet piece from Summit, but the one we ordered did not have provisions for the knock sensors and the cool look gets covered by the intake anyway so we saved it for another project. This factory cover has the knock-sensors.
24. The cam sensor in the block goes right behind the valley cover. If you choose to run the LS2 front cam sensor, then the block will need a plug. As a side note, you need to know this before you buy parts, because the front sensor requires a different timing gear set, and LS1-type rear sensors engines need a cam with the built-in timing lug.
25. GM used two types of crank triggers: 24-tooth and 58-tooth. The 2004-earlier LQ4 used a 24-tooth reluctor wheel. Changing the sensor type is not easy, but you can use a converter module to emulate the 24x signal with a 58x engine. Black sensors are 24x, gray sensors are 58x.
26. Another potential pitfall of building an LS without a donor motor is in the oil pan. Chances are, you’re doing an engine swap, so you need a pan that will fit your chassis. We used the Holley 302-2 oil pan, which comes with the correct oil pickup tube. Don’t forget the o-ring.
27. The factory windage tray interferes with the Holley pickup tube, so we marked where it hit for trimming.
28. How you cut the tray does not matter, we used a band saw. The important part is to make sure that any shavings are removed, including any loose edges. Buzzing the cut with a file or die grinder is good insurance.
29. With the tray cut, the new pickup dropped right into place.
30. The Holley 302-2 oil pan has increased clearance for GM f-body chassis; it will also work well in A-body (64-72) frames. The 302-1 pan has a deeper front sump and does not clear the A-body steering when the engine is in the stock SBC location. It will work if the engine is raised up about a ½”.
31. Holley’s LS pans are cast aluminum and feature the stock oil filter location. The oil filter nipple comes in a bag in the box, so don’t forget to the thread it in.
32. Another added feature of the Holley pans is the oil trap. This stamped-steel plate helps trap oil in the sump. The pan comes with the bolts, don’t forget the threadlocker.
33. With the pan assembled, it was dropped onto the block and the ARP stainless steel bolts torqued to spec. Remember, most of the LS fasteners are torque to yield, so an ARP fastener kit is a real godsend, because they are reusable and really nice looking too.
34. There two types of LS intake gaskets, either individual o-rings like this FAST intake, or all-in-one gaskets with all 4 ports on a single gasket. If you have the wrong type, you may be waiting for them to show up, sidelining your build.
35. The FAST intake has two ports for the MAP sensor, one in front and one in back. Neither are drilled, so you need to choose which one works best for your application and drill it out. Drilling the rear location requires disassembly of the intake, which is not difficult.
36. This is the front MAP location. Use a vacuum in the throttle body opening to suck out any plastic shavings.
37. The assembled engine is now ready for install into the car. There are vehicle-specific options, such as the accessory drive and headers that will need to be selected as well.
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