Welcome back to our project LT motor build. As you'll recall in the April 2013 issue of GM High-Tech, we tested a bunch of simple mods for the admired LT motor and came up with some token gains that came in small increments. We have decided to throw some bigger and badder parts at this thing to show the levels in which this motor can still perform. We saddled up and went back to TPIS in Chaska, Minnesota to see what they had come up with. We chose some popular choices you guys out there will most likely be looking at when choosing to upgrade the power in your LT1. The theme for these modifications is more air equals more power!
Test #1 – Our baseline motor
Max Power – 340.3HP, 374.5TQ
Avg Power – 279.7HP, 348.1TQ
First, let's recap. We started with a basic stock GM LT1 engine with a .040 bore with a stock crankshaft, heads, exhaust manifolds, intake, 1.5 rockers, oil pan, OptiSpark, 48mm throttle body, 24-pound injectors and the stock fuel pressure set at 43 psi. We upgraded a few parts to make sure it didn't grenade on us accidently. The parts we upgraded were the factory rods to Scat versions with a stock length, Speedpro hypereutectic flat top pistons and a zero decked block with 10.5:1 compression. Fuel was the typical blend you'll find at any gas station with a 91-octane rating.
During our first round of tests we upgraded the plugs and wires, added a 6AL MSD box, a TPIS airfoil, an Airaid air filter, a larger MAF housing and an electric water pump. This all added up to a respectable 336 horsepower and 380 ft-lb of torque. As with all things, we ran into a problem with the electric water pump and had to replace it with a stock unit. Thankfully the water pump isn't driven by the crankshaft so we didn't get too excited about its loss.
We reran the motor to make sure our numbers were consistent with where we left off. Our baseline numbers reassured us that we were pretty close to the previous tests and had a solid number. Again, as with the last set of tests, we ran each part through three dyno runs to make sure none of them got a bum pull. And just like the previous tests, each of these will be progressive, meaning that unless otherwise specified all parts will be left on the engine for each subsequent test.
Test #2 – A popular header bolt-on
Max Power – 353.8HP, 389.6TQ
Avg Power – 289.0HP, 358.5TQ
Cost – $700 (uncoated)
As we mentioned last time, an engine is essentially a glorified air pump with the basic theory that more in and more air out means more power. We surmised after the last tests that this engine was being highly restricted by the stock exhaust and could benefit from a set of headers. A set of headers allows the exhaust gases to exit the engine more efficiently by having a larger tube for the air flow. This allows the air to exit the heads faster which means more power. The primaries on the stock units are quite small and restrictive. These TPIS long tube headers made for the 93-97 Camaro and Firebird, boast 1.75-inch primaries with a 3-inch collector and are made of mild steel. We were relatively pleased with the results, we made a solid 10 horsepower throughout the power band and 15 peak ft-lb of torque. Headers are a must with any performance build and this test just proves that even a mild build can really benefit from a set of headers.
Test #3 – A bolt on 52mm throttle body
Max Power – 357.9HP, 401.1TQ
Avg Power – 295.7HP, 366.9TQ
Cost – $280 with exchange
The stock 48mm throttle body is quite small, let's be honest. That means a lot less air is getting into the combustion chamber and robbing you of power. Any constraint in the air flow into the intake is going to steal power from you and this is no exception. A larger throttle body will obviously allow more air flow and hopefully more power. For this test we used the TPIS 52mm throttle body and for the cost it seemed like a decent buy. We gained roughly 6 horsepower and 8 ft-lb of torque through the powerband on average. Not a bad performance, but we think that we'll see a greater effect from this piece with more impressive parts.
Test #4 – GM LT4 Hot Cam – Stock Rocker
Max Power – 415.4HP, 417.9TQ
Avg Power – 324.3HP, 388.6TQ
Cost – $235 (Summit Racing)
The amount of air that gets into the motor is completely worthless unless it's carefully controlled. That's exactly what the camshaft does, it correctly times and accurately measures the amount of air that gets into the combustion chamber through manipulation of the valve duration and lift. Essentially, think of the camshaft as the device that holds the valve open for a certain period of time and at a certain height. That height and length of time can be changed with various cam options. This cams specs at 218-inake, 228-exhaust at .500 duration with a 5.25 lift on the intake and exhaust with a lobe separation of 112. Since the GM LT4 Hot Cam was designed to be used with a 1.6 rocker, we were interested to see what would happen if we left the 1.5 rocker in as we know some of you might not necessarily follow the instructions to the letter. To complement the cam we are running a stock diameter TPIS valve spring with dampers with titanium retainers and Manly pushrods that are good up to a .560 lift. The stock cam provided 20-inches of vacuum while the GM Hot Cam produced 16-inches. Vacuum is often a good way to measure a camshaft's efficiency with higher numbers being better.
As you can tell from the results, we found the problem and in a big way. We jumped nearly 60 max horsepower and 16 ft-lbs of torque at max but gained 22 ft-lbs throughout the engine powerband. For the cost this has easily been one of the best buys we've made thus far.
Test #5 – GM LT4 Hot Cam with a 1.6 rocker
Max Power – 423.9HP, 422.8TQ
Avg Power – 330.2HP, 395.3TQ
Cost – $330 (Summit Racing)
To complement the cam (as recommended by the instructions) we added a 1.6 rocker set from Comp Cams and Howards Cams hardened pushrods at the stock length of 7.200-inches. The rockers are their Pro-Magnum version and are not self-centering like the stock stamped steel version; we were required to add the Comp Cams guide plates. Adding a set of rockers with a greater ratio will in effect allow the valve to open slightly more as it increases the lift by .030 and it will most likely benefit smaller cammed engines than ones with larger cams as it can kill lower end power. That said, we found a pretty positive gain in this simple switch. Another benefit that we like is once the lash is set, it doesn't have to set for quite a long time unlike traditional stamped steel rockers that can come out of adjustment too easily with some mild abuse.
Test #6 – TPIS ZZ409 Cam swap (left ZZ409 Cam, Right GM LT4 Hot Cam)
Max Power – 436.7HP, 430.2TQ
Avg Power – 334.8HP, 399.5TQ
Cost – $375
The cool thing about working with TPIS is that they have virtually anything on hand to build an LT motor, including camshafts. To contrast the GM Hot Cam we went to the shelf and picked out the proprietary TPIS ZZ409 cam to test. This cam measures in at 226/266 intake and exhaust at .500 duration. It has a 520/520 lift intake and exhaust with an LSA of 112 and produced 17-inches of vacuum. As you can tell by the numbers, this cam holds the valve open longer but slightly less height. There's a lot of variables when it comes to cams so it helps to call the manufacturer to make sure you're getting the right cam for the job. Thankfully, our ZZ409 cam worked quite well and we saw some significant gains even over the GM Hot Cam. As we add more parts we expect the full potential of this cam to be realized.
Test #7 – TPIS ported factory casting heads
Max Power – 471.7HP, 432.6TQ
Avg Power – 339.8HP, 401.8TQ
Cost – $1250 with exchange
Swapping a set of heads onto your motor isn't the most straight forward job but it will make a world of difference. Along with the cam, a set of heads is probably the best bet for making bigger power. Heads come in all shapes and sizes. The heads direct flow and house the valves which is the essence of how a motor makes power. Thankfully, a head swap isn't nearly as bad as a camshaft swap so after doing two cams, we were ready for some light labor. The heads we used were a set of stock aluminum LT heads that were hand ported by TPIS. As you tell by the flow numbers the ported heads performed generally better in every aspect at virtually every lift data point. That clearly would make sense since the runners and exhaust ports were enlarged. We made a significant jump in horsepower at the top end but kept roughly the same amount of torque. We think that we could get a few extra MPH at the drag strip from this swap. We suspect that if we went with an aftermarket head and had a port matched intake we'd do a lot better all over the spectrum.
In a moment of full transparency, we feel it's necessary to say that at this point in the game the stock tune that we have been using in all of our tests just wasn't cutting it. We were getting AF ratios in the neighborhood of high 14's so we felt it best to reprogram it to a more healthier 13—give or take a point or two.
Test #8 – 58mm throttle body
Max Power – 473.2HP, 435.2TQ
Avg Power – 343.2HP, 405.7TQ
Cost – $425 with Billet aluminum IAC housing
Just as we did with the 52mm throttle body, we felt it was important to test the 58mm throttle body with its built in air foil and custom made housing. This helps direct the air flow with a much bigger inlet and hopefully more power. It's important to mention here that the stock intake is only ported to 52mm's in size. We have no clue why that is. It just is. So, to step up to the 58mm throttle body you'll need to port match the intake as to maximize the air flow.
What does this test result tell us? To the unseasoned eye it may appear that the 58mm throttle body doesn't work as well as advertised. However, Jim at TPIS tells us that in their vast years of experience, most LT motors will not need anything beyond a 52mm throttle body unless it's making 500 horsepower or more than that. So lesson learned.
To wrap things up, we tested a number of common parts that you guys will want to try out on your ride. Thankfully, we did all the dirty work to show you what really works and what's worth your hard earned dollar. In the end we unlocked about 130 horses and 60 ft-lb of twist. There's always room for more with careful planning. Virtually everything we tested made power so that's always a plus, now more than ever the answer to the old adage, “how fast do you want to go?” is “How much money you got?” rings more true than ever. To be fair to this motor, we should mention that we had to reprogram the ECM several times, each time adding more and more fuel. We noticed that despite the extra fuel our power numbers were virtually the same throughout the tests. We've come to the conclusion that we've maxed out our injectors and we'll probably have to upgrade those as the next source in search of big power for our rented donkey motor. From here on out, the mods to your LT motor are only going to go up so brace your pantaloons! Look for the next series of tests on this LT motor for fun and for profit!