The Fifth Dimension, Part IV
Dyno testing the Gen V LT1 to the tune of 518 hp out of the crate!
If you’ve been following our series on the LT1 then you’re up to speed on our look at Chevy’s latest-generation small-block. We finally aligned all our ducks beak to tail and mounted the LT1 up on Westech’s engine dyno; the purveyor of truth, justice, and the cool power numbers. So let’s get right to it because there is some excellent power and information to be squeezed out of this Gen V engine.
GM rates the normally aspirated LT1 at a rather cautious 460 hp. There are reasons for that conservative number that we’ll get into but with a little bit of timing and fuel adjustment we were able to crank a much more impressive 518 hp and 520 lb-ft of torque out of this direct-injected engine. But peak numbers only tell part of the story. There’s much more data hiding in between the lines on the dyno curves.
There are several reasons why there is a big disparity between the numbers we generated on Westech’s SuperFlow dyno and the factory numbers and it’s worth discussing why the numbers are different. Yes, our numbers enjoyed the advantage of a set of headers but that might only be worth 10-15 hp. So how do we account for the other 40-odd horsepower? Some naysayers will immediately claim that Westech has a “happy” dyno. Westech’s testing procedure is very different from the OE version and that’s where the numbers begin to diverge. Let’s get into why both the GM and aftermarket dyno numbers are accurate yet different.
Before the early ’70s, there really were no specific rules on advertised horsepower so the factories used the more optimistic gross horsepower numbers and used the then-standard correction factor of sea level pressure (29.92 Hg), zero humidity, and an inlet air temperature of 60 degrees F. This would be a really cool day at ocean side with no humidity. As you can imagine, this isn’t a condition that occurs very often, except at the beach.
By 1972, the factories began using the new J1349 standard that changed the correction factor to a much warmer 77 degrees F and lowered the air pressure to 29.23 Hg while retaining the zero humidity point. This
reduced the crankshaft power from the previous correction factor by roughly 5 percent. An engine making 400 hp on the new standard would make 420 hp using the old correction factor.
Later, other changes were inaugurated, including requirements that engines run at normalized operating temperature and that the full accessory drive and exhaust also be included. All of these requirements reduced the power output compared to the older “hot rod” version correction factor that is used in all magazine stories.
Now let’s look at how the magazines test engines at Westech. They use the old standard hot rod correction factor but also test engines with hot oil and a starting water temperature of around 140 degrees F. On a 400hp engine, this change in water temperature alone is worth 10 hp compared to testing at 180 degrees F. Plus, Westech prefers to eliminate the entire accessory drive from the front of the engine and use an electric water pump. This makes cam swaps easier, allows cooling the engine in between runs, and frees up some power. A recent LS accessory drive test we performed revealed between 8 and 11 hp improvement when we removed the LS accessory drive.
Our LT1 testing started with a set of headers. We originally wanted to baseline our LT1 with the truck-style manifolds because we didn’t have a set of adapters to connect the stock Corvette exhaust manifolds with 3-inch exhaust pipe. We thought the truck manifolds used the same three-bolt exhaust flanges but only the passenger side was the same as our flanges so that didn’t work either. So we began our testing with the JBA headers that were intended for a '16 Camaro. These are long-tube headers with a short 3-inch collector that we fed into a length of 3-inch tubing from Summit Racing and attenuated with a pair of Flowmaster mufflers.
So if we start with GM’s 460hp rating and add 20 hp for the difference in correction factors, 10 for the water temperature change, another 8 for the accessory drive, and 10 more for the headers, we’re almost exactly at our 507 hp initial power number. These numbers are approximations and it’s likely the headers and exhaust are
worth even more.
But thus far, we’ve looked at just the peak numbers and they don’t tell the whole story. If you study the torque this engine makes at the beginning of the test, you should be impressed with the 480 lb-ft of torque figure at 3,000 rpm. This is not a misprint. While the long-tube headers certainly help at this rpm, this is a big bump over a “normal” 6.2L torque of an LS3 of around 380 to maybe 400 lb-ft. Much of this torque production can be attributed to a combination of this direct-injected engine’s increased compression ratio, its direct injection, and the magic of variable valve timing (VVT). Here’s where VVT is your friend. Too many people want to immediately disable this function, but it’s obvious from our testing that VVT is a good thing.
According to Jason Haines who owns Product & Service Solutions, an engineering and product development company, the VVT system has the
capacity to move the cam throughout a tremendous 62 crankshaft degrees of movement (31 camshaft degrees). The ECU manages oil pressure to move the cam and for the LT1 swings the cam over 20-plus crankshaft degrees of movement. At low rpm it advances the cam and then slowly retards it from full advance as engine speed increases toward peak horsepower. The control is actually far more sophisticated than that description, but for the sake of this story that will suffice.
We experimented with moving the cam in the VVT segment using HP Tuner’s software and quickly discovered, not surprisingly, that the GM engineers have this area covered and with the stock camshaft configuration, there might be 1-2 hp to be gained by moving the cam around slightly. Realistically, they’ve maxed out the VVT improvements for the stock engine and camshaft.
To put this into perspective, we have a lightweight, all-aluminum, 376ci engine that makes 480 lb-ft of torque at 3,000 rpm and over 500 hp at its peak. Those are mild big-block Chevy numbers. As a point of comparison, the Chevrolet Performance 454 HO makes roughly the same torque at 3,000 rpm, peaking at 500 lb-ft at 3,500 and only 438 peak horsepower at 5,300 rpm. So our header-equipped LT1 is roughly 150 pounds lighter while twisting more torque and more horsepower than a 454 HO. So there’s
something to all this technology.
Next, we plugged the LT1’s power curve into the Quarter Pro dragstrip simulation program. We plugged in a 3,400-pound car with a driver, an automatic trans, 3.50:1 rear gear, and 26-inch-tall rear tires. The simulation says the car would run 11.50s at 118 mph all day long. That’s outstanding performance for a stock engine. If you plugged this engine into a lighter 3,200pound car, the numbers fall to 11.20s at 121 mph! That’s knocking on the door of the 10s with a near-stock motor.
So to sum this up, the LT1 is a winner. Right out of the box it makes serious 500hp power with no mods and big-block torque right off idle with the help of factory VVT. Plus, with the LT1’s direct injection and factory tuning, cruising with the help of an overdrive trans you could expect 20-plus miles per gallon with the same engine that will run mid-11s! Some rodders may have issues with late-model performance, but it’s hard to argue with these numbers. The future of performance has arrived
With all of the preliminary conversion work out of the way, it didn’t take too long to mount the engine on the dyno. We did discover that the top two bolts for the rear cover hit the bellhousing and needed button head bolts to clear. Westech’s Troy Goldie also had to machine a little haircut off the top of the scattershield to clear a hub on the back of the passenger side cylinder head. Westech used special metric ARP 12-point bolts for the flywheel. Note that all Gen V engines use an eight-bolt flywheel that is the same as the previous LSA engines and others.
While Chevrolet rates this normally aspirated LT1 at 460 hp, we made significantly more with final tuning delivering 518 hp and 520 lb-ft of torque with headers. But there’s much more to this story than just the peak power numbers.
The Gen Vs all use a unique exhaust flange compared to Gen III/IV engines. It only uses five exhaust flange bolts and the gasket will only fit one way as the bolt flange is not symmetrical.
We used a set of Patriot/JBA 1-7/8-inch headers originally intended for a late-model Camaro for the dyno test. The primary tubes clear the spark plug boots if you remove the metal covers and slightly bend the connectors.
The JBA headers came with oxygen sensor bungs already in the collectors and sealed with a slick V-band flange, so we ordered a couple of simple Summit Racing V-band flange clamps and our buddy Scott Gillman from Galpin Auto Sport (GAS) welded the flange to the Summit 3-inch tubing.
The LT1 uses a different spark plug configuration than the older Gen III/IV engines with a longer thread length called the reach. This is the stock factory A/C plug.
These late-model engines are very sensitive to placement of the mass airflow (MAF).This sensor is both directional and should be placed within a straight length of 4-inchdiameter inlet tubing in order to function properly. This length of straight Spectre tubing has the proper MAF fitting welded in, which saved us some fabrication work.
Chevrolet Performance’s instructions suggest running with a pulse-width-modulated (PWM) fuel pump, but a traditional pump and regulator will work fine as long as it’s capable of 45 gpm at 72 psi. The Aeromotive A1000 is capable of roughly 120 lb/hr of fuel at 70 psi so fuel feed was not an issue.
Because the stock MAF requires a significant length of straight tubing on either side of the sensor, we placed the MAF roughly in the middle of this 30-inch overall length of straight Spectre tubing.
Westech’s Eric Rhee performed the tuning on our LT1 with help from HP Tuners software. Details on the screen are too small to read in the photo, but the software displays air/fuel ratio as equivalence ratio. At 3,933 rpm, the equivalence ratio was 0.837 that equates to 12.3:1 air/fuel ratio (14.7 x 0.837 = 12.3).
We also had to integrate the factory fuel pressure sensor into the fuel delivery system so that the factory ECU knew fuel pressure was constant at 68-72 psi.
That’s dyno guru Richard Holdener facing the camera who has all but taken up residence at Westech doing dyno testing for the magazines.
Installing the ECU and harness isn’t difficult, but it may look intimidating. Here, Steve Brulé is doing his best Sgt. Rock imitation with an LT1 harness instead of crossed ammo belts.