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Corvette Crate Motor Curves

Is the claimed 405hp from GM's all-aluminum LS6 for Real?

On paper at least, GM's crate motor program appears to offer engines that deliver excellent results in terms of bang for the buck. But the speed equipment business in general seems to thrive on optimism. Nowhere is this more evident than when it comes to making power claims. Although one would expect a big, reputable corporation like GM to be honest it would not go amiss to have such independently verified.

What started as a passing interest was the introduction of GM's latest crate offering--the Z06 Corvette version of the LS6 (GM part # 12578104), ended up as a major test project. Here was a lightweight, sophisticated, all-aluminum engine which, in smog legal form, has a claimed output of 405 SAE hp. It pulls from dead smooth idle to the redline at 6600 and delivers great mileage to boot. A little research revealed that, in the form shown in our heading shot, a copy of this engine can be had for a street price of some $7,300 (Scoggin-Dickey Parts Center). Try building a comparable 23-degree small block Chevy for anything less than about $12,000.

If this Z06 crate motor makes the claimed power then it's certainly a good buy, but as hot rodders other considerations also influence our purchases. To appreciate this we need to consider what drove the original small-block Chevy to such popularity. In a word--it was 'potential'. As it came from the factory it was good but there was a lot left in it and that was what made it so attractive to hot rodders. This leads us to ask if GM has done all the hot rod work for us on this Z06 engine. Is it essentially 'topped out' or is it such a good design that in spite of producing big numbers in stock form there is much more to be had? The intent here is to find out just what this engine can deliver in both stock form and modified.

For a dyno that has LS6 engines run on it almost daily the services of More Performance in Charlotte, North Carolina were called upon.

Baseline Runs
All our tests on More Performance's 901 SuperFlow dyno were done to standard corrected conditions and with the engine accelerating at 300 rpm/second. The power figures GM quotes are steady state (which produce slightly higher numbers) but are corrected to the more conservative SAE rating. For our test mule to produce the figures claimed by GM it had, on our dyno, to produce 410 hp. After a 2-hour break-in the good news is that it made 401 foot-pounds of torque together with nearly 417 hp (Fig 1). All this was done with the stock iron manifolds supplied with the engine and the stock calibrations in the computer.

As impressive as our initial numbers were they proved far from the whole story. What is difficult to convey here is how smoothly the engine produced these numbers. Regardless of how hard it was pushed the delivery of power always seemed effortless. At this, the first step into our project with the Z06 engine, it has to be said that GM gets top marks for a world class engine that delivers more than they claim.

Before going on its worthwhile asking why this engine has such a healthy output. The answer lies in a number of areas. Probably the most significant factors are the deep breathing characteristics of the heads and the design of the intake. The heads, just as GM makes them, rival the flow characteristics of many functional aftermarket 23 degree heads as used on what we traditionally call Chevy's small block. The intake manifold is essentially a masterpiece of engineering. Other than being very light, the plastic it's made of has far less tendency to conduct heat into the incoming charge and that must be worth 10 foot-pounds right there over aluminum. Secondly it's port runner lengths, diameters, plenum volume and overall form appear to be close to optimum for the rpm range over which the engine is called on to operate.

Headers--Power Adders or Budget Busters?
Although GM's Z06 crate motor ran like a charm right off the delivery pallet it was equipped with iron exhaust manifolds that, though certainly a cut above average, were heavier, and in our estimation, somewhat less power orientated than a set of good aftermarket headers. In the real world most of those buying a crate motor of this stature are unlikely to run the engine with heavy stock iron manifolds. Assuming this to be the case we elected to make a manifold change our first upgrade on this already powerful 346-inch engine. The principal question here is whether or not the engine will respond in a positive manner without any reprogramming of the ECM.

The headers used for this test are made to a specification developed by Kook's Custom Headers for LS6 engines that have entry- to intermediate-level modifications. In essence that means engines from about 415 hp to about 550. Our engine obviously just squeaked into this range. With just the headers installed and no reprogramming to correct for the possible introduction of fuel and spark errors the engine produced the results shown in Fig 2. From the curves it can be seen that the gains were very minimal. This was not wholly unexpected as many engines fail to respond to a normally functional mod because the required fuel and spark parameters change such as to offset most or all of the potential gains. With that in mind Joe Huneycutt, More Performance's computer guru, reprogrammed the stock computer until optimum results were seen. The ECM reprogramming allowed the generation of the curves shown in Fig 3. From these curves you can see that, from 4800 rpm up the headers took off. From about 5000 rpm to the redline the gains were typically 20 foot-pounds and 20 hp.

More Air
As of our last test the Z06 is sitting at 442 hp and 425 foot-pounds of torque. We were already ahead of our hoped for output here so the hurdle was moved to 430 foot-pounds and 450 hp. The question now was what simple bolt on we might do to achieve that goal. One of the moves that More Performance does on the LS6 engines going through their shop is to airflow the throttle body. Whereas this makes little difference to the lower powered engines in this range it does help to better satisfy the higher air demand of the more powerful LS6 variants. These mods involve cutting one side of the throttle shaft within the air stream away and thinning the remaining half. In addition to this the edges of the butterfly are formed to better split the air. Lastly the passages that connect the throttle body to the IAC valve and the valve cover vent are filled and two small holes that allow the function given by the large and now filled holes are drilled. All this adds up to a substantial 150 cfm plus in terms of extra airflow. Also, because the diameter of the throttle body has not changed the velocity of the air into the manifold plenum is increased. As this higher velocity enters the plenum it slows and some of the kinetic energy involved is translated into pressure. This helps boost the density of the charge entering the cylinders. At least that's the theory involved. On the dyno our Z06 with the More Performance throttle body produced the results shown in Fig. 4. In short our new target was met and surpassed. This Corvette crate motor was now producing 430 foot-pounds and 453 hp.

Lube Considerations
Things were looking good at this stage but one factor was presenting a relatively minor issue that needed to be addressed. This crate motor is shipped from GM with 0-30 weight Mobil 1 as a break in lube. Being of low viscosity one would expect this lightweight oil to be good for power. About two years ago this writer started testing a new oil produced by BND that was rapidly gaining popularity with some of the front running Midwest sprint car builders, because it showed some real improvements in reliability and reduced wear. The guinea pig vehicle used to test this oil was a 2000 model 4.8 GMC Sierra extended cab truck whose main purpose in life was towing 9,000 lbs of trailer and a race car. For the first two years the Sierra had been run on Mobil 1 which was changed at never more than 4000 miles. The reason Mobil 1 was used was because of it's proven anti wear properties. By any yardstick it is a top quality oil and my tests have shown that Mobil's ads concerning its anti wear properties fall well short of reality. This point is being made because the intent was to do an oil analysis wear comparison between the BND Quantum Blue oil and the proven performance of Mobil 1.

The lab used here was CTC Analytical (Division of Stavley Labs) and without going into a whole load of peripheral details the results showed Quantum Blue cut wear of iron parts by some 30 percent and bearing parts by some 15 percent. Unlike other oils Quantum Blue is custom blended for a given application and customer. When you get the oil from BND it will have your name right on the container. Like many early LS type engines the 2000 Sierra suffered lifter noise. The oil BND brewed had an additive package that specifically focused on reducing lifter noise. At the beginning of the test there was a great deal of skepticism about this but after about 2 months all sign of lifter noise was gone. This oil had more than proven its capability as a means of extending engine life--but what was it like for power? We had an engine on the dyno with an oil good for power but the only Quantum Blue on hand was the 15-45 oil specifically blended for a truck expected to haul 9,000 lbs up a long grade on a 110 degree summer day in the Mojave desert. The thinking here was that if Quantum Blue cut wear by means of friction reduction then this might offset any viscous loss due to being a 15-45 blend versus the 0-30 Mobil blend currently in the sump. Well there was one way to find out so Joe Huneycutt dumped the Mobil oil, changed the filter and refilled the sump with Quantum Blue.

Almost immediately after starting one major factor was apparent: the oil pressure at any given temperature was at least 15 psi higher than with the 0-30 weight oil. All previous tests with the 0-30 weight oil were done with the temperature around 200 degrees F. At that temperature the output with the Quantum Blue was marginally down but running it at 220F (where it still maintained at least +15 psi) the power was virtually the same (Fig 5). These results encouraged the planning of tests on a blend of Quantum Blue done specifically for our Z06 engine.

Conclusions
For a street price of about $7300, GM's Z06 crate motor looks to be a real value-for-money deal both in terms of output and sophistication. But owning the motor and being able to run it can be two distinctly different deals. Here you may want to avail yourself of More Performance's crate motor service. If you ship the LS6 directly to More Performance, for $650 they will break in the motor, give it a full post-break-in service (Quantum Blue oil, filter change etc), make the appropriate power runs and check the calibrations as required. If you want to go the header route they will power test with the headers and calibrate the computer as required. Stainless steel LS6 F-body or Corvette headers will cost about $820 a set and the reprogramming will run $550. To do this they will need your PCM, or they can supply one for an additional $550. If you want the modified throttle body to bring the whole deal up to the 453 hp we achieved figure in an additional $250.

What you need to run this engine in your car

Assuming the worst-case scenario to run an exotic crate motor such as we are testing here will call for some specialized external hardware.

First you will need a wiring harness. More Performance can supply this principally using Painless Wiring as a source. Additionally a PCM suitably programmed will also be needed. If the vehicle you intend to install this engine in is of an early carbureted variety you will need to install a fuel return line for the injection as well as equip the fuel system with a suitable capacity fuel pump. Also because the point of air entry into the engine is not on top but up front you may have to do some serious re-thinking on what will be needed for an air cleaner.

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