Part II: Building the top end and dyno testing

Doug Flynn - October 25, 2012 10:00 AM


For Your Information:


1 The L92 heads’ CNC porting by S.A.M. didn’t increase volume, but concentrated on properly shaping and profiling the ports. Everything was hand-smoothed as a final step.


2 The Ferrea valves, dual-valve springs, titanium retainers and locks from Straub Technologies will make for a light, bullet-proof valvetrain.


3 GM L92 heads use an offset intake and standard exhaust rocker arm. They were upgraded with new trunions and needle bearings from COMP Cams. The intake rockers were purchased new from GM at an economical price.


4 The engine was topped off with die-cast aluminum valve covers from Holley. They eliminate the unsightly factory coil brackets. They come in polished, black, and uncoated versions.


5 Here is the turbo on the engine in all its glory. The BorgWarner 76mm unit features OEM quality and design and will work great for this application.


6 Hooker Headers’ new cast iron exhaust manifolds were used in a reversed fashion in lieu of expensive fabricated turbo headers.


7 All the exhaust plumbing was fabricated from stainless 2½-inch and three-inch tubing. Both banks collect at the “merge” and feed the turbo. You can see the large 66mm Precision Turbo wastegate which will have plenty of bypass volume capability. The “down pipe” is four inches in diameter.


8 Dual Holley 1000cc water/methanol injection solenoid and nozzle assemblies were placed into the four-inch air intake tube. These will reduce intake air temps, increase octane and allow running without an intercooler.


9 The TiAL blow-off valve is mounted in the air intake tube and will allow for excess inlet pressure to be vented when the throttle is shut quickly. The blow-off valve and wastegate were both purchased from Moore Racecraft.


10 LS engines have steam vents at all four corners. The factory blocked the rears early on, which can cause vapor to be trapped in the heads in higher power applications, causing detonation. We remedied this by using Earl’s plumbing products to vent it back to radiator.


11 The Holley Hi-Ram intake is a modular system. The lower base is available for Rectangular Port (L92), Cathedral Port and LS7-headed engines. Different plenum tops can be used for both EFI and carburetion. We are using the 102mm front-facing inlet top.


12 The Hi-Ram intakes use an O-ring around the intake ports, much better and easier than gaskets. LS engines use O-rings exclusively throughout. This makes sealing much easier than older style engines that are guaranteed to leak oil somewhere.


13 We used Holley’s new Dominator twin fuel pump system on the dyno which will be used in the vehicle as well. The unit has two pumps that can be activated independently. This pump will support around 1,800 HP.

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Last month we assembled the bulletproof bottom end for our turbo 6.0L LS engine build. This month we’ll cover the top-end assembly and see what she’ll do on the dyno with and without the turbo.

There are a lot of great aftermarket cylinder heads available for LSx engines, but they’re all out of my “family man” price range. The best budget option was a set of new L92 rectangular port heads (p/n 12582713) that have been sitting around, waiting for a project. The School of Automotive Machinists (S.A.M.) checked and assembled them. And just so there would be no shortage of airflow, the guys at S.A.M. left them in their CNC machining/porting center for a while, which increased airflow dramatically to 358 cfm on the intake and over 220 cfm on the exhaust.

After researching the various aftermarket valve options available, I chose a set of Ferrea 6000 series 2.16-inch intake and 1.59-inch exhaust valves, purchased from Mike Lewis Racing Engines, to fill the holes in the heads. The intake valves didn’t break the bank and are a hollow-stem design to keep weight down without a strength penalty. The valve springs, locks, retainers, and pushrods were purchased from Straub Technologies to match the camshaft. The valve springs are a dual-spring design with closed/open pressures set up at 160/360 lbs. The retainers are titanium to reduce weight.

I was going to use the factory hydraulic roller lifters, but my good friend Robin Lawrence donated a set of Morel low travel link-bar lifters to the cause. The factory rocker arms are decent pieces as-is, but they were upgraded to a new set of trunion and needle bearing units from COMP Cams. The engine was topped off with Holley’s new polished cast-aluminum valve covers that allow the unsightly factory coil brackets to be removed. I’ll sleep well knowing this package will easily handle the heat while being 7,000-plus rpm reliable.

The last thing any enthusiast wants to do is choke an engine that can breathe like this, especially while stuffing boost in it. While the factory GM composite intake manifolds are pretty good for their intended purpose, I needed something capable of gale force air movement for this build. A cost-effective, high-flowing alternative is Holley’s new versatile Hi-Ram series. They are serious pieces intended for big displacement, high rpm screamers as well as boosted applications such as ours. Feeding it is a stock GM Corvette 90mm drive-by-wire throttle body.

For our turbo, I contacted the folks at BorgWarner Turbo Systems for a recommendation. After going over the same parameters given to Chris for the cam, engineer Seth Temple recommended a S400SX3 unit with a 76mm compressor wheel, and 1.10 A/R turbine. Turbos are a lot like camshafts, you don’t just pick the biggest one at the bottom of the page. It may make bragging-rights power once it gets working at high rpm, but it will be lethargic and lazy at low rpm.

The huge turbos used on high powered heads-up cars require trans-brakes and a lot of effort to build boost when they launch. I don’t plan to use a trans-brake and need the turbo to build power immediately when I drop the hammer off the line.

For exhaust, I started with a set of Hooker Headers’ new cast iron LS exhaust manifolds flipped around backwards. I designed the rest of the “hot side” using 2½-inch by .063-inch stainless tubing from each manifold into a three-inch merge pipe right to the T4 flange on the turbo. Then I conned my friend Todd O’Neill into doing all the beautiful TIG welding. Controlling boost pressures is the job of a Precision Turbo 66mm wastegate along with a TiAL blow-off valve on the intake side. The four-inch downpipe from the turbo outlet runs to a single muffler at the rear bumper.

Engine and powertrain management is being handled by Holley’s Dominator EFI system. I’m using all the features this system offers: plug-and-play capability for the LS engine, boost control, nitrous control, drive-by-wire control, electronic transmission control (4L80E), and water/methanol injection, along with a full data acquisition system on the car. For the water/methanol injection, I decided to reduce a lot of intercooler plumbing complexity and weight by replacing it with two small solenoids and a small fluid reservoir of 50/50 water/methanol to cool the intake charge. The methanol also increases octane as well.

The day finally came when it was time to strap this thing to the dyno for its first break-in pulls without the turbo. With low static compression, a turbo spec cam and a high rpm intake, I had no illusions of big horsepower numbers while in this naturally-aspirated configuration. Also unexpectedly, as soon as the engine fired, the oil pressure pegged the bypass at 122 psi at 4,000 rpm. After some discussions and a few phone calls, I couldn’t resist and chanced just one quick dyno pull. With only 25 degrees of timing and no tuning, it was great to see 455 hp at 6,300 rpm with things still climbing. Torque was 412 lbs-ft at 4,800 rpm. Not bad for an 8.8:1 compression engine.

The high oil pressure issue turned out to be self-inflicted, due to the use of a GM displacement-on-demand oil pump. These have a very high oil pressure relief spring internally, and an additional lower pressure bypass spring in the oil pan, which of course I didn’t have. Luckily, the engine was still on the dyno, making it simple to install a Melling standard volume pump with the optional high pressure spring.

With that handled, it was time to bolt on the hairdryer and see what this thing had in it! Once running, things were incredibly quiet and docile with the turbo in place and holding a steady 15 inches of idle vacuum. On the street, I’ll tune for 10 psi of boost and 93 octane pump gas, but for safety 116 octane race gas was used while boost, timing and water/meth tuning was accomplished. I started with a 9 psi wastegate spring, 22 degrees of timing and the display read 669 hp at 6,500 rpm and 577 lbs-ft at 5,200 rpm. Next, we connected the Holley Dominator boost control so we could increase the boost over the 9 psi wastegate spring. In this configuration, intake pressure is controlled by the EFI via increase and decrease solenoids that are added to the top of the wastegate diaphragm. This allows instant boost changes with just a few clicks of the keyboard.

As boost was increased, the engine initially responded well. But as more pulls were made back to back, power was dropping around 5,500 rpm, compared to previous runs. Certainly concerning, there was nothing in the data logs indicating trouble, except it was consuming less fuel and making less power on each subsequent pull. The spark plugs looked fine, and showed little heat. One of my friends, who is very sharp at analyzing data, suggested I may have been injecting too much water/meth mixture, with the excessive amount reducing the volumetric efficiency of the engine. Back-to-back pulls could be compounding the problem as higher temps will evaporate the water/meth mix earlier than previous pulls. The system was definitely doing its job, reducing the intake charge from 190 to 200ºF to 120 to 125ºF. I had to take a break for the day to think it through.

Bright and early the next day, I set about testing the new theory. I first made a baseline pull at lower boost levels, and then reduced the water/meth flow rate by 50 percent, which immediately added 30 hp, even though the intake temps were up eight to 10 degrees. I reduced the water/meth again, but power stayed the same with higher intake temps. At this point I’d found the sweet spot, so it was time to increase boost again. Power was up everywhere!

Plus, I could make back-to-back pulls with no reduction in power and the intake temps were still being reduced from 200ºF to 130ºF. “Only” 38 pulls since initial break-in had produced an optimized timing curve and the proper water/meth flow rate. We ended the day making 797 hp at 6,500 rpm and 693 lbs-ft at 5,600 rpm with 16 psi of boost. Full boost was available around 3,500 to 4,000 rpm. The engine ran perfect during every hard dyno blast and while I know there is more power available with a more aggressive tune and more boost, my part selections were able to deliver the response and reliability I wanted. Who would ever complain about an 800hp engine that idles like a stocker, and is capable of 25 mpg?