Photo: Dart/Moore Good Ink

Photo: Dart/Moore Good Ink

Years ago, I worked for the old Bracket Racing USA magazine. One of the most popular features the late Dale Wilson (Editor of the magazine) and I hatched involved the construction of “paper” racecars.  We called them “Paper Tigers” and we used computer simulation to test the cars and engines. It turned out to be an excellent series and plenty of readers actually built combinations similar to what we built on paper. Dale is gone now, but when The Burnout editors called, it occurred to me that I could dust off that old simulation software (Engine Pro) to see how well our paper LS motor worked. Now there are more sophisticated software programs available today, but I always found that Engine Pro was quite reliable. And if anything it was often on the conservative side.  But enough  back-story.  Here’s how the computer sims went on our hypothetical LS motor.

The first test of our 427 (actually, the displacement works out to 428, but what’s a cubic inch between friends?) produced a series of results we more or less expected. The custom LS motor cranked out a very respectable 641 horsepower at 7,000 RPM.  The torque peak of 476 foot-pounds occurred at 5,700 RPM.  Engine Pro recommended a shift point of approximately 7,700 RPM.  And that’s entirely possible with today’s high RPM hydraulic rollers (although everything needs to be right and most likely light).  Typically, though, a shift point 5% above peak horsepower will be a good starting point.

In terms of mechanics, our LS combination has a bore to stroke ratio of 1.03:1.  The rod ratio is 1.53:1 and it has a maximum piston speed of 7715 feet per minute at peak power.  You’ll need a pretty good size header for the combination too:  Something in the order of 2.00-2.125-inches in diameter with a primary length of approximately 32-inches.

Bottom line here?  This is one stout yet relatively mild combination – one that will go rounds without much fuss.

But then, what’s a “dyno test” without testing stuff?  It crossed our mind too, so the first thing we did was to swap the 850 Holley for a larger 950.  With no other changes, our 427 barked to the tune of 686 horsepower at 7,150 RPM.  Torque went up too – all the way up to 509 foot-pounds of torque at 5,800 RPM.  That folks, is a serious improvement.  Here, the mechanics didn’t change (aside from a small increase in piston speed to 7880 feet per second).  The software did recommend a bit larger header (and rightfully so, considering the amount of air going through this engine).  We stoked. Now what?

While we were on a roll, we decided to plug in a Crane solid roller camshaft – one with a split duration of 262-degrees intake and 268-degrees exhaust (@ 0.050-inch tappet lift) and a lift of 0.670-inches.  We went back to the baseline 850 Holley carb too.  The power production was extremely impressive:  736 horsepower at 7,300 RPM.  Peak torque was 547 foot-pounds at 6,100 RPM.  Here, the maximum piston speed was measured at 8045 feet per minute at peak power.  The header primary can probably be shortened by an inch or so with this setup.  And the shift point can go up too – we’d start at 5% over peak power and test all the way to 10% over peak power (8,000 RPM) to see which is quicker and faster in the car.

The next test was pretty simple:  Swap back to the 950 Holley carburetor.  And as you might have expected, we once again saw an improvement.  It was simple swap, but the power increase was more than we expected:  Our hypothetical 427 LS cranked out a mind-numbing 787 horsepower at 7,450 RPM!  Maximum torque worked out to 583 foot-pounds at 6,200 RPM. Piston speed is up due to the increase in RPM (8211 feet per minute), but it’s tolerable.  This combination works out to 1.84 horsepower per cubic inch. Considering the off-the-shelf parts we picked in the build, it’s pretty impressive.   If the car is equipped with an automatic, you’ll have to pick the converter carefully, and to be honest, it will likely work best with a three-speed.

At this point we figured it was pretty much done and we’d stick a fork in it.  But then we thought about the combination for a bit. What if we increased the compression to real racecar levels (honestly, an 11:1 LS can probably run pretty well on pump gas)?  If the CR went to 13:1+, we figured it might make a difference. And it did:  By bumping the compression ratio to 13.2:1 (keeping the mechanical roller cam and the 950 carburetor), the LS hammered out 809 HP at 7,550 RPM.  The maximum torque measured 611 foot-pounds at 6,200 RPM.  As you can see, increasing the compression ratio does wonders for torque production – this is common on most engines.  Basically, we gained 32 horsepower and 28 foot-pounds of torque with the change.  Keep in mind this is race fuel only combination. But it’s a stout one.

In the end we think one major thing stood out with the LS engine: Its one very capable power plant and probably an outstanding choice for a bracket car.  Yes, the parts are more expensive than they are for a conventional small block or a big block.  But an 800 horsepower 427 is hard to argue with!

We used an old race engine simulation program for our tests. It’s called Engine Pro.  Yes, there are more sophisticated Sims out there today, but over the years, we’ve found the software provides reliable results.

We used an old race engine simulation program for our tests. It’s called Engine Pro. Yes, there are more sophisticated Sims out there today, but over the years, we’ve found the software provides reliable results.

 

We ran five Sims, beginning with a baseline, working our way up to a whopping 800+ horsepower combination. What it does show is how responsive Chevy’s LS architecture is to modifications.  It’s definitely a serious bracket race platform.

We ran five Sims, beginning with a baseline, working our way up to a whopping 800+ horsepower combination. What it does show is how responsive Chevy’s LS architecture is to modifications. It’s definitely a serious bracket race platform.

 

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So You Want to Be A Drag Racer: Buying, Building, Wrenching and Racing

The allure of the drag strip is easy to understand – a place where  it takes less than 10 seconds to make a stand, prove your skill, speed, and nerve.  But the road to the races can be intimidating.  The Burnout wants to make that road a lot smoother for aspiring racers, whether it’s through building a new car, modding a used one, or taking that ride all the way up to the burnout box and beyond.  This series is a work in progress, an ever expanding comprehensive guide to all the things that take drag racing from concept to reality.

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