Chevy Performance Tech Q&A - September 2014

Kevin McClelland Aug 1, 2014 0 Comment(s)
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Rolling Old-School

Back in the day, no one had enclosed trailers at the local or Sportsman level. Today, you roll into any dragstrip around the country and you’ll see Renegade-style motorhomes or toterhomes pulling a stacker trailer with at least two cars prepped and ready for action. It’s amazing how our sport—or motorsports as a whole—has changed in the past 50 years at the local and Sportsman level. Back in the ’60s, even the Top Fuel and Funny Cars rolled out in the elements to promote their cars, and show that they were in town for a match race. They used the rolling advertising, with the car out in the breeze, to bring the fans to the track.

This brings me to next weekend. Daniel and I were scheduled to travel up to Las Vegas and run the NHRA Lucas Oil Divisional race with our cars. Every dime I have to play with is sunk into our cars to make them as competitive and durable as possible. To get our cars to the track I have my ’96 Chevy truck and a 15-year-old 24-foot Pace Shadow enclosed trailer for my Super Gas car. The wagon is relegated to our flat-tilt-bed equipment trailer behind our ’93 Chevy Suburban. We’re pretty self sufficient and stuff all the tools and equipment into the Pace, which I bought back in 1998 as the Mac family’s first enclosed trailer.

As luck would have it, Daniel has to leave for China on a 14-day business trip tomorrow, so he’s out. After very little thought, I’ve decided that I’m going to roll up to Vegas with the Suburban and open trailer and race Super Street with the wagon. A grade point is awarded for either class, which is what I need for qualifications at Nationals. I’m going to throw a small tool box, a 5-gallon fuel jug (the beauty of running pump gas) to fill each day at the local Shell station, a 1,000-watt Yamaha generator, a battery charger, a weather station, my log book and calculator, a couple of chairs, and small cooler in the ’Burb and hit the road.

I’m so looking forward to it. I haven’t raced the wagon since I ran it in Stock Eliminator back at the 2011 Summit Nationals in Vegas. Super Street is where I really cut my teeth index racing, and many of my good buddies are still racing the class. I hope I can do the wagon proud, as Daniel really has gotten the attention of the class. We raced it three times in Super Street last year at the divisional and national level. He’s lost in the fourth round all three races. I’ve got quite a high target to hit for my first race. Boy, this should be fun!

Pump Gas Not!

Q I have a question about which cam would be best for my application. I’m building a 406 small-block Chevy. It’s a 0.030-over GM block with an Eagle 4340 forged crank, Eagle 6-inch rods, and SRP forged flat-top pistons. The heads are 23-degree CNC-ported Dart Pro 1s with 250cc intake runners. The valves come in at 2.10/1.60-inch and the heads have been milled to approximately 58 cc, so the compression ratio should be around 12.5:1. My rocker arms are full rollers and are 1.6:1 on intake and exhaust. I’m running a ported Brodix 1002 intake with a 1050 Dominator Holley and 1 7/8-inch Hooker headers. The ignition is undecided but will probably be all MSD or Pertonix. It’s all going in a ’73 Camaro with a TH400 trans, and the converter will be matched accordingly to the cam and 4.56 gears in the rear with 275/60/15 drag radials.

The first cam I have is a solid roller with a 0.626/0.626-inch max lift, 262/271 duration at 0.050-inch, and is ground on a 106 degree lobe separation. Those specs are with a 1.5:1 rocker. The other cam I have is a solid roller with a 0.723/0.726-inch max lift, 274/282 duration at 0.050-inch tappet lift with a 112 degree lobe separation—this is with a 1.6:1 rocker. The car will see some occasional weekend driving to the local cruise-in but is definitely not a daily driver and will be on the dragstrip most of the time. I’ve also heard people talk about running a lot of duration and wide lobe separation like the second choice on high-compression engines like this and getting away with pump gas. I was curious if that’s possible because, if not, I’ll be running 110-octane racing fuel. My goal is 700 hp naturally aspirated, and I’d also like to keep the max rpm under 7,000-7,500. Thanks for any help.

Clark Greene
Via email

A You’ve got quite a nice build going on here. Your parts selection is going to make some steam. The parts you have chosen will need to run on race gas with the 12.5:1 static compression. Yes, you can run long-duration camshafts and bleed off cylinder pressure, but the max squeeze on pump gas would be in the 11:1 range. We’ve also heard, like you, that some guys have run high compression on pump gas, but we would only trust it if you can completely control the engine temps and it’s a race-only combination. Putting any load on the engine at lower engine speeds could spell instant disaster. By the time you think you notice the engine knocking, it could be too late.

Keeping with the engine speed limit you’re looking for, we’d recommend going with your first camshaft selection. With 1.6-ratio rockers your max lift will come in at 0.668 inch. This will put you right into the meat of your flow curve of the Dart Pro 1s. Also, the snap that the smaller camshaft will give you over the wide-center, long-duration camshaft will make your Camaro very entertaining to drive.

Now, 700 hp is right at 1.72 hp/ci. On pump gas we usually see numbers around 1.5- to 1.55 hp/ci on Gen I small-blocks and big-blocks. The LS engines have given a little more power per cube. LS engines can stand a little more squeeze and will tolerate around 11.5:1 on pump gas. Small-blocks will live in the high 10s to 11:1 max. On big-blocks we’ve run out of power gains at 10:1 and the engines become knock limited. These numbers are using these engines for dyno mules or drag race applications. To do this on the street you have to be very careful.

Good luck with your 406 and enjoy the ride. You should run deep into the 10s at 125-plus mph with your combination. Remember, making power is only one part of the equation. You must also get the power to the ground. Have fun!




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