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Chevy Performance Tech Q&A - September 2014

Kevin McClelland Aug 1, 2014
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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!

Oil’s Well

Q My engine oil pressure has got me baffled. It’s a newly rebuilt 355-cid small-block, with a new Eagle crank, Eagle H-beam rods, Speed-Pro pistons, a solid lifter COMP cam and lifters and pushrods, and used Crane aluminum roller rockers. When I start the engine cold, oil pressure is great at 75-80 psi, on my new Auto Meter electrical oil pressure gauge. However, when the engine warms up, the oil pressure goes down as the temperature gauge goes up. At idle, with the engine temperature at 185 degrees F, the pressure is only 5-10 psi. I know technically that’s acceptable, but I don’t like—or understand—why it drops so much. When rpm increases, the pressure goes up. Driving down the road, the oil pressure is good, around 30-35 psi. I’m using standard 10W-30 oil with Lucas Engine Break-In oil additive. Why is the pressure dropping so much when the engine warms up? Thanks for any help!

Gary Giguere
Augusta, ME

A Pressures that low would make us nervous too. Sure, as you stated, according to the factory GM manuals this pressure is acceptable. Again, it’s just a little too low for our liking. It’s tough to diagnose your pressure problem with an assembled engine. Let’s talk about all the leaks that are in our engines.

You said this is a fresh rebuild with all Eagle components. Did you measure all the bearing clearances during the assembly? The lubrication system in an internal combustion engine is just a controlled leak system. If you have too much leakage for the volume of oil your pump is producing, you’re going to have low oil pressure. When we blueprint our small-blocks to run on 10W-30 oil, we set the rod bearing clearances between 0.0022 and 0.0024 inch. Then you want the mains to come in around 0.0024-0.0026 inch. The rear main will usually run a little looser, in the 0.003 inch range. This is fine, as the bearing surface is wider and the leak must lubricate the thrust bearing surfaces. You mentioned that you’re running COMP Cams flat-tappet camshaft and lifters. If for some reason your lifter bores are slightly oversize, you can leak quite a bit of oil around the 16 lifters. The lifters should measure at 0.842 inch, and the GM spec for the lifter bores comes in at 0.8438-0.8443 inch. This will give you a lifter bore clearance between 0.0018 and 0.0023 inch. When you get up over 0.003 inch clearance, you will lose oil pressure.

What did you use for an oil pump? Usually, a standard-volume pump with a high-pressure spring with the above clearances will give you mid-40s for hot oil pressure and 65-70 psi at speed. Again, this is with 5W-20 to 10W-30 oil. If you’re confident with all your clearances, we would try stepping up the weight of your motor oil; try 20W-50 oil. If the hot pressure gets into the 15-20 psi range, and 40 psi range at speed, you should be good to go.

Of course, you could have something really weird, like a crack in the lifter valley through the main oil gallery, which opens up with engine heat and creates a leak. Cracks in the lifter valley area on production small-block cylinder blocks aren’t that uncommon if the block has seen some rough service and has gotten hot in a previous life. This crack would show up in a Magnaflux test on the clean block during the rebuild. If you have the proper clearances in all the leak points, and can’t find any other reason for the low pressure, you may need to break the engine down and have it tested.

Finding these types of problems can be a real feat. Hopefully, adding the thicker oil will get you into a range that you’re comfortable with. Good luck.

Can’t Beat The Farm Trucks!

Q First off, I’d like to say how much I love your magazine! I’ve been getting it for a little over a year and I look forward to getting it in the mail every month.

My story is that of a typical kid in a small town trying to fix up an old farm truck. For about two years now I’ve had a ’72 GMC K-2500 Sierra for driving back and forth to school. I love the truck; it’s old, it’s rusty, and it’s got a set of wake-the-neighbors Cherry Bombs that complete the package, along with factory tach, bucket seats with center console, and a sliding rear window.

About a year ago, I dropped a new engine in it because the numbers-matching 350 was knocking and smoked a little. I bought the engine currently in the truck from a guy here in town who bought it from O’Reilly’s for a ’71 C10. I got the engine with an Edelbrock 1406 carb, a Performer series aluminum intake, and a chrome dress-up kit with the truck for $1,000 (by number crunching I’ve come out WAY on top in that deal). The engine runs great, but there’s just one problem: It’s a gutless turd. I can accelerate up to about 45 mph fairly quickly because the truck is geared like a tractor, but it’s pretty well dead until I get good torque at around 65 mph. I’m turning such high rpm I can’t go much faster, and I suck gas like CRAZY.

As the engine sits, it has iron heads with casting number 468642, which means it has a valve size of 1.72 inch on the intake side and 1.5 inch on the exhaust. The combustion chambers are 76cc, giving it a compression ratio of 9:1 if flat-top pistons were installed. What I would like to do is get rid of the iron heads and go with aluminum, if my current ones are not worth messing with. I also would like to swap out my cam to a COMP Cams XE250H because of the low-end torque it’s supposed to add. Roller rockers and long-tube headers with Series 40 Flowmasters are also in the mix.

Can I make good low-end torque with my cast-iron heads and the cam I chose, or do I need to go ahead and shell out the cash for aluminum heads? I know the lack of torque is only going to be worse when I regear my truck with 3.73s (from 4.56s) and add overdrive so I can take it to college. If you have any suggestions on cam/head combinations for improved low-end torque I would be very grateful. I love my truck, but I just don’t want to have to put my foot in it every time I want to go up a hill running down the interstate.

Peyton L. Barrett
Winchester, KS

A We’ve all grown up with either “farm cars” or “farm trucks.” We had both growing up. Our first truck was a ’63 C10 with a 292 six-cylinder and three on the tree, which we beat to death until we built a nasty 301-inch six-cylinder, and painted it Corvette Yellow with polished Centerlines. This was 1976. During that same time, our Fiat altered car that we raced was lovingly called a “farm car” by our good friend Bobby DeVour, who at the time worked for Mr. Gasket and Hays clutches. He helped us work out our 1961 chassis with an injected big-block and Clutch turbo transmission. Let’s help you get to college.

The 350 that you dropped into your pickup is a good building block to start with. I would bet that the engine doesn’t have flat-tops, but rather dish pistons and you have a whopping 8:1 compression with the 76cc cylinder heads. We really like your COMP Cams selection to create great slow-speed torque. It’s really a nice grind for torque with 206/212 degrees duration at 0.050-inch tappet lift, 0.432/0.444-inch max lift, and is ground on 110 centers. With this cam we’d recommend a nice set of aluminum street heads, like the Edelbrock Performer PN 60909. These fully dressed heads feature 170cc intake runners, 2.02/1.60-inch valve sizes, 64cc combustion chambers that will bump your compression up into the low 9:1 range, based on how far down in the hole the rebuilder short-block pistons end up. These heads are dressed with 1.46-inch valve springs for hydraulic flat-tappet cams. With the Edelbrock heads, they recommend using 0.100-inch-longer pushrods to give you the proper valvetrain geometry. Edelbrock also sells these pushrods under PN 9629.

Finally, since you’re going to go with roller rockers, pick up a set of 1.6 ratio rockers to give you some additional lift and a couple of degrees duration. The 1.6 ratio rocker will give you a max lift of 0.461/0.474 inch with the XE250 cam lobes. This will give you full advantage of the flow potential of the Edelbrock heads. It will also bump the camshaft timing up around 208/214, which doesn’t sound like much, but between the lift and duration change on this combination it can add around 10-15 ponies. With this combination of parts, you should be right at 345-350 hp, and between 400 and 410 lb/ft of torque.

This will be a very nice running small-block for your truck, and we guarantee you won’t be burying your foot to climb slight grades on the interstate any longer. Good luck in college, and let us know how your engine package works out.

No Replacement For Displacement

Q I could use some advice on an engine build I am undertaking for my ’65 Evening Orchid Chevelle SS convertible. This may seem like idiocy to your readers, but I am set on building a 327 for the car as I am a bit of a purist (I know) and want to run an engine in the car that could have come from the factory. I plan on using the stock heads (3782461 iron), intake (3844461 aluminum), and exhaust manifolds, trying to build the engine to at least look stock. I know I am leaving performance on the table using these parts. I’d like to build as much engine as I can with these parts, trying to strike a balance between low-end torque (primary) and horsepower, along with streetability. I am leery to use too wild a cam, since I am installing power brakes and live at 6,000 feet. Good engines don’t make 10 inches of vacuum in this air. However, I don’t want the cam to sound too plain at idle. It has the factory two-speed PG tranny. I may swap that out later, not sure for what yet.

Could you be able to recommend a CR, cam, and valvetrain that would meet these goals? Anything else I would need to think about? Thanks for your expertise!

Derek Knapp
Denver, CO

A You want to build an engine that looks completely stock but expect the performance level to satisfy your need for power. Then you tell us that you’re over a mile high and that Mother Nature isn’t coming to the power party!

We completely get that you want to re-create the stock appearance of your stock ’65 Chevelle. However, if you select the best parts to build up your 327, using the production HP aluminum inlet and stock exhaust manifolds, you’ll be limited to around 350 hp at sea level. Throw in the nosebleed altitude and you’ll be lucky if you can build 275-300 ponies.

We go with the tried-and-true “walk softly and carry a big stick” motto. If you want to build a stock-appearing engine then we’d add as many cubic inches as you’re comfortable with. The easy math is to build a 383. You can still use your original 327 block and add the 3.75-inch stroke crankshaft. Let’s say that with the right parts you could actually build 300 usable horsepower at 6,000 feet with your 327. That’s 0.92 hp/ci. Now, multiply that by 383 inches and you have a 352hp engine. Not only will the horsepower be up, but also the torque will come in around 360-370 lb-ft. The engine can look completely stock and you’ll be able to build an engine that will perform and behave much better than the smaller-displacement engine.

Now, let’s go back to your cylinder heads. You will want to have these rebuilt and have, let’s call it, a stage 1 porting done to the heads. The 461 castings were a great performance head for their time. They came with a 1.94/1.50-inch valve package. We would leave the 1.94-inch intake valve and increase the exhaust valve to 1.60 inches. The majority of porting needs to be done in the bowl area of the cylinder heads and a full exhaust port. You will want to keep the intake velocity up in the thin air. Check with Speier Racing Heads in Hays, Kansas; this is a full-service racing cylinder head shop that offers custom hand porting. Give them a call at 785.623.0963 to discuss your thoughts of using production cylinder heads and making power.

As for compression, do you always plan to stay on the hill with your Chevelle? If it’s always going to be in thin air, you can push the squeeze up to gain a little efficiency out of the little oxygen you have. If it’s going to cruise around and get down to sea level, you will be limited to 9.5:1 with the production iron heads. If you stick around on the hill you could push the compression up to 10.5:1, which will work well with a mild-torque-type camshaft.

For the valvetrain you can stay somewhat stock. When rebuilding your cylinder heads you will freshen up the springs and hardware with the camshaft manufacturer’s recommended spring package. Check out a COMP Cams XE256H, which specs out at 212/218 at 0.050-inch tappet lift, 0.447/0.454-inch max lift, and is ground on 110 centers. Yes, this is a conservative camshaft, and will have a slightly noticeable idle, but your power brakes will work and you’ll feel the torque in the seat of your pants. If you go much larger at altitude, and with the stock exhaust manifolds, the thing could be a real pig downstairs in the rpm curve. The complete camshaft kit (PN K12-234-2) includes camshaft, lifters, timing chain set, springs, retainers, and locks. To round out the valvetrain, try a set of Magnum roller-tip rockers (PN 1412-16), which have a ratio of 1.52. This will bump the valve lift up from the camshaft specs about 0.006 inch.

Now that we’ve blown up your 327 party, everything recommended above will carry over to the smaller build, if you truly wish to build the little Mouse. We just want you to be satisfied with the expense and work you’re going to put into this project. Hopefully, we haven’t strayed too far away from your dream.


Comp Cams
Memphis, TN 38118
Torrance, CA 90503
Speier Racing Heads



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