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July 2010 Chevy High Performance Letters - Performance Q & A

Kevin McClelland May 24, 2010
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A Class For Everyone Over the past couple of years you've seen CHP spread its interest beyond what just goes straight; from the 24 Hours of Lemons to open track days, CHP is getting into all facets of motorsports. Funny thing is, I've always been heckled by road racers saying drag racers never make a turn. My response to most of them is that we turn at least twice, "Once onto the track, and once off!" I invite others to come sit in my Super Gas Roadster when it's running wide open on a cold winter day. All you're doing from the starting line to the finish is turning the wheel to stay in the center of the groove.

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Well, way back in the late '80s, I was the chief mechanic on an SCCA Showroom Stock team; this was the closest I got to going around turns. Then, when my son Daniel was 11, we got started in Karting; in the final year he raced (four years later), we both ran the same kart-Daniel in the Adult class and me in the Grand Masters, with the rest of the old guys. We had an absolute blast that year and both finished in the top five for the season.

Now here we are in Southern California, where there are all types of motorsports events every weekend. Daniel has gotten to know an SCCA Pro Solo team and they invited him out to test in their car-of course he jumped at the chance. I'd never been to one of their events, and it was a lot of fun and very easy to race your street car at the club level. If you're not familiar with Autocross, they set up a track (usually in a parking lot or airstrip) using cones to mark off the circuit. You start from a standing start and are timed through the course, then you're given an elapsed time at the end of your run. So we've picked up a set of slicks for my Mazda Miata (Hey, I've got to get around L.A.), and we're back to going around turns.

Check out the Sports Car Club of America's website ( for all the information you need to get out to a local club event and race around the track, including the rules and classifications for any type of car. You can see where your car stacks up against other brands and which class you fall into. There are regional clubs all around the country, and all you have to do to race is get a weekend pass and volunteer to help with the event. They run practice sessions throughout the day, which can give you up to 12 runs, and breaks when you work the track.

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Daniel has been invited to drive the Pro Solo team's car at the National here in SoCal this summer, so I guess we'll be burning up some tires practicing until then. I hope my little Miata is up to the abuse, since we'll both be trying to break it. If you're looking to try something a little different, get out there and have some fun!

Finer Points
Q: I'm trying to get some final answers on my '71 Nova build. With so many different views and ideas, I have to go to the pros at Chevy High. I have a four-bolt main 350 block with a steel crank and 0.060-inch over pistons that is fully balanced. I have a Comp Cams XE274H-10 and aluminum roller rockers. The top end is a Dart Pro 1, 180cc kit (PN 01111111) with a dual-plane intake. I will be installing a set of Hooker long-tube headers, 13/4-inch primary and 3-inch collectors into 21/2-inch duals out back. Torque is key to me, and a redline of 6,000-6,500 is tops. This is my street car. There will be a 3.08:1-geared 10-bolt rearend for now with 26-inch-tall tires. I have a great all-new ignition system and have not bought the hood for the car yet, so hood clearance isn't an issue if spacers are required. So should I use my Holley 750-cfm carb with vacuum secondaries or an EZ EFI from FAST? Do I use my TH400 with a 2,200-stall or a TH350 with a stall speed that I'm not sure of? Will I have any trouble running pump gas? Can you estimate the torque and horsepower, please? Thanks for your time.
Dave Lucki
Big Valley, AB, Canada

A: We have been very impressed by FAST's EZ EFI. This is a very user-friendly EFI system with complete self-calibration built right in. With the use of a wideband O2 sensor, the system can trim the fuel tables in a matter of minutes! And it's constantly trimming the fuel curve to the optimum air/fuel ratio for both peak performance and fuel economy. This would be a great addition to your engine package. You'll be very happy with the bolt-on tuned performance and time saved dialing in your Holley carb. The EZ-EFI base kit PN 30226-KIT comes with the throttle-body assembly, an EZ-EFI control unit, a handheld control module, a power adapter and cable, a wideband O2 sensor, a bung and plug, a coolant temp sensor, and a wiring harness. The EZ-EFI Master kit PN 30227-KIT includes everything listed above, plus an EZ-EFI 600 HP Fuel Pump Kit (pump, fittings, adjustable fuel pressure regulator, reusable billet fuel filter, relay harness, and pressure gauge).

With the power level your little 350 is going to produce, the TH350 would get the nod from us. They weigh quite a bit less, have less rotating weight, and take less horsepower to turn. The beauty of the TH350 is that the torque converter from your TH400 will drop right in; however, we don't think your 2,200-stall is going to be enough for your XE274 camshaft selection. You'll need to step up the stall into the 2,800-3,200 rpm range. This brings us to your high 3.08:1 rear gear with 26-inch tires. You'll be cruising in the stall anytime you're not at freeway speeds, ultimately building quite a bit of heat. At a minimum, you will need 3.73:1 gears in the rear.

The Dart Pro 1 Top End kits are nice packages to top off any engine. With the heads come a dual-plane intake, gaskets, ARP bolts, Dart valve covers, and the proper heat range spark plugs. The kit you have purchased has 64cc combustion chambers. With the Speed-Pro forged flat-tops, the Fel-Pro head gaskets supplied in the head kit, and the pistons 0.020-inch down in the hole, it'll yield 9.5:1 compression. If you have zero-decked the engine, the compression will step right up to 10:1, and with either compression, you'll be fine on pump gas.

Finally, the power and torque should come in right around 420 for both. We've used this camshaft with a similar dual-plane intake and ported aluminum L98 heads that were in the 180cc range, and this is what it produced. It gives you a very flat torque curve and is all done in the early 6,000 rpm range. This will give you a very respectable street small-block. Enjoy. Sources:,

Don't Limit Me
Q: I have an '05 Cobalt LT with the 2.2L Ecotec and a manual trans. Is there an easy way to reprogram the ECU to get rid of the speed limiter, or possibly a performance chip that could do the job? I haven't found much online and any help would be appreciated.
Matt Abeling
Bloomington, IL

A: You're right; there isn't much on the Internet for your Cobalt. Jet Performance offers its V-Force Plus Module (PN 68021), an in-line tuning device that allows you to adjust timing and fuel and monitor 14 screens with various parameters, such as AFR, throttle position, and MAP pressure. We were unable to get an answer if you could modify the speed limiter.

The speed limiter is put there for a reason. It's not there to keep you from breaking the law; it's to protect you. The original tires on a vehicle are where the speed limit usually comes from. If you've upgraded your tires from the original speed rating, it's not a problem to raise the speed limiter. This is the case with your Cobalt passenger car. Now, on the chassis dyno, we've seen very nasty results of raising speed limiters. Trucks and SUVs have speed limits based on the driveshaft's critical speed limit. When this limit is surpassed, the driveshaft begins to flex, and once the shaft has bent beyond a minimal amount, you have reached a point of no return. The shaft bends to the point that it pulls the driveshaft right out of the transmission with catastrophic results. It usually damages the transmission, the undercarriage, the fuel tank, and whatever else gets in its way. Then the shaft comes out from under the vehicle at tremendous speeds and takes out the observers of the dyno test! Please respect the vehicle speed limits applied by the OEMs on trucks and SUVs unless you have upgraded the driveshaft with either a thicker wall thickness or a larger-diameter shaft.

Finally, to gain full tuning ability of your '05 Cobalt, check out HP Tuners. They offer the closest to GM development software that I have ever worked with. Just about any parameter is available for modification with their software. Yes, it's pricey, but with their VCM Suite of tuning software you get enough credits to tune at least two vehicles, and sometimes four. If you can get a buddy to go in with you on the package, the dollars are less than buying two tuning modules from other aftermarket tuning companies.

One Tough Truck
Q: I'm building an S-10. The motor in progress is a 434 Dart block, all forged bottom end with AFR 210cc Competition heads, a Victor Jr. intake, and a Holley 850hp carb. It will not be a daily driver, but will be a radical street truck with an occasional trip to the local track. My question concerns the cam. My plan is to use a solid roller. The compression comes in at 10.5:1. I know a hydraulic roller is best for the street, but I can't find one with enough lift to take advantage of the excellent flow these heads produce. What would your advice be on the best cam? Solid may be right, but will a hydraulic roller work? And maybe your opinion on how much power this combination might produce. Thanks a lot, guys, and keep the wrenches turning.
Donnie Griffin
Baxley, GA

A: This is going to be one fun truck to drive. A fellow line mechanic we worked with back in 1979 had a '76 LUV truck with a 377 small-block in it that was a real handful. That truck wanted to go every which way but straight. Luckily, it never met anything very solid!

As for your camshaft, we'd stick with a solid roller for many reasons. You're spot on that you can have better profiles with the solid design, and the mechanical design will be a much lighter valvetrain package. This will aid in valvetrain stability when the thing sees high rpm that we're sure it will. Check out one of the new Lunati Street/Strip roller profiles for your pickup. The camshaft that should work quite well with your package is PN 501B2LUN, which specs out at 243/251-degrees of duration at 0.050-inch tappet lift, 0.582/0.582-inch max lift, ground on 110 centers. These new cam profiles give you the flexibility to drive on the street without beating up the valvetrain. We'd recommend going with 1.6:1 ratio rockers on the inlet side to bring the max lift up to 0.620-inch. This will bring the intake and exhaust lift within 2 to 3 cfm of your AFR Competition cylinder heads' peak flow.

With this camshaft, your compression ratio, and aluminum heads, you should be able to run this engine on pump gas. We'd start with 30 degrees total timing and check the performance. Remember, when jetting race-type engines on pump gas, you need to increase the main jet around 6 to 8 jets sizes, compared with proper jetting on race gas. Pump gas is an oxygenated fuel carrying its own oxygen. Start safe and jet accordingly.

As for power, you should see tons of torque; we'd target the horsepower to come in at 580 to 600 on pump gas. Yes, you could push the power much higher with a larger camshaft, more compression, and larger inlet track; however, this will be one fun street brawler that will push your S-10 around with ease. Good luck, and don't scare yourself.

LT4 Secret
Q: I am upgrading my ZZ4 after many years and good performance. I'm going 0.030-inch over, good rod bolts, and the crank is still standard. I've upped the valve sizes and was lucky enough to score a new Chevy Hot cam and new 1.6 Chevy rockers w/studs (no lock nuts) at E-Town. At home I opened the stud box, and to my dismay, the studs are 10mm (as are the rockers) with a small threaded stud on the end. I have tried everywhere to find 10mm studs with lock nuts so that I can make the valves adjustable, but no luck. Can you bail me out? I look forward to your answers every month, as they are the most informative of all the mags. Thanks.
Rich Larrimore
Via email

A: You have run into the little LT4 secret. The valvetrain on the one-year-only (1996) LT4 is a net-lash design. What this means is that those 10mm rocker studs have a mating nut that tightens against that small stud (forget the size) at the end of the rocker stud. The nut bottoms out on the shank of the rocker stud applying a specific amount of lifter preload.

First, you didn't mention if you got the rocker stud nuts with your collection of parts. You'll need to order a set of nuts. Next, you need to mock up the valvetrain of every cylinder. You can adjust the valves by adding shims under the rocker studs to adjust the lifter preload. We ran into the same situation on our LT4 bracket engine in our Malibu Wagon. We cut the deck down to 9.00 inches, clipped the heads by approximately 0.020-inch, and run thin 0.028-inch head gaskets to get the compression up to 11:1 with a flat-top piston. This put too much preload on the valvetrain. Using 7/16-inch AN-style washers, we were able to get between 1/4 and 1/2 turn of preload on each lifter. The AN washers come in two thicknesses, 0.032- and 0.063-inch. You can pick up these washers in bulk from Pegasus Auto Racing Supplies under PN AN960-716L (0.032-inch) and AN960-716 (0.063-inch). Pegasus is a great source for racing hardware and little trick components that make race car fabrication a breeze. Mainly catering to the road race community, but many of the parts don't know if they are going straight or around turns.

The LT4 rockers are extremely strong and have the least amount of deflection of any aluminum roller rocker on the market. GM really pushed the envelope with these rockers, as they are the only aluminum roller rocker ever offered on a production engine. Hope this helps in getting your engine together. Good luck with your ZZ4 upgrade.

Watch Out For The Iceberg
Q: I need some help putting together a 406 small-block for my '73 Nova SS. Here's what I have: a rebuilt 400 short-block bored 0.030-inch over, stock rods, stock crank, and dished pistons with four valve reliefs. For heads, I have a pair of aluminum Procomp 190cc runners, 2.02/1.60-inch valves, and 64cc chambers. My math puts the compression around 9.8:1 and I'm going with an all roller setup; a Comp Cams 270HR with 0.500-inch max lift. I also have an Edelbrock RPM Air-Gap with a Holley 750-cfm carb up top. For the exhaust I have a set of Hedman 13/4-inch headers with Flowmaster mufflers. Would this be a well-balanced setup? The trans is a rebuilt TH350 with a shift kit and 3.08:1 gears out back. The plan is to drive the car nearly every day from spring to fall and I'm wondering if it'll get up and go on a chilly Maine morning with no exhaust crossovers and an Air-Gap manifold. Also, how fast can I safely spin the motor with a stock bottom end?

I apologize for the assault of questions, this is my first engine and I want to do it right. Thanks for any input!
Matt Leighton
Houlton, ME

A: We never experienced carburetor icing until we lived in Northern California, and it took quite a while to figure out what the problem was with early morning performance. The engine was equipped with an Air-Gap-style manifold and a 750-cfm Holley with no choke. The car would start and run fine until we got a couple of blocks from home; then the engine would turn very rich. After looking for all the normal rich-running Holley issues, we found it on the engine dyno at work. The Dyno cell temperature was in the mid-30s one day and after starting the engine and running it for a few minutes, it began to run very rich. We quickly went out and pulled the air turbine and found ice on the throttle blades plugging the transfer slots on the idle circuit. This caused the engine vacuum to suck fuel straight out of the idle circuits and go pig rich.

With extreme cases of carburetor icing, the throttle shaft can stick in an open position. We wouldn't be concerned about it if your engine will start and run in the cold conditions; instead our concern would be from the carburetor icing. Putting some type of lubricant into your gas helps prevent icing because the ice can't stick to the throttle blades. We had Red Line Oil blend up some additive to run on the engine dyno and snuck a gallon home for the El Camino. Carburetor icing is probably a regular occurrence in Maine and your local auto parts store should have some magical elixir for your situation. If not, check with Red Line Oil.

As for a max rpm for your stock short-block 400, stay conservative. Unless you just have to run it out, stick to a 5,500 rpm limit. The stock cast crank, cast pistons, and short 5.565-inch rods put a tremendous amount of side-load on the cylinder walls. The higher you spin it, the more frictional load you will see. Also, all those cast components flying around would make us nervous running higher than this. The 400 is going to make great mid-range torque, and shifting at 5,500 rpm will drop the engine speed right back into the sweet spot of the torque curve. Enjoy the fun of big torque!

Headers For You
Q: I'm having a really difficult time trying to find a set of headers for the GM 385 FastBurn. This engine is going into a '69 Firebird. It has quick-ratio power steering and no A/C. I believe this can be the same setup as a '69 Camaro. I have talked to a GM tech, Hedman, Hooker, and Doug's, and because of the raised roof they don't seem to have any suggestions on header. Hedman told me I could use its PN 68270 headers, but it has a 15/8-inch tubes and the corners would be very close with the D-port and may get blown out. One fellow told me I couldn't even use the stock manifolds. ANY help or suggestions? I'm desperate.
Bart Wankier
Via email

A: Helping you find headers will help every other Camaro owner out there. You're correct that a Camaro header will fit your Firebird, and at least you're putting a real engine into your Tin Indian!

The Hedman tech was correct in its assumption that the corners of the standard street header may blow out the header gaskets. However, in the Hedman Hustler line of racing headers there's a great one for your application. We use the same Hustler line on our Malibu wagon with LT4 heads that have the same D-port exhaust. Hedman offers these headers for the Camaro in either 15/8- or 13/4-inch primaries and 3-inch slip-on collectors. We'd recommend going with the 15/8-inch header, PN 65018 (the 13/4-inch are PN 65019). This header will fit with power steering. They will not fit with A/C. Hedman specifically points out that these headers will fit with raised exhaust ports, and angle plug heads.

Good luck with your project. If you would have started with a Camaro you wouldn't have had any problem. Well, maybe so, but enjoy your new powerplant.

Technical questions for Kevin McClelland can be sent to him at



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