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January 2011 Chevy High Performance Q&A - Performance Q&A

Tom Truty Dec 9, 2010
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We've Come Too Far!
Since when have you been able to drive off the showroom floor and onto the dragstrip then knock down mid-12-second e.t.'s and 115-mph runs with a completely stock Detroit-built hot rod? With an automatic trans and the traction control on? I haven't been paying too much attention to the late-model iron, namely the Corvette. Now you might be thinking, "Kevin, you know the LS7 505hp ZO6 has been out for years?" or "Wow, how could you miss the release of the ZR1 supercharged LS9 with its outstanding 630 ponies on tap?" I'm not talking about these pure-breed race cars. I'm talking about your bread-and-butter, standard, '08-and-up Corvette with the Gen IV LS3 6.2L producing 430 SAE horsepower; this is one of the most amazing feats of engineering to date. You could put your grandmother in this car and she wouldn't know she was driving a hot rod down to the local market. Nary a chop to the idle, smooth power from the electronic-controlled throttle; this package has it all. Now stand on the throttle and boy, will it open your eyes.

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One of our fellow racers at Fontana has been racing an '06 GTO for years. He has been so successful with late-model-electronics cars that he and his GTO won the Summit ET World Championship at the NHRA Finals in the Sportsman class. Well, this past weekend he didn't have his usual Yellow GTO-the car you hated to see in the other lane-but instead a paper-plate '09 Silver auto-equipped Corvette. He would roll into the water, turn off the traction control, and do a short burnout. Reengaging the traction control, carefully staging the car, and as quiet as a mouse, thunder down the track to a 12.30 e.t. at over 115 mph. Again, I was floored. It's only a matter of time before he has this car completely sorted out and killing the competition on a weekly basis. Then he'll drive it back down to San Diego, knocking down nearly 30 mpg on the way.

I hope the insurance police and politicians won't get in the way of our advancements in technology. I can't wait for the next 10 years. All I can say is that I'm going to be paying more attention to the new hot rods from now on. I just need to rob a bank so I can own one!

Shiftless In San Diego
Q: I am having a terrible time setting up the Proform 750-cfm carb on my 454, mainly finding brackets that would accommodate the throttle cable and the TV cable. I'm running a 700-R4 trans and have not been able to adjust the TV cable to get the trans to behave! After five different brackets, I finally found that the one that mounts using two of the carb mounts works fine. So now I have this awesome setup, and it runs great, but it won't shift. I've tried all the methods to adjust a TV cable, and it still won't shift correctly. Also, the Lokar pedal and throttle cable assembly won't give me full throw on the carb, no matter how I set it up. Should I be using a bell crank of some sort? No one has the answers, and I feel like I'm the first person to run into these issues, but I know that's not true! Please help if you can.
Morgan Walker
San Diego, CA

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A: Adjusting the Throttle Pressure cable on a 700-R4 transmission can be a real challenge. Many a trans has been burned up due to incorrect adjustment or incorrect travel because of the centerline of throttle shaft-to-cable mounting location. The distance from the throttle shaft to the cable mounting pickup point must be around 1.125 inches. Any less and the TV cable won't move in its full range and can't get to full TV pressure. If this distance is too great, the cable will run out of travel and adjust too quick, which will really lower your part-throttle transmission line pressure and cook the trans.

Holley carburetors have a very convenient hole at the bottom of the throttle bracket that looks like it would work perfectly; however, it's around 1.375 inches from the centerline and is too far forward as compared to a mid-'80s Q-jet. The best template to use would be an old Q-jet and duplicate this cable mounting point on your Holley throttle arm bracket. We usually make a very short tab that will bolt into that hole on the throttle arm; it will allow you to move the cable pickup toward the centerline of the throttle shaft and move the cable mount slightly rearward. Between these two adjustments, you will have a pickup point very close to the original Q-jet design.

As for full throttle, there are several throttle cable mounting holes in the throttle arm. The top hole usually won't give you enough travel to achieve full throttle. Unless you have a good deal of pedal travel in the car, you won't see full throttle. Move the throttle cable mount to a lower pickup point in relation to the throttle shaft centerline. This will give you full throttle, but the throttle will be more sensitive.

After checking and adjusting your TV cable ratio and cable mounting, we hope your transmission shifts. It doesn't take much driving with low line pressure to hurt the gearbox. Good luck with your project.

Beyond Old School
Q: I have a '56 Chevy Bel Air with a '59 283 bored 0.060-inch over and completely blueprinted. It is the engine from Jon Calendar's old '59 Chevy that he won Jr. Stock with at Indy in 1965. It still has the original heads and all the old-technology parts in it. I was considering upgrading the top end to a set of aluminum heads and a better cam, probably around 0.500-inch max lift. It now has an aluminum intake and a Holley on it that was from an early '70s Z28. When I was racing it, if you missed a shift, it was very easy to bend a valve. With more cam, I would think the valves would be nearly hitting the pistons. Are the newer heads of a different angle so the valves won't hit the pistons? If you have any recommendations on a cam I would appreciate it. I always look forward to reading your column and I am amazed on your wealth of knowledge on the Chevy engines. Thanks in advance.
Jerry Marteney
Louisville, OH

A: You actually drove the car back in the valve-bending days? Look how far we've come ... we're still bending valves in Stockers in the water box if you rev the engine too quickly during a burnout! At least there are rev limiters to help with the missed-shift overrevs.

With any engine, you can run out of piston-to-valve clearance based on the duration and lift curve. The original heads on your '60's race engine have 23-degree valve angles. This is the same angle on 95 percent of the small-block cylinder heads on the market, until you get into the very specialized racing heads. With these heads, they have flattened out the valve angle (18 degrees or 15 degrees) to reduce chamber size and burn efficiency of the combustion space-nothing you're going to want to do with your little 283.

As for a camshaft for your little Mouse, you've given us very little info on what you intend to do with the engine. Is it going to be used to pull your '56 around on the street? We'd assume this with the max lift in the 0.500-inch range. We're sure the major issue with the valves hitting the pistons back in the '60s was the lack of valvespring pressure. As soon as you missed a shift, the revs went north of 8,000 rpm. When this happened, the lifter had no chance of staying in contact with the lobe and lofted right off the nose of the camshaft. When the piston came up the bore it was introduced to the intake valve! Now we have plenty of spring pressure and camshaft lift profiles that will keep everything under control. You'll want to install an ignition system that will allow you to control the max rpm if things get out of hand.

Again, if you're looking for a street camshaft, we'd run one of the Comp Cams Thumpr series to give the car the right sound for the period. Comp has three levels to choose from starting with the Thumpr, then the Mutha Thumpr, and the largest is the Big Mutha Thumpr. If you're looking for the true Stocker sound for your Mouse, the Mutha Thumpr (PN 08-601-8) will deliver the goods in both sound and performance. It specs out at 235/249 degrees duration at 0.050-inch tappet lift, 0.522/0.509-inch max lift, and is ground on a tight 107 separation angle. Use the complete camshaft valvetrain package offered by Comp under PN K12-600-4; it comes complete with camshaft, lifters, springs, retainers, keepers, and a double roller timing chain set. This will ensure that you have the proper spring set for the camshaft design. You'll need to check your piston-to-valve clearance when assembling the engine. A good benchmark is to maintain at least 0.080-inch on the intake and 0.100-inch clearance on the exhaust so you won't have any issues if you miss a gear or two. Please don't ask what we run our Stocker intake valves down to. (0.038 inch!) Sources:,

CFM vs. HP
Q: I currently have a '67 Camaro RS convertible with a nice 327 with a mild Lunati cam, headers, and a Tremec five-speed with 3.31gears and am in the process of building a torquey small-block 406. I do not see it going over 6,000 rpm on any regular basis. I have noticed articles that mention the cfm to support horsepower and am leaning toward a set of AFR 195 Eliminators and mild a hydraulic roller with max lift somewhere in the 0.550-inch range and duration at 0.050-inch tappet lift of 230 degrees. Is there a published formula, like compression or engine cubic inches?
Jeff Foster
Via email

A: Well, we could easily get into trouble with this one. First, there isn't a direct correlation to cylinder head flow on a flow bench and the horsepower it will support. We use the flow bench as a yardstick to compare cylinder head flow figures against each other. Airflow on a flow bench is constant flow. The flow of air and fuel into a cylinder of an engine is interrupted flow, with many factors affecting its ability to fill the cylinder to its fullest. If an engine achieves 100 percent volumetric efficiency, it is completely filling the cylinders with exactly the amount of air and fuel that the engine specifically displaces. It's our goal to overfill the cylinders through tuning and sizing the runners, manifold, and headers and camshaft tuning to achieve in excess of 100 percent. Any time you can achieve over 100 percent volumetric efficiency (VE), the engine is larger than the engine truly displaces.

Back to your question. We think you want to know if your AFR 195 Eliminator heads are going to support the 406-cid engine you're building? Yes, these heads will give you a very well-performing 406 with great torque and horsepower potential. Is there a simple formula, like a compression ratio or cubic inches? No. To come up with the theoretical 100 percent VE number for your 406, multiply the cubic inches by the max engine speed (rpm), then divide by the constant 3,456. This gives you a cfm number for your 406 at 6,000 rpm of 705 cfm. This is, again, at 100 percent VE. Most street performance engines may achieve right at 100 percent VE at or near torque peak. As the engine speed increases, the VE falls off due to the time it takes to fill the cylinders, and that the intake runners and exhaust headers are tuned to peak around torque peak. This gives you the broadest powerband for a nice driving package. If this were a race-only engine, you would tune all components around a very narrow powerband where you wished to achieve peak horsepower.

It's All About Communication
Q: In your Oct. '08 issue, you said to machine down the center divider 0.500-inch on an Edelbrock Performer RPM for cylinder communication from all four barrels. Why wouldn't you machine the whole divider down for full flow from the carb?
Larry Freeman
Cleveland, OH

A: The trimming of the center divider is an old-school trick to increase communication between the upper and lower planes of a dual-plane manifold. We're sure it was tried before this, but it was widely used on the early big-block aluminum manifolds back in the '60s. This communication effectively raises the powerband (rpm) of the engine, and makes the engine think that the carburetor is larger than it really is. It's basically a poor man's single plane intake.

Cutting the center divider down 0.500-inch on the Performer RPM inlet manifold will give you a few extra ponies at higher engine speeds without killing too much slow-speed performance. The 0.500-inch point was a rocking point of gains. Anything more than this didn't give you anything upstairs, and would hurt slow-speed torque below and at torque peak. We mapped this out on the engine dyno on a 450-plus-horsepower, pump-gas 350 small-block. You can achieve similar gains by adding a 1/2-inch open spacer under your square flange carburetor. We cut down the divider because we didn't want to run a spacer. Having the engine dyno gave us the tools to map out the proper amount to cut without ruining the intake.

Flyin' Norwegian
Q: I have a '70 Camaro SS with a 383 stroker engine, built by Smeding Performance. It's a mild stroker with 371 hp at 5,000 rpm and 441 lb-ft at 3,800 rpm (dyno tested). The camshaft is a hydraulic roller tappet, 0.480/0.480-inch max lift, 212/222 duration at 0.050-inch tappet lift, on a 112 lobe center. The cylinder heads are aluminum 2.02/1.60-inch stainless steel valves with 64cc combustion chambers, 175cc intake port volume, a Performer EPS dual-plane, and 9:1 compression ratio.

The car has a Tremec TKO 500 manual transmission with 0.68 Overdrive in Fifth gear. The rearend is a 12-bolt with 3.42 gears. Will I need a higher numeric rearend, because I really have no use for the Fifth gear unless I drive it at a very high speed at the motorway (as we call it here in Norway), far over the speed limit. I'll guess 3.73, 3.90, or maybe 4.10 will be my options.

The Camaro is street only. What would you recommend? Thanks.
Svein Erik Josefsen
Sandefjord, Norway

A: Your thought process is right until you run into your 3.27 First gear. Going lower with the rearend gear will make First more useless than it all ready is. The gear multiplication you have with the 3.27 and the 3.42 rear gear give you a combined First gear ratio of 11.18:1. With your torquey 383, you'll blow through First by 36 mph at your horsepower peak of 5,000 rpm. This is assuming that you have a 27-inch tall tire on your Camaro. If you wish to go lower with your rear gear, we wouldn't recommend going any lower than 3.73 gears.

Yes, you have an 0.68 Overdrive Fifth gear. This will just mean that your 383 will live longer. Trying to achieve peak vehicle speed in Overdrive shouldn't be your worry. Get all the speed you wish in Fourth and let your engine loaf along the motorway in Fifth. Enjoy your Camaro over there!

Ram Jet Injection
Q: Let me first say I subscribe to automotive magazines based on their technical Q&A. Therefore, I just get one magazine, CHP. Enough flattery. I have a complete Ram Jet 502 injection system, less fuel pump. Is this unit capable of supporting a much more aggressive engine? I currently run a 462 with 10.2:1compression, Brodix Racerite heads, and a hydraulic roller with 236 degrees of duration at 0.050-inch tappet lift. This is a street/strip car that weighs in at 4,300 pounds ('68 Impala), 4,000 stall, and 4.11:1 gears. The car runs 7.26 eighths at 90 mph. Is this injection system going to hurt my performance, or should I stick to my Holley 950? Also, who could help me on injector size and programming the ECM? Thank you for your advice.
Tyler Murdock
Cordova, AL

A: Ram Jet 502 intake manifolds are great for making torque. It just might be the ticket getting your 4,300-pound land yacht moving. However, you gave us just enough information to make us dangerous. What intake manifold are you currently running under the 950 Holley? Is that Holley a 950 4150 square flange carburetor or a Commander 950 TBI? The Commander 950 has a 700-cfm four-barrel throttle body. You can see where we're going with this; please send us as much info on your questions. We can always edit them down. Thanks.

Back to your question. The Ram Jet injection system was originally designed and sold by Arizona Speed and Marine. This EFI injection system has been around for many years. It's offered in both oval- and rectangular-port configurations. The manifold you have is the oval-port design that is installed on the GMPP Ram Jet 502. Those systems come equipped with 38-lb/hr injectors, which support around 520-540 hp. From your eighth-mile e.t., we'd guess that you would run somewhere near 11.30 quarter-mile at around 115-116 mph. To get your 4,300 pounds running this quick, you're currently pushing out around 600 hp out of your 462. To support that kind of horsepower with a little headroom we'd recommend going with 45-lb/hr injectors. That's an impressive number out of a mild 462. The Ram Jet may give you a little more torque than your current system, but we doubt you'll see that type of horsepower for various reasons. First, the runner length, and second the size of the 48mm two-barrel air valve. You could install a larger throttle body to get more air through the system, but the lengths of the runners are going to set the tuning of the intake.

Finally, OBD Diagnostics Inc. has very nice tuning software for all families of the Delco MEFI controllers. OBD offers tuning services and sells both standard- and professional-level software. The standard software gives you the ability to change fuel and spark calibrations, injector sizing, rev limits, and engine displacement.

You have a very nice package right now. The EFI would be trick, and may help in consistency with weather changes. We'd think long and hard before jumping in with both feet. Give OBD a call and get a feel for the calibration challenges. Sources:,

Missed it!
Q: I was reading your latest tech questions and saw a gentleman asked about some performance issues on his newly rebuilt TPI for his '92 Z28. Your mention of the wrong gaskets on the wrong sides of the TPI could certainly cause a vacuum leak, but he also mentions using a geardrive, which of course is a big no-no on TPIs and other EFI engines. Just thought I'd see if you can get that information to the reader.
Chris Maucere
Jamestown, NC

A: Sometimes we don't see the forest for the trees! You're referring to the noise and harmonics that come from a geardrive system will wreak havoc with the knock sensors and really screw up the spark timing. This could happen anywhere in the rpm band from idle, or throughout the powerband-or everywhere.

Now that you mention the geardrive scenario, this also goes for mechanical lifter camshafts, high-clearance forged pistons, and even sometimes roller rockers. The knock sensors are calibrated to a specific noise frequency that engine detonation puts off. These mechanical components will sometimes mimic that same frequency, which will also drive the knock sensors crazy.

This is something you must really keep in mind as many more builders are retrofitting their early cars with EFI systems. They may have a very nice small-block between the fenders of their rides. Dropping a knock sensor-equipped EFI system on a geardrive-equipped early small-block could drive a man to drink, chasing problems. Thanks for your help, Chris.

Carb Help
Q: We built a 383 engine for my '69 Camaro in 2004. We've had no problems with it, and it runs great. However, lately it has an issue when we drive it and let it sit for anything more than 10-15 minutes. It will start and run maybe 5 seconds, then die. I have to floor the pedal as if it was flooded to restart it. I've been told it may be boiling some of the gas out of the carburetor. I have checked the temperature on the carburetor immediately after shutting it off and it's between 118 and 146 on the bowl casing. The carburetor is a Holley 650 with manual choke, and I do run headers. There is a 1/2-inch spacer between the carb and the Edlebrock Torker intake. Is boiling the fuel out possible? What would cause this problem to start after six years? Thank you for your help.
Danny Meyers
Taylor, MO

A: Before we started chasing fuel percolation, we'd be looking to the power valve, located in the primary metering block. Holleys can blow the power valve diaphragm during a backfire situation. Especially after many years of service, these diaphragms dry up and can crack on their own. With the diaphragm damaged, the fuel will leak under high-vacuum conditions, like at idle, making it difficult to fuel the engine correctly at idle. Also, the fuel will seep through while sitting and drain the fuel bowl. You will notice it after the vehicle has sat for a couple of days and you must crank the engine to get fuel back into the bowl before the engine will run. In short periods of time, as you mentioned, it could cause a hot engine to act flooded.

While you're in there changing the power valve, we would replace the needle and seats for good measure. If the needle is worn and has a poor sealing surface, it could be allowing fuel to migrate into the bowl after the engine is turned off. If your fuel pump check valves are in good shape it will retain pressure on the seats for quite some time after the engine is shut down. If the needle and seats cannot control this pressure, as the engine heat soaks it will raise the fuel level in the bowl and drip over through the main boosters.

Either way it may be a good time to rebuild your carb, replace the internal components, and install new gaskets. This will take care of all the simple nagging troubles we've mentioned above. Get the Holley list number off of the choke housing on the primary side and order the appropriate carb rebuild kit from Holley. The original gaskets and components are the best. Don't use an auto parts store rebuild kit on a Holley. You're just asking for trouble.

Retro Roller Runner
Q: I am finishing a total resto of a '67 Camaro with the original 327 bored 0.030-inch with KB flat-tops, Edelbrock Performer heads (2.02/1.60-inch valves, 64cc), using an Isky RR-265/272HYD roller on 108 centers. The cam was installed using a Torrington bearing and a thrust button.

When the heads were installed on my engine, the guy mistakenly used Fel-Pro 1074 head gaskets (LT1) instead of the correct 1003 gasket. After adding coolant and finding water in the oil pan, I pulled the heads and the lifters to clean and relube. I noticed that the cam lobes are positioned farther forward (not centered) in the lifter bores than normal. What is the correct way to install a retrofit roller in a first-gen small-block? Also, any idea on estimated power for this build? The other components are Comp Cams 26918 springs and Pro Magnum 1.6 rockers. The intake is an Edelbrock EPS with a 650 Edelbrock carb. I'm using a DUI ignition, Muncie four-speed and 3.55 posi, Hedman 15/8-inch headers with an X pipe, and Be Cool electric fans and radiator. Thanks for any help you can offer
Keith Anderson
Ft. Worth, TX

A: Installing retrofit hydraulic rollers into an early small-block is very simple. Using a Torrington thrust bearing behind the timing gear, and a thrust button to control the endplay, is the right way to go. Your question about the lobes lining up with the tappet holes is a little worrisome. Yes, they will sometimes be slightly off, but the roller wheel must be in full contact with its matching lobe, and the lobe can't be so out of line that it will hit its neighboring lifter. Our best gauge if the camshaft is lining up properly in the block is how the distributor gear on the cam lines up with the distributor tunnel in the block. This should be quite centered. The distributor gear shouldn't run off the edge of the camshaft distributor gear.

When you say you have a thrust bearing behind the camshaft gear, it must be machined for this bearing. If it wasn't and you installed a bearing behind the gear, the timing chain wouldn't line up with the crankshaft sprocket.

Checking out the Isky PN RR-265/272HYD, it is a direct retrofit hydraulic roller for '57-87 first-generation small-blocks. The cam specs out at 217/225 degrees at 0.050-inch tappet lift, 0.485/0.505-inch max lift, and is ground on 112 centers. You must have had a custom grind done for your 327 at 108 separation angle. We like the profile for your little Mouse. With the combination of components you have listed, you should see the horsepower come in at around 400. The torque is going to fall in around 375-380 lb-ft. This should give you a very nice-running package with a great idle quality. At the higher engine speeds it should sound like the late '60s all over again. Enjoy.

Technical questions for Kevin McClelland can be sent to him at



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