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February 2011 Chevy High Performance Q&A

Under Pressure

Kevin McClelland Jan 11, 2011
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My son, Daniel, and I were trying to beat the clock by purchasing a totaled ’06 GTO to steal its LS2 for his ’94 Mazda RX-7 engine swap. We got all the cool hardware from the GTO that we wanted to make the swap a dream. Well, this past weekend was time to break down the engine for the camshaft and heads upgrade we had planned.

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With the rear suspension/differential rebuild and the front suspension completely gone through, it’s time for the powertrain. The GTO didn’t look to be that well taken care of. At 42,000 miles, it was already on its second set of (baked) tires. As we split the engine and the trans, the first thing we noticed was the nice blue color of the pressure plate of the clutch! I’ve changed my fair share of clutches, and the hue of blue of this clutch was impressive.

With the engine now up on the stand we were ready to break it down to the short-block. The plan was to install a custom-ground camshaft that I had selected. Our goal is to make this car completely California emissions-legal and go through the referee process. Once approved, you get a decal in the doorjamb and you can have the car inspected at any smog station in California. So I had chosen to stick with GM-designed camshaft lobes but mix them up a little bit since I had access to both LS6 and LS7 camshaft profiles. I had a stick ground with the LS7 intake lobe and the LS6 exhaust lobe. This specs the camshaft out at 210/218 degrees duration at 0.050-inch tappet lift, 0.562/0.547-inch max lift, with 1.7 rockers. This is all ground on an emissions-friendly 116 separation angle. As for cylinder heads, we’re going to try out the Cadillac LSA Gen IVs, very similar to the rectangle-port Gen IV L92 engine’s except for a swirl vane in the inlet port to promote high swirl, and a unique kidney-shaped combustion chamber to promote tumble. With this mixture motion, they are much less susceptible to detonation than their L92 counterparts. The only thing we’re not real keen on is that they are down about 30 cfm at max lift, but they beat the L92 heads all the way to 0.400 inch of lift. I know they’ll make killer torque and horsepower until our mild camshaft runs out of headroom.

Back to the condition of the engine, as Daniel was taking it apart he called me over to check out the monster oil spill in the floor of the manifold plenum. The breather system on the LS engines can be less than effective. If you have any leakage of cylinder pressure it can force oil vapor right through the valley and into the intake manifold. This also answered why the rear main seal was leaking slightly. This guy had fun with his Goatbut didn’t service it too often. We’re down to the short and the engine looks fine except for some residual oil on the heads of the pistons. Well, those fresh new pieces are going to have to stay in their boxes a little longer. We’re breaking down the short for a quick ring and bearing swap. I will be much happier now knowing we’ve touched everything before dropping it in his car. Don’t get under pressure to finish your projects. What’s a little more work anyway? Until next month, have fun with your projects.

Aluminum Rods On The Street
Q: First off, fantastic magazine. I love your tech articles. I’m building a 477 big-block, and during the build I happened across a set of used Venolia aluminum rods at a swap meet for $250. I had them checked out for cracks and straightness, and had them bushed for floating pins. Ever since I first mentioned using aluminum rods on a street/strip engine I have gotten the response: You’re going to run aluminum rods on the street? Man, you’re brave. So what’s the big deal?
Loren Bustin
Via email

A: Aluminum rods have a finite life expectancy. There are forged and billet aluminum connecting rods and each has a limited number of cycles that they will withstand before coming apart. Some very high-quality aluminum connecting rods are available from sources like BME, GRP, MGP, and Venolia. Most of the new aluminum rods on the market today will give you quite a service life, but please follow the manufacturer’s recommendation. If you lose a rod you won’t have much left to build from!

As for used swap meet aluminum rods, you have no idea what they have been through. Before the above high-quality alloy rods hit the market, we would only put a 100 dragstrip/dyno-pull life expectancy on them. We had a set of brand-name aluminum rods come apart in one of our drag-race-only big-blocks back in the mid-’80s. They were new and died at 80 passes! It took everything out and put us out of racing with that car for over 10 years as we scraped together every penny to get an engine back together. Check out the websites listed below for quality aluminum rods. If you choose to use your secondhand rods, you have been warned. You may want to invest in an engine diaper!

Bunch Of Iron
Q: I have a set of cast-iron, rectangular-port GM heads with the casting number 3964291. Plus, GM 3T and Hi-Perf are cast into them. What I have found out (I believe) is these heads came off a ’70 460hp LS7 engine. On a paper from cylinder head casting numbers, an asterisk followed the casting number. That asterisk said: The LS7 engine was not produced for retail sales. So how rare are these heads, if at all? How much would they be worth? Any information would be greatly appreciated. Thank you.
Michael Jamison
Gallatin, TN

A: Any of the early iron is basically worth whatever someone is willing to pay for them. People are paying stupid money for the original stuff. The cylinder heads you have are early ’70-and-earlier castings. These are rectangle-port, closed-chamber Hi-Perf heads used on 396, 427, and very early 454 engines. The 454s that were production engines were LS6s. The early LS6s had these closed-chamber heads, and somewhere through the ’70 build they switched to the 3964292 casting number, which is the open-chamber head. Until this letter, I believed that all LS6s were open-chamber engines. You can teach old dogs something!

The LS7 engines were sold as off-road-only crate engines through the late ’90s and used the 292 casting heads with 12.5:1 compression pistons. The 3964291 and 3964292 cylinder heads were also sold as service replacement parts. You will need to identify the casting date on the heads to see if they were truly production install parts or over-the-counter service parts.

Good luck selling your cast-iron gold. If you truly have production-casting-date heads you may find someone restoring their early iron who needs your parts. It would be a match made in heaven.

Hot Under The Collar
Q: My ’76 Chevy Monte Carlo has had some overheating trouble. Six years ago I had a 402 big-block built and it’s had overheating issues ever since. I’ve replaced the radiator, fans (twice), and thermostat (twice), and have even taken down the top-end of the engine to check the gaskets and heads. I’ve drilled holes into the engine to match the heads and replaced the gaskets to allow for more water flow, hoping that would cool down the engine. When we drive in town, the temperature is lower than if I drive on the freeway.

I’m very frustrated and don’t know what else to do. Would you be able to offer some suggestions on what else to look at? Thanks for your help.
Chris Mount
Oakdale, MN

A: Overheating can take all the fun out of our cars. Worrying about being caught in traffic and having water blow into the overflow and then onto the ground is a quick way to ruin a nice day. I’m worried about a few things you mentioned. Let’s discuss them.

You tore down the top-end of the engine and drilled out the block to match the cylinder heads? Your 402 engine is a Mark IV big-block, which has a specific deck surface design to transfer water up into the cylinder heads. With this design, GM was able to make the cylinder heads and head gaskets interchangeable from the left to the right side of the engine. The coolant passages in the head gasket controls the amount of water flow from the block into the cylinder heads. If you notice, the water comes into the block from the water pump and is forced to travel to the rear of the block before most of the water is allowed to travel up into the cylinder heads. If you modify these holes in the head gaskets or drill new holes in the deck surface to modify this water flow, you can bypass cool water from the front of the engine right up into the heads. This would send this cool water out of the engine into the radiator before it’s done absorbing heat. The front of the block on a Mark IV big-block’s deck surface is solid and has no water transfer holes like it does in the rear; this prevents the water from going right into the cylinder heads from the water pump.

As I said, GM used the block to control the water on the Mark IVs. On the ’91-and-later Gen V and VI big-blocks, the front of the block does have the water passages, and they used the head gaskets to block the transfer of water in the front of the block, however, you cannot use Gen V or VI head gaskets on a Mark IV. The gaskets will not seal several water passages at the top of the deck and will leak water in the lifter valley of the engine.

The last year that GM built a big-block Monte Carlo was in 1975. We take it you have outfitted your ’76 with a big-block radiator, fan, and shroud to cool the beast? The fan shroud is very important on the Monte Carlos because of the distance from the water pump to the radiator. Also, make sure you have the factory air dam that was attached to the bottom of the core support to prevent hot air from the engine compartment migrating back into the front of the radiator and recirculating hot air back through the radiator.

Finally, if you are having heating issues at speed on the highway, and not at idle around town, we’d look for a lean condition, or not enough spark advance at cruising speeds. Make sure you have a working vacuum advance system on your distributor. At part-throttle cruise you would want to see 40-44 degrees of spark advance putting down the road. This will help with fuel economy and engine temps.

Hopefully, you haven’t drilled passages in the deck to circumvent the flow logic of the cooling system. Make sure you’re running all the factory shrouding and the proper clutch fan to engage when the engine temps climb. Hope these tips get you cooled off.

Dry Bowls
Q: I have been fighting a starting problem with my ’63 Chevy Impala SS with a 340hp 409 with two Edelbrock 600-cfm carbs. I know the 340hp engine didn’t come with this setup. My problem is the fuel always leaks out of the clear fuel filter I have between the pump and carbs. Then when the car sits for a while, I have to crank the engine for at least 10 seconds before it starts. (I’m pumping the fuel pedal all this time.) I have changed the fuel pump (Edelbrock PN 1721), put a check valve between the pump and carbs, rotated the carbs (front to back, back to front), and installed 1/2-inch wood-fiber heat gaskets (Edelbrock PN 8722). I have progressive linkage for the carbs. I know the big-block 409s have both carbs working at the same time, and I believe I read in a CHP article that if fuel leaks down from the filter, something in the carb is letting it leak by. If it is possible, could you help me with this problem? Many thanks.
Dan Williams
via email

A: The Edelbrock Performer carburetor design is not known for bleeding down fuel into the intake manifold. There is really no leak path with the Edelbrock (Carter) carburetor like with other designs. However, the condition you are experiencing sounds like dry fuel bowls.

This may be a pain, but the next time the car sits for a period, you need to check a few things. Yes, the fuel will bleed out of the fuel filter as the car sits. As the fuel evaporates, the floats will drop, allowing the remaining fuel to feed into the bowls from the fuel lines. Before you crank the engine we’d recommend removing the air horn (lid of carbs) to see if the fuel bowls are dry. The only way this is occurring is that the fuel is evaporating out of the fuel bowls as the car sits. With the 1/2-inch wood-fiber heat gaskets, we’re surprised the carbs are getting hot enough to boil the fuel out. With your dual fours, that is a lot of fuel to disappear in a couple weeks. If you said the car sits for a month or so and you have to crank to get fuel, we’d say that is normal, but it’s tough to imagine they could be dry in 10 days.

If you pull the air horn and the bowls are dry there is only one thing you can check. If the air bleeds on the idle circuits of the carbs are plugged, fuel will siphon right out of the float bowls into the intake manifold. The odds of all four idle air bleeds being plugged is a stretch. If this was the case, any time you went to fire up the engine it would be loaded up, and the idle mixture screws would have little if any adjustability. We find it really hard to believe this is the problem.

Leave It Locked
Q: What are the good and bad points of locking out the distributor? My ’89 Camaro has a 406 small-block with fully ported Brodix TR-1 heads, Eagle crank, KB pistons with 11.5:1 compression, COMP Cams Xtreme solid roller (254/260), and COMP Cams roller rockers. For the rest of the driveline I have a T56 six-speed, a Moser 9-inch with 4.56:1 gears, and a Mark Williams locker. I drive this car on the street and currently run it with an MSD Pro Billet distributor locked out at 36 degrees. It runs fine so far on Sunoco 94. Thanks for your advice.
Ron Anderson
Westland, MI

A: There are very few street applications we’d recommend running a locked-out distributor on; however, you’re definitely one of them. That is a very nice small-block that you’re calling a street engine. With the amount of overlap area your COMP Cams roller has, you are bleeding off a good deal of cylinder pressure at slow engine speeds. Also, with the very low rearend gearing, and the First gear ratios of your T56 trans, you get the engine up to torque peak very quickly and past the point of detonation that would cause a problem with street driving. Also, since your car is a manual trans vehicle, you have the ability to control the gear to run the engine with very little load on it. One of the major benefits of running that much spark advance at idle is the quality of the idle and throttle response the engine will have. Again, yours is one of few we would recommend running locked out.

As for the bad points, hot starting can be an issue with that much timing. The engine can kick back and damage the starter. Usually when you run locked-out distributors or crank trigger ignitions in a race car, you will get the engine cranking over, then fire off the ignition. This will allow the engine to spin freely without a load. Many ignition systems have built-in start retard options that will do the same thing. One last thing is that you could probably get a little better fuel economy with more cruising advance but with the engine package you’re running, we don’t think you’re particularly looking for mileage!

Twister Redux
Q: In the Chevrolet HT 383 EngineThe Twister, Part III you wrote the stock guides must be cut. You said, We also knew that the stock iron Vortec heads would need some work to accommodate the much more aggressive cam. The first order of business was to machine the valvespring seats for the larger 1.43-inch diameter dual springs. This is necessary because the stock spring pads are designed for a 1.25-inch-diameter spring. The stock guides must also be cut down to clear the additional lift. How much must they be cut?
Daryn Winhofer
Richey, MT

A: The stock Iron Vortecs were set up for mid-0.450-inch lift. This was based on the retainer-to-seal clearance and the coil bind clearance of the stock valvespring. Giving a blanket dimension for cutting down the valveguide is virtually impossible. Not knowing the lift of your performance camshaft or the type of valve seal and retainer you’re going to use, there cannot be a spec given.

Once you have chosen your camshaft and valvetrain hardware, you will want to check the seal-to-retainer clearance with the valve closed. Once you have this clearance, compare it to the max lift of your new camshaft. To be safe, whatever your max lift is on your new camshaft you will want to cut the valveguide an additional 0.050-inch for clearance. This will prevent the retainer from coming in contact with the seal and any chance of the retainer pumping oil down past the seal.

Sorry we can’t give you a number that will work for everything. We could tell you to cut 0.200-inch off the guide and it would be safe for almost any street-performance camshaft, however, you want the valveguide to be as long as possible to control the valve and reduce wear.

Safety Cutoff Switch, Part II
Q: In the Sept. ’10 issue you responded to a question concerning a safety cutoff switch and how to wire a single-wire alternator to it. I have the same concern. In your response, you stated that you use a smaller-gauge wire as a fusible link. Is it OK to use a fuse/fuse holder rated 10 amps above the rated alternator output, and if so is that a better option than a fusible link? Thanks in advance.
John C. Barnhardt
Via email

A: First, we need to clarify that we recommended using fusible link wire, a special alloy wire with proper insulation to prevent fires when the wire melts from over-amperage draw. We’ve seen fuses as high as 120-150 amps because of the alternator output and accessory draw on these tech-laden, late-model vehicles. If you check out your local wrecking yard you can find some really trick OE-type fuse holders and wire them in to protect your systems. The main reason we go with fusible links is the vibration of race cars. Unless the power feed wire is shorted out to ground, the link is going to live to win another race.

Preventive Maintenance
Q: I like to have my ducks in a row. I currently have an I-5 Colorado Chevy pickup. When should I change the timing chain? Thanks.
Ron Esbaugh
Via email

A: The GM Atlas inline cylinder engine family is offered in four-, five-, and six-cylinder configurations. These engines are equipped with a timing chain system instead of a timing belt. The timing chain is a non-serviced item, unlike timing belts, and has specific guides and a hydraulic tensioner that keeps the chain on track and in the proper tension. The chain and tensioner should give you trouble-free service for the life of the engine. The only time we would consider swapping it out is if you are in the engine for a valve job or head gasket change.

With the top end off the engine it’s just a little more work pulling off the front cover to replace whatever is worn. Timing chains are the way to go with overhead camshaft engines!

Gen V Makeover
Q: I recently bought a Gen V big-block out of a ’94 dualie and dropped it in my ’70 Monte Carlo. I’d like to install some aftermarket heads on it. The 454 has just over 40,000 miles. I have already installed an Edelbrock dual-plane Performer intake with a 750-cfm Holley carb and Hooker headers. Would I gain any more power by installing a good set of heads? If so, what would you recommend? The lower end is stock.
Tony Jones
Bay City, MI

A: Lying around are many big-blocks just waiting to be picked up and installed in our early iron. Finding a low-mileage, late-model Gen V big-block will give you great service in your weekend cruiser. Swapping out a few components will really wake up the manners of your engine.

The ’94 Gen V 7.4L 454 goes under the L-19 engine designator. This was a throttle body fuel-injected engine with what are lovingly called peanut port oval-port cylinder heads. It is also equipped with a hydraulic flat-tappet camshaft. The four-bolt main, one-piece rear main seal short-block will give you a great foundation to build upon. A very nice swap is the Edelbrock Performer aluminum oval ports, PN 60459. These heads feature an 110cc combustion chamber with the 290cc early big-block-type oval ports and will raise your compression ratio to about 8.75:1 from the 8:1 your engine currently has. They come completely assembled with 2.19/1.88-inch stainless valves and dual valvesprings for hydraulic flat-tappet camshafts. These cylinder heads will wake up the torque and horsepower of your Monte, easily giving you around 40 hp over the peanut ports.

The only thing left is to swap out for a mild camshaft to work with your top end and headers. The production L-19 camshaft is a very mild truck profile and specs out at 192/204 degrees of duration at 0.050-inch tappet lift, 0.390/0.450-inch max lift, and is ground on 110 centers. This camshaft is great for a stock TBI engine that was made to pull families around in their Suburban. Your Monte needs a couple more degrees of duration and some lift to boot. Go with a COMP Cams Xtreme Energy XE256H. This will give you all the grunt that big-block has to offerand pick up a good deal of horsepower too. This camshaft comes in with numbers of 212/218 at 0.050-inch tappet lift, 0.480/0.485-inch max lift, ground on 110 centers. The heads and camshaft will wake up the mild truck engine you have. It will make over 500 lb-ft of torque, and in the 400hp range for power.

The heads would give you a nice boost, but the camshaft will round out the package. Also, why would you want to dive in there again after you find that the stock cam won’t rev past 4,500 rpm? Enjoy your new power!

Cut And Shim
Q: I am building a small-block 400, which had a flat-tappet camshaft, but now I’m installing a COMP roller cam. I also have a one-piece aluminum timing cover and I’d like to know which cam button to use. Also, how do I set up the backlash? Thanks for your help.
Anthony Obrien
Ocala, FL

A: With the stack up of components you must measure and cut or shim the camshaft button to achieve the desired endplay of 0.005-0.015 inch. There are a few tricks and different buttons available: Torrington bearing thrust buttons (PN 200) and Nylon thrust buttons (PN 202) are available from COMP Cams. You can also get aluminum buttons from Milodon (PN 10775) that work great with steel front covers. Finally, we like using a camshaft lock plate, which has tabs to lock the bolts in place, and also retains the thrust button in the camshaft gear. Check out COMP’s lock plate, PN 4605.

On a racing-only engine, we prefer the Torrington bearing thrust button, but on the street, a solid-type button is preferred. The chance of losing one of the little needle bearing rollers is just too great for long-term street use. Also, since you’re running an aluminum front cover, we wouldn’t want to run aluminum-to-aluminum and chance the two pieces getting happy with each other and galling. You could use the nylon-type button with your aluminum cover. Hopefully, your one-piece aluminum front cover has a hole plugged by a 1/8-inch pipe plug. This hole is in the cover to check the endplay of the assembled front drive and it allows you to run a dial indicator through it and comes in contact with the camshaft timing gear. If your cover doesn’t have this hole, you’ll need to check the endplay at the rear of the camshaft before installing your rear cam plug. Assemble the cam drive system and install the button for a baseline measurement. Using the front cover gasket you intend to use, install the front cover and torque the 101/4-inch fasteners to 100 lb/in. Make sure the cover is pulling up to the gasket. If not, check the slight air gap between the cover and the gasket for your initial cut of the button. With a dial indicator either through the front cover or on the rear of the camshaft, check the endplay. You can move the cam by gently using a screwdriver through a lifter hole lightly on the side of a camshaft lobe. If you have no endplay, cut the camshaft side of the bushing 0.010-inch at a time until you achieve an endplay reading. If you have a slight amount of endplay and you’re below the desired 0.005-inch, cut the button to get you between 0.005 and 0.010 inch. If you have over the spec of 0.015 inch of endplay, you’ll need to add a spacer between the button and the face of the camshaft; stainless shim stock or very thin washers work very well for this.

Well, there is your long answer for a short question. It’s a simple process that takes a while to get right. Be patient and take your time. Check everything twice and cut once. Good luck. CHP

Technical questions for Kevin McClelland can be sent to him at



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