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August 2010 Chevy High Performance Q & A - Performance Q & A

Kevin McClelland Jun 17, 2010
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All Dried Up
Several weeks ago, we were racing our wagon in bracket mode at Auto Club Raceway in Fontana, California. This was our second race back with our pump-gas LT4 350 engine under the hood, and Daniel and I were both racing the car in the same class under a double entry. Over the two days of racing, we made more than 20 runs. As I would have expected, Daniel went one round deeper into eliminations each day!

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I usually go to the line to watch his staging technique and the launch of the car. On Saturday, I noticed a very slight drip of fuel coming from our MagnaFuel 275 pump just as he was about to stage. Getting back to the pits, we could let the car idle, shake it, run the fuel pump alone, and it wouldn't leak. I tightened the pump cover slightly (nothing was loose), and off to the next round we went. I ran at the beginning of eliminations that round and Daniel didn't see anything, so I thought we had it fixed. Well, as Daniel was staging that round, there was the unsightly drip again, only it caught the attention of the starter. Luckily enough, with the amount it was leaking it wasn't an issue.

Now that I have the pump off the car, I think I've figured out the problem. I certainly don't blame MagnaFuel. I attribute it to the fact that we run both Rockett Brand 111-octane race fuel for the stocker engine and Chevron's finest 91-octane pump gas. The amount of alcohol blended into pump gas these days is tough on seals, non-stainless lines, and steel-braided lines. Pumping the system dry to switch over from fuel to fuel is also taxing on the fuel pump shaft seal, where it appears the leak was coming from.

This will be the last time I'll be pumping it dry. I stopped pumping as soon as the fuel was out of the system, but even that was too long and I've since resealed the pump with a fresh rebuild kit and it's happy again. Please keep an eye on any steel-braided lines you may run on your street cars. I've seen the lines fail and leak right through the braiding. If these are anywhere near hot exhaust or spark, it could be the end of your toy-or worse yet, someone could get hurt-so be smart and be safe out there.

Head Play
Q: I am putting a ZZ502 into my '67 Malibu, and I got rectangular-port heads with it and don't know what compression ratio I will end up with. All parts are factory and have never been started. The heads that go with this ZZ502 are PN 12363390 oval-port with 110cc combustion chamber, 110cc exhaust, and 290cc intake. The heads I have are PN 12363400, also new, with an 118cc combustion chamber, 110cc exhaust, and 300cc intake. The 502 with the oval-port heads are 9.6:1 ratio. I guess what I am saying is I don't want the ratio to get too low. This car is just a street machine, driven a few times during the summer. If you could get back to me with your thoughts, I would be eternally grateful as I am about ready to put the heads on if you think they will work OK. Thanks a bunch in advance.
Richard Griffith
Via email

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A: Very cool car-'67s are a favorite two-year body style. Stuffing a ZZ502 in one only makes it better. If we were you, we'd keep the oval-port heads on the engine. Let's get into the reasons why.

The rectangle-port GM Performance aluminum heads you have are based on the oval-port heads on your ZZ502. The only difference is that the port entrances are opened up to the rectangle shape. This is why the port volume is only 10cc larger than the oval-ports. We've spent many hours with a grinder, porting the GMPP rectangle heads just to get them up to where our good cast-iron rectangle-ported heads are-we were hoping for much more.

The other downfall is that the chambers are 118cc. You can clip them about 0.035-inch and get them down to 115cc, but you really start cutting into the intake valve seat. As you stated, the 110cc oval-port heads give you a static compression ratio of 9.6:1. With the larger 118cc chambers you'd drop the compression down to 8.75:1. With the camshaft installed in the ZZ502, the lower compression will drop your idle vacuum, and power will drop significantly.

So stick with those oval-ports. You'll be very impressed with the massive torque this engine puts out. It'll make your '67 a real blast to drive.

Let's Get Wired
Q: I'm building a street/strip Nova for my brother while he's away making license plates, and I can't get her to start up all the time. Usually she just gives me the starter "click" and won't even try to turn over. The motor is a 383 SBC, around 10:1 CR; the starter is a Powermaster Ultra Torque and has been bench tested and works as it should. The battery is a brand-new, fully charged DieHard Gold with 795 CCA. I have a kill switch mounted at the back of the car and a junction block under the hood to provide power for the fuel pump, fan, small air compressor for rear shocks, and ignition. I have it wired as follows: battery ground to unibody near passenger-side rear wheelwell, battery hot to switch, hot side of switch to starter and junction block, alternator directly back to battery hot, and then I have one ground strap from the engine block and one from the fender to the subframe. Everything works: the lights, compressor, pump and so on; the car just won't start. Electrical has always been my weak spot and any help would be appreciated.
Via email

A: Wow, where does one find a brother like you? Very cool, and thanks for the nice wiring diagram to explain your wiring. Usually, when the battery is relocated to the trunk it's a ground problem.

You have the battery grounded to the unibody near the passenger-side wheelwell, and then you have a ground strap attached from the block to the subframe. You also have a ground strap going from the fender to the subframe. The factory subframe is mounted in rubber, which insulates the subframe from the unibody. The only chance of a ground is through the strap from the fender to the subframe. Usually there is too much paint between the fender and the body where it attaches to have a very robust ground. After many years of trying to use the unibody as a ground path for battery relocation, we went to running a ground cable directly from the battery to the tailhousing of the transmission. This ensures a direct ground path from the battery to the engine block via the trans case. We've never had a ground issue with battery relocation since. Even on full-frame cars, we run ground cables from the battery to the trans. It just gives another level of insurance that you won't have an issue.

We've seen where the battery will try to find a ground through anything. It usually attacks the trans shifter cable and welds it together! Install a ground cable and your starting issues will be a thing of the past. Hope your brother appreciates all your hard work, and again, very cool.

Old-School Buggy
Q: I have a '70 LT-1 with original pistons, 76cc heads, and a Chet Herbert cam, and the specs are 0.480-inch max lift, 248 degrees duration at 0.050-inch tappet lift, and 106 lobe separation angle installed at 103. I'm running a 4,200-stall converter, and the engine is installed in a 3,800-pound buggy.

The problem is timing. I need to get 36 degrees at 3,000 rpm and 16 degrees at idle. Right now it is 20 degrees at idle and 42 degrees at 3,500 rpm. I achieved this using manifold port for vacuum. I would like to get rid of vacuum and somehow make stop bushings for the mechanical advance. Is this possible on a stock HEI? MSD does it; why can't a stock HEI achieve the same? Also, do you think an Edelbrock Torker II with a carb spacer would be OK? Max rpm is about 7,200 rpm.
A fan
Lansing, MI

A: You're right on track with getting your timing off vacuum control. As you open the throttle and the manifold vacuum drops, you are losing ignition timing. Once you get your mechanical advance dialed in, you won't believe how much power you will pick up.

The MSD distributor gives you the ability to adjust the amount of mechanical advance by swapping different diameter bushings that adjust the amount of advance. The larger the bushing diameter the less mechanical advance you have. You can achieve the same result by welding up the slots in the mechanical advance plate and limit the amount of advance. Dissemble your HEI by driving out the roll pin in the distributor gear. Make note of the dot machined into the side of the distributor gear by the roll pinhole. Take a good look at the mechanical advance top plate where the rotor attaches. Record where the rotor locating tag is and its relationship to the dot on the distributor gear. You must reassemble it in the same location. Once you have dissembled the mechanical advance mechanism, you'll see where the pins on the advance plate slide through the slotted holes in the distributor shaft plate. These slots are what you want to weld up to reduce the amount that the mechanical advance can travel. We'd start by reducing the travel by a third. This should reduce the distributor's mechanical advance to around 8 degrees. When you double this at the crankshaft, it will give you 16 degrees. If you go with 20 degrees initial advance and add the 16 degrees from the mechanical advance, you have a total of 36 degrees. This should work very well with the large camshaft you're running.

Next, tailor the rate that the advance comes in by using different tension springs. If you have someone local with a distributor machine (a lost art), you can spin up your distributor and set it up on the bench. However, there aren't many machines around anymore. You can do the same thing with your engine, a timing light, and a tachometer. Check out the HEI Performance Advance Curve kit from ACCEL. The complete kit comes with weights, an advance cam plate, and three sets of springs to custom-tailor your advance curve. This kit, with your limited mechanical advance travel, will get your spark right where you want it.

You have blown right past the design limits of your Torker II manifold. Also, the manifold really doesn't like any type of carb spacer. It really messes with the mixture distribution. For your application, you're right between an Edelbrock Performer RPM (PN 7101) and a Victor Jr. (PN 2975). In a buggy you want as much torque as you can get. We'd swap out for an RPM for the best all-around performance. You may lose a few ponies up at 7,000 rpm with the dual-plane design, but what you gain everywhere else will make up for it.

Enjoy your new power. If you've been using the vacuum advance to tailor your advance curve we'd estimate that you've been losing around 10 percent of your engine's output. Be careful when this thing gets dialed in.


Leaky Runners
Q: I saved up about $3,000 in two and a half years; it all went into rebuilding a 5.7 TPI engine with a Comp camshaft and roller rocker arms, a geardrive, a 10-inch stall converter for a 700-R4, and a transmission cooler for my '92 Z28 convertible.

I picked up the car and after driving about a block I knew right away it was not running like it should. My mechanic adjusted the timing, but he didn't really know what else to do. From what I can hear, see, and feel from driving it around, it just seems like it's completely underpowered. The strange thing is, it's burning a lot of fuel and I can hear air leaking from the engine; it's idling high, and the "check engine" light stays on. For the time being, I'm not driving it because I have too much invested and I'm scared of burning it up. Please help! I really need your expertise on this one. Tigs Pacoima, CA

A: You've got a very common problem with the TPI injection. The TPI system is comprised of a plenum, runners, and a manifold base. These components have gaskets to seal them to each other. The four tube runners have an additional small tube that on one side transfers the idle air to the manifold base to equally distribute the idle air to each cylinder, and on the other bank the small tube is used to transfer exhaust gas from the manifold base up to the plenum to feed the EGR distribution holes directly behind the throttle body. If you accidentally put the left gasket on the right side, there will be a large vacuum leak, which creates all kinds of problems like those you're experiencing. The only way to fix the problem is to dissemble the intake and replace the gaskets. You can try to swap the gaskets, but they are rather fragile. Also, you don't want to have to take the thing apart again.

Get the gaskets on the correct side and enjoy your convertible. Sorry your mechanic did the switch-a-roo. We're sure he won't want to hear this answer. Don't beat on him too hard-we've all done it!

Hard Line
Q: I loved the article on brake line replacement by Sean Haggai in the Dec. '09 issue. I have a '70 Chevelle and am getting ready to change from drum to disc on the front. I'm also rebuilding the frontend and am glad to see they have a new set of lines and rotors that will work with my 14-inch wheels. I really like to buy American-built products and plan to get my kit from Inline Tube. What can you tell me about silicone brake fluid? I don't know anyone who has used it. Can it be used in the new system or should I stick with the original? Also, what is the advantage of the 2-inch drop spindles? I like my Chevelle's stance the way it is, but I also know things change with new products. What do you think? Love to read your articles; they are informative and entertaining!
John C. Moore
Trenton, SC

A: Glad to be of service. New brake lines from Inline Tube really clean up any restoration. Over the years, the original lines can rust out and have the fittings rounded off by abuse or, in your case, by adding front disc brakes.

Silicone brake fluid (DOT 5) is some really nasty stuff. This came on the scene about 30 years ago. It was going to revolutionize brake fluid with its very high boiling point and resistance in attracting moisture. Well, the first thing that happened is people added silicon fluid to standard DOT 3 fluid and, well, the two fluids really don't like each other and the combination turns the fluid to a congealed mess. If someone does this, they basically have to replace the entire hydraulic system. There are a few motorcycles and other specific applications that use silicone fluid. Please read any owner's manuals and make sure what type of fluid is used in any application.

The best bet is to stick with a quality DOT 3 brake fluid and flush the system approximately every 30,000-50,000 miles. You can tell when the fluid is getting contaminated with moisture when it changes color and goes from near clear to a brown tint, then to black. Moisture-contaminated fluid is when you'll get rust in your calipers, wheel cylinders, and master cylinder. It's much cheaper to swap out the fluid occasionally than to replace these expensive components.

Drop spindles do just what the name states. They raise the spindle in relation to the ball-joint mounting, whatever the dimensions of the design. A 2-inch drop spindle will lower the ride height with no other changes by 2 inches. The benefit of lowering a car with drop spindles is that you do not reduce the suspension travel. When you lower a car by lowering springs you lose that amount of suspension travel on the compression side-and alter the suspension geometry. The added benefit of using drop spindles is that you lower the center of gravity of your car, which gives you improved handling by reducing body roll. However, if you like the stance of your Chevelle with The General's spindles, then leave it alone!


Vapor Trail
Q: I have been enjoying your Performance Q&A column for a few years now; you do a great job. Now I need your help. My son and I have a '69 Camaro we take to track days. Unfortunately, it has had a nagging coolant leak since we first dropped in the ZZ385 crate engine about a year ago. The first leak was at the back of the intake manifold on the driver side, right where the head, intake, and block come together. We fixed that and soon had another leak at the head gasket, just above the headers. It wasn't long before we noticed vapor coming out of the tailpipe. We will be changing the head gasket soon, PN 12557236, but I am not sure what may be causing this. Could it be the Dexcool-equivalent coolant we are using? Or the lack of a bypass hose between the water pump and intake manifold? The engine only has a few thousand miles on it. Track officials frown on leaking fluids, and any suggestions would be appreciated. Also, do you know the head bolt torque setting we should use on the aluminum heads?
Gene Welch
Daly City, CA

A: First, I've never liked the Vortec bolt pattern for the intake manifold. This, combined with the fact that your Fast Burn heads are dual-bolt pattern (both early and late Vortec manifold patterns), you have very little sealing area between the cylinder head, manifold gasket, and manifold. Finally, the production plastic/silicon sealing ring manifold gaskets have issues leaking on the production L-31 Vortec engines.

The ZZ4 short-block that your Fast Burn 385 is built on has an internal bypass at the front of the passenger-side deck that passes from the cylinder head and into the inlet side of the water pump. This is a very small bypass in relation to the volume that can be pumped. If the engine is run at high rpm before the thermostat has a chance to open, you can build very high pressure in the cooling system. This could compromise the gaskets. For many years on all big- and small-blocks we've been drilling a couple of 3/16-inch holes around the perimeter of the thermostat. This gives you additional bypass volume and gets the hot water up to the thermostat to open quicker.

When you remove your cylinder heads to replace the gaskets, replace the factory-style intake manifold gaskets with Fel-Pro PN 1255. These are composition-type gaskets that will compress and give you a better chance to seal the limited sealing area. When installing these gaskets we prefer to use a contact cement gasket sealer to hold the gaskets in place. Gasgacinch Gasket Sealer has been around forever, and you can't beat it. Paint the cylinder head side of the gasket and the intake flange of the head with sealer, and let it dry. Then use a high-quality silicone sealer like Permatex #598 Ultra Black Hi-Temp RTV around both the head and manifold side of the intake gaskets in the water passage region. It doesn't take much. A very thin layer of sealer around the water ports will do it. Once you have coated both sides of the gasket around the water ports with silicone, place the intake gaskets to the head flange. Be very careful when placing them on the heads. You will want to be in perfect alignment when you set them down. The Gasgacinch will hold them right in place where you place them. Now, use Ultra Black to seal the end seals of the block to manifold with a nice 1/4-inch bead.

Finally, we don't think your issues are due to your coolant. Your cylinder head bolts should be torqued to a value of 65 ft-lb. You'll want to apply a Teflon sealer to the threads of the head bolts to prevent water from migrating around the threads and up around the heads of the bolts. The head bolts come from the supplier coated with a sealer. Clean off the remainder of the sealer with a wire wheel and apply new Loctite PST #565 Thread Sealer. This will best replicate the factory sealer.

Good luck sealing up your little small-block. Following the above practices should give you a leak-free seal. Sometimes it's tough to find Gasgacinch at your local auto part stores. Edelbrock has sold Gasgacinch packaged in its containers for over 30 years and can be order under PN 9300 through any of the mail-order outlets


Saftey First
Q: I recently bought a used NOS Super Powershot kit with a bottle heater and purge valve kit, and I want to make sure I am doing everything right. It's going on my '79 Malibu. The motor is a 350 with a stock bottom end, cam specs unknown (very mild), a 670-cfm Street Avenger on a Edelbrock Performer intake PN 2101, Hedman full-length 1 5/8-inch headers and 2 1/2-inch dual exhaust with an X-pipe running through Flowmaster Super 40 mufflers. The rest of the drivetrain is a TH350, soon to be replaced with a TCI TH700-R4, an 8.5-inch 10-bolt with 3.42:1 gears, and the tires are P245/60R15. I've never run nitrous before but have read quite a bit about what is needed. I was planning on starting at a 75 shot and not going any higher than 100. Any advice you could give would be greatly appreciated. Mike Senay Pitt Meadows, BC, Canada

A: You're taking the right approach by reading up and asking questions on the front end. Nitrous power can be intoxicating, and moving up the jet sizes is very easy. Let's go through this for things to look out for.

First of all, you'll want to make sure your fuel system is up to the test. Nitrous is an oxidizer and carries no energy (fuel) with it. Any power increase made with nitrous must be accompanied by additional fuel. If not, it can be just like a cutting torch burning through pistons and blowing out head gaskets. It's not a pretty sight. The factory fuel delivery system on the '79 Malibu is weak at best. The fuel pump barely keeps up with a stock 350, not to mention one with some performance add-ons. You'll want to upgrade the mechanical fuel pump to a Carter mechanical pump PN M5900P, from Jeg's or Summit Racing. It's very user friendly, delivering 5.5 to 6.5 psi of fuel pressure and doesn't require a fuel pressure regulator after the pump. It will deliver 120 gph fuel flow, feeding your 350 and small nitrous system with enough fuel.

Now that we have enough fuel to feed the beast, let's look at the nitrous side. Since you are the second owner of this system, look over all the solenoids and make sure that nothing is plugged or stuck. Also, some of the AN fittings feeding the solenoids may have stainless steel screens to prevent trash from entering the valves. Check that all screens are clean and clear. When installing the bottle, lines, and hardware, purge a small amount of nitrous through the line before connecting the feed line to the nitrous solenoid. This will blow out any trash that may be sitting in the long feed line from the trunk.

Using a bottle heater is the best way to maintain the optimum 900 psi of bottle pressure. The nitrous system jetting is based on a nitrous line pressure of 900 psi and approximately 4 psi of fuel pressure. This gives you a safety margin. If the nitrous pressure drops below 900 psi the mixture from your system will be on the fuel-rich side. Conversely, if the fuel pressure drops below 4 psi you'll be lean on fuel and damage could occur.

Small nitrous shots (75-100 hp) won't require you to retard the ignition timing. Any higher than 100 hp and we'd recommend retarding the timing approximately 4 degrees for a 125hp shot.

The last safety precaution we'd recommend is that you incorporate an MSD Window RPM Activated Switch PN 896 into your system. This will allow you to select when the nitrous is applied by rpm. To prevent engine damage, engage the system when the engine is at full throttle and above 3,500 rpm. Set the high side of the window switch to 5,500 rpm. This will give you a window of 2,000 rpm that the nitrous is activated and prevent excessive cylinder pressure at low rpm, where most of the engine damage occurs. Use this switch in conjunction with a Wide Open Throttle switch to ensure that you're at full throttle before the nitrous is engaged. Another nice safety feature of this is that you have both hands on the steering wheel when you're playing with the nitrous.

This should get you safely into the nitrous age without damaging your engine. You'll have a blast with the added boost of instant power. There's nothing like the surge of torque when the nitrous comes on. Have fun and be safe!


Technical questions for Kevin McClelland can be sent to him at



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