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NHRA Chassis Certification - Performance Q & A

Kevin McClelland Feb 15, 2010

Kevin McClelland

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All Cracked Up!
When was the last time you checked all the welds on your race car? Probably never. NHRA requires that the chassis of a race car that goes 9.99 seconds or quicker, or 135 mph or faster, to be certified every three years. This certification is an inspection of the thickness of the chassis tubing with a sonic tester. There are a multitude of specs for the different diameter tubes and their location in relationship to the driver.

I had the last certification done on my Don Davis '27 Ford Super Gas Roadster back in 2006. This year it came up for recertification, and NHRA has changed the SFI specifications for this type of side-steer Roadster, now requiring helmet bars in the rollcage, rollcage gussets, and several new bars in the driver area. The car was originally built back in 1995 and I'm the third owner. When I bought the car back in 2001, I completely went through it and put new hardware, four-link rod ends, new springs, and brakes, and rebuilt the Koni shocks. I've done regular service to the rest of the car over the years.

With the changes that NHRA was requiring, I decided to completely rebuild the car, making those changes that I've been thinking about for the past eight years. The car is completely down to the bare tubing. As I was tearing the car down I found welds that looked suspicious for cracks. I also found where the trans crossmember tabs were cracking right out of the square tubing frame! The chassis is currently at the sandblasters having all the paint and primer stripped off. This will give me complete access to all the welds to inspect for irregularities.

I'm finding this on a standard mild-steel chassis. Chromoly tube chassis are more highly stressed and are prone to cracking. Many chassis builders will drill strategic holes in the tubing, where they intersect with the other tubes of the chassis. These holes will create an air path throughout the entire chassis. If you plan out the build of the chassis you can install a 1/8-inch pipe bung in the tube so you can pressurize the chassis to check for cracks. This is a very simple and effective way to inspect and repair your race car.

Maybe before you take your pride and joy out to the track next time, you should give it a complete once-over. Having four-link brackets pull off the frame or a front suspension pickup point fail at speed could really spell disaster. Take the time to make sure that you and your toy are safe.

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Loaded Question
The driving force behind this is the article in the Dec. '09 issue, "LS Motors Decoded." So in the interest of putting some amazing 21st century technology into my '68 Corvette while keeping the original factory 427ci she was built to contain, I have a question that I'm sure has been at the back of everyone's mind: What are the maximum bore/stroke combinations that these Gen III and IV LS engines can take? Thank you in advance. Jason Bellevue, NE

This is truly a loaded question. There is a displacement max for factory production engines. Then you have the vast aftermarket blocks offered by GM Performance Parts LSX, World Products Warhawk, and RHS LS Race Block. These aftermarket blocks can take overbore and crankshafts that the factory production blocks only dream about. Putting a 4-inch stroke crankshaft into a production block is old hat. We've heard of windage problems with stroke lengths over 4 inches, but there are many buildups out there using factory blocks with 4.250-inch strokes. The factory sleeves in the LS engines will only take minimal overbore, but you can replace the factory sleeves with aftermarket sleeves. You can even go to the extreme of adding deck plates to increase the cylinder wall length for more stroke capacity.

As for the maximum engine displacement of an LS engine design, the GM Performance Parts block comes in the winner at a max bore of 4.250 inches and a stroke length of 4.50 inches. With this combination you will have a displacement of 511 ci! Now that's one nasty small-block.

With a production Gen IV engine block of 4.060 inches and a 4.125-inch stroke crank you achieve a displacement of 427 inches. If you step up with an LS7 block, with its 4.125-inch bore, or sleeve a production LS1 with the 4.250-inch stroke, you will see 454 inches of nastiness. Hope this has whetted your appetite.

Aussie Runner
If you can help me with this one-off special I'd be very grateful. I'm not trying to reinvent the wheel, but here goes. To satisfy the rules of the Lawmen we are restricted to a 308-cid engine, so we want to use a few legal and irregular options based on a 350 block and a 3.1-inch-stroke crank which should fit nicely (I hope). Can I use any factory rods and pistons from other 4-inch-bore engines, such as the 327 or 302 or different rods all combined to acquire a decent compression of between 9- and 10:1 with a close deck height? The cylinder heads would be 461s and the cam would be 222/222 from the 350/290hp series flat-tappet, which is plenty for my needs. The carb would be a Barry Grant 575 Demon and I would use the standard GM HEI. Hope you can help, and all the best from Noel in Oz. Noel Foreshew Sydney, Australia

Where did you come up with a 3.10-inch-stroke crankshaft? Here in the States GM only used that in Gen I engines in 1975 through very early '77 in Chevy Monzas and Novas in their 262ci small-blocks. This engine was very short lived because of its weak 110hp rating. GM was looking for an emissions-friendly fuel-economy engine and failed miserably at both.

Down under, Holden may have used this combination longer for you to have your hands on one of these cranks. Or do you have a specially ground crankshaft that was used in some type of racing engine? Either way, you could use factory 302 pistons for your 308 buildup. The only issue is that the pistons are going to come up out of the deck by about 0.025-inch. You can have a set of factory 5.7-inch small-block rods offset-bushed 0.025-inch down and shorten the rods to 5.675-inches. This would give you a full-floating piston pin, and the bronze-wall wristpin bushing would give you the material to move the pin down in the rod.

Going with a slightly shorter connecting rod will allow you to use factory 302 small-block pistons. They had nice forged TRW slugs from the factory with an approximately 0.125-inch dome, which gave you 11:1 compression with 64cc combustion chambers. Speed-Pro now only offers one piston with a 12:1 dome. For a really nice piston check out Wiseco Pro-Tru forged pistons, PN PT042H, offered in 0.030-, 0.040-, or 0.060-inch overbore. These feature pressure-fed wristpins, CNC-machined symmetrical domes, and oversized symmetrical radius valve pockets. They come in at 11.1:1 compression with a 64cc combustion chamber. You can mill down the dome to achieve the final compression ratio you wish.

Hope this keeps the Lawmen happy. Good luck with your little Mouse.

Hot Big-Block
As an avid reader, I really appreciate the effort you put into helping people with their problems. I was hoping you could help me with mine. My '68 Camaro has a 325hp 396 with 5,000 miles on it. On hot days, say 90 degrees F and up, if I get stuck in traffic the temperature climbs from 180 until it overheats at 230.

I've tried everything: an oversized 26-inch aluminum radiator, a Weiand high-flow water pump, numerous thermostats (high-flow, low-flow, 160, 180, 190), and three electric fans (the last being a Flex-a-lite 3,300-cfm). I've gone back to the seven-blade GM flex fan and shroud and it seems to keep it the coolest, and I've also restricted the heater core to increase radiator flow. I can't determine if it's airflow or coolant, as it definitely benefited from both of these.

The car has stock pulleys, and I was thinking about altering or restricting the water pump bypass or adding a pusher fan. I'm out of ideas. Please help!
James Hodgson
Heidelberg, ON, Canada

We had similar problems with my dad's '55 Chevy with a 468 big-block. Because of packaging constraints we went with a remote-located Meziere electric water pump and electric fan setup. This finally took care of the slow-speed build of temps. We don't think you're there yet.

The Flex-a-lite 3,300-cfm fan arrangement should have taken care of the airflow requirements at idle. Is it possible that the air is recirculating back in front of the radiator, feeding hot air to the radiator over and over? Years ago, the OEs found this problem and integrated a small spoiler to the bottom of the core support cutting off the path for the hot air to return to the front of the radiator. Without making any other changes to your system, we would create a simple (cardboard) spoiler to attach (duct tape) to the core support. Since the overheating problem is while the car is in traffic, you should be able to do this test in your driveway.

Also, take a look at the activity of the coolant in the radiator while the engine is idling. Of course, do this on a cold startup so no one gets hurt. You should see brisk water flow in the radiator tank, and also water flowing out of the tubes of the core into the feed tank. You'll need to watch the tank and feel the upper radiator hose to know when the thermostat has opened. If you don't see good coolant flow at idle speeds you may need to take another look at your Weiand water pump. Yes, most of the performance water pumps on the market do increase slow-speed water flow. Sometimes parts can be built out of tolerances, and it may flow well at higher engine speeds but have low flow at idle.

You'll find a solution to your heating problem. We really like what you've already tried. Restricting the water bypass will help. You can completely block the bypass and drill a couple of 3/16-inch holes around the perimeter of the thermostat. This not only gives enough water flow for cold start, it also bleeds out all the air in the cooling system when filling. Find that problem soon so you can enjoy your Camaro.

Bleed Baby Bleed
I did the Hotchkis upper control arm upgrade on my '78 Chevy Malibu and have had a soft brake pedal ever since. Now my emergency brake light is on. I have the stock drums in the rear. Do I need to change my master cylinder? Or is there something else? Thanks for your help.
Joshua Eye
New Bern, NC

When you installed the Hotchkis upper control arms, did you remove the calipers, or did you just support them out of the way? It sounds like you had to remove them and didn't properly bleed the brakes (remove the air from the brake hydraulic system). When you have air in the system, you will have a soft or spongy brake pedal. Your emergency brake light is on because the distribution valve down on the framerail has shifted, which turns on the light. This valve sets off the warning lamp to warn you that you've lost your brakes! Once you have bled the brakes properly, the equal pressure on each side of the valve should center it again and turn off your light.

Bleeding the brakes is very simple. Put the car up on jack stands and remove the front wheels. Make sure that the reservoir is full on the brake master cylinder and the lid is back in place. Have a helper depress the brake pedal and release it three times, holding pressure against the brakes at the end of the third stroke. First, open the passenger-side bleeder on the brake caliper. This should release some fluid and the pedal will drop to the floor. Before your helper releases the brake pedal, close the bleeder valve on the caliper. Now you can release the brake pedal. Do this cycle about three times and refill the brake master cylinder. You should find that at some point that you will have a burst of air come from the bleeder at the caliper. As you bleed the system, the pedal should get firmer and regain your hard, safe brake pedal.

Anytime you break the hydraulic system of the brakes, or a hydraulic clutch system, you must bleed the air out. Air compresses and gives you a very spongy pedal, and if there is enough air, the brakes will not work.

It's A Spring Thing
My '69 Camaro is about to get a 350 LT1. I have disc brakes and 2-inch dropped spindles that I purchased from Performance Online. The brakes consist of 13-inch rotors with dual-piston aluminum calipers. To round out the frontend package, I also have a set of Performance tubular A-arms. I intend to put QA1 single-adjustable shocks on it. What front springs do I use: stock or 2-inch drop? It will be used for street, and maybe an occasional dragstrip or autocross. Also, it will have A/C. Thanks for your help.
Scott Langston
Fort Wayne, IN

Which front springs you choose is completely dependent on what you wish to use your car for. You stated that you would like to drive it on the street, play on the dragstrip, and toy with autocross. All three of these disciplines take different types of springs and finding a happy medium can be a challenge.

What do you wish the ride height to be? The aftermarket drop spindles have already lowered the car 2 inches by moving the spindle centerline up 2 inches in relationship to the lower ball joint. If you also install 2-inch lowering springs, the car will be 4 inches lower than stock. The front subframe may find the pavement driving around on the street in normal driving. You need to answer this question first. Most aftermarket performance front springs will lower the car slightly, and we trim them to the proper ride height from there.

Springs are designed differently for handling versus the dragstrip. For handling you'd want to increase the spring rate of the spring to prevent body roll and load the outside tire for grip. In drag racing you aim to run the lowest spring rate possible that will support the weight of the car. A light spring-rate spring that is highly compressed will aid in the weight transfer to the rear tires on the launch. We would go for a street-handling performance spring. Check with Eaton Detroit Spring; we've used them several times to make springs for oddball applications. Eaton has the factory prints from all the domestic auto manufacturers in the muscle car years and could build you a big-block spring-rate Camaro spring that will give you a stock ride height, or build the spring at the ride height you wish based on your measurements. Give Eaton a call for more information and visit the website and bone up on Spring Tech 101. This is a very informative handbook to educate you on the finer points of spring design and selection.

Cam-Converter Honeymoon
I'm selecting a camshaft and torque converter for my '69 Corvette Stingray. This will not be a daily driver and will need to run well on pump gas. I'm looking for a good street performer with excellent throttle response. I'm more interested in low to midrange torque than high-end horsepower. The car is equipped with a 3.08:1 gear in the rearend, so I know that will make things a little more challenging. I'll also be upgrading from the TH400 to a 700-R4 at this time. I just feel like the relationship between the camshaft profile, torque converter stall, transmission gear ratios, and rearend ratio are critical to get the performance I'm looking for. I'm also concerned that with a 3.08:1 rear ratio, I have the proper powerband to enjoy overdrive in Fourth gear.

Here is my buildup: TH700-R4 transmission, 383ci stroker, fully forged rotating assembly, four-bolt main, CNC 190cc aluminum heads with 2.02/1.60-inch valves. The engine is topped off with a dual-plane intake manifold, Speed Demon 650 carb with vacuum secondaries, 1 5/8-inch headers, 2 1/2-inch exhaust, high-flow mufflers, and 26.5-inch tires.

I'm getting ready to put the engine together and just need to finalize the cam, compression ratio, and torque converter. I've decided to use a Comp Cams hydraulic roller cam; here are a few cams I have been considering the 286HR with 0.050-inch duration numbers of 230/230, 0.560/0.560-inch max lift, ground on 110 centers. On the milder side I'm leaning toward the 280HR that specs out at 224/224 duration at 0.050-inch lift, 0.525/0.525-inch max lift, also 110 separation angle.

Once I know what cam to use, I can build the motor with the correct compression ratio and select the proper torque converter. Thanks.
Ken Newberry
Via email

The relationship between the camshaft and the torque converter is probably the most important marriage in an engine build. If they don't like each other no one will be happy! You're building up a really nice package. If you've been reading my column for any time you know I'm going to err to the small side. This will give you a better all-around driving package. Let's see what else Comp has to offer.

You have chosen two very nice camshafts. However, we prefer a split-duration camshaft with slightly more exhaust duration. That said, we'd go with an XR276HR profile. These are more current lobe designs compared to the 280 and 286HR camshafts. The XR profiles have 4 degrees more intensity and quicker opening between advertised duration numbers and 0.050-inch duration numbers. The XR276 comes in at 224/230 degrees of duration at 0.050-inch tappet lift, 0.502/0.510-inch max lift, and is ground on 110 centers. This will give you a very decent idle quality without having to run an overly loose converter. With this camshaft in your 383 we'd recommend a stall speed of around 2,400 rpm. Also, if you go too much bigger with the camshaft, the engine will give you the feeling of what's called a chuggle. This is a slight bucking that you can feel in Fourth when the converter is locked at slower engine speeds.

By using the smaller camshaft we wouldn't worry about pulling the 3.08:1 gear out on the open road. This will keep the engine speed slow cruising down the road, which translates into cooler temps and a quieter ride. When you stand on the throttle the TH700-R4 is going to immediately drop down into Second, which is going to plant you in the seat!

Emissions Camino
I am putting a ZZ4 H.O. 350 in my '86 El Camino and have two concerns. First is the ignition. My El Camino has the original four-wire HEI distributor and associated computer in the passenger-side kick pad. I think I'd like to retain the computer and smog stuff to keep it legal in California. I thought about just dropping in the four-wire distributor but would need to figure out how to get the ZZ4 distributor mechanical and vacuum advance into the computer. Do you have any suggestions? The vacuum advance of the ZZ4 will pose a clearance challenge if I use the ZZ4 HEI distributor.

My second concern is the existing exhaust system, cast-iron manifolds piped into single exhaust with an air-injected cat converter. I don't know of anyone who makes headers that would be temperature and mechanically friendly to the air pump, A/C, and lots of other little wired sensors, so I'm leaning toward keeping the cast-iron manifolds and going to dual exhaust with a small cat converter on each pipe before the muffler(s). Any thoughts or suggestions?

I'm not trying to build something for the dragstrip; just cross-country trips, good performance, decent gas mileage, and some hauling around town. I currently get 15-21 mpg with the 305 V-8 holding it down at 70 mph and just want something a bit stronger. I put a ZZ3 in my '65 El Camino and loved it. The rest of the package was a TH350, A/C, P/S, disc brakes, HD suspension, and 14x7 rally wheels, and I just enjoyed running hard through the curves and having people wonder what was going on. A moving van creamed me and the '65 some years back, otherwise I'd still be driving it.

I look forward to any suggestions you might share with me. I am a little busy working and going through chemo in Houston this year. Thanks and regards.
Brad Stone
Los Angeles, CA

Hearing about your '65 getting wasted by a moving van breaks our heart. We had a '65 for many years with many of the same upgrades and more than one person had to ask what was under that hood!

Back in the early '90s GM created the H.O. Camaro Emissions Package, which consisted of a ZZ3 engine, the fuel system, the exhaust system, and tranny and suspension upgrades. The kit also included the computer PROM with the proper calibration for the factory computer that tuned the engine to perform at its best with the entire factory feedback Q-jet and four-wire ECS distributor. The beauty of this package is that it produced 308 hp, emissions legal, through the factory cast-iron manifolds, single high-flow cat, and dual-snorkel air cleaner. You can replicate this package with some minor tweaks that will pass California's emissions regulations-and push the horsepower up around the 325 mark.

Let's start with the exhaust. Edelbrock offers a complete TES (tubular exhaust system) for the '83-88 Monte Carlos, Malibus, and El Caminos. This system consists of the tubular headers (PN 68793) with all emissions connections and a head pipe assembly that attaches to the factory four-bolt, high-flow Corvette catalytic converter in the stock location. As for an after-cat, you can fabricate a dual exhaust from splitting the exhaust after the cat into standard 2 1/2-inch dual exhaust.

Contact Tom Woodside at GMCOPO. He was one of the engineers on the Camaro project for GM from the beginning. He has a stash of the PROMs for the factory computer and firsthand knowledge of the modifications necessary to make your El Camino a really clean runner. You can reach Tom at 248.275.5828. He really enjoyed this project and wants to see as many on the road as possible.

Technical questions for Kevin McClelland can be sent to him at



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