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1996 LT4 Chevy Corvette Bullet Engine - Under Pressure

Performance Q&A

Kevin McClelland Dec 1, 2006
0612_chpp_01_z 1996_chevy_corvette_lt4 Cylinder_head_valve 2/1

This week at work we finally got an engine running on the dyno that had been pushed back many times by other projects. It was the original development engine for the GM Performance Parts HOT engine. It started life as a '96 LT4 Corvette bullet. We developed a cam for GM (the HOT cam) and worked with them on the dual-plane carbureted intake for the Gen II reverse-flow-cooling engines. We freshened up the engine, zero-decked the block, cleaned up the cylinder heads (minor porting), and bored the block 0.020 inch over. With the zero deck and the shave of the heads, the final compression ratio came out at 11:1. The final home for this engine is my bracket-racing '80 Malibu wagon. Back in 1996, when we originally built the engine, it produced 420 hp and ran extremely well in my '65 El Camino.

I'm a firm believer in the stock oiling system of a small-block. The only simple mod that the oiling system had was the installation of a 70-psi white pressure-relief spring from the 302 Z28 and 350 LT-1 engines. Well, when we ran the engine in and set the timing at a very conservative 28 degrees total, the engine produced 441 hp through 211/42 dual exhaust! I was very pleased for an engine this mild to produce that kind of power, and have over 15 inches idle vacuum at 750 rpm. As I was looking over the dyno sheets, I noticed that the oil pressure was hitting 82 psi at the peak rpm of 6,600 with 200-degree-F 10W-30 Castrol. This was with a stock-volume 31/44-inch pick-up and production pump. Well, we promptly removed the pump and put the production late-model Corvette pressure-relief spring back in the pump. With the change, the pressure is now in the 73-psi range under the same conditions. Now here is the fun part: The horsepower jumped from 441 to 448 just from reducing the pressure by approximately 10 psi. This was due to the load of the oil pump on the distributor and camshaft and the reduced windage in the oil pan. I'm very tempted to remove the pump again and clip a coil off the spring. I would be happy with 55 to 60 psi, and see where the power would go. Please stay away from high-volume oil pumps in small-block Chevy engines. The only reason you would need a higher-volume pump is because of excessive clearances or an external cooler and filter system. This change really got my attention.

Klickity Klack
Q I have rebuilt my engine and I installed a noisy geardrive. I tried to adjust my valves by loosening and listening for the clatter with and without earplugs. I just can't hear it. Every time I think that I have it right, I shut the engine off and the rockers are loose. The engine is a 350 small-block with a Comp Cams 280 Magnum hydraulic flat-tappet cam. The rest of the valvetrain is rounded out with a Comp Cams kit. Do you know of another way to adjust the valves or have any other suggestions?Steve Summers

A Nothing is worse than a clicking tappet noise that you can't hear! You can't hear the valvetrain noise over the geardrive whine? That sure is one loud gear drive. OK, get those covers off and let's lash the valves.

Have you ever heard of the exhaust-opening/intake-closing method (EOIC)? This is when you adjust the valves on one cylinder at a time. You rotate the engine until the exhaust valve just starts to open. This is when you adjust the intake valve. Loosen the intake adjuster until you have excessive lash. Slowly tighten the rocker adjuster while rotating the pushrod between two fingers. As you tighten the adjuster you will take up the lash until the pushrod has resistance to rotation. At this point you have achieved zero lash. Then you should tighten the adjuster a half-turn past zero lash. Now rotate the engine until the intake valve just closes. Repeat the procedure to find zero lash and give the exhaust a half-turn preload. Go on to all the other cylinders. (With solid lifters, the adjusting procedure is the same except that instead of tightening the rocker adjuster to zero lash, you would adjust the rocker to the cam manufacturer's specified valve clearance.) This should give you a good performance valve adjustment. Don't burn your fingers!

Very Early Rat
Q I have an engine block with casting number 3855961. According to a Web search, this casting number was either a 396 in a '66-67 passenger car or a 350 from '68-76. Is there a way to tell if the engine is a 396 or a 350? It is just the bare block with no heads or crank to compare. Also, the block is missing the main caps. Will any other set of main caps fit, and will the caps have to be machined in any way to ensure a tight fit? The guy I purchased the block from 18 years ago said it was a virgin block out of a Corvette! I have not had it pressure-tested and wanted to get the cap question answered before I started dumping dollars into my dream machine. Thanks.Frank Flore

A After checking on, my favorite casting-number Web site, I found that your block is a 396 from a '65-66 passenger car that could have had either two- or four-bolt mains. This could have been an original Corvette block if it has four-bolt mains, but if it's a two-bolt, it is probably from a more pedestrian Impala or the like. Yes, you can install other main caps from a donor block. However, you will need to find a set-and a good machine shop to install them. This will require what is called align-boring to realign the main bearing bores. If the block is a four-bolt, it would be worth it; however, if it's a two-bolt, you should look for another block.

A quirk of the early big-blocks was that the oil-lifter galleys were fed oil through a groove in the rear camshaft journal and a grooved rear camshaft bearing; this was only on the '65 and '66 models. Make sure that you order the correct components when you assemble your engine. You will need the grooved cam and bearing. For '67 and later, GM grooved the camshaft-bearing housing in the rear of the block to feed this oil supply.

Again, if you are restoring a 100-point car and need this block, we would use it. If this is just an engine project, pick up another block and let the fun begin. Make sure that you get a '67-and-later block so the interchangeability that the big-blocks are so famous for will be your friend.

Shocking, Isn't It?
Q I have a '73 Chevy 350 in my '71 Chevy Nova, and one of my cylinders is not firing. How would I go about checking which one it is, and what can I do once I find which one it is? Any help is greatly appreciated.Joe Raggio

A Engine misfires can be pesky to find (at best). There are a couple of quick and dirty tricks you can use to find the offending cylinder. First, do you have headers in your Nova? Hope so! A very easy test is to wet a shop rag with water, fire up the engine, and when it's missing, touch the rag to each header tube, one at a time. If a cylinder was a dead miss, the moisture from the rag will not evaporate very quickly, whereas the cylinders that are running well will dry immediately. If you don't have headers, use insulated pliers to disconnect the spark-plug wires from the distributor cap. You will do this one cylinder at a time. Disconnect the plug wire, and if the miss gets worse, reconnect it. If the miss doesn't change, you have found your cylinder.

As for why your engine is missing, it could be a hundred different things! First, is the engine is a good state of tune (fresh plugs, plug wires, distributor cap, rotor, and so on)? If so, go straight to a compression test of the offending cylinder. You should check all the cylinders and record the results. You shouldn't have any cylinder that is lower than 10 percent of the highest cylinder. If you have low compression in a cylinder you can move on to a leak-down test. This is a special tester that regulates compression through a set of gauges that read out in percentage of air leakage. With this air pressure you can pinpoint if the leak is through the intake valve, the exhaust valve, or a blown head gasket.

If you find that you have good compression, pop off the valve cover for the missing cylinder. Check for a flat camshaft-you should be able to see this with your eyes. Turn the engine over and watch the valve lift on the intake and exhaust. They should be very similar-looking in max lift.

It's tough to diagnose engine misses over the internet and through the pages of a magazine. I hope I've given you enough clues to look in the right places. Be patient and double-check everything.

CCC System
Q I recently rebuilt the 305 in my '84 Camaro Z28. I bored and stroked it to 334 cid and installed a Lunati cam (204/ 214 duration with 0.420/0.442 inch max lift) and a set of Edelbrock TES headers. All emissions equipment was reinstalled and is functioning (as it must be in New York). I am also using the stock ECM and the computer-controlled distributor and Rochester Quadrajet. I set the timing at the factory-recommended 6 degrees BTDC. Although I did not cc the heads (GM Vortec with a Vortec dual-plane manifold) I believe that the compression ratio is about 9.1:1. The stock compression ratio with the old 58cc heads was 9.5:1. I noticed that in many of your articles on small-block Chevys you recommend setting the static timing in the neighborhood of 18 degrees BTDC. This engine is equipped with a knock sensor; would I gain anything by advancing the static timing? I'm thinking that the distributor and the ECM will control my total timing no matter what I do to the static timing. Any ideas?Steve ParsellLyons Falls, NY

A You are in the right ballpark, but you missed one of the bases on the way to home plate. Yes, the ECM controls the spark advance based on a three-dimensional map of engine load, engine speed, and engine temperature. The base timing of 6 degrees is a reference value for the spark-advance table calibrated into your ECM. If you advance the static timing to, let's say, 18 degrees, the total timing that the ECM would give the engine would also be increased by 12 degrees! Have you ever checked the spark timing after you have reconnected the four-wire connector that bypasses the computer? If you have, you should have noticed the idle spark advance was up around 16 to 18 degrees, based on the engine speed and coolant temperature. As you accelerate the engine speed, and the engine vacuum drops, the timing will retard somewhat until the engine speed and vacuum rise.

You didn't mention which 305 your Camaro came with stock. The LG4 low-output 305 had a very conservative spark curve compared with the L69 H.O. 305. Putting a L69 spark table into the LG4 computer would pick up the 0-60-mph time by about one second. That shows you how conservative that calibration really is.If your engine is the LG4, increase your base timing to 10 degrees with the four-wire connector disconnected. This will step up the performance significantly. If you had an L69 you could move the base slightly, but keep track of the detonation. Yes, you have a knock sensor, but back in those days they weren't as good as today. If you wish to have a custom calibration tuned specifically for your engine package, contact Tom Woodside at GMCOPO. There is a limited number of these early chips left, and he has a good database to support your engine. You can reach Tom at 248.275.5828 (Eastern Time).

Mighty Mouse
Q In this age of $3.00-plus gas, I recall an engine built by Jeff Smith for a Chevelle that used long rods out of a Ford six-cylinder. I think Duttweiler was involved. It was supercharged, small on cubic inches but big on power. Am I dreaming, or was this actually done? I'm thinking about building an engine for a project, and thought I should look into the past for info.John Alden

A Boy, did you make Jeff Smith's day when I called him! Yes, he did a build on the nasty mini Mighty Mouse. He sent me a three-page e-mail with the info. Let's see if I can get to all the facts.

The engine was originally built as a technology demonstrator for the Hot Rod Power Tour. It was installed in his '65 Chevelle with a Richmond six-speed and 3.55:1 rear-end gears. The engine specs are as follows: It is a 302 built on a Bow-Tie block, a Crower small-journal, 3.00-inch stroke, 6.00-inch small-block aftermarket rods, JE pistons that he believes to be 9.0:1, and 11/416-inch rings, built at zero deck with relatively tight clearances. They bolted on a set of AFR 195 heads (180s weren't out yet). He said that the biggest challenge was the camshaft. He went with the smallest Crane mechanical street roller that spec'd out at 210/220 degrees at 0.050 inch lift, and the lobe separation angle of 114 degrees, using 1.6 roller rockers. For induction he used the Lingenfelter/ACCEL SuperRam with the idea that he could build torque to help the small displacement. Then they stuffed a Vortech Supercharger on it. He forgot the specific size, but it was small by today's standards.

On Kenny Duttweiler's dyno it made right around 300 hp, normally aspirated, which was cool considering the very small cam. Jeff kept the camshaft small to have lots of cylinder pressure at low rpm for fuel mileage. With the blower he ended up with 28 degrees total timing and 14 psi of boost-on pump gas. With this tune-up the engine produced 550 hp and knocked down an average fuel economy of 25 mpg for the entire Power Tour-this was idling around on cruise nights and running down the road between 70 and 90 mph!

You know when you can't leave well enough alone? Well, Jeff showed up at Myron Cottrell's shop, TPIS, with the engine and they swapped out the intake for one of his Mini Rams with a water-to-air intercooler and a 220-degree-at-0.050-inch camshaft, on less boost, and kicked down 600 hp.

Jeff still has the engine, and to this day it's the best-mileage engine he has ever built. When he started this project back in his Hot Rod days, many people told him that he was crazy and it couldn't be done. As always, it's very fun to prove the truly crazy people wrong. Now that we have contacted Jeff he wants to take the engine a step further. He still has the engine and would like to install Magnuson's new High Helix 122-cid Eaton blower that recently made over 700 hp on one of Duttweiler's LS2 engines. Jeff thinks with the Magnuson bypass design at part-throttle and the efficiency of the design, the little Mouse could kick down 675 to 700 hp at around 6,500 rpm! He said he would let us know if his new dream ever comes to life.

Getting Charged
Q I own a bone-stock '70 Monte Carlo that came from the factory with a 350-cid small-block. Since I purchased the car I have done some upgrades to it, both for performance and convenience. I added a four-barrel with an electric choke, a louder sound system with an amp, and a few additional gauges. Is my stock alternator enough, or should I go for a more powerful alternator? Mine is externally regulated, and the more powerful alternators are internally regulated, so how would I go about doing this upgrade? What needs to be done to the existing wiring harness and external regulator? Any help with this matter will be greatly appreciated. Thanks.Fred Pugh

A It is very easy to overtax the factory charging systems on our early Chevys. It doesn't sound like you have gone too far for the factory system unless you have added a bank of amps and four 12-inch woofers back in the trunk. That said, there are far better internally regulated alternators that would be a nice addition to your car.

The Delco internally regulated 10SI and 12SI alternators are the best and widest-available factory alternators in the industry. They are what the aftermarket has grabbed up and converted to one-wire-style alternators. The 10SI alternators were introduced back in '70 for limited use and were in most GM vehicles by '74. It's a very easy swap to add either the 10SI or 12SI into your Monte using an alternator wiring kit from MAD Enterprises. Mark Hamilton has done it again with a complete, very straightforward instruction manual, explaining changes to the factory wiring harness. All the factory GM connectors, wire terminals, and shrinkable tubing, 8 feet of 8-gauge Tuff-Wire for the main power feed, and a diode to prevent engine run-on are included in the kit. Mark doesn't sell alternators, but he has sourced out the correct 10SI and 12SI alternators for purchase. For a 63-amp 10SI alternator, pick one up for a '78 Camaro with air conditioning, and for a 94-amp 12SI model, ask for an '84 Camaro with an L69 H.O. 305. You can get these at any auto-parts store across the country. This prevents you from being stranded out on a cruise or a long road trip. Also, Mark recommends not going with a one-wire-style alternator. The factory three-wire system will sense the load on the electrical system and charge accordingly. To pick up the alternator kit, it's sold under PN ALT-1.

Whip It. Whip It Good
Q I have an '01 Silverado with a 4.8L Gen III engine in it-not the typical vehicle for a CHP reader. I have gotten a tune, put in some electric fans, and am in the process of installing headers and building a custom exhaust.

I thought that I should get a baseline dyno run before all this. The truck has a 72-inch driveshaft. You might see where I'm going here-with my setup in Third gear (1:1), I got up to 5,000 rpm/124 mph...when time all but stopped as I heard a huge boom and saw my driveshaft drop into view and rattle around under the truck! The trans was toast. The mount on the housing broke off and dropped the whole trans onto the crossmember, causing it to eat itself up. I have a new trans ordered, so that's not my concern. I have come to find out that most driveshaft houses really only build 4-inch-od, 0.125-inch-thick driveshafts in 72-inch lengths. This has a lower critical speed (4,900 rpm) than my stock 5-inch-od, 0.083-inch-thick driveshaft (6,200 rpm). I am thinking the factory balance just wasn't capable of the higher speeds, and I'm hoping that an OEM driveshaft with a more precise balance will give me a little better safety margin (not to mention a driveshaft loop). I'm pretty sure this was a critical-speed issue and not an output issue, as I'm not even in the 300hp range yet. Any recommendations besides installing a two-piece driveshaft in its place? Thanks.Andrew GreifBallston Lake, NY

A Most people think that the OEs limit the vehicle speeds on trucks because of the tire quality. Well, with your electronic tune and eliminating the 100- to 105-mph top-speed limiter, you have met your driveshaft! I'm sure that you would rather have been introduced in another fashion. Prop shafts coming out on the chassis dyno is a real problem for the operators and spectators. There's a ton of energy in that shaft when it comes loose; look at the underside of your truck at the evidence of its attack on your trans.

Driveshaft critical speed is based on the length, material weight, and diameter. Yes, your driveshaft balance could have just driven it over the edge and started the whip that finished you off. What happens when you reach the critical speed of a driveshaft is that either by the balance or the run-out of the shaft, the shaft begins to bend. As the shaft speed increases, this bending creates an even greater imbalance, and the shaft shortens and pulls itself out of the transmission at the slip-yoke. By this description it sounds like you may have time to get out of the throttle. But as soon as the shaft begins to bend, it's all over!

GM went back to a two-piece driveline in its '06 trucks. The only truck that still has a one-piece driveshaft is the11/42-ton shortbed standard cab. Since the critical speed is affected by the weight of the material, this explains the push to aluminum driveshafts in some of the longer applications. Driveshafts are made out of steel (1053), chrome-moly (4340), 6061-T6 aluminum, metal matrix composite (MMC) aluminum, and carbon fiber. They come in many thicknesses and diameters. We would not trust our truck (or our life) to another production OEM driveshaft. If you're going to run over the factory-designed limited speed, give Dynotech Engineering a call. This company builds some of the nicest driveshafts I've ever used, with shafts constructed out of all the above-listed materials, and will build you the proper shaft, engineered for the speeds you would like to achive. Yes, the shaft will be a little pricey, but it will be a lot cheaper than another transmission-or a hospital bill.

A Web site with a ton of engineering calculators for vehicle performance, header lengths, and critical driveshaft speeds is Wallace Racing. It's a killer site, and you'll be there for hours playing with the calculators.

'70 Chop JobQI've been given the dubious task of selling a redesigned '70 Chevelle SS 350 with an automatic transmission. It now looks more like a kit car and has a rectangular fiberglass body. The engine is supposedly freshly rebuilt with 2,200 miles on it. My question is about the engine. The only number I find on it is T0215CK1 or CKL (hard to read under the dirt). Can you give me any information about this engine? Thanking you in advance.Pamela Meath

A I'm not asking how you adopted this "work of art." It's unfortunate what some people thought would look cool years ago. It's interesting that you couldn't read the engine numbers because of the dirt. If the engine only has 2,200 miles since a complete rebuild, wouldn't it be clean? The CKL is the correct engine code for a '73 350ci, 145hp ,8.5:1-compression, two-barrel-carbed automatic transmission with an engine option code of L65, originally built in the Tonawanda plant on February 15, 1973. It is certainly not the numbers-matching engine for this car. I hope this has given the information you were looking for. Good luck on moving this piece of history.

If you have technical questions for Kevin McClelland, send him an e-mail at

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