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Chevy LT1 Head Questions - Performance Q&A

Kevin McClelland Jun 1, 2009
0906chp_02_z Chevy_lt1_engine_performance_questions Chevy_small_block_engine 2/2

Neglected Tools
If you're like most of us, servicing your vehicle isn't way up there on the to-do list. It's more fun installing a set of headers, swapping out the latest intake manifold, or if you like to keep your hands clean-and need instant gratification-blowing in a new program into your PCM. There's one tool many of us have that I know gets neglected. How about the wheel bearings and brakes on your trailer? Many of us have trailers, and some have more than one. What if you lost a wheel bearing going down the road with your prized possession on its back? This is what happened to a good friend of mine on his way to Las Vegas with his triple-axle, gooseneck Pace trailer! As he came to a stop, the axle in question was up in flames! His trailer even had the self-lubricating bearings that were submerged in a bath of gear oil! The point I'm trying to make here is that we all do it. We come home from the races or whatever activity and unload our cars, then stash the trailer until next time.

With my family's move to Southern California coming up this month, I decided to service the bearings on both my trailers before we struck off. I couldn't afford to be stuck on the side of the road trying to find bearings or, worse yet, needing a new axle. I've had one of the trailers, a 24-foot Pace Shadow, for 10 years and 40,000 miles. I've been very nice to the electric brakes, using up the tow vehicle's brakes more than the trailer's. I've heard horror stories about electric trailer brakes and the expense of replacing them.

Popping off the wheels and drum, I came to find that the bearings were just fine. The axles and brakes are made by Dexter and have a nice feature that allows you to inject grease into the axle, which packs the hub assembly full of grease. My problem wasn't neglecting the bearings; it was the brakes. At first glance, everything looked great. The lining was about half worn, but there was cracking in the lining throughout the shoe.

Next I found that because I had not kept up on the brake adjustment, the electromagnet that rides on the brake drum when engaged had overshot its mating surface. This had worn the magnet excessively but luckily had not damaged the drum. So I'm off to the brake store for shoes and electromagnets! Again, if I would have stayed up on the adjustment I wouldn't have been looking at this expense! Think of this the next time you dump your car off the trailer and park it for next time.

As for the move down south, I have found a place to hang my shingle. K&N Engineering has taken me in as Special Project Manager. I'll be looking for new opportunities for K&N to apply its filter technologies. Also, I'll be digging around for groundbreaking uses within our industry. It really feels good to finally move from the dirty end of the car up to the clean end! Stay tuned for new adventures.

Round? Who Needs Round?
Q: I got an engine block from a friend who didn't want it because it had water damage to the cylinders. Well, after a few hours of sanding and a honing tool, this block ended up looking great! The casting number is 10125327, confirming it's an LT1. Can I put any heads on this engine, or do they have to be LT1 heads?
Freddy Reyes
Santa Ana, CA

A: Taking sandpaper to cylinder walls can be very dangerous. If you used very fine (1,000-grit) sandpaper to clean a little surface rust off the cylinders, I wouldn't worry. However, sanding for a few hours and then using a honing tool is what worries me. Was the honing tool a bottle-brush glaze breaker or a true shoe type-stone hone? If you take 400-grit sandpaper to a cylinder wall and track the damage with a micrometer, it will surprise you how much material you can remove easily. This creates an out-of-round condition that the rings will never have a chance to seal.

As for the cylinder heads needed for your block, you are correct that you have an LT1/LT4 casing-number block. These blocks were offered in both two- and four-bolt main configurations. The cooling system is a reverse-flow design, which requires either production LT1/LT4 heads or aftermarket heads specifically designed for the reverse-flow cooling system. These engines came in '92-97 Camaros, Corvettes, and Impalas. A few of them snuck into '98 Camaros as that model was swapping over to the LS1 engines. There are plenty of heads out there to choose from.

Back to your cylinders. Make sure before you build up this engine that you measure the cylinder walls and check for out-of-round bore diameters. It's better to find them on the front side of a build.

It's All About The Math
Q: My '67 Camaro has a 402 big-block and a TH400 transmission with 3.55:1 gears. My 60-foot time is 1.749, and my eighth-mile e.t. is 7.727 at 85.68 mph. In the 1,320, I have run as fast as 12.128 at 109.57 mph. This car has a 3,000-stall converter, a single-pattern cam with 302 degrees duration and 0.544 inch max lift, and an Edlebrock Torker II intake with a Holley 850-cfm double-pumper. I understand that the dual-plane would probably work better, but I can't get it under the hood without a scoop. Can you give me a ballpark estimate on the horsepower for the car with full interior and the spare and jack in the trunk? How much can I gain with a lower gear ratio? Everyone around here bracket-races in the eighth-mile. Do you have a table for gears such as 4.11, 4.56, 4.88, and 5.13 running a 26x10 Hoosier slick? Thanks!
Marcus Humphries
Dawson, TX

A: Your Camaro is running very well for its minimal modifications. If I were to throw a number at the power of your engine, it would come in around 425 hp. The car is moving well on the torque built by your 402. The main problem with lowering the gearing to match the eighth-mile racing distance is that your First gear becomes so low that it's almost impossible to hook the car up! You have a good 60-foot time for a basic street car, and the 26x10 Hoosiers are doing their job. Putting a ton of gear to match your horsepower peak to the finish line might give you fits.

With the 3.55:1 gears and a 26-inch tire, we'd say you're probably in the low 4,000 range going across the eighth-mile line. There are gear ratio calculators online that you can use. Check one out at Or you can use this formula to calculate your engine speed based on any gear you wish to try. First multiply your tire diameter by your desired engine rpm. Next choose a gear ratio and multiply by 336. Then divide the tire diameter result by the gear ratio result. This will give you the miles per hour of this combination without any slippage. Remember, the miles per hour may vary due to tire growth and converter slippage.

Always keep in mind: Mild big-blocks move the car mostly on torque. Chasing the horsepower peak to lower your e.t.'s may not give you the results you're looking for. Running much lower than a 4.11:1 gear may cause you more trouble in the 60-foot than it's worth. Good luck, and drive a tight stripe!


Spline Count
Q: My '84 Camaro Z-28 has the HO 305 VIN code "G" engine, coupled to a TH700R-4 transmission. I don't know if the transmission input shaft is a 27- or 30-spline. I have read that in '87s and later they were 30-spline. Some say the switch was made in the '86. I also read that the switch occurred mid-year in the '84. I'm confused. Is there a way to tell if my transmission is a 27- or 30-spline input, short of removing the transmission and visually examining the input shaft? Thanks.
Steve Parsell
Lyons Falls, NY

A: Man, I think this has turned into a great game of telephone! You know, when information gets distorted as it passes from person to person.

In mid-1987, GM improved the TH700R-4 transmissions with an increased number of vanes in the front pump to stabilize line pressure and volume. GM increased the spline count to the input shaft at the same time. This was a great improvement to this transmission, giving it better durability and life. If your Camaro is equipped with the original transmission, it's very safe to say it is a 27-spline input. If you're still in doubt, get the trans code off the side of the case and give Ken Casey a call at Burt Chevy (800.345.5744). He can identify the trans for you from the factory ID numbers. The only problem with this is when the trans has been rebuilt and modified with later-model components. Good luck with your Camaro project.


She Be Lean
Q: I have an '84 Camaro with a 350 that has been bored and flat-decked. It has World Sportsman II 72cc heads, a Lunati Voodoo cam (PN 60101), Speed-Pro flat-top pistons, an Edelbrock Performer RPM intake, and a Holley 670 Street Avenger carb. The distributor is a stock HEI with vacuum advance out of a '77 Camaro. It runs great when the weather is warm, but as soon as it cools down to 55 degrees, it surges cruising down the road and falls on its face when accelerating, and I have to ride the clutch when I take off or it will die. I have considered fuel injection, but it is a little cost-prohibitive. Also, I'm going to install a Mallory Hyfire 6 EXL soon, but I don't know if that will help or not. Can you please give me some ideas on what I can do to give it better cold-weather drivability? I don't want my car to have to sit for six months every year. Thank you very much for any help.
Mike Kennedy
Via email

A: What you have is a lean condition. When the ambient temperature is higher than 55 degrees, you have just enough fuel to satisfy the engine's fueling requirements. When the temp drops, the air density increases and you have more oxygen in the inlet air. This leads to the lean surge you're feeling, the bog when you try to accelerate, and the stumble on take-off while slipping the clutch. Going to a stronger, hotter ignition system can help fire a lean mixture. But it sounds like you need to increase your jetting.

First, make sure that when the carb was installed, the float level and idle feed screws were set properly. If the float level is low or the idle feeds are on the lean side, this would also give you lean stumble conditions. Check out Holley's online FAQs for the correct information on adjusting your Holley 4150 model carb. If the adjustments are correct, we'd increase the primary jet size by two. I would also increase the accelerator squirter from the factory 0.028 inch up to 0.031 inch. This will aid in the initial step on the throttle. With these two changes, you should be able to make it through the winter.

Also, if your calibration is this sensitive, we bet it's too lean for max performance during the summer. Adjusting the jetting of a carburetor is a very subjective adjustment based on the experience of the tuner. The folks at Innovate Motorsports have brought us affordable wideband O2 sensors to help dramatically with any tuning. The LC-1 kit gives you the wideband O2, wiring, software (PC), and cabling to your PC to know for sure that you have the proper calibration. Also offered are dash-mounted gauges to give you convenient, real-time AFR. Check out Innovate's online forums to help the novice tuner dial in his car.


What a Gas! Natural, That Is
Q: I'm building a '58 Chevy Apache frame-off resto. I want to step up to the plate by going green. Do you guys have any idea where I can get the kit/equipment for CNG conversion for a Chevy short-block? I figure I might as well step into tomorrow and get cheaper fuel at the same time. Also, I'd be able to fill 'er up at home. Is it possible you guys could do an article on a small-block CNG conversion? What do you say? By the way, keep up the good work!
James Walter
Via email

A: CGN is sure a hot topic these days. T. Boon Pickens is going on TV and telling everyone that we could be running on CNG today. That's the truth, but the likelihood of everyone doing it is another story. Also, outfitting older vehicles is a challenge compared with the late-model EFI vehicles. We dug around for a while and will list several websites where you can do some research. After you've looked into natural gas, you can decide if it's for you.

One of your comments is that you could fuel your truck at home. While this is technically true, the compressor to do this today is around $4,500. This price is just for the compressor, not any of the conversion components and the fuel storage tanks that are DOT-legal. These fuel tanks are made from composite material and hold the natural gas under a working pressure of 3,600 psi. A tank that would hold the equivalent of 10 gallons of gas is priced around $2,800. The conversion kits we found online were from all around the world. The prices varied, but they come in around $1,800 for EFI systems, higher for carbureted systems. There have been tremendous advancements in the EFI side of the conversion market. There are systems available that are OBD II compliant and can be installed on current-model-year vehicles and retain the factory warranty!

Check out the sites below for more information. If you would like to speak with someone in person, give Impco Technologies a call (714.656.1200). Impco has been the premier mixer and regulator manufacturer for propane conversions ever since propane came into favor. I worked with the company years ago on a CNG project in the Texas Panhandle, where Don Hardy Race Cars was outfitting irrigation pump engines to run on natural gas. CNG is being used all around the globe to fuel cars and industry. As for CHP doing a conversion story, it may be a little early in the learning curve. We'll have to wait and see.


Early Iron Flow
Q: I have been clawing my way through the Internet, looking for small-block Chevy head flow data. Specifically the mid-'60s double-hump heads with the casting numbers of either 3782461 or 3782461X. If you could point me to a website that has this info, I would be very thankful.
Red Slover
Norco, CA

A: The early iron double-hump, or camelback, cylinder heads flow very similarly. The 461, 462, 486, and 492 heads all had very similar port volumes and valve sizes. Most of these came equipped with either 1.94/1.50- or 2.02/1.60-inch valves. Here is the typical double-hump or fuelie casting stock head flow.

One interesting note is where the exhaust port saturates. It reaches max flow at 0.400 inch valve opening and is flat up to 0.600 inch. This is where adding a larger-lift camshaft has minimal affect on performance. A simple valve job and increasing the throat diameter and blending the short-side radius will correct this problem. This will unlock a ton of performance from these early heads.

For the best technical information on cast-iron Chevy heads, check out Brzezinski Racing Products, which offers complete porting services, legal and "cheater" heads for limited-rules racing classes, and a complete line of very trick flow bench tools.


El Cam OverdriveQ: I've been a subscriber for years and love the rag. I have a '74 El Camino SS 454 with a factory big-block and a TH400, a 10-bolt with a 3.73:1 Posi. The engine has a Performer RPM Air Gap, a 750 Holley double-pumper, headers, and a camshaft with approximately 230 duration at 0.050 inch tappet lift. The automatic is quick but boring. I want to swap in a five- or six-speed manual. What would fit the best? I don't want to cut up the tunnel more than I have to.
Paul Van Slyke
Amherst, NY

A: That's a very nice Elco you have there. Does it still have the factory SS bodywork on it? There were the Laguna Malibus, and some of the SS El Caminos had some of the different bolt-ons in the front. Lucky for you, the later, larger A-bodies had quite a bit of room under them. A five-speed swap should fit with no floorpan modifications if the model was originally equipped with a four-speed.

Classic Chevy 5 Speed and Keisler Engineering have a complete line of five- and six-speed swap systems for a number of applications. They have everything, and it's the easiest and most complete way to put a high-strength, modern overdrive Tremec TKO five-speed transmission in your GM A-body with automatic transmission.

As for your big-block car, we'd go with the TKO 600. This transmission is rated at 600 lb-ft of torque and features a 0.64 overdrive in Fifth, which will allow you to enjoy the performance of your big-block with some fuel economy. They have both factory mechanical clutch linkage and optional hydraulic clutch linkage. They can supply you with just what you're looking for.


Offset Rear
Q: I have a problem with my '72 Nova rearend. I moved the leaf springs over and centered my rear up off the pinion. But when I measure off the rim with a tram gauge, the passenger side is off 1 inch. When I measure the perches they are fine. I thought the quarter-panel was messed up, but the body shop says it's not. I have to run two different backspacing rims-the driver side is 5 1/2 inches and the passenger side is 4 1/2. Hope you can tell me how to fix it.
Randy Panozzo
Muskegon, MI

A: Did you notice that the engine and transmission in your Nova are offset to the passenger side for steering box clearance and to fit the floorpan better? When you centered up the rearend off the pinion to the framerails, you offset the axle to the driver side! If you measure the crankshaft centerline between the front frame, you should find that the engine is offset about 1 inch, and then measure the output shaft of the trans and see where it falls. It should be slightly less offset at the rear of the trans.

Is this going to cause you a problem with your car except for the wheel offset? Not really. The U-joints are just going to work a little harder with the added inch of offset compared to the trans output shaft. Sorry about this, bud.

Bulletproof Baby
Q: I am considering a small-block engine build for my '85 Chevy pickup. I am not interested in a high-revving engine. I'm looking to build a torque monster, a high-torque tow vehicle. I have a used 350 four-bolt block with a two-piece rear main and cranks that I could build into a 355. Or I could stroke it and build a 383. Or I could sell them and use the money toward a Dart 400-cid short-block.

In the end, by the time I get a roller cam and rockers and all the other goodies, the total dollar difference will probably be less than a grand. My block would have to be machined for the 350-more so for the 383. The 400 block would come all machined, so my starting costs would be close.

Is this a case where there is no substitute for cubic inches? Also, could you recommend an iron head and cam?
Bob James
Franklin, IN

A: Building a mild-mannered torque monster for your tow truck is all about displacement. The larger you can make the engine, the milder you can go with camshaft profiles and cylinder head port sizes to create gobs of torque.

We really like the new Special High Performance (SHP) blocks from Dart ("Minimal Assembly Required!" May '09). This purpose-built block for street performance hits right on target. The days of using 400 blocks from the junkyards are behind us. These new blocks, which Richard Maskin and Dick Arons came together to design, feature all the upgrades you would want in a street-performance small-block.

Designed for high-performance and heavy-duty applications producing up to 600 hp, the block features Siamese cylinder bores that have a minimum of 0.230 inch of wall thickness even when bored out to 4.165 inches! It also has a true priority-main oiling system, ductile iron main bearing caps (with splayed four-bolt caps on center mains), thicker decks with blind head bolt holes, and clearance for long-stroke crankshafts. The blocks are machined to accept all factory hydraulic roller hardware and factory thrust plates. The block even has both clutch cross-shaft pivot ball locations. The block comes fully machine with semi-finished bores for final honing. The 4-inch bore PN is 31161111, and the 4.125-inch is PN 31161211.

Dart also features two short-blocks using this block, a complete 372-cid and a complete 400-cid assembled short-block. These dyno-proven packages feature a torque-plate-honed block, hypereutectic flat-top pistons with full floating pins, cast-steel crankshafts, forged 4340 I-beam rods, Hastings moly rings, Clevite bearings, and coated cam bearings. To round out these packages, top end kits are available for both, with the 372 producing 470 hp and 470 lb-ft of torque with a mild 224-degree hydraulic flat-tappet cam. The 400 steps it up a notch with a hydraulic roller camshaft spec'd out at 230 degrees duration at 0.050 inch tappet lift, which produces 525 hp and 525 lb-ft of torque.

Now for your torque monster. We'd go with the Dart 180cc Iron Eagles on the 400-cid engine. You will need to build a dish piston to keep the compression right around 9:1 for heavy-duty use. Dart recommends its 200cc runners on the 400-cid engine, but again, you're not looking for big top-end numbers. It's torque, baby. The 180cc/72cc Iron Eagles come either bare (PN 10210010) or assembled with a 1.437 dual spring assembly (PN 10211112). You may wish to go with the bare heads and use the associated valvetrain recommend by the camshaft manufacturer.

As for the cam, this will be the heart of the torque-building package. You could push the duration slightly, but we recommend sticking to the conservative side. Look to the low to mid-teens for duration on the inlet side, and low to mid-20s on the exhaust side. Check out the Xtreme Roller line from Comp Cams.

Of the two camshafts that would work great in your towing application, we lean toward the XR264HR, which specs out at 212/218 degrees duration at 0.050 inch tappet lift, 0.487/0.495 inch max lift, ground on 110 centers. The largest camshaft we'd use is the XR270HR, with specs of 218/224 at 0.050 inch, 0.495/0.502 inch max lift, also on 110 centers. These camshafts will produce right at 500 lb-ft of torque, with the shorter producing around 425 hp and the larger closer to 450.

Round out your package with a large dual-plane intake, either the Dart Iron Eagle/Pro 1 dual-plane or the Edelbrock RPM. And finally, don't be temped to put primary tube headers larger than 15/8 inches on the engine. The 400 will love the small primaries, but they must be long-tube headers to support this engine.

This should give you a very nice, totally bulletproof small-block for your tow rig. Good luck, and let us know how it turns out!


Need A Lift?
Q: As a longtime subscriber to CHP, I hope you can help with my problem. The '82 El Camino that I bought new now has 70,000 miles. Because of my health problems (lungs), the VA gave me a handicap lift and scooter, mounted on the El Camino. Everything was fine for about three months and then the OE factory air shocks started to leak down to 20 pounds in about four days. I had a friend replace them with Monroe air shocks. They leaked down in one day! They were replaced three times with the same results. We checked every possible way to find leaks and couldn't find them. My friend seemed to think they were leaking through the rubber around the shocks in a way that we couldn't detect. I had him install Monroe Sensa-Trac (load adjusting) shocks. I measured the height at the rear wheelwell. It was 27 inches, and after we installed the lift (100 pounds) the height was 25 inches. Loading the scooter (150 pounds) the height went to 21.5 inches. Do you know of heavier rear springs that could be installed maybe from a 1/2-ton pickup? I don't care if the El Camino rides 2 or 3 inches high in the rear when I'm not carrying my scooter, and the lift stays on at all times. Hope you have an answer. Thanks.
Via email

A: Boy, we're sorry you've been fighting with the air shock system on your Elco. The factory air shocks are a really good system. It's unfortunate that they got tired and gave up. Yes, there are springs out there that will work. Let's take a look.

Moog Chassis Part, a division of Federal Mogul, offers what it calls its Cargo Coils just for your needs. They're variable-rate springs that change resistance as they compress and become stiffer as the load increases. This is accomplished by winding the springs with a progressively tighter wind toward the top. The looser wind at the bottom gives you a normal ride with no load in the bed, but as soon as the loose wind compresses, the stiffer, tighter windings hold up the weight.

You have two choices: The springs that are spec'd out for your Elco are PN CC627, or you could go with the stiffer wagon springs under PN CC507. We've used Cargo Coils before with great successes, and the standard El Cam springs should take care of your 250-pound payload. Both part numbers are available from Summit Racing.

This should take care of all your problems hauling your scooter. Hope this will get you around a little easier. Good luck and good health.


Technical questions for Kevin McClelland can be sent to him at



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