Chevy Performance Tech Questions - Performance Q&A
This is a discussion on Chevy Performance Tech Questions - Performance Q&A within the Camaro / SS forums, part of the Vehicle Specific category; Chevy Performance Tech Questions - Performance Q&A Trick Part Of The Week II If you remember my column from last ...
07-24-2008, 07:40 PM #1
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- Aug 1999
- San Diego, Ca
- 383 Procharged & N20 Vert
Chevy Performance Tech Questions - Performance Q&A
Chevy Performance Tech Questions - Performance Q&A
Trick Part Of The Week II
If you remember my column from last month, it spelled out the trials and tribulations of getting the engine together for our stocker wagon. The good news is that the car made three complete passes in qualifying! This was quite a feat, as we'd loaded the car onto the trailer with only a burnout in the parking lot of my shop. Daniel qualified 0.25 second under the index. This isn't saying much except that it was my first class-legal engine and, as I told the NHRA tech officials, the engine was "laughably legal!" Like I said last month, I have a newfound respect for the racers and engine builders in Stock Eliminator. The best part of the whole trip was the 30 minutes I got to spend with the tech department, discussing the finer points of engine teardown and what they looked for. This will help me find some more horsepower in the future.</br>
Back to the first round: The car wasn't a bolt of lightning, but it would leave quite well off of a 2,600-rpm two-step rev limiter, and this seems to be where we ran into some problems. Daniel was paired up with a C-stock automatic Camaro with a 375hp 396. This car was dialed in at 10.79 and we were dialed at 12.95. With the burnouts complete and both cars staged, the tree came down and the mighty wagon crawled off the starting line like a turtle, picking up speed about 30 feet out! I stood at the starting line in disbelief. The toughest part was walking past all our fellow competitors back to the pits, with them all asking what happened.
Back at the pits, I asked Daniel what he thought had happened. He said, "It was like it was loaded up, and it cleaned out about 30 feet out." Jumping in the car, I fired it up and everything seemed fine. I set the two-step and went to full throttle. Lo and behold, the rev limiter was holding the engine at 1,600 rpm, not 2,600 rpm like it was supposedly set to. Our "trick part of the week" adjustable rev limiter box is mounted in the glovebox for easy access and upon popping open the glovebox, we saw that the 1,000-rpm wheel of the limiter box was knocked down to 1,000 rpm, not 2,000 rpm! No wonder the big old wagon wouldn't move. The only way the box could have been changed would be that when the tire gauge was tossed in the glovebox it hit the rpm box. We've raced the car for almost six months and over 100 runs down the track without this ever happening. What luck, first round-and Daniel's first National event. I guess it's fitting; I lost my first round at my first National too. What do they say about things like this building character? Hopefully, it won't happen much more to Daniel. We don't need any other characters in our family.
Q I've just installed an Edelbrock Performer rpm manifold on my 350 for my '69 Chevelle. I noticed when I went to install the distributor that it fit loosely in the inlet manifold and it wobbles all over the place. Is there any fix for this? Thanks for your help.</br>Billy Jones
A The distributor hole in the production inlet manifolds of small-block and big-block Chevys is quite oversized. Edelbrock machines them even larger than the production inlet manifolds to take into account the variables of engine buildups. You may have noticed that the distributor doesn't sit perfectly straight up and down in the engine; it is offset to the right side of the engine by approximately 4 degrees. When you mill cylinder heads, cut the deck surfaces on the block, mill the intake manifold surface to match the cylinder heads, or use different thickness head and/or intake gaskets, you change the location of the distributor hole in the block and its relationship to the manifold. When the engine is produced by the factory, it is for a given deck height, gasket thicknesses, and head thickness, and the distributor hold can be kept at a closer tolerance.
What is your concern? Do you question if the distributor hold-down can do its job, or are you worried about an oil leak? First, the hold-down will have no problem keeping the distributor in place. There is practically no load on the distributor housing itself. As for a leak path, we put a very thin layer of silicone sealer on both sides of the distributor gasket. This seals it up perfectly. The only catch is that you must do this last, right before fire-up, and set the timing immediately. This will give the silicone a chance to seal in the proper location. To tune the car, get your dialing-in done either at the track or on a dyno. Then remove the distributor and seal it up. Either way, you won't have a problem with the oversized hole in the manifold.
Q I have heard in the past that switching to synthetic fluids (motor oil and transmission fluid) for vehicles with over 50,000 miles can be dangerous since the smaller molecules of the fluid could leak past the seals. I believe this was a major concern when synthetics first made it big onto the scene around 15-20 years ago. Is this still a concern? I have a '99 Chevy Silverado with a 5.3L with approximately 50,000 miles, and in the quest for more horsepower I am looking to upgrade. Any thoughts? Thanks.</br>Matt Crow
A You're spot on with your synthetic assessment. The biggest issue we had swapping to synthetic oils years ago was the quality of the shaft seals and gaskets in our engines. That synthetic stuff would find a leak path where "dead dinosaur" oil couldn't.
Really, any engine built after the early '90s should have no problem swapping over to synthetic liquids. In the late '80s and early '90s, GM swapped over to one-piece rear main seals and a silicone-based oil pan gasket with torque limiters built right into the gasket to prevent overtightening. Now, you can incorporate many of these new technological features into our early Gen I small-blocks and Mark IV big-blocks. There's no reason you can't have a dry undercarriage. Your friends will really appreciate it when you don't leave spots in their driveways!
It's just fine to swap synthetics into your late Chevy truck. With the price of gas these days, we'll take any slippery fluid that increases fuel economy and performance.
Q I am 19 years old and about to graduate from college to be a mechanic, and I want to get a job on a drag racing team. How would I go about doing this? Should I e-mail them, talk to them in person, or call them on the phone? I don't know how to find a drag racing team willing to hire a fresh college grad ready to learn anything and everything about drag racing. Any help would be appreciated.</br>Marcus Fishburn
A Yes, it can be quite difficult to get into the inner sanctum of any professional racing team, no matter what division. However, with your education and enthusiasm to learn, it's worth a shot. What's the worst thing that could happen? They just say, "No, thank you."
If drag racing is where you wish to find a job, check out the NHRA Web site. Once you're there, click on the Drivers tab. On the pull-down you will find the Crew Chiefs/Team Owners selection. If you search through this list of professional teams, you can choose which crew chiefs you wish to send rsums to; then, search online to find the contact information for these race teams. Send a printed copy of your rsum to the crew chief's attention, and shoot an e-mail of your request to the team Web site, addressed to the crew chief. Is everyone going to respond? No. But remember, all you need is one who is willing to give you your first break. If you get in, keep your head down and learn. Rise above their expectations, and you may have a career for life!
You may want to check with the School of Automotive Machinists. Another option is to look into WyoTech trade schools; an official sponsor of the NHRA, they do place graduates into the racing community in areas ranging from drag racing to NASCAR to the IRL. They may be able to give you some direction. Good luck with your search, and hope to see you at the races soon.
Sources: nhra.com, samracing.com, wyotech.com
Head Gasket Worries
Q I'm coming to the assembly of my small-block engine buildup. I had the engine bored 0.030 over. Do I need a special head gasket for the larger bore, or will the stock gaskets work fine? I don't want to mess this up and have to take the engine apart after all this work. Any help would be great.</br>Fred Miller
A Running the incorrect head gasket in an engine can cause real problems in several ways. Most production head gaskets are well over the bore size in the proper application. For instance, a small-block 350 composition head gasket from GM has a diameter of 4.100 inches. A small-block 350 has a bore size of 4.000 inches. You can easily use the factory head gasket for up to a 4.060-inch overbore with no worries. GM pretty much figured this into the equation when it built the gaskets.
As for performance head gaskets, Fel-Pro's very popular 1003 and 1010 head gaskets are built to a gasket diameter of 4.166 inches. As you can see, this is well over the bore size at the largest 350 overbore. I really prefer to use the smaller-bore size gaskets because this larger gasket allows spent exhaust gases and carbon to live in this crevasse. During the exhaust stroke, there is no real way to evacuate this area, and the remaining spent combustion gases can mix with the incoming charge and reduce the power potential.
The bottom line is that the head gasket must be at least 0.020 inch over the bore size to prevent the fire ring of the gasket from protruding into the combustion space. If the fire ring gets into the combustion space, the stainless fire ring will be superheated and act as a glow plug and cause pre-ignition. This can be disastrous for your engine. Follow these simple recommendations and you'll be able to keep your fresh, clean engine sealed up.
Q I have a set of 305 heads off an early-'80s small-block. I'd like to install these on my 350 to raise the compression. Shouldn't this make my 350 run strong, since it's increasing the compression ratio, and compression equals more power? My 350 is a mid-'70s smog engine with 76cc combustion chambers. The 58 cc on the 305 should really wake this thing up. Any help would be appreciated.</br>Phil Mathews
A Compression ratio squeezes the fuel and air in the combustion space, creating more heat, which equates to more power. There are several rules to the amount of power you can expect. Most people believe that if you change the compression of an engine 1 point, you should realize a power gain or loss of 4-6 percent. When we've done these compression drills, the most we've seen on the dyno is around 4 percent. On most 350-cid engines, 10 cc of change works out to about 1 point of compression change. This is a pretty good rule to follow on a 350 small-block.
Back to your 305 heads. You didn't say which heads they were. If you're trying to use 305 TBI-style heads, they have a very poor intake port, which would kill the power potential. If you're taking about LG4 or L69 carbureted 305 heads, they are the best 305s out there. Their casting number is 14014416 and they feature 1.84/1.50-inch intake/exhaust valves with 58cc combustion chambers. Why I'm getting down to the numbers is because this is the exact head we have to use on our 305 Stock Eliminator engine for our wagon. I had a set of virgin 416 heads that had never had a valve job except from the factory and had never been surfaced. After we had done our performance valve job, we cc'd the heads to estimate how much we needed to cut off to get down to the 55cc rule limit. The heads cc'd at 64 cc! Boy, was that a surprise. We've now cut more than 0.060 inch off the heads and we still are not down to the limit.
Let's say that you drop your combustion chambers down 12 cc-you should boost your compression around 1.2 points. If your mid-'70s small-block is an 8:1 engine (should be), you will have raised the compression to 9.2:1. If you apply the 4 percent rule to the 250 hp you're probably making now, you have a whopping 260 hp! After all that work, you would want more power than just 10 hp. Also, the exhaust ports on the 305 heads leave a lot to be desired.
We would look to a set of aluminum performance street heads. For nearly the same money to freshen up a set of iron heads properly, you can score a set of aluminum heads. The swap to aluminum heads from the iron 350 heads would give you an easy 40hp bump. If you play your component right, you will see even more. Don't go backward, use new technology and move forward.
When They Go Boom, They Sink
Q I purchased a used Airboat with a 350 small-block. I fixed it up and put in aluminum heads, a stainless steel exhaust system, and an aluminum manifold. After all these upgrades, the bottom half of the engine blew a hole in the block, resulting in catastrophic engine failure! I was thinking about replacing the block with an aluminum one. Is the weight difference worth the price and effort, and which 350 aluminum small-block would be best for the job? Airboats need low-end torque. Also, keep in mind that the mounts on the cage are set up for a '75 Chevy small-block 350. Thank you.</br>Jim Delaney
Deerfield Beach, FL</br>
A Wow, I bet that that engine failure was exciting. Nothing went through the hull of the boat? You're still around to write about it!
It never fails. You take a perfectly good, running engine and boost its speed and power output, and the engine expires. Think about it for a second. You buy a little old lady's Camaro or Nova with an engine that never saw the top side of 3,000 rpm with her driving it. It only has 80,000 miles on the clock. And because the engine never really sees operating temp, the cylinder wall wear is terrible. The top ring has worn a nice ridge into the cylinder. Now, you get your hands on this really clean musclecar. You give it a tune that it really deserves and take it out for a drive. Maybe it lived through this, but when you swap in a small camshaft, aluminum heads, and a set of headers, all of a sudden the engine loves to run to 6,000 rpm. When this happens, everything stretches to the point that the top ring is running into that ridge in the cylinder and either breaks the top ring or-worse yet-breaks the top ring land in the piston. Power drops and you're wondering why. It ran great for the first trophy dash. Once you've cracked a cast piston, it's just a matter of time before it scatters.
As for installing an aluminum block in your Airboat, I think it's going to come down to cost. A production 350 iron block weighs around 170 pounds, and aluminum blocks on the market come in between 90 and 100 pounds. Dart Machinery, GM Performance Parts, and World Products all offer very nice aluminum blocks that you could use for your engine buildup; however, for the cost of an aluminum block, you could build a really nice 383, which would have a bunch of torque right in the rpm range you need. Also, most of the aluminum blocks out there are set up for racing, with very large cubic inches. The camshafts have been raised and the pan rails are spread to clear stroker crankshafts. All of this causes you to use specialized components, equaling dollars.
Before you start your build, find out the peak rpm your Airboat's prop will handle. It's very important that you do not overspeed the prop. The prop's limiting speed is determined by the diameter. When you overspeed a prop, the tips of the blades go sonic (the speed of sound) which will cause the blade to break over time. When this happens, you definitely don't want to be in that boat. Once you have this limiting speed, build your combination around this number for maximum torque. Also, we'd recommend installing a rev limiter several hundred rpm below this threshold just to be safe. Happy boating!
Sources: dartheads.com, gmperformanceparts.com, orldcastings.com</br>
Q I purchased a '78 Malibu bracket car from an estate sale, and according to the e.t. slips I found, it ran 12.40s at 107 mph. I need some help in a couple of areas: identifying whether it has forged or cast pistons, selecting a solid flat tappet cam, and determining what slick size to run. I'm guessing the car weighs 3,300 to 3,400 pounds (it has been stripped for racing). It has a 0.040-inch-over 427 BBC (435 cid); a cast GM crank (3904815), pistons (2385P), and closed-chamber factory heads (3904390); a Weiand 7544 single-plane intake; a 1-inch carb spacer; and a too-small 650 Holley double-pumper. The rest of the drivetrain is a TH400 trans, a 3,000-stall B&M Holeshot, and a Ford 9-inch rear with 4.11:1 gears. The engine had a Crane Cams CCH-304-2 NC hydraulic cam, which specs out at 234/244 at 0.050-inch tappet lift and 0.553/0.576-inch max lift, and is ground on 114 centers. One lobe on the cam has me concerned so I don't plan on using it again. Currently, the car has a set of worn-out Goodyear 30x9.0x15 slicks on it. According to my research, with help from my good friend Google, it seems the pistons are Speed-Pro/Federal Mogul, but I can't find out if they are cast or forged. I have looked at cams from Comp Cams, Crane Cams, and Herbert Cams, and will also install the cam manufacturer's valvesprings. Lastly, I'm thinking of running 28x9.0x15 slicks but am unsure what rpm the engine will be pulling though the traps. What do you recommend?</br>Gene Reedy
A It appears your engine was built around an L36 390hp 427 from 1967. From the factory, all 390- and 400hp 427s came with cast 10.25:1 compression pistons. However, the Speed-Pro piston number you gave us was one of the approved performance replacement pistons for the IHRA Stock Eliminator engines. The Speed-Pro number was in good company with CP, JE, TRW, and Venolia forged replacements. Could I find a direct listing to confirm that your pistons are forged? No, I couldn't. However, if you inspect your pistons and look for a flat steel plate cast into the piston to reinforce the wrist-pin area between the skirts, they are cast. If your pistons are a nicely smooth, molded piston without any noticeable cast patterns and steel reinforcements, that's definitely forged. Also, check your piston-to-wall clearance with a feeler gauge. If it's around 0.002-0.003 inch, they're cast; if it's 0.006-0.007 inch, they're forged. Sorry, but this is the best we can do.
With the time slips you found in the car, we worked out the top-end rpm with the 30-inch tires. With a slight amount of converter slippage, the car would have been turning around 5,000 rpm in the lights at 107 mph. Going with a 28-inch-tall tire will step the engine speed up closer to 5,500 rpm. This should be a much better rpm for that engine, and with some upgrades, we don't see any reason why it won't run 110-112 in the lights at high 11s. This is a great speed for the engine because it will live forever, and it's where your stock oval ports run out of air.
As for the camshaft, we would stay to the conservative side and run on a bunch of torque. Of all the short mechanicals out there, we like the looks of the Comp Cams Xtreme Energy Mechanical XS274S. It specs out at 236/242 duration at 0.050-inch tappet lift and 0.568/0.578-inch max lift, and is ground on a 110 separation angle. This cam should be stronger than the earlier hydraulic and isn't too big for your stock oval ports.
Since you mentioned you didn't like the looks of one of your lobes, let me reinforce how critical cam break-in is, especially in these days of junk engine oil. They have taken all the zinc out of our oil to satisfy the Smog Police and it's killing our camshafts. Make sure you follow Comp's recommendation on break-in and use its oil additives. Also, as I have mentioned before, Joe Gibbs Racing has specific break-in oil that isn't regulated by the aforementioned Smog Police, and Lucas Oil has just released a specific oil additive package called TB Zinc Plus (PN 10063), just for engine break-in. Check it out. Good luck and see ya at the races!
Sources: compcams.com, lucasoil.com
If you have technical questions for Kevin McClelland, send him an e-mail at email@example.com.
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