Shifting Gears
Now from the title you're probably expecting a manual-transmission theme. No, what I'm referring to is changing direction when you're in the middle of a project. As many of you know, about three years ago, my son Daniel and I started restoring a '65 Chevelle. We put about two years into the car and have many stories about the buildup, like the one about finishing the car one day before running the first race of the season last year. The car ran perfectly, as predicted, and he made it to the semis in the car's first race. The only thing we hadn't done yet was paint the car. Well, two days after this great day at the races, the Chevelle was introduced to a UPS delivery truck. As you can expect, the Chevelle didn't fare the introduction very well. Unfortunately, the car was totaled.
So many times a buildup project morphs into more than you'd planned. Well, this is exactly what happened with Daniel's Chevelle. The main goal of our building this together was for Daniel to learn the ins and outs of working on cars, and he wanted an American musclecar to race and play with. The further we got into the project the nicer and nicer it was turning out. It got to the point that, when we were finished with the car, Daniel was somewhat afraid to take it anywhere. This wasn't what we wanted at all. We'd lost sight of our original plan.
If you read last month's column, you know that we've been looking for a car to replace the Chevelle. This past month, through many horse trades, we have in our garage his next project. A first for the McClelland family, we've brought a '68 Nova Chevy II into the fold. It's a very clean, dead-original six-cylinder, Powerglide-equipped starter car. We've outlined exactly what we want and we're going to stick to it. Luckily, the Chevelle's entire drivetrain came through the accident just fine. We're not going to try to restore the car to any specific build. With this in mind, looking for the high-dollar factory buckets, console, gauges, and the like is not our plan. Building a very nice, purpose-built bracket car that he can cruise on the weekends is our goal. A simple coat of white paint, to give it our team colors, and a spartan black bucket interior will be just fine. With this he can enjoy taking the car for drives without the stress over something happening to it. I'm sure over the next year or so you guys and gals will read about our misadventures building another car. What else would we be doing?
Squeeze Me, Baby
Q I have been an automotive enthusiast all my life. My interests have been focused on 4x4s and off-roading; I have yet to own a vehicle that was not four-wheel drive. In the past few years, however, my interests have been changing. I now prefer to read Chevy High Performance over 4-Wheel & Off-Road. I just ordered a subscription of CHP today. This new interest in street performance led me to acquire a new project last fall. I bought a '72 GMC K1500 Sierra Grande (couldn't shed my 4x4 roots) from a second owner in Oregon. Although this truck is still a 4x4, it will see little or no time off-road. I intend to have a ball with this truck just cruising and wrenching and attending a few local car shows.
Reading CHP has caused me to give more thought to my engine and its combination of components. In particular, a letter to you in the Feb. '07 issue from a fellow in Denver regarding proper compression ratio has left me wondering about the compression in my engine. I live at about 2,700 feet above sea level. While this is not as high as Denver, it is certainly higher than the 300 feet where I bought the truck. The previous owner had replaced the original 350 with a '73 454. The engine received a 0.030-inch overbore, and the original oval-port heads received some porting and new stainless 2.19-/1.88-inch valves. The cam is a Comp Cams hydraulic roller that provides a single pattern of 0.578 inch max lift, 232 degrees duration at 0.050 inch tappet lift, and is ground on 110 centers. Comp springs, retainers, keepers, and roller rockers round out the valvetrain. The intake is an Edelbrock RPM Air Gap with a Performer 750-cfm carb. The ignition consists of an MSD billet distributor with a 6AL box. The headers are Hooker Super Comp, 1 7/8 inches.
I got a build sheet on the engine. With the flat-top pistons, the previous owner said it should provide 8.5:1 compression. The build sheet lists the combustion chambers at 119 cc. The head-gasket thickness is 0.041 inch, and the deck height is 0.007 inch in the hole. With a 4.280-inch bore and a 4-inch stroke, I calculate the compression at about 8.24:1. Is my math right? Is that an appropriate compression ratio at my elevation or, more importantly, with the other components in this engine? I see performance pump-gas big-blocks offered by GMPP and World Products that have 9.5- to 9.6:1 compression. Is that more appropriate? Would that produce a noticeable increase in performance? Would that require aluminum heads? In order for my engine to achieve 9.5:1 compression I'd need a 100cc combustion chamber. The only head I can find with that size chamber is an Edelbrock Performer 454-O high-compression. Would that work on this combination? Any advice would be greatly appreciated.Tod PickerellTaber, AB, Canada
A Welcome, brother. We know it will take you a while to get the 4x4 out of your blood and stuff that 454 into a lightweight street car, but we're willing to wait. Once you stand on a musclecar with a 454 and feel the torque, you'll be out of those trucks.
The previous owner has built you up a very nice truck. Unfortunately, you're spot-on about your low compression. First, for your 2,700-foot altitude I wouldn't recommend rebuilding the engine based on that elevation. Yes, there is a little power loss with your altitude, but nothing that a little tuning won't take care of. Now for your compression calculation. Did you add the volume of the intake valve relief into your piston, and also the ring land volume? One other thing: Your head gaskets may be 0.041 inch thick, but the bore of the gasket is at least 4.330 inches to cover the maximum standard overbore. With these volumes added into your calculation, you come in with a compression of 7.8:1. This, tied to your 232 degrees of camshaft timing, can leave an engine quite lazy downstairs. Your engine could use a serious influx of squeeze.
Without stepping up the pistons to a domed configuration, the Edelbrock Performer 454-O cylinder heads are the perfect upgrade. Edelbrock takes its oval-port aluminum head and angle-mills the deck 1.5 degrees, which rolls the head over to the exhaust side, raising the inlet ports. All these things are good for performance. With these cylinder heads, you will see around 9:1. When trying to estimate the power increase from compression changes, you might be told to expect anywhere from 3 to 6 percent of a power increase with a full point of compression increase. Your oval-port iron heads with the rest of your package probably put you in the 400hp range at sea level. With the head change, you will not only see the increase from the compression, but also a much better exhaust port. It wouldn't be out of the question to see a 25- to 30hp increase. Not only will you get that top-end power, but the added drivability of the slow-speed torque will be very noticeable. Edelbrock sells the heads bare (PN 60489) or fully assembled (PN 60499).
Yes, most performance big-blocks with aluminum heads do fall in around 9.5- to 9.6:1 compression. This is a safe ratio for a mild-performance street engine running on pump super unleaded. The head change will get you much closer, but you'll need new pistons to get above the 9.0:1 range. Good luck and have fun on the streets!
What's That Shaking?
Q I am building a 460 (454, 0.030-inch over) bottom end for my '71 Chevelle street rod. This engine will be street driven and should never see the top side of 5,600 rpm. I have all the parts, and the machinework has just been completed. I'm now ready to begin engine assembly. However, before I begin putting everything together, I thought I might consider balancing. Each of my eight new coated Speed-Pro Hyperutectic pistons/bushed Eagle Specialties SIR forged capscrew rod combinations weighs 55 grams less (yes, I said less) than the stock Chevrolet 454 cast piston/stock rod combo did. My question is this: If I'm planning to reuse the OEM 454 cast (just performance-polished) crankshaft, should I be concerned about this 55-gram piston/rod weight difference? What's your feeling on the expense of engine balancing, given the above info?Frank "Bowtie" RileyLenexa, KS
A Professional balancing is a must in your position. When engines are balanced, they attempt to keep the bob weight (combination of rod, piston, pin, rings, bearings) within 2 grams of one another. When you have a drastic difference like 55 grams, the engine won't be happy. You mentioned that the engine should never see above 5,600 rpm, but the first point you'll notice a vibration is about 900 rpm. The next will come at 1,800, then 3,600 after that. Notice a pattern? It's the first, second, and third order of harmonics. The next rpm range will double again if you would ever get there. Spend the money and enjoy the seamless power your big-block will deliver, and it will live a long and happy life.
All Fired Out
Q In Scott Crouse's article "All Fired Up" (Apr. '07), he installed a Pertronix Second Strike CD ignition system. My confusion set in when he was dyno testing. His baseline timing was set to 36 degrees, and the CAO (crank angle offset) was set at zero. His next run was to set the CAO to begin firing the CD spark 6 degrees after total timing. I would have to bow to the young man's expertise-I'm too old to be reading your magazine anyway-but how do you get something to occur after you reached total advance dialed in? I can't understand the difference between the CAO set at zero and the CAO set at 6 degrees after total timing occurs. Even in timing advance, I think 30 comes before 36. What's this old fart missing?Bill C. BodellFarr West, UT
A OK, Scott's done it again. He can be quite tricky using the latest gadgets and testing procedures. I must agree, it's very tough to make something happen after it has already happened!
First of all, let's look at how the Pertronix Second Strike CD ignition system works. As the name implies, this system fires a secondary spark after the primary ignition system (in this case an HEI) has fired. The CAO dial on the Second Strike system adjusts the CAO, which is when the second ignition firing occurs. If you adjust the CAO dial from 0 offset to 6, it will produce a secondary spark 6 degrees after the initial firing of the HEI.
This is where I think the confusion comes in. Let's throw out that we are running two different ignition systems on the car. First, spark timing is expressed as a timing value that occurs before top dead center (BTDC). This means the piston is traveling up the cylinder to the top of its travel before it begins down on its power stroke. It is called spark advance because it occurs BTDC. If your timing is set at 36 degrees BTDC, this value is advanced from 30 degrees BTDC. If you read back in the story, you'll see Scott's total timing is set at 36 degrees. When he adjusted the CAO to 6, it basically retarded the timing of the secondary ignition system by 6 degrees. The primary spark occurred at 36 degrees BTDC, then the secondary spark happened 6 degrees of crankshaft rotation later, at 30 degrees BTDC. Again, as the crank rotates clockwise and the piston is traveling up the bore towards top dead center, the crankshaft degrees are counting down as they reach TDC. A timing value of 36 degrees BTDC happens 6 degrees before 30 degrees BTDC.
Finally, you certainly are not too old to be playing games with us here at CHP. We need OGs around to keep us in line. I hope this has explained the timing mystery Scott had produced.
Burnt Out
Q I have a '72 Chevelle Super Sport with a stock 350 four-bolt main and a 4-bbl carb that is hooked up to the original four-speed Muncie trans. The problem is finding a nonstock clutch. I am a novice rebuilder, but I have had experience putting in clutches (about six in the past three years). I keep burning the stock equipment out before it's time or I completely demolish the center ring in the plate. I believe I need a more powerful clutch and flywheel combo, but there are so many choices. I can't decide; like I said, it's an original stock engine and tranny combo, and I use it for regular driving and occasional Saturday night fun on the boulevard. I can't keep spending all my money on stock clutches. Any suggestions would be helpful.Kevin ComfortSyracuse, NY
A Six clutches in three years? There are only 26 Saturday nights in six months. Production clutches should hold up behind a stock small-block unless you're having a little too much fun. Let's take a look at a clutch that will stand up to your abuse.
We'd recommend installing a Centerforce Dual Friction clutch into your Chevelle. These have a very subtle increase in pedal effort, but outstanding clamping force using a centrifugal weight system to apply more clamp force as the engine rpm increase. Also, the pressure-plate side of the clutch disc has a full facing for drivability and longevity and, on the flywheel side, carbon composite puc-style (segmented) facing for a positive engagement and increased holding capacity. As the heat increases in the clutch, you get more grip from these carbon composite pucs. This gives you somewhat of a Dr. Jeckel-Mr. Hyde clutch that is the best of both worlds. The 10.4-inch dual-friction pressure plate and disc for your application is sold under PN DF271675. Centerforce also offers billet-steel flywheels to match its clutches. Your flywheel has a 153-tooth ring gear and weighs 30.2 pounds, and is sold under PN 700100.
This will give you a very stout clutch assembly. Not to say that you can't kill this one too, but you'll really have to beat this one to get the best of it. It's much more fun cruising your Chevelle than it is lying underneath it with a Muncie on your chest.
'Burb Engine Swap
Q I hope you can help an old Chevy freak who's been out of it for 25 years. I recently purchased a '69 El Camino with a 350 and a TH350. This particular engine is a 2-bbl and is locked up solid from years of sitting. I plan to rebuild it, but for now I have sitting in my driveway a '91 11/42-ton Suburban with a 5.7L 350. I've just purchased a new vehicle and thought I would drop the 'Burb's engine into the Camino.
Problems: I don't even know what generation engine this is, or if it has a two- or four-bolt main, one-piece seals or not-told you, out of it! I will not be using the EFI or electronic controls, and I'd like to utilize the TH350 trans in the Camino. I have a good Quadrajet I can use, but I don't know what intake I would need. I'd like to put a slightly hotter cam in it, if you could make a recommendation. What other concerns are there? Timing, vacuum advance? Since I plan on using this engine only until all restoration work is done on the original engine, body, and suspension upgrades, I will be keeping the computer, EFI, and wiring harness for a future project. All recommendations gratefully accepted.Harold L. HiteTulsa, OK
A Sorry, you're not going to get away with the "out of it" excuse. You asked way too many very pointed, intelligent questions to be someone out of it. In fact, it looks like you've covered most of the bases. Let's dive right in.
First, the 'Burb engine is a Gen I LO5 TBI 350 small-block that is probably a two-bolt, but less likely could be a four-bolt. Also, these truck engines may or may not have a hydraulic roller camshaft. The block is machined for the roller-tappets, but most of the trucks still had a hydraulic flat-tappet camshaft in them. Second, the LO5 engine came equipped with swirl-port cylinder heads, which make great slow-speed torque but really run out of air in the upper rpm range. This will make a great donor engine until you have the original one built up to your specs. With all this being said, we'd leave the stock camshaft in the engine unless you're going to swap out the cylinder heads too.
We'd recommend swapping out the stock TBI inlet manifold for an Edelbrock Performer manifold PN 2104. This specific Performer has the canted center manifold bolts to match the odd angle these cylinder heads were machined to. This manifold is designed to use either a standard Q-jet or a Holley square-flange carb. This will satisfy your Quadrajet requirements.