Basic modifications for newbies
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| − | + | ==Overview== | |
| + | There are numerous sources of information to assist the untrained individual in the rebuilding or repairing of specific components of a vehicle, but there needs to be a place where he/she can learn what to do and what not to do in the modification of their vehicle(s). This article will attempt to fill in the blank spaces in their understanding concerning these modifications. | ||
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It is usually cheaper and easier to begin making mods to the motor and that's where most everybody starts in their quest to make the vehicle faster/quicker. | It is usually cheaper and easier to begin making mods to the motor and that's where most everybody starts in their quest to make the vehicle faster/quicker. | ||
| − | The problem with this approach is that you're starting at the wrong end of the vehicle. Unless you're starting with a scratch build, you're probably modifying an OEM vehicle which was engineered at the factory to provide good gas mileage (numerically low | + | The problem with this approach is that you're starting at the wrong end of the vehicle. Unless you're starting with a scratch build, you're probably modifying an OEM vehicle which was engineered at the factory to provide good gas mileage by using a high rear gear ratio (numerically low), probably something in the 2.70:1 to 3.00:1 range, and a tight torque converter having somewhere around 1,200-1,400 rpm stall speed. |
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| − | + | This type of vehicle was designed for all sorts of people, the vast majority of these owners expect good fuel mileage, dependability, and quiet operation. The cam, intake and exhaust systems, gear ratios, torque converter stall speed, and other parts that came stock on the vehicle were designed to accomplish this goal. When you begin changing parts, you are upsetting this balance of systems and characteristics that were built into the vehicle at the factory. | |
| − | + | The first things that are often changed are the exhaust system, cam, intake manifold/carburetor (if working on a pre-EFI motor) in an effort to make the ol' hoss a world beater. | |
| − | + | First, the #1 mistake is believing that changing the camshaft alone will make a lot more horsepower. A cam change can make more power, but he cam must be matched to the static compression ratio (SCR) of the motor. The most important timing event on a camshaft is the '''intake valve closing point'''. The intake valve begins to open at some point before the piston gets to top dead center (TDC) on the exhaust stroke. The piston descends in the bore with the intake valve open and the cylinder is filled with air/fuel mixture. After the piston gets to bottom dead center (BDC) and starts back up on the compression stroke, the intake valve closes and compression begins. If we are beginning with a stock motor on which the static compression ratio is somewhere around 8.5:1 and put a cam in that has more duration and closes the intake valve later than was designed for at the factory, the piston will push some of the air/fuel mixture back through the still-open intake valve and cylinder pressure will be lower than it was with the stock cam that closed the intake valve at exactly the right point to work with the stock static compression ratio. | |
| − | + | So if you're going with more cam, then raise the SCR so that the cam and static compression ratio are matched. The OEM's have super computers that tell them exactly the timing points to be ground into the cam to match the SCR and make power at the rpm the general public expects. This is usually idle to ~4,000 rpm or a little higher. Any cam will have an operating range of roughly 3,500 rpm. In other words, it will be efficient from idle to 4,000 or 1,000 to 4,500 or 2,000 to 5,500 or 3,500 to 7,000 or whatever, depending on the valve opening and closing points ground into the cam when it is manufactured. It will also have a wide lobe separation angle or "LSA" (max lift intake point after top dead center added to max lift exhaust point before top dead center and divided by 2) for good manifold vacuum to properly operate power brakes and other vacuum operated accessories and contribute to a smooth idle (Grandma doesn't want the motor going RUMPTY-RUMP when she's on the way to bingo and there are a lot more little old ladies buying cars than there are hot rodders). An OEM cam might be measured at 114 to 118 degrees LSA for instance. | |
| − | + | You can figure the LSA yourself. Let's say that the intake centerline is 106 degrees after top dead center (ATDC) and the exhaust centerline is 114 degrees before top dead center (BTDC). Add 106 to 114 and divide by 2 to find a LSA of 110 degrees. You might also see LSA expressed as lobe displacement angle. This is not to be confused with lobe center. Lobe center is the point of maximum lift of the lobe, ATDC for the intake lobe and BTDC for the exhaust lobe. | |
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| − | + | Now, say the decision is made that the motor needs more cam. In most cases, the SCR of the motor is unknown. Also unknown is the piston deck height, the squish clearance, or anything else. All that's known is that he wants the RUMPTY-RUMP that he heard coming from the Super Comp motor he heard at the drag strip or the hot rod down at the Sonic Drive In. What he may not know is that the motor in that Super Comp car has upwards of fifteen to twenty thousand dollars invested in it and is maximized for racing. It idles like that because the cam has to be very aggressive to work with the 12.0:1 to 16.0:1 SCR that is built into the motor. It may have been designed to make power from 4,500 to 8,000 rpm for instance and will be coupled to a very loose torque converter that stalls at around 5,000 rpm for instance. As far as the hot rod down at the Sonic, that owner may have used a cam such as a Thumpr to get that sound and the car may not be as fast as it sounds. | |
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| − | + | I'm just throwing these numbers around to show you that the cam in the Super Comp motor will not work in your street-driven 350 Chevy. The Thumpr cam may work, but you may be able to make more horsepower and torque by matching the other motor characteristics to the proper camshaft and still have your rump-rump. | |
| − | + | I've gotten a little off track with my explanation. We need to go back to what a newbie should do to his vehicle FIRST. | |
| + | After rebuilding the brakes, steering and suspension the first modification done to an otherwise stock auto/truck should usually be a different gear ratio. A good compromise between mileage and acceleration in a street car is somewhere around 3.70:1 ratio. If the owner intends to change this vehicle into a semi-serious street/drag car, then additional aftermarket traction devices such as anti-wheel hop products and tires with different rubber compound should be considered, along with strengthening and stiffening the chassis/body. Even more serious competitors should consider mini-tubs or full tubs in the car to accommodate wide racing slicks, along with a roll cage to tie the chassis together better. A large number of racers who show up at my track mount slicks on separate wheels (wide steel wheels will work just fine) to be bolted to the car after they drive it in off the street. | ||
| − | + | See [http://www.crankshaftcoalition.com/wiki/Why_a_shorter_rear_gear_will_accelerate_the_car_quicker Why a shorter rear gear will accelerate the car quicker] | |
| − | + | Of course, when it comes to traction, a limited slip differential like the Chevrolet Posi-Traction or aftermarket Detroit Locker or Auburn units or similar units will do an excellent job of hooking up both tires. However, these are not mandatory to get both tires to pull and not spin the passenger side tire. | |
| − | + | With a front-motor, rear-drive vehicle, the chassis twists diagonally upon application of power. The left front gets lighter and the right rear gets lighter. The right front and the left rear get heavier. This is why you will see the right rear tire spin while the left rear hooks up on a car with a "peg-leg" or "open" differential. The right rear is light and needs additional weight applied to it. This can be accomplished cheaply and easily by installing an air shock to replace the conventional shock absorber on that side, or an air bag on the RIGHT REAR ONLY. Experimenting with the air pressure in the shock/bag will allow you to equalize the weight applied to both rear tires on acceleration and "hook up" both tires without going to the expense of installing a locking device in the differential. Just keep adding air pressure to the shock until you have two equal-length black tire stripes on the pavement when accelerating from a stand-still. I've done this many times and have seen other racers do it with equal success. An additional benefit is that the car will be easier to drive at the strip with an open differential that has been "weight equalized". | |
| + | Now, with the rear end nailed down and operating, it's time to move on to the middle of the car and take a look at the transmission and torque converter, assuming an automatic transmission will be used. If the transmission is a manual shift, then overlook the following information and go lower higher numerically) on the rear gear (4.10, 4.56, etc.). | ||
| + | If the car is very light (under 2,800 lbs with driver aboard), then a 2-speed automatic like the Powerglide will work well on the drag strip and should work on the street as well. Heavier cars should use a 3 or 4-speed AT. If fuel mileage is a concern in your world-beater, then a 4-speed overdrive auto is probably the better choice. I'll leave it to someone else to go into detail about the choices here, but the GM 700R4 has shown to be a good choice for non-computer applications. They can be beefed up to take considerable abuse. | ||
| − | + | The next component to be addressed is the torque converter. It is mandatory that the converter is matched to the camshaft you'll be using. As was stated earlier in this article, stock converters will stall at around 1,200 to 1,400 rpm, depending on the amount of torque produced by the motor among other things and that's fine when you are using a stock-type cam that begins making power at idle. But when you change the cam out for a longer duration/higher lift model, you're no longer making power from idle and the car will be a dog until the rpm increase to the point where the motor is making power. One way around this is to install a converter that stalls higher than stock so that the motor comes up on the cam quicker and the car accelerates faster. If you install a cam that operates between 3,500 and 7,000 rpm and use a converter that stalls at 1,200, you can see that the motor will not be producing enough torque from 1,200 to 3,500 to move the car efficiently. The car will be a D-O-G. On the other hand, if you use the 3,500-7,000 cam with a converter that stalls at around 3,500, then when you nail the loud pedal, the motor will rev up close to the stall speed of the converter and you'll be making power and applying torque to the rear tires sooner. (PLEASE NOTE THAT EACH APPLICATION IS DIFFERENT AND THAT A PROFESSIONAL TORQUE CONVERTER MANUFACTURER SHOULD BE CONSULTED FOR THE EXACT CONVERTER FOR YOUR APPLICATION). If I could get a little plug in here, I know Jim Hughes personally for many years and I can, without question, recommend Hughes Converters. Jim is a man of honesty and integrity, both personally and professionally. | |
| − | DISCLAIMER: THE FOLLOWING INFORMATION WAS GLEANED FROM MANY DIFFERENT SOURCES. SOME OF IT MAKES SENSE TO ME AND SOME OF IT DOESN'T. USE WHAT YOU THINK IS REAL AND THROW OUT THE REST OF IT. I HAVE NOT USED ALL OF THE SUGGESTIONS LISTED HERE. THROUGH THE YEARS, I HAVE ACCOMPLISHED MANY SUCCESSFUL FLAT TAPPET CAMSHAFT BREAK-INS, BUT I HAVE ALSO ROACHED A FEW. USE THIS LIST AS A GUIDELINE SO THAT YOU REMEMBER TO CHECK ALL THESE THINGS WHEN INSTALLING A NEW FLAT TAPPET CAMSHAFT. DO NOT TAKE EVERYTHING POSTED HERE AS GOSPEL. IF THE MANUFACTURER OF THE CAMSHAFT YOU'RE USING RECOMMENDS PROCEDURES THAT DIFFER FROM WHAT IS SHOWN HERE, USE THE MANUFACTURER'S RECOMMENDATIONS TO THE LETTER AND DISREGARD THIS INFORMATION. | + | ==Mistakes that could frag your flat tappet cam and lifters== |
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| + | '''DISCLAIMER:''' THE FOLLOWING INFORMATION WAS GLEANED FROM MANY DIFFERENT SOURCES. SOME OF IT MAKES SENSE TO ME AND SOME OF IT DOESN'T. USE WHAT YOU THINK IS REAL AND THROW OUT THE REST OF IT. I HAVE NOT USED ALL OF THE SUGGESTIONS LISTED HERE. THROUGH THE YEARS, I HAVE ACCOMPLISHED MANY SUCCESSFUL FLAT TAPPET CAMSHAFT BREAK-INS, BUT I HAVE ALSO ROACHED A FEW. USE THIS LIST AS A GUIDELINE SO THAT YOU REMEMBER TO CHECK ALL THESE THINGS WHEN INSTALLING A NEW FLAT TAPPET CAMSHAFT. DO NOT TAKE EVERYTHING POSTED HERE AS GOSPEL. IF THE MANUFACTURER OF THE CAMSHAFT YOU'RE USING RECOMMENDS PROCEDURES THAT DIFFER FROM WHAT IS SHOWN HERE, USE THE MANUFACTURER'S RECOMMENDATIONS TO THE LETTER AND DISREGARD THIS INFORMATION. | ||
*1. Failure to remove all [[rust]]-preventative from cam and lifters with solvent once you get them home. (This advice does not include removing coatings applied at the factory such as phosphates. It is only suggesting to remove rust-preventative grease that may or may not have been applied to the cam/lifters to prevent rust in storage. This grease will not have the extreme pressure characteristics that Molybdenum Disulphide has and should be removed so that MD can be applied properly. MD is the black, tar-like extreme-pressure grease that is recommended by some camshaft manufacturers to be applied to the lifter crowns/cam lobes for initial camshaft break-in). | *1. Failure to remove all [[rust]]-preventative from cam and lifters with solvent once you get them home. (This advice does not include removing coatings applied at the factory such as phosphates. It is only suggesting to remove rust-preventative grease that may or may not have been applied to the cam/lifters to prevent rust in storage. This grease will not have the extreme pressure characteristics that Molybdenum Disulphide has and should be removed so that MD can be applied properly. MD is the black, tar-like extreme-pressure grease that is recommended by some camshaft manufacturers to be applied to the lifter crowns/cam lobes for initial camshaft break-in). | ||
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*9. Failure to check for piston/valve clearance..... 0.080" on the intake and 0.100" on the exhaust is considered by many to be the minimum clearance acceptable. You will probably find the closest near-miss at the exhaust valve on overlap, when the piston is chasing the exhaust valve back onto its seat. | *9. Failure to check for piston/valve clearance..... 0.080" on the intake and 0.100" on the exhaust is considered by many to be the minimum clearance acceptable. You will probably find the closest near-miss at the exhaust valve on overlap, when the piston is chasing the exhaust valve back onto its seat. | ||
| − | *10. Failure to run the motor at high | + | *10. Failure to run the motor at high rpm (2500 or higher, alternating 1000 rpm up and/or down to allow the crank to throw oil in different places at different revs) for the first 40-45 minutes of its life. NO IDLING. NO IDLING. NO IDLING. The motor should not be run at less than 2500 rpm for a minimum of 40 minutes. If a problem develops, shut the motor down and fix it, then resume break-in. The main source of camshaft lubrication is oil thrown off the crankshaft at speed, drainback from the oil rings and oil vapors circulating in the crankcase. At idle, the crank isn't spinning fast enough to provide sufficient oil splash to the camshaft/lifters for proper break-in protection. |
*11. Failure to clearance lifters in their bores so that they spin freely. Lifter clearance should be 0.0012" to 0.002", with 0.0015" (one and one/half thousandths) considered close to ideal. Too loose is as bad as too tight. | *11. Failure to clearance lifters in their bores so that they spin freely. Lifter clearance should be 0.0012" to 0.002", with 0.0015" (one and one/half thousandths) considered close to ideal. Too loose is as bad as too tight. | ||
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*Just a note to make you aware of the loading between the camshaft lobe and lifter crown. That pencil-point of contact, if carried out to a square inch, would be somewhere between 250,000 and 300,000 POUNDS PER SQUARE INCH. | *Just a note to make you aware of the loading between the camshaft lobe and lifter crown. That pencil-point of contact, if carried out to a square inch, would be somewhere between 250,000 and 300,000 POUNDS PER SQUARE INCH. | ||
So, it is incumbent on the engine builder to do everything in his/her power to assure that all precautions have been taken to protect parts with this much pressure between them. | So, it is incumbent on the engine builder to do everything in his/her power to assure that all precautions have been taken to protect parts with this much pressure between them. | ||
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| + | ==Additional reading== | ||
| + | [[Valve Train Points To Check]] | ||
[[Category:General hotrodding]] | [[Category:General hotrodding]] | ||
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