Tuesday, January 5, 2010

HIGH LIFTS / HOT CAMS

HOW TO SELECT YOUR NEW CAMSHAFT


This is a basic guide for proper camshaft selection. There are always exceptions, and lots of people ignore the guidelines, but if you stay close to them you will have a combination that works well.

Getting The Right Cam - Engine RPM Calculations - Basic Parts Selection Guide
Which Specs Are Better?

Accelerated Motion Home Page

Getting the camshaft that is right for YOU
The most important thing to remember when designing your engine is how it will be used most often. All of the components that you choose for your engine must match your primary use (and each other) or you will be disappointed with the results. This is especially true for internal engine parts such as pistons, heads, and cams. If you make a mistake choosing one of these items you will have a lot of expense and work ahead of you to make the corrections.
Over-camming the engine is the most common mistake made when choosing a cam. A big cam will not give better bottom end power and big horsepower numbers also won't happen at low rpms without big cubic inches or a supercharger.
Another common mistake is building a high compression engine and then choosing a Torque/City or RV/Commuter camshaft to match the type of driving the vehicle will be used for. Unfortunately this will produce cylinder pressures that are too high for pump gas to handle. This is the way to go only if you plan to run on propane (107 octane) or natural gas (130 octane).

So how DO you choose your camshaft?
First, you must decide how the vehicle is going to be used most often.
If you are using it daily to go back and forth to work, how much of that time is in city traffic? And how much of your traffic time is spent sitting in line at the light? These questions might seem unnecessary, but if you spend 25% of your time at idle and another 50% of your time in traffic between 0 and 50 KMH (30 MPH), this information becomes important. This would be the speed that determines the low end of your RPM range.
Next you will have to determine your usual cruising speed and/or top speed. If you have a tach it is easy to get your normal operating range by checking your engine speed as you drive. If you don't have a tach in your vehicle some calculations will be required to determine what RPM you are running at. For this you will need to know your Tire Outside Diameter (O.D.) and your Rear Axle Ratio. If you do not know your Rear Axle Ratio there is often a tag on one of the differential cover bolts that will tell you. Or you can find out the hard way:
Block the front wheels
If your vehicle doesn't have posi:
Raise one of your rear wheels off of the ground and properly support your vehicle
Put a chalk mark on the raised tire and on the driveshaft
With the transmission in neutral and the emergency brake off rotate the tire two full turns (to compensate for the action of the differential) while counting the number of times the drive shaft turns.
If your vehicle has posi:
Raise both of your rear wheels off of the ground and properly support your vehicle
Put a chalk mark on the same position of both tires and on the driveshaft
With the transmission in neutral and the emergency brake off rotate both tires in the same direction one full turn while counting the number of times the drive shaft turns.
Check to make sure the lines on the tires still match position. If they aren't in the same positions as at the start something is wrong.
The number of driveshaft turns is your Rear Axle Ratio. The common gear ratios are 3.08, 3.23, 3.55, 3.73, 3.91, 4.10, 4.56, and 4.88.
To get your correct tire diameter measure from the ground to the center of the wheel and multiply by 2. Measuring from any other point on the tire will give you a larger diameter than your vehicle actually uses.


Here are your Vehicle Speed To Engine RPM calculations
KILOMETERS:

KMH
1 --- = KM per minute
60

2 KM per minute X 100,000 = cm per minute

cm per minute
3 --------------------------- = Tire RPM
(cm Tire O.D.cm X 3.1416)

4 Tire RPM X Rear Axle Ratio = Engine RPM


MILES:

MPH
1 --- = Miles per minute
60

2 Miles per minute X 63,360 = inches per minute

inches per minute
3 ------------------------------ = Tire RPM
(inches Tire O.D. X 3.1416)

4 Tire RPM X Rear Axle Ratio = Engine RPM




Keeping your idle requirements in mind, work out the low end of your RPM range. For a vehicle that is driven daily in the city it will be your idle rpm. For a drag vehicle it will be the launch rpm. For an oval track vehicle it will be your rpm at re-start.
Now repeat the formula for your top speed. For a street vehicle the highway cruising speed (90 KMH or 60 MPH) will be the top of your torque range. For a drag vehicle peak horsepower and rpm will be at the fast end of the strip. For an oval track vehicle peak horsepower and rpm will be at the fast end of the straights.
Now you know what RPM range you require for your driving.
The optimum RPM range of a cam is really only about 3000 RPM from the beginning of the torque range to the end, with another 1000 rpm to peak horsepower. They will operate above and below this but not to the best performance. If you require an RPM range that is wider than this you will have to make a compromise. Which RPM range is the most important to you? For hydraulic lifter cams, Rhoads variable lifters will add about 1000 rpm to to lower end of the camshaft's normal operating range.


Basic Parts Selection Guide
This guide uses 8 typical performance levels from mild to wild. If you are not sure which range to use, be conservative. If you choose too high an rpm range it will be less reliable, harder on parts, and rarely be used. An rpm range that is lower than you need will still be used even if your top end is slightly limited.
Each performance level suggests the range of Accelerated Motion camshaft, air/fuel requirements, compression ratio, exhaust type, gear ratios, and ignition, that will work together the best for that performance level. Maximum engine HP (not including nitrous or supercharging) and expected idle speed are also shown.
The RPM range that a cam works best in will change with the engine size and head design. Recomendations shown in this guide are for average engines. See the web parts catalogue for more specific recomendations.

TORQUE AND CITY
(idle to 3600 rpm, max. HP @ 4600 rpm)
Good fuel economy, light to medium towing and improved low-end for city use. No internal engine modifications are required.
ENGINE CAM RANGE*
151 4 cyl. up to 19477
181 4 cyl. up to 19767
189 6 cyl. up to 19393
250 6 cyl. up to 19686
300 6 cyl. up to 20220
302 V8 up to 19567
350 V8 up to 19827
400 V8 up to 19830
454 V8 up to 20190
500 V8 up to 20617
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 9.0:1 or less, Propane 10.5:1 or less
Exhaust: Stock or dual exhaust
Fuel Inj.: Should work with factory EFI computers
Gear Ratio: 3.7:1 and lower (numerically)
Idle: 600 rpm or less
Ignition: Recurved distributor and electronic ignition



RV AND COMMUTER
(1000 rpm to 4000 rpm, max. HP @ 5000 rpm)
Good fuel economy, medium towing and improved mid-range performance for every day use. No internal engine modifications are required.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 19477 to 20277 222 to 278 cfm Max. 121 HP
181 4 cyl. 19767 to 20567 266 to 333 cfm Max. 145 HP
189 6 cyl. 19393 to 20193 278 to 348 cfm Max. 151 HP
250 6 cyl. 19686 to 20486 368 to 460 cfm Max. 200 HP
300 6 cyl. 20220 to 21020 442 to 552 cfm Max. 240 HP
302 V8 19567 to 20367 445 to 556 cfm Max. 242 HP
350 V8 19827 to 20627 515 to 644 cfm Max. 280 HP
400 V8 19830 to 20630 589 to 736 cfm Max. 320 HP
454 V8 20190 to 20990 668 to 836 cfm Max. 363 HP
500 V8 20617 to 21417 736 to 920 cfm Max. 400 HP
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 9.5:1 or less, Propane 11.0:1 or less
Exhaust: Stock, dual exhaust, or small tube headers
Fuel Inj.: Factory EFI computers might require modification
Gear Ratio: 3.9:1 or lower (numerically)
Idle: 650 rpm or less
Ignition: Recurved distributor and electronic ignition



MILD PERFORMANCE
(1400 rpm to 4400 rpm, max. HP @ 5400 rpm)
Fair idle, moderate fuel economy, improved mid-range performance and enough torque for medium/heavy towing. Nice for ski boat.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 20277 to 21077 250 to 309 cfm Max. 136 HP
181 4 cyl. 20567 to 21367 300 to 371 cfm Max. 163 HP
189 6 cyl. 20193 to 20993 313 to 387 cfm Max. 170 HP
250 6 cyl. 20486 to 21286 414 to 512 cfm Max. 225 HP
300 6 cyl. 21020 to 21820 497 to 615 cfm Max. 270 HP
302 V8 20367 to 21167 500 to 619 cfm Max. 272 HP
350 V8 20627 to 21427 579 to 717 cfm Max. 315 HP
400 V8 20630 to 21430 662 to 819 cfm Max. 360 HP
454 V8 20990 to 21790 752 to 930 cfm Max. 409 HP
500 V8 21417 to 22217 828 to 1024 cfm Max. 450 HP
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 8.5:1 to 10.0:1, Propane 10.0:1 to 11.5:1
Exhaust: Stock dual exhaust or small tube headers
Fuel Inj.: Factory EFI computers will require modification
Gear Ratio: 3.1:1 to 4.1:1
Idle: 700 rpm or less, slight lope
Ignition: Recurved distributor and electronic ignition



PERFORMANCE
(1800 rpm to 4800 rpm, max. HP @ 5800 rpm)
Good upper mid-range performance. Works well for medium and heavy towing with low (high numerially) gears.
Good for jet boat and skiing. Biggest for I/O boat.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 21077 to 21877 279 to 341 cfm Max. 151 HP
181 4 cyl. 21367 to 22167 334 to 409 cfm Max. 181 HP
189 6 cyl. 20993 to 21793 349 to 427 cfm Max. 189 HP
250 6 cyl. 21286 to 22086 461 to 565 cfm Max. 250 HP
300 6 cyl. 21820 to 22620 554 to 678 cfm Max. 300 HP
302 V8 21167 to 21967 557 to 682 cfm Max. 302 HP
350 V8 21427 to 22227 646 to 791 cfm Max. 350 HP
400 V8 21430 to 22230 738 to 903 cfm Max. 400 HP
454 V8 21790 to 22590 838 to 1025 cfm Max. 454 HP
500 V8 22217 to 23017 923 to 1129 cfm Max. 500 HP
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 9.0:1 to 10.5:1, Propane 10.5:1 to 12.0:1
Exhaust: Dual exhaust, headers are recommended
Fuel Inj.: Performance EFI system recommended
Gear Ratio: 3.3:1 to 4.3:1
Idle: 750 rpm or less, small lope
Ignition: Recurved or perf. distributor, electronic ignition



HOT PERFORMANCE
(2200 rpm to 5200 rpm, max. HP @ 6200 rpm)
Strong upper rpm performance. Not for towing. Good in jet boat with A impeller. Biggest for skiing. Multi-angle valve grind is recommended.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 21877 to 22677 308 to 373 cfm Max. 166 HP
181 4 cyl. 22167 to 22967 369 to 447 cfm Max. 199 HP
189 6 cyl. 21793 to 22593 386 to 467 cfm Max. 208 HP
250 6 cyl. 22086 to 22886 510 to 617 cfm Max. 275 HP
300 6 cyl. 22620 to 23420 612 to 741 cfm Max. 330 HP
302 V8 21967 to 22767 616 to 746 cfm Max. 332 HP
350 V8 22227 to 23027 714 to 864 cfm Max. 385 HP
400 V8 22230 to 23030 816 to 988 cfm Max. 440 HP
454 V8 22590 to 23390 926 to 1121 cfm Max. 499 HP
500 V8 23017 to 23817 1020 to 1235 cfm Max. 550 HP
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 9.5:1 to 11.0:1, Propane 11.0:1 to 12.5:1
Exhaust: Dual exhaust with headers
Fuel Inj.: Performance EFI system required
Gear Ratio: 3.5:1 to 4.5:1
Idle: 800 rpm or less, has a lope
Ignition: Recurved or perf. distributor, electronic ignition



TRACK PERFORMANCE
(2600 rpm to 5600 rpm, max. HP @ 6600 rpm)
Strong performance above 2500 rpm. Expect low manifold vacuum. Mild port work and multi-angle valve grind are recommended. Automatic transmissions may require a high stall torque converter.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 22677 to 23477 338 to 405 cfm Max. 181 HP
181 4 cyl. 22967 to 23767 406 to 485 cfm Max. 217 HP
189 6 cyl. 22593 to 23393 423 to 507 cfm Max. 227 HP
250 6 cyl. 22886 to 23686 560 to 670 cfm Max. 300 HP
300 6 cyl. 23420 to 24220 672 to 804 cfm Max. 360 HP
302 V8 22767 to 23567 677 to 810 cfm Max. 362 HP
350 V8 23027 to 23827 784 to 938 cfm Max. 420 HP
400 V8 23030 to 23830 896 to 1072 cfm Max. 480 HP
454 V8 23390 to 24190 1017 to 1217 cfm Max. 545 HP
500 V8 23817 to 24617 1120 to 1340 cfm Max. 600 HP
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 10.0:1 to 11.5:1, Propane 11.5:1 to 13.0:1
Exhaust: Dual exhaust with headers
Fuel Inj.: Performance EFI system required
Gear Ratio: 3.7:1 to 4.7:1
Idle: 850 or less, has a lope
Ignition: Performance distributor and electronic ignition



PRO STREET AND RACE
(3000 rpm and up)
Super top-end performance. Manifold vacuum might be too low for power brakes and automatic transmission modulators. NOT for daily driving. Mild port work and multi-angle valve grind are recommended. Automatic transmissions will require a high stall torque converter.
ENGINE CAM RANGE* AIR/FUEL RANGE HORSEPOWER
151 4 cyl. 23477 and up 369 cfm and up 181 HP and up
181 4 cyl. 23767 and up 443 cfm and up 217 HP and up
189 6 cyl. 23393 and up 462 cfm and up 227 HP and up
250 6 cyl. 23686 and up 611 cfm and up 300 HP and up
300 6 cyl. 24220 and up 734 cfm and up 360 HP and up
302 V8 23567 and up 738 cfm and up 362 HP and up
350 V8 23827 and up 856 cfm and up 420 HP and up
400 V8 22830 and up 978 cfm and up 480 HP and up
454 V8 24190 and up 1110 cfm and up 545 HP and up
500 V8 24617 and up 1223 cfm and up 600 HP and up
*The cam range refers to the 2nd half of the Accelerated Motion part number.
Compression: Gasoline 10.5:1 and up, Propane 12.0:1 and up
Exhaust: Dual exhaust with headers
Fuel Inj.: Race EFI system required
Gear Ratio: 3.9:1 and higher (numerically)
Idle: 850 rpm or more, will be rough
Ignition: Performance distributor and electronic ignition




Minimum chassis horsepower required to reach a 1/4 mile speed:
HPq = (0.00426 x MPH) x (0.00426 x MPH) x (0.00426 x MPH) x WEIGHT



What makes one cam in the range better than another?
There are many myths and legends about which cam is better, single pattern (intake and exhaust the same) or dual pattern (intake and exhaust different). The fact is that unless your exhaust ports are very restricted there is no way to tell. On the dyno you would always be comparing apples to oranges.

Lobe Center Separation is as big a consideration as duration. Lobe center separation plays a role in determining how much valve overlap (the amount of time the intake and exhaust valves are both open) your engine will have and what your vacuum and idle quality will be. Street cams with wide lobe center separation (114) generally will have a good idle, high vacuum, and a nice wide RPM range. Separations closer to 108 (less separation means more valve overlap) can create problems for some computer engine controls due to their rougher idle and lower manifold vacuum. They have a shorter RPM range but produce much stronger mid-range power with some improvement to the top end.

Now we get to valve lift. Many customers believe that the cam with the highest lift will perform much better than a moderate lift cam. While it is true that a high lift cam will provide better flow by getting the valve further out of the way, there are limits to this as well as other considerations.
The high rate of lift required to achieve high lift on a short duration cam is very hard on the valve train and causes valve to piston interference problems (especially with narrow lobe separations). High lift also causes several other problems including valve spring retainer to valve guide/seal interference, rocker arm to stud interference, and valve spring coil bind. Adjustable rocker arms are often required to take up any clearance created in the valve train when the valve is closed. All of this must be checked and corrected before a high lift cam can operate properly.
If you are using a cam with enough duration to make a high lift effective, the usual limit for noticable improvement is reached when the lift equals 25% of the valve diameter. This means that if your valve diameter is only 1.84 you will get the best flow at only .460 lift. Lifts higher than 25% of the valve diameter will add more duration at the maximum flow point but excessive lifts will cause more problems than they are worth in an engine that is not fully race prepared.
The bottom line on cam lift is that it is pointless to go overboard. All newer designs have adequate lift for the operating range of the cam. The minimal gains from an extra high lift cam are not worth the extra work in a street vehicle.
Here are some basics for choosing a cam from your range:
Large cars: Use short or medium duration, exhaust can be longer. Wide lobe seperation is better.
Small Cars: Use long intake duration, exhaust can be longer. Lobe center seperation can be short.
Propane and Natural Gas: Use short or medium duration single pattern. Wide lobe seperation is required.
Trucks: Use short duration. Wide lobe seperation is better.
Nitrous or Supercharger: Use long duration. Wide lobe seperation is required. Supercharger compression must be lower than shown in the guide.
Turbos: Use short or medium duration, exhaust can be shorter. Wide lobe seperation is required. Compression for turbos must be lower than shown in the guide.

Courtesy :-www.amotion.com
Burnaby, B.C. Canada
cams@amotion.com
(Above info is not related to any Indian cars...So please take it as a knowledge.)