Tips on Choosing the Right Cam
Contents
1. End Ratio 24 26 Finding Overall Tire Diameter RPM MPH or Rear Axle Ratio OVERALL TIRE DIAMETER MPH x Axle Ratio x 336 RPM MPH x Axle Ratio x 336 Tire Diameter RPM x Overall Diameter Axle Ratio x 336 Axle Ratio RPM x Tire Diameter MPH x 336 866 388 5120 386 236 9983 FAX Advanced Tips to Choose the Proper Camshaft Although pages 14 and 15 in this catalog out line the very basic steps in selecting the best camshaft for a particular application we can certainly add to the criteria needed for the best possible results For general street or marine applications the following will help provide an enhanced guideline Exactly what engine is it This sounds really obvious but a lot of folks aren t really knowledgeable on what they re working with For example I ve got a small block Chevrolet It could be a 1957 87 power plant that was originally equipped with a flat faced lifter camshaft or it could be a 1987 96 style engine that came with a hydraulic roller camshaft Each basic engine requires a differ ent style camshaft Similar choices can also occurs with the evolution of big block Chevrolets small block Fords small block Mopars and many others In the 1970 s General Motors exchanged the Buick Oldsmobile and Pontiac bodies and engines with some folks not understanding that the Buick 455 Oldsmobile 455 and Pontiac 455 V 8s are all totally different engines Any infor mat2. Basic Tips on Choosing the Right Cam Cam selection accuracy begins with knowing how you intend to use the vehicle engine and drivetrain modifications already made or planned and the lifter type Hydraulic Hyd Roller Mechanical Solid or Flat Tappet or Mech Roller you wish to use You ll find addi tional information to help you choose the cor rect cam on Pages 14 through 17 We urge you to take a little extra time now in making your selection This will insure that you make the right choice the first time To choose the correct cam and valve train for your engine vehicle and application follow the steps below What To Look For First First find your engine make number of cyl inders year and original engine displace ment as listed in cubic inches or metric refer ence Example Chevrolet 1986 350 cu in Decide Which Lifter Style Decide on the lifter type you wish to use in your engine For convenience and ease of maintenance we recommend a hydraulic cam and lifters either flat face or hydraulic roller for most street performance and daily driving applications NOTE Passenger car engines up through 1987 model year generally used conventional hydraulic or mechanical solid lifters and cams In the GM family 1988 up pass car and 1996 up truck engines were factory equipped with hydraulic roller cams and lifters Light trucks pick up s etc generally used flat face lifters and cams up thro
3. der cam profile Be sure to specify the Part Number when ordering Choose Your Valve Train Components The Valve Train Buyer s Guide Pages 284 through 385 contains additional product applications and additional information not found on the regular applications pages Be sure to consult these pages for optional products that will add even more horsepow er torque rpm response and reliability to your cam selection Crane Cams amp Valve Train Products Section Getting Information How to Determine Your Cruising RPM at 60 MPH 1 Hold a constant 60 MPH and check the tachometer if so equipped You can also hook up a test type tachometer providing it has a sufficient RPM range 2 Using the reference chart below locate your tire diameter height and rear end ratio then read the RPM indicated How to Determine Your True Rear Axle Ratio 1 The actual ratio or a reference code will normally be found on either a tag attached to a bolt or will be actually stamped into the axle housing Your car dealer can tell you how your vehicle is marked 2 Raise both rear wheels of the vehicle with the transmission in neutral Make sure that you support the vehicle with safety stands and block the front tires Make a reference mark on the driveshaft and on the housing Next without rotating them make a mark on both of the tires and the fenderwells With a friend watching the driveshaft carefully rotate both tires at the same time exactly on
4. e revolu tion The number of turns the driveshaft makes indicates the ratio i e 3 2 turns 3 5 to 1 234 turns 2 75 to 1 etc You an also use the above procedure the next time you have your vehicle lubed at the service station 3 Many vehicles are equipped with overdrive type transmissions If this occurs you must multiply your rear end ratio by the final transmission ratio EXAMPLE You have a 3 23 rear end ratio and a 85 high gear in the transmission 3 23 x 85 2 75 final drive ratio How to Determine Your Engine s Compression Ratio 1 If your engine has stock type pistons and the original cylinder heads you should be able to locate the compression ratio by A Checking your owner s manual B Checking a repair or service manual such as Chiltons or Motors C Call your car dealer s parts department with the engine description or serial number 2 If your engine has non stock pistons refer to the piston manufacturer s catalog NOTE If the cylinder heads are not stock check to see if they have the same size combustion cham bers If not refigure the compression ratio Milling the block or heads also affects the compression ratio Contact a Crane Performance Consultant for additional information 14 CRANECAMS COM Crane Cams amp Valve Train Products Section Getting Information continued RPM Shown at 60 MPH Cruise RPM RPM FORMULA MPH x Axle Ratio x 336 Tire Diameter Tire Diameter Rear
5. ion that can be obtained to verify which engine that the customer has will help make the correct choice the first time What cubic inch displacement is the engine A smaller engine will usually require a shorter duration camshaft than a larger engine given all other factors being equal What compression ratio is the the engine An answer of stock is not really sufficient as compression ratios of most engines changed during their production runs due to differing horsepower ratings emissions concerns the vehicle that it was originally installed in etc A basic generalization that higher compression ratio engines can use camshafts with larger more radical duration figures will normally apply Crane Cams amp Valve Train Products Section What cylinder heads do you have Iron or aluminum stock or or ported standard combustion chamber size or milled These fac tors are also critical Aluminum cylinder heads dissipate heat more readily enabling them to use slightly milder camshafts for best torque characteristics A good approximation is that going from iron heads to aluminum heads is like lowering the compression ratio 0 75 i e a 9 25 1 engine with iron heads will have similar characteristics to a 10 00 1 engine with alumi num heads Installing heads with smaller combustion chamers will raise the compres sion ratio so don t forget to take that into account High compression combined with too mild a camshaft
6. mpression gauge This is still a very valuable tool to verify your cylin der pressure as it will illustrate the effects of a camshaft or compression ratio change which a leakdown tester won t Higher pressures will give an indication of how much ignition tim ing that you can run what octane gasoline that s required to prevent detonation and help to provide a tuning baseline for varying atmospheric conditions Headers or stock exhaust manifolds A good exhaust system can be really beneficial in most any application Going to really large diameter systems in a mild application can hurt the torque curve so don t get carried away there In V 8 situations a crossover pipe is advised for dual exhaust systems What transmission do you have Manual vs automatic how many gears addi tional stall speed in the converter This will help determine how broad the power curve needs to be with milder cams traditionally having better torque and drivability over a wider RPM range What s the rear end ratio and rear tire diam eter This will provide the basic operating and cruis ing RPM of the vehicle one of the most critical portions of the camshaft selection process Each of our grinds lists a basic operating band to help in the selection How much does the vehicle weigh Heavier cars may need milder camshafts with wider torque bands for best results 866 388 5120 386 236 9983 FAX Crane Cams amp Valve Train Products Sec
7. tion BANE Advanced Tips to Choose the Proper Camshaft continued What altitude will this engine normally be used at An engine at sea level will normally use a more radical camshaft than one at 5 000 feet we re back to the compression gauge cylin der pressure factor again What idle quality and drivability factor are you looking for This is the one area where the customer s indi vidual desires can influence overall choices If a radical idle is wanted with no concern for vacuum readings go with the higher dura tion narrower lobe separation options If a smooth idle with lots of low end torque is the choice use the shorter duration wider lobe separation cam All of this adds up to formulating a workable combination to produce the best overall per formance that s needed to get the job done We see combinations every day that are put together with little thought to the overall pic ture Too much compression ratio in too heavy a car and a single plane intake mani fold with low numerical rear end ratios no camshaft will be able to make up for a drastic mismatch of components If possible try to help the customer obtain the correct compo nents from the beginning of his project This will produce the best results with time and money being saved by not having to repur chase items that were poorly chosen the first time
8. ugh 1995 model year We offer many different hydraulic roller cams our exclusive Crane Cams hydraulic roller lifters drop in installation correct length pushrods and other valve train com ponents for converting a flat face lifter engine to the tremendous power benefits found with a Crane hydraulic roller cam Look under Hydraulic Roller Retrofit Cams for spe cific engine details 866 388 5120 386 236 9983 FAX Crane Cams amp Valve Train Products Section BANE Determine Your Vehicle s 60 MPH Cruise RPM Determine your Cruising RPM At 60 MPH by reading Page 14 Getting Information Match your Cruise RPM At 60 MPH with the information found under Application See the gear ratio tire diameter chart on Page 15 to help you determine this RPM Note This is critical in making the right choice for a vehi cle that is street driven Be sure your informa tion is accurate Choose Your Cam Use the Cruise RPM At 60 MPH numbers and match this RPM range with the RPM Power Range numbers shown on the left hand page Be sure to consult the Application info before you make your cam choice Pay particular attention to the recommended engine compression ratio Also engines using aluminum cylinder heads dissipate heat more rapidly and can therefore use approximately 75 three quarters point compression ratio Example Iron heads 9 0 1 c r Alum heads 9 75 1 c r Remember If you are in doubt always choose the next mil
9. will cause problems with detonation and reducing the ignition timing to compensate for this will usually hurt the torque and horsepower everywhere through out the power band What intake manifold is on it In carbureted applications a dual plane mani fold will favor low end and mid range power with a single plane unit being good for upper RPM usage If you ve got a single plane mani fold on a relatively mild street machine you may want a milder cam to pick up the bottom end torque Do you have a supercharger turbocharger nitrous oxide All of these enhancements will greatly influ ence the camshaft recommendation Supercharged combinations tend to have slightly lower compression ratios with slightly milder camshafts on wide lobe separation Turborcharged engines might have slightly lower compression ratios or not if an inter cooler is used with a mild cam used to mini mize overlap area Heavy NOX applications might need a longer exhaust duration with a wide lobe separation in order to relieve the greater exhaust heat that s generated Section Continued gt 16 CRANECAMS COM What carburetor throttle body are you using The larger units favor upper end performance so a proper match here is essential to put the power into your intended RPM operating range What s your cranking compression With the advent and widespread usage of the cylinder leakdown checkers most folks have forgotten about the co
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