Engine Blueprinting 101 Part One
Contents
1. 050 040 Degrees 4 5 BTDC 2 BIDC 11 5 ATDC 24 ATDC 37 ATDC 51 ATDC 67 5 ATDC 85 BBDC 73 BBDC 51 BBDC 24 BBDC BBDC ABDC ABDC ABDC ABDC ABDC EXHAUST Degrees Lift 040 050 100 A150 200 290 300 300 363 300 300 290 200 150 100 050 040 46 4 43 28 5 11 3 Olea 86 84 86 61 5 45 1297 BBDC BBDC BBDC BBDC BBDC ABDC ABDC ABDC BIDC BTDC BTDC BTDC BTDC BTDC BTDC ATDC ATDC opening and closing points but expect you to determine these numbers from the duration and lobe center figures Perhaps the most critical number is intake closing as this is where true cylinder compression starts The later the intake closes ABDC the higher the rpm at which peak torque will be produced Figure that the torque peak rises roughly 100 rpm later in the power curve for each degree of later intake closing For instance Do you want more low rpm power than stock Advance the cam Do you want the same low rpm torque as stock If so choose a cam that has nearly the same intake clos ing as stock Would you like the maximum torque 500 rpm later than stock Choose one with the intake closing roughly 5 later Lift is obvious More is typically better but to get much more other Intake Duration 040 lift 232 5 050 lift 227 Lobe Center 111 5 If stock cam is advanced 4 040 lift Intake opens2. 8 5 BTDC closes 44 ABDC Exhaust opens 44 4 ATDG closes 8 5 ATDC ATDC After Top Dead Center BTDC Before Top Dead Center BBDC Before Bottom Dead Center ABDC After Bottom Dead Center ence in the indicator s movement will throw off the measurements With this done several important figures will be known Lift duration and lobe cen ters Lift is self explanatory Duration is the time in degrees of crankshaft rotation that the valves are open given from either the 040 or 050 lift points Higher lift and longer duration with different cams are the time honored ways to add flow capabil ity The lobe center numbers are meant to be an easy way to visualize the alignment point of maximum lift given in degrees either BTDC for exhaust cams or ATDC for intake cams For intake cams you divide the duration in half and subtract the number of degrees the cam opens before TDC during the overlap phase For exhaust cams divide duration in half and subtract the number of degrees the cam is kept open after TDC during overlap With these numbers it s easy to com pare your stock and aftermarket cams Note that aftermarket cams do not specify the Exhaust Duration 040 lift 239 050 lift 232 Lobe Center 107 changes will usually need to be made The stock valve springs may not be strong enough to control the valve accelerations at high speed if the lift is much higher Your cam
3. maker will usually recommend the necessary springs The stock valve to piston clearance may also be inadequate if much higher lift is used The time honored method of checking this is to clay the clear ance You must reassemble the cam and top end placing pieces of mod eling clay lightly oiled on both sides in the piston s valve cutouts turn the engine over remove the head carefully slice through and remove half the clay and measure the thickness But if you are careful with a dig ital caliper you can check clearance with out a mock up assembly and disassembly A minimum of additional clearance is nec essary the precise amount dependent on the size of the motor and the rpm antici pated as much as 080 on big exhausts and up to 100 inch for big intakes Nat urally the costs of special valve springs will need to be calculated about 200 per four valve cylinder and located as well as the expense of piston valve pocket machin ing if you get greedy with lift But as our focus is optimizing the stock engine we don t have to worry about that What We Found As expected the stock cam is biased toward the lower end of the rpm range good for dual sport and off road use Supermoto applications would suggest a new cam that raises the torque peak maybe 500 rpm road racing perhaps even more Engine tuning is about compro mise giving up something to get some thing more in a different place Analyze your fav
4. t close at the bottom of the piston s Intake stroke which would seemingly give the rising piston its max imum possible compression Instead the engine designer will leave the valve open much longer abbreviating the Compres sion stroke utilizing the inertia of the intake flow to continue filling the cylinder as the piston rises for a significant portion 30 FEBRUARY 2011 MOTORCYCLE CONSUMER NEWS by Dave Searle of its travel An engine designed for strong low rpm running will have the intake valves close about 45 50 of crankshaft movement after bottom dead center ABDC on the Com pression stroke while a high rpm racing engine may keep the intake valves open until 100 ABDC or more Incidentally a high static compression ratio is required when the compression stroke is shortened this way and compression ratios are always figured as if the intake valve s close at BDC Of course the same backflow sit uation will happen with late intake closings at low rpm only this time the intake charge will reverse direc tion and push back out through the carb or throttle body reducing vol umetric efficiency This quantity of Si regurgitated fuel air mixture will typically be contained in the airbox so it doesn t escape entirely but it will then be treated to a second shot of fuel as it is drawn back in on the next intake cycle ruining its mixture accuracy Exhaust timing is adjusted so that val
5. Engine Blueprinting 101 Part One Measuring Cam Timing amp Lif LUEPRINTING IS A time honored B method of achieving more power from a production engine Although the term is often associated with racing the techniques are equally applicable to the street bikes that you and I own Remember that production engines perhaps aside from the best superbike motors are not built using the greatest care or very best machining practices but are objects of mass production subject to all manner of cost controls 2 and variable production tolerances This fact gives a careful mechanic the _ opportunity to improve power signif F icantly with relatively small expense The term blueprinting means to bring all the dimensions to the ideal f numbers called out in the engine s blueprints but it can also mean opti mizing the range of allowable varia tions to achieve precisely those that will deliver the best power We ll confine our series to the top end and our current Project Bike Suzuki s DRO650SE will be the model but the techniques shown M apply to virtually any engine The Camshaft The business of the camshaft is to coordinate the openings and closings of the valves on our four stroke engines so that on every second revolution combus tion occurs creating the power that drives our motorcycles forward The chant Intake Compression Power Exhaust that every shop student learns by heart o
6. ction is possible to achieve but not instantly by any current means so the accelerations induced in the valve train must be carefully calculated The valves springs retainers and keepers plus shims rocker arms clearance adjusters pushrods and lifters if the engine has them all have their own inertial weight and some are even slightly flexible in addition The quicker we move the valves the stronger the valve springs must be to control them and the highest rpm the engine will attain determines the required spring pressure This spring force should not be taken lightly when considering a change of camshafts as even 1n the best of circum stances it causes friction and wear between the lobes and lifters which already constitute one of the most difficult lubrication jobs in the motor Compression is cut short by extending the intake cycle to take advantage of inertial ramming The compression ratio is raised to compensate for the degree of reduced Power stroke is cut short by early opening of the exhaust valve after combustion pres sure has done the majority of its work This is called blow down and helps to evacuate the cylinder of burnt gases Exhaust starts early and lasts past TDC to aid intake flow during overlap Too much overlap can cause backflow into the cylinder at lower rpm hurting the engine s ability to draw in fresh air fuel piston travel before closing the gastank to ensure that no dirt
7. e valve operates on each side With the engine at TDC on the combustion stroke Home made piston stop Created from an old sparkplug with a vise hammer and drift with threaded rod epoxied inside both valves fully closed eliminate the valve lash on the most accessible intake and exhaust valves left side on the DR This is easy with the DR s screw and locknut adjusters Very carefully turn the adjuster screw by hand until it just stops and then carefully snug the locknut with out moving the adjuster any further On the second intake valve unscrew the adjuster as much as possible without let ting it fall out this way it won t compress the valve saving the extra effort to com press its springs Do the same on the exhaust side Shim adjusted valves in a DOHC engine will require thicker shims to be fitted in order to exactly zero the 32 FEBRUARY 2011 MOTORCYCLE CONSUMER NEWS lash Pro engine builders will leave noth ing to chance and measure the timing of every single valve to make sure that all lobes are matched for duration lobe center and lift Position your dial indicator s tip on the top of the spring retainer on the valve you are measuring with the gauge compressed far enough that full compression of the valve is within its range then rotate the indicator s bezel to align the zero mark with the pointer on its face Because a rocker arm moves across the valve as it compresses you ll find it difficu
8. falls inside the motor when the covers have been removed Make sure that any pas sageway into the motor is plugged with clean rags or paper towels as you proceed There s nothing worse than multiplying your efforts just to retrieve a clip or washer that s fallen into the bottom of the motor when it didn t have to happen ey iii pe O 5 crt Sn ritst titra tt 2 e n which hose goes where Rather than just dive in a little time spent on these details will remove a lot of potential stress later It s possible the motor will be apart for weeks if you only have time to work on it nights and weekends like we did and it s easy to forget details that seemed insignificant at the time The DR s cam timing is not given in the factory service manual but even if it were we d need to verify it Lift overlap opening and closing times and lobe centers are all important information that provide reference points when appraising the degree of tuning from the factory or choosing an appropriate aftermarket cam Then if you download the figures for the possible aftermarket cams available you ll be able to see how they compare to your stocker Cam timing that s off by just 2 at the crankshaft due to manufacturing toler The DR s intake valve at full lift The temp tation to increase lift for more flow is great but stronger springs may be required increasing friction wear and parts expe
9. ition by Haynes Publishing Probably the best single reference book on the sub ject Highly recommended Hardcover 60 98 available from Amazon com for 23 94 or even less in used condition Degree wheel Competition Cams 7 5 Sportsman wheel Part COC 4787 14 25 from www 888murrays com Central Tools 1 travel dial indicator with magnetic holding fixture Mfg 3D102 Model 112202 71 20 from www toolsource com Cam degreeing kit everything needed with video Web Cam AP 144 265 Web is also a good source for instruc tional info www webcamshafts com Visit us at WWW MCNEWS COM FEBRUARY 2011 33
10. lt to ensure that the rocker arm and dial indica tor don t interfere at full lift Don t force anything which could spoil the measure ments and possibly damage the expensive indicator and check to make sure every thing is good before proceeding with the measurements Always turn the crank in the direction of engine rotation If you exceed your mark back up a short distance and turn forward again carefully we don t want cam chain slack to alter our readings Get out your notebook and record the measurements Cam manufacturers will typically give lifts at either 040 equiv alent to 1mm or 050 traditional in the US Be sure to record both these num bers as well as the additional steps at 100 150 200 etc until the cam lift peaks record this figure too and then as it returns to its seat We d suggest you record the smaller numbers the point of initial movement and steps at finer incre ments like 010 020 and 030 also These smaller lifts happen much more gradually and represent the opening and closing ramps on the cams designed to smoothly take up slack before moving the valve quickly Double check your mea surements Repeatability is your assurance it s correct Keep working until you ve achieved this A slightly loose holding fix ture overtightened adjuster or interfer DR650SE INTAKE Lift 040 050 100 150 200 250 300 300 361 300 300 250 200 o0 100
11. n the first day of class would make you imagine that each phase of the process takes precisely half a turn of the crankshaft but that s not true In fact the Intake stroke steals time from the Compression stroke and the Exhaust stroke steals time from the Power stroke The intake valve opens just before the piston starts the downward Intake stroke and the exhaust valve s closing is typically delayed by a similar amount to take advantage of the gas flow inertia at work as the engine runs By leaving both valves open for a moment as the piston reaches top dead center TDC at the end of the Exhaust stroke the out rushing exhaust gases will tend to create a suction effect on the intake side initiating fuel air flow before the piston s descent works to create its own pull This phase when both valves are open is called Overlap Engines tuned for a broad torque range and good low speed power like our dual sport will use a brief overlap period of perhaps 20 while engines designed for high rpm power will use from 50 75 Long overlap is reserved for high rpm motors because at lower revs a delayed exhaust closing will tend to backflow into the cylinder and hot exhaust gas will take up significant space making filling the cylinder with fresh air and fuel impossible to accomplish The other valve timing events are sim ilarly adjusted to make the most efficient use of these inertial flow effects The intake valve won
12. nse ances will change valve events by twice that amount which is very significant to how well your motor runs Adjustable Only the desmodromic system used by Ducati escapes this conundrum Tools A factory shop manual is essential It will not only contain nearly all the speci fications you ll need but it will also illustrate the correct routing of all the hoses and wiring you ll disturb as you disassemble the machine Once again the DR650 s big single cylinder engine makes disassembly easy and simplifies many subsequent opera tions We found the entire top end job can be done without removing the motor from the frame And it s always important to begin with a clean bike especially under On the DR it doesn t take much more than an hour to disconnect everything attached to the top of the motor airbox boot carburetor exhaust pipe oil cooler sparkplugs etc If you carefully put the various bolts in egg cartons from left to right and top to bottom you ll find it easy to reverse the sequence when it s time to put it all back together Take pictures of the various hose routings with your digital camera to serve as maps if your service manual doesn t detail these ade quately Use masking tape tags to note cam sprockets or modifications to your stock sprockets will allow you to correct or alter timing without buying a new cam but even a new cam needs to be checked and will probably also require adjustmen
13. orite type of riding What would be ideal In fact we learned our DR s cam timing is retarded by 4 from the common split overlap the intake lobe center at 111 5 ATDC and the exhaust lobe center at 107 ATDC Such retarded timing is unusual and evenly split or advanced timing should improve performance adding effective compression low speed power and reduc ing the tendency for back flow on the intake and exhaust Although dyno tuning is required to optimize the exact timing fig ures we feel comfortable advancing the stock cam timing by 4 to achieve split overlap which we will cover in Part Four of this series when we reassemble the motor after verifying and correcting the actual compression ratio in Part Two and cleaning up the ports and machining the valve seats in Part Three Comparing our stock cam with the most popular aftermarket alternative was also illuminating The new cam s timing was almost identical and the new cam s lift was actually less Although we d really need to know all the lift degree figures to be absolutely sure which are not normally divulged by cam manufacturers the com parison suggests we d be wasting our money if we hoped for more power and dyno tests by other tuners using this cam back up our numerical analysis The surprises continue in Part Two so stay tuned we think you ll enjoy the trip RESOURCES Reading Four Stroke Performance Tuning by A Graham Bell 3rd Ed
14. res are offered on the internet 100 can buy all three Set Up The first step is to locate Top Dead Center Of course you ll find TDC marked on your ignition rotor to be lined up with a corresponding point on the engine case but it can t be trusted Manufacturing tolerances allow all sorts of misalignments Make a sturdy pointer to serve as your degree wheel s reference point We made one from the steel rod in a pants hanger sharpening the end on the bench grinder Secure the degree wheel so that the engine s marked TDC corresponds to the pointer The piston stop is next This will prevent the piston from reaching the top of the stroke so that by carefully rotating the engine back and forth to reach the stop the degree wheel will show if the factory mark is perfectly aligned Any discrep ancy will give a different number of degrees BTDC Before Top Dead Center and ATDC After Move the degree wheel to split the difference and you ve located the true TDC point Make sure the degree wheel is then well tightened so that it cannot be shifted accidentally From that point on rotate the motor by turning the rotor and not the degree wheel to avoid possible misalignment Don t be surprised if this is more difficult than you imagined Even with the sparkplugs out the rotor s magnets and especially the valve springs create significant resistance This can be minimized on four valve engines by measuring while only a singl
15. t to achieve the intended timing A minimum of special tools are neces sary You ll need a large degree wheel that will be attached to the end of the crankshaft a piston stop a dial indicator and a holding fixture to secure the indica tor in position over the valve spring retainers to measure movement with crankshaft rotation Visit us at WWW MCNEWS COM FEBRUARY 2011 31 A P IECNANIC With the indicator compressed enough to record full movement and the lifter on the cam s base circle zero the bezel The tip of the indicator must contact the spring retainer without being hit by the lifter over the full range of its travel Precisely set valve lash to zero before hand in order to read cam timing and get an accurate measurement of lift You can make a piston stop from an old sparkplug held in a vise Breaking off the top and pounding on the center electrode with a drift will drive the porcelain through the middle so a length of threaded rod can then be epoxied inside Be careful not to allow interference between the stop and the valve heads or you could bend a valve Because the DR has a pair of spark plug holes we used the outermost hole to keep a safe distance away from the valves The length of the stop can be estimated with a thin screwdriver inserted in the plug hole with the engine 10 15 from TDC Degree wheels are available from all the camshaft manufacturers and dial indica tors and holding fixtu
16. ves will open well before the pis ton s downward Power stoke ends at bottom dead center BDC Again the engine s intended use will determine when and tends to range from 45 50 before bottom to as much as 75 or more This early opening scenario is called blow down and is done in order to aid in emptying the burnt contents of the cylin der after the combustion pressure has done the majority of its work and before the ris ing piston expels the remainder Remem ber that the volume of the combustion chamber rapidly expands as the piston descends reducing the effective working pressure on the crankshaft Aside from the timing of the valve events which are carved into a fixed arrangement by the hardened steel shapes of the cam lobes valve lift is the other key to camshaft performance To see with your own eyes how small a distance the valve actually moves away from its seat 1s to appreciate the potential for flow increase with higher lifts See image This is a fundamentally different prob lem than cam timing and duration We would prefer to open the valves instantly to the full height that will eliminate flow Intake Overlap phase begins before TDC on the Exhaust stroke so that negative pres sure in the exhaust pipe will initiate intake flow before the piston s descent creates its own suction effect restriction between the valve and its seat but we can t The lift necessary to elimi nate any restri
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