Re: Comp ratio vs cam duration I think Eric summed it up pretty well. You can't think of each item - compression ratio, valve timing events, or intake system- independantly. They're all dependant on each other. That's why you see so many cars that are just turds with stock heads/compression and a big cam Notice that the range of operation (3400-3600 rpm) remains constant as the grind gets wilder. It simply moves up the scale with more duration and requires more static compression ratio to maintain the same cylinder pressure. The slug of air/fuel mixture running down the intake runner into the cylinder has inertia Find the flaw in the following combination: a '67 Impala running a 327 small-block with stock heads, 8.5:1 compression, a 305-degree-duration cam, a two-barrel carb, stock exhaust manifolds, a. On that very same cam, if you narrow the lobe separation, the power band will come-on a little higher in the RPM range, but when it comes-on, the power curve is steep and brutal. This is why hard core race cams have explosive power bands. The static compression never changed, but the effective compression surer did Compression Ratio: The true measured compression ratio is a very important fact in determining which camshaft is best for your combination. Stock compression in a Mopar can run from 7.5:1 to 10.5:1, so, using stock is a good way to make a bad mistake. Using the pistons advertised compression ratio can be very misleading too
The compression ratio (CR) based on swept volume vs combustion chamber volume is determined by design and it's fixed, but the mass of air+fuel getting into the cylinder does change as a function of camshaft parameters (lift, duration, overlap) and how open the throttle is. So the camshaft + throttle changes the effective CR The effective compression ratio is 5.06:1. The cranking pressure is 111 psi absolute (96 psi gauge pressure). The V/P Index is 45. As you see, the size and compression ratio increases still don't bring the motor back up to the stock figure when the cam is this hot - the V/P is down more than 6% Proper camshaft selection is a combination of first and foremost, your experience coupled with the determined usage; engine displacement, compression ratio, fuel system carbureted or injected, RPM range power desired, transmission type/converter stall speed, vehicle weight, final gear ratio, tire height, cylinder head and valves, head flow. Re: Comp ratio vs cam duration Nope. The centerline of the lobe is the point of peak lift, not necessarily the center of the lobe. A lobe doesn't need to be symmetrical, whereas the opening ramp and closing ramp are identical. Thus, centerline of the lobe doesn't need to be square in the center. It's the point of peak lift How does compression ratio affect camshaft selection? The key fact to watch here is cylinder pressure. If you have a lower compression motor, say 9.5:1, and you use a camshaft that is fairly large (increased overlap between lobes allowing both the intake and exhaust valves to be open at the same time) then you will bleed off cylinder pressure.
Higher compression ratio not required, Larger valves not recommended. Typical lobe separation 108º - 112º. Power Range: Small Capacity. If a hydraulic cam is being replaced with a solid cam, the 0.050 duration needs to increase by 80 or 100 to obtain the same effective duration With a given static compression ratio, you will always have a higher reading on your compression tester gauge with a stock or low duration cam, because you will be closing the intake valve earlier on the compression stroke. The resultant longer effective compression stroke always delivers a higher gauge reading. Now switch to a longer duration cam The ratio of the cylinder volume at IVC over the volume above the piston at TDC represents the dynamic compression ratio. The DCR is what the air fuel mixture actually sees and is what counts, not the static CR. Because DCR is dependent upon IVC, cam specs have as much effect on DCR as does the mechanical specifications of the motor
Camshaft Duration Vs. Compression Ratio. Jump to Latest Follow 1 - 2 of 2 Posts. M. mikemustang289 · Registered. Joined Nov 23, 2003 · 1,233 Posts . Discussion Starter • #1 • Jan 10, 2004. I here a lot of guys talk about what their compression ratio is.. The effective compression ratio is 8.03:1. The cranking pressure is 178 psi absolute (164 psi gauge pressure). The V/P Index is 331. Another 12% improvement! And 36% above the base-line low-compression motor. Last, an increase to 12.0:1, giving a chamber volume of 5.00 or 81.9cc. The effective compression ratio is 8.73:1
Just considering duration and lift isn't really taking in the whole picture of how a cam does or doesn't respond with a particular compression ratio in an engine. LSA will have a big affect on how a cam works, and a wider LSA will make cams with identical lift and duration work much better than a close LSA works Where I fall down is when static compression ratio is quoted as a maximum ( usually 10.5 to 1 for cast Pistons) and yet compression is down due to cam duration. I do understand that when an engine. The camshaft determines the engine's horsepower and torque curves, so the cam has to match not only the application but all of the other components that go into the valvetrain, the cylinder heads, compression ratio and induction system. It is important for engine builders to seek out as much information from the customer on the build as they can Duration at .050 inch is a measurement of the movement the lifter in crankshaft degrees from the point where it is first lifted .050-inch off the base circle on the opening-ramp side of the camshaft lobe, to the point where it ends up being .050 inch from the base circle on the closing ramp side of the camshaft lobe On the other hand, if the long-duration cam does a better job of filling the cylinder at high rpm than the short-duration cam, more air and fuel will be trapped in the cylinder and the resulting dynamic compression ratio will be higher. So what the rewards of high compression that justify the risk of detonation
As a rough rule of thumb, you can look at this combination from the standpoint that as duration on the camshaft increases, you can also squeeze the static compression ratio a little tighter. Conversely, if the duration is only slightly above stock, it's going to be dangerous to squeeze much more than a typical 9:1 compression ratio without. The relationship between compression ratio and intake closing can be easily measured with a cranking compression gauge. The combination of a low static compression ratio with a long duration camshaft shows up as extremely low cranking compression. Shoot for an acceptable cranking pressure of 180 to 190 psi Improved ramp design results in low valve train noise. Meant for engines up to 96 and 10:1 compression ratio. 3000-5000 rpm. 520: A replacement part for S&S emissions certified engines, this is a short duration emissions cam with very little overlap to reduce emissions of unburned hydrocarbons. Requires high lift springs and normal clearance. A word of warning here though: short duration cams and increased compression ratios don't agree as well. A conservative camshaft needs a conservative compression ratio as well. More about compression ratios later. Vehicle weight and transaxle gears Generally speaking, the lighter a car's curb weight is, the hotter the cam's specs can be If you simultaneously and appropriately increase the static compression ratio and add more duration, then you'll keep the effective compression ratio correct. Back to our cam selection. We wanted more power from 4500 to 6000 rpm but no losses below that range
The article above tells me that with the XE282HR cam which has 232* intake duration I need 10.5 to 1 compression. At 9.7 to 1 I'm leaving power on the table, especially on the bottom end. That may explain my soft launches and 1.8 60 ft times This is because compression cannot begin until the intake valve closes. This means that a late closing intake point (with a long duration cam) reduces the engine's dynamic compression ratio. If you put a mild cam in a 13:1 compression engine, the dynamic cylinder pressure might be equivalent to 15:1 with a larger cam I think the cam has a lot to do with your engines compression ratio because a bigger cam will bleed off more dynamic compression. 1981 Chevy monte carlo 396 BBC .060 over 10.25:1 voodoo 60203, 3:42 Posi GTA rim I have seen a 100-plus-hp increase from a 355-ci small-block Chevy with 25 degrees more cam duration, 0.100 more lift, and 2 points more compression. When we go back to the basics, the big increases seen with a combo of more compression and cam are easier to understand Most Cam Cards will list duration. However, if you want to find the duration for the camshaft in your engine, you can calculate it. Using a Dial Indicator and Degree Wheel, find the opening and closing points of the valves at 0.050 in. of lift. If the intake valve opens AFTER TDC, use a negative value
Camshaft Basics From the February, 2009 issue of Chevy High Performance By Bob Mehlhoff . It's Greek jargon, or street parlance to the rest of the world, but it often defines us. Whether we're talking about axle ratios, compression, carburetor size, timing, or e.t.'s, our hot-rod language sets us apart Therefore with the mild cam it will have a high dynamic compression ratio, probably 9.5:1+ which would be way too high to run safely on 91 octane gas. However, that same 11:1 static compression ratio engine with the radical 259/269 duration camshaft would have a dynamic compression ratio in the neighborhood of 7.5:1, totally acceptable to run. You only find this on short-duration cams, but it is important to note if you're making calculations with a small cam. Calculating Valve Lift. Net valve lift is a function of camshaft lobe lift and rocker arm ratio. Lobe lift (sometimes called cam rise) is the height of the eccentric portion of the cam lobe above the base circle comment: performance street cam, 9.5:1 compression, 2000+ stall convertor chevrolet big block v8 1967-95 396, 402, 427, 454 c.i. / 1969-90 366 c.i. (chain drive) hydraulic flat tappet cams mc22127 hyd 2 192 202 261 272 .439 .464 106 114 idle-4500 smooth 817 b comment: good fuel economy
Camshaft Valve Timing Degrees Calculator Find out your camshaft's valve timing events @ .050 lift by inputting intake & exhaust duration @ .050, LSA, and intake centerline. This calculator is useful for finding out your IVC @ .050 number when your cam is a brand like Comp Cams which typically only provides you with an IVC @ .006 number Comp Cams has a good hydraulic cam for you, part number CCA-21-404-4. It features 214/229 degrees duration at .050 lift, and .442/.482 inches of lift with a 110 degree lobe center. This is a single-bolt cam. We have assembled several camshaft guides to help with your cam questions: The 9 Things You Should Know Before Ordering a Camshaf A low duration camshaft works best at lower RPMs. Even though the stock cam has a duration of about 250 degrees, a mild aftermarket cam like the Engle 100 (duration 270 degrees) will still move the point of maximum torque/horsepower further up the RPM range. A cam such as the Engle 10 When modifying an engine, it is important to match the compression ratio with the duration of the cam. While additional cam duration can produce more useable power, to much duration can hurt the performance. The problem is created when too much duration results in lower cylinder compression pressures at low RPM which reduce the low RPM torque.
Details: Long duration cams delay the closing of the intake valve and substantially reduce the running compression ratio of an engine compared to the SCR. The cam spec we are interested in to determine the DCR is the intake closing time (or angle) in degrees I have to admit I always seem to regret anytime I go conservative. I wish I had more cam, more compression, more gear, etc. Just for comparison that cam has more duration than the cam in my 428 and it shifts at 6500-6600 rpm. The cam in my 428 is a solid flat tappet with 240/246 duration, .587/.597 inch lift after lash Modern heads like the Vortecs don't need big intake duration to make the power with 9:1 compression. Why have more cam duration than you need vs. the engine compression ratio if there are are minimal benefits but lots of downsides. The L82 cam design really only works well with 10:1+ compression and installed about 4° advanced Use this calculator to see what the effect of bore, stroke, rod length, cam timing, compression ratio, boost pressure and altitude is on your dynamic compression ratio. Of the variables, the most important is cam timing which has a dramatic effect on your dynamic as opposed to your static compression ratio
It featured a 9.0:1 compression ratio, cast iron 882 heads, and a Quadrajet induction system. It also offered a healthy at the time camshaft with a .450/.460 Lift and 222 degrees of duration. Run on the Dyno in the stock configuration with long tube headers it produced 313 HP @ 5,400 RPM and 355 Lb-Ft of torque @ 3,800 RPM . There is no formula to find the rpm range for a camshaft. If you have questions, the best course of action is to contact the manufacturer. How does it affect performance? The rpm range has a lot to do with Duration. Generally, cams with smaller duration numbers make peak horsepower at lower rpm Most late model smog engines work well with a supercharger due to their lower compression ratios and smaller cam profiles. Supercharged Engine Guideline 1) 7.0:1 to 9.0:1 compression ratio: The optimum compression ratio is 8.0:1. 2) 4-7 psi boost level: This range of boost has proven to be the best compromise for power and reliability Hey guys, whats the stock compression ratio of a F54 block with P79 head? I have read in various places everything from 8.3-1 to 8.8-1. Doing my own calculations I have come up 8.5-1. This is with a bore of 3.385, stroke 3.11, combustion chamber CC of 53.6, zero deck clearance, and a .049..
. This leads to the question, why do cam manufacturers often advertise a certain minimum compression for a given camshaft? The answer has to do with responsiveness. In the NASCAR Craftsman Truck Series, the rules limit compression to. Cam Specs: Custom Cam Grind .494 Intake .494 Exhaust 268 Intake / 268 Exhaust duration @ .006 106 degree lobe separation Special R&D Propitiatory lobe profile for a quiet valve-train and long spring life Can be ordered through Terry Walters Performance Parts 5016 Benois Road Roanoke, VA 24018 Telephone: 1 855 722 324 If your engine is high compression, and you put a lot lower duration cam in it, you will get into pre-ignition at the lower rpm range, as you are experiencing. Compression must match cam duration. Do you know the compression ratio ? Mac_49 Premium User. Mar 27, 2018 #5 Same car, same engine. Through Bama tuning I was able to achieve low end.
Once you have a cam duration figure in mind, attention must be paid to compression pressure. Optimum compression pressure is 160 - 170 psi, at least with old Pontiacs. Too high a compression pressure will yield too high a peak combustion pressure and thus cause detonation Since cam timing has a major influence on compression, cam events and compression should be coordinated when designing an engine. An engine with a long-duration cam will experience a significant loss of low-end torque unless the corrected compression is matched to the cam timing, specifically intake valve closing One chooses a cam shaft first to match intended use and rpm range and THEN you set static compression ratio to establish dynamic compression ratio based on the desired fuel to be used. The longer the cam duration at .050 lift the greater the static c/r needed to keep the dcr in the correct operating window Camshaft timing events must be directly tied to compression ratio. The longer the duration, the lower cylinder pressure and working compression. The shorter the duration, the less air brought into the cylinder, which also affects compression. Your objective needs to be the highest compression possible without detonation, which harms the engine So if the long duration is necessary on a high compression NA engine in order to properly fill the cylinders, then is a supercharger the best way to increase efficiency with a short duration cam? Or does it matter because some unburned mixture will be pushed out of the exhaust side at the same rate as it would on a high duration NA engine
For example, no matter how much duration you have, a stock Model T motor is never going to turn 5,000 RPMs. To achieve higher engine speeds you must have a head and manifold that will flow freely and a high enough compression ratio. As an example, a stock Model T has a 4:1 compression ratio, poor air flow and a poor head design The proper method of selecting a camshaft is complicated and involves many factors including cam lift, duration, compression, and engine breathing. Compression to some extent is the smallest piece. As long as dynamic CR is between 9 and 11:1 the cam is appropriate for the application To see what the effect of bore, stroke, rod length, cam timing, compression ratio, boost pressure and altitude is on your dynamic compression ratio, simply enter the seven variables and the calculator will display the results in a new pop-up window Sometimes people take a car that starts off with a 9000 rpm redline, has an 11.5:1 compression ratio, and a 280* duration camshaft, and an aggressive naturally aspirated-esque timing curve and decide to supercharge it for more power
You shave the head to increase the compression ratio. This will increase compression pressures in the cylinder. You then add a cam with more duration, and the delayed closing of the intake valve reduces compression pressure (assume the cam grind has very mild valve overlap, which is more ideal for a turbo motor as opposed to an NA motor) Static Engine Compression. When modifying an engine, it is important to match the compression ratio with the duration of the cam. While additional cam duration can produce more useable power, to much duration can hurt the performance Cam Duration: Rear Gear Ratio: Engine Characteristics: SMALL BLOCK: BIG BLOCK: Street Rodder™ Stock to 260° Stock to 3.23: Smooth Idle, Stock Compression: 1500-1700 : 1700-1900 : Saturday Night Special® Stock to 265° Stock to 3.23 : Smooth Idle, Stock Compression: 1600-1800 : 1800-2000 : Breakaway® 265° to 280° 3.00 to 3.73 : Fair Idle. The following figures were generated with a 9.5:1 compression ratio, mild porting, stock valves, stock Strombergs, and a header. In short, a mildly hot-rodded TR6. All plots and data assume a valve lift of 0.390 intake and exhaust, and intake duration = exhaust duration (i.e., symmetrical) With a long duration cam and late intake close, you lose dynamic compression, so static compression ratios have to rise to compensate for the low dynamic compression, caused by the cam's late intake close.....compression has to rises to whatever you need to get cranking/running pressures up again
Once you have a cam duration figure in mind, attention must be paid to compression pressure. Optimum compression pressure is 160 - 170 psi, at least with old Pontiacs. Too high a compression pressure will yield too high a peak combustion pressure and thus cause detonation Detonation can be cured by running the correct high octane fuel, reducing the compression ratio, adjusting for richer carburation, using cooler plugs, increasing the cam duration, adjusting timing, or a combination of these methods. Using a high lift cam with a stock or lower displacement engine may be an exercise in futility
Lower compression heads and hydraulic cam. The H.0. engine was a seperate engine with VIN engine code R. This engine is almost identical to a 71 R code Boss 351, and was even refered to as the Boss 351 in Ford literature. but the lawyers made them change the name. It actually had a larger lift cam the 71 version, although the duration was less 10.5:1 compression ratio; dual plane intake (the 318 had a single-plane manifold with a two barrel carburetor). 1969 - Unchanged, except manual transmission 340 engines also had the (formerly) automatic-transmission camshaft. 1970 - Two distinct versions of the 340 high performance engine were made For example A 10:1 compression ratio simply means that 10 units of air will be compressed into the space of just 1 unit. The compression ratio (CR) plays a big part in how well an engine performs. The problem of knock, (where the air fuel mix prematurely ignites) is controlled to a large degree by the compression ratio Low compression, mild cam. The thing actually ran pretty good. Being new to the game, and finding a good used 509 cam for $75, I decided to try it. .509 lift, and 292 duration. Well it ran noticeably worse after putting the 509 cam in there. So I next built a high compression 451, put the 509 in it, and that motor screamed
I have the SE MVA heads with high compression forged pistons in the bike so far, just put them in . I am looking to go with a more compatible cam then the 255 cam, the 255 opens to early for this combo. I believe that the 777 cam has more overlap then the 259E cam and that is why I am leaning towards the 777 An interactive camshaft calculator where engine builders can see how valve overlap (and boost efficiency) is affected by a camshaft's physical design. How to use MGI's Camshaft Calculator When shopping for camshafts from different manufacturers, enter each of their supplied cam card specs into MGI's Camshaft Calculator I have a 1962 383 with Dual 4 Barrels, 3 inch exhaust, 10 to 1 compression ratio, 2500 Stall and a 3.91 rear end. I presently have a Comp Cam 21-222-4 with 218/224 degree duration with 110 lobe separation The stock rocker ratio was 1 to 1 on early 40hp engines, and this ratio changed to 1.1 to 1 on late 40hp engines and all 13/15/1600cc engines. This ratio is the relationship between pushrod movement and valve movement. Simply, a camshaft with 0.300″ lift will open the valve 0.300″ with 1 to 1 rockers and 0.330 with 1.1 to 1 rockers
. It had a 10.3:1 compression ratio and new cams. Actually, there were two different sets of camshafts for automatic and manual transmission applications. Engines, which go with automatic transmission, had the following camshaft specs: duration 240/240 degree, valve lift 8.7/8.2 mm Your dynamic compression ratio is 9.15 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 189.01 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 0 PSI is 9.15 :1. Then I ran the 10.4 SCR and Toda A the RIGHT cam. CR requirements - The bigger the cam (duration), the more compression ratio it needs to work right. A low CR motor, will be extremely sluggish at low RPMs, when used with a big cam. Likewise, a small cam in a high CR motor, will ping like crazy, all the time, due to excessively high dynamic compression ratio. Here is a. The second is the effective compression ratio, which the engine sees when the intake valve closes against the valve seat. A number like 7:1 is common. This is determined by the interactions of the static compression ratio, the rod ratio, and cam timing for closing the intake valve Agree, just put a normal performance cam vs the extra small duration rv cam. You'll gain more in power than you lose in the cylinder pressure. Engine will always be a bit sluggish without additional compression, crutch that by advancing the cam and running more than normal timing advance. Sent from my SM-A102U using The H.A.M.B. mobile ap
. Gross lift at the valve. Rocker arm ratio. Compression Ratio. CID. Head Type and valve size. Head flow if possible. Car weight. Gear Ratio. Convertor stall. Trans type (OD?) Max Shift RPM. Current carb type and size. Fuel Pump Brand and Size. Filter types and location in fuel system. Fuel Line sizes from the cell to the. It has big port raised-exhaust port heads and squared, 0.005 in the hole with Wiesco +0.020 dome pistons. The static compression ratio seems to be around 11:1. It produces 180 psi when closing all cylinders. It has 7 inches of vacuum with a Lunati hydraulic roller cam that lifts .629-629 with duration of 250 in, 255 ex., 110 centerline and 112. Free Engine Piston Compression Ratio Calculator and Engine Size Calculator. Use this compression calculator tool to figure the compression you will get with the specifications you provide. You can change the head ccs, deck height, overbore size, etc. to see the affects on compression Changing to the thinnest, smallest bore head gasket you can find will get you somewhere on the compression ratio. I don't think the 097 cam needs 10:1 compression - it came in 9.0-9.5 compression engines from the factory. I don't think the valve to piston clearance would be a problem with the later cam It is most affected by the effective camshaft intake valve duration (usually measured at .006 lift on hydraulic cams). It's also affected by the amount of advance or retard of the camshaft. Of course the static compression ratio is a large determining facor in DCR too
Most of the time a camshaft and engine combination that has pulling and low speed torque in mind is set up with a short duration camshaft and a moderately low static compression ratio. For instance the 460 in my pickup uses the D3VE heads and a KB piston which is + about .005 to get 8.4:1 When comparing LS rockers to SBC rockers at a stock level, the LS version are stud mounted to the cylinder head. The stockers have also been increased from a 1.5 to a 1.7 ratio - even to a 1.8 on the LS7. While that means more lift for any given cam lobe profile, it also means that more power isn't as easy as a rocker swap . More duration will drive DCR and cranking compression down, earlier ICL will drive it up, and later ICL will drive it down You absolutely cannot go by a shop manual for cranking compression on a modified engine
First, here are some definitions to common camshaft terms: Duration carburetion, compression ratio, etc). So where the 1914cc beings to bottom end torque at about 255 degrees @ .050″, the 1907cc could keep a healthy and wide torque curve with about 262 degrees @ .050″. Crank stroke length and cam timing go hand in hand Understanding Dynamic Compression Ratio. If the intake valve is open at all there is no compression ratio. Compression does not begin until the intake valve closes; not at bottom dead center which is the physical beginning of the commonly stated compression stroke, but at some point up the bore where the intake valve closes and the piston can actually begin compressing the trapped mass in the. In general, higher compression ratios need longer duration cams Bolt in type cams are intended for stock compression ratios. Hot street cams for 96-103 inches. 90+ rear wheel HP possible with well tuned 96, more with 103+ inches. Smooth idle, broad torque (2200-5600 RPM) 9.0 to 9.5 C. In reality, a cam with 220º at 0.050 and a lobe center angle of 112º will have the exact same mechanical overlap as a cam with 217º at 0.050 and a lobe center angle of 109º. If you compared these two cams side by side in identical engines, the first cam would actually have a slightly better idle and would produce slightly more peak power. Once I switched rockers to the larger ratio, the cranking effort and exhaust note dropped way off. In effect, the exhaust vale is being held open, (increased duration) longer with the higher ratio rocker. This bleeds off some of the compression, (lower psi) at cranking speed. It is right at 175 psi currently. That motor is around 10.5 or 11:1 If I were to do it again, I would probably stick with this cam as I really like how it sounds and performs, but I could (mathematically at least) afford to add a little more compression ratio. My static compression ratio of 10:1 yields a dynamic compression ratio of around 8.0:1 with this cam