what is a long duration cam? im assuming there are also short durationa as apposed to what normal cams? what is the difference between the two? i have an fr32 cam, is this long duration? what are the pro's and con's
simply refers to the amount of time the valve stay open and hence the amount of overlap when both valves are open at the same time. Long duration if
IRC are for high speeds giving the air more time to move in and out the cylinder but produce less torque at low speeds due to more of the inlet charge
escaping out the exhaust valve (hence never producing any work) and short durations work best at low speeds producing higher torque. Normal cams as
supplied by the car manufacturer are a compromise between the two types depending on what the car is intended to do.
[Edited on 7/8/08 by Mr Whippy]
so how do i know if my fr32 cam is long or short?
look up the code on the manufactures site, normally they give all the details.
like this on the kent cam site -
FR32 Camshaft Sports ' R '
Application Power Band Cam Lift(mm) Valve Lift(mm) Duration Timing Full Lift VC (mm) LTDC Required Parts
Sports ' R ' 2500 - 7000 6.98 I 11.22 E 10.92 I 285 Deg E 280 Deg 34/71 68/32 108 Deg I 0.25 E 0.30 I 2.18mm CF36 / VS9
http://www.kentcams.com/product/prodDets.aspx?PartNum=FR34&CatID=1&PartID=160&VehPartID=788&ModEngID=225
[Edited on 7/8/08 by Mr Whippy]
http://hometown.aol.com/dvandrews/cams.htm
quote:
Originally posted by omega0684
what is a long duration cam? im assuming there are also short durationa as apposed to what normal cams? what is the difference between the two? i have an fr32 cam, is this long duration? what are the pro's and con's
I am getting better only overlapped the post 21 mins.
Cams with big overlap usually produce more power because you get better venting of the exhaust from the cylinder. Trouble is you may also get some of
the intake charge shooting of the exhaust valve so emissions go up too.
On a forced induction set-up "wild" cams with big overlap can actually reduce power because instead of the pressure building up the intake
charge pressure goes hooning out of the exhaust!! Hence forced induction cams are often quite "mild" compared to wild NA cams.
If the cam is out of the car you can quite easily measure the overlap....
Short duration - big overlap cams where the valves are open for longer over TDC at the end of exhaust - beginning of induction stroke tend to push
the peak power higher up the range.
With twincam heads retiming altering the angular relationship of the cams to each other has a major effect of the rpm peak torque occurs at.
With a single camshaft with both inlet and exhaust lobes altering the timing has much less effect (and any effect is usually negative) because the
durration is fixed when the lobes are ground.
Short durration cams often can only be designed to have have limited lift because of valve train accelerations.