Cam question

[Rick@AP]

Hopefully some of you "smarter than I am" guys will reaffirm my conclusion.

I am looking at three cams and trying to determine which would be the larger cam: FP3x, BC 280's and Crane "Stage 3".

The FP3x's specs are as reported:
Gross lift: .430/.414
Duration @ .050": 212/212

The BC specs are as reported:
Gross lift: .422/.418
Duration @ .050": 218/216

The Crane specs are as reported:
Gross lift: .443/.424
Duration @ .050": 224/216

Going strictly by the spec card, the Crane cam would be the largest. However, FP notes that their cams have an increased ramp rate over other cams that allows the valves to open sooner. I still believe that the Crane cam would be larger overall. My reasoning is that although the FP's ramp rates could be higher than the others, the added lift plus extended duration time of the Crane cam would make up for the increased ramp rate in the long run and actually keep the valve open longer.

However, if the valve only has to open "x" amount before maximum flow is reached does the added lift really make any difference?

Thoughts? (...other than this cam is more proven, Shep, Rau and etc., use this cam)

 

[daren_p]

I'm not an expert on all things cams but from what I have experienced, I'm going to say the Crane & probably the BC will net you more top end flow compared to the FP but the FP will probably net you more at slightly lower rpms. I base this mainly on the duration differences. I believe the increased ramp rate will yield better flow but only in the region the cam profile was designed to make power in (if that makes any sense). Here's my example.

I went with the FP1X cams because I still wanted to keep the car emissions friendly. It has the same duration as as the standard FP1 cams but has the increased ramp rate & has the same lift as the FP2 cams. I figured great, these cams will work excellent for emissions/almost stock sounding but should give me more top end compared to the std 1's because of the extra lift/ramp rate. Well it appears to me now that these cams still basically net the same sort of power curve as the std 1 cams, just even more power in that region, as there airflow still seems to taper off compared to FP2's (FP2's just have longer duration compared to 1X's) in the upper rpms, even though when I compared profiles, they booth looked to hold the valve open the same amount (just in different spots) The FP3X's have the same duration as the FP2's (& believe the BC Stage 2's/272's) so this should tell you where their "sweet spot" is.

 

[TSIfreek]

Rick we need more info on motor size? RPM the motor will see, turbo used? Theres more power in cam profile than just lift. If is for a stroker go with the 3xs with heavy springs.
On a 2.0 go with the BCs.

 

[Rick@AP]

Rick we need more info on motor size? RPM the motor will see, turbo used? Theres more power in cam profile than just lift. If is for a stroker go with the 3xs with heavy springs.
On a 2.0 go with the BCs.

Thanks, but I'm not looking for recommendations on which cam to buy. I'm trying to figure out more so the nuances of different aspects of the cams shape.

 

[Rick@AP]

I'm not an expert on all things cams but from what I have experienced, I'm going to say the Crane & probably the BC will net you more top end flow compared to the FP but the FP will probably net you more at slightly lower rpms. I base this mainly on the duration differences. I believe the increased ramp rate will yield better flow but only in the region the cam profile was designed to make power in (if that makes any sense). Here's my example.

I went with the FP1X cams because I still wanted to keep the car emissions friendly. It has the same duration as as the standard FP1 cams but has the increased ramp rate & has the same lift as the FP2 cams. I figured great, these cams will work excellent for emissions/almost stock sounding but should give me more top end compared to the std 1's because of the extra lift/ramp rate. Well it appears to me now that these cams still basically net the same sort of power curve as the std 1 cams, just even more power in that region, as there airflow still seems to taper off compared to FP2's (FP2's just have longer duration compared to 1X's) in the upper rpms, even though when I compared profiles, they booth looked to hold the valve open the same amount (just in different spots) The FP3X's have the same duration as the FP2's (& believe the BC Stage 2's/272's) so this should tell you where their "sweet spot" is.

I think I understand what your saying and it seems to make sense.

 

[dsm-onster]

I'm likely not smarter than you. This is from my experience, education, and research.

Thanks, but I'm not looking for recommendations on which cam to buy. I'm trying to figure out more so the nuances of different aspects of the cams shape.

Increased ramp rate will broaden your power band vs. a cam w/ the same duration and lift but less ramp rate. You will gain more below where the lesser ramp rate cam "comes on". You'll gain slightly more up top after the low ramp rate cam dies.

Opening a valve earlier and closing it later increases duration. This increases VE higher in the rpm range. Having an accelerated ramp rate on the same cam duration causes the valve to open higher earlier. And stay higher later even though the duration at 0.05" lift is identical. So accelerating the ramp rate, in effect, allows for a higher power band. The air is not choked as much as it is rushing in the CC during the upper revs where the momentum of the incoming air is high and the air can pack itself in the chamber even when the piston starts rising back up the bore. This is the same principle used to yield more power up top through increasing duration. Total duration has a greater effect, but accelerating the ramp rate can still yield more up top vs. the same duration cam w/ a more normal ramp rate.

Concerning more "oomph" down low. A high ramp rate will do very similar to advancing both cams' overall timing. This will yield more power down low since the air is more "lazy" at low velocities. Opening the valve earlier simply lets the cylinder begin filling earlier. And, consequentially more mass has time to enter said cylinder. If the ram rate causes the valve to open higher at the same degree, then the cylinder can accept more air earlier and thus fill the cylinder more completely early on in the rpms. Advancing the cam timing or running less duration will have a greater effect on the power band down low. But, accelerated ramp rates will have more of an effect on low revs than high revs.

Simply put accelerated ramp rates give lots more down low vs. a cam of the same duration; and a little more up top. Accelerated ramp rates allow a high duration cam to more easily idle like stock.

Because of this, accelerated ramp rates can cause a cam to be more versatile when running cam gears. Advancing/retarding cam timing can shift the power band. But a certain duration number works best at a certain rpms. If you want more power down low you can advance the timing on a set of 272s but you'll be less efficient than 264s at where you're attempting to shift the power band. WRT accelerated ramp rates: Since the uplobe open height and down lobe open height at any given point on the duration is higher than another cam, then the air "thinks" it is running at a higher duration (once the valve opens), and isn't choked so much at the down lobe open points before valve close. This will give you the ability to retard a set of lower duration cams and yield the same results as a higher duration cam w/ the same lift but less ramp rate w/out the inefficiency of the low duration in that higher rpm range. Thus you could go w/ a set of fp3X cams and retard the cam timing and have it stay strong up high equally to the higher duration cams, though their durations are more suited to the higher rpms. Keep in mind, if you feel you want more torque lower then advancing the other two higher duration cams to the power range of the fp3Xs would still not provide the power the fp3Xs already do in the same lower rpm range.

Note. If you have a 2.0, then retarding an fp3X intake cam 3 degrees and fp3X exhaust cam 9 degrees yields the same profile as fp2Xs but w/ a higher peak lift. So a set of fp3Xs and a pair of adjustable cam gears would make fp3Xs run fantastic over a 2.0L block. And you'll have a better ramp rate than the BCs (allowing you to retard the timing more for the same power as the BCs up top if you decide to really rev her out). Also you'll have much better lift.

If you're going to stick w/ a 2.0L, I'd definitely go w/ the Cranes for PEAK performance and a 1/4 mile ideal setup. One thing about increasing stroke, you can have a car idle fine w/ higher duration than would idle fine running a smaller stroke. If you get the Cranes, then decide to upgrade to a stroker, then you can always throw on a set of cam gears and adjust for more overlap and advance the centerlines a bit more and have a REALLY high lift cam. But keep in mind, depending on the ramp rate, advancing such a high duration far enough to yield good results on a stroker rev range will likely be less efficiency than getting a cam duration more inline w/ the rev range you're after. Remember, ramp rate can increase a cam profile's versatility.

 

[daren_p]

Without doing alot of research on the different cams, looking at the specs, my first though would be if your building a motor, probably a stroker & will be using the stock or slightly higher rev limit, the FP3X's would probably be the best choice to make the most "power under the curve". Now if I was sticking to a stock 2.0L & was planning on seeing a good amount of revs above the stock limit, this is where the Crane or BC's would probably be the better choice.

 

[Rick@AP]

Thanks for the info and feedback guys.

My sticking point in this whole situation is, looking at this from a 360 degree perspective and very much hypothetically. If cam "a" achieves a lift of .400 at 20 degrees of rotation and holds that lift for 80 degrees of its rotation, and cam "b" has a larger duration which would cause the valve to be open longer than cam "a" and a higher lift value, wouldn't cam "b"'s ramp rate have to be near or faster than cam "a"'s in order to have the valve timing events occur as they should since cam "b" has to have this longer duration and lift in relatively the same area as cam "a"? (if this makes sense)

Matt, your post makes a lot of sense and was very well thought out. However, with the higher VE of the stroker motor wouldn't the Crane's make more sense?

 

[dsm-onster]

. . .and cam "b" has a larger duration which would cause the valve to be open longer than cam "a" and a higher lift value, wouldn't cam "b"'s ramp rate have to be near or faster than cam "a"'s in order to have the valve timing events occur as they should since cam "b" has to have this longer duration and lift in relatively the same area as cam "a"? (if this makes sense)

Open events have nothing to do w/ rates. Reaching the same lift or even a little less w/ a shorter duration actually guarantees that the ramp rate MUST be accelerated more for a shorter duration. There is LESS time in crank degrees for the valve to open given a shorter duration vs. a larger duration. The lobe has to then quicky open/close the valve for a peak lift to be near a broader duration cam. The only way a lobe can more quickly open a valve is to increase the ramp rate.

Note that the numeric value of the ram rates themselves can change along the lobe rise and fall. Most performance applications discuss an accelerated ramp rate for lobes that display such a characteristic around the first 30% of the lobe rise. This causes the lobe to "square" . . . the profile on paper (lift vs. crank degrees) become more shaped like a square-wave. With this style of accelerated ramps, a short duration cam can easily reach the peak lift of a high duration cam. Stout springs are almost a necessity here.

 

[Rick@AP]

Open events have nothing to do w/ rates. Reaching the same lift or even a little less w/ a shorter duration actually guarantees that the ramp rate MUST be accelerated more for a shorter duration. There is LESS time in crank degrees for the valve to open given a shorter duration vs. a larger duration. The lobe has to then quicky open/close the valve for a peak lift to be near a broader duration cam. The only way a lobe can more quickly open a valve is to increase the ramp rate.

Note that the numeric value of the ram rates themselves can change along the lobe rise and fall. Most performance applications discuss an accelerated ramp rate for lobes that display such a characteristic around the first 30% of the lobe rise. This causes the lobe to "square" . . . the profile on paper (lift vs. crank degrees) become more shaped like a square-wave. With this style of accelerated ramps, a short duration cam can easily reach the peak lift of a high duration cam. Stout springs are almost a necessity here.

That's what I was looking for.

Thanks for the help out.

 

[dsm-onster]

However, with the higher VE of the stroker motor wouldn't the Crane's make more sense?

BTW, VE is ALMOST totally determined by the head, not the block. So a stroker will have no more VE than a 2.0L w/ the same head. In fact it will have less VE every where in the rev range. If a certain port shape, valve diameter, and lift promotes a certain VE for a .5 litre cylinder. Then a cylinder demanding more volume (.6 litre for a stroker) may or may not get the same percentage of the cyliner filled but may never get any more percentage filled. Likely more mass enters the cylinder but not because of higher VE. VE is a percentage not a volume or weight.

I state "almost" because the stroker piston travels at an accelerated rate. and likely more mass is traveling per unit time per revolution. Higher mass is harder to stop and faster mass is harder to stop. Momentum. Thus running more duration allows the "packing" to take place earlier in the rev range. But, VE is still determined by the duration no matter how high or low; by port design; by plenum volume; by valve lift; by valve diameter. Stroking shifts the VE curve to an earlier rev range the total area under the curve remains for the most part the same. There are little to no increase in the VE numbers themselves when stroking

Determining the best duration takes Momentum (velocity AND mass) of the aircharge into consideration. Rev range determines velocity of air where displacement is not altered. Velocity then is the only difference in momentum P=mv). So determining the best duration takes only velocity into consideration when not altering stroke/bore. However, raising the displacement raises the "m". Thus momentum goes up earlier in the rev range. Thus a higher duration cam "comes on" earlier than would be expected w/ a lower displacement block.

Now, I've seen 212 @ 0.05" lift cams (fp2/2Xs) still pull hard to 8500rpms over a 2.0. A stroker really should not be taken this high unless you have $$$. But regardless, 212 duration suggest a certain momentum at 8500 rpms. Where does that same momentum number rear up w/ a stroker? 20% earlier? I don't know. Likely more than 20% earlier because of piston speed. If I had a a dyno sheet of two identical setups except one being a stroker and one not then I could PROBABLY analyze the curves and determin the difference in momentum changes beween the two. I do know that momentum number IS earlier. If it is only 20% earlier, this would put that same momentum at 6800 rpms. A good peak for a stroker.