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I have reviewed Jrods cam threads but did not see anything specifically for my interest
I’m looking at a cam that would work well for street driving (good low speed drivability) I read on another forum someone saying that smaller duration with more lift would be better then higher duration vs lower lift.
im just making numbers up but lets just say truck cam
214/214 .600”/.600” 112 lsa
vs
224/224. .550”/.550” 112 lsa
i know ramp rates would come into play for long term durability
can someone advise On the science and why you would close one over the other ?
I think the smaller duration could act like the larger duration because it is allowing ~10% more lift but will be good for low speed drivability
A standard pattern cam is definitely old tech and i would skip them both over there.
Those 2 wont act anything alike though and are sp different should not be compared.
Id go with something in the middle more like a 216/22x or even like our high lift hot cam at 218/228. The added exhaust duration will make it react better to nearly any ls head, promote better power in the upper rpms and add more range.
Also the added lift would make more power everywhere plus likely help with the upper rpm range extension.
But those 2 cams, id pass on.
Tsp has a nice 223/226 that is better than their 224r and has .600 lift also.
When any ls head can flow to .600 easily, why waste that potential?
you probably should think less about duration and more about valve events and overlap. then you can start to see why more of a split can help. there's a whole sticky about it, i forget which one it is. "why lsa doesn't matter?" eh, not sure. there's lots of info on the internet about it as well.
however, having a close split isn't really bad. i have a 230/232 that performs quite well.
The advantage with a single pattern camshaft is that you get better under the curve power and you also make more torque.
The larger exhaust duration does lose torque and some under the curve power in exchange for a little better hang on above 6000rpm.
This may not show on the dyno but it will during driving.
The single split camshaft will feel more crisp under throttle and be stronger till about 5500-6000rpm.
This is coming from Iskenderian.
If LS heads flowed equally on the intake and exhaust a single pattern camshaft would work best.
My thread here was to gain a little more knowledge on the differences in duration vs lift. There are almost no threads that show
Low duration / high lift
vs
high duration/ low lift
I read the valve events post and the lsa one as well and don’t have questions on that
you probably should think less about duration and more about valve events and overlap. then you can start to see why more of a split can help. there's a whole sticky about it, i forget which one it is. "why lsa doesn't matter?" eh, not sure. there's lots of info on the internet about it as well.
however, having a close split isn't really bad. i have a 230/232 that performs quite well.
This all damn day long!
OP, lift vs duration is an interesting proposition, and they are not independent of each other.
An example is the GM hot cam at 219/228 - .525 lift. Ws6 store made the lobes MORE stable by increasing lift.
Imagine throwing a football. To throw further, you naturally throw higher. But there is a nice arc that it follows. Now, try to throw the football straight up, have it go straight across the field, then drop straight down. It is unnatural and will not happen without external forces acting in it.
Valve travel is very similar. If you want to be fast off the seat, higher lift is better. If you want to be fast off the seat AND have a bigger duration, your lift needs to be more higher.
Larger duration will generally make your power band move up in rpm. Higher lift at lower rpm will generally raise your torque curve but keep the power band in a lower rpm range. Generalities, but something to go off of.
And the opposite of the GM hot cam would be something like the LPE GT2-3 with a relatively mild 207/220 duration, but a healthy 573/580 lift (large for back in the day).
Darth_V8r Agreed that part is a good visual.
In comparison to the below cams that Lift vs duration is not a lot
I know my made up numbers may not have been the best example
Your visual makes sense but on a larger scale
From my digging to find a cam that had a close enough overlap to have an comparison i came across these 2
Duration is a small difference but i think this would be the best possible comparison.
Of course the Valve Events are what would dictate what application it is best for
I know not many would make an high duration with an low(er) lift
BTR makes a Truck Cam NSR (no springs required) with fits this case
But in my mind this would be for an driving improvement not a High performance or Race / Competition
While is has impressive Dyno numbers i think one would want more lift if in a Performance build https://www.briantooleyracing.com/bt...truck-cam.html
On a 212 lobe about the best lift you will get is .578. Where a 216 lobe you can get .603 lift.
Cathedral heads lift over .550, the air does some funky things due to the short radius. Ls3 heads are a big different and then ls7 heads with the raised runner, issue is mitigated.
The advantage to higher lift on cathedral heads is increased duration at .550 lift. That is stock. Aftermarket castings are a different animal.
You might find running a 1.8 rocker is more beneficial. That way you could get the 212 lobe to .612 lift. The benefit would be increased torque, all else being equal
Darth, TSP sells a cam with a 212 intake lobe with .600 lift. Is that too much lift for that duration? I'm just trying to understand this.. not disputing.
Darth, TSP sells a cam with a 212 intake lobe with .600 lift. Is that too much lift for that duration? I'm just trying to understand this.. not disputing.
No. Tsp just has different lobes. They are likely just not aggressive ramp rates like the old lsk lobes
On a 212 lobe about the best lift you will get is .578. Where a 216 lobe you can get .603 lift.
Cathedral heads lift over .550, the air does some funky things due to the short radius. Ls3 heads are a big different and then ls7 heads with the raised runner, issue is mitigated.
The advantage to higher lift on cathedral heads is increased duration at .550 lift. That is stock. Aftermarket castings are a different animal.
You might find running a 1.8 rocker is more beneficial. That way you could get the 212 lobe to .612 lift. The benefit would be increased torque, all else being equal
I think i see that limitation for the LSA and lift numbers as you just mentioned
I recall a note from one of the cam spec videos I assume its all about the science in Geometry and Lobe design limitation
Now that you bring up the cathedral heads point i do have
CNC 243 heads so i think that staying near the .550 would be a good choice for me
no mater what cam i choose will have increased duration at the .550 mark which will help with flow overall
I think i see that limitation for the LSA and lift numbers as you just mentioned
I recall a note from one of the cam spec videos I assume its all about the science in Geometry and Lobe design limitation
Now that you bring up the cathedral heads point i do have
CNC 243 heads so i think that staying near the .550 would be a good choice for me
no mater what cam i choose will have increased duration at the .550 mark which will help with flow overall
Really just saying the the advantage to higher lift is actually increased duration at .550 lift. Not so much increased flow from increased lift
Really just saying the the advantage to higher lift is actually increased duration at .550 lift. Not so much increased flow from increased lift
Interesting! I was talking with Richard at West Coast Cylinder Heads a few weeks ago about his 5.3 Stage 2 program. The intake flow peaks at .500, drops a little, then upslopes gradually again at .550. I asked which lift would be most advantageous for that head, and he said .550 max, as the duration at max flow (.500) would be maximized, rather than use a .500 max lift cam. The guy knows his stuff....
01-20-2020, 09:16 PM
Cam Lift vs duration 
