Mopar Performance Purple Mechanical Camshaft - P4120653AE Cam Card

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Good job AJ. Well done, well done.

Running a high compression engine with iron heads on pump will ether require some retarded timing or race has mix of 50/50. The highest I personally run on iron heads was 10-1. A Hyd cam @ 248. 93 was fine.
 
Good job AJ. Well done, well done.

Running a high compression engine with iron heads on pump will ether require some retarded timing or race has mix of 50/50. The highest I personally run on iron heads was 10-1. A Hyd cam @ 248. 93 was fine.
On my 273, I'm at 9.68 with a Isky E4 ( 216° @ .050/260° advertised .425 lift 108°) No detonation but I wonder if the polished chambers help.
 
Polished chambers? Big help.
Would you have the cam card handy?
That I don't but I will look.

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Polished chambers? Big help.
Would you have the cam card handy?
Looked in my notebook downstairs but no dice. It must be buried in 10 years of paper.

#390144 {E-4}
Lift ....................... .425 / .425"
Duration ................ 260* Intake / 250* Exhaust
Duration @ .050 " .... 216* Intake / 214* Exhaust
Overlap .................. 44*
Center-Line ............ 108*
Lash ...................... .020" / .020"
 
>I have seen hydraulic rollers with ramps from "advertised to .050s", of between 53degrees and to over 80 degrees, per pair (opening plus closing).
In the Comp case above, you are looking at 274 less 224=50*@.050....... but at the advertised, the valves are still stated to be, .006 open! So you gotta watch those specs like a hawk!
I think this is an unfair practice, but what do I know. Why? Because you think you are buying a 274/282/110, but if the valves are not yet closed, then what are you actually getting? This cam may act like a 274/282/110 after 3000rpm, but what if the intake valve doesn't close for another 8 or 12 or 16 flipping degrees.... This is how you get unhappy streeters. They think they are buying a 224 at .050, but not all 224@.050s are equals.
My guess is that the ramps are very very slow, from .006 to on the seat and not leaking. Lets say the opening ramp is another 10* long; a conservative number, that would make the Ica, at plus 4 degrees advanced, to be 73* ; which is pretty late.
With a 73* Ica, the Wallace predicts 153psi CCP, and a VP of just 112; which will make the engine feel like a 318LA at under 3000/3400 rpm; so you will need a bit of a stall to get past that.
Sooooooo, if you want to run this 274 cam, 153psi leaves plenty of room for improvement in the Scr.
Butum if the ramps are longer, well it will just be more doggie.

Now:
Swapping to a solid-roller lifter will cure that , but now you have a different problem; namely, with the same .050 numbers, your intake valve may close too early and very likely your pressure will be too high.
For solid rollers, I have seen numbers from Zero-lash to .050 of as little a 39 degrees. If you happen to get one of those, then the 224@.050 becomes 263 at zero-lash, so if a 110 cam installed at 106, then the Ica becomes 57.5, and the Wallace predicts over 180psi with a now very healthy VP of 153.....
But you cannot run 180psi with iron heads, on pump gas at WOT.
That will take alloy heads.

So now, with a solid roller, and iron heads, you are sorta forced (at 10.5Scr) to go bigger on the .050 to get the intake valves actually closed on the seats, a lil LATER.
AJ you are correct the current cam Comp XR274 HR-10 is a dog below 3000rpm hence my addition of a 3000 stall converter.
I have been playing with the Wallace calculators trying to come up with a new cam that would add some low end torque, I'm not there yet.
I did rerun my static compression several times and found it to be 9.91:1
not the 10.5:1 that I original got 3 years ago. I did not keep records so I cant figure out what I did wrong but I do believe the 9.91:1 to be correct.
I spoke with Jim today at Racer Brown and he also was a bit baffled by the current cam and the results. He said that the cam needs to be "smaller" for a good street application and he needed to think on it.
So stay tuned
 
>I have seen hydraulic rollers with ramps from "advertised to .050s", of between 53degrees and to over 80 degrees, per pair (opening plus closing).
In the Comp case above, you are looking at 274 less 224=50*@.050....... but at the advertised, the valves are still stated to be, .006 open! So you gotta watch those specs like a hawk!
I think this is an unfair practice, but what do I know. Why? Because you think you are buying a 274/282/110, but if the valves are not yet closed, then what are you actually getting? This cam may act like a 274/282/110 after 3000rpm, but what if the intake valve doesn't close for another 8 or 12 or 16 flipping degrees.... This is how you get unhappy streeters. They think they are buying a 224 at .050, but not all 224@.050s are equals.
My guess is that the ramps are very very slow, from .006 to on the seat and not leaking. Lets say the opening ramp is another 10* long; a conservative number, that would make the Ica, at plus 4 degrees advanced, to be 73* ; which is pretty late.
With a 73* Ica, the Wallace predicts 153psi CCP, and a VP of just 112; which will make the engine feel like a 318LA at under 3000/3400 rpm; so you will need a bit of a stall to get past that.
Sooooooo, if you want to run this 274 cam, 153psi leaves plenty of room for improvement in the Scr.
Butum if the ramps are longer, well it will just be more doggie.

Now:
Swapping to a solid-roller lifter will cure that , but now you have a different problem; namely, with the same .050 numbers, your intake valve may close too early and very likely your pressure will be too high.
For solid rollers, I have seen numbers from Zero-lash to .050 of as little a 39 degrees. If you happen to get one of those, then the 224@.050 becomes 263 at zero-lash, so if a 110 cam installed at 106, then the Ica becomes 57.5, and the Wallace predicts over 180psi with a now very healthy VP of 153.....
But you cannot run 180psi with iron heads, on pump gas at WOT.
That will take alloy heads.

So now, with a solid roller, and iron heads, you are sorta forced (at 10.5Scr) to go bigger on the .050 to get the intake valves actually closed on the seats, a lil LATER.
I should add that when this engine goes back together with a new cam that I will also be bolting down the same X heads but they will be CNC ported which is way more air flow than I need but the CNC program is what it is.
280cfm @ .650 lift
260cfm @ .500 lift
 
I should add that when this engine goes back together with a new cam that I will also be bolting down the same X heads but they will be CNC ported which is way more air flow than I need but the CNC program is what it is.
280cfm @ .650 lift
260cfm @ .500 lift
280 ::: very nice on oem head
 
It's not that the cam needs to be smaller.
What it is, is that the intake valve needs to close sooner, to trap more mixture/pressure at LOW rpm. Once the Rs get up to around 3000, there is LESS TIME for the mixture to turn around and go backwards up the runners where it just came from, so as the rpm rises, the engine traps more pressure, and starts to make some power.
Now, as it happens with Roller cams, the acceleration ramps are quite long, to get those heavy lifters moving without causing the lifters to bleed down, the pushrods to bend or whatever. Once the roller-lifters are moving they can be accelerated faster than flat-tappet hydros, which have a different problem. So the end result is that, the theory goes, that roller lifters will make more power because of the lobe design made possible by the roller.
So in most cases, yes, it takes a smaller cam to get that earlier closing intake valve....... but not always.
Now a 224@.050 is already pretty small for most guys, so IMO, you don't want to go any smaller. But a 224 has the power peak in a good place at about 5000rpm, which works very well with 3.55s. So, I mean I had a 223/230/110 Hughes HFT that I really really liked. In fact, more than the 230/237/110 that I replaced it with; and I ran them both at the same pressure (CCP). So there is nothing wrong with a good 224 cam. In your case you just need to get the pressure up a lil.

With the new Scr number of 9.91 this is gonna be even more important. IMO, you will need to run the pressure to the max with iron heads on best pump-gas, with roller-lifters, to get the low-rpm torque you are looking for.
To that end, at 9.91 and for 91 gas, the Wallace spits out an Ica of 60* for 164psi, and the VP is up to 136. This is not a great number but sure beats the current VP, which I no longer recall. 136 with a 3000stall and 3.55s will be fine in your lightweight streeter, which being at least 10% better than the current combo.

Ok remember that number; 60*
Your engine doesn't care how you get that 60*
You can put it on a 114 LSA or a 110 or a 106 or whatever you like. But here's the deal, the wider you go, the smaller the cam will be and the tighter the LSA the bigger you can make it.
Now, you already have a 3000TC, so there is no way I would put it on a 114, nor a 112, there is no reason to widen the powerband. A 110 is the norm. But in your case with a 3000# car, a 3000TC, and 3.55s....and those hi-flo-heads; I see an opportunity here for a 108. Maybe even a 106LSA. Lets run some numbers;
Ok so, I'm liking a SOLID roller lifter at zero lash; for 272/278/106. This, installed at 104(+2), will get you that 60*Ica, and 64* of overlap to boot! This kind of cam is gonna start off pretty good for a 340, and then pick up speed as the Rs climb, then about 4500 it is gonna wham to the finish line, a bit like a pipey 2-stroke dirt bike. I shortened the split to 6* so the dumb thing will make some decent hiway mileage, if you cruise it at 65=3000 with 3 or 4% TC slip, with those 3.55s. You don't need any more than 6* split.
Now; this cam COULD be 272 less say 40* for ramps =232@.050........ which being 9* BIGGER than the current Comp 223. That is about 1.28 sizes bigger, so your rpm of peak power just went up about 1.28 x 200=260 rpm so from about 5000 to 5260, good deal. That should be good for 20 hp or more ............ With, remember, an INCREASE of low-rpm torque as well.
Most guys will tell you that running a 106LSA with an automatic is a bad idea, because the powerband is too narrow, and the engine will fall off the cam . That is true, if your stall is 2200 like is stock, and you have hiway gears. The 1-2 split in the 904/727 is 1.45/2.45=.592....... meaning, at whatever rpm you outshift, the rpm will drop to .592 or 59.2% .. So if you are just cruising around town with a low power at low rpm combo, like the XR274 in your 9.91Scr 340, and you outshift First into Second at say 3400, the Rs will fall to .592 x 3400=2000, but the TC might be a 2200, so the engine spools up to 2200, but there is no CCP down there so you rightly say the 340 is a dog.
That was like your old combo.( but with a stock stall)
This new solid-lifter combo, is maxing out at 164psi so lots of CCP. And your TC is a 3000; which with your new more powerful bottom end, will be a true 3000. So now, you can outshift first at 3400, and by the math, the Rs should fall to 2000 same as before, but your TC spools up to 3000 where the engine is already eager to go. ............. so no problem.
Would I try a 106LSA?
With a 3000 and 3.55s, Yes I would.
And if that cam had 64* of overlap, oh yes!, I would. (mine has 61* so I know what that runs like.) and
if the .050s were 232/238 (mine is 230/237) , You better believe I would.
And if at the same time as all this is , that engine pulled 164psl CCP, and a VP of 136 as good as it gets; Daymnrights I would try it.
But, I'm also the kindof guy that tries stuff because I am always willing to back up the bus if it doesn't work out. I do all my own work, so it usually only costs me time and gaskets. But I even got that covered using a lot of re-usable stuff.
But Heck-if-I-know if you can even get a cam of this size, or approximately this size.
Remember that number? 60 degrees. This is the smallest ICA that you can run at ZERO-lash for 164psi to run best gas at 91. If you try to run more pressure, your name better be yellowrose, or you will likely need to run an anti-detonant at WOT, in the tricky zone of 2800 to 3600. But you got that partly covered with the 3000stall. And the rest you can probably make work with a slightly delayed PowerTiming. Time will tell.
Run it past your cam-guy and see what he thinks.

Keep in mind that a solid lifter cam will require a way to set the lash. Which may be an added expense for you.

I didn't talk about lift because, I have no idea how much lift your cam-grinder can put on these rather small lobes.

A cam with 232* of intake duration is the biggest hydraulic FLAT tappet I would run on the street, because the advertised is pretty big, (mine is 276/286/110+2) which makes the ICA as late as I am willing to run. (mine is 66*). I run alloy heads and 11/1Scr and my CCA is a tic under 180. With 367 cubes, this is all the performance I can handle. I liked the previous 223/230/110 cam better, and have been waiting since about 2004 for this 230/110 cam to puke, so I can go back to a smaller one ............... but this one just keeps going and going and going..... and I just can't justify throwing away a good cam, lol.


Now, having said all that, if your engine is out and apart, you can get 164 psi by just increasing the Scr to run the XR274......... 10.7 will do it, with a true Ica of 69*.................... but your VP will still lag at 126, due to the long ramps, which, with a 3000TC should not affect you.
 
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Wow! Compliment the guy and he writes a ton!
That was a hard read.

Please explain this impossible thing to me.
Even more so the bold!

You can put it on a 114 LSA or a 110 or a 106 or whatever you like. But here's the deal, the wider you go, the smaller the cam will be and the tighter the LSA the bigger you can make it.
 
U aint kidding # I need a cigarette and I dont smoke !!!
He laid it down though
AJ does try his best to fully explain & help so you understand. You can’t beat that.

The hardest thing (besides reading the ultra long post:poke:) is what he was saying. Finding a cam with the best theoretical valve timing points for the task at hand. Often, it is simply not made.

There was a time …. I would search for these things after I did the math. If the cam companies know this math, why are they not available? Hummmmmmm

These days, along with the hordes of people searching for a cam or a better one, it is difficult to find “THAT” cam. It’s made worse without a cam card or actual events. Like the MP cams. Through the experiences of others, we have all learned that advancing the cam (or retarding a cam) will produce certain results.

I have not seen this done or suggested in this thread though the results and it’s effects would probably not produce what the OP is looking for. Help some? Yea!
Help enough? Probably not. At least from reading this thread probably not.

:popcorn:
 
AJ does try his best to fully explain & help so you understand. You can’t beat that.

The hardest thing (besides reading the ultra long post:poke:) is what he was saying. Finding a cam with the best theoretical valve timing points for the task at hand. Often, it is simply not made.

There was a time …. I would search for these things after I did the math. If the cam companies know this math, why are they not available? Hummmmmmm

These days, along with the hordes of people searching for a cam or a better one, it is difficult to find “THAT” cam. It’s made worse without a cam card or actual events. Like the MP cams. Through the experiences of others, we have all learned that advancing the cam (or retarding a cam) will produce certain results.

I have not seen this done or suggested in this thread though the results and it’s effects would probably not produce what the OP is looking for. Help some? Yea!
Help enough? Probably not. At least from reading this thread probably not.

:popcorn:
No doubt about that he is very very knowledgeable
 
:rofl:

Yes, outthinking cam companies…..

When Jacobs Ignition was in biz, I called up with a stack of questions not on the ignition (well, some) but the legalities of various states (my own being the biggest PIA) of getting the E.O. number passed. It got so bad for the poor tech guy, (Sorry DF) I ended up with Doc Jacobs on the phone for a chat on law, the physics of the ignition (BRILLIANT by the way)

Afterwards, knowing my state, I decided a call to the board that look at and approve of such things was a fruitless endeavor. It wouldn’t surprise me if there were to many hands outstretched ungreased.

I suggest a call to a few cam companies with a stack of questions along the thought processes above and ask out loud why? Don’t forget to tell them it doesn’t make sense!
 
Always highly informative when AJ and rumblefish are involved!
I too am very interested in this statement: "the wider you go, the smaller the cam will be and the tighter the LSA the bigger you can make it."
especially in regards to the original question regarding the MP .528 cam and it's 241 duration on a 114 LC compared to say a similar sized cam but 230-236 duration but on a 110 or 108 LC.
 
Always highly informative when AJ and rumblefish are involved!
I too am very interested in this statement: "the wider you go, the smaller the cam will be and the tighter the LSA the bigger you can make it."
especially in regards to the original question regarding the MP .528 cam and it's 241 duration on a 114 LC compared to say a similar sized cam but 230-236 duration but on a 110 or 108 LC.
This is the same thing that Jim at racer Brown cams told me yesterday.
 
I have an idea what it means but I want to shut the trap before I remove all doubt that I missed it, don’t know what I’m talking about or just simply learn I’ll something new. I’m in! Oh yea!

I want to be clear. This way I’m on the same page.
What he wrote is possible in one sense and impossible on another. If he writes what I think he will, then I’ll be checking an agreed icon. (I think I will be doing so.)

AJ has a good handle on cams and with the calculators, it’s good. However, calculators are mathematically correct (science!) and the world isn’t. (Chaos!) Everything falls into the category. Room for error and changing conditions often prove otherwise. It is what it is and that’s the world we live in.

@AJ/FormS Work today? Hope it was a good day.
Cool and cloudy here.
 
It's not that the cam needs to be smaller.
What it is, is that the intake valve needs to close sooner, to trap more mixture/pressure at LOW rpm. Once the Rs get up to around 3000, there is LESS TIME for the mixture to turn around and go backwards up the runners where it just came from, so as the rpm rises, the engine traps more pressure, and starts to make some power.
Now, as it happens with Roller cams, the acceleration ramps are quite long, to get those heavy lifters moving without causing the lifters to bleed down, the pushrods to bend or whatever. Once the roller-lifters are moving they can be accelerated faster than flat-tappet hydros, which have a different problem. So the end result is that, the theory goes, that roller lifters will make more power because of the lobe design made possible by the roller.
So in most cases, yes, it takes a smaller cam to get that earlier closing intake valve....... but not always.
Now a 224@.050 is already pretty small for most guys, so IMO, you don't want to go any smaller. But a 224 has the power peak in a good place at about 5000rpm, which works very well with 3.55s. So, I mean I had a 223/230/110 Hughes HFT that I really really liked. In fact, more than the 230/237/110 that I replaced it with; and I ran them both at the same pressure (CCP). So there is nothing wrong with a good 224 cam. In your case you just need to get the pressure up a lil.

With the new Scr number of 9.91 this is gonna be even more important. IMO, you will need to run the pressure to the max with iron heads on best pump-gas, with roller-lifters, to get the low-rpm torque you are looking for.
To that end, at 9.91 and for 91 gas, the Wallace spits out an Ica of 60* for 164psi, and the VP is up to 136. This is not a great number but sure beats the current VP, which I no longer recall. 136 with a 3000stall and 3.55s will be fine in your lightweight streeter, which being at least 10% better than the current combo.

Ok remember that number; 60*
Your engine doesn't care how you get that 60*
You can put it on a 114 LSA or a 110 or a 106 or whatever you like. But here's the deal, the wider you go, the smaller the cam will be and the tighter the LSA the bigger you can make it.
Now, you already have a 3000TC, so there is no way I would put it on a 114, nor a 112, there is no reason to widen the powerband. A 110 is the norm. But in your case with a 3000# car, a 3000TC, and 3.55s....and those hi-flo-heads; I see an opportunity here for a 108. Maybe even a 106LSA. Lets run some numbers;
Ok so, I'm liking a SOLID roller lifter at zero lash; for 272/278/106. This, installed at 104(+2), will get you that 60*Ica, and 64* of overlap to boot! This kind of cam is gonna start off pretty good for a 340, and then pick up speed as the Rs climb, then about 4500 it is gonna wham to the finish line, a bit like a pipey 2-stroke dirt bike. I shortened the split to 6* so the dumb thing will make some decent hiway mileage, if you cruise it at 65=3000 with 3 or 4% TC slip, with those 3.55s. You don't need any more than 6* split.
Now; this cam COULD be 272 less say 40* for ramps =232@.050........ which being 9* BIGGER than the current Comp 223. That is about 1.28 sizes bigger, so your rpm of peak power just went up about 1.28 x 200=260 rpm so from about 5000 to 5260, good deal. That should be good for 20 hp or more ............ With, remember, an INCREASE of low-rpm torque as well.
Most guys will tell you that running a 106LSA with an automatic is a bad idea, because the powerband is too narrow, and the engine will fall off the cam . That is true, if your stall is 2200 like is stock, and you have hiway gears. The 1-2 split in the 904/727 is 1.45/2.45=.592....... meaning, at whatever rpm you outshift, the rpm will drop to .592 or 59.2% .. So if you are just cruising around town with a low power at low rpm combo, like the XR274 in your 9.91Scr 340, and you outshift First into Second at say 3400, the Rs will fall to .592 x 3400=2000, but the TC might be a 2200, so the engine spools up to 2200, but there is no CCP down there so you rightly say the 340 is a dog.
That was like your old combo.( but with a stock stall)
This new solid-lifter combo, is maxing out at 164psi so lots of CCP. And your TC is a 3000; which with your new more powerful bottom end, will be a true 3000. So now, you can outshift first at 3400, and by the math, the Rs should fall to 2000 same as before, but your TC spools up to 3000 where the engine is already eager to go. ............. so no problem.
Would I try a 106LSA?
With a 3000 and 3.55s, Yes I would.
And if that cam had 64* of overlap, oh yes!, I would. (mine has 61* so I know what that runs like.) and
if the .050s were 232/238 (mine is 230/237) , You better believe I would.
And if at the same time as all this is , that engine pulled 164psl CCP, and a VP of 136 as good as it gets; Daymnrights I would try it.
But, I'm also the kindof guy that tries stuff because I am always willing to back up the bus if it doesn't work out. I do all my own work, so it usually only costs me time and gaskets. But I even got that covered using a lot of re-usable stuff.
But Heck-if-I-know if you can even get a cam of this size, or approximately this size.
Remember that number? 60 degrees. This is the smallest ICA that you can run at ZERO-lash for 164psi to run best gas at 91. If you try to run more pressure, your name better be yellowrose, or you will likely need to run an anti-detonant at WOT, in the tricky zone of 2800 to 3600. But you got that partly covered with the 3000stall. And the rest you can probably make work with a slightly delayed PowerTiming. Time will tell.
Run it past your cam-guy and see what he thinks.

Keep in mind that a solid lifter cam will require a way to set the lash. Which may be an added expense for you.

I didn't talk about lift because, I have no idea how much lift your cam-grinder can put on these rather small lobes.

A cam with 232* of intake duration is the biggest hydraulic FLAT tappet I would run on the street, because the advertised is pretty big, (mine is 276/286/110+2) which makes the ICA as late as I am willing to run. (mine is 66*). I run alloy heads and 11/1Scr and my CCA is a tic under 180. With 367 cubes, this is all the performance I can handle. I liked the previous 223/230/110 cam better, and have been waiting since about 2004 for this 230/110 cam to puke, so I can go back to a smaller one ............... but this one just keeps going and going and going..... and I just can't justify throwing away a good cam, lol.


Now, having said all that, if your engine is out and apart, you can get 164 psi by just increasing the Scr to run the XR274......... 10.7 will do it, with a true Ica of 69*.................... but your VP will still lag at 126, due to the long ramps, which, with a 3000TC should not affect you.
I have read your reply several times and it is pretty clear except the part of the 60* "ICA"
The only ICA term I am familiar with is - Installed Cam Angle - the installed relationship between the cam and crank i.e. advanced or retarded.
60* ICA I dont yet grasp a further explanation please.
 
I have an idea what it means but I want to shut the trap before I remove all doubt that I missed it, don’t know what I’m talking about or just simply learn I’ll something new. I’m in! Oh yea!

I want to be clear. This way I’m on the same page.
What he wrote is possible in one sense and impossible on another. If he writes what I think he will, then I’ll be checking an agreed icon. (I think I will be doing so.)

AJ has a good handle on cams and with the calculators, it’s good. However, calculators are mathematically correct (science!) and the world isn’t. (Chaos!) Everything falls into the category. Room for error and changing conditions often prove otherwise. It is what it is and that’s the world we live in.

@AJ/FormS Work today? Hope it was a good day.
Cool and cloudy here.
I found this old Motortrend article informative.
Understanding Cam Specs - Mopar Muscle Magazine
 
I have read your reply several times and it is pretty clear except the part of the 60* "ICA"
The only ICA term I am familiar with is - Installed Cam Angle - the installed relationship between the cam and crank i.e. advanced or retarded.
60* ICA I dont yet grasp a further explanation please.
ICA = intake closed angle
 
oh you guys are too funny!, lol.

Ok here it comes;
Lets start with keeping the 60* Ica, and see what happens for three cams of 106/110/and 114. And keep in mind that these are NOT the only combinations. I chose a split of 8* so that I could put the cam in at whatever it took to still get the Ica of 60*.. And, I am working with hydraulic FLAT TAPPET cams, which is what I am most familiar with.
EDIT: Ica is Intake closing angle; the point ,in crank degrees after bottom dead center, when the intake valve is at the advertised point of minimum lift (which is seldomly actually closed and sealed, but at some arbitrarily number chosen by the manufacturer, like .006tappet rise for a hydro.) The engine, especially at low-rpm, cannot begin to build pressure until that intake is closed.

>for the 106LSA cam, the events are;
268/120/116/276/66; and in at 106 the Effective overlap is 56*,
>For the 110LSA cam, the events are;
262/120/114/270/46; and in at 109, the Effective overlap is 44*
>For the 114Lsa cam, the events are;
258/120/110/264/44; and in at 111, the Effective overlap is 32*

>Since the Ica is the same for all three, and therefore the compression degrees are the same; then, in a given engine, the CCP will also be the same in each.
>Now, follow the progression in intake durations, the numbers in blue. Notice how the cam got progressively smaller , while the compression in black remained at 120*. To make this work, I stole/traded whatever degrees I needed from the overlap, so take a gander at those; in red.
> Notice the 268 cam has 116* of power extraction; which is a lot. You could easily trade that down to 110, to compression,like the 258 has, which would then be 124*. The CCP would pick up about 6psi, but your effective overlap would shrink, killing some power at peak. About what you get at the bottom in ftlbs is what you might lose at the top. For a streeter, the torque at the bottom is usually more valuable than at the top. But don't confuse torque and power. 6 ftlbs at 2800rpm is 3.20hp, and 6 ftlbs at 5000 is 5.72hp. So keep that in your head.
Ok so that's how that works.
---------------
Now lets address what @rumblefish360 rightly said; namely math versus realworld.
As 512Stroker already found out, that hot XR272 was not what he expected it to be and was in the real-world, doggie down low. And we probably traced that to the long acceleration ramps from .006tappet rise to valves actually closed and not leaking.
EVERY hydraulic lifter cam has this gray area. No exceptions.
Some cams have an advertised tappet-rise rating at .006, some at .008, others at .001 So, if you don't know what you bought, it's a crapshoot, what the very low rpm will be like.
>The usual way around this for an automatic-equipped car is to just get past that soft area with a higher stall TC, which lets your engine spool up to where the power is.
>Another way around this, the way I took, is to install very high compression alloy heads, which pulls up the CCP, and so the hi-stall can be a lot less. But this comes with a caveat; Your CCP can be 175psi and more, and, as a streeter, it will probably run just fine on 87E10, full-time. The reason is because, detonation is caused by heat, and the alloy heads are really good at getting rid of it....... most of the time. See, as a streeter, you are seldom on the gas for more than a couple to a few seconds atta time because of a thing called the speed-limit. But at the track, in 95*Plus air-temp heat, your engine might spend 12 to 14 seconds or more, at WOT, doing everything it knows to do, making massive quantities of heat. So now, at 175psi CCP, maybe 87E10 is no longer adequate .... for full PowerTiming, to stay out of detonation.. No big deal, just install better gas for track-days. (For reference; My 367LA combo went 93 in the Eighth at 3467 pounds on 87E10 with 34* of PowerTiming ....... at 177/180psi. Your results may vary.)
But if you have a manual trans (like I do), you cannot afford to have that soft bottom end; because, you are almost always in that stinking soft zone. Riding the clutch is NOT acceptable.
So getting back to the ramps.
For you, OP, committed to iron heads at 9.61 Scr; IMO; you cannot afford to run a long-ramp Hydraulic roller cam. IMO, you have been forced into running a SOLID roller, in the which you can control with lash, exactly when the intake valve closes. Were I in your position, I would not hesitate to make the switch. As far as I can tell, your only other option, to use the XR274, is more Scr to get the CCP up, but that is a limited endeavor, because of what pressure pumpgas will support with those heads. They say, and I have no experience to comment, that iron open-chamber heads, depending on the quench, are limited to 160psi, using pumpgas; maaaaybe 165 with reverse domed pistons to get the Q to under ~.045.
 
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oh you guys are too funny!, lol.

Ok here it comes;
Given in Ica or intake closing angle and lets just stick with the afore-mentioned 272/278
if you put that on a 106LSa cam, that is to say, one on which the offset between the intake lobes and the exhaust lobes is 106degrees, then you get the cam I described, namely one with events as follows;
intake/compression/power/exhaust/overlap
272/120/114/278/64. Installed at 104LSA (lobe center-Angle), aka +2, or 2* advanced; then the Ica will be 60*
now
lets open the LSA to 114 cuz you will instantly see what is going on; your new events are;
272/120/97/278/47. To get the 60* Ica, you would need to install this at 104* same as before. But this steals a bunch of exhaust duration (now just 97*), and it messes up the overlap. In the first instance, the overlap is split at 32* to intake and 32* to exhaust, so split overlap. In the Second instance 32* still goes to intake, but now the exhaust is closing at just 15* ATDC. So the EFFECTIVE overlap cannot be more than twice the smaller number, which then comes to 30*, instead of 64* as in the first example.
Nobody would install this cam in such a manner. If they did, it would suffer a severe loss of power from the mid rpms to the peak and over the top; because the overlap is as good as gone, so the headers cannot do what they are designed to do.
Furthermore; with just 97* of power extraction, the exhaust leaving the chambers will still have a lot of energy in it, that could have been used to propel the vehicle. This will be especially noticeable at low to mid rpms.
To make this cam work, it would need to be retimed to something like in at 113*. The new events would be;
272/111/106/278/47. The overlap is still 47, but the Effective overlap is now up to 46*. And the Ica is no longer 60*, but rather, it is 69*! But it's the same stinking 272/278 cam, just on a new LSA with an accompanying later Ica.
But there is something else to consider;
The compression degrees have shrunk from 120* to just 111*, which being a loss of 9 degrees. This will manifest as a loss of CCA, in the amount of perhaps 11 to 14 psi. These are huge numbers, particularly if you have modest pressure to start with. It can easily ruin your low to midrange driving experience.
But it gets worse;
With just 97* of power extraction,
That is alot to sift though, I like it
I now know that there is no such animal as the "perfect camshaft".
Gain in one area and lose in another. But the numbers dont lie.
 
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