How do you calculate how much seat pressure you need?
12-16-2005, 05:44 PM
#1
How do you calculate how much seat pressure you need? I've tried searching this, but the search engine seems to be down right now...
Is there a formula or link anyone knows about to use for calculating the seat pressure needed to prevent valve float for a given max RPM?
For example:
I'm using a XER lobe 242/250 cam on a stroker. It has .611/.619" lift, and I plan to build it to run to ~6800 rpms. What kind of valve seat pressure should I plan on? I have patriot golds, but will that be enough?
Is there a formula or link anyone knows about to use for calculating the seat pressure needed to prevent valve float for a given max RPM?
For example:
I'm using a XER lobe 242/250 cam on a stroker. It has .611/.619" lift, and I plan to build it to run to ~6800 rpms. What kind of valve seat pressure should I plan on? I have patriot golds, but will that be enough?
12-16-2005, 07:02 PM
#2
Originally Posted by V-10 Killer
I've tried searching this, but the search engine seems to be down right now...
Is there a formula or link anyone knows about to use for calculating the seat pressure needed to prevent valve float for a given max RPM?
For example:
I'm using a XER lobe 242/250 cam on a stroker. It has .611/.619" lift, and I plan to build it to run to ~6800 rpms. What kind of valve seat pressure should I plan on? I have patriot golds, but will that be enough?
Is there a formula or link anyone knows about to use for calculating the seat pressure needed to prevent valve float for a given max RPM?
For example:
I'm using a XER lobe 242/250 cam on a stroker. It has .611/.619" lift, and I plan to build it to run to ~6800 rpms. What kind of valve seat pressure should I plan on? I have patriot golds, but will that be enough?
12-16-2005, 07:27 PM
#3
I'm just going from what I learned from JRP's cam guide sticky.
Now here's from my Comp SS3 cam card:
Part number 54-000-11
Duration @ .006" tappet lift
INT 291, EXH 297
Duration @ .050"
INT 242, EXH 250
Now 291-242=49, and 297-250=47, so by the sticky, it's an XER lobe.
I'm not saying you're wrong, I'm just showing why I said what I said.
- If you know the advertised duration (.006) of a cam you can calculate the ramp rate. To do this you take the duration @.006 and subtract it from the duration @ .050. A number of 53 or higher denotes an XE lobe or other mild lobe and a number of 49 or lower denotes an XE-R lobe or other aggressive lobe (Beast and 99 Black Bird T/A)
Part number 54-000-11
Duration @ .006" tappet lift
INT 291, EXH 297
Duration @ .050"
INT 242, EXH 250
Now 291-242=49, and 297-250=47, so by the sticky, it's an XER lobe.
I'm not saying you're wrong, I'm just showing why I said what I said.
Last edited by V-10 Killer; 12-16-2005 at 07:33 PM.
12-17-2005, 08:36 PM
#4
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I believe there are some programs out there which can do this for you but you must know everything about your valve train weights. I've got an interest in this is well. In general it's always good to er on the more pressure then needed side. Remember, valve springs generally use a few pounds the first time you run them/break them in.
12-19-2005, 09:51 PM
#6
This probably could be done mathematically if you new the mass and inertia of all the valve train components and the exact profile (maybe in 1 deg increments).
Even then, you would want to back it up with testing on a valvetrain simulation. One test is work a thousand calculations.
So, typically you would ask the cam manufacturer. Comp has extensive engine builder support.
And you talk with others who have done similar things. The hard part with that is knowing the durability. Working for 1,000 miles/30 hours/2,000,000 cycles is not the same as lasting 20 times that.
Performance Trends Engine Analyzer Pro makes an attempt. However, you need the know the weights of all your valve train pieces and your cam profile in a cam doctor or equivalent file or use their approximations.
Even then, you would want to back it up with testing on a valvetrain simulation. One test is work a thousand calculations.
So, typically you would ask the cam manufacturer. Comp has extensive engine builder support.
And you talk with others who have done similar things. The hard part with that is knowing the durability. Working for 1,000 miles/30 hours/2,000,000 cycles is not the same as lasting 20 times that.
Performance Trends Engine Analyzer Pro makes an attempt. However, you need the know the weights of all your valve train pieces and your cam profile in a cam doctor or equivalent file or use their approximations.
12-19-2005, 10:18 PM
#7
Originally Posted by V-10 Killer
I'm just going from what I learned from JRP's cam guide sticky.
Now here's from my Comp SS3 cam card:
Part number 54-000-11
Duration @ .006" tappet lift
INT 291, EXH 297
Duration @ .050"
INT 242, EXH 250
Now 291-242=49, and 297-250=47, so by the sticky, it's an XER lobe.
I'm not saying you're wrong, I'm just showing why I said what I said.
Now here's from my Comp SS3 cam card:
Part number 54-000-11
Duration @ .006" tappet lift
INT 291, EXH 297
Duration @ .050"
INT 242, EXH 250
Now 291-242=49, and 297-250=47, so by the sticky, it's an XER lobe.
I'm not saying you're wrong, I'm just showing why I said what I said.
Comp XE-R's do stop at 248 degrees. I tried to order one larger than that and they said they could not grind it. Technically, the lobe you listed is 47 degrees's diffrent. All XE-R's are 49, so it isn't an XE-R. Although I am interested in knowing what it is because the XE-R has long been the most aggressive hydraulic lobe out there. I've never seen one harder than 49. Is there a lobe number for the exaust on the card? 37xx or something similar? Trending Topics
12-19-2005, 11:21 PM
#8
Actually, I did notice it said Beast in the sticky, but I thought it was still worth posting.
I remember seeing the grind numbers on the card, and tried searching for them on Comp Cams website but got nothing. I'm at work now, but will post them tomorrow.
I remember seeing the grind numbers on the card, and tried searching for them on Comp Cams website but got nothing. I'm at work now, but will post them tomorrow.
12-20-2005, 09:44 AM
#9
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i do things the lazy man way,i just call comp or whoever i get the cam from and see what the seat pressure and open pressure is and see what springs and retainers they reccomend.
12-20-2005, 10:14 AM
#10
Originally Posted by DavidNJ
This probably could be done mathematically if you new the mass and inertia of all the valve train components and the exact profile (maybe in 1 deg increments).
Even then, you would want to back it up with testing on a valvetrain simulation. One test is work a thousand calculations.
So, typically you would ask the cam manufacturer. Comp has extensive engine builder support.
And you talk with others who have done similar things. The hard part with that is knowing the durability. Working for 1,000 miles/30 hours/2,000,000 cycles is not the same as lasting 20 times that.
Performance Trends Engine Analyzer Pro makes an attempt. However, you need the know the weights of all your valve train pieces and your cam profile in a cam doctor or equivalent file or use their approximations.
Even then, you would want to back it up with testing on a valvetrain simulation. One test is work a thousand calculations.
So, typically you would ask the cam manufacturer. Comp has extensive engine builder support.
And you talk with others who have done similar things. The hard part with that is knowing the durability. Working for 1,000 miles/30 hours/2,000,000 cycles is not the same as lasting 20 times that.
Performance Trends Engine Analyzer Pro makes an attempt. However, you need the know the weights of all your valve train pieces and your cam profile in a cam doctor or equivalent file or use their approximations.
Lobe Profile, Valvetrain Mass and RPM range are the three big considerations.
More aggressive, heavier and higher RPM mean more spring pressure and stiffer parts to get the job done.
The easiest thing to do to get more life out of the setup is to take mass out of the system.
Bret
