cam sizing
12-20-2006, 12:14 PM
#1
PTV with LS7 heads I am gonna call and have a custom cam ground for my application when I finalize my head choice. My shortblock is finished, and my pistons are .030 out of the hole. They are diamond -7cc. The valve reliefs are machined on a 15 deg. angle. Flycutting is not an option. I plan on running either a .051 gasket or a .060. ROUGHLY how much duration will I be able to run with a LS7 head before I start running into PTV problems. I want something pretty nasty. If you need any more info please post up and I will find out anything I can. thanks
Keith
Keith
Last edited by Stang's Bane; 12-20-2006 at 12:29 PM.
12-22-2006, 03:39 PM
#3
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Hopefully I can offer some insight. First off, you mentioned your "pistons are .030 out of the hole". I must assume that you were referring to the oversize and not the deck height as most pistons are usually "in the hole".
I am in the process of getting a 238-240 .640-.645 112LSA and know it will clear in my LS7.
I have received input from many others who actually have a tad more cam and they have had no issues. Granted, the springs, retainers/locks and pushrods were all upgraded.
I am somewhat concerned about the 15 degree valve angle on your heads as the LS7's have 12 degree so this may be an issue.
At the very least, I would mock up the assembly with the factory cam and measure what clearance you initially have to get a base line.
You should not have any coil bind issues with your heads and hopefully, you will have ample room (VTP) with the stock cam as you want at the very least .080-.090 VTP clearance with the aftermarket cam.
I have ran clearances this tight with an aluminum rod engine so I know it is safe on steel/titanium rod versions.
What are the specs on the cam you are currently interested in?
I am in the process of getting a 238-240 .640-.645 112LSA and know it will clear in my LS7.
I have received input from many others who actually have a tad more cam and they have had no issues. Granted, the springs, retainers/locks and pushrods were all upgraded.
I am somewhat concerned about the 15 degree valve angle on your heads as the LS7's have 12 degree so this may be an issue.
At the very least, I would mock up the assembly with the factory cam and measure what clearance you initially have to get a base line.
You should not have any coil bind issues with your heads and hopefully, you will have ample room (VTP) with the stock cam as you want at the very least .080-.090 VTP clearance with the aftermarket cam.
I have ran clearances this tight with an aluminum rod engine so I know it is safe on steel/titanium rod versions.
What are the specs on the cam you are currently interested in?
12-24-2006, 10:31 PM
#4
I am referring to deck height. From what I have been able to gather it is common on a LS1 to be .010 out. By block had been machined previously so the deck was a little lower. I want to run about a 246 x 256 or so. I don't have the stock cam.
12-29-2006, 10:22 AM
#6
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What is the LSA on the cam? if it is tight 108-110, VTP will be crucial as well as having your piston protrude .030 out.
With a .051 gasket, you will have a quench area of roughly .020 which will make VTH as well as VTP tight.
Your best bet is to mock up the assembly and if things are too tight on either the intake or exhaust side, you may be able to free up a few thousands by moving the cam timing around.
If you want to take a chance, I would not run anything less than .070 as a bare minimum (especially on the exhaust).
If you decide to notch your pistons, then by all means dissassemble your engine and have a machine shop do them instead of using a mock dummy valve cutter.
With a .051 gasket, you will have a quench area of roughly .020 which will make VTH as well as VTP tight.
Your best bet is to mock up the assembly and if things are too tight on either the intake or exhaust side, you may be able to free up a few thousands by moving the cam timing around.
If you want to take a chance, I would not run anything less than .070 as a bare minimum (especially on the exhaust).
If you decide to notch your pistons, then by all means dissassemble your engine and have a machine shop do them instead of using a mock dummy valve cutter.
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12-29-2006, 12:26 PM
#8
Originally Posted by Meegle
... as most pistons are usually "in the hole"....
Nope LSx are pistons out of the hole (or above the deck). Most of the ones I have measured are between .005 and .008... Seems, like I just read about someone here assembling their own engine and the pistons were below the deck... but that is very unusual...
12-29-2006, 01:06 PM
#9
Yeah, nobody has a clue about what pistons you are running which is only one of many issues here. The other characteristics of the motor and car and what you want them to do, rather than what is the biggest cam I can fit in here BS. You might be able to put in a 250/260 120LSA cam or a 220/230 104LSA cam, but neigther one is going to get you what you want.
Bret
Bret
12-29-2006, 02:24 PM
#10
As far as the biggest cam reference, it is a joke. I am not asking anyone to spec a cam out out for me, the reason I am asking what is the biggest I can fit is I want to know how much I can use. If I can fit the 250/260 120 does it mean I am going to use it? NO, I just want to know ROUGHLY how much cam I can run before I run into problems. As far as what I want out of it, I want to run a 10.7x in a 3500 lb Camaro. All supporting suspension mods will be on the car. looking at about 12-1 scr. If you need anymore information about my setup let me know. I am more than happy to tell anyone everything about my car that they want to know.
12-29-2006, 03:47 PM
#11
Originally Posted by Stang's Bane
I am gonna call and have a custom cam ground for my application when I finalize my head choice. My shortblock is finished, and my pistons are .030 out of the hole. They are diamond -7cc. The valve reliefs are machined on a 15 deg. angle. Flycutting is not an option. I plan on running either a .051 gasket or a .060. ROUGHLY how much duration will I be able to run with a LS7 head before I start running into PTV problems. I want something pretty nasty. If you need any more info please post up and I will find out anything I can. thanks
Keith
Keith
12-29-2006, 05:21 PM
#12
Originally Posted by Stang's Bane
As far as the biggest cam reference, it is a joke. I am not asking anyone to spec a cam out out for me, the reason I am asking what is the biggest I can fit is I want to know how much I can use. If I can fit the 250/260 120 does it mean I am going to use it? NO, I just want to know ROUGHLY how much cam I can run before I run into problems. As far as what I want out of it, I want to run a 10.7x in a 3500 lb Camaro. All supporting suspension mods will be on the car. looking at about 12-1 scr. If you need anymore information about my setup let me know. I am more than happy to tell anyone everything about my car that they want to know.
Bret
01-08-2007, 08:49 PM
#14
I spoke with diamond pistons. Basically what they told me was that the pistons in no way shape form or fashion matched up with the ls7 heads. So basically I have to act like I have no valve reliefs in my pistons. Bump for any more advice. I hate to call one of our sponsors and basically have to tell them to fire a shot in the dark.