comp xe270ah cams
02-17-2010, 02:40 AM
#13
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Yes. As always, they should be checked for PTV clearance upon install. This is the case with any cam. If those cams are installed correctly, you should be fine. Make sure to take it to someone who REALLY knows what they are doing.
Steer clear of adjustable timing gears. The stock cam gears can have the keyways ground to allow adjustment without running the risk of them coming apart like the adjustable ones.
Steer clear of adjustable timing gears. The stock cam gears can have the keyways ground to allow adjustment without running the risk of them coming apart like the adjustable ones.
02-17-2010, 05:59 AM
#14
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Actually, Comp Cams recommends 109 ICL, which is why if you install them at 113 you might have PTV issues. I am not a cam expert, but I almost put this exact grind in my motor and spent quite a bit of time doing research about the PTV issues with this one in particular. The problem is with the 238 duration on the exhaust side and if it is not degreed properly the piston will hit it when the valve is still partially open.
http://www.compcams.com/Cam_Specs/Ca...?csid=969&sb=2
The reason why these cams get such a bad rap is because guys have installed these things using the stock cams gears (unmodified) that can be as far off as 8 degrees either way. That can be disastrous with a lot of cam grinds.
http://www.compcams.com/Cam_Specs/Ca...?csid=969&sb=2
The reason why these cams get such a bad rap is because guys have installed these things using the stock cams gears (unmodified) that can be as far off as 8 degrees either way. That can be disastrous with a lot of cam grinds.
The thing to remember is that it's the ICL that causes ptv clearance problems, not the ECL. This happens around 5-10 degrees after TDC. Same with the duration...it's the intake again that causes the potential problem, and the 234 intake duration that the 270's use is just too big. The exhaust side has much more room. So, basically if the ICL is a 109 (vs 113) it will further reduce clearance.
I agree 100% that the stock cam gears can be several degrees off, which would further aggravate the clearance issue. MHS sells matched cam gears that have been set to 0 degrees (i believe they are also welded) which eliminates the need for degreeing, and ensures the best possible clearance.
Check out their site. Nick has measured these particular Comp cams on a PI motor with the cam gears at 0 degrees, and found a whopping .005"-.015" clearance, which is WAY too tight IMO, as well as many others.
Last edited by mrtstang; 02-17-2010 at 08:08 AM.
02-17-2010, 06:19 AM
#15
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This is backwards, at the 109 you will hit the valve for sure with a stock PI head. Comp retarded this cam back to 113 somewhere along the way (at least the last couple sets I did were 113) At 113 you will have about 0.005"~0.015" give or take with a stock head on this cam.
The smaller the ICL the less PTV clearance you have all else being equal.
02-17-2010, 06:34 AM
#16
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This is backwards, at the 109 you will hit the valve for sure with a stock PI head. Comp retarded this cam back to 113 somewhere along the way (at least the last couple sets I did were 113) At 113 you will have about 0.005"~0.015" give or take with a stock head on this cam.
The smaller the ICL the less PTV clearance you have all else being equal.
The smaller the ICL the less PTV clearance you have all else being equal.
02-17-2010, 04:16 PM
#17
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I will admit when I am wrong, so I did have my advance/retard relation to degrees mixed up. I knew that Comp had retarded the timing by 4 degrees since they were originally released to try to solve this issue, when I looked up the specs on their website I saw a 4 degree diff and didn't stop to think that it was the wrong way.
As the cam is advanced in timing the ICL will get smaller. As far as the exhaust 238 duration being the problem, that is what every tech from Comp Cams told me when I ordered these cams a little over a year ago. They were very aware of the PTV clearance issues that these cams that people have had, and that's why they were changing the ICL. And this made sense of course to the exhaust valve hanging open too long.
mrtstang, of course if you change the ICL.....you change the ECL too. The intake lobes arent seperately adjustable from the exhaust lobes. If the cams are off, you can most certainly have trouble on the exhaust side too.
In short, I'm sure you will agree nick, these cams will work just fine when degreed properly for these engines. Be that 113, 114, 115 ICL.
As the cam is advanced in timing the ICL will get smaller. As far as the exhaust 238 duration being the problem, that is what every tech from Comp Cams told me when I ordered these cams a little over a year ago. They were very aware of the PTV clearance issues that these cams that people have had, and that's why they were changing the ICL. And this made sense of course to the exhaust valve hanging open too long.
mrtstang, of course if you change the ICL.....you change the ECL too. The intake lobes arent seperately adjustable from the exhaust lobes. If the cams are off, you can most certainly have trouble on the exhaust side too.
In short, I'm sure you will agree nick, these cams will work just fine when degreed properly for these engines. Be that 113, 114, 115 ICL.
Last edited by tbirdscwd; 02-17-2010 at 04:18 PM.
02-17-2010, 07:04 PM
#18
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I will admit when I am wrong, so I did have my advance/retard relation to degrees mixed up. I knew that Comp had retarded the timing by 4 degrees since they were originally released to try to solve this issue, when I looked up the specs on their website I saw a 4 degree diff and didn't stop to think that it was the wrong way.
As the cam is advanced in timing the ICL will get smaller. As far as the exhaust 238 duration being the problem, that is what every tech from Comp Cams told me when I ordered these cams a little over a year ago. They were very aware of the PTV clearance issues that these cams that people have had, and that's why they were changing the ICL. And this made sense of course to the exhaust valve hanging open too long.
mrtstang, of course if you change the ICL.....you change the ECL too. The intake lobes arent seperately adjustable from the exhaust lobes. If the cams are off, you can most certainly have trouble on the exhaust side too.
I understand what you're saying, but the intake valves themselves are located closer to the piston, and also have a thicker lip that sits deeper in the chamber....thus creating less ptv clearance.
In short, I'm sure you will agree nick, these cams will work just fine when degreed properly for these engines. Be that 113, 114, 115 ICL.
As the cam is advanced in timing the ICL will get smaller. As far as the exhaust 238 duration being the problem, that is what every tech from Comp Cams told me when I ordered these cams a little over a year ago. They were very aware of the PTV clearance issues that these cams that people have had, and that's why they were changing the ICL. And this made sense of course to the exhaust valve hanging open too long.
mrtstang, of course if you change the ICL.....you change the ECL too. The intake lobes arent seperately adjustable from the exhaust lobes. If the cams are off, you can most certainly have trouble on the exhaust side too.
I understand what you're saying, but the intake valves themselves are located closer to the piston, and also have a thicker lip that sits deeper in the chamber....thus creating less ptv clearance.
In short, I'm sure you will agree nick, these cams will work just fine when degreed properly for these engines. Be that 113, 114, 115 ICL.
I understand what you're saying, but the intake valves themselves are located closer to the piston, and also have a thicker lip that sits deeper in the chamber....thus creating less ptv clearance.
I also agree that those cams will work fine if you retard the centerline enough. Only problem then, is that you'll push the power band up higher, and loose valuable mid range hp & tq, which will result in a slower car. At that point you'd be better off with cams that don't require this.
Last edited by mrtstang; 02-17-2010 at 08:31 PM.
02-17-2010, 08:05 PM
#19
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I'm sure Nick knows his stuff. I also know the intake valves are bigger than the exhaust valves. If is that is the case that the intake valves are the problem it just surprises me that the techs at Comp Cams that I dealt with could be so far off in their explanation to me.
02-17-2010, 08:15 PM
#20
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I know, there's so much bs out there when it comes to cams. It's really hard to know what to believe. Trust me, i've talked to them all... Hitech, Comp, MPH, Bullet, Lunati, CMS, etc. You know what??? They ALL had different answers to my questions lol.