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Maximum valve lift for L28 engine?


turbogrill

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Hi,

 

What is the maximum valve lift before the valve hits the piston on a 280zx?

Seems like everything <.500" is fine but I can't find any exact numbers. Some people are running low .500" as well.

 

I cannot seem to find an answer to this pretty simple question!

 

Thanks

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There is no simple answer to your question. The first thing you'll find is that the valve hits the stem seal after about .470 lift. If you use shorter seals you can go higher, but then the duration of the cam will need to be such that it doesn't put piston and valve in the same place at the same time. If that happens, you can flycut the pistons for clearance. There are L engines running .610 lift cams. I think that's the highest I've seen, but you need quite a bit of modification to do it, and the valvetrain won't last very long with those kinds of specs because you need strong valve springs to close the valves and they wear everything faster.

 

I would ***GUESS*** that most .500ish lift cams won't hit on a stock head with stock pistons, but the right way to check is to put clay on the pistons and rotate it around and see how much clearance is there.

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I just ordered a camshaft from Isky and the fellow I spoke to on the phone seemed very sure that the .540 lift, 270 duration cam would not make contact with the flat top pistons I am running in my F54 block.  As I, perhaps mistakenly, understand it, it's not just lift that makes contact, but duration and lobe separation which both alter where the piston will be in relation to the valve.  .

I'll be running Schneider springs and retainers, and those fancy Ford V6 viton stem seals.  

 

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I just ordered a camshaft from Isky and the fellow I spoke to on the phone seemed very sure that the .540 lift, 270 duration cam would not make contact with the flat top pistons I am running in my F54 block.  As I, perhaps mistakenly, understand it, it's not just lift that makes contact, but duration and lobe separation which both alter where the piston will be in relation to the valve.  .

 

I'll be running Schneider springs and retainers, and those fancy Ford V6 viton stem seals.  

 

 

 

The "fellow" you spoke with was probably Ron Iskenderian. ;)

 

I run that same cam in my flat-top L28 (Isky L6 grind). I took measurements and documented them in my build thread: http://forums.hybridz.org/topic/111062-leons-other-260z/

Edited by Leon
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Maximum valve lift has very little to do with piston to valve clearance issues. Duration and lobe separation is what you need to look out for. By the time the valve is anywhere near max lift the piston is way down the bore. Long duration with lots of overlap means opening the valves when the piston is near TDC and this is when you need to flycut the pistons for valve reliefs.

 

So, moving from that, your question is really open ended. .600" ish seems to be about where most of the L cams offered around seem to max out. Past this you are looking into custom territory where you are going to be paying for one off parts. In saying that, .700" is possible. For a 'normal' performance L build, around .550" is where I would be aiming. 

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I just ordered a camshaft from Isky and the fellow I spoke to on the phone seemed very sure that the .540 lift, 270 duration cam would not make contact with the flat top pistons I am running in my F54 block.  As I, perhaps mistakenly, understand it, it's not just lift that makes contact, but duration and lobe separation which both alter where the piston will be in relation to the valve.  .

 

I'll be running Schneider springs and retainers, and those fancy Ford V6 viton stem seals.  

I'm running a .540 lift Isky cam and it does not have issues with valves hitting the pistons, at least not with my grind and my pistons.  

 

You will definitely want to check the clearance between your valve spring retainers and the valve stem seals at max lift, though.  I had to find the shortest stem seals possible and cut the tops of the valve guides down, such that the seals sat pretty much flush with the spring seat in order for everything to clear properly at max lift.  Also a good idea to check to make sure that the springs don't bind at max lift, regardless of what lift they claim the springs will work with.  Check both the inner and outer springs.

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The "fellow" you spoke with was probably Ron Iskenderian. ;)

 

I run that same cam in my flat-top L28 (Isky L6 grind). I took measurements and documented them in my build thread: http://forums.hybridz.org/topic/111062-leons-other-260z/

Great read with a lot of useful info in there, might save me from some real headaches - thanks for the heads up!  

 

 

 

I'm running a .540 lift Isky cam and it does not have issues with valves hitting the pistons, at least not with my grind and my pistons.  

 

You will definitely want to check the clearance between your valve spring retainers and the valve stem seals at max lift, though.  I had to find the shortest stem seals possible and cut the tops of the valve guides down, such that the seals sat pretty much flush with the spring seat in order for everything to clear properly at max lift.  Also a good idea to check to make sure that the springs don't bind at max lift, regardless of what lift they claim the springs will work with.  Check both the inner and outer springs.

Will be sure to double check everything, thanks!  I have an extra set of aluminum retainers that were ran on my old E31 head with a .520-ish lift cam, which might be a useful backup option.  The N42 I am using on my engine right now has stock retainers though, so I will be moving to Schneider ones.  I think I have read of folks running into some difficulties with valve stem clearance on high lift when running them, but we shall see.  Hoping things work out with the viton seals.  

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  • 5 years later...
On 8/30/2016 at 3:16 PM, JMortensen said:

There is no simple answer to your question. The first thing you'll find is that the valve hits the stem seal after about .470 lift. If you use shorter seals you can go higher, but then the duration of the cam will need to be such that it doesn't put piston and valve in the same place at the same time. If that happens, you can flycut the pistons for clearance. There are L engines running .610 lift cams. I think that's the highest I've seen, but you need quite a bit of modification to do it, and the valvetrain won't last very long with those kinds of specs because you need strong valve springs to close the valves and they wear everything faster.

 

I would ***GUESS*** that most .500ish lift cams won't hit on a stock head with stock pistons, but the right way to check is to put clay on the pistons and rotate it around and see how much clearance is there.

 

Can always count on your years-old comments being helpful Jon. I will need to do the clay test on my L24 head with the .500 lift. What is an acceptable margin at TDC and max valve opening, between the valve and the piston?  1/16"? I recognize there is always a risk when factoring valve float, rpm, etc. Was curious if there was a "rule of thump" for L-series motors. 

 

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18 hours ago, JMortensen said:

Can't help you on that one. I think it might be in "How to Modify" but I sold that book 10 years ago. 


darn, I left my copy with my machinist. I must have read the section on heads dozens of times. Il ask him for a recommendation based on his experience. Thanks Jon.

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  • 3 weeks later...

When you call Ron at Isky and tell him you want an "all out performance cam" after all these years he realizes there are two kinds of people out there, and his first question is "do you mind cutting your pistons?"

If the answer is yes... ohhhh the wonderful things he has for you!

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