What is max lift without PTV issues?
08-10-2007, 11:13 PM
#1
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What is max lift without PTV issues? is it possible to come up with a definate number for this?
on Stock LS1 heads and +4 cam advance what would be the max allowable int. and exh. lift without any PTV problems?
I guess it would also depend on lsa/ica .....
on Stock LS1 heads and +4 cam advance what would be the max allowable int. and exh. lift without any PTV problems?
I guess it would also depend on lsa/ica .....
08-11-2007, 10:42 AM
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Originally Posted by N4cer
Too many factors: LSA, ICL, and duration are the ones that really matter. Lift isn't usually even considered when figuring PTV issues.
that's incorrect.
08-11-2007, 10:50 AM
#4
Oh, so you're the new guy on here asking about something that isn't an issue, and I'm the guy who has swapped a couple of cams, even knowing that I had to flycut, and you say I'm incorrect. Explain and I'll gladly admit that I'm wrong.
Last edited by PREDATOR-Z; 08-11-2007 at 11:52 PM. Reason: No need to slender, just explain why!
08-11-2007, 10:53 AM
#5
I can't wait to hear you explain why I'm wrong, and that lift actually matters. Because then you can get a degree wheel and a dial indicator and go outside and tear down your motor and see that it's the duration that causes PTV issues since almost any lift gets the valves in the way, it's the duration that determines when they open and close to get out of the way of the piston. So explain why I'm wrong. And then explain why you would comment like that when you're the one that's wrong.
08-11-2007, 10:59 AM
#7
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oh don't get your panties in a jumble....
i didn't know that any lift would cause PTV.
I thought that with say....a stock cam...the valves wouldn't actually get enough lift to hit the pistons.
sorry man i was wrong~
i didn't know that any lift would cause PTV.
I thought that with say....a stock cam...the valves wouldn't actually get enough lift to hit the pistons.
sorry man i was wrong~
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08-11-2007, 11:01 AM
#8
Duration at 0.05" lift is what matters. This will dictate when the valve is off the seat and headed towards the piston. Max valve lift doesn't occur till the piston is almost 2 inches away from the head. If you are running a cam with 2" of lift, you aren't running an ls1.
All you need to do is start to read about how cams work, and learn what lsa, icl, duration, and lift mean with a cam and you'll realize that lift isn't even a factor for PtoV clearance. Figure out what the lift of the cam is at TDC, which is determined by cam duration, and you'll be able to figure out your PtoV clearance.
All you need to do is start to read about how cams work, and learn what lsa, icl, duration, and lift mean with a cam and you'll realize that lift isn't even a factor for PtoV clearance. Figure out what the lift of the cam is at TDC, which is determined by cam duration, and you'll be able to figure out your PtoV clearance.
08-11-2007, 11:08 AM
#9
I AGREE AND DISAGREE WITH THE ABOVE FACTS...
IMO everything mentioned plays into PTV in some cases
if your running a big cam then yes you need to consider that your clearences are changeing as the piston travles so although you could have xxx lift @ XXX duration when the cam a few micor secconds later you no longer have that much to play with
In my mind the way i look at it as the valves are tring to chase the piston down (opening) and are being chased by the piston on the way back up (closing)
in theory there is probaly a small enough cam to where the lift is fine at any point in the combustion cycle
but in pratice, lift duration and much more can play a part
hopes this helps
IMO everything mentioned plays into PTV in some cases
if your running a big cam then yes you need to consider that your clearences are changeing as the piston travles so although you could have xxx lift @ XXX duration when the cam a few micor secconds later you no longer have that much to play with
In my mind the way i look at it as the valves are tring to chase the piston down (opening) and are being chased by the piston on the way back up (closing)
in theory there is probaly a small enough cam to where the lift is fine at any point in the combustion cycle
but in pratice, lift duration and much more can play a part
hopes this helps
08-11-2007, 11:09 AM
#10
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Aside from all the guys arguing haha. They are right, lift plays a minimal factor in PTV clearance. You mainly need to look at your duration and lobe separation.
08-11-2007, 11:35 AM
#11
Find out what your valve free drop is @TDC, FACTOR IN CRUSHED HEAD GASKET THICKNESS and .006 PISTON OUT OF THE HOLE. Then look at this Compcams chart for TAPPET LIFT @ TDC.
Do the math...tappet lift @TDC x 1.7 or 1.8 rocker ratio = valve lift @TDC.
Allow for .070 valve to piston clearence.
Do the math...tappet lift @TDC x 1.7 or 1.8 rocker ratio = valve lift @TDC.
Allow for .070 valve to piston clearence.
Last edited by gollum; 08-11-2007 at 12:14 PM.
08-11-2007, 02:45 PM
#13
You've been around here a while. You surely have seen it said that a G5X3 on a 114 fits with sufficient clearance. That's a 234/242 +4. So it only stands to reason that one with a wider LSA and no advance ground in would fit. But of course you'll wanna clay it just to be sure.
08-11-2007, 11:50 PM
#14
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Poeple get confuse between tappet lift and .050 lift.
That is why most assume that high lift cams are an issue.
If you look at .050 numbers, the max lift occurs at BDC and not TDC where issues occur, now with "Tappet lift" that is a different story.
That is why most assume that high lift cams are an issue.
If you look at .050 numbers, the max lift occurs at BDC and not TDC where issues occur, now with "Tappet lift" that is a different story.
08-12-2007, 03:33 PM
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Originally Posted by gollum
Intake valve freedrop with new unmilled 243 head on uninstalled flat surface is .175. 241 head should be very close to same measurement ?... I don't know.
