Valve drop
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
Originally Posted by 02sierraz71_5.3
Whats the minimum safe valve drop distance?
What other factors come into consideration when measuring valve drop?
--chris
What other factors come into consideration when measuring valve drop?
--chris
BTW, we are talking about valve drop as in deck to valve measurement, right?
Originally Posted by KCS
Minimum safe valve drop would be zero. I think it should be ok as long as you have a seat cut for the valve to seat on and it won't cause any P-V issues. Why do you ask? Are you milling some heads?
BTW, we are talking about valve drop as in deck to valve measurement, right?
BTW, we are talking about valve drop as in deck to valve measurement, right?
Last edited by 02sierraz71_5.3; Jul 27, 2007 at 10:11 AM.
Originally Posted by 02sierraz71_5.3
Measuring piston to valve by how far the valve drops at TDC, what is the minimum safe distance
Originally Posted by brad8266
I think you are meaning to say piston to valve clearance. The safe margins are .800 intake/.100 exhaust
Where did you get those figures?
--chris
Trending Topics
I think somebody got a decimal in the wrong place there! That would be .080" clearance. Chris, the closest place is not nessecarily at TDC so you want to measure the entire range.
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Originally Posted by 67SS509
I think somebody got a decimal in the wrong place there! That would be .080" clearance. Chris, the closest place is not nessecarily at TDC so you want to measure the entire range.
Originally Posted by 02sierraz71_5.3
Are those numbers just at TDC or throughout the entire stroke
Where did you get those figures?
--chris
Where did you get those figures?
--chris
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Valve drop and P to V clearance are two seperate things. If you set your head down on a table with no springs on it then the valve drop is how far the valve has to move down to touch the table surface. Say a stock LS1 has .150 valve drop and then the head gasket gives you another .051 down to the table. You would have .201 total valve drop now but say your pistons stick .010 out of the hole or anotherwards take away .010 from your valve drop number now you would have .191 total valve drop till the valve touched the piston with no valve reliefs in your engine at TDC.
If you had .080 tappet lift at TDC and you have 1.70 rockers then you would have approximately (.080 X 1.70) or .136 valve lift at TDC. So as far as P to V clearance at TDC you would have about (.191 - .136) or .055 P to V clearance on your intake at TDC.
Usually your P to V is closest on Intake around 10 degrees after TDC and your Exhaust P to V is closest around 10 degrees before TDC. At 10 degrees before or after your piston is about .040 or so in the hole but the valve is open more at those times so the clearance is even closer. Another words even though you have gained an addition .040 of valve drop at 10 degrees after TDC on the intake the valve has now opened even more than .040 more so the clearance tends to be closest at that point on intake.
You can look at how much more the tappet lift changes and see how much more your valve lift will really be at 10 degrees away from TDC. In the Comp Cams catalogue say you see that going from 110 ICL and advancing the lobe to 106 ICL we go from .079 tappet lift at TDC to .095 tappet lift at TDC so we gained .016 tappet lift in 4 degrees of crank movement near TDC. So if I move 10 degrees I can estimate that I will gain 2.5 times what I did in 4 degrees or about .040 more tappet lift now than at TDC.
Of course I still need to muliply that times my rocker ration too at 1.70 so I get another .068 of valve lift or .136 + .068 or .204 total valve lift at 10 degrees after TDC. My valve drop was .191 and now is has improved to .191 at TDC to another .040 at 10 degrees after TDC or .231 total valve drop now at 10 degrees after TDC. So now at 10 degrees after TDC I have (.231 - .204) or .027 intake P to V.
So basically I am (.055 - .027) or .028 closer on intake P to V at 10 degrees after TDC than at TDC.
If you really measure everything you will also see that you will usually have more than the calculate number since you often have .015-.030 valvetrain deflection with the springs on etc. and the rocker ratio isn't really 1.70 in that range of valve movement either. Basically it's always best to check it all out.
Now you have your aftermarket pistons in there and you automatically add another .150-.200 more to those numbers since you now have valve reliefs so you can run MUCH bigger cams with no issues whatsoever. The main thing causing valves to hit are the larger lobes like 240+ and on up and tightening the LSA which again causes more lift in the TDC area where the valves can hit. The total actual valve lift isn't as important as longer lobes or tighter LSAs.
If you had .080 tappet lift at TDC and you have 1.70 rockers then you would have approximately (.080 X 1.70) or .136 valve lift at TDC. So as far as P to V clearance at TDC you would have about (.191 - .136) or .055 P to V clearance on your intake at TDC.
Usually your P to V is closest on Intake around 10 degrees after TDC and your Exhaust P to V is closest around 10 degrees before TDC. At 10 degrees before or after your piston is about .040 or so in the hole but the valve is open more at those times so the clearance is even closer. Another words even though you have gained an addition .040 of valve drop at 10 degrees after TDC on the intake the valve has now opened even more than .040 more so the clearance tends to be closest at that point on intake.
You can look at how much more the tappet lift changes and see how much more your valve lift will really be at 10 degrees away from TDC. In the Comp Cams catalogue say you see that going from 110 ICL and advancing the lobe to 106 ICL we go from .079 tappet lift at TDC to .095 tappet lift at TDC so we gained .016 tappet lift in 4 degrees of crank movement near TDC. So if I move 10 degrees I can estimate that I will gain 2.5 times what I did in 4 degrees or about .040 more tappet lift now than at TDC.
Of course I still need to muliply that times my rocker ration too at 1.70 so I get another .068 of valve lift or .136 + .068 or .204 total valve lift at 10 degrees after TDC. My valve drop was .191 and now is has improved to .191 at TDC to another .040 at 10 degrees after TDC or .231 total valve drop now at 10 degrees after TDC. So now at 10 degrees after TDC I have (.231 - .204) or .027 intake P to V.
So basically I am (.055 - .027) or .028 closer on intake P to V at 10 degrees after TDC than at TDC.
If you really measure everything you will also see that you will usually have more than the calculate number since you often have .015-.030 valvetrain deflection with the springs on etc. and the rocker ratio isn't really 1.70 in that range of valve movement either. Basically it's always best to check it all out.
Now you have your aftermarket pistons in there and you automatically add another .150-.200 more to those numbers since you now have valve reliefs so you can run MUCH bigger cams with no issues whatsoever. The main thing causing valves to hit are the larger lobes like 240+ and on up and tightening the LSA which again causes more lift in the TDC area where the valves can hit. The total actual valve lift isn't as important as longer lobes or tighter LSAs.
