minimum piston to head clearance?
minimum piston to head clearance? I noticed that the upper flat part of the piston (what I call "above the M" or valve reliefs) would hit the head when I originally mounted the head and attempted to rotate the crank with no head gasket.
I was claying my heads, checking P to V clearance and placed the cometic head gasket on and noticed that this area in question left the clay about .030" thick with the heads torqued down to 60 ft pounds. Is this OK?
I was claying my heads, checking P to V clearance and placed the cometic head gasket on and noticed that this area in question left the clay about .030" thick with the heads torqued down to 60 ft pounds. Is this OK?
Last edited by ROCNDAV; Dec 4, 2005 at 03:38 PM.
I would definately not feel safe running like that. I believe most people shoot for a minimum of .080 ptv clearance. A few have run it tighter than that, but I dont think ive seem people run it closer than .050. Id also like to know what others think about this as Ill be running into this problem soon.
Launching!
Joined: Jun 2005
Posts: 202
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From: longview, tx
.030 is considered around the optimum squish distance for many people when setting that clearance. That tight gap there forces or squishes the good part of the combustion into the center or chamber of the head where it works more effectively. Some folks will venture to run the clearance even closer but not many. Do a search on squish and you'll come up with lots of good info on this subject.
Launching!
Joined: Jun 2005
Posts: 202
Likes: 0
From: longview, tx
.030 is considered around the optimum squish distance for many people when setting that clearance. That tight gap there forces or squishes the good part of the combustion into the center or chamber of the head where it works more effectively. Some folks will venture to run the clearance even closer but not many. Do a search on squish and you'll come up with lots of good info on this subject. The way you stumbled upon the clearance may not be the best method for checking it though. The clay may force the piston to rock in it's bore and could skew the actual dimension. It could possibly be only .020. I'd lay a good straight edge on the piston or block(whichever is taller) and use a feeler gauge to measure the gap all the way around the piston in four places and average that for the distance.
Originally Posted by krexken
.030 is considered around the optimum squish distance for many people when setting that clearance. That tight gap there forces or squishes the good part of the combustion into the center or chamber of the head where it works more effectively. Some folks will venture to run the clearance even closer but not many. Do a search on squish and you'll come up with lots of good info on this subject. The way you stumbled upon the clearance may not be the best method for checking it though. The clay may force the piston to rock in it's bore and could skew the actual dimension. It could possibly be only .020. I'd lay a good straight edge on the piston or block(whichever is taller) and use a feeler gauge to measure the gap all the way around the piston in four places and average that for the distance.
Also keep in mind that hydraulic lifters may pump up, especially if your valvesprings are on the lighter side of the spectrum. If youre already running a close PTV, lifter pumpup could put you even closer.
-T
Originally Posted by GuitsBoy
I think youre making an incorrect assumption that the valves will be closed and the the closest piston to valve clearance happens at TDC. In reality, neither is true. It is true that quench is optomized IMO around .035 - .040, but that only tells you piston to head clearance. The valves are pushed down past the bottom deck of the head and into the cylinder. The cam duration (moreso than lift) and valve event timing play the largest roles in determining wether the valve will come down into the piston before the piston moves out of the way... or if the piston comes back up before the valve is pulled back into the seat. It is different for every cam profile and depends on how far your heads have been milled and the vaqlve seat height. You can not figure on PTV clearance the way you described.
Also keep in mind that hydraulic lifters may pump up, especially if your valvesprings are on the lighter side of the spectrum. If youre already running a close PTV, lifter pumpup could put you even closer.
-T
Also keep in mind that hydraulic lifters may pump up, especially if your valvesprings are on the lighter side of the spectrum. If youre already running a close PTV, lifter pumpup could put you even closer.
-T
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Originally Posted by Beast96Z
I think the original post is about his quench area, not P/V clearence.
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Verdad Gallardo Thanks guys. I indeed was talking about quench/squish. Using a straight edge and feeler gauge a well as a machined block and digital calipers, I measure the difference between the deck and the top of the piston like this:
.030" at 12 O'clock
.015" at 3 & 9 O'Clock
.002" at 6 O'clock
To me, that is telling me that the top of the piston is cocked/tilted, is this correct?
If I average the High and low readings above, I get .016"
If I press on the piston at the 12 O'Clock position, I can bring it down to .016" and that brings the 6 O clock position up to about .014"
I reclayed it. My PtoV is .083", Squish is .031" with the head /ARP head studs torqued to 50 ft pounds. (I know I have to go another 10, but I was afraid of messing up the gasket doing this step so many times).
As a reminder, I have AFR 225 heads, Cometic C5318-040 (4.160 Bore, .040" thick) head gaskets. My rotating ***'y is a Lunati EA035-395: which shows an out of block height of .008" : http://holley.com/products.asp?product=EA035-395
These are my pistons: http://holley.com/products.asp?product=LS4RT2SD
Am I sketching on this, thinking too much into it, everything cool, or should I be looking into a thicker (and ye more money) head gasket? This is a DD Camaro, no Nitrous or Power Adder will be used.
.030" at 12 O'clock
.015" at 3 & 9 O'Clock
.002" at 6 O'clock
To me, that is telling me that the top of the piston is cocked/tilted, is this correct?
If I average the High and low readings above, I get .016"
If I press on the piston at the 12 O'Clock position, I can bring it down to .016" and that brings the 6 O clock position up to about .014"
I reclayed it. My PtoV is .083", Squish is .031" with the head /ARP head studs torqued to 50 ft pounds. (I know I have to go another 10, but I was afraid of messing up the gasket doing this step so many times).
As a reminder, I have AFR 225 heads, Cometic C5318-040 (4.160 Bore, .040" thick) head gaskets. My rotating ***'y is a Lunati EA035-395: which shows an out of block height of .008" : http://holley.com/products.asp?product=EA035-395
These are my pistons: http://holley.com/products.asp?product=LS4RT2SD
Am I sketching on this, thinking too much into it, everything cool, or should I be looking into a thicker (and ye more money) head gasket? This is a DD Camaro, no Nitrous or Power Adder will be used.
For starters I assume you used a dial indicator to get TDC. If infact you are averaging say .015 out of the hole maybe your block was decked or different pistons or rods were installed. I would be reluctant to use anything other than the OEM graphite head gaskets which are .054.
Why are you using a 4.160 bore gasket when you have a stock/honed bore? At minimum, it's .160" to big. It's also .040 thick, which is really thin when dealing with the LS-1's average "out of hole" of .010". The best place to measure your deck height is the center of the piston. This is where you'll get the least amount of rocking. So you know, the piston is supposed to move around in the bore.
TECH Regular
Joined: Oct 2005
Posts: 430
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The piston rock described sounds like a ton! How do the other seven look? Once/if you get accurate, consistent measurements (most guys say LSx pistons are stock ~ 0.006" -0.008" out of the block), thousands of builders use as little as 0.030" piston to head clearance on iron small block engines, some as little as 0.025". An aluminum block, warming from 70 degrees F. to 200 F. will grow 0.0065" more than an iron one. That said, the penalty for being a little too tight on squish, vs. a little too loose is disproportionate to the potential gains...
The gasket was suggested to me from one of our sponsors. I thought it was a 4.1 gasket, but when I was copying the data off of the package, I realized it read 4.160. I was told I shouldn't use a 3.905 gasket as the diameter of the 225's combustion chamber is too big. The gasket's cylinder diameter isn't bigger that the OEM sleeve area on the deck. I know I'm not the only guy using an AFR 225 on a stock bore.
I have read that when using AFR's, people generally go for a tighter squish (.030") than OEM heads (.040") due to swirl.
I have also read where pistons come out of the block .007", so I was freaking a bit when I measured .015" (average). It is possible that the machines shop or previous block owner decked the block. I will have to check with the machine shop that I used, unfortunatley that was over a year ago, so I doubt if they will remember.
The center of the pistons (9 & 3 O'clock positions) repeatidly measure .015" above deck, so it does sound like the block could have been deacked .007-.008". With the amount of rocking that I was able to pushdown on the piston top and bottom, if I subtract .008 from .030" (max rock height) that would leave me with .022, is that still excessive?
During a compression stroke, does the compression keep the piston rocked back (so the piston appears to come up flat)? If so, is there a worry?
If there is a worry, I guess my next choice is a .050" gasket, giving me a .040" squish? and possibly selling these to someone who may want them (fat chance).
I have read that when using AFR's, people generally go for a tighter squish (.030") than OEM heads (.040") due to swirl.
I have also read where pistons come out of the block .007", so I was freaking a bit when I measured .015" (average). It is possible that the machines shop or previous block owner decked the block. I will have to check with the machine shop that I used, unfortunatley that was over a year ago, so I doubt if they will remember.
The center of the pistons (9 & 3 O'clock positions) repeatidly measure .015" above deck, so it does sound like the block could have been deacked .007-.008". With the amount of rocking that I was able to pushdown on the piston top and bottom, if I subtract .008 from .030" (max rock height) that would leave me with .022, is that still excessive?
During a compression stroke, does the compression keep the piston rocked back (so the piston appears to come up flat)? If so, is there a worry?
If there is a worry, I guess my next choice is a .050" gasket, giving me a .040" squish? and possibly selling these to someone who may want them (fat chance).
I haven't had a chance to call Luanti and ask them about the maximum piston rock.
Does anyone else building a lunati rotating ***'y have as much rock? OR is it just an exaggeration due to possible deck height?
Does anyone else building a lunati rotating ***'y have as much rock? OR is it just an exaggeration due to possible deck height?
OK, I just hung up with AFR as well, and they said to go with a thicker head gasket too. Dave said I should be looking for a squish of .035-.040"
so I guess a .050" or .053" thick gasket will do. I'm debating spending the money on cometics again
so damn expensive. What would I be looking for 6.0 liter head gaskets? (I need the 4.100 bore gaskets)
so I guess a .050" or .053" thick gasket will do. I'm debating spending the money on cometics again
so damn expensive. What would I be looking for 6.0 liter head gaskets? (I need the 4.100 bore gaskets) 