Tight PTV
 

Is anyone running Piston to Valve clearance tighter than .080.??
Would I be "flirtin' with disaster" to run .070??

A trex cam is typically in the mid .020-.030's if that tells you something. For normal street use I try to stay at .050 or more

Is that both or one or the other?

This is good:
http://www.mifbody.com/vbulletin/sho...-free!-(almost)

That's really tight!! And, these clearances are being used without cutting in valve reliefs??

You wouldn't believe how tight a lot of shop grinds are. :)

According to Geoff@EPS .060 is fine.

I have seen .080 recommended several times but I'm beginning to think that is kind of like a standard "in writing" disclaimer, if you know what I mean. In an "off the record situation" maybe the limits get pushed a little more? ;)

That's the way I understand it. :nod:

if I was in your shoes I would carefully measure all valves with a dial indicator and be sure you have eliminated any source of potential measurement uncertainty.

assuming that checks out, run it!

Running .066" here... .070", you're clear in my opinion. Never hurts to double check your measurements though.

IMO how tight is safe is a bit relative to the overall combo operating range.
1- High revving = need for more clearance. Instability becomes more pronounced as rpm increases; contact more imminent.
It is simple logic guys, the more you push the odds, the higher the risk.

i think im running .110 on the exhaust and .090 ish on the intake. ls3 heads here. i just turned the limiter up to 7200. goin to the dyno in 2 weeks to see where power falls off...

I take it this is the intake valve. Where is the minimum value? Is it after the piston passes the top? If that is the case and the valve is chasing the piston I would be OK with it.

Im running just a hair over .100 on my Exhaust valve and 4 out of my 5 measurements came out at .060 on my intake. One was .057 and I am running it. I bought everything to flycut my pistons and was ready to go home and flycut and after talking to multiple people on here and Martin at Tick and a couple people at TSP I was talked out of it an hour before I was about to do it. I wouldnt sweat it... Im one of those paranoid people when it comes to this stuff where I want to eliminate all possibilities of failure. One thing that did relieve me was my exhaust valve was in this "textbook" guideline for clearance and I dont worry about the intake valve as much since the valve is chasing the piston down. I also run a very stout and stable valvetrain. But if I were you I wouldnt worry about it. I have about 500 miles on mine since the build over the winter and its seen 6500rpm's quite a bit in that 500 miles and I have had 0 issues. Just measure and then measure again and probably another time after that and on a couple different cylinders to get a consistent number. And if all is well put it together. Like they said above many people run as close as .020 which works but too close for my comfort if something did go wrong. But I would run as low as .050 and not worry about it. Just make sure you have a stable valvetrain (correct springs, pushrod length, rockers and trunions etc.)

I have run .045 in A4 cars on the intake and .060 on the exhaust without any issues so far. Make sure your using a good DUAL valve spring and stiff pushrods to reduce float/deflection and you will be good.

One other comment. The running clearance will likely increase over what you measured since all the parts in the valve train will flex to some degree during operation.

yes, the tightest spot is when the intake valve is chasing the piston down but that doesn't make running a close PTV any safer.

Really? On a stock LS1 bottom end??