Safe clearance for 440

[dusterrcr]

Mocking up new motor now.Ross flat tops, 440source H -beam rods,915 Closed chambered heads piston is .020 out of the hole.Builder recomends .050 compressed thickness head gasket for .030 overall clearance.He says this should give us about 13:1 This is race only.So good gas not a problem.And I dont want to give up any compression if I dont have to.Will .030 be safe?

[perfmachst]

hello, in a single word, no. this is not enough clearance. mopar wants to see .055 min piston to head clearance. cutting piston tops, you won't loose very much comp. I'd give up comp for clearance any day. just food for thought.

[John Kunkel]

With steel rods .030" shouldn't be a problem. Quench pistons require a minimum of .040".

[dave571]

I know the mp book says .055 min, but most of the piston manufacturers recommend .040 for there to be quench. I have .043 on my own engine with 915's.

Quench is good, and the real benefit of a closed chamber head.

I would be concerned that .030 will hit, since, I have heard of guys saying they have seen it on disassembly. I'm not disagreeing with John, I'm just saying it would keep me up at night...LOL

I would try for .035 as a min. with .040 being optimal. my .02.

[DartGT66]

I have 0.033" in a 4.5" bore BB. Still could use a little less than that to keep the quench area shiny. Do you have dome pistons, or is this a stroker? Most likely yes, since with flat tops even with a .030" clearance you should only have 61cc chambers to achieve 13:1.

[dusterrcr]

Not a stroker.I am using Ross flat tops with valve reliefs

[djswwg]

anything less than .040" is taking a big chance. you will for sure see the piston part number on the underside of the head if the clearance is that close when you take the engine apart. there are three things that are going to move the pistons closer to the head; piston rock, rod and piston expanding length-wise due to heat, and a tiny bit of stretch in the rods at big RPM. do yourself a huge favor and shoot for .040" (up to .043") clearance. the quench factor will still be close enough for the benifits it brings and you'll still have crazy compression, especially with steel heads. you better have race gas for this monster!!!!!!!!!!!!!!!!.........djs P.S. I built a stroker with Ross pistons/Eddy heads at .030" clearance (customer insisted) and you can read the piston part # on the underside of the heads-no damage, but that's a little to hairy in my opinion. hope your cooling system is up to the task too

[DartGT66]

If you are not using stroker pistons, what are your head cc's? I mean the 13:1 sounds incredible with flat tops and factory heads. And what kind of cam are you using? There is a chance, that if your heads are milled so much thta you can achieve 13:1 (I don't know if that's even possible), you may need deeper valve reliefs too.

[dusterrcr]

O.K. Thanks for the input.As tempted as I was with running .030 clearance.We broke down and ordered SCE Pro Copper head gaskets .062 compressed.Should give us about .042 They claim you can re-use them up to 5 times.Not bad for 115 bucks a set.The bore is a little large.4.38 and we are only .030 over on bore.So O.K. pistons are Ross flat tops with valve reliefs,.020 out of the hole.Head gaskets .062 with compressed volume of 15.3 cc,s Heads are 915,s Not milled to my knowledge.Any ballpark guesses on compression? Cam is a small one.ADV. DURATION 290/298 DURATION @ .050 252/260 VALVE LIFT .540/.558 LOBE CENTER 110" Should have good cylinder pressure.And with the lighter pistons and rods and small cam,Should be really snappy! Just what we need--More broken driveline parts and traction issues!

[dave571]

Originally Posted by dusterrcr

O.K. Thanks for the input.As tempted as I was with running .030 clearance.We broke down and ordered SCE Pro Copper head gaskets .062 compressed.Should give us about .042 They claim you can re-use them up to 5 times.Not bad for 115 bucks a set.The bore is a little large.4.38 and we are only .030 over on bore.So O.K. pistons are Ross flat tops with valve reliefs,.020 out of the hole.Head gaskets .062 with compressed volume of 15.3 cc,s Heads are 915,s Not milled to my knowledge.Any ballpark guesses on compression? Cam is a small one.ADV. DURATION 290/298 DURATION @ .050 252/260 VALVE LIFT .540/.558 LOBE CENTER 110" Should have good cylinder pressure.And with the lighter pistons and rods and small cam,Should be really snappy! Just what we need--More broken driveline parts and traction issues!

that info gives me 10.8:1 on this calculator assuming 6 cc valve reliefs

http://kb-silvolite.com/calc.php?action=comp