Some Math about piston to valve clearances

[Curiousyellow71]

I completely agree with the the measuring. I completely understand why many would shy away from recommending a cam off someone's measured clearances. Way to many unknowns...

But these 2355 pistons have been around in some form for 50 years..I think a better a question that could be answered is what solid cam has been run in a 440 with 906 headsand these pistons.

The cam we last used with 2355 and 906, no milling of any kind, ductile 1.5s, 2.08 and 1.81
Mopar performance .557 solid 296, [email protected]. 110cl installed 108.

I think it would be interesting to hear what others have used of any type?

 

[PRHeads]

Still way too many variables to not measure, IMO.

Block decked? How much?
Heads milled? How much?
How many valve jobs on the heads?
2.08 or 2.14 valves?
How thick are the valve margins?
Where is the cam installed?
What’s the rocker ratio?
Head gasket thickness?

If you don’t actually measure it, and you have an issue........ no one to blame but yourself.

264/268-106 solid, zero deck, heads milled a bunch, big valves....... not even close to working with 2355’s.
Had almost zero clearance.

Had to fly cut the pistons big time.

 

[TN Mopar]

Still way too many variables to not measure, IMO.

Block decked? How much?
Heads milled? How much?
How many valve jobs on the heads?
2.08 or 2.14 valves?
How thick are the valve margins?
Where is the cam installed?
What’s the rocker ratio?
Head gasket thickness?

If you don’t actually measure it, and you have an issue........ no one to blame but yourself.

264/268-106 solid, zero deck, heads milled a bunch, big valves....... not even close to working with 2355’s.
Had almost zero clearance.

Had to fly cut the pistons big time.

.002 Block was decked lightly to true and clean
unsure here Heads were cut lightly Machine shop said it was very light and we lost about 2 CCs (head volume 88 to 86)
2.5 valve jobs The heads were stock when cut for 2.14/1.81 valves Then run about 5k miles & sat for 20 years Machine shop cleaned them & reset the spring heights /w new seals
I did not measure valve margins
108 installed center line
1.5 Ductile iron rockers
0.020 steel shim head gasket

Total clearance as measured by the clay after three cycles of the engine was 0.140 (6 revolutions of the crank)

I measured what I knew and in retrospect I should have asked more questions and measured more or perhaps differently

 

[PRHeads]

I wasn’t really asking any questions, as much as pointing out several of the things that will impact the V/P clearance....... and why looking at someone else’s results doesn’t have that much bearing on what kind of clearance you’ll have....... unless everything between the two builds is exactly the same.

Using the clay like you did is not accurate(imo), and can get you into trouble.
I’ve seen it first hand.
“Clay clearance”, .060” on the intake.
Motor drops a valve in the burnout box of the attempted first pass.
Valve pieces travel from hole to hole...... pretty much destroys entire motor.

They assemble enough stuff to do an actual measurement of the V/P clearance, so I go to their shop and check it out.
I measured it at basically “zero” clearance.
All the pistons had witness marks from hard contact with the intake valves.

Yet, plenty of clearance with clay.

 

[Curiousyellow71]

We do hard contact first...then clay to make sure the flycut is wide enough for the valve.
Last one we flycut was a 13.6:1 440 with 286@ .05 solid roller cam... it still hit with nice pistons with a big relief.
The bigger the engine the more room for a cam. Strokers are easier in that regard..

 

[wyrmrider]

You can easily use an "Isky tool" to flycut the pistons while in the block- isky has a loaner program you will be taking each head off 8 times but you only need a couple of headbolts
Closest P to V is NOT at TDC but depends on how far ahead of tdc intake opens and the steepness of the ramps and how far after tdc ex closes
(in addition to the lobe shape the LCA changes this obviously) grinders should give you this approximate data (exact data varies with stroke and rod length also)
Chrysler long rod engines dwell longer which is why chevy and other short rod engines have to start opening the intake earlier(to have it open when flow is needed) than needed for a MOPAR
Mopars can run better with less overlap than short rod motor