I'm putting together a 440 and would like to know how tight I can run piston to cyl head clearance. Currently I'm .031 in the hole and would like to up the compression. The rotator assembly has already been bought and balanced, so piston change/chamfering is not an option. Rule changes say I can run more compression than I current have (10.9). This motor (iron block, stock LY rods, NHRA legal CP pistons w/906 heads) will never see 6500rpm. Right now the piston-head clearance (w/.020 steel gasket) is .067. Can I knock .020 off the deck and still be safe? What is an acceptable clearance on a motor with negative deck height?

I run .040 and shift at 6800 with Ross pistons and steal rod. Some people set them up tighter but .040 is very safe with those pistons.

Theoretically most like .055 piston to head clearence,many run tighter for quench,.035.We like to be safe at .045 to .050.Many set pistons to deck .000 to -.015 and adjust with the head gasket thickness.

Mine was .039 with six pack pistons .018 down and steel shims, i used to rev to around 7000 at the line.

0.000 or -0.005

Look in the Mopar engine "Bible" it states .043 Min. piston to head clearance.

Brian

My old 511 which is in my friends challenger now was .033 with steel rods. Shifted it at 7k.

maximum e...The heads have been cut to 79cc chambers.
Using the Diamond Racing c/r calculator, if I go with .010 piston-deck height, it looks like I can get 11.55 cr. This will give .047 piston-head clearance.
Thanks for the replies.

i've gone as tight as .032 in a steel rod engine that never goes over 7000 rpm. no sign of contact. i try for .040 just so i can sleep at night. bear in mind piston clearance and skirt length factor into the situation as well. i know i'm forgetting some other considerations, but the old grey matter ain't what she used to be.

When checking your piston to head clearances make sure and ROCK the piston in the bores and check both sides(cam side and motor mount side of the block) at the edge of the pistons Make sure and check all 8 pistons when assembling a new, blueprinted motor, especially with stock rods don't ask me why I know that , I have seen .008 differences in centers between stock LY rods( A rods versus G rods ) I have also seen 20 grams differences in the weights if this is a NHRA stocker and you will not buy a set of the "legal" aftermarket steel replacement rods you might want to round the top of balancing pads off the rods like the stock street hemi rods come from the factory If your building a NHRA stocker make sure and get the blueprint sheets from NHRA and follow them to the T don't allow any exta clearances for insurance, set it up dead nuts on the specs, Ma Mopar wants it that way

All things being exact rod length, crankshaft stroke, piston compression height, you can run .035" with no problems. Piston rock is a big factor with a bigger bore (4.500")+. For your application your fine @ .049"

Thanks for the feedback. Looks like I'm safe with my numbers.

my bore is 4.505 and getting ready to order pistons soon... (steel rods) I have .040 cometics and I was gonna shoot for .045 quench! do some of you more experienced builders feel this is too close due to the piston rock with the big bore!

Been running .041 for years at up to 7500 rpms and when I freshend up my heads, there were no signs of contact.........steel eagle rods and je pistons.

you live on the edge with everything dont ya man

So I`ve been told........... Did I ever tell ya about the time.......Oh forget it, you wouldn`t believe me if I told you.

What does everybody do to get their measurements?
Advertised compressed thickeness?
Clay?

Any indications that any brands "spring" back a bit showing a thicker number than actually compressed?

Any variations between advertised #'s and actual #'s?

Anybody been using the white Corteco gaskets that ROL purchased? They have 2 small block gaskets with the performance version advertised at .045" and the other at .038" if I remember correctly.