piston head clearance

[racing89]

Anyone run piston head clearance as low as .030 ? Thinking of swapping out felpro 530sd(.052 compressed) to a victor(.043 compressed) in my 5.0l stroker. 5500 would be max rpm

[maxparrish]

Anyone run piston head clearance as low as .030 ? Thinking of swapping out felpro 530sd(.052 compressed) to a victor(.043 compressed) in my 5.0l stroker. 5500 would be max rpm

I've not built a stroker (yet) but as no one has answered your query, I'll give it a shot. According to Tony Hewes in the youtube video series 258 rods can expand as much as .040 during operation. He zero decks, uses a .045 gasket, and has a .005 safety margin.

Seems to me that it is safest not to go below .045, depending on predicted rod expansion. One guy here is building his with a .38 quench, which sounds very tight - but hey, I am no expert and may be confused about where quench is measured.

[BADASYJ]

Yeah I zeroed the deck and run a mopar gasket. No issues as of yet.

[SilverXJ]

I have a zero deck and .43" head gasket. No problems. Ive had the head off several times and noticed no piston to head contact. You may be able to run .030" quench as that with our bore size there wouldn't be as much piston rock as on a Chevy small block or big block. I've heard them even running with .030" quench but you have to worry about piston rock at TDC. Piston rock can raise the edge of the piston several thou, the larger the piston, shorter the short, more rock. I wouldn't run it that tight though. The generally accepted standard when using steel rods is to keep quench between .035 and .045. There is no way the 4.2L or 4.0L rod expands as much as .040" during operation, more like .004". An aluminum rod wouldn't even stretch that much. Plus we aren't revving to high numbers anyhow.

[racing89]

I HAVE a 4" bore, and a forged piston that sticks out .013 "
was why I had concerns. Was already running .038 or.039 piston-head clearance but wanted to increase comp. ratio a bit ( will change from 10.5 to 10.75 with the proposed gasket change) but will make my piston head clearance in the .030 to .031 range. thanks for input.

[bbarrett]

I know this post is over a month old but, I have 2 pistons that come out of the block 12 thousants, (should have indexed ground my crank) I have a mls gasket that if memory serves me correct is somewhere in the lower 40s compressed. I have had zero issues with the pistons being out of the block. But i hardly ever go over 4 grand before i shift.