Deciding on piston to wall clearance for L2322F TRW

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dibbons

dibbons

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I have been searching and searching for some literature/manual/guide to help me decide on the proper piston skirt clearance for a NOS set of old school TRW dome forged piston. Today, I finally found a chart on the Hughs Engines website that might help me make the correct choice. Chart shows street as .0035" to .0045" and drag is .005" to .007 for bores up to 4.100". This will be a street car with occasionally drag strip time runs (for fun).

piston clearance chart.png


L2322F.png
 
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Yes those are normal clearances for forged pistons. I beat on a 351C engine with TRW forged pistons for years and started at .004-.0045" clearance and it was fine. Spun it to 6500 RPM quite regularly.
 
That's the same piston I use BTW. I modified the dome a bit. Mine went in at .004
 
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Those are high compression and very heavy. like 11.5 to 1 or more compression depending on the chamber volume. I'd consider having the domes machined down to lower the compression and lose some weight, or trade them for some lower compression pistons. Better have some race gas if you decode to use them as is, and plan on head studs/o-ringing the block. Small blocks with 4 head bolts per cylinder don't like high compression without some help.
 
These are for de-stroking a 340 to a 305, I will loose over a full point of compression in the process (hopefully won't be too high when all is said and done). That is why i am using the dome pistons on this motor. With a 68cc chamber and .038" gasket a stock 340 works out to 12.25/1 and a 305 works out to 11.21/1 (still too high). Milling off the 10.7 cc dome works out to 10.6/1 for a 340 and 9.71/1 for a 305.

I will first have to wait and see how the open chamber cylinder heads check out and go from there.
 
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airgrabber said:
Those are high compression and very heavy. like 11.5 to 1 or more compression depending on the chamber volume. I'd consider having the domes machined down to lower the compression and lose some weight, or trade them for some lower compression pistons. Better have some race gas if you decode to use them as is, and plan on head studs/o-ringing the block. Small blocks with 4 head bolts per cylinder don't like high compression without some help.
Click to expand...


I run 11:1 on pump gas. Someday, all this CR stuff will die off.
 
I run that piston, and with the open chamber W-2 heads and a .557 moar SFT cam, no problems with 93 octane. chambers are polished and new ferrea valves, chamber volume was 69cc
 
Machine shop just informed me the 340/305 short block is finished and the piston skirt to cylinder wall clearance was about .0045".
 
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