Offset piston pins

[dlmwtvl]

Has anyone used pistons made with offset pins in their Nailhead?
 Since custom pistons are the only choice on a performance rebuild, it seems like this would be a great option.
 Already spending a grand on custom pistons. It seems like having 4 lefts, and 4 rights, couldn't add too much more to the piston cost.
 Forged pistons need more clearance, and offsetting the pins reduces piston slap, and wear, on the rotating assembly by placing the rod angle not parallel with the bore when the piston is at TDC.
 Smoother running engine, with less friction. could only add to efficiency and longevity, it seems.....
 How much offset to use, and how much, exactly, that calculated offset, will add or take away from the stroke, are formulas I have yet to locate....
 It seems I have done all the math for my 401 rebuild. Now, this x factor has me thinking I might integrate this into the equation.......
 This is what I have come up with, so far:

 Bore - 4.197"
 Stroke - 3.69" - crank offset ground to use BBC rods. 2.20" rod journals.
 Rod length - 6.8"
 Gasket bore - 4.24"
 Gasket thickness - 0.016"
 Deck height - 10.00"
 Top ring down - 0.30"
 Head chamber volume - 125cc
 Piston dome volume - (-50cc)
 Deck to piston - 0.020"
 Compression height - 1.335"
 CID - 409
 Static compression - 10.91:1
 Cam - TA25
 Dynamic compression - 8.02:1 w/cam installed straight up
 Dynamic compression - 8.29:1 w/cam installed advanced 4 degrees.

 Agree, disagree, or agree in part?

[WkillGS]

The Forged Autotec pistons that Tom offers are 4032 alloy. They don't expand as much as the old forged pistons. Figure about 0.0035" to 0.0045" piston-wall clearance for a street engine, according to Keith Black. Unsure what Autotec recommends.
I have the Keith Black 4032 alloy pistons (IC944) in my stroked Jeep. It's only noisy for about 30 seconds after startup in the winter.

I'll have to look into the BBC rod. Is it forged? Better than the stock forged Buick rod? Longer?

Your compression is rather high. Likely won't like pump gas.
Nice job on the math! Too many guys just put them together without those considerations, and then wonder why their rebuilt engine makes less power than stock.

[Buick_65]

With as bad as the flame spread is in these motors, you might still get away with super if need be. Russ at centerville has most of the answers.

[telriv]

If the engine is running properly you won't find a better flame travel in a stock "Other" type engine. The pent roof combustion chamber & the all important "Squish/Quench" area are ALL important factors when assembling ANY engine.

[dlmwtvl]

Over a year later, and I finally have block and heads done. Pistons ordered.
The final specs are somewhat different from my original post.

Finished Bore           - 4.210"
Stroke                     - 3.690"
Rod length               - 6.800" bbc
Head gasket bore     - 4.240"
Head gasket thick    - 0.020"
Deck height             - 9.978"
Ring to piston top    - 0.200"
Head chamber         - 125cc
Piston dome volume - 44cc
Piston to deck          - 0.020"

compression height  - 1.313"
Wrist pin offset        - 0.030"
Displacement           - 410.93 cubic inch
Compression ratio    - 10.25:1

TA-25 Camshaft

Has anyone experimented with cam timing with this cam?
David