Help Identify this TRW BB piston (also manage attachments test)

[Wayne M.]

Finally doing some archaeology on this 3855961 (2-bolt passenger 396) May 14th 1965 cast block that I bought from a friend 13 years ago. He, in turn, bought it off someone else, so I have no history. Supposedly, it was a running engine. Other than being 30 thou-over, it seems stock, with its original small port heads 3856206, dated F_9_5. It even has its original Holley cast iron manifold 3866948 cast (E_27_5)

So the TRW pistons and the oil pump, and (maybe) the rod and crank bearings are all I can see that have been changed so far. Does anybody have an old TRW catalog ? I think these pistons are relatively old, before TRW became Sealed Power or Speed-Pro. The underside of the piston has the non-italicized font, and the top is stamped "1687", without L or F prefix/suffix. The main purpose of this thread is to determine the spec's on this piston ie: what compression ratio was it seeing with its original '206' heads (combustion chamber volume 97.2 cc's, per Colvin book).
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OK; the 2nd purpose of this post is to see if I could attach photos using the "Manage Attachments" button, when using my old backup Windows XP computer (fresh update), with Firefox 24.0 browser, and it appears that it works, as evidenced by this post. But I selected 3 pics from the most recent 20 that I have uploaded. There's still another 1800 of my thumbnails on the system that I can access by [User profile/Miscellaneous/Attachments], yet not import into a new post. This is the problem that the Technical group is working on (Gary Chesnut) and I thought I'd try this combo of operating system and browser.

[Duke W.]

Re: Help Identify this TRW BB piston (also manage attachments test)

What's the crown to top of dome distance? Measure it as accurately as possible.

Duke

[Wayne M.]

Re: Help Identify this TRW BB piston (also manage attachments test)

What's the crown to top of dome distance? Measure it as accurately as possible.

Duke

Duke -- averaging many measurements with dial micrometer, I get 0.337" from piston crown (flat) to top of dome (flat). The depth of the valve relief (below flat crown) is 0.140" (@ max.).

[Bob J.]

Re: Help Identify this TRW BB piston (also manage attachments test)

Wayne,
I went through my old TRW catalogs but no 396 or 427 pistons were listed with your number.
Bob

[Duke W.]

Re: Help Identify this TRW BB piston (also manage attachments test)

The oldest catalog I have is Federal Mogul Performance X-3009 1995. It appears at this point FM had changed piston part numbers from the original TRW numbers.

This catalog shows three basic pistons for 396-based engines - L2240NF, L2242F, and L2287F.

The L2240NF-30 has a dome height of .182" and is listed for '65-'69 396-325/350HP.

The L2242F-30 has a dome height of, .335" with a net dome volume of 38.3 cc, 1.765" compression height and is listed for '65'-'69 396-375 HP. I expect this is what you have, and it's the L-78 OE design.

The L2287F-30 has a dome height of .508" and is listed for '65-'69 396-375 HP with aluminum closed chamber heads. I'm not aware that such a configuration was ever offered in production for any Chevrolet model.

You can use these data in a compression ratio calculator with various deck clearances, and gasket thicknesses, but I think it will be too high with the head chamber volume you mentioned. The catalog lists a computed CR of 10.58:1 with a nominal deck height block, .0385" gasket, and 109.4 cc head chamber.

Duke

[Robert G.]

Re: Help Identify this TRW BB piston (also manage attachments test)

This document lists a Perfect Circle 224-1687 for 65-69 396/375. Maybe that's a clue, though yours is stamped TRW.

http://www.nhra.com/userfiles/file/NHRAAcceptedProducts.pdf

[Patrick B.]

Re: Help Identify this TRW BB piston (also manage attachments test)

The TRW marking is on the underside of the forging, like on GM marked pistons. Perfect Circle probably used TRW forgings or just resold TRW products.

[Wayne M.]

Re: Help Identify this TRW BB piston (also manage attachments test)

Thanks to all who responded.

John -- I'm going down to Pomona CA for the swap meet March 2nd; so now I've got an excuse -- to search for a period TRW piston catalog . Well, other than to catch some rays.

Duke -- that's what I was afraid of; that with that dome in closed chamber heads I'd need av gas to avoid detonation. Too bad I can't speak to the guy who last ran this motor. On the other hand, I drive like a 70-year old old gasbag [that I am], so maybe no problem.

Robert & Patrick -- that partial "1687" in the NHRA list must bear some relation to what's stamped on the top of mine. Did those numbers change for over-bores (ie 1686 for STD; 1688 for 40-over, etc ?).

I've heard that all TRW's were forged, not cast. These have pressed-in pins.

Please ignore the attached photo -- it was a test to check if I could use an old pic from years ago on the new server, using Windows XP (updated) with Firefox browser. Seems to be OK, but I had to hold the CTRL and F5 keys simultaneously (once) as suggested by Gary C., for the entire file of my thumbnails to be available (pages 1 to 87, at 20 pics per page).

[Duke W.]

Re: Help Identify this TRW BB piston (also manage attachments test)

Thanks to all who responded.


Duke -- that's what I was afraid of; that with that dome in closed chamber heads I'd need av gas to avoid detonation. Too bad I can't speak to the guy who last ran this motor. On the other hand, I drive like a 70-year old old gasbag [that I am], so maybe no problem.

If the dome is "solid" you can cut it down to reduce the CR, but it will take a little math to determine how much to cut.

The CR calculator is your friend.

Also, you should measure the actual head chamber volume. I'm not aware that any closed chamber heads were less than over 100 cc, but then I'm not fully up to speed on all the BB configuations.

Duke