What is the compression height of an original FOMOCO 292 piston, and does anyone have heights for some of the common cast replacement pistons (sterling, silvolite, badger, etc.) available.

 

I've got some of this, but it will take a bit to get it together. Work lately.....some nice 18+'ers.

 

Silvolite 1072 (292): 1.76 compression height; cast piston w/offset pin; flat head w/no valve reliefs; replaces B5A-6108B & EDB-6108B-C

Silvolite 1066 (312): 1.76 compression height; cast piston w/offset pin; flat head w/no valve reliefs; replaces B6A-6108F & ECZ-6108G-H

Sterling (owned by Federal Mogul), Speed-Pro/Sealed Power, Federal Mogul.....no longer producing ANY Y block replacement pistons. Their part listings have been completely gutted over the past year.

More on Zollner & Badger later tonight- maybe.

 

Zollner got sold to Kolbenschmidt Pierburg in 1999. Actually, a division of it: Karl Schmidt Unisia - ZOLLNER Division, Inc. The plant is still in Fort Wayne but as far as I've been able to determine they no longer make any older inventory. Finding anything out has been like pulling teeth.

This same company bought Badger sometime in the '90s & sold it to Dynagear in '95; Dynagear collapsed in 2002-03 & Badger was reformed, by old Badger mgmt. people I've been told. Dynagear ran quality into the ground...the new mgmt. is dedicated to improving quality & has done so from all I've heard. I haven't been able to get a look at a new catalog & my elderly one is in storage along with most of my junk.

46, ya got any 292 OE slugs layin' around? I think they may have been made by Zollner anyway, a lot of OE pistons were. TRWonderful supplied quite a few OEs in the '60s as well, but I'm not sure about the '50s.

 

The original compression height was 1.781". So far, the only manufacturer I have found that maintains this spec is Egge Machine. www.egge.com

Silvolite and all the rest will put your pistons down in the hole another .020" plus the initial .025" =.045" down plus .045" for the gasket = .090" down.

All this adds up to- No compression, lots of detonation. My 312 has Jahns 11 to 1 pistons and runs fine on pump premium. The long rods in the y-block allow this to happen.

 

Long rods...or, more accurately, a higher R/S ratio compared to a smaller one in the same engine/deck height.....can, at times, INCREASE the tendency for detonation, because the piston spends a longer time (dwell time) at or near TDC, due to the rod angularity.

An interesting example of this can be found in the pre-2006 Engine Masters PHR contests, which were basically exercises in controlling (short-term)detonation. Jon Kaase, a two-time winner, & of IHRA fame, used extremely short rods. This was to, in his words, "yank the piston away from TDC as fast as possible" in an effort to minimize detonation. Then you get into a tradeoff between having an increased compression height (& greater piston top strength, possibly, to endure), vs. a relatively heavy piston.

His solution was to use very short (comparatively) rods, an exaggerated stroke, reasonably short compression height, & to sleeve down the bores (on his BBF) to keep CI within contest limits. He also physically moved the valves & plugs in the chamber to reduce shrouding & lessen flame front distance. This kind of effort is the primary reason why they altered the rules for the '06 contest....& one reason why the Cleveland hybrids dominated this year.

If I had to make a guess, I'd say that it sounds like you paid proper attention to deck height, & possibly the fuel/ignition curves...combined with the Y wedge chamber design & smaller bore diameter....& maybe cam overlap...rather than the rod length one way or the other. Either way, it works...so it's all good!

 

Thanks for the dimensions buns.