trw piston question

[shady]

20 - 30 years ago I bought a set of trw L2291A pistons at Carlisle. they were brand new in the box with the rings. I've see L2291F's but not A's.
anybody know what they are? were they troublesome? can I use them or should I just scrap-em? they are marked .030 over & I only paid $30 bucks.
the box had 390 forged scribbled on it. thanks for your input.

[Joe-JDC]

Have you measured them?  Diameter, pin height?  That will tell you.  TRWs were heavy back in the day, but dependable for rebuild.  If you are trying to make lots of horsepower, or high revving, then they might need a second look after determining what size they actually are.  Try Google for the part number.  It says 390 + .030.  Joe-JDC

[Barry_R]

Probably actually "AF"...
All the forged TRW pistons carried the "F" suffix for marketing

TRW engineering used the A and N as indications of engineering revisions.
Nothing that altered application.
Could be weight, valve pockets, lock design - something that kept them from being interchangeable with prior iterations.

[thatdarncat]

I checked my 1978 TRW catalog and as Joe confirmed, they are listed for '69-'70 390 4bbl., forged stock replacement. I do see a reference to both a L2291F and a L2291AF. I looked all through the catalog and I do not see any reference to what the "A" means. The pistons generally were sold individually or in a set with rings separate - were your rings packaged in the box with the pistons? Just a wild guess that maybe that is the difference? You would think if the "A" was important they would explain it, the catalog is very detailed. TRW's were generally regarded as an excellent "off the shelf" piston back then and used in a lot of racecars, but also like Joe said they are heavy compared to what is offered now. I would check them dimensionally to be sure they are in spec, always a chance there was a reason someone was selling them cheap back then, but if they suit your build no reason not to use them. And while I was typing I see Barry added some insight.

[Louie]

IIRC, they were intended to go into truck engines. If you look, you should find HD thick wall pins on them. At least that is what my set has.

[thatdarncat]

Nope, not truck pistons, there was a different piston for truck 390's. Application is passenger car. Any Galaxie, Torino, Mustang, etc. They also became the replacement piston for 390 4bbl in '66 to '68 car applications, looks like the ring pack may have been a little different. No reason you couldn't use them in a truck 390 now, but they weren't the direct replacement, different specs.

[Louie]

Maybe Bill Ballanger can pipe in, but he is what led me to the answer. http://www.network54.com/Forum/74182/thread/1027904859

I have had a set in the garage for the last 15yr or so and have gone over them completely. The HD pin is the only difference. Bill stated they are for a 360 and if so that makes them a low comp truck piston.

[thatdarncat]

Louie, you are correct in that they are ALSO a 360 pickup truck piston ( not a 390 pickup engine ) and my answer was not complete as I just looked in the 390 section of the catalog. The reason they are a low compression piston in a 360 is due to the shorter stroke 3.50" crank, the pistons will be way down from the deck at TDC. When used in a 390 with a 3.78" stroke crank they are closer to the deck and higher compression. And it looks like Louie is correct about the pin, different pin is used in the L2291F than the L2291AF. That probably agrees with Barry's explaination the the "A" means a revision change.  And again, no reason you can't use them in a 390 pickup, you'll just have the same compression the car motor would have had.

[shady]

the rings also TRW were in a separate box, but the pistons were all together in the original box dated 1983. I have a 64 390 block that should clean up at .030 with C3AE-C rods. I may have a set of C7 rods somewhere though. is there a rod diff. that they are listed as 66 & up or is it more to do with comp. ratio or head  cc? the wrist pin location & size & ring groves are exactly the same as the orig. 64 390 piston. If it were a 360 piston I would imagine the pin would be farther down. the 64 pistons have valve reliefs & are dished in the center, these are flat tops with reliefs. I was thinking of just building a mild fresh motor for the 62 in case my 352 goes south. Maybe the voice in my head is one of Barry's 445s are calling to me.

[thatdarncat]

Ford used those pistons in a 360 without changing the pin location for the purpose of lowering the compression for the trucks. Ford did the same thing on some 390 Pickup motors by using the 410 Mercury piston, which normally went with a 3.98" stroke crank and had higher compression in the cars, with the 390's crank it puts the piston lower in the hole. No reason not to use those pistons in your truck build other than the compression ratio. You'd want to measure head cc, gasket, etc. and take your cam into consideration to know if you could use today's pump gas.

[shady]

Many thanks guys. No wonder the 360's were gutless gas hogs. I would have never imagined that's how ford lowered comp. When I googled these there wasn't much info out there other than a set on ebay. now if I'd only bought all those shorty cast headers at Carlisle when they were $50 bucks.........