L-2291F Clearance?

[gt350hr]

   TRW/Speed Pro pistons  "were" forged from an alloy called MS75. That is a high silicon ( up to 12%) alloy so it is typically a low expansion material. To confuse things even more they did use 2618 (low silicon) alloy in some applications and "tin plated" them for scuff resistance. They obviously ran at greater clearance. Clark - Wellever the actual company that made the pistons , had a limited amount of "cam turn" profiles and a common way to make the piston live was to add clearance. While they were "the industry standard" and most of us used them , they are way outdated compared to modern computer controlled , complex skirt shapes. The "contract was not renewed with C-W and they disappeared for some time. Now back in production , Speed Pro has tried India and Mexico for manufacturing bases. The alloy has changed and the surface texture has also changed possibly due to a material spec change. Pricing has also shot upwards making other aftermarket pistons more attractive.

[wayne]

Google forged piston clearance for some good reading

[gt350hr]

   Be careful on generalizing about piston to wall clearance. It "can be " very manufacturer specific besides alloy changes and where the piston is measured .

[frnkeore]

I have the 1978 TRW Engine Parts catalog, I got it new and it's one of my favorite books. To bad TRW are not still around.

Here is all the info I could find on the meanings of the part numbering system they use. The A suffix isn't directly addressed but, I think I found the meaning of it, seen in the one picture but, not in the general description areas. Do later versions add the A in the general info area?

Frank


 

[falcongeorge]

   Be careful on generalizing about piston to wall clearance. It "can be " very manufacturer specific besides alloy changes and where the piston is measured .

Damn straight. And VERY material specific. And there are a TON of different ways to make an aluminum alloy, and a TON of different material characteristics based on those differences. gt350hr, IIRC, you work for, or used to work for Racetec, correct? For anyone getting hard engine building advice from google searches alone, well, you would want to proceed with considerable caution...   

[falcongeorge]

   TRW/Speed Pro pistons  "were" forged from an alloy called MS75. That is a high silicon ( up to 12%) slloy so it is typically a low expansion material. To confuse things even more they did use 2618 (low silicon) alloy in some applications and "tin plated" them for scuff resistance. They obviously ran at greater clearance. Clark - Welliver the actual company that made the pistons , had a limited amount of "cam turn" profiles and a common way to make the piston live was to add clearance. While they were "the industry standard" and most of us used them , they are way outdated compared to modern computer controlled , complex skirt shapes. The "contract was not renewed with C-W and they disappeared for some time. Now back in production , Speed Pro has tried India and Mexico for manufacturing bases. The alloy has changed and the surface texture has also changed possibly due to a material spec change. Pricing has also shot upwards making other aftermarket pistons more attractive.

There were a LOT of problems when they transferred production to India, especially with pin bores being out of square. Although I recently talked to some engine machinists that have told me those issues have been fixed, I wouldn't bother buying the current ones, especially when you can find lots of NOS or lightly used ones that were made before the transfer to India for $100-$250 like I mentioned. If you are going to go out and buy new "TRW" or Speed Pro forged pistons, the price is close enough that you may as well just buy Racetecs.
FWIW, I think modern skinny rings with a napier cut second and the lower oil ring tension that the napier second permits is probably worth a solid 20hp on a 500hp motor, but I don't see that many guys really taking advantage of that on street motors. They will buy modern pistons, but put very little thought into the ring package, and that's where the power can be found. For sure, if you are going to step up to a modern piston design, there is considerable power on the table in the ring package, if you are going to really pursue that.
There are also the Total Seal spacers designed for use in Stock elim motors, so you can conceivably pursue a state of the art ring package with older 5/64 ring groove pistons, but the cost of the ring spacers is such that you just as well pony up for a Ross or RaceTec forging at that point.

[gt350hr]

    Yes I do work for Racetec but am looking forward to retirement soon as in "the next few months". Before here it was a 14 year stint at JE. That's where I got "inside information" like the stuff about C-W as they were searching for someone to buy their operation.
   Randy

[427mach1]

I still have a nice 1979 TRW Engine Parts catalog, I'll get some particulars on that L number tonight when I get time.

I was thinking last night about scanning a couple of pages of FE pistons and posting them, kinda help make this the "definitive FE TRW piston post".

Would one of you please post or send me the page showing the L2298 pistons (427 bore, 428 crank)?  I believe it should indicate which heads the pistons will work with.  I had to modify mine to get them to work with CJ heads....

[falcongeorge]

I still have a nice 1979 TRW Engine Parts catalog, I'll get some particulars on that L number tonight when I get time.

I was thinking last night about scanning a couple of pages of FE pistons and posting them, kinda help make this the "definitive FE TRW piston post".

Would one of you please post or send me the page showing the L2298 pistons (427 bore, 428 crank)?  I believe it should indicate which heads the pistons will work with.  I had to modify mine to get them to work with CJ heads....

That piston would be in the "Racing Pistons" catalog, not the Main catalog, I'll dig around and see if I can find that catalog.

[thatdarncat]

I still have a nice 1979 TRW Engine Parts catalog, I'll get some particulars on that L number tonight when I get time.

I was thinking last night about scanning a couple of pages of FE pistons and posting them, kinda help make this the "definitive FE TRW piston post".

Would one of you please post or send me the page showing the L2298 pistons (427 bore, 428 crank)?  I believe it should indicate which heads the pistons will work with.  I had to modify mine to get them to work with CJ heads....

Yes, the edge of the 428 CJ head combustion chamber will possibly interfere with those 427 pistons. I used 428 CJ heads on one of my 427’s with the L2299 pistons and modified the CJ chamber to make it work. The recommended heads were the 427 MR/HR/TP. Here’s the info from the TRW catalog.

[falcongeorge]

Wow, that was fast^^

[TomP]

I have L2298F-30 in my engine. Bought them in 1980. I first ran Cobra Jet heads so the domes were milled off to clear the chambers. Now with the High Riser heads the compression is lower than ideal but it'll run on 94 octane pump gas.

Oh , and 010" clearance too, mostly because of a couple rehonings.

[falcongeorge]

I have L2298F-30 in my engine. Bought them in 1980. I first ran Cobra Jet heads so the domes were milled off to clear the chambers. Now with the High Riser heads the compression is lower than ideal but it'll run on 94 octane pump gas.

Oh , and 010" clearance too, mostly because of a couple rehonings.

Those pistons are from the race pistons line, different alloy and drilled oil ring lands, so they are supposed to be out around .007-.008, so .010 isn't that bad.
FWIW, that fake 270hp 283 you saw hanging on the engine stand at my place has +060 L2148F/2149F TRW 270hp/fuelie replacements in it, which are from the OEM replacement line. The block is a '57 283 (no side mounts, one year only, rare as hell) and it was already .060 when I got it. The bores were round and straight, so I CAREFULLY ball honed it, but I am still at around .006-.007 on several holes, that's a LOT looser than I would like with those pistons, they should be around .002/.0025. Hopefully I wont hear the piston slap over the .028 valve lash . But with '57 283 blocks being as hard to find as they are, the only other option would be to go out to 1/8 and build a 301, I'd rather not do that, so I will just have to cross my fingers. 283's are REALLY forgiving, and the bottom ends are like anvils, so its probably ok, but its far from ideal, and I do worry about it a little.

[427mach1]

Yes, the edge of the 428 CJ head combustion chamber will possibly interfere with those 427 pistons. I used 428 CJ heads on one of my 427’s with the L2299 pistons and modified the CJ chamber to make it work. The recommended heads were the 427 MR/HR/TP. Here’s the info from the TRW catalog.

Thanks, that is exactly what I was looking for.  I had the domes milled down and modified the chambers on my CJ heads, ended up with a little over 12:1.  I knew they recommended certain heads but couldn't recall if MR were included.  I'm thinking about a pair of Edelbrock heads CNC'd by Craft Performance.  Edelbrock advertises a MR chamber so they should work...

[Pentroof]

I went through this with these pistons on my last 390 truck build. I couldn’t believe it, but it’s true. Minimum clearance for those pistons is 0.0015”, according to the card that came in the box with my pistons.
Not all forgings grow a lot. Those pistons have a ton of Silicon that contributes to the low thermal expansion. Your choice of 0.002” is right on the money.

I posted my findings here
http://fepower.net/simplemachinesforum/index.php?topic=6818.msg74661#msg74661