Inliners International Forums General Discussion Hi Performance TRW NOS forged pistons question

As many on here likely do, I have been collecting parts for a few years now and have some forged TRW 2289 .030 pistons I'd like to run in my engine when it comes rebuild time. Also just took delivery on some .030 Perfect Circle rings (circa 1978 according to the ink stamp).
Are the 2289's considered the LPG pistons?
Do they have any effect on compression ratio?
Lastly, being NOS they have their fair share of knicks and scratches but nothing I would consider critical; what should I look out for and is this common?
In other words, they don't look like a set of Tom's custom Ross pistons by a long shot!

You will need to show a pic of the piston top. They have a 1.655 CH and if they are dished, then no they are not a LPG piston. Bet they are just a forged stock replacement piston. Do they have a chamfer on piston top near the ring?

Thanks Tom, I'll try and get some pics up. They have a slight dish, no outer edge chamfer.

Another question came to mind, been reading a lot of David Vizard books lately, are there any good sources for lightening pistons?
What are your thoughts on reducing the skirt length on a stock styled piston?

Here's a pic of some .040 pistons. Both have about an .070 dish

Not a good idea, it'll create more piston rock. Under the pin bosses are a better spot to remove material. The old 12-1/2:1 440 domed pistons were like cinder blocks weight-wise and I've taken a huge amount of weight out of a bunch of those in those areas. Lighter wrist pins are also an option. Just know that in a street engine, you will never know the difference if the pistons are 10 pounds each or 2 pounds each. In a race engine you will.

I know those chamfered pistons, they will give you 8:1 compression if you have zero deck. Lower compression than stock pistons.
They are heavy , but I ran a lot of nitrous with those & they never failed while detonating


MBHD

I'll make sure I don't use the chamfered pistons, 8:1 doesn't sound do great!

I was looking at the pistons and the top of the pistons seem to have a good bit of material, as well as the pin bosses. Not sure if I'll actually sit down and get after it but I did buy a small milling machine a few years back so this might be a worth while project; if only to learn. I have twelve .030 over NOS pistons that I've separated into 1st choice and 2nd choice. I'm thinking I might give it a go on the 2nd choice set.

If you do, you'll need to use a ball mill....

I thank you for that, much appreciated.

A piston vise or some type of holding fixture so you can cant the piston 90 degrees to the wrist pin is needed also.

So your plan is to make flat tops from the non chamfered ones? Everything you take off will reduce compression if you don't push the piston farther up the hole or bring the deck down. Custom rods? I don't Know it there is .070" On the deck. Another thing is that all replacement over size pistons I've measured have a shorter deck height than stock. When oversize pistons are made the pin height in raised to drop the bigger piston to maintain the stock compression ratio. So they are already a few thousandths shorter.

In the "old days" they screwed plates to the top of the piston to raise compression. Of course it was still low compression by our standards, rpm rarely reached 2,500, and they often didn't last long.

Now that you ask that question I'm wondering why I included the chamfer piston to begin with. I think for comparision sake. Anyway, the plan is to run the 2289 piston, maybe lighten it (maybe not) by methods described by CNC-Dude. My question was referencing a potential increase in compression vs stock pistons (to which mine are chamfered).

I think for a street engine it is more important that they weigh the same than be lighter. I don't know when you have to be concerned with the balance between the rods & pistons and the crank counter weights.

My idea is to follow as many of the good block prep and rotating assembly prep best practices as I can, tools and talent permitting. Not sure I will be able to call it balance and blueprinting but that's the bar; hopefully that effort nets a positive effect and I don't make too many detours!

Any tips on getting the wrist pins out of the pistons? They don't want to move.

Boiling water?

The rods have to be heated normally it does make it easier to remove them. But they can just be pressed out.

I am told the cosmoline used gums up over time and makes them difficult to remove. Larry, these are the NOS pistons, never ran, just been sitting a long time!

If the wrist pins are stuck in the piston just soak them in some carb cleaner Or a good degreaser. like purple stuff . It work even better if you heat up the purple stuff.

I'll give it a try!

found this online from Hot Rod Magazine:

"The minimum safe thickness of a piston depends on many factors, including the specific application, the operator's tuning expertise, quality of fuel, tendencies towards detonation, and the alloy and heat-treat process used by the particular piston manufacturer. For TRW-type forgings made from VMS-75 alloy, a minimum .250-inch thickness is recommended for oval trackers, .280 for street use with average states of tune and poor quality fuel, and .210-.225 for bracket racers using commercially manufactured racing fuel. Professional drag racers may even get down to .170-180 on some areas of the piston flat, but that's cutting it mighty fine. For blown applications, "You can't get the piston thick enough," according to TRW engineer Dennis Novotny. Such engines, when running under boost conditions, experience tremendous pressure buildups due to the greater cylinder filling densities, and are hence quite susceptible to detonation. On these engines .280-inch is the absolute minimum, and the top ring groove should be no closer to the piston deck than .220.250."

Update: got the pins out of the pistons, turns out you just need to let them soak a few years and they free right up!

Update; spoke with Mike at MrHotRod 6 and he recommended getting some stronger rods for the heavy TRW forged pistons if I wanted to go much above 5000rpm. Unfortunately most aftermarket 250 rods these days are configured in the 6" size versus the standard 5.7" size. As luck would have it, Eagle is spinning up production on these again so I got a set ordered for the build. Now I can be confident that if/when I add forced induction my rotating assembly will be stout enough for the added pressure and rpm! Thanks to Ray from Eagle and Mike/MrHotRod6!

Anyone know what the approx cc is for the dish on the 2289 piston (above right), thanks!

You can check CCs yourself using a piece of clear plexiglass and a syringe and have a very good ball part idea.

You could just use the diameter (radius) of the dish and its depth to come very close.

Radius = 1/2 of diameter
Area of dish = radius x radius X 3.14
multiply that by .070 (depth of dish) then convert that to cc