[71Formula]

I've come across a 400 motor for sale that has a "new" set of cast TRW pistons with 8 valve relieve(they are old but never installed). I believe the TRW cast pistons like this are to work with both the 428 and 400 valve clearances. They are for 4.15 bore (+.030). The engine has 4x heads that are 98cc so it would be a low compression motor, probably around 7.5:1. But I have #13 heads that are 75cc that I could install to get the compression up to around 9:1.
My questions; are these pistons any good? Is it worth replacing these "new" pistons with forged? Anyone know what the valve relief CC's are on the 8 valve relief pistons so I can accurately calculate compression?

I think it's a good deal on the motor ($250) but it's been disassembled for years and it's rusty and it has cast pistons. So I'm trying to decide if its worth it or not. All parts included (just not all the parts are what I want).

Roy

[Brian D'Amico]

All depends what your going to do with it.. If it's for a Sunday cruiser.. then the cast pistons are ok.. but If your going to romp on it from time to time.. go with the forged. I bought a set of forged pistons with rings & rods for $200. (from a member on PY) If the cylinders are rusty, your going to have to have to have them checked. They may go over .030.. then the cast pistons are useless. Best bet.. find a cheap solid 400 core block, and start building with the parts you want. Good Luck!!

[Skip Fix]

Their forged pistons with 8 reliefs are listed at 6.6cc.

[Ron Landis]

are what came in GTO's, aside from the IV's and V's. They are lighter, hence easier on rods. I would not concern myself unless you are going to severely punish them and/or spray the thing. Good luck. Ron

[71Formula]

Wow 6.6cc is all? They look more like 15cc but maybe they just look that way....

[Jeff Walker]

Can you post a pic of one of the pistons. If it's the style I am thinking of, they are about a 13cc valve relief area. You will have a pretty decent combo then with the 13 heads.

[Skip Fix]

15cc is 1/2 an ounce, 3 teaspoons worth(1 TBS).

[71Formula]

Here is a picture I found of the sam type of pistons, not the same motor but I believe it is a 400 +.030 with cast TRW 8 valve relief pistons.

[Jeff Walker]

Yep those are the ones I thought they were. IMO they would be fine for mildly built street engine. With the #13 head you will have a decent pump gas combo.

[71Formula]

Thank you for your opinion, that is what I was looking for. I think for 250 bucks I can't go wrong.

Thanks much!
Roy

[Big Injun]

As everyone has stated, those will work fine for a street performance engine. I ran those in a 400. They were designed to be used in either a 389 or 400 depending on your head choice...valve angle.

You will want to run .006-.007 piston to wall clearance.

[69birdboy]

I believe those have 15cc reliefs, and a compression height of 1.7, which puts them .040 in the hole.

[BillyGoat]

I used these pistons in a 400 that I built 6 years ago with no problems. The thing that I liked about them was that the CR came to 9.4 with a 72 cc head. These pistons added 16 cc's to the CR calculation which is just what I was looking for to run 670 heads.

[firebirdcrazy1959]

I just bought a very nice set of the same ones from joegio to use in a 400 built up.

[Going Topless]

My 69 GTO was not knocking on 91 octane gas when I bought it. Pulled the heads and the pistons looked exactly like those. I filled 1/2 of the reliefs with moleling clay. The clay displaced about 7cc of water in a graduated cylinder (14cc total for the piston). The pistons also measured .040" down in the block. With a .039" gasket, that is about .080" quench. That is way more than is suggested. If you are building it from scratch, I would suggest a piston/deck height that would be more favorable in the long run. Now is the time to do it right.

[71Formula]

How important would a full balance be with these pistons?

[Mr. P-Body]

Balance is always important to an engine that does not use original or "replacement" parts.

Those pistons are for use in 400s with either the early or later heads. The early '67 models had the same valve angle as 389 (except the "large valve").

If those things really have the old TRW number on them, they ARE OLD! Still, a good choice for a lowered-compression 400 with the 72 CC heads. No nitrous, please...

Skip, I'd be interested in the part number of the forged version, having never seen them. They're not listed in Speed Pro or Sealed Power catelogs (current "owners" of the TRW process). The current part number for the casting is "411NPxxx".

Jim

[Cliff R]

The problem with those pistons is that they usually end up WAY below the deck at TDC. Most are .030-.050" from the top. The last time I had one of those engines in here we cc'd everything above the piston at TDC and came up with around 22cc. NOT a good thing for trying to make a decent compression ratio or optimum power. Pontiac engines respond much better to zero deck height at a higher static compression ratio, than the other way around. Some of the worst running hot/overheating/detonating 400's we've seen had those pistons in them!.....Cliff

[71Formula]

Thanks for all the feedback. I have not decided to buy the motor for sure, but if I do I'm not going to use those pistons. I've decided I'd like to build a more efficient motor with the zero deck and run a more agressive cam, probably a '068 or '041. If I use the '041 cam I will use the rhoads lifters. Basically going to follow Jim Hands advice from his book and many arcticles I've read.

Cliff, I agree with what you said 100% and I think that's why I was concerned with these pistons in the first place. Sounds like many guys get away with these pistons in MILD steet motors. This will be a street car, but I don't want it to be mild. I'd like a 13 sec ETA car if I ever get around to taking it to the strip.

Thanks again for all the advice.

[OINK 1]

TRASH them, they totally F**k up the compression swirl pattern.

Pontiac Gregg