1970 Z/28 Pistons-Replacements?

Evilredcamaro

New Member
Mar 31, 2022
16
Does anybody make good quality replacement pistons for the 70 Z? Correct compression etc? Were the stock ones forged?
 

450bench

Veteran Member
Feb 25, 2002
3,710
memphis, tn-shelby
Yes they were forged.

TRW L2304 is the replacement piston to used.
They’re 11 to 1 compression with original 186 or 041 64cc heads.
 
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sandlapper

Veteran Member
Oct 9, 2020
1,622
SE CSA
OE 70Z pistons were forged and too heavy and had old-fashioned thick tractor rings.
If that's what you want --- L2304 is same old, same old --- literally.
2022 we have much better Forged piston offerings --- lighter and with thinner-lighter metric ringpaks (which seal far better than tractor rings and last much longer and create less power-robbing friction and create less bore wear). Dozens of modern offerings from many top quality manufacturers. What's not to like? --- Nuthin'
Consider: all the OEMs went to thin metric ringpaks decades ago.
 

G72Zed

Veteran Member
Sep 8, 2015
4,220
Canada
Does anybody make good quality replacement pistons for the 70 Z? Correct compression etc? Were the stock ones forged?

Most exact replacements are obsolete and no longer available by most piston manufacturers,( and for good reason), unless you find some older stock out there.

I would strongly suggest looking at the Mahle Power Pak offering, mainly the #930200000 if original 4.00 bore, or #930200030 if you are .030 overbore.

The advances in piston design have come a long long way. Going from those old TRW tractor slugs to these Mahle PP are a step in the right direction in every dept, and available through the parts stores for about $750 USD in either 4.00 or 4.030, and come with metric rings.
 

Allison Winn

Veteran Member
Jan 10, 2021
457
And you have to de tune to run them on premium pump gas. On my rebuild I went with forged flat top 2 valve reliefs with the thinner ring set. Mine will run on 90 non ethanol in full tune
 

sandlapper

Veteran Member
Oct 9, 2020
1,622
SE CSA
FWIW --- they WERE TRW
although TRW did manufacture the OE 70Z pistons --- business has changed much in past 50 years
Looong ago, TRW divested & got out of the piston business --- Now those pistons come from sealed power aka speed pro. SP also manufactures much more modern designs to fit 70Z & that era.
As G72Zed says above --- the Mahle pieces are nice --- a few more good makers are Bullet, CP, Diamond, JE, Ross, SRP & Wiseco.
Also, PBM markets their own piston line and have a nice selection that're made for them by Mahle --- same pieces except sans Mahle's signature skirt coating.
 

tom3

Veteran Member
Aug 1, 1999
14,898
ohio
If you are not boring the cylinders check the bore dia. and the piston to cylinder wall clearance. Those old forgings were set up some loose while the newer stuff is designed to run tighter. And that stock bore is probably hogged out some from wear and tear. But I'd guess it'll get a rebore?
 

sandlapper

Veteran Member
Oct 9, 2020
1,622
SE CSA
FWIW
cast/hyper/forged piston alloys include some amount of silicon
other factors at play to some extent, but in general: percent silicon content is inversely proportional to nominal skirt clearance.
OTOH, and in general: silicon content is proportional to brittleness (brittleness is opposite of ductility).
 
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