Piston weight?

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Captainkirk

Captainkirk

Old School Mopar Warrior
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Question for all you professional engine builders out there:
When building a Mopar performance smallblock (340), what should the max allowable weight variance between pistons be? (in grams)
 
I do + or - .2 of a gram, but I'm crazy. I think most sets are within 2 grams. Call a good machine shop and ask them also.
 
As close to the same as you can. Rods and pistons should be done separately. Lighten each piston to the match the lightest one. Same on the rods.
 
my 1967 coronet factory manual shows the 426 Hemi piston weight as 841-845 gms. that is the only one in the book that shows a range of weight. the others just have one weight.
 
Captainkirk said:
Question for all you professional engine builders out there:
When building a Mopar performance smallblock (340), what should the max allowable weight variance between pistons be? (in grams)
Click to expand...

Generally,

Custom Pistons will come in at {+ or - 2.5 Grams}, one way or another.

In other words, they can be {5 Grams} off from one piston to another.

For a Street Performance Engine, those weight differences are acceptable.

The 'old' {Heavy-Bastard} TRW Power-Forged Pistons, can be off as much
as 7 Grams.

As a general rule, for high-revving Street Performance Engines, after
'Balancing', a {2 Gram} variance is acceptable.
 
69 Cuda 440 said:
Generally,
The 'old' {Heavy-Bastard} TRW Power-Forged Pistons, can be off as much
as 7 Grams.

As a general rule, for high-revving Street Performance Engines, after
'Balancing', a {2 Gram} variance is acceptable.
Click to expand...

I'm showing about a 4 gram difference on the "Heavy Bastard" piston I 'fixed' and an untouched one. Guess I need to 'fix' them all.


66fs said:
I do + or - .2 of a gram, but I'm crazy. I think most sets are within 2 grams. Call a good machine shop and ask them also.
Click to expand...

Personally, I don't find .2g to be anal at all. That's why they make grinders.
 
Captainkirk said:
I'm showing about a 4 gram difference on the "Heavy Bastard" piston I 'fixed' and an untouched one. Guess I need to 'fix' them all.




Personally, I don't find .2g to be anal at all. That's why they make grinders.
Click to expand...

Make them all weigh the same as the very lightest one...............pretty easy.
 
+1 on the easy part, my machinist used a drill press on the undersides of the piston heads for my 360 when I had it balanced (several light touches no deep holes obviously)... just have your scale sitting next to the drill and you can probably get it within .2g no problem.
 
Machine shop I use gets them within + or - .5 gram. He builds mostly high revving race engines.
 
If you can get them dead perfect, why not?
 
Heavy Bastard TRW Power-Forged Pistons

If you can get them to a 2-Gram difference, that will be excellent for a
High-Revving Street application.

But even at a 4-Gram difference, they will still be fine. I have seen some
TRW Slugs come out of good running 340 Engines with a {+ or - 7 Gram}
difference.

Yes, 14 Grams difference between one Piston and another.
 
Precision Engine Balancing

Piston Weight Level Difference for Application

Basic .......................................... 3.0 to 5.0 Grams
General Street and Industrial ......... 2.0 to 3.0 Grams
Street Performance ....................... 1.0 to 2.0 Grams
High-Performance ......................... 0.6 to 1.0 Grams
Race Ready .................................. 0.1 to 0.5 Grams
 
Good info.
What Im trying to find is the max allowable weight difference(total between all old pistons vs replacement pistons) you can have before needing machine shop to balance everything?
Thanks
 
Last edited:
moe7404 said:
my 1967 coronet factory manual shows the 426 Hemi piston weight as 841-845 gms. that is the only one in the book that shows a range of weight. the others just have one weight.
Click to expand...
the factory hemi pistons were trw`s back in the day, heavier than he-- !!
 
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