440 stock flat top pistons

[RGAZ]

This is probably a dumb question. I have a 71 440 I am assembling and the pistons are flat top (with small notches on one side), can I assume these are the stock pistons? If so, without fully measuring, can we guess at the compression would be? I am pretty sure they are the pistons that came with the block but now I am slightly doubting it. I am basically trying to determine if I should get new pistons if the compression will be 8:1 smog era with these.

Thoughts,
RGAZ

I have been off this forum for a while working on my A-body now I am back on my B.

 

[RJ Squirrel]

I have an 8-1 flat top piston 440 in my Roadrunner. It runs very well on regular pump gas (it is a driver, not a garage queen) and has plenty of power for my cruising around needs. Pretty happy with it.

 

[RGAZ]

I have an 8-1 flat top piston 440 in my Roadrunner. It runs very well on regular pump gas (it is a driver, not a garage queen) and has plenty of power for my cruising around needs. Pretty happy with it.

Stock heads?

I am going aftermarket so I guess I could improve the compression with the head a bit.

 

[RemCharger]

Need to measure either deck height or compression height
Pick your flavor

 

[BSB67]

I have a 71 440 I am assembling and the pistons are flat top (with small notches on one side), can I assume these are the stock pistons?

No, they are not stock pistons.

If so, without fully measuring, can we guess at the compression would be?

No, there is no reasonable guess. These are not factory pistons.

Just get the part number, and measure the compression distance and we can tell you everything you need to know.

 

[RemCharger]

No, they are not stock pistons.

What makes you say that? They should be dished?

 

[BSB67]

He did not say dished. And, With valve notches?

 

[RGAZ]

No, no valve notches, Just small (like 1/4") notches in the corner Likely for piston direction indication. They are totally flat.

 

[PRHeads]

Measure from the top of the piston to the center of the pin.
You’ll need to use something like a caliper to get a fairly accurate number.

 

[RGAZ]

Measure from the top of the piston to the center of the pin.
You’ll need to use something like a caliper to get a fairly accurate number.

I can do that easily tonight. Generally, what kind of numbers am I looking for and how do they correlate?

 

[RemCharger]

He did not say dished. And, With valve notches?

Nor did he say " valve" notches. But I see your position now.

 

[PRHeads]

I can do that easily tonight. Generally, what kind of numbers am I looking for and how do they correlate?

With the compression height known you can better approximate how far down the pistons will be at TDC.
That’s an important part of the CR equation.

It will likely be a number a bit shy of 2.00”.

 

[BSB67]

Nor did he say " valve" notches. But I see your position now.

Sounds like you’re correct. Not valve notches. More like front or back.

 

[1 Wild R/T]

Measure from the top of the piston to the center of the pin.
You’ll need to use something like a caliper to get a fairly accurate number.

First measure from the top of the pin hole to the top of the piston, add .0545 to that... .0545 is half of the pin diameter so that takes you accurately from the edge of the pin bore to the center of the pin bore...

 

[Thunderdan]

First measure from the top of the pin hole to the top of the piston, add .0545 to that... .0545 is half of the pin diameter so that takes you accurately from the edge of the pin bore to the center of the pin bore...

you mean .545, not .0545. that would be a *very* small wrist pin....

 

[1 Wild R/T]

you mean .545, not .0545. that would be a *very* small wrist pin....

Yup, damn decimal points...

 

[RGAZ]

With the compression height known you can better approximate how far down the pistons will be at TDC.
That’s an important part of the CR equation.

It will likely be a number a bit shy of 2.00”.

Yep, 1.97” flat top to pin center.

 

[BSB67]

That puts you 0.100” in the hole or more unless the deck was cut a bunch

 

[1 Wild R/T]

Yep, 1.97” flat top to pin center.

Well... The normal number is 1.991 And I agree that should leave the piston about .100 in the hole.... And with a standard open chamber iron head that puts you around 8.5-1

 

[Kern Dog]

First measure from the top of the pin hole to the top of the piston, add .545 to that... .545 is half of the pin diameter so that takes you accurately from the edge of the pin bore to the center of the pin bore...

THIS is extremely helpful. I often wondered how to accurately determine the measurement without having some means to put one end of the calipers in the center of the wrist pin.