Piston compression ratio

[John/1]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Hey,thanks for the 1" down in the hole method.I was wondering how to calculate my dome.This will calculate piston relief and my lower ringland aswell.
John

[harleytuner]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

[Admiral Akbar]

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

Yeah, I guess I'm always just lucky 

You amuse me, Max.

It's funny.. I got the same argument from the Dynojet engineer on dynos..    He had 2 DJ  dynos, one old and one new, that agreed on numbers for the same car so his dynos were more accurate than brand X.. And all the dynos in between had to be the same..

[Admiral Akbar]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

Don't forget the error in wetting the cylinder.. Was talking to a bartender at a distillery and he was saying that you could get 2 more shots out of a bottle of bourbon if you wet the glass before filling..

[Bigbluff]

Sounds like Max is buyin'!...providing we wet our glasses first...

[Rugby_fxdwg]

I'm in for the Bourbon....or Irish Whiskey

[jsachs1]

If you go into the "Homemade Tools" section of this forum, you will see the most accurate way to measure piston dome or dish volume.
Easy to make a known volume fixture to get an accurate answer. 
John

[harleytuner]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

Don't forget the error in wetting the cylinder.. Was talking to a bartender at a distillery and he was saying that you could get 2 more shots out of a bottle of bourbon if you wet the glass before filling..

Lol. I don't buy that for a second. How big a bottle?

[GregOn2Wheels]

Piston "compression ratios" are what you might see if you used the piston in an application it was designed for.  Personally, I ignore this "piston compression ratio" altogether since my application might not be typical and even if it is, I want a more accurate calculation of the theoretical mechanical compression ratio of a build then the "ballpark" ratio provided by the piston maker. After all, the piston maker has no idea what my head chamber volume, my deck height or any of my other measurements which impact compression.  Instead of piston compression ratio, the figure I look for is dome volume since its the one that tells you how the piston is going to work with the other parts you selected or had machined that ultimately determine compression ratio.  I find it aggregating that almost all manufactures of pistons used in HD motors make the pistons "compression ratio" figure readily available, but make you search for the dome volume. In fairness, some make this an easier figure to find than others, but I'm yet to find one that specifies dome volume as prominently as they do the "compression ratio".

[Admiral Akbar]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

Don't forget the error in wetting the cylinder.. Was talking to a bartender at a distillery and he was saying that you could get 2 more shots out of a bottle of bourbon if you wet the glass before filling..

Lol. I don't buy that for a second. How big a bottle?

You tell me..

[gordonr]

I ran across this video while looking for an inexpensive burette and it really doesn't get any cheaper than what this guy uses.

https://www.youtube.com/watch?v=bWze92nt9OU

[harleytuner]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

Don't forget the error in wetting the cylinder.. Was talking to a bartender at a distillery and he was saying that you could get 2 more shots out of a bottle of bourbon if you wet the glass before filling..

Lol. I don't buy that for a second. How big a bottle?

You tell me..

Well let's see. A fifth is 750ML. 750ML = 25.36 ounces. 1 shot = 1.5 ounces so a fifth yields approx 17 shots. 2 shots lost would be 11.76% of the bottle. Must be some pretty porous shot glasses.

[Admiral Akbar]

FWIW using the piston in the cylinder method ain't very accurate.. Better to make a fixture to capture the dome then calibrate it against a flat surface..

Our pistons are all made to our specs by CP. I've double checked some of them (not all) using the 1" down method, comparing the answer to the specs we gave them. Dead nuts accurate.

The key with the 1" down method is to accurately place the piston. Do that correctly and it's right on the money. It helps to know the dome height, but CP puts that number right on the spec sheet.

Not sure if anyone want to go through the tolerance stackup on the measurements but I'd say you got lucky.. Questions that need answering first are:  How do you set the piston position?  Do you compare to a referenced flat surface in the cylinder? What do you use for a cylinder? What is the diameter?   What do you use for measuring volume?  What is the accuracy of the volume measurement system?

Add.. How close are the numbers?

You forgot to ask what temperature everything is at when he measures. Gotta allow for shrinking and expansion.   

Don't forget the error in wetting the cylinder.. Was talking to a bartender at a distillery and he was saying that you could get 2 more shots out of a bottle of bourbon if you wet the glass before filling..

Lol. I don't buy that for a second. How big a bottle?

You tell me..

Well let's see. A fifth is 750ML. 750ML = 25.36 ounces. 1 shot = 1.5 ounces so a fifth yields approx 17 shots. 2 shots lost would be 11.76% of the bottle. Must be some pretty porous shot glasses.

Good you can figure it out.. was actually over a shift.. Not sure how many bottles that would be..

Add

Tho it is not correct..  First off it is not a loss but a gain..

25.35 oz will get you 16.91 shots.. Which means you really only have 16 shots.. But OK lets say 17.. Say wetting the glass gave 19 shots the end results would be 19 x 1.5 = 28.5 oz   So the water in the wet glass would have added   28.5 / 25.36 - 1= 0.123  or 12.3 %

If when the glass was wetted some of the water stayed on the bottom it may not be noticed..

[glens]

If when the glass was wetted some of the water stayed on the bottom it may not be noticed..

There'd be a tell-tale wet ring on the bar?