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Higher compression pistons?

S

Sponsored1

New CEG'er
Joined
Jun 19, 2003
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Buckingham, Pa
Ok so im putting my 3.0l together right now. Ive decided on using the 3.0l heads and my only concern is i would like a little higher compression(around 10.5:1). I'm not planning on doing anything past this, so its pointless to spend $600 on some custom pistons. Since the lincoln ls has 10.5:1 compression, and the bore and stroke are the same, does anyone know if the pistons are higher compression pistons or if its just a smaller combustion chamber that makes the compression difference?
 
From everything i read, i assumed my 3l was 9.5:1 compression. And yes, im anal, so 1 point of compression is worth it to me.
Regardless i did order a piston today from an ls, so if anyone was curious, ill know soon.
 
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Sponsored1 said:
From everything i read, i assumed my 3l was 9.5:1 compression. And yes, im anal, so 1 point of compression is worth it to me.
Regardless i did order a piston today from an ls, so if anyone was curious, ill know soon.
Click to expand...
The difference in the compression ratio of the 3.0L DAMB engines used in the Jaguar and Lincoln LS comes from reduced cylinder head combustion chamber volume. The pistons are the same between 3.0L RFF and 3.0L DAMB Duratec engines.
 
Gee, couldn't you just have called your Ford dealer and asked for the part number to cross reference to see if they're the same or not?

Rick
 
I called my ford dealer. They are complete morons and couldn't or wouldn't cross reference it for me. So i just said order one and if its not what i want they will return it.

procyon: Do you have somewhere where i can get all the combustion chamber volumes and piston dome specs for the 2 engines?
 
Sponsored1 said:
I called my ford dealer. They are complete morons and couldn't or wouldn't cross reference it for me. So i just said order one and if its not what i want they will return it.

procyon: Do you have somewhere where i can get all the combustion chamber volumes and piston dome specs for the 2 engines?
Click to expand...

Try using a calculator :idea: since you are already given the static compression ratios......

You already know the bore is 89mm, the stroke is 79.5mm. Total swept volume of the cylinder is: 494.58 cc's
Therefore if you squeeze it down in the ratio of 10:1 you get 49.46 cc's on the non-Lincoln combustion chamber.
Therefore 494.58/10.5 = 47.1 cc combustion chamber on the Lincoln
 
That would be great but my pistons that came out of my 3.0l arent flat tops and i dont have a way to measure the dome on them right now.
 
Sponsored1 said:
That would be great but my pistons that came out of my 3.0l arent flat tops and i dont have a way to measure the dome on them right now.
Click to expand...

So what does that have to do with it?

The pistons are stated to be the same. The published static compression ratio is 10:1 and 10.5:1 respectively. This calculation would take into account the shape of the piston dome. This should be sufficient for anything you need unless you change the shape of the combustion chamber from stock. Then you would need to measure it.

If you have the head off you can calculate the volume like I have done in the past. I laid the head flat upside down with the valves and spark plugs in the cylinder and I put a glass plate over the head chamber. Then at the edge I use a pipet to add liquid carefully and topped it off 1ml at a time using a .5ml pipet for accuracy until it was full.

1ml = 1cc
 
2.5L RFF chamber volume is 44.5cc
3.0L RFF chamber volume is 48.2cc
3.0L DAMB chamber volume is 45.7cc

Keep in mind that you would need major fab work to make a DAMB head work. Search the forums, including the archive, for more info. Many before you have asked about using the 3.0L Lincoln LS/Jaguar heads. The costs far outweigh any gains.
 
procyon said:
2.5L RFF chamber volume is 44.5cc
3.0L RFF chamber volume is 48.2cc
3.0L DAMB chamber volume is 45.7cc

Keep in mind that you would need major fab work to make a DAMB head work. Search the forums, including the archive, for more info. Many before you have asked about using the 3.0L Lincoln LS/Jaguar heads. The costs far outweigh any gains.
Click to expand...

So there you go. I take it that this is pure combustion chamber volume and does not take into account piston reliefs and such?
 
Procyon i appreciate the info. I searched the forum and archives and couldnt find that info. Warmonger, the combustion chamber volume has nothing to do with piston reliefs and the dome of the piston. You cant just figure out the chamber volume without knowing the piston dome volume, gasket thickness, and deck clearance of the piston.
 
Sponsored1 said:
Procyon i appreciate the info. I searched the forum and archives and couldnt find that info. Warmonger, the combustion chamber volume has nothing to do with piston reliefs and the dome of the piston. You cant just figure out the chamber volume without knowing the piston dome volume, gasket thickness, and deck clearance of the piston.
Click to expand...

You're right...you know all about it. :rolleyes:

And just to prove you wrong...
By definition a chamber is a closed in space of some volume.
chamber
n 1: a natural or artificial enclosed space
2: an enclosed volume (as the aqueous chamber of the eyeball or
the chambers of the heart)
Click to expand...
So the piston is the bottom or floor of the chamber. Therefore logically if your floor has a depression in it or a projection it will affect the volume of the chamber.
What happens if you install a piston with a big dish in it? Does the VOLUME WHERE THE FUEL COMBUSTS GET ANY LARGER????
I think it does.
The OEM engineer designed the chamber and knows the volume. Then he knows the swept volume of the cylinder because he designed the bore and stroke length. Therefore he knows the volume of air that can be held in the cylinder at Bottom dead center.
THEREFORE he makes the calculation from these two facts and comes up with the static compression ratio....which is then published for the engine.

NOW YOU take two variables of the calculation and you can back-calculate the third variable... i.e. the volume of the chamber that INCLUDES piston reliefs, gasket thickness, head volume.

Take the volume calculated and subtract of the 1mm thick gasket and the piston reliefs and I'm sure it will come in right about what was given by Procyon.

So see, I gave you the tools to figure it out instead of spoon feeding you and I don't get any thanks... :(
 
Sponsored1 said:
Procyon i appreciate the info. I searched the forum and archives and couldnt find that info.
Click to expand...
Sponsored1 said:
Warmonger, the combustion chamber volume has nothing to do with piston reliefs and the dome of the piston. You cant just figure out the chamber volume without knowing the piston dome volume, gasket thickness, and deck clearance of the piston.
Click to expand...
These specs have been posted countless times over the years and most are on my website as well.

Then to quote you...
The combustion chamber volume has noting to do with piston reliefs or domes because you can't figure out the chamber volume without knowing the piston dome volume, etc, etc. Did you even read what you posted? :blackeye: You contradict yourself! :shrug:

You use cylinder head chamber volume (as in head chamber cc's) as one of the variables to calculate final/total volume area. They are two different things. Cylinder head chamber volume does not include piston relief/dome information but the head chamber volume is just one variable (which include piston dome/relief) in calculating compression ratio. Much less one of several more required when calculating dynamic compression which is far more important then just the static compression figure.


Also about your silly comment about thinking .5CR is worth spending $700-800 for custom pistons and rings. That is roughly 1% more power under ideal consitions. The power to dollar ratio is beyond pathetic. You'd be better off going to a 90mm bore with SP pistons/rings ($150) and getting ~10.24CR. That's 1/2 the gain (CR) plus 1/15 (CID) for 1/5 the money. It's still pathetic in the cost ratio analysis. You are talking 1-2HP either way you cut it.

Stock compression of the oval port 3L engine is 10.07 to 1. Again this information has been posted ad nauseam.
 
Not to mention the possibility of poor ring seating with aftermarket. You might be anal but your reasoning sucks duder.
 
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