New to engine work - stupid question?

[80083r]

I'm fairly technically savvy, but lacking a great deal of knowledge in this area. I'm studying hard and reading lots, but sometimes it's faster to ask the stupid question than searching forever.

If the crank is the same on the 7MGE and 7MGTE are the same, how is the compression different? Obviously after the turbo spools up, there is more compression due to adding more air to the same stroke...

Is the air intake modified by having to pull past the turbo?

I told you it was a stupid question - is it all just how much air (and fuel) is sucked/pushed into the cylinder during intake?

 

[Turbo Habanero]

Don't quote me on this just yet but I believe the pistons are different.


And ask all the stupid Questions you want sir. Some will let it bother them but most of us don't mind to help.

 

[Slayr504]

Don't quote me on this just yet but I believe the pistons are different.


And ask all the stupid Questions you want sir. Some will let it bother them but most of us don't mind to help.

I'm almost positive the pistons are different between the 7M and 7MGTE. Pistons would probably be the easiest way to either reduce/increase compression. I have a Haynes Repair manual for the 7M & 7MGTE. I'll check when I get home from work and let you know for sure.

 

[80083r]

shouldn't the pistons being different (I assume you mean length) affect the displacement rather than the compression? The ratio would be decided by the stroke, wouldn't it?

 

[Turbo Habanero]

Diameter would change the displacement like if you go with a .020 over sized or .040

 

[egesledder]

Turbo pistons are dished to add more volume to the combustion chamber size at TDC. Bore/stroke are the same, so they displace them same, but the volume of air at TDC for the turbo version is larger than the N/A version. This makes the compression ratio lower and, in this case, the cranking compression lower (those two are not always tied together).

 

[Slayr504]

^^^What he said lol

 

[80083r]

Well, apparently I've got some more reading to do. Thanks for the info!

 

[Slayr504]

The height of the pistons or length of the rods should affect compression, whereas the diameter of the cylinders/pistons should affect displacement. I'm definitely not an expert, but that's always been my understanding.

 

[radiod]

In short, GTE pistons are lower compression (8.4:1) and GE pistons are higher compression (9.1:1). They will both fit, but I wouldn't recommend using GE pistons in a turbo application unless you know what you're doing. There can be advantages to running the higher compression, but you need to understand what else is going on before just dropping them in and turning up the boost.

The height of the pistons or length of the rods should affect compression, whereas the diameter of the cylinders/pistons should affect displacement. I'm definitely not an expert, but that's always been my understanding.

Boring it out will give you a tiny bit less compression. You're making slightly more space in the combustion chamber with the same stroke. It's not going to be hugely significant, but it will make a tiny difference. Same reasons as specified above and why using different head gasket thicknesses will affect it as well.

Other than the pistons, the rest of the block is pretty close to the same. GTE block has oil squirters, the hole drilled for the turbo oil return all ready, and knock sensor ports tapped for 2 rather than 1.

 

[Slayr504]

In short, GTE pistons are lower compression (8.4:1) and GE pistons are higher compression (9.1:1). They will both fit, but I wouldn't recommend using GE pistons in a turbo application unless you know what you're doing. There can be advantages to running the higher compression, but you need to understand what else is going on before just dropping them in and turning up the boost.



Boring it out will give you a tiny bit less compression. You're making slightly more space in the combustion chamber with the same stroke. It's not going to be hugely significant, but it will make a tiny difference. Same reasons as specified above and why using different head gasket thicknesses will affect it as well.

Other than the pistons, the rest of the block is pretty close to the same. GTE block has oil squirters, the hole drilled for the turbo oil return all ready, and knock sensor ports tapped for 2 rather than 1.

Yea totally forgot about the head gasket lol good explanation. In my head I can picture and know what's going on, I'm just terrible at putting it to words lol

 

[IndigoMKII]

The height of the pistons or length of the rods should affect compression, whereas the diameter of the cylinders/pistons should affect displacement. I'm definitely not an expert, but that's always been my understanding.

The stroke will also increase displacement.

 

[Slayr504]

The stroke will also increase displacement.

Like I said, I'm definitely not an expert lol. I throw in my $.02 every now and then anticipating a more knowledgeable individual will correct me or add to what I was saying and in turn I learn something new. So thanks for being that individual in this instance :thumbup: