Mitsubishi Lancer Evolution Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
675 Posts
Discussion Starter · #1 ·
Hi guys, going to fit a set of forged rods to my X over the winter and the supplier has recommended Cosworth 1,5mm head gasket. Is this the right thickness as I understand they come in different thicknesses? Cheers, Ken
 

·
Registered
Joined
·
11,115 Posts
Yep, OEM unless you need one for an overbore.

OEM gaskets have always ruled the evo market.

Also, you are doing pistons with those rods I hope? Please don't try to do just rods.
 

·
Registered
Joined
·
675 Posts
Discussion Starter · #7 ·
Yep, OEM unless you need one for an overbore.

OEM gaskets have always ruled the evo market.

Also, you are doing pistons with those rods I hope? Please don't try to do just rods.
Over here the "specialists" are divided over whether you should automatically fit pistons with rods...... Some say the new pistons won't fit correctly in used bores, others disagree?
I'll be checking them for sure, any doubt and forged pistons will be going in!
On the head gasket, nobody over here uses oem? Don't know why not....
My supplier says to use HKS 1,5mm, any thoughts?
 

·
Registered
Joined
·
15 Posts
Over here the "specialists" are divided over whether you should automatically fit pistons with rods...... Some say the new pistons won't fit correctly in used bores, others disagree?
I'll be checking them for sure, any doubt and forged pistons will be going in!
On the head gasket, nobody over here uses oem? Don't know why not....
My supplier says to use HKS 1,5mm, any thoughts?
It really depends on the condition of your cylinders. Many times people get away with just honing them. But if there is any irregular wear, going over is recommended, if not, required if you want longevity. I don't know how robust the stock pistons are, but it seems counter-intuitive to crack open an engine only to replace the rods.
 

·
Registered
Joined
·
561 Posts
Over here the "specialists" are divided over whether you should automatically fit pistons with rods...... Some say the new pistons won't fit correctly in used bores, others disagree?
I'll be checking them for sure, any doubt and forged pistons will be going in!
On the head gasket, nobody over here uses oem? Don't know why not....
My supplier says to use HKS 1,5mm, any thoughts?
Mine's 1mm oversized, oem wasn't an option :)
 

·
Registered
Joined
·
675 Posts
Discussion Starter · #11 ·
Cheers guys, still none the wiser! Oem sounds good, but what about Cosworth or HKS stopper type? Improvement or not.......
 

·
Registered
Joined
·
2,068 Posts
Cheers guys, still none the wiser! Oem sounds good, but what about Cosworth or HKS stopper type? Improvement or not.......
I know this is an old post, but....

Some things to think about that no one seems to be bringing up at all.
The reason for different thickness head gaskets has to do with whether or not a head or block has been decked (milled or shaved).

The idea is to keep the head the same distance from the top of the block.
There are two reasons for this, CR and quench area. The 4b11 is a quench head.
Therefore the piston is in close proximity to the head at TDC.
So there are two issues to address. During compression, if the quench area is increased, detonation is more likely due to reduced turbulence in the combustion chamber. During the exhaust cycle, if quench height has been reduced, then the piston has the possibility of striking the head at high rpms due to rod stretch.
The consensus seems to be that Absolute minimum height is .036 or .9mm with steel rods. Otherwise contact can occur. The maximum varies between .040 and .050 depending on who you talk to. Obviously better fuels can run a larger quench due to better detonation suppression. But after .050 you lose the benefits of a quench head altogether.

So stock quench height is .040or 1.0 mm.

The other factor is rpm. If you are staying at stock. You could push the quench down to .9mm for better pump gas performance. As you increase rpm, rod stretch increases as well. So the minimum quench height grows to avoid contact.

So when choosing a head gasket you need to consider mostly the bore diameter and your overall assembled piston to head clearance. CR should not be a deciding factor in head gasket selection, that is determined by piston, rod and crank and chamber shape.
 

·
Administrator
Joined
·
24,202 Posts
I know this is an old post, but....

Some things to think about that no one seems to be bringing up at all.
The reason for different thickness head gaskets has to do with whether or not a head or block has been decked (milled or shaved).

The idea is to keep the head the same distance from the top of the block.
There are two reasons for this, CR and quench area. The 4b11 is a quench head.
Therefore the piston is in close proximity to the head at TDC.
So there are two issues to address. During compression, if the quench area is increased, detonation is more likely due to reduced turbulence in the combustion chamber. During the exhaust cycle, if quench height has been reduced, then the piston has the possibility of striking the head at high rpms due to rod stretch.
The consensus seems to be that Absolute minimum height is .036 or .9mm with steel rods. Otherwise contact can occur. The maximum varies between .040 and .050 depending on who you talk to. Obviously better fuels can run a larger quench due to better detonation suppression. But after .050 you lose the benefits of a quench head altogether.

So stock quench height is .040or 1.0 mm.

The other factor is rpm. If you are staying at stock. You could push the quench down to .9mm for better pump gas performance. As you increase rpm, rod stretch increases as well. So the minimum quench height grows to avoid contact.

So when choosing a head gasket you need to consider mostly the bore diameter and your overall assembled piston to head clearance. CR should not be a deciding factor in head gasket selection, that is determined by piston, rod and crank and chamber shape.
Good write up!

I always try to stay north of .040" quench.
 
1 - 15 of 15 Posts
Top