Changing Head Gasket On Rb25det

[Skyline1989]

Hey All...

As title says, i need info on head gaskets on Rb25's...

I'm looking to produce between 250-280 rwkws, but i'm unsure if i have to change the head gasket?

Some people say it's fine and you don't need to crack the head open, but i want a reliable 25.

If i do need to change gaskets... what type of gasket should i be looking for? what thickness, without loosing too much compression and driveability?

Help is muchly appreciated

[PM-R33]

Keep the stock one, if there is nothing wrong with it, don't change it.

[Papu]

I'm thinking about the same thing. I understood that if you want bigger boost (over~1,2bar), you need a stronger gasket. Can this be true? Or does it depend on something else?

[EVL-R33]

If you still decide to change your head gasket, get a Cometic 1.2 or 1.3mm by 87mm, you wont lose too much compression if any.. also id recommend getting the ARP head studs, i am in the process of changing mine at the moment..

[PM-R33]

Metal headgaskets are more likely to hold together and not blow out when there is a bit of detonation due to the increased strength from the metal walls around the cylinder, a standard one will usually blow out but will hopefully save your engine. Think about it as the weakest link in a chain giving out first.

The reason many people change to a metal one is due to the larger thicknesses available so they can lower compression. Lowering compression usually means that you can put more timing into the engine on the same boost level without it knocking, in essence usually making more power. However with lower compression you will sacrifice some bottom end power and boost response.

Hence if you don't need to replace it with a thicker size, then just replace it with a standard one. There is a lot more to this and i cant be bothered writing it all, but unless you are putting through a lot of boost and timing with over 300kw, there is no great reason to swap to a metal one unless you want to lower compression or if you have a strong built engine and know the metal gasket will still probably let go before a rod.

[Papu]

So I don't need to change the head gasket yet as the power figure for next year will be about 260-280rwkw, thanks for the advice. I was about to do it this winter while the car is standing in the garage.

I'll change the metal gasket later, at the same time with the forged internals when we are going after more power.

[joeyjoejoejuniorshabadoo]

how much bottom end loss are we talking?

i'm thinking about doing this as my head is coming off to fit an oil restrictor and custom oil return lines

[Unkn0wn]

On 11/26/2008 at 7:22 AM, joeyjoejoejuniorshabadoo said:

how much bottom end loss are we talking?

i'm thinking about doing this as my head is coming off to fit an oil restrictor and custom oil return lines

i am digging up an old thread, but im also wondering the same thing - as golbys sell the 1.3mm gasket and head bolts together it must be a common combo?

Edited March 4, 2019 by Unkn0wn
cant spell

[GTSBoy]

Don't change the head gasket unless you're aiming for serious power.  Just put ARP studs in one at a time.

[Unkn0wn]

ill be removing head to do the oil restriction and rear head drain.. so ill do all the power upgrades ahead of time.

 

[GTSBoy]

 

Well, if you're pulling the head off then you HAVE to replace the gasket.  So you might as well put a decent MLS one in there.  But be aware of the surface prep/finish requirements.

Also, don't put a thicker HG in there if your aim is to reduce the compression.  That's '90s thinking.

[bilk06169]

ive pulled mine off and put a cometic mls gasket in and arp bolts and now it leaks water into cylinder 2.  both attempts to use mls and the same thing water in cylinder 2, both head and deck straight. 

now putting a genuine gasket back in. moral to the story, get head and deck machined to mirror finish quality !!

[Dose Pipe Sutututu]

24 minutes ago, bilk06169 said:

ive pulled mine off and put a cometic mls gasket in and arp bolts and now it leaks water into cylinder 2.  both attempts to use mls and the same thing water in cylinder 2, both head and deck straight. 

now putting a genuine gasket back in. moral to the story, get head and deck machined to mirror finish quality !!

you can use a Tomei headgasket, as they're o-ringed - same with the Nitto ones. Cometic requires you to deck the block and the head so they're perfectly flat.

Nothing wrong with Cometic, but it has it's requirements. I generally use and recommend Tomei ones.