head gasket thickness

Soo the leggys starting to eat coolant, figured it was a leak or bad rad cap but the pushed out dipstick and oil everywhere is kinda confirming the HG, correct? anyways, im running 25d heads with a 251 block, anyone know the thinnest cometic headgasket im able to run without running into valve clearance problems? or would I be better off just running oem sti?

OEM STi gasket is pretty thin itself. You could clay the motor with an OEM STi gasket and see how much clearance you have.

Factory thickness is 0.030" and the thinest gasket cometic makes that will work is 0.027'

 

What year pistons are you using in the 251 block?

 

Guys running EJ251 motors (lower end and heads) with 0.027" gaskets yield about 11.5:1 compression. The pistons in that motor are very close in design to the 95 EJ25D pistons, so I don't think you'll have any clearance or overly high compression issues running a 0.027' gasket

251 block and bottom end, out of a 99 lgt, factory sti headgaskets are 0.030"?

Yeah the cometic ultra thins are a bit thinner than oem mls, very slight compression bump...probably not noticeable though, mls is cheaper and you know are reliable. Cometic are reliable as well I used those on my hondas every time and I was running 10.2 compression on a b18...I punished that little go-cart and never blew one.

 

I own a 2.2 so I have never had hg problems with Subaru...

the sti headgasket on my engine measured .045 via dial caliper and i measure it at a place that the gasket didnt quite get to the outside of the block, basically measure how far the head is away from the deck

251 block and bottom end, out of a 99 lgt, factory sti headgaskets are 0.030"?

 

Okay, so you have EJ25D pistons then. And no, the OE gaskets for the motor from your car are 0.030" in thickness. Factory compression is an actual 9.7:1 and will go up to maybe an actual 10:1 compression.

25d pistons in a 251 block? i thought they just put the 25d heads on the 251 block and pistons? you can definetly tell its got more pickup then my 25d did.

25d pistons in a 251 block? i thought they just put the 25d heads on the 251 block and pistons? you can definetly tell its got more pickup then my 25d did.

 

The 99 "25D" is actually a 251 with 25D pistons & heads.

Even the gasket should be that of a 25D so if you're using a 251 head gasket on that engine, the compression ratio will be a little more since 251 gaskets are thinner.

 

Using a 96 block w/97-99 25D heads & a 251 head gasket will be a high compression engine with a nice N/A powerband (might have to check for valve clearance doing this). The peak TQ on a 96 25D is unreal where it starts in the rpm (EARLY).

i thought a 96 block and bottom end was very similiar to the 251 block and bottom end?

i thought a 96 block and bottom end was very similiar to the 251 block and bottom end?

 

No, they are almost completely different.

 

The 96 block uses thicker head gaskets, has high compression type pistons that come up above the deck (Phase 2 pistons are below the deck), thinner rods & rod journals, & it has the thrust bearing in the 3rd position instead of the 5th as a Phase 2 block would have.

 

If anything, the only thing they have in common is the 99mm bore.

Everything else is different, even the block casting (Phase 2 blocks are tougher than those of Phase 1.)

25d pistons in a 251 block? i thought they just put the 25d heads on the 251 block and pistons? you can definetly tell its got more pickup then my 25d did.

 

It really has no more grunt whatsoever... The difference is that the transmission is smoother, and the motor is MUCH smoother. The whole setup is just smoother.

 

The 99 "25D" is actually a 251 with 25D pistons & heads.

Even the gasket should be that of a 25D so if you're using a 251 head gasket on that engine, the compression ratio will be a little more since 251 gaskets are thinner.

 

Using a 96 block w/97-99 25D heads & a 251 head gasket will be a high compression engine with a nice N/A powerband (might have to check for valve clearance doing this). The peak TQ on a 96 25D is unreal where it starts in the rpm (EARLY).

 

Correct. 99 25D is actually a 251 lower end with 25D pistons and top end.

 

But, 99 25D motors do not use the same head gaskets as the 251 motor. They use the same ones as the rest of the 25D's do.

 

a 251 lower end with 96 25D pistons and a cometic 0.027" head gasket and 97-99 25D head would be the ultimate NA build. I was planning on it until I sold the 96 GT and the 99 OBL to a buddy...

 

Clearance would be fine.

 

Yes, the torque is definitely different but honestly it makes no difference... There really is no noticeable difference in the way a 96 GT and a 98 GT 4EAT drive.... The only real difference is between the 4EAT and 5MT, honestly.

 

i thought a 96 block and bottom end was very similiar to the 251 block and bottom end?

 

No. Not at all. It is the same as EVERY single other 25D from 96 to 98. It just has different pistons. But, the pistons are VERY similar to the pistons of the 251.

 

No, they are almost completely different.

 

The 96 block uses thicker head gaskets, has high compression type pistons that come up above the deck (Phase 2 pistons are below the deck), thinner rods & rod journals, & it has the thrust bearing in the 3rd position instead of the 5th as a Phase 2 block would have.

 

If anything, the only thing they have in common is the 99mm bore.

Everything else is different, even the block casting (Phase 2 blocks are tougher than those of Phase 1.)

 

All correct, except that Phase 1 25D pistons do not actually come up above the deck. They are right there though. There is zero +/- deck clearance. I've measure.

so cr on a 99 25d is equal to that of a 25d correct? the only thing different is the 251 being a lil stronger than the 25d block? if I want high CR would 22e heads be the absolute best way to go? you yeild an easy 11.5 CR with that build if im not mistaken, which i have been aot recently lol.