s13turbohatch

I'm doing my first engine build and decided to build a ka-t. I am clueless on choosing a head gasket size and ive searched for like 2 hours. The parts list is supertech 9:1 comp pistons .020 over bore, eagle rods, clevite main and rod bearings, ARP fasteners. With the block getting bored .020 over for the pistons i'm clueless on what sized head gasket to get. I've been looking at cometic but everyone gives them a bad rep. I'm open to any recomendations for a head gasket. As far as the engine goes its being built for boost. I have a t28 for it but plan on upgrading to an undecided bigger turbo.

jr_ss

Stay away from the Cometic... You'll need a headgasket that is .5mm larger than your original one. I'm not sure what the KA bore is from the factory.

.020in = .5mm

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c-los13

Stock hd are good up 300hp.

90240sx07

ya you would need a 90.5mm headgasket stock headgaskets are 89.5 i would go with the new cosworth if you can afford it or get a cometic til you can save up but since your doing a full engine build id just get the cosworth while your at it there known for there hi performance and high pressures of boost and roughly 170 dollars tunermt on here knows quite a bit about them and also sell them or go to brewedmotorsports.com

rcdad123

what is wrong with the cometic head gasket?

s13turbohatch

Thanks for the info! I like the idea of getting a cosworth i'd rather do it right with a quality head gasket the first time rather than pull the head later. I just looked one up real quick on 240sxmotoring.com, i don't care about the price if i'm getting what i pay for. But anyways the size was 90.5mm bore and 1.1mm thick. And as a few people said before that sounds like the perfect size? I'm guessing the 1.1mm thick wouldn't be a problem but then again i don't know what im talking about with head gaskets.

s13turbohatch

And future plans for the engine are to go higher than 300bhp so oem is out of the question but Cosworth is a respectable trusted brand.

90240sx07

ya the thicker the headgasket the lower your compression will be after its all put together not a huge difference but ya 90.5x1.1 will defiantly work and your welcome for the info good luck on the build

fliprayzin240sx

BS...if the engine is properly decked and matched evenly, you can push over 500hp on a stock HG with some ARP headstuds.

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waxball88

I used 20 over supertechs.
OEM bore felpro
Have beaten the shit out of it, and its holding up great. T3/T4 550cc enthalpy tune. 8.6:1 comp
You don't need one that is 20 over.

Your lack of experience is showing.

This man knows what he's talking about.
I guess this is zilvia.....

As for cometics, you have to look at that dynamic. Cheap asses aren't going to deck the head, and finish the blocks mating surfaces. A metal headgasket, by nature is going to be MUCH less forgiving. You don't have good surfaces you're fucked. OEM style crush gaskets aren't as picky with the sealing surfaces as they press into the material, it WANTS to seal.

jr_ss

I know because that would be a huge variance in HG bore size from .020/.5mm. If he had his cyls bored .020 over, he needs a HG that is .5mm larger than his factory one.

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s13turbohatch

Obviously i don't have any expierence if this is my first engine build... no need to be an asshole. I'm here to figure out from expierenced people what is a good HG and what size i need. I was taking the word from the one guy that said oem will only hold 300hp, and yes my block is getting decked.

waxball88

Sorry i failed to recognize you were the OP.
I'd go with a fel-pro based on my experience so far. You're running a t25, it'll be more than enough, and they are cheap. Can always upgrade in the future unless you wanna just put the chips up and go cometic, in which case just make sure you do it right.

s13turbohatch

I plan on upgrading my turbo in the future and im making sure the mating serfaces on the head and block are perfect when i take them to the machine shop, so im pretty sure ill spend the money on a cosworth now in the building process rather than find problems for any reason later. And as far as the cosworth goes I only looked on one website and the bore was 90.5 on all then you could just choose different thicknesses. This is my first build and im learning things here and there but getting a 90.5 bore kinda makes sence to my knowledge but theres a good chance im incorrect.

90240sx07

you would need the 90.5
stock bore of a kade is 89mm stock hg size is 89.5
so since you bored it out to 89.5mm you would need a hg .5 bigger than that which would be the 90mm hg but 90.5mm should work id ask when you order your gasket or bore it out another .5mm
just trying to clear this up and help you out and give you the theory

s13turbohatch

Yes this is just the explaining I was looking for!! That clears up everything thanks for the help. I may make a build thread but it wont be much different than most bullet proof ka-t builds so I probably wont bother but I know I will have more questions later in the build. Thanks for the info.

Turbo Nismo

I had 3 cometic hg and the last 2 leaked. I'm not going to use cometic anymore, I'll go with a felpro and fire rings on all cylinders with Arp head studs like always.

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jr_ss

If he bored his motor .020/.5mm over, and stock KAs are 89, then he'd be at 89.5. Then ideally he needs a 90mm headgasket. Although I'm sure 90.5mm should be fine.

My only complaint with Cosworth headgaskets, is that they don't have a fire ring built in. Don't get me wrong, they are great headgaskets, but higher HP applications need that ring.

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rcdad123

the shop i used to work at had used cometic head gaskets with everything we built that a stock head gasket cannot handle(unless it was a honda engine that came with a stock metal head gasket). but if we bored out the engine bigger than a stock head gasket, we used cometic head gaskets. we used head studs and a product called hylomar. hylomar is like a spray adhesive that we applied on both sides of the metal head gaskets(even on stock honda metal head gaskets). it`s like copper spray but works way better. we had an sr20 powered 91 sentra that had cometic head gasket. i`ve built an ls vtec that was bored out to 87 mm(stock is 81 mm) that made 618 whp with cometic head gasket. like what waxball88 said, as long as both mating surfaces are resurfaced, cometic or metal head gaskets are perfectly ok, from my experience anyway.

s13turbohatch

I found this on cosworth's website. It seems their HG is pretty good with even sealing, but i will only get that seal with perfect mating surfaces.

s13turbohatch

The sealing almost seems too perfect to be true.

jr_ss

I ran a Cosworth on my last SR setup. Held up fine to my 400hp and daily flogging. Great gaskets for sure.

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s13turbohatch

Ok nice, thats what im going to go with the 90.5 bore 1.1mm thick. Thanks for the help everyone!

RealStreet

As mentioned before there is nothing wrong with the Cometic. If both mating surfaces are prepped correctly (ie decked) then you will be ok. If you blow one at that point chances are you where going to blow whatever headgasket was in there. It's always easy to blame somebody else. With that said the Cosworth unit is very good as well. The Cosworth headgasket is 90.5mm bore already, and Cometic can make it any thickness you want.

AS240

when building my friends ka, we used the factory headgasket with the motor bored .020 over. that was over a year ago and still runs flat out without any problems.
I second what rcdad123 said about the hylomar spray. we used permatex copper on ours but i would most definitely use one of the two.
headgaskets are important and i know for a fact the stock one can handle upwards of 500hp, but if something catastrophic goes wrong with your motor, it's nice to have a weak link. i'd much rather pop a hg and spend the weekend replacing it rather than cracking a cylinder because i bought the strongest possible hg that i could find. that's just my opinion from personal experience.

Nkelley

OP make sure you specify with the machine shop that you are going to be using a metal headgasket, cometic requires a surface finish of at least 50ra for the gasket to seal properly.

s13turbohatch

Thats a good point to have a weak link that if something goes wrong. That pushed me more towards just buying a felpro. I'm all over the place, I hate decisions.

oero_ballin16

im doing my first head gasket replacement, so im not to familiar with these things so bare with me, do you have to remove the fuel injectors and all that? or can it be worked around?

s13turbohatch

I mean you will have to pull the head off, and taking off the intake manifold would only make it easier, And you might as well remove the manifold with the fuel injectors still connected.

kickahlick

has anybody looked into the new tomei mls head gaskets and if im building a ka-t which one of these size gaskets should I use 1.0 , 1.2 , 1.5 they are all 90.0