At what point should one look at upgrading the head gasket?

[Bazooka]

I am starting to piece together the bits needed to build a 4AGTE 20V engine. Simply this engine will be a 4AGE 100kw bottom end using the crank and rods, 4AGZE factory pistons and rings, a Blacktop 20V head and RB25 turbo. This will not be any dyno mule and I am not looking for insane power. I was wondering while purchasing a rebuild kit whether it would be wise to upgrade the head gasket for something other than a factory Toyota item. From what I have read the Toyota gasket should be just fine but I am interested to see what others have to say about it. I am also considering ARP head studs and conrod bolts, would these items be overkill or an essential part of the build?

[BeRad]

I would, while the head is off you may as well put a metal gasket on, saves any future hassells

[MRMOPARMAN]

not sure bout the headstuds, but i would be putting them in for piece of mind, the conrod bolts are a must
i would be choosing the headgasket on the desired thickness as opposed to brand. the toyota ones are fine, they've been used a million times before on turbo builds, but do they come in a thickness freindly to your desired comp ratio? if not your only choice is aftermarket.

[Bazooka]

i would be choosing the headgasket on the desired thickness as opposed to brand. the toyota ones are fine, they've been used a million times before on turbo builds, but do they come in a thickness freindly to your desired comp ratio? if not your only choice is aftermarket.

And what thickness should I be looking for?
Whats the formula to work to?

[MRMOPARMAN]

well it depends on quite a few things..
deck height on the block
combustion chamber volume
headgasket thickness
piston compression height + - depressions/doming etc
rod length
crank stroke
bore size

all this will determine what comp ratio your gonna get. your comp ratio will depend on how hard you want to lean on the motor (tuning wise) off boost drivability and max boost etc..

generally the thinner the headgasket the better. ive got a comp ratio calculator i made that i could can mail ya, im not sure how id go about putting it up here on the forum (and yes its been tested, quite accurate) it needs all the info to be spot on to be accurate though..

its good in your case that your doing the 4age, most of the info is readily available..

[Bazooka]

Yes I understand that all those things can effect the compression ratio but I was hoping that by listing all the parts I intend to use (all factory items) that someone might be able to say what would be best to look for. The compression ratio calculator sounds like a good thing (ill send you a PM) and I will look into that as well.
I actually ordered a Cometic head gasket and ARP head stud kit for a 2JZGTTE engine today. They listed 51 and 74 thou (i think it was) for this enigne. Dont know if it will be the same for the 4A but will check tomorrow. I believe that they do not do a gasket specifically for the 20V either. Does this matter in my case?

[Bazooka]

Well I bit the bullet and ordered a TRD metal head gasket for the 20V. This is apparantly 0.8mm think. Should arrive with the rebuild kit from NZ in around a week.

[-GT-]

There was some discussion regarding the trd mhg and turbo application recently, a quick search should bring it up. In regards to your desired compression ratio, the gze pistons with blacktop head/cc will alter the comp ratio far more drammatically that 0.4mm of gasket; have you checked what sort of comp ratio that combo will give you?

I'm pretty sure gze pistons in 20v has been done a number of times already so the info should be readily available with a little searching, but definately something to confirm. Then if need be you can go thicker or thinner with the gasket to lower or raise the comp ratio a little if you want.

Generally, as you're not going ballistic with boost/power, the factory gasket will be as sufficient as aftermarket, proper prep is just as important.

Edit: here you go;
http://www.toymods.net/forums/showth...657#post501657

[Bazooka]

Yeah I read that post earlier but it never says what the compression ratio is with this setup. Once again it is all speculation and no evidence.
No matter as I will be getting the TRD gasket and the factory Toyota item in the same shipment. I can decide which one I need before they even turn up.

[-GT-]

I meant that was the thread i referred to in my first sentence, not to imply it would confirm what your compression ratio would be with gze pistons. And btw, it's not speculation in that thread, it's common sense and theory regarding how the head gasket can change the compression ratio, it just doesn't have actual calculations. The only speculation in that thread is from the person who says 'she'll be right' once or twice in contradiction to advice he'd been given...

I still recommend you do some research on what your comp ratio will be with your piston/head combo.

[The Real Roadrunner]

is the blacktop open or closed chamber design?

cheers
linden