OEM HG Question

csnow

csnow

Matthew 6:33
Apr 5, 2005
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Palm Bay, FL
I am thinking of going the 7M JDM route as my current 7M has over 212 thousand miles on her :biglaugh: Yes, I am trying to save money because I got two kids getting ready to go into braces by summer :aigo:

Since the block and head need to have nearly a perfect finish for a MHG, I was thinking of just using an OEM one. This will allow me to just remove the head (resurface if needed) and put a set of ARP studs on it @ 85ft.lbs and go. Isn't the cause of the 7M BHG due to low factory head bolt torque, not the head gasket itself?

Maybe I am wrong, but I don't see where I would need a MHG staying in the mid 400hp range. The main cause of HG failure is detonation and I don't think that would be a problem with the MAFT-Pro, 550's, Walbro, AFPR, and a Greddy T67 at around 17psi. I know the MHG is only $250, but I don't really want to tear the bottom end apart and send the block off for machining. Even then, the machine shop may not put a finish on it good enough for a MHG. I personally think most of the BHG's seen here and on SF are due to people putting MHGs on substandard block/head finishes when an OEM would have done just fine. Anyone agree, or is the flaming going to begin???
 
supra90turbo

supra90turbo

shaeff is FTMFW!
Mar 30, 2005
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Granted you will get a Toyota gasket... There is nothing wrong with that.
You have the right ideas already. I see no fault to your plan.

BTW: how'd that antenna work out for you?
 
Loki

Loki

The Future is Unwritten
Mar 30, 2005
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You could always look into a Cometic HG, the RA doesn't have to be nearly as low as the other MHGs out there. I'm going to be putting a Cometic into my JDM motor I'm getting, and I don't plan to get the block machined. I'm just going to clean it up really good, and then spray it with Brake Quiet and put it back together with some ARP bolts.
 
Thermactor

Thermactor

Been there, done that
Jun 23, 2005
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Loki said:
You could always look into a Cometic HG, the RA doesn't have to be nearly as low as the other MHGs out there. I'm going to be putting a Cometic into my JDM motor I'm getting, and I don't plan to get the block machined. I'm just going to clean it up really good, and then spray it with Brake Quiet and put it back together with some ARP bolts.
Click to expand...
don't buy into the cometic lie
 
shaeff

shaeff

Kurt is FTMFW x2!!!!
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Thermactor said:
don't buy into the cometic lie
Click to expand...

why not? i'm having no issues with mine whatsoever, and i didnt have my block surfaced. try that with an HKS MHG! :)

-shaeff
 
C

Caplax40

Grand Tourer
Feb 12, 2006
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Okay so I read this since my car is about to go under knife to get the HG tended to. And after reading this, am I correct in saying that I can simply purchase an OEM head gasket from Toyota and install it with some ARP head bolts at 85lbs and be done with it? Surely, it can't be THAT simple.

My car ('90 Turbo, 120k miles, full 3" exhaust, intake, stock otherwise) has never had a BHG and I want to prevent that from happening.

If this is the case, then this is going to save a ton of money. Hello new wheels and suspension mods!
 
Joel W.

Joel W.

Just A Jedi
Nov 7, 2005
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id say if your going to keep your boost under 12-14psi, oem may be ok, i had my OEM up to 20psi on accident a few times already with no issue except ping of course from popped vacume lines..And only for a second.. but with those 550's you probly wont ping so the gasket may be good...

i dont know for how long mine will last as i drive it pretty hard almost daily, anything over 14psi i would go with a metal type gasket. my 2 cents..

edited: as i have no experience with cometics..
 
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Nick M

Nick M

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Sep 9, 2005
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Surely, it can't be THAT simple
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It isnt. The deck surface of the head and block must be flat. It doesnt have to have super smooth finish, just flat. No deep grooves you can hang a finger nail on.

Or you will end up like so many other MA70 owners who "only did the head" or something like that and 4 months later have another thread about another BHG.
 
csnow

csnow

Matthew 6:33
Apr 5, 2005
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Palm Bay, FL
I would say it is that simple if you are staying OEM. I am from a background of V8 high compression powered cars and no one ran MHG's even the low compression supercharged V8s. It is not uncommon for people to want the HG to be the weak link on a race setup. It is much cheaper to replace a head gasket than to replace the bottom end of a motor if things go wrong. I will still argue that under 475 hp an OEM will work fine if the job is done right. A MHG is unforgiving with block and head surfaces and everyone going the JDM route is not pulling the bottom end apart to send the block to be properly decked. This is why people have the dreaded BHG shortly after the job is finished. I guess a rule of thumb could be if your setup requires forged pistons due to high psi requirements then go MHG. And if you are running boost high enough to require forged internals and a MHG, one should not be using piggy backs anymore and should be standalone to have control over timing. If you are running around 1 to 1.2 bar with cast pistons you can stay with the OEM HG and piggybacks. To sum it all up, it appears most people go over board in some areas and skimp in others instead of setting goals and building the setup to meet those goals.
 
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C

Caplax40

Grand Tourer
Feb 12, 2006
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Nick M said:
It isnt. The deck surface of the head and block must be flat. It doesnt have to have super smooth finish, just flat. No deep grooves you can hang a finger nail on.

Or you will end up like so many other MA70 owners who "only did the head" or something like that and 4 months later have another thread about another BHG.
Click to expand...


So if the head is smoothed and the block has no warpage, an OEM will be thick enough and provide sufficient protection from a BHG, then?
 
K

koulee

New Member
Oct 11, 2005
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johnathan1 said:
hmmm, what is the optimum torque spec for the ARP studs, with a factory Toyota gasket?
Click to expand...

I've heard 75 lbs max or you will squish the headgasket.
 
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