Toyota HG design and power capability?

[SupraTurbo1989]

Hi guys. I heard that Toyota had updated their head gasket design a couple times since the 7M came out. Is the newest one the same type of material and quality on the 2J? How much power can the new 7M head gasket from Toyota hold with some ARP's?

The reason I ask is because I will probably be doing the head gasket this winter along with rebuilding the head but I don't have the option of pulling the block and taking it to a machine shop. I have also heard the Cometic MHG is very forgiving and can seal if you wetland the block very smooth since it has a rubberized coating.


I am not sure how true this information is so please forgive me, I probably sound like a total newb.


Thanks
Jeff

 

[airhead04]

Wasnt necessarily the design of the hg, but the torque of the head. Toyota only torqued the head down to about 56ft/tq, when it really needed about 72-80 ft/tq.

 

[SupraTurbo1989]

Wasnt necessarily the design of the hg, but the torque of the head. Toyota only torqued the head down to about 56ft/tq, when it really needed about 72-80 ft/tq.

Hmm, I swear I heard that Toyota changed the head gasket design for the 7M a number of times since it was released.

 

[rakkasan]

the 7M head gasket has always been made of composite material, never metal as the 2J's. It failed because the lack of torque as airhead pointed out

 

[IJ.]

Wasnt necessarily the design of the hg, but the torque of the head. Toyota only torqued the head down to about 56ft/tq, when it really needed about 72-80 ft/tq.

They changed materials way back from an asbestos based HG and that's where the Tq setting became screwed as the Non asbestos HG's need more clamp force to stay compressed.

There have been quite a few "revisions" over the years.

 

[SupraTurbo1989]

They changed materials way back from an asbestos based HG and that's where the Tq setting became screwed as the Non asbestos HG's need more clamp force to stay compressed.

There have been quite a few "revisions" over the years.

So are they good now? I know the factory 2J head gasket can hold upwards of 1000hp. I doubt the newer 7M ones can hold that much but do you think it can do 500-600 without worries? What are the real limitations of the head gasket?

 

[IJ.]

Jz's have a MHG stock so of course will hold far more pressure before failure.

Look at a composite HG as a burst panel, it will fail before mechanical damage occurs (hopefully)

"If" you can keep it detonation free with a perfect tune then 600 is doable but this rarely happens in the real world and one hard rattle will kill it, BUT if you have a MHG with cast pistons that same rattle will break the ringlands but the HG will be fine.

 

[SupraTurbo1989]

Jz's have a MHG stock so of course will hold far more pressure before failure.

Look at a composite HG as a burst panel, it will fail before mechanical damage occurs (hopefully)

"If" you can keep it detonation free with a perfect tune then 600 is doable but this rarely happens in the real world and one hard rattle will kill it, BUT if you have a MHG with cast pistons that same rattle will break the ringlands but the HG will be fine.

So you wouldn't recommend a MHG with cast pistons? So then I wonder why Toyota chose to use a MHG on the JZ motor with cast pistons?

 

[IJ.]

Very different cast pistons + a factory tune = no failure.

 

[SupraTurbo1989]

Very different cast pistons + a factory tune = no failure.

I hate to sound like a newb but can you please explain? It kills me that I see all the local 2J's making 800+hp on un-opened motors, I'm just curious why a 7M couldn't be the same way with just a properly torqued head gasket. I was under the impression the pistons and rods are very similar.

 

[7Matt-GE]

if you plan on modding your car, i would go with a metal head gasket. if you plan on staying stock go with a stock head gasket and torque it down

also don't skimp out on either case. get ARP head studs.

 

[IJ.]

I hate to sound like a newb but can you please explain? It kills me that I see all the local 2J's making 800+hp on un-opened motors, I'm just curious why a 7M couldn't be the same way with just a properly torqued head gasket. I was under the impression the pistons and rods are very similar.

You asked why Toyota specced the cast pistons with a MHG, the Jz uses hypereutectic pistons so they're stronger than those used in the 7M right off, they also have a very safe factory tune where after 75% throttle they just tip open the injectors so there's little chance of rattling the engine.

Now we shift to the 7M, most are "old" so there are piston to bore issues right off, couple this with the mindset that it's a "Supra so I can crank in a pileOboost" on a budget with no proper fuel control or tuning and suddenly you end up with dead 7m's left, right and centre.

You can't treat it like a Jz it isn't, the 7m can work well but it's an unforgiving bitch if you cut corners.

 

[SupraTurbo1989]

So is it not uncommon for people to make good power with a new Toyota HG properly installed with ARP's torqued down sufficiently? What would my concerns have to be if I am running a composite head gasket? I want to eventually make good power(500ish) but it's not in my budget right now to take apart the whole motor to get the block decked.

Currently I am pushing around 13-14 psi on the stock turbo with a DDP, intake and exhaust. Ideally, I would like to push around 18 psi on an upgraded CT26 or bolt-on turbo in the near future but I do not want to be worrying about blowing my head gasket all the time. I am under the impression that the reason for the common BHG is from improper torque from the factory. So taking that into consideration, if I were to install a fresh Toyota HG with ARP studs, what kind of reliability and power capability would I expect?


I apologize if I sound redundant but I just want to be 100% sure! I have been searching the forum all weekend about this but I have not found a definitive answer yet.




Thanks!

 

[87M-GTE]

As far as modded 7Ms go, the HG is rarely the issue.
User error is to blame 99% of the time.

I remember a while back, some guy dyno'd 600s on a stock 7m bottom/hg.

Sam

 

[SupraTurbo1989]

As far as modded 7Ms go, the HG is rarely the issue.
User error is to blame 99% of the time.

I remember a while back, some guy dyno'd 600s on a stock 7m bottom/hg.

Sam

Wow, really? Is that the only person or are there other people who have had great success with a new Toyota HG?

 

[airhead04]

That is a rare occasion. Go MHG and have the piece of mind knowing it more then likely wont blow. obviously if something really bad happens and it blows, different story. But running a stock hg and trying to get to 500+ hp on a dd is not going to end well. Youd have to tune that car almost perfect for it not to destroy that hg. And that means youd have to tune it ALL the time, because everyday has a different element affecting the car. And a MHG can be reused over and over again. Just go MHG.

 

[bombinuass]

That is a rare occasion. Go MHG and have the piece of mind knowing it more then likely wont blow. obviously if something really bad happens and it blows, different story. But running a stock hg and trying to get to 500+ hp on a dd is not going to end well. Youd have to tune that car almost perfect for it not to destroy that hg. And that means youd have to tune it ALL the time, because everyday has a different element affecting the car. And a MHG can be reused over and over again. Just go MHG.

+1

 

[SupraTurbo1989]

That is a rare occasion. Go MHG and have the piece of mind knowing it more then likely wont blow. obviously if something really bad happens and it blows, different story. But running a stock hg and trying to get to 500+ hp on a dd is not going to end well. Youd have to tune that car almost perfect for it not to destroy that hg. And that means youd have to tune it ALL the time, because everyday has a different element affecting the car. And a MHG can be reused over and over again. Just go MHG.

Well I would do that, the only thing I am concerned about is getting the block surface smooth enough to seal properly with a MLS head gasket. Although I heard the Cometic brand is a tad more forgiving when it comes to surface preparation, I am still weary if I can get the block smooth enough with it still in the car.


On the other hand, I have heard that I could buy a lapping block and lap the block myself with it still in the car, but after hours of searching, I have yet to find where I could purchase/rent on of these so-called "lapping blocks".

 

[ForcedTorque]

True Story 1.....I came from the Mississippi/Alabama coast with Noah89T to CHI2K7, and he took the crown as the highest HP MKIII at somewhere close to 450hp @ 5000RPM (wastegate problem) on a stock gasket and ARP's. That car is still running on that gasket to my knowledge.

True Story 2.....I was in Justin727's garage around that same time frame watching him use a rented/borrowed lapping disc. I'm not sure where he got it though. It did not look like a difficult procedure.

 

[IJ.]

Well I would do that, the only thing I am concerned about is getting the block surface smooth enough to seal properly with a MLS head gasket. Although I heard the Cometic brand is a tad more forgiving when it comes to surface preparation, I am still weary if I can get the block smooth enough with it still in the car.


On the other hand, I have heard that I could buy a lapping block and lap the block myself with it still in the car, but after hours of searching, I have yet to find where I could purchase/rent on of these so-called "lapping blocks".

Lapping is a finishing process used AFTER the block/head is machined NOT as an alternative...