Head Gasket Differences
 

What did Toyota do to reduce/eliminate the BHG problem that the 87-91 Turbo Supras have? Did they just increase the bolt torque or did they add more bolts?

According to this site, the MKIV and 1JZ motors came with metal head gaskets.
http://www.jza70.com/articles/engine...omp_chart.html

That would be one factor.
The common head gasket failures with the MKIII's are due to lack of torque from the factory.
They really should have recalled them!
It does not take that long to tighten up the headbolts, but instead many MKIII's seen the junkyard instead of what could have happened....


EDIT: by the way, is there a reason why you posted this in the MKIV section?
Were you trying to get the feedback from the MKIV'ers and their take on all this?

I've done a bunch of searching and couldn't find any good answers. The 1990 Supra I recently bought only had 65k miles, and it ran fine for several months. The previous owner said he had retorqued the head bolts ~40k miles, and I believe him. At ~72k miles the HG started leaking slightly into cyl. 6 and a tiny bit into #2. Pulled the head off right away-no heat damage. The head bolts were right ~70 ft. lb.


So, I think I had a case of some previous HG damage from the orig. low torque, but retorquing did not prevent the BHG.

Since it appears that the Mark IV's don't usually have the problem, I just wondered what Toyota did differently. Looks like they kept the same 14 bolts but raised the torque--and maybe used a better HG.

Well having a higher torque upon original installation and torquing the head gasket down after many many years is not exactly the same thing.

I would think that the MKIV's have better head gasket sealing due to the MHG and I would think that toyota placed it in between a flat and smooth head and block (what some individuals don't do when using MHG's).

It is said that detonation is one of the biggest reasons for head gasket failures also.

I think the winning formula to for the ultimate sealing would be to get the block and head milled to a low RA (roughness average) of 40 or less and then use Permatex Brake Quiet in the can form and spray that onto the metal gasket, then install the gasket and the head and tighten it to 85-90 foot pounds of torque.

To be honest with you, the reason why so many have bad luck is because they don't do things the right way and take short cuts.
That applies to many other jobs and not just the BHG repairs.

Good post/info, Tony!

Another piece of (related) info is that the oem head bolts don't hold past about 37psi of boost. Oem-sized ARP's do a little better than that, but many Mkiv Supras running over 40psi of boost have gone to 1/2" ARP studs.

Btw, I'm curious: what does the Permatex Brake Quiet do? Fwiw, I'm aware of a number of 1000hp+ 2jz-gte's built without it, using the oem headgasket, with no headgasket leaks/failures. Will an organic compound like that stand up to 1000hp+ combustion forces? Also, will it make the head more difficult to remove later?

Thanks you, sir. :) I try.
Yep, I have heard that. That is something that is a trend amongst the MKIV guys...I just don't hear of many MKIIIers doing that (except for one...maybe others keep it as a "secret"...).
Well it helps seal up the gasket. See, many don't get their block milled to a low enough RA to use a MHG as suggested from the MHG manufacturers. It sort of fills in and helps with that situation (but can only do it to a degree).

This one guy that has a 1000 HP 7M started using it, and others have tried it too with good results. At first I was sort of unsure of what to think of it since it is was relatively new thing, but so far, nothing but good results have come of it as more and more people are using it.
Seems to be the most sure way of getting the gasket to seal up right--has the highest success rating.
I don't think so...not as far as I know or have ever read or heard of.

Glad we got to discuss this with you, Phil.
Had I moved this thread to the MKIII section (where the BHG area is heheh), we would not have traded posts. ;)