what h/g should i buy
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http://www.horsepowerfreaks.com/price/Toyota/Supra_86-92/Cometic/Engine/Head_Gaskets
There are different types of Cometic HG's, what do they all mean? (and I mean the MLS normal, and MLS standard)
There are different types of Cometic HG's, what do they all mean? (and I mean the MLS normal, and MLS standard)
Matt - stock 7M block and head surfaces have imperfections. That's why Toyota used a composite HG...it will "squish" to help fill those imperfections. Toyota saved $$$ by not making the 7M block/head surfaces very smooth.
A MHG is a different story. It is multiple layers of flat precision steel with a vitron coating to help seal the block/head sides. Flatness and smoothness is critical to a MHG for it to seal properly. The good thing is once thay do, a MHG can take much higher boost levels. The MK IV is an example...Toyota used a MHG on the 2J...the block and head are much smoother. That's why they can take huge amounts of boos.
If you don't want to pull the block, (and I don't advocate this) you can strip the factory coating off a MHG and use a spray sealer on the clean MHG to help fill the imperfections on the block. Get the head surfaced to the proper RA spec...it's off anyway.
A MHG is a different story. It is multiple layers of flat precision steel with a vitron coating to help seal the block/head sides. Flatness and smoothness is critical to a MHG for it to seal properly. The good thing is once thay do, a MHG can take much higher boost levels. The MK IV is an example...Toyota used a MHG on the 2J...the block and head are much smoother. That's why they can take huge amounts of boos.
If you don't want to pull the block, (and I don't advocate this) you can strip the factory coating off a MHG and use a spray sealer on the clean MHG to help fill the imperfections on the block. Get the head surfaced to the proper RA spec...it's off anyway.
With the smoothest finish my shop could give me using Diamond tooling I still ended up with a mild BHG after a 30 psi pull on the dyno, part of this might have been the Permatex used during assembly.
Last build I used a HKS Stopper Dry with my Lapped surface bumped the compression up and it survived a 32psi overboost without a sign of leakage so what JDub's saying about surface finish is 100% correct!
My car is an extreme case and more than likely you can get away with less prep.
Last build I used a HKS Stopper Dry with my Lapped surface bumped the compression up and it survived a 32psi overboost without a sign of leakage so what JDub's saying about surface finish is 100% correct!
My car is an extreme case and more than likely you can get away with less prep.
GotToyota? said:
Yes it does! The only thing to think about using the stock HG is plans for boost...they are good to about 14 psi or so. If you are happy with that, the stock HG is a good choice.
One other factor in this discussion in favor of a MHG. Our aluminum head and iron block expand at different rates. This causes a "scrubbing" effect where the surfaces mate...you guessed it...the HG. A composite HG will deteriorate over time as a result. A multi-layer MHG will "give" between the layers to cushion this effect....they last a lot longer and are less prone to failure.
GotToyota? said:
Maybe-
Make sure the block deck is flat.
The Toyota is much more forgiving than a MHG, but it has limits also.
I attemped to fix a BHG, and after all the work the toyota HG only sealed for a few minutes! turned out the block deck was not flat and had enough imperfections so that the OEM hg could not seal.
I am not saying in your case it wount work, just providing personal experiance.
Your head will probably be warped, make sure that you get that checked and might as well rebuild while it is apart.
Ij touched on a important point.
"How do you get all the grit out of the engine"
You must remove all the old gasket from the block deck and at the same time keep all the crap from entering the oil/water/cly.
That was a concern when I did the HG the first time. When I pulled the engine after the HG failed and opened the oil pan there was a good amount of shit in it that may have caused a problem down the road.
Sorry for the long post, just providing my own experiance to help you with your decision.
Ste ve
so lets say i get my head lapped to the 50 RA speck for the cometic. and the bock deck is staight but is at say.. 60 or 70 RA. would it still hold? and has anyone ever checked to see what the stock RA is? i want to avoid disassembling my bottom end.
againstdawall06 said:
So go with a composite headgasket, it'll still hold 400-500 HP if you tune carefully and use arp hardware. It's either that, or take a big chance, and if you're anything like me that's not cool to always be worrying about whether or not the headgasket will hold!! Do it right the first time!
I got both the block and head decked, however since i was unable to actually find a profileometer to measure the RA, so to sleep better at night i went ahead and lapped the block anyways!
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