what is ra value?

[bowtiebuba]

what is ra value, i dont know weater to get comitec or titan, i was reading something on ra value, but dont know what it is what head gasket should i go with

 

[Turkish]

RA value is a roughness standard. In other words how smooth the surface in your case the head needs to be in order to properly install said head gasket.

 

[TONY!]

Roughness Average

The lower the number, the smoother the surface -- many think of it the other way around (it is not like sand paper).

 

[Justin]

cometic is the most forgiving. its like a 40 Ra or lower

 

[TONY!]

http://www.supramania.com/forums/showthread.php?t=2324&highlight=cometic

I have another post about this topic here (currently post 12).

 

[stratoayu]

haha i was going to say roughness average, but i didnt wanna get flamed and say i was wrong but good to know that i was right at least... looks like ill graba cometic when i do a mhg...

 

[bowtiebuba]

i read that other post very informational, so should i go with the comitec then?

 

[Justin727]

Yea sure Cometic is great!

 

[Reign_Maker]

Cometic and a set of ARPs are great! On my last Supra I buitl, I went with a Cometic 1.3mm mhg and ARP head bolts torqued to 78 pounds... I went with Cometic because they had the most lenient ra, and they have a really good reputation... Not to mention that Luis is running 40 pounds of boost on a cometic mhg... So I fealt comfortable with them... Also, I wasnt planning on pulling my motor to lap the block, so I needed a forgiving gasket...

 

[zurud]

What is the rivet for on cometic?

 

[Reign_Maker]

It's a multi layered metal head gasket... The rivets hold all three layers together... SOME of their mhg's you have to remove a rivet, mine didnt need that... All you have to do is place the mhg on your block,a nd make sure that when the head sets down, it doesnt crush a rivet... If it is going to hit one, then punch it out...

 

[stratoayu]

so is there any way to measure an ra value ? cuz it would be nice to know if im going to need to pull the block or not...

 

[Blue87T(Dan)]

The block will need to go to a properly equipped machine shop to measure the RA.

 

[bluemax]

Surface roughness is accurately measured using a machine. Most good machine shops will have one.
There are comparison panels too, but they're used for estimating surface roughness.

 

[stratoayu]

dammit, so what your saying is, i might as well jut pull the block...