Cometic head gasket bore difference

[Young_240_Guht]

Dude, why do they make a 91 and 90 MM bore on the cometic head gasket? I know about the thickness part, but i dont know if i want the 91 or 90 lol, and also, on Horspowerfreaks.com http://www.horsepowerfreaks.co...skets they show Nissan 240SX #273395 and a price, but no specifics...

You guys goin turbo what head gasket are you using. I'm 100% sure I'm going to use cometic, but i dunno what one.

I'm also gonna do some porting and polishing on the head, along with ARP studs, Valve train, and i have 2 exhaust cams, so that will be swapped in. Also gonna remove some of the EGR stuff, along with the intake butterfly mod that is on here *ya, i've been doing some homework, about 4-6 hours everyday after work LOL *And finally gonna turbo it, hopefully with a gt28BB and AMS mani.

ALso while im posting a new thread, this may belong in KA-t, but i plan on getting a SAFC neo, but will i still need a computer tune? I see some people send in there computer to enthalpy, and have a controller as back up. I dont have that kinda money right now, but are both necessary? I mean, if i tune it myself with the SAFC, take it to a dyno at least, that will do the same as ECU tune right?

I'm not forgetting the inj, pump, and WBO2... and a N60 right?

[yellowcar]

umm If you bore the block to 90 you buy the 90 If you bore it to 91 you buy the 91

[Young_240_Guht]

so i cant use 91 on stock bore?

[Dammitboy]

so i cant use 91 on stock bore?

sigh...

[yellowcar]

Well you *can* use a 91 on a stock bore you also *can* wear size 13 shoes if you have size 9 feet.

Before getting into the technical aspect I wonder why a person would do this? Why use the wrong gasket when the right one is available?

Technically it is the wrong thing to do because it exposes the edge of the cylinder creating the potential for a hot spot, reduces compression due to the bigger cylinder area and creates a little pocket around the cylinder for air fuel mixture to hide in.

[Young_240_Guht]

i just wasnt sure of the bore and didn't know if 1MM made a difference.

umm If you bore the block to 90 you buy the 90 If you bore it to 91 you buy the 91

[yellowcar]

Yea you need to know the bore before buying the gasket.If you really want to buy the gasket before you tear the engine down you can look up the stock bore if you are just going to hone the cylinders If you are going to bore it you can just decide now how big you are going to bore it