Help Choosing the Right Headgasket

[Rustys14]

So the headgasket on my ca18 recently went out and after shopping around and doing some research I have narrowed down a few different options on what to run.

Option 1: ARP studs and a OEM Nissan Headgasket

Option 2: ARP studs and a Tomei 1.2mm MLS Headgasket

Option 3: ARP Studs and a Tomei 1.0mm MLS Headgasket

Now my questions lie in what would be the best setup for me and my needs with the car. The head will be sent off to be cleaned and checked (right now it seems that the head does not need to be decked) but I don't plan on doing anything to the bottom end other then cleaning the mating surface as best I can.

This brings me to my first question, which is weather or not the Tomei MLS headgasket will have trouble sealing since the block is not being machined? I know there are issues with Cometic gaskets when the surfaces have not been machined but my research has not shown any issues with Tomei gaskets in this department.

Now my second question is that provided the Tomei gasket will be fine, what thickness should I run? According to Tomei the 1.0mm gasket should yield a 8.7:1 CR while the 1.2mm gasket should yield the factory 8.5:1 CR on my factory 83mm bore engine. Should I take this opportunity to slightly increase the CR of my engine?

Finally my third question is if the 85mm bore Tomei headgasket will be fine to run on my 83mm bore engine? I know this is a noobish question and it seems that a lot of people have done this without issues, but it just doesn't seem right to me. I've never really looked into whats normal for headgaskets before so I'm not sure if running a larger bore gasket is normal or not so I just need some peace of mind before ordering.

The car will be mainly used for HPDE and Friday at the track events at VIR and Summit Point as well as some normal driving around town on weekends. For now the engine will remain stock but future plans are for a S15 t28, 550 cc injectors and a PFC. Thanks in advance for any help!

[Rustys14]

Bump, anyone?

[Dillinja666]

Tomei 1.2mm, but order after you hear back from the machine shop that they didn't have to shave the head. Also if they resurface the head find out how much they remove. It its 0.3mm you will have to get a 1.5mm gasket to keep stock CR.

[KAT-PWR]

Talk to machine shop, how much are they taking off?
Determine desired CR
Order thickness to achieve desired CR

[Rustys14]

Thanks for the replies. I know to compensate for the amount taken off if the head has been decked. My main concerns are should I shoot for the factory CR or bump the CR up slightly to help with spool when I go for the larger turbo and if the Tomei MLS will have any issues sealing since the block mating surface is not being machined? Also the Tomei headgasket only comes in 85mm bore, will this be an issue?

[Dillinja666]

No that small of a bump in CR will not be noticeable in spool and will just hurt your timing to control knock later on.

also stock pistons are 86mm not 83. the 87mm gasket will be fine.

[Rustys14]

No that small of a bump in CR will not be noticeable in spool and will just hurt your timing to control knock later on.

also stock pistons are 86mm not 83. the 87mm gasket will be fine.

Thanks, that was the answer I was looking for. As for the bore question, factory bore on the CA18 is 83mm according to my UK FSM. I think you are confused with the ka24de which is 86mm if I'm not mistaken.

[Dillinja666]

Yeah didn't see the CA18 in the main post. Same info still applies, 84mm gasket fits the 83mm bore.

[Croustibat]

No that small of a bump in CR will not be noticeable in spool and will just hurt your timing to control knock later on.

also stock pistons are 86mm not 83. the 87mm gasket will be fine.

It is a CA, bore is 83mm.

If you are going big turbo, get LESS CR right from the start. The important thing about HG is how clean and flat ALL surfaces are. If the block is not flat either, then you are just throwing money in the bin.

[Rustys14]

It is a CA, bore is 83mm.

If you are going big turbo, get LESS CR right from the start.

Response is more important to me then power because of what I want to use the car for, which is why I was thinking about upping the compression a bit. I'm not going to be running a huge turbo or a lot of boost so I figured a small bump would be fairly safe. Based on some of the responses I think I'm going to stick with the factory CR though.

[pacotaco345]

Have the machine shop deck the head just so you have a completely flat, clean surface for the headgasket to mate to. When I built my SR I didn't touch the deck of the block but I had the head decked for good measure even though the motor had never been overheated too badly, with a 25 ish year old motor its just best to be safe IMO. Also, I just cleaned both surfaces very well and slapped the hg on with no issues. Tomei gaskets are the business. Also if you're stock 83mm bore get the 84mm hg and 1.2 thickness. Should get you close enough to stock after the head has been milled.

[Kingtal0n]

It is a CA, bore is 83mm.

If you are going big turbo, get LESS CR right from the start. The important thing about HG is how clean and flat ALL surfaces are. If the block is not flat either, then you are just throwing money in the bin.

This, and, the inverse also applies to some extent, low-rpm small turbo daily drivers should get higher compression ratios for better fuel economy.