2x head gasket

[Guest Anonymous]

Does anyone know if I 2x the Nissan head gasket to lower the CR, enough for decent psi boost 5-9 psi, in order to prevent blowing my engine through the hood. Has anyone done the math or could would the CR that I will have, and what I should have?? I am using my rebuilt 77 L28E, with P90A head and 280zxt parts and I/C. I do not want to have two engines for the same car esp. since this is almost a new engine. ANY help will be apprecaited

Thanks Mark

[Lockjaw]

HKS offers a head gasket that is 2mm thick, which is roughly the thickness of two factory head gaskets. You should be able to get one from NOPI or TOP END.

 

I am not sure I would recommend two stock ones to gether. The HKS one is supposedly reusable too.

 

What pistons does your engine have? If they are dished, I doubt you need a thicker head gasket, if they are flat tops, I would recommend the thicker gasket.

 

If you have a good intercooler, then it may not matter what piston head gasket combo you run.

 

I have flat top forged in my turbo engine, and they are about 10 thousandths down in the bore at tdc, and my P90 head has been shaved slightly and I use the stock head gasket and I can run 18 psi with my hybrid on pump gas.

[Lockjaw]

http://nismoparts.safeshopper.com/7/cat7.htm?482

 

Try this one for head gaskets too. They have a 2mm thick one. Not cheap though. But neither is the HKS unit.

 

I am sure I did not drop that in there right, I am not a computer geek. Sorry.

[Guest Anonymous]

I should have flat tops but I have not taken the head off because the car is a daily driver and drives soooo sweet right now. Is the stock head gasket only 1mm thick??? Thanks Lockjaw and all you guys for all your help so far

Mark

[Lockjaw]

Yeah I believe I read that in one of the Nissan hotrod books. That would be its compressed thickness BTW.

 

Unless you went to a ZX shortblock, I am kind of thinking you have dished pistons. I am not an expert on this, but I know for a fact that the Zx engines with a P79 head were flat tops. Surely someone could tell from you block type. I think F54 is for flat top. Not sure about that.

 

Either way, if you had dished or flatop, I doubt the thicker head gasket would hurt you. Ultimately you may be able to run more boost at the expense of a little response off boost.

 

But it is like Corky Bell says, if you don't have boost, you don't have that huge torque increase to look forward to, and hence, no fun.

 

 

You may be able to pull out a plug and scope out the piston top and tell, or stick something in thru the spark plug hole and check for a lip on the edge of the piston. I am thinking of something like a heavier zip tie or something that won't scuff things up, like say a coat hanger. The dish is pretty pronounced.

 

Ah what the heck, boost it and see what happens, its only money right?

[Kennysgreen280zt]

with the dished pistons and P90 , your compression is already at 7.4 or so to 1. do you really want to go lower. your car will be a dog off boost. personally I would stick with what you got. If you have the stock 77 pistons watch out for detonation. I had 4 broken ring lands when I pulled my 75 apart after having an overboost and lack of fuel if you watch the A/F mixture and watch the boost you should be alright.

~Kenny

[Lockjaw]

ENGINE CASTING CODE

L24 ('70-73 240Z) #P30 (flattop pistons)

L26 ('74 260Z) #P30 (flattop pistons)

L28 ('75-80 280Z) #N42 (dished pistons)

L28 ('81-83 280ZX) #F54(flattop/dished pistons, siamesed cylinders

 

Here is the block info numbers I have found. According to what I saw, the f54 block with a p79 head is the only one with flat top pistons, all other L28 engines had dished pistons.

[Lockjaw]

http://geocities.com/zgarage2001/heads.html

 

Try this link for more info. It has some good stuff on it.

[Guest Anonymous]

Thanks guys I have a P79 head and F54 block, and I am planning on using 280zxt parts for both oil fuel and timing. But I am really worried about the CR being too high for stock pistons to get decent boost 5-7psi

Thanks Mark

[Tony240ZT]

Looks like you'd have flat top pistons, but CR is only 8.52:1 I would say it's safe to add pleanty of boost to that. Like you've heard, just watch your air/fuel ratios and all will be well.

[Lockjaw]

If you have flat tops, which I am going to assume you do since you have the proper block and head to have them, I would suggest you get the 2mm thick head gasket.

 

There are a couple of differences between the stock turbo piston and the flat top you have, mainly in the location of the ring pack. Generally on an NA engine, the ring pack is closer to the top of the piston than a turbo one. I also thing the stock turbo piston has a beefer pin boss than the NA.

 

Just be very careful with detonation. You won't have much wiggle room at all with that NA piston. You should probably see about an intercooler as well. If you are really worried about it, put a stock turbo intake manifold on it with the pop off valve in the back, and that will save you from any boost spikes. You should be able to run 5 to 7 psi with the thinker headgasket. Keep it full of 93 octane, and put a better fuel pump in the back. Those nissan pumps don't do well with extra boost. Cartech makes a good one called a peirburg or something.

[DAW]

Sounds like you're starting with an F54 ZX engine, 8.8:1. That's a bit high for static c.r. on a turbo engine but you can do it if you intercool it and limit boost. Volvo does this on their "low pressure" turbo engines. This would be a great auto-X engine. As pointed out above, the turbo pistons ring lands and rings are different and they are stronger, with drilled holes beneath the oil rings instead of long slots like the na pistons have. DAW

[Lockjaw]

Yeah, I forgot about those slots. DAW is correct about those. Both turbo and NA in the ZX use a chrome ring, and they seal well, but they are kind of brittle. The factory fuel injection can hanlde about 10 to 12 psi max with the stock turbo.

 

I would really recommend an intercooler for your application. It would really help as far keep detonation in check. You should be fine for a stock boost level with or without a thicker head gastket. Get a good boost guage installed.

 

One of the things that happens to people when they first get a turbo and start messing with boost is they like the power increase they get as they turn up the boost, so they keep turning it up, beyond the limits of their engines and fuel injection. Just be conservative, the stock turbo will continue to make additional power up to about 15 psi or so. You will want to turn the boost up higher, trust me.

 

Mine has worked its way up to over 20 psi, and I just keep leaded race gas in it all the time now since I don't drive the car very often. Once you experience that sort of thing, turning the boost down makes your car feel like a pig. NOS is like that too. I guess it is kind of addictive.

 

Good luck, and be careful.

[Guest Anonymous]

Thanks for the help I do have a Volvo I/C and I am getting gauges: Air/Fuel and Boost. Thanks for the concern and I will control the urge to boost it too high I donot want to ruin a rebuilt engine. I will follow you guys instructions on the project.

Thanks Mark