Dished pistons for NA?

[NMcKe97]

I just recieved my new pistons and rings from the machine shop for my NA l28. I had to have the walls slightly honed so I required oversized pistons.

I recieved a set from safety pistons with hasting rings. The part number is "SP123 -2 nissan (datsun)81-83 : 280zx 6v 81-83 : l28e eng 2753cc / 86.0 mm"

The set of pistons I got from the machine shop were dished unlike my original flat top pistons and my uncle, who I'm building my car with, said that's how they are supposed to be even though it will lower compression.

Through all the reading and searching I've done I thought that you only really wanted flat top pistons on the NA set up and dished pistons for turbos because of the lower compression.

So my question is, are these the right pistons to be using or am I supposed to have flat tops for my set up.

I've had the head  machined .005" and the block machined, I need to figure out how much material the shop took off the block but it's not much. Im also using a fel pro head gasket which I've heard it is slightly thinner than stock. My uncle said we needed to use dished pistons because of those modifications is this the case?

If I do need to re order pistons what brand should I get or who should I order them from?

Thanks in advance for the help and input it's much appreciated!

-Noah M

 

Edited September 13, 2017 by NMcKe97

[Zed Head]

Which head are you using?  Look between the #1 and #2 spark plug holes, down at the edge.  It will say N42, N47, P90 or P79.

[NMcKe97]

Sorry I got ahead of myself and forgot to mention which year and model I have. It's a 1981 280zx 2+2 with a f54 block and p79 head.

It's a stock engine with no work done on it up until now since I've been working on it. It's been a family owned car its whole life so I know exactly what has or hasn't been done to it.

Thanks for your time.

-Noah M

Edited September 13, 2017 by NMcKe97

[siteunseen]

Tough call.  The 2+2s are heavier so the extra pep from flat tops would be nice.  The stock '81 (I think) 2+2 junkyard motor I bought and tore apart had a P79 with flat tops.  

You don't want to make your helper mad but most folks get flat pistons from ITM, they are all over ebay.com.  Are the pistons already connected to the rods?  If your not looking for a hot rod and I'll say you're not, 2+2 ZXs are heavy, just stay the course.  It may be a bunch of trouble for no noticeable gain.  If you're having fun you'll end up with an earlier and lighter car to build a hot motor for.  

Here's a compression calculator that I've never been able to figure out but you might have better sense than me.  http://www.ozdat.com/ozdatonline/enginedesign/

[Zed Head]

The turbo engine uses dished pistons.  Their catalog shows both engine types but says that they don't have the turbo pistons.  Seems odd.  They might have their part descriptions backward.

https://www.opticatonline.com/part/safety-auto-parts-corp-sp123-engine-piston

[NMcKe97]

It sounds like we are going to find another set that are flat top pistons, definitely will need the extra get up and go for the build as I was already using every ounce of hp she had stock so I definitely can't go backwards.

16 hours ago, siteunseen said:

 

You don't want to make your helper mad....

You hit the nail on the head with that one Siteunseen, he's given me an unbelievable amount of help so the last thing I want to do is cause a problem or stress him out!

Thanks for the link to that calculator, that will definitely come in handy at some point or another. Probably not this build cause I'm to lazy to gather all the numbers and plug them in right now but nonetheless thanks for the tool.

Unfortunately the pistons have already been attached to the rods but I can't have compression drop from 8.8:1 to 7.3:1 so we will be getting the right flat tops. I don't even want to know what the hp output on something like that would be, it sounds awful.

If I had a different head or a turbo laying around with all the other little goodies needed then the dished pistons wouldn't be a problem but unfortunately that's not the case.

I wondered the same thing zed head but the box and website both specify it's for the l28e so I'm not really sure what to think, it'd make more sense if it were an early 280z but what do I know. They imaginably have a reason for it or maybe they are just out of touch with the z pistons, who knows.

I think you'd be modestly surprised to see how the 2+2 drives, I've pulled on a number of cars with more hp including evos, bmws, subarus, and more. Probably has something to do with me knowing how to drive but I'd like to accredit it to the ol' Daty puttin in work!

For now I'm going to stick with the 2+2, it's done surprisingly well for me so far and that's with it being stock. You'll have to take my word when I say I've driven the $^!# out of her and really put her through her paces.

I've nonchalantly removed 100+ pounds of interior from her before and it had a real nice get up and go so I imagine if I really wanted to lighten it up it wouldn't be to tough. I believe I recall people lightening it to 2600lbs or less if memory serves me correct.

I know most people aren't a fan of the 2+2 but I've genuinely enjoyed every bit of it, it has a nice get up and go as well as great steering and handling. I could care less for the cruise control and all the other luxury bs, especially cause most of it doesn't work, but it's nothing I can't remove or fix.

Do you guys want pictures of the build or should I save my time and forum space?

Thanks again for the help, advice, and taking the time out of your day to help me gentlemen, it's very much appreciated, hopefully I can return the favor someday!

-Noah M

[jonathanrussell]

P79 head originally came with flat top pistons and was used for NA ZX cars. I personally would never build a P79 head with anything but flat top pistons. And, most folks who build the P79 head follow a process where they shave the head far more than you have.

Guy can speak to this more....

@Diseazd

[Zed Head]

It's not uncommon to find bad part information out there in the aftermarket world.  I had not even heard of Safety Auto Parts until this thread.  99.999% chance that they just acquired the part specs somewhere and are having them made overseas, for cheap.  Doesn't mean they aren't good, but they're just sending numbers over there and receiving metal back.  Somebody misread a document and put bad info in their catalog.

They call themselves a parts "sourcing" company.  

http://www.safetyautoparts.com/

[NMcKe97]

Thanks for confirming that jonathanrussel, I knew that they came stock but I wanted to reaffirm that you aren't supposed to use dished pistons.

Good to know that my piston to valve clearance won't be a problem, I was slightly worried about that, I'll probably check just to be safe anyways.

Yea when I saw the box the pistons came in I got a little bummed out because it was a brand I never heard of and have never seen anyone talk about on the forums, so the quality was definitely a concern.

Upon more searching I couldn't find much about there quality, didn't read anything bad about them but I'd rather not be the guinea pig and use something tried and true.

I'm now in search for 86mm flat top pistons with .020" overboard(or any overboard at this point). I can't find ANYTHING. I've called my machine shop, ITM, motorsports auto, zcardepot, datsun california, and northern auto parts, all of them are on back order for a few months and wont have anything for 4+ months they said. I found a single .030" flat top piston but that leaves me needing 5 more and at 40 bucks a pop it's not cheap. I also found a engine rebuild kit with .050" over but its 500 bucks and I don't have that kind of money.

It would help me out sooo much if you guys could give me a hand locating some pistons. If you know of a company, private seller, or anyone that might have something please let me know or talk to them, I would greatly appreciate it!

Thanks as always for the information and help guys, you're always very insightful and resourceful!

-Noah M

Edited September 15, 2017 by NMcKe97

[rturbo 930]

Maybe it would be easier right now to use the pistons you have now, and swap to an N42/N47 head.

[NMcKe97]

Unless I'm able to find a good deal on a head I REALLY don't have the money for it, I just got laid off and am looking for new work so at the moment I have no income and a shallow savings account.

If I inevitably have to use these pistons then maybe it was ment to be and I'll be going turbo in the near future, but I don't see that happening.

Thanks for the advice rturbo, I hope that's not the route I have to take but I appreciate the recommendation, I hadn't considered that option beforehand. I'd like to stick with the stock head and compression if possible but we will see what happens.

Thanks for your time, advice, and insight, I sincerely appreciate all you guys helping me!

-Noah M

[rturbo 930]

Hit up the junkyard, and see what you can find. I can't imagine that a head would be too expensive. Or, are you actually interested in turboing the car in the future?

Given your current financial situation, I'm wondering if maybe it would be best to take a break while you gather your thoughts - and funds - before you make a decision. It sounds like there isn't much you can do right now.