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Head/piston combos


Zellthetunerr

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Ok. Time to make myself sound stupid. I have a 1983 280zx N/A F54 + P79 and flat tops. Now, I plan to turbo this thing, but with the stock compression, it’s going to be detonating like crazy. A universal solution that a lot of people recommend is a 2mm head gasket from HKS. 
 

  Others say that this will affect quench and make detonation worse instead of fixing it.
 

And also people say to just get dished pistons from any L28ET and use the stock head gasket. But others say that this will ruin the quench/squish and not utilize the combustion chamber design of the P79/P90 properly. 
 

I have found bits of information here and there but nothing to clarify it completely to the point that I know the next step. 
 

it IS easier to get a turbo engine…. If you can find one. Which there isn’t one near me. I’ve tried looking. 
 

I need help clarifying what has worked as for running boost without detonation. My application is a street car that I can have fun with. Not a drag car. So I look to push 11-15 psi. Nothing too crazy but enough to have fun with. 

 

Thanks for all your help. I look forward to learning more…. 
 

 

Zell

 

Edited by Zellthetunerr
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Dished pistons never have any "real" "quench".  The turbo engines aren't quench chambers.  "Quench" or "squish" is a word that is usually undefined and unmeasurable.  Usually determined by eyeball.  There's a theory, combustion gases squirting and swirling around, piston tops being cooled, etc.,  but I don't think that you'll find anything anywhere where anyone has shown that they compared "quench" to non-quench in an L engine and saw an effect.  Most of the discussions center around the old "engineers did it it must mean something".  No offense to anyone intended here.  If someone has data that would be cool.

 

While you're researching, look for stuff on the exhaust port liners and turbos.

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@NewZed. Thanks for the reply. So I CAN throw a 2mm head gasket and push boost/tune? Or is there a lot more to it than just that? According to the 'L series engine calculator' , I can lower the compression to ~ 7.8 if I use the 2mm head gasket. Which is pretty low, pair that with the head cooling system mod that I plan on installing from Godzilla Raceworks, aluminum radiator, Isuzu NPR intercooler, I should be good for the amount of boost that I'm pushing. Right? Maybe not, maybe I'm not searching the right topics. Anyways thanks for your .02

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If you install a thicker head gasket then you will change the cam timing. My preferred way of dealing with that is to also install an adjustable cam timing gear, then property timing the cam, which you should do regardless.

 

Agreed with Madkaw and NewZed. How about simply running what you have now, then adapt if you want more later? I run 8.5:1 static cr on 20 lbs of boost but it's a heavily modified engine, lightly ported head, and custom cam, all done by Rebello.

 

Regarding exhaust port liners, you should be aware that there is a risk of trashing your turbo that if a liner breaks and releases FOD into your turbo. There are people who ran them with no issues and some that had problems. It's a bit of a gamble. The liners can be removed but it's a lot of work. There are a couple of YouTube videos on the subject.

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21 hours ago, NewZed said:

Dished pistons never have any "real" "quench".  The turbo engines aren't quench chambers.  "Quench" or "squish" is a word that is usually undefined and unmeasurable.  Usually determined by eyeball.  There's a theory, combustion gases squirting and swirling around, piston tops being cooled, etc.,  but I don't think that you'll find anything anywhere where anyone has shown that they compared "quench" to non-quench in an L engine and saw an effect.  Most of the discussions center around the old "engineers did it it must mean something".  No offense to anyone intended here.  If someone has data that would be cool.

 

While you're researching, look for stuff on the exhaust port liners and turbos.

 

I think advancing chamber design is probably a combination of numerical and finite-element methods thanks to computing, and a bunch of empirical testing (R&D) at the OEM's. The high fuel efficiency standards really put a lot of pressure on engine manufacturers in the last two decades to up the static CR and get every ounce of efficiency they could. That coupled with real-time knock sensing (had not seen this on NA motors in the 90's) has really pushed the envelope on how high manufacturers are willing to push CR on pump gas. All this to say, I agree and its proprietary 🤣

 

I don't think us laymans understand it well enough speak intelligibly on all the variables at play, and how we would design something. I have seen RB26's routinely running 9:1 and modest boost, which I could never reproduce on an L-series (I tried...blew two L24 blocks in the process). Couldn't precisely tell you what makes the difference. Still, if someone out there has experience in this, would love to hear!

 

PS: the F54 turbo block I am building for the street car will run 8.2:1, and around 22psi. Im going with an air-to-water to reduce the IC plumbing to help with lag. On the head, chamber polishing, deburring and smoothing out the transitions (including excess plug threads) should help a bit too. OH! and pic the right spark plug temp. 

Edited by AydinZ71
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@Dat73z
 

Was OK at 8, started detonating at 16 even with severe ignition timing retard. I did not have a good means of verifying knock (no sensor), but I was able to tune it successfully at 12. Unfortunately, it only lasted 6mo like that. The rings eventually wore and had terrible blow-by. I blamed very high chamber heat as a result of high static CR and boost. It was not catastrophic in that case, literally just wore it out. 
 

My next motor was an OEM L28et which I ran at 16psi boost for years without a problem. Super low CR (7.4:1 I think?), and the turbo pistons have the rings mounted down lower from the crown vs NA. 
 

Getting the L24 to boost with the L28 manifolds, oil pan and independent EFI was not difficult. 


PS: the other blown L24 was catastrophic. Was at el mirage dry lake bed trying for 150mph, and blew 2 of 6 pistons (naturally #5 & 6). Boosted on 4 remaining just to get home. Max she could do was 60mph. That one I blamed on a poor tune. This was 20 years ago and I was just a young kid screwing around. Learned a lot though! 

Edited by AydinZ71
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@madkaw @rossman 
 

All great responses, truly appreciated. Yes, I have seen that the exhaust port liners can come apart and go straight into the turbo. I will look more in depth on those videos that show the process of removing them. As for how much boost I’m running, it could be that I’m just a numbers addict and won’t know what it actually FEELS like to run 10 psi. My uncle has a 300zx z31 2+2 with a straight pipe. It sounds mean and is really fun to drive. I like to drive it but I KNOW that my car is going to be faster. 500 lbs less and a few more horses. Maybe I will try that before going crazy on boost. Thank you to all. 

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35 minutes ago, Zellthetunerr said:

I have seen that the exhaust port liners can come apart and go straight into the turbo.

Have you personally experienced it or know somebody who has?  There is a lot of talk of this happening but I'm unsure if it is common or more internet myth than anything else.

 

I think this and this are good discussions on the subject.  The only people in the threads, who I trust for good, sage advice are John Coffey (RIP) and BRAAP.   Both were admins and general zcar gurus on HZ for many years.

Edited by rossman
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10 minutes ago, AydinZ71 said:

What I have heard from the old timers is the criticism was overblown. 

Agreed, but I have to admit that I may be a little biased. My son's 1981 280zx that we are planning to turbo has only 89K on the engine and appears to be in very good shape.

Screenshot_20220324-193046.png.f1aa984a9c0836cb50107f21a8c9df33.png

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I think the liner issue for a turbo is fairly isolated. I have noted that there is a difference in casting quality from early liner heads and later ones. Look at a early n47 compared to a MN 47 or p79 . 
I have personally removed the liners from a MN47 and I see no way they would come out unless they disintegrated . They are extremely hard to remove . The later years have better casting supports for the liners to sit on and much better casting in general.  

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@rossman

 

no, there isn’t much of a Z craze here where I live. Just a bunch of Hondas with loud exhausts, unfortunately. Me and my uncles are the only Z owners around town. Even if it was a better casting, it’s still a gamble I’m not willing to take. So I’ll find ways to remove them…. How has this affected your exhaust port flow/ flow performance? See any changes with or w/o liners?

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On 3/25/2022 at 7:00 AM, Zellthetunerr said:

How has this affected your exhaust port flow/ flow performance? See any changes with or w/o liners?

We plan to run it with the liners.  Given the lack of solid evidence, except the one noted in the linked posts above, I think the risk of one of the liners breaking up and trashing the turbo is low. 

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I DID find a P90 head for sale (and for really cheap 🤩) but it’s really far away and I’ve texted the guy and tried to contact him. Nothing…. That really sucked because it was used but it was cheap.  so no worrying about the liners at all and a better cam for turbo. But since the guy doesn’t respond I guess I’ll have to either keep looking or make a trip to the local hardware store and get started.

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