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New from UK seeking P90 knowledge

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Hey I’m From UK and come seeking knowledge from the hybridz melting pot.

  I have an L28 and a 260z box I’m trying to fit in my C130 and from googling it seems here is the best place to be for z related help.

 I’ve hit a stumbling block with my L28’s head. It seems I somehow found a P90 with exhaust emissions liners fitted. N42’S are hard to find here across the pond, so I’m hoping You guys can point me in the right direction.

  Is it worth removing the liners and porting or should I just keep holding out to find a good N42 or P90 without liners when a unicorn poops? 



Edited by mrroboto
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Welcome to the forum!


The square ports are what I'm used to seeing over here, but understandably different on the other side of the world.


I've been told removing them is quite tedious and not much benefit in the past. I'll let those more knowledgable chime in though.

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There are some threads here about liners vs no liners. The biggest concern is typically if they're loose, especially if you have a turbo. If they're in good shape I think the effort to remove them isn't worth it for the negligible gains you'll see. I've read from most people with more experience than I have that there's nearly no reason to remove them.

My two cents: if they're in good shape just run the head as is until you find something more suitable or have the budget to do the work at a proper level that will actually yield some benefit unless you're going to a turbo build. P90 with flat top pistons will give you higher compression than a stock N42/N42 combo with dished pistons anyway, and you'll have the benefit of the improved combustion chamber design. Even if you're trying to go for a high compression NA build with the P90 it'll require a lot of work to the head regardless due to needing to shave the head and cam tower shims to compensate. 

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I have a motor with an N47 with liners removed, and was ported/polished that the previous owner built. I've done some research on the matter, and my understanding is that removing the liners is a bad idea. I believe the reason is that the  ports end up too big, and the air velocity ends up too slow, which hurts flow, although you really research that for yourself further for the details. My understanding is that a head with exhaust liners can be ported and polished for some decent gains while keeping the liners in place, and for a more serious build, you'll want to use a head that never had the liners. 


Very interesting that you have a P90 with liners, I'd expect that to be a P79. 


Here is one thread that briefly discusses the matter. The consensus: a head with liners removed is junk.



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Thank you guys, I really appreciate the information in your replies and you taking the time to help.

   Just to elaborate. I’m not making a turbo build just NA and looking to make a usable 200-220.

 Both the machinist I use and trust and his friend who has professionally built and raced Z’s  both said to try and find out more but in their opinion I should just look for an N42 as that’s the route they have always taken. (Never used a P90 before)

  That’s proving harder than it sounds and even though I have seen some available in Japan for sale by the time I ship and tax gets added I’m probably better trying to source one from the USA. 

  So if I were to use the P90 for now as you guys suggest, is it worth taking that .080 off to reach 10:1 then just add a cam, adjustable tensioner and adjustable cam wheel to dial in?

 Presumably all this parts can transfer to a N42 or square port P90 at a later date?
 I hadn’t read about cam tower shims before so I’ll have to research that. 

 Thank you again and please keep the knowledge coming, it’s of great help 

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