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Compression: heads, blocks and pistons.
- Thread starter Mr.G
- Start date
There are two different versions of the 280 engine as fitted to the two ZX models. early cars ie 79 to 81 had engines with dished pistons and an N42 head casting number on the head near No1 plug. Later cars ie 82/83 had engines with a higher compression due to use of flat top pistons and a P90 head casting. so check your head to see what you have got.
Mr.G
Club Member
Thanks Pmac,
It was registered in 79 so I guess its dished pistons with an N42 head. Is it quite complicated to upgrade to the P90 head and flat top pistons? Does that compression make a huge difference??
I'm really showing my ignorance here but its the only way for me to learn. <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'>
It was registered in 79 so I guess its dished pistons with an N42 head. Is it quite complicated to upgrade to the P90 head and flat top pistons? Does that compression make a huge difference??
I'm really showing my ignorance here but its the only way for me to learn. <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'>
STEVE BURNS
Club Member
Hi George
if you go to the links section and log onto zhome.com scroll down to the documents section and click onto the index of technical articles and you will find 3 write ups explaining heads and head combinations.don't ask me to explain it all as my technical ability consists of picking up the phone and asking the bearded one in Essex <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=''>
if you go to the links section and log onto zhome.com scroll down to the documents section and click onto the index of technical articles and you will find 3 write ups explaining heads and head combinations.don't ask me to explain it all as my technical ability consists of picking up the phone and asking the bearded one in Essex <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'>
Mr.F
Inactive
Affectionate bearded one in Essex says - this needs some maths! You have to take the effect of all components - bore diameter, stroke, piston type (to dish or not to dish), combustion chamber volume (ideally measured, not read from a book) and compressed gasket thickness in order to calculate your compression ratio. You only need to do this if you are building a serious engine from scratch.
By the way, the P90 head is the "turbo" head and has all the valves moved up by 2mm to give a bigger combustion chamber (reduce compression). The UK cars with P90 heads have "flat-top" pistons to restore compression to normal for a 280ZX. In very simplistic terms, if you want a 2.8 with high compression, use N42 head with flat-top late pistons (great for normally apsirated) and if you want a 2.8 with low compression for turbo, use P90 head with dished pistons. Note that increasing bore size also increases compression ratio. More maths - I can highly recommend "Auto Math Handbook" by John Lawlor (HP Books 1020) if you want to get into this properly......
By the way, the P90 head is the "turbo" head and has all the valves moved up by 2mm to give a bigger combustion chamber (reduce compression). The UK cars with P90 heads have "flat-top" pistons to restore compression to normal for a 280ZX. In very simplistic terms, if you want a 2.8 with high compression, use N42 head with flat-top late pistons (great for normally apsirated) and if you want a 2.8 with low compression for turbo, use P90 head with dished pistons. Note that increasing bore size also increases compression ratio. More maths - I can highly recommend "Auto Math Handbook" by John Lawlor (HP Books 1020) if you want to get into this properly......
Now that God has spoken on the subject we lesser mortals can feel suitably humbled.
I am in fact taking God's advice and building a high compression 280 motor using a late bottom end with flat top pistons and a N42 cyl head. This will be installed later this year in my trusty(and slighly scruffy) Fairlady 280ZX. I will run the late injection system on this motor.
You can have a test run in it, but dont hold your breathe. I dont ever complete anything on schedule.
Adding a six branch manifold might also be on the cards.I would also like a weber big body throttle kit but they are a bit pricey, perhaps i will just leave the air filter off to increase air flow! Peter Mac.
I am in fact taking God's advice and building a high compression 280 motor using a late bottom end with flat top pistons and a N42 cyl head. This will be installed later this year in my trusty(and slighly scruffy) Fairlady 280ZX. I will run the late injection system on this motor.
You can have a test run in it, but dont hold your breathe. I dont ever complete anything on schedule.
Adding a six branch manifold might also be on the cards.I would also like a weber big body throttle kit but they are a bit pricey, perhaps i will just leave the air filter off to increase air flow! Peter Mac.