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N42 block P90 combo question.


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#1 srgunz

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Posted 22 January 2013 - 12:37 PM

I currently run the 75 N2, N2 combo that has the 8.3 C.R.

I was reading about the heads but did not see this specifically.

I do have a P90. If I shave that 80 thou. and shim, can I get another

full point of C.R.? (9.3) I am thinking as well that Its about time to upgrade

to a head with the steel seats for the non leaded fuel.

I am running Mikunis as well.

Thanks.


Steve
72 240Z, second owner.
L28. Mikuni's. 5speed. MSD. Koni's

#2 skirkland1980

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Posted 22 January 2013 - 01:00 PM

If you shaved the P90 and installed flat tops you will increase compression.


:1983 280zx turbo, L28ET, all stock internals, 96 saab 900 intercooler w/2.25/2.50" piping, 3" mandrel bent exhaust, megasquirt II v3.0, 440cc injectors, walbro gsl392 255lph fuel pump, aeromotive regulator, -6 supply lines, custom fuel rail, accel 8.8 300+ ignition wires, MSD 8202 coil, homemade boost controller, Garrett TC4305 turbo, 70mm throttle body, Godzilla BOV, Turbonetics wastegate, custom intake, Cooling Mist H2O/meth injection, 20psi boost, all stock body, stock interior and wheels, TH350 trans 4000 stall with B&M 'street stick' shifter, dunlop tires 205/65/R15. best 1/8 mile of 9.40@81 mph on the slipping Jatco tranny and stock intake w/ 60mm tb.

:1983 280ZX NA. L28E, 5 speed, MS2 V3.57, 440cc injectors. Otherwise completely stock.


#3 brianZortiz

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Posted 22 January 2013 - 02:19 PM

check out "zn42p90" on youtube, he runs the n42 block and p90 head combo in Japan. I forgot his compression numbers, but its high and he has a really fast car. 


1973 260z GC coilovers 200f/225r tokico illumina. 3.9 LSD+extra clutches. ZG flares. upcoming engine L28et SDSem46f.
1972 240z no engine. in storage. Just waiting.

#4 srgunz

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Posted 22 January 2013 - 03:24 PM

If you shaved the P90 and installed flat tops you will increase compression.

Correct, but not going to change out pistons.

Bottom end is in great shape. Has no leaks and

does not burn any oil.


Steve
72 240Z, second owner.
L28. Mikuni's. 5speed. MSD. Koni's

#5 skirkland1980

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Posted 22 January 2013 - 05:13 PM

You need about a 40cc combustion chamber to get that compression ratio. I'm not sure what cc the heads would be after .080" mill.


:1983 280zx turbo, L28ET, all stock internals, 96 saab 900 intercooler w/2.25/2.50" piping, 3" mandrel bent exhaust, megasquirt II v3.0, 440cc injectors, walbro gsl392 255lph fuel pump, aeromotive regulator, -6 supply lines, custom fuel rail, accel 8.8 300+ ignition wires, MSD 8202 coil, homemade boost controller, Garrett TC4305 turbo, 70mm throttle body, Godzilla BOV, Turbonetics wastegate, custom intake, Cooling Mist H2O/meth injection, 20psi boost, all stock body, stock interior and wheels, TH350 trans 4000 stall with B&M 'street stick' shifter, dunlop tires 205/65/R15. best 1/8 mile of 9.40@81 mph on the slipping Jatco tranny and stock intake w/ 60mm tb.

:1983 280ZX NA. L28E, 5 speed, MS2 V3.57, 440cc injectors. Otherwise completely stock.


#6 Xnke

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Posted 22 January 2013 - 08:21 PM

Don't bother. If you're not going to change out the pistons, just shave an N42 head 0.030" and you'll be at 9.5:1.

 

The P90 head is good, but it really should have flat-top pistons to have any kind of advantage over the N42.

If you want a bolt on solution, that will work. But why raise the compression on a good running motor? The P90 head is a deep, modified wedge chamber. It's designed to work optimally on a flat-top piston. Running it on the dished piston in the turbo motors was done specifically to lower compression, but even running it as a flat-top motor would have been perfectly acceptable for the stock boost levels.

 

Bottom line, unless you're willing to change out the pistons for flat-tops, don't go to the trouble of modifying a P90 head. Cut an N42 or N47 thirty thou and you'll be at the same compression, with a LOT less time, trouble, and money.


Edited by Xnke, 22 January 2013 - 08:26 PM.


#7 srgunz

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Posted 23 January 2013 - 12:36 PM

 

Bottom line, unless you're willing to change out the pistons for flat-tops, don't go to the trouble of modifying a P90 head. Cut an N42 or N47 thirty thou and you'll be at the same compression, with a LOT less time, trouble, and money.

 

Ok, that sounds like a better plan. I assume I should have them shorten the valves too by .030?

I will put the p90 away for now in case I do pick up a flat top later on.

Thanks


Edited by srgunz, 23 January 2013 - 12:36 PM.

Steve
72 240Z, second owner.
L28. Mikuni's. 5speed. MSD. Koni's

#8 Xnke

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Posted 23 January 2013 - 04:32 PM

No, you don't shorten the valves, you shim the towers up 0.030". There are 0.015" thick shims and 0.020" thick shims available.



#9 srgunz

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Posted 25 January 2013 - 09:11 PM

Time for another donation to Hybrid Z for all the helpful info.

Just reading Tony's replys is worth the $$.  :icon10:


Steve
72 240Z, second owner.
L28. Mikuni's. 5speed. MSD. Koni's




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