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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

#10 rick240zed

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Posted 29 April 2014 - 10:26 AM

I assume I should have them shorten the valves too by .030?

 

 

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.

 

A couple of questions.

 

1. When i read the DatsunZGarage article (http://datsunzgarage.com/p79/) I conclude that however much you shave the head, you shim the towers by that much to keep timing chain, etc lined up, but then you need LONGER valves by the same value. The answers here imply you do not change valve length - :unsure:

 

2. How much can you safely shim the camtowers in a P90? MSA on their site where they sell their camtower shims states it should never be shimmed more than .045" but it seems the general wisdom talks about .080" shaving and shimming.


Edited by rick240zed, 29 April 2014 - 10:27 AM.


#11 Xnke

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Posted 29 April 2014 - 11:49 AM

If you cut 0.080" then you can swap for readily available longer valves and not have cam geometry problems.

If you are only cutting 0.030" you don't need to worry about it, you will just take up the error in the lash pad thickness.

There is a lot of half-information out there. if you are modifying the L engines, get the book and make the annotations where the book is incorrect...they're mentioned all through this forum section.

#12 rick240zed

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Posted 29 April 2014 - 04:21 PM

If you shave your head by .080 what does that make the volume of the combustion chamber?



#13 roger280zx

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Posted 30 April 2014 - 06:33 AM

Watch out with the open chamber, dished piston, 9.5:1, carbs, and pump gas.  There is far more power to be had at 8.5-8.8 running good timing, and you get to keep your pistons.  The open chamber/dished piston combo is notorious for not liking much compression - especially without the aid of 02 sensors and fuel and timing control.  If you are racing and can run good gas go right ahead, but I would caution if your trying to do it with a small cam and 93 octane.



#14 rick240zed

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Posted 30 April 2014 - 07:33 AM

Yeah, I think the head shave is beyond what i need for my street driving. I think i will be just P90 head rebuild without shave (mild cam, rockers and HD springs), and put on a block (flat tops, minor overbore, balanced and polished crank).

 

Any advantage to F54 over N42 for block?

 

I was certain that all 81-83 had F54 but just talked to someone and he was adamant that only turbo were F54. He's wrong on that - right?



#15 NewZed

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Posted 30 April 2014 - 08:07 AM

In this new age of information, with so many people spelling out in detail how to get the most power out of these engines, it's amazing how many new people end up with the same plan, from the same sources, that will provide no real increase in performance, maybe even a decrease, spending money on things that probably don't even need doing.  Maybe the shrinking of the technology interface to phone size has counteracted the increase in knowledge available, leaving most people at the very same place they would be in the 1980's.  Fascinating!

 

rick240, browse through the FAQ's and you'll probably realize that none of what you're planning is really worth spending money on.  Seriously, I'm just trying to help.  You could get an old 280Z or 280ZX engine complete and spend time tuning it to run right, without even cracking it open and probably be better off and save money.  

 

The F54 block was introduced in 1980 for NA and turbo engines.  Don't listen to your adamant friend anymore.



#16 rick240zed

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Posted 30 April 2014 - 01:43 PM

rick240, browse through the FAQ's and you'll probably realize that none of what you're planning is really worth spending money on.  Seriously, I'm just trying to help.  You could get an old 280Z or 280ZX engine complete and spend time tuning it to run right, without even cracking it open and probably be better off and save money.  

 

I've owned my car for 34 years now. It had 75,000 miles when I bought it, and over 300,000 now. I've put in rebuilt 240 engines and used 240 engines - and it is again due for something.

 

So although I could save money by putting in a used engine, I intend to put in the best engine (and drivetrain) yet. And I want to do the major refresh now and not have to need to consider it in 3 - 7 years down the road because I chose a used engine again. I want this one to be as close to new as possible, so with maybe a top end refresh in 10 - 12 years this'll be OK for me to drive when I turn 75 in 21 years :)  Always assuming we can still drive carburated vehicles in 20 years.

 

The F54 block was introduced in 1980 for NA and turbo engines.  Don't listen to your adamant friend anymore.

 

I was pretty sure of that - thanks for confirming.

 

 

But with a carburated P90, is there any advantage to a F54 over a N42 block?






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