1976 L28 Rebuild With P90 Solid Lifter Head

[wheee!]

So is going the route of removing the FI and installing an older carb set up better? Or a four barrel carb manifold? I thought the fuel injection would still be better than carbs....?!

 

As for the P90, I am under the impression is is a solid lifter head, unlike the hydraulic lifter P90a head... Or am I wrong? I thought the P90 was similar to the E79 only better?? Excuse my cylinder head ignorance please....

 

edit info from web:

 

 

• Nissan made only three US 280ZX heads from 1981-83, the P79, P90, and P90a. 
  
  - The P79 came on the non-turbo L28s
  - The P90 and P90a came on the 1981-83 turbo ZXs. 

  All three heads used the same valve diameters (44m intake/35mm exhaust), combustion chambers and intake runners. While I don't have numbers, one would have to assume that Nissan designed its turbo heads for one thing: to flow lots of air. The important difference was that the P90/P90a came with square exhaust ports instead of the lined "diamond" shaped ones on the P79. 

  The P90a is identical to the P90 except for it's unique feature of having hydraulic lifters under the rocker arms which no other Z head had. This made for a nearly quiet engine needing no valve adjustment, but could not use high-lift aftermarket cams because of the lifters and was costly to rebuild. P90a replacement lifters were about $50 each, but have been unavailable for years. This made the P90a a great head, but not the best choice for modifying. Keep in mind that the a P79/90/90a on a flattop piston L28 will give 8.8:1 compresion, on a dished piston motor 7.4:1. 

• 

• 
  THE P90 PROFILE

  - square exhaust ports with no liners (like the N42/E88/E31 heads) 
  - .100" deeper chambers than the N42/47 
  - nearly straight exhaust runners and high-quench/swirl combustion chambers 
  - steel valve-seats

  • INTAKE RUNNERS
    The P79 and P90/P90a combustion chambers are deeper than other L28 heads. By making the chamber deeper, it lines up the valve bowls with the intake runners and greatly straightens out the short-side radius "bump". N42/N47 heads have a sharper "bend" as the runner transitions to the bottom of the intake valve. 
  • 
    
  •  
  • FUEL PUMP HOLE 
    Strangely, while the P79 has the mechanical fuel pump hole sealed over, the P90 actually still has it, the ZX power steering pump flange covers it. I'm guessing the same casting dies for the square port N42 were used by Nissan. Why else would they leave the hole there?

 

[TomoHawk]

The bottleneck is still in the small intake runners and the small ports & valves on the cylinder head.  You won't be getting any improvements on the L28 engine until  a performance cylinder head and intake is designed and produced.

[wheee!]

 

• The bottleneck is still in the small intake runners and the ports & valves on the cylinder head.  You won't be getting any improvements until  a performance cylinder head is designed and produced.

 

 

But will the smaller combustion area and better quench with flattop pistons be better than the stock configuration on the 76 N42?

[EuroDat]

Yes the P90 has better quench and the runner design was improved over the N42. Does it make it worth all the extra work to use it on a street driven car? I would think only if the N42 is in worse shape than the P90.

Changing to a P90 head because it breaths better and keeping the stock EFI is not going to give you any real noticable hp gain. You still have the intake, throttle body and AFM restricting everything. The Turbo intake, the P82 will flow a little better than the N/A intake, but you still have the stock ECU holding you back.

If you change the EFI for carbs. A four barrel won't be all that much of an improvement. The L6 runs lean on cylinders 1 and 6 and rich on 3 and 4. The old SU's or tripples would be a better alternative. That would give you the freedom to modify the engine a lot more.

To add to your reseach above. The 280ZX came with the N47 in the early days up to about mid 1980.

Cheers

Chas

[siteunseen]

Some good info here, http://datsunzgarage.com/

[wheee!]

SO I guess the question now becomes, should I leave the engine stock and just do a rebuild and header back exhaust (147,000 miles) or should I modify the engine slightly by going flat top pistons and the P90 head with headers and exhaust?

 

I am seriously thinking of leaving this engine stock at this point unless someone can offer me a better solution for a mild performance build. Triple webbers would be awesome but are extremely hard to come by up here in Alberta. I know I can order a set from a dealer with intake for a couple thousand dollars, but that seems a little steep for a street dd build.

 

I also have the extra L28 engine that I can build on the side after the stock motor is finished. Experiment with it so to speak.

[EuroDat]

If you want to read up on the stock EFI system. There is a guy Paul goes by the name Braap on hybridz did a great write up on it.

http://forums.hybridz.org/topic/95316-braaps-l6-efi-induction-advice-and-tips/?hl=braap

Enjoy. I did.

Chas

[TomoHawk]

The write-up BRAAP did was pretty good and thorough, but it basically says what I wrote in post #14.  It is stil worth reading, though.

[Zed Head]

BRAAP's writeup says a lot more than just a statement about cylinder heads.  That's a gross over-simplification.

 

I think that where people tend to get misdirected on "performance" is in focusing on peak numbers.  There are many ways to increase the maximum power that an engine will produce but, with the stock EFI system, it will probably run poorly everywhere else.  Most of the tuning that is done with aftermarket EFI systems is "everywhere else", to make the car drivable.  Lean spots at certain RPM will make the engine balky and weak at certain times, rich spots will make it stink and might foul plugs.  I have an essentially stock setup, and I rarely get the engine above 5000 RPM, where max power would be.  What makes mine a pleasure to drive, for me, is the way it pulls cleanly from idle at a stop light up to the next shift point, and the way it responds to throttle from cruising at 2,000 - 2,500 RPM.  Or the way it cruises at 3,500 RPM if I want a little more jump when I hit the gas.

 

Almost all of the performance stuff you read is race-focused,which is mostly wide open or closed throttle.

 

Many people say that adding a tunable EFI system to the stock engine parts will add more "performance" than adding parts to the stock EFI system.  Even higher peak numbers.

[TomoHawk]

Yeah, and I think those peak numbers are over a small RPM range too, and a dyno pull lasts only a few seconds, so do you really get relatable information? The dyno test is unlike a drive up a mountain or down a curvy racetrack.  Maybe you could try pulling that 10,000 LB boat instead of a 10-second dyno test.  I like mine at the cruising range (or just a little higher, about 2,700-3,200 RPM) also.  It's nice to be On the freeway and be able to get around slow-moving traffic or a big truck quickly, then back to a nice 60 MPH cruise.

 

We should get Superlen to  tell us about the performance increases and longevity of the increases.

[EuroDat]

Mine is stock except for the GM Hei module and the temp sensor tweak. I have had it on a dino 2 years back at a local shop that builds rally subarus. I have spent the last two years trying to get it back to factory specs. Crazy thing is, it felt great before the dino run.

Since the dino run I have done the injectors, all the injector conectors, fuel pump seals, petronics flame thrower ignition module, petronics coil, checked and calibrated afm, temp sensor tweak and clean all the ecu harness terminals.

With the lightened flywheel, close ratio 5 speed and the 3.7 diff it is so muchmore enjoyable to drive.

Im happy with the "stock" setup and like Zed head rarely go above 5,500rpm.

A lot of people think there engine is producing what it should according to specs, but mostly over the years wear, ecu drift, poor adjustments and simply old aged parts slowly reduce the power that you don't notice it or you bought the car already like it.

In the end you have to decide what you want to do with the car. Read a much as you can without getting lost in the jungle, so to speak. Thats the problem I find with the internet, you read so much that you get confused or read so much contradicting information that you can make your mind up.

Chas

[wheee!]

The sad part for me is that I have never driven a 280Z and have no baseline. I can't compare it to my 370Z!

I just want it to be a fun, safe, spirited driver.

The aesthetic mods like a shaved intake and fuel rail are more for the OCD part of me. I hate a cluttered engine bay.

My big advantage is that I am doing a complete restoration much like Hazmatt has done. I don't need it as a driver and I will take my time doing it right.

Sent from Canadia