1976 L28 Rebuild With P90 Solid Lifter Head

[wheee!]

Hi!

 

I am going to be rebuilding my 76 L28 this year and would like to know what pitfalls to be aware of in the process. I am planning on using a P90 solid lifter cylinder head and flat top pistons. I would like to end up with between 10:1 - 11:1 compression. We have 94 octane fuel in my area.

 

This will be a daily driver for my wife and will not be raced or tracked. Aftermarket Exhaust headers will be used and probably a Pallnet fuel rail with 14mm injectors.

 

Thank you in advance for your tips and help. This forum is full of very helpful people!

[Zed Head]

Most of the guys that have built engines will say that the slight bump in CR, and the headers won't improve performance much at all, on their own.  The CR increase will make the engine more likely to knock, even with 94 octane (does Canada use the same octane rating as the US?).  The stock exhaust manifolds are pretty good.  The P90 head might flow a little more air than the other heads (the square unlined exhaust ports), but not much.

 

The fuel rail and the injectors certainly won't do anything at all for performance.  You'll need to find some injectors that match the stock injectors almost exactly or you'll screw up the ECU's fuel control.  The aluminum Pallnet rail will probably help with the heat soak though, so that's an improvement.  But you can do that with the barbed injectors.

 

Most of the changes you're planning won't add much over stock, and will cost more money and complicate things.  What are you hoping for?  A rebuild with stock parts would probably get you the best running and most dependable engine, using the stock EFI system.

[wheee!]

I would like to see a reasonable gain in HP & torque with a slightly higher CR, but I am not looking for huge gains. I know the stock configuration with N42 head has a lower CR mostly to combat emissions during the production era. The higher quench and better flow of the P90 head should make for a small gain in performance I would think. The flat top pistons I thought would raise the CR enough that all I would need is Premium fuel in order to avoid detonation. 

 

The P90 is in need of a milling and I was assuming that I would be able to take off .080 without too much of an issue. I am not sure if the head has been milled before, but I will confirm that before re-milling. A thicker head gasket could solve any issues there I would assume.

 

The fuel rail is more to clean up the engine bay than anything else. I like the look of the shaved intake and Pallnet fuel rail. The 14mm injectors are so I can use the low resistance Audi style 14mm injectors that have the same harness connections. Performance there is not really a concern and I would hope that the stock FI computer could manage that.

 

Having said all of that, I am starting with two complete '76 L28's with N42 heads and all accessories, so I have two of most everything. The  solid lifter P90 is coming from a friend who has a spare early 5 spd and 3.90 R200 for me as well.

 

In the end I would like a spirited driver that has a small bump in performance over stock.

[madkaw]

I think your plan falls short with the stock ecu. As stated above, changing to 14mm injectors and having an engine that will run differently than the stock might not bode well with stock tuning . Not sure about the thicker gasket idea? Going with the P90 for better quench area and than defeating that with a thicker gasket? Consider an aftermarket ECU and tune away!!!! 

Headers for the wife? I would opt for a performance exhaust from the manifold back and keep it quieter to keep her quieter-.

Seriously though, for your plans the header might be waste. Good luck

[wheee!]

I think your plan falls short with the stock ecu. As stated above, changing to 14mm injectors and having an engine that will run differently than the stock might not bode well with stock tuning . Not sure about the thicker gasket idea? Going with the P90 for better quench area and than defeating that with a thicker gasket? Consider an aftermarket ECU and tune away!!!! 

Headers for the wife? I would opt for a performance exhaust from the manifold back and keep it quieter to keep her quieter-.

Seriously though, for your plans the header might be waste. Good luck

 

Thanks for the input!

 

I am not familiar with the stock ECU (I actually have 4 of them now, ). I was under the impression that the larger cc injectors will operate at the factory pressure/volume based on the ECU output. The advantage being that later on I might be able to upgrade the engine without having to replace the fuel rail/injectors (for a megasquirt system for example). Which aftermarket ECU should I be considering? I run UpRev tuning on my 370Z...

 

Thicker gasket was in relation to having to shave the P90 head down and adding the flat top pistons. I was trying to stay around 10:1 compression and assumed I would need a thicker head gasket or have my pistons machined to avoid valve collsions/too high compression. Again, I plan on running 94 octane in the motor when it's done.

 

Headers for the wife? Ha Ha! Funny thing is I put the HKS and berk exhaust on the 370 and now she hates the sound... (I love it). But the exhaust headers were to clean up the engine bay/cylinder head area and gain a few HP. My wife drives sports cars and is used to over 300HP so I wanted it to have a little more oomph and headers are usually an easy gain for cars. Performance exhaust will of course be part of the plan but I may slip a small Cat in there to eliminate any fuel smells from the exhaust. A 200 cell unit should do the trick and keep the sound down a bit too. She is aware the 76 Z is going to be a little louder than her Turbo Veloster...

 

Thanks for the excellent feedback guys! I am learning a lot on this forum!

[madkaw]

I think you are 'hoping' that the ECU handles these changes and adds HP, it might just turn out to be a headache. If you are familiar with tuning you might consider Mega Squirt or another to maximize your upgrades. Not too much that I have read that has gone your route with stock ECU and brags success, but maybe you can be one of the first. It is 40 year old tech!!

Assuming header bolt on means HP is probably wrong. I would actually think that sticking with stock exhaust would keep the stock ECU closer to a proper tune.

I think your formula p90/flat-top= (+HP), but you won't be able to tune it to it's optimum which will cause frustration.

There is a member here that is creating a plug in ECU for your year, but it hasn't materialized yet. I have documented a MS install here and on Hybridz.      

[wheee!]

So would you recommend sticking with the N42 head, swapping to flat top pistons, and keeping the stock exhaust manifold as the best route to go? Small increase in compression and no changes to the EFI?

 

I still have an extra L28 that I can use the P90 on later if I go all LD28 crank and overbore on....

[EuroDat]

Like Steve and Zed Head already mentioned. Reasonable HP gains and standard old basic ECU don't mix. The ECU doesn't compensate much and basically the only tweek you can do is the temperature sensor.

You will spend a lot of money and get very little results. It could turn out to be such a dog to drive that the wife refuses to drive it.

The standard N42 (Fed) or N43 (Cal) exhaust manifold performs goed on a stock system and a header will not add much more to it. I would probably stick with the N42 head and exhaust manifold. Have it rebuilt with new steel seats and get the ports matched to the manifolds. If the heads is untouched it will have silicon/bronze seats.

I think the biggest improvement you can make on the standard setup is a lightened flywheel. You can get the original lightened or go the safer route and buy a fidanza 143281. They cost around $300 if you look hard.

Replacing the fan with an electric unit will also help a little and reduce the fan noise.

Thinking further: Depending on what top speed you want. A late model 280Zx 5 speed close ratio and a 3.7 or 3.9 diff out of a Z31 300ZX will improve driver enjoyment.

The lightened flywheel, 280ZX tranny en 3.7 diff certainly improved my 280z.

Chas

[wheee!]

Like Steve and Zed Head already mentioned. Reasonable HP gains and standard old basic ECU don't mix. The ECU doesn't compensate much and basically the only tweek you can do is the temperature sensor.

You will spend a lot of money and get very little results. It could turn out to be such a dog to drive that the wife refuses to drive it.

The standard N42 (Fed) or N43 (Cal) exhaust manifold performs goed on a stock system and a header will not add much more to it. I would probably stick with the N42 head and exhaust manifold. Have it rebuilt with new steel seats and get the ports matched to the manifolds. If the heads is untouched it will have silicon/bronze seats.

I think the biggest improvement you can make on the standard setup is a lightened flywheel. You can get the original lightened or go the safer route and buy a fidanza 143281. They cost around $300 if you look hard.

Replacing the fan with an electric unit will also help a little and reduce the fan noise.

Thinking further: Depending on what top speed you want. A late model 280Zx 5 speed close ratio and a 3.7 or 3.9 diff out of a Z31 300ZX will improve driver enjoyment.

The lightened flywheel, 280ZX tranny en 3.7 diff certainly improved my 280z.

Chas

Good points.... I am liking the input here and I am realizing I might be better keeping the engine fairly stock. I can port match and redo the seats for sure. The lightened flywheel concerns me as clutch engagement is different and can sometimes lead to stalls at low rpm's. My wife tends to shift a little heavily... Plus the chatter. Clutch, not her

 

I already have the early 5 spd and R200 3.90 lined up for the build. That should help too.

 

Thanks for all the tips!

[madkaw]

TUNE TUNE TUNE. Without an aftermarket ECU, you just need to optimize your stock tune. I've driven a very nice 77 all stock and it ran good. Very torquey! Everything was in good repair and the tune was spot on. Gearing is also a good way to quicken things up too. Or just say hell with EFI and go whatever engine combo and slap on some nice SU's or triples better yet.

[TomoHawk]

I thought only pushrod engines had solid lifters.  How hoes the P90 cylinder head use lifters?

[Zed Head]

Semantics.  It's actually the rocker arm pivot that is self-adjusting via hydraulic pressure.