N/A Dished piston F54?

[Flatout_friesen]

So I bought a 1981 Datsun 280zx with a stock N/a l28e engine in it...OR so i thought. We tore this thing apart and found that it had an F54 block with an N42 head, BUT, with dished pistons. So I'm not sure if these are early n/a dished pistons or just a turbo block that has been changed to run n/a.

 

Anyway, the original plan for this car was a low boost turbocharger upgrade. so i bought a P79 head for it, dropping the compression ratio to 7.8:1, compared to the factory 8.7:1 with the flat top pistons.

 

I started a new thread because i haven't seen one thread that i can relate to with this Mix-n-Match motor that i have.

 

My questions are:

 

1. Why do you think this block has been pieced together from many different years of Zs and using dished pistons for an N/A build?

2. how much boost would be safe to run with that compression ratio (7.8:1) provided my AFR is in a relatively stoich range? I have a wide-band for it so i can monitor the mixture and will have an intercooler, bigger injectors, etc.

 

Thanks to those who take time to reply.

[luseboy]

Perhaps the pistons were replaced with dished pistons at some point but were flattops originally?  If it is a turbo block there may be another way to tell for sure but I would also try and identify which rods you have.  If they're l24 rods then your compression ratio would be higher than that.  I wouldn't be too surprised, considering it seems to be a pieced together engine, and perhaps someone would have done that to counteract the lower CR of the dished pistons.  If it is indeed a turbo block, I believe the only difference between the P79 and the P90 are the exhaust runners and the cam.  I know there is a fair amount of fear among many about the exhaust liners with a turbo behind them, but apparently many people have had no problems with decent power.  

 

It seems that you've done your homework so I assume you know that an L with a turbo is very susceptible to detonation, which is often a shortcut to the grave for these engines. If the comp ratio is about what an N/A motor would be, it seems that a "safe" amount of boost would be around 10psi, but this is assuming everything else is set up right.  There's a fair amount that needs to be set up right for the turbo swap.  You're going to need to deal with ignition timing, be it locking out your dizzy or going for an EDIS system.  You will want to make sure you're still getting enough fuel pressure to the injectors under boost (boost regulated fuel pressure regulator and a fuel pump that can support the full fuel pressure: normal pressure+highest boost pressure), among other things.  I'm sure there's some things you'll need to do with the EFI to make it work right but I'm not an EFI guy. There's a lot to consider here, and if these things aren't dealt with then no boost level will be "safe."  

 

Personally, I'm starting to plan my own low-pressure turbo setup on my F54/P79 with flattops.  In my case I will be going blow-through with a holley carb but will be running EDIS. I'm hoping to run around 10psi but reliability and longevity will be a large factor so that number may have to be lower.  In order to do this I will be doing some extensive modifications to the holley, pulling my engine apart and freshening it up, and very carefully tuning to avoid detonation.  I will also need the boost regulated fuel pressure regulator so that I don't run out of fuel under boost.  But before I do any of this I'm replacing my transmission with a 240sx unit and my differential with something beefier (haven't decided what yet).  In addition, I'm going for a 240mm clutch.  I would recommend that you really consider the state of your drivetrain before putting a turbo on it as well, it would really suck to have a sweet turbo set up with a blown transmission or a clutch that slips when you get on it, etc.  

 

Keep in mind: I know little to nothing about EFI, I have never owned a turbocharged car and don't know all that much about them.  I have also not done this swap, yet.  But I have been doing a ton of reading on adding a turbo to an N/A L28 and these are the things I have come up with.  There are many people on here who have a ton of knowledge about this stuff, and they will hopefully chime in and give you better answers from their own experience.  

Edited May 7, 2016 by luseboy

[z-ya]

Looks like a turbo block that someone put an N42 head on. Should be a decent setup for NA. CR should be around 8.5:1

[malibud]

Z ya is right sounds like a turbo block with n42 head. I ran up to 17lbs with a 2mm HG with that set up. Remapped ECU from a 300 zx. and intercooler