Engine changes by year 76-81

[afbrian13]

I was wondering what the actual changes were from 76 to 81/82 to lower the HP on these motors by 40-50hp(ish). I've read through the different physical differences and I know emissions stuff changed but still!

 

I have NA 81 in my car (it was cheap and runs well) but it doesn't have the guts the stock motor did. Is there a difference in how the computer is setup? Can it be "backdated"? I have electronics from different years including the stock 76 stuff.

 

This is all for fun anyway until I build a 302

[JSM]

The 1975-80 L28 motors put out a rated 135hp while the 1981-83 L28 motors were 145 net. The little plate on the shock tower in the 1975-78 280Z's engine compartment may say 170hp SAE but thats gross HP...a sneaky 1970s way of saying 135 net.

 

Taken from here: http://datsunzgarage.com/engine/

[afbrian13]

hmm ok. I thought I had read that the HP dropped off as the years went by, but maybe that was based on the fictional numbers. I knew the shock tower was just silly. Maybe its just an ill-calibrated butt dyno that has gotten used to the car.

I put a 4 speed I had lying around in my car this morning because 2nd is gone on my 5 speed, so we'll see how she feels today. 81 motor, 4 speed trans and stock 76 rear.

 

Early 90's FI 302 anyone?

[NewZed]

 

I have NA 81 in my car (it was cheap and runs well) but it doesn't have the guts the stock motor did. Is there a difference in how the computer is setup? Can it be "backdated"? I have electronics from different years including the stock 76 stuff.

 

 

So you're running the F54/P79 block and head with the 76 ECU and AFM? Comparing power to the 76 N42/N42 with 76 ECU and AFM?

 

Curious. I have a spare 81 NA engine and wondered how it would do with the 76 EFI.

[afbrian13]

no-i'm running everything from the 81-complete motor, wiring harness and ecu. I pulled it all together from a good running car without even disconnecting the harness from the engine. I'm using the 81 relays instead of the old ones. Plus no transistor box to deal with. starts right up 20deg or 105deg. Just feels like it could use some more umph! Then again it is a 31 yo motor with 140,xxxmi on it!

[NewZed]

Well, thanks for the info anyway.

 

It's really hard to tell which engines made more power. The only good comparison I've found is in a compilation of R&T road tests, but I don't know how they get their HP numbers. The numbers don't match the car ID plates, so maybe they actually dyno-test each test car.

 

In a the R&T 1979 ZX road test they report 135 Bhp@5200 RPM for the N47/N47 block/head combo. An earlier R&T test says that the 1975 N42/N42 combo produced 149 Bhp@5600 RPM. But they should be essentially the same engine, except for liners in the N47 exhaust ports, so that's confusing.

 

In a later test they also reported another 79 ZX at 132 Bhp@5200 RPM in a four car comparison test. So that's two N47/N47 combos at 132 and 135 Bhp.

 

A later test of a 1981 ZX produced 145 Bhp@5500 RPM for the F54/P79 combo. That's the new engine with flat top pistons and 8.8 CR, but a different cam profile.

 

In the text they say that the 1981 ZX engine is making 13 more HP than the 79 engine, apparently comparing to the 1979 ZX in the four car test, mentioned above.

 

To top it off, none of the numbers in the R&T tests match what's on the ID plates. My 76 plate says 170 HP@5600 RPM (SAE), even though it's essentially the same engine as in the 1975 280Z, which R&R reported at 149 Bhp.

 

Hard to tell where these numbers come from. Maybe the most telling thing is that the torque peak dropped from 4400 RPM for the 75 and 79 cars, to 3000 RPM for the 1981 car.

 

Just to fill it out, here are the 1/4 mile times and a comparison table.

 

1975 17.3 s@81 mph 2875 lbs (4 speed, 3.54 final)

1979 17.2 s@82 mph 2825 lbs (5 speed, 3.36 (!) final), same first 4 gears as the 75 4 speed)

1979 18.1 s@80 mph 2900 lbs (automatic, 3.54 final)

1981 16.8 s@81 mph 3000 lbs (lots of options, "close" ratio 5 speed, 3.54 final)

 

1975 N42/N42 149 Bhp@5600 RPM, 163 lb-ft @4400RPM

1979 N42/N47 135 Bhp@5200 RPM, 144 lb-ft @4400RPM

1981 F54/P79 145 Bhp@5500 RPM, 166 lb-ft @3000RPM

[JSM]

 

1975 17.3 s@81 mph 2875 lbs (4 speed, 3.54 final)

1979 17.2 s@82 mph 2825 lbs (5 speed, 3.36 (!) final), same first 4 gears as the 75 4 speed)

1979 18.1 s@80 mph 2900 lbs (automatic, 3.54 final)

1981 16.8 s@81 mph 3000 lbs (lots of options, "close" ratio 5 speed, 3.54 final)

From the research I've done I'm not aware of a 3.36 coming in a 79'. They only came in a 74' 2+2. Also, I'm not aware of the 3.54 in 81' 5 speed. Turbo automatic, sure. At least for the US.

Edited August 11, 2012 by JSM

[NewZed]

The 3.36 thing pops up now and then, mostly when talking about the R200. The 1979 FSM specs the 3.36 as an option, in both R180 and R200. Some people say that the 1974 R200 came in a 3.36 also, although the FSM only shows an R180.

 

Anyway, I just copied what was written in the R&T articles. 3.54 in an 81 ZX is an odd one also. Most come with 3.9s.

 

Also, another odd thing - the 81 close ratio 5 speed has a 3.06 first gear, compared to a 3.321 for the 75 and 79 transmissions. So it ran a 16.8 1/4 mile with a heavier car and a taller overall first gear than the 75 and 79 cars, according to R&T. Maybe that 2-3 shift with the wide ratio boxes is as bad as it feels.

 

Just some weird things from the past.

Edited August 11, 2012 by NewZed