Dropping 83 ZX Motor Into My 77 Z

[Captain Obvious]

I'm going to replace the motor in my 77 Z with one from from an 83 ZX and I'm trying to figure out what parts I should use from the 77 and which parts I should use from the 83. Two of the specific areas of decision making are the intake and exhaust manifolds...

The 83 intake manifold is webbed while my 77 is not. Anyone know why Datsun started webbing the intake manifolds? Is that for heat? Strength? Something else? Given a choice, which is better?

The 83 exhaust manifold has an O2 sensor while my 77 does not. Are there performance gains to be had by switching over to the ZX fuel injection controller that uses the O2 sensor or does it not really matter?

Basically I'm trying to build the best motor from the two and I would like to keep it looking like a 77, but if there are compelling reasons to use 83 specific parts beyond block, head, timing cover and oil pan, then I'd like to hear about it.

[siteunseen]

The 83 intake manifold is webbed while my 77 is not. Anyone know why Datsun started webbing the intake manifolds? Is that for heat? Strength? Something else? Given a choice, which is better?

I anxiously await an answer for this question. I bought some kind of bastard N42 intake with the EGR mount and tunnel without the small holes into the runners nor the bigger plugged holes on the bottom side with the 10mm allen fitting. It was half webbed and I spent 2 days with a die grinder & Dremmel cutting that stuff out.

[madkaw]

If the 83 is together, then why separate . I see no gains in going to an early intake except I like the non webbed look, but you still have an EGR.

As far as the exhaust - the 77 is square port right? The 83 is round port. Not sure if that has a bearing. Could you use the O2 sensor hole to run a wideband? That would be one advantage .

So you want to run the 77 intake to keep it looking original?

[Zed Head]

My thought has been that the webbing is just a way to reduce the number of parts needed. It replaces the old heat shield and its three bolts. The ZX intake manifolds are designed with more taper though, if you take a look. Maybe to get better distribution of air to the cylinders. The 02 sensor only comes in to play during cruise, so you'd only gain gas mileage and cleaner emissions, but not acceleration.

Note though, that the manifolds are designed to fit the car also. The intake manifold has the throttle body placed backward a small amount so your hoses won't fit fit quite right. And the exhaust manifold is shorter so would require a new head pipe to be fabricated.

If you have a late 77 with an N47 head then you'll have a round port exhaust manifold which will fit fine. If you have an N42 head, you'll have the square port manifold which will work also, the square ports are bigger than the round holes in the head so there's no restriction.

I have an 81 ZX motor and have considered the same things. I haven't installed it yet, but will probably keep the old Z manifolds on the ZX motor, maybe with an O2 bung installed on the head pipe if I use a different EMS. Seems like too much work to get the ZX manifold to work. But the ZX intake manifold looks interesting just because it might be a better design (you would hope).

[Captain Obvious]

You guys have pretty much nailed my thoughts... All things considered equal without any other input, my plan would be to strip down the 83 and redress back up looking like a 77. A little simpler, a little lighter looking, and certainly more authentic for a 77. But I'm happy to give up on looks if there are tangible reasons such as performance to do otherwise.

My 77 is square exhaust port, but I'm running a header that the PO installed. I was planning to switch back to a cast iron manifold of some sort as part of this job, so in other words... I know I've got some exhaust work to be done no matter what route I proceed on. I don't like the exhaust work from my PO and I was planning to rework everything anyway.

So it sounds like there are some fitment issues with the ZX intake in the earlier years, and no known performance gains to be had by using the webbed manifold? Zed Head, I'll take a look at that intake manifold taper you mentioned and the location of the throttle body. I didn't notice either of those. There are six years of technological advancement possible between my 77 and the 83... You would sure hope that there were some improvements, right?

[Jeff G 78]

What head do you have on the '77 engine? If it's the original head, it will be an N47 and have round ports. If that's the case, either exhaust manifold will work. If it's an N42 head, you will have to keep the '83 manifold on the new engine.

Dumb question... What is the reason for the engine swap? If the old head is good, why not keep the N42 or N47 and drop it on top of the F54 block to give it a compression bump?

[Captain Obvious]

You're right Jeff. I currently have the N47 head and it sounds like I've got round exhaust ports unlike what I said above. My desired plan on the exhaust manifolds would be to keep the 83 manifold on the new engine and use the O2 sensor location for a wideband some time in the future as suggested earlier.

The reason for the engine swap? My current engine runs fine, but has dubious quality:

My oil pressure is good but not great.

My compression is good but not great.

I think I've got a minor head gasket leak.

I've got a couple stripped valve cover bolt holes from an overzealous PO.

I've got a stripped distributor mounting hole on the timing cover from a PO.

I've found one or two glass beads coming out of the oil pan on two successive oil changes.

Bottom line is there's a bunch of small stuff wrong with it, none of which is known to be insurmountable at this time. But I'm figuring that if I'm going to invest time and money in a motor, I could start with a better base. Of all the items above, I'm most worried about the head gasket (and the glass beads). My PO did a head gasket right before I bought the car and I think I've still got issues. I've seen pics of hairline cracked N47's and I'm thinking that might be what's going on with mine.

I know the different head/block combos have been talked to death and I know the answer to the question I'm about to ask is available out there if I were to search for it, but... Off the top of your head, do you know what compression ratio I would end up with if I were to plunk my current N47 on my new F54 block? Assuming the head isn't cracked of course...

[Jeff G 78]

Off the top of your head, do you know what compression ratio I would end up with if I were to plunk my current N47 on my new F54 block? Assuming the head isn't cracked of course...

If your N47 head hasn't been milled, it will yield a CR of 9.83:1 with a Nissan gasket. I run that combo on my street Z with a stock cam and it runs nice. It does force you into premium gas (I run 93), but I've had no other issues. I did have to add a variable resistor into the water temp circuit to add a bit of fuel, but that was a $10 mod.

Your other option is to shave the P90 head. I run this combo in my other Z and I love it. It's shaved 0.050" and I still use the stock valves with no tower shims. I made my cam gear adjustable with the small block Chevy offset bushing kit per the How to Modify Your Nissan OHV book. This combo gives you the better chamber shape and bumps the CR to about 9.3:1. I can run more advance with that combo than I can with my N47 engine. If you want more info, let me know.

[Captain Obvious]

Thanks Jeff.

My 83 engine is a non-turbo, so I've got the F54 block with flat top pistons and a P79 head, not dished and a P90 head. I thought the compression ratio of the non-turbo motors was pretty good even without milling the head.

I thought dropping the N47 on with the flat top pistons resulted in an unusually high CR.

Did I miss something?

Edited September 1, 2013 by Captain Obvious

[Jeff G 78]

Oops, I was thinking the '83 had a P90. That would actually make it the same as mine. I have a P79/F54. Without shaving the P79, the CR is only like 8.3:1.

People get worried about the N47/F54 combo, but it's fine. Less than 10:1 in the Eastern states is no big deal. Out West, the max octane rating is only 91, so they have a bit tougher time running that setup, I guess. Mine runs great with zero problems.

I paid $150 to shave the P79 and it is a sweet engine. It pulls strong to 7,000 and makes about 170 - 180 hp at the wheels. I haven't dyno'd mine, but a friend with nearly the same exact motor got 178 at the wheels with his. My cam is a bit bigger, but he did some mild porting. I'm guessing they ended up about the same.

[EuroDat]

It seems you guys covered about everything so far except the webbing. The webbing was introduced as a heat shield and replaced the metal plate under the inlet manifold.

The inlet manifolds N42, N43, N47 (208Z manifolds) and U87 280ZX all flow pretty much the same and you will notice very little difference in that field. The P82 used on the ZX turbo flows marginally better and will bolt onto all 3 NA heads.

Chas

[Captain Obvious]

Sorry Jeff, my bad. I'm looking for input and didn't even fully describe what I had.

I'm planning to drop in the P79/F54 combo, and I'm not even going to pull the head off the block right now. I know it runs now and I ran a compression test on it as well. It's 180 psi across the board, so I'm going to drop it in as is. If I open it up sometime in the future, I'll probably mill a little off the head, but for now, the plan is that it's going in as is.

Chas, Thanks for the input. So the general consensus is that the webbing is simply a heat shield... OK... I can live without that. If there are indeed fitment issues like where the throttle body ends up, then I'll probably redress with my 77 intake.

So my bottom line at this point sounds like it will be:

• P79 head on the F54 block
  
• Use the 77 intake manifold because the 83 intake moves the throttle body
  
• Use the 83 exhaust manifold because it has an O2 bung that I can use for a wideband