n42/n47 na build

[Rij Martin]

 

こんにちは,

It's been a while since I have been on but we are finally in our new home and I have had some spare time to pull the z apart.

So my question is, what would be the best build for a n42/n47 na set up? That's the block and head I have right now and I believe it shouldn't be a bad place to start. Any of you have experience with this build? I have read mountains on the n42 head but I can't find much on the n47. From the few things I have found some good ideas might be replacing the dished pistons for flat tops. From familiarity on the head I assume it would bring compression up to about a 10:1 and you would have to be crazy to not put a new cam in after that. (270 - 280 degrees on that cam, correct?) After that you would want your head matched up to your exhaust and intake for better flow. What else might you want to do? I currently am running round top SUs and the stock exhaust. The exhaust will be replaced for 2.5 and, if dreams come true, I will switch to some triples. What ideas can you folks dream up for this motor/head? I am not looking for any crazy power upgrade, just something to put a smile on my face. I wan't to make sure I can still daily it without putting racing fuel in it. 

Thank you in advance, the support I get from this forum by far makes it my go to place.

[siteunseen]

If you could find a zx motor from a junkyard and use the flat top pistons and the p79 head you would be better off in my opinion. The n47 is the least desire able head there is. 

Google datsun z motor calculator and try different components. The n42 head would be able the first one with bigger valves already then the n47, then the better p79. Google " diseazed motor build classiczcars.com" or go to datsungarage.com and find the motor sub category and then the cylinder head mod.

I can post those links in the morning as I have them bookmarked on my laptop.

[siteunseen]

12 hours ago, siteunseen said:

I can post those links in the morning as I have them bookmarked on my laptop.

Good stuff here if you haven't already read it. 

datsunzgarage.com, http://datsunzgarage.com/engine/

P79 head, http://datsunzgarage.com/p79/

Cylinder heads in general, http://datsunzgarage.com/heads/

Engine calculator, http://atlanticz.ca/zclub/techtips/calcs/engine builder/index.html

[Zed Head]

site, the N47 head is essentially the same as the N42 head.  Nissan added the exhaust liners for cleaner emissions but didn't change anything else.  So if you're not planning to do any porting work, or add a turbo, the two are about the same.  The N47 typically comes with the oiler cam also.

With carbs, exhaust and cam are probably the simplest power increasers.  Increase air flow through the engine.  After that, port work on the head.  But even with port work, it's mostly intake, not exhaust.

There is a lot out there about how effective compression ratio increases really are.  They don't do much, on their own.  I would read up on CR and its effects before going to the trouble of installing flat top pistons.

There's a lot of money you can spend without really gaining much.  Plan first then act.

[siteunseen]

Would the N47 work as well with flat topped pistons compared to a P79?  I wasn't really recommending an N42 just stating it was the first one with the bigger valves.  Sorry for any confusion. 

[Zed Head]

People report mixed results when raising the compression ratio by using flat top pistons.  Apparently, fuel quality differs across the states so some people get knocking and others don't.  If you don't shave the head the N42 or N47 gets you almost 10:1.

http://www.ozdat.com/ozdatonline/enginedesign/

There are so many opinions out there it's crazy.  Some people like the rumpety-rump cam noise, some like the 7500 RPM screamer, some like the torquey 3.1 liter engine.  RM needs to decide what makes him smile, I'd say, and get those details.

[Zed Head]

Damn, the site is getting Gallery imaged again...  Hate it when that happens.

[Diseazd]

49 minutes ago, Zed Head said:

People report mixed results when raising the compression ratio by using flat top pistons.  Apparently, fuel quality differs across the states so some people get knocking and others don't.  If you don't shave the head the N42 or N47 gets you almost 10:1.

http://www.ozdat.com/ozdatonline/enginedesign/

There are so many opinions out there it's crazy.  Some people like the rumpety-rump cam noise, some like the 7500 RPM screamer, some like the torquey 3.1 liter engine.  RM needs to decide what makes him smile, I'd say, and get those details.

I like the torquey 3.1 liter, 7500 rpm screamer that goes “rumpety-rump!”   

Edited April 13, 2018 by Diseazd

[siteunseen]

Guy's trifecta.

[madkaw]

22 hours ago, siteunseen said:

Would the N47 work as well with flat topped pistons compared to a P79?  I wasn't really recommending an N42 just stating it was the first one with the bigger valves.  Sorry for any confusion. 

I believe the 79 head has a bigger combustion chamber so compression would much less , but doable with flat tops.  79 head has the better of the combustion chamber shapes - which helps with fighting detonation. 

So many choices ....

[Rij Martin]

Thanks for the replies!

A thought to consider. With flat tops in the p79 head, wouldn't you just have a zx motor? Siteunseen, those are great reads, loads of information on there.

[siteunseen]

2 hours ago, Rij Martin said:

Thanks for the replies!

A thought to consider. With flat tops in the p79 head, wouldn't you just have a zx motor? Siteunseen, those are great reads, loads of information on there.

Yes it would be  ZX motor, pretty much but the reason they did the flat tops on the zx was to make up for the power to weight ratio. Zxs are a good bit heavier, they have power steering power windows and heavier safer bumpers. 

Knowing now what I've learned on this forum I would definitely go with a zx motor in my light Z. The p79 has better fuel quench and like Madkaw says lowers the risk of pre detonation I think they call it or "pinging". That will eat up your pistons.

I've been told my n42 block with flat tops and my n42 head would be a good motor/head combo. I have the flat tops and eventually will swap them in place of the dished I'm currently running but it runs so good now, not a performance motor just good running dependable motor I cant make myself tear it back apart for a little more power. The police keep me from building a hot rod.

Good luck and don't worry about asking, we have plenty of opinions for all the choices you're up against. 8^)

Cliff