My N42 head

[JessZ]

Okay Jon and others, I'm a bit confused. I took my block and head into Lesco (engine shop) and Stephen (the mechanic) said my head is not too good? I am doing the L28, N42 head, flat top piston set up, and from what I've learned here it is a great set up, proved a correct combo by Rebelo. The head is in great condition, this is not the problem, the deal is that Stephen said this head had a poor quench area and that the brass intake and exhaust valve seats may prove detrimental. When Stephen mentioned this about the valve seats I thought of the N47 head. I thought it was the N47, and not the N42 head, that had those emission valve seats.

 

Stephen asked if I had another head, and I do, it's the early E88 head. I don't want to spend thousands on a head, in fact I prefer to just polish it up myself. As I've read the N42 is a great choice for a street perfomer and needs nothing more than a polish, if anything. I need to get back to Stephen to let him know what's up. At first I felt like I knew what I was doing, now, again, I'm not sure.

[JMortensen]

This is a never ending debate. You can search to find the detailed explanation, but bottom line is that I think that Stephen is right. That being said, lots of guys have made pretty good power with that head, without changing the combustion chamber. Dan Baldwin is making 255 whp with his stroker. I think Norm is using a pretty stock combustion chamber, cleaned up but not welded up. So the quench thing isn't the end of the story. You CAN still make good power with that head.

 

The other cheap option is to get a P90 head, shave it .080 and then shim the cam towers up. It has the better quench area and if I were building another street L engine that's what I would do. Then you can run the N42 valves in the P90 head and get about 10:1 compression. There used to be a page called The Datsun Z Garage by Bryan Little, but I guess it's gone now. It had all the details on that head modification.

 

If you were going to run race gas I'd say get the Maxima N47, which is like the P90 but with a smaller chamber so higher compression. The early E88 head is similar to the E31 I'm running right now. Compression is too high for pump gas with flat tops.

[JessZ]

I know it's a never ending debate, and I applogize for pressing. Stephen just made sense with his comments, and I started losing confidence with the N42. I guess we'll just see. Thanks again.

[coyotegary]

i ran that set up with flat tops and an N42 for 2 years. fantastic performance with a few mods and it never let me down

[JessZ]

This link shows a N42 head. Mine has these brass, or gold colored rings pressed into the intake port, and a silver one in the exhaust. Does this seem right?

[coyotegary]

yep, sounds right to me. intakes have brass seats and the exhausts have steel

[Darrel]

Here is bryan little's site.

 

http://www.geocities.com/zgarage2001/z.html

 

Why don't you have the bronze seats replaced by hardened seats? I had that done with the n42 I had.

[AK-Z]

Isn't the brass seats for leaded gas? And the steel seats for unleaded?

 

I've read this somewhere but I don't remember where.

[Guest norm[T12SDSUD]]

If you shave the head you can end up with a nice combustion chamber shape . Look at the photos in my link at the bottom of my signature and you can see what the chamber looks like after a .070" shave.

BTW, replacing the seats is childs play for a machinst. Why does this guy think it's such a big deal?

 

Later,Norm

[JMortensen]

I don't think that changing the seats was the big deal. It was the combustion chamber shape. You have a pic of your combustion chamber Norm? I bet it looks a lot like an E31...

[Guest norm[T12SDSUD]]

Yeah Jon just click on the link at the bottom of my signature. And yes it does look like an E31 however the CC is way smaller at 35.1 cc.

[JMortensen]

Still quite a bit more open than the E31, but closer for sure. I always thought the chamber shapes were pretty similar looking. One problem is that if Jessie went that far on shaving the head he wouldn't be able to run CA pump gas.

[Guest norm[T12SDSUD]]

Well he could shave it .090" and use dished pistons which are plentifull and be right about 10:1 CR.

The dished pistons are often better then flat tops as the raised area forces the air charge into the center of the chamber.

I have read in both Hot Rod and Car Craft that more power can made from using dished pistons as long as the CR stays high.

[JMortensen]

'']The dished pistons are often better then flat tops as the raised area forces the air charge into the center of the chamber.

That's the purpose of the quench area. With flat tops and a small chamber, when the flat top comes close to the flat head, it "squirts" the air/fuel into the chamber area, making it tumble and mix more evenly as it does so. You're basically talking about the same thing, but using the piston as part of the combustion chamber. Nothing wrong with that I suppose, two different ways to skin a cat.

[Guest norm[T12SDSUD]]

The head would be much less likely to detonate and ping with a .080" shave and dished pistons than it would be with an unshaven N42 and flat tops. I have talked to a number of people through the years whose flat top motors with unshaven N42's pinged like crazy.

[JMortensen]

'']The head would be much less likely to detonate and ping with a .080" shave and dished pistons than it would be with an unshaven N42 and flat tops. I have talked to a number of people through the years whose flat top motors with unshaven N42's pinged like crazy.

Add one more to the QUENCH column!!! :D

[Guest norm[T12SDSUD]]

Yes the ideal quench distance is .035" and that is exactly what I have on my 10.7:1 stroker motor with dished pistons and .070" shaved N42 head.

 

I also read in HotRod magazine where reducing CR with a lower piston deck height and a resulting larger quench distance will result in INCREASED pinging!

 

You gotta get the squeeze for mixture turbulence!

[2003z]

']Well he could shave it .090" and use dished pistons which are plentifull and be right about 10:1 CR.

The dished pistons are often better then flat tops as the raised area forces the air charge into the center of the chamber.

I have read in both Hot Rod and Car Craft that more power can made from using dished pistons as long as the CR stays high.

Norm,

I've got a P90 and dished pistons, running NA. You think shaving is a more cost effective way than changing the pistons to motorsports pistons? I can get the set of those for around $350.

[Dan Baldwin]

Tee hee, here we go!

 

FWIW, please note that I've NEVER suggested that the N-heads are superior, or that quench is worthless. Only that respectable results have been achieved on L-series motors with no-quench, open-chambered heads.

 

My setup has NO quench. the pistons are ~.003-.004 below the deck, I've got a 1.17mm thick head gasket, so .050" between piston and head deck, a moderately shaved (~.010 or so) open-chamber N42 head. 11:1 CR, big cam. No pingie, no problem. Max power on 93 pump at 34 - 38 deg. ignition advance, max power on race fuel (less than on pump fuel!) at 38deg plus advance.

 

However, Z-ya's L28/flattops/N47 build (should be 9.8:1) for the club race car DOES have to run with timing retarded to 26deg, but STILL made a very respectable 164 rwhp at the dyno (stock head, stock cam).

 

Anyway, long/short, I don't think you have to worry about running the N42. As for the valve seats, either replace 'em, or keep up with your valve clearances. For the years I ran with stock seats, I didn't have any problems.

 

 

Regarding your "early" E88, it has the closed chambers? In a very old issue of "SportZ Magazine, D.L. Potter said this was the best-flowing L-series head. He oughta know. If you do use that head, you might go with the bigger L28-size valves.

 

My .02!

[Guest norm[T12SDSUD]]

Hey Dan ,are your pistons domed or flat top?