Mystery Big Valve Ported N42 Head.

[Chickenman]

1976 Nissan Comp Catalog. Note Part # 13001-E4651. Big $$$ even in 1976. 

 

[DATZ]

On 1/11/2018 at 12:12 AM, Gollum said:

 

You mention that the chambers were welded, how much quench pad is there? If a lot, then a thicker gasket might be hindering more than helping. Google quench pad and quench distance to learn more. Also, pics are always nice.

It’s hilarious how everyone throws out the term “quench”.  This head has the best quench”, “if you do this, you’ll get more quench”….
 

Here’s the rule: if quench isn’t perfect, YOU DON’T WANT IT!

 

When you’re raising compression, Quench is the primary cause of detonation - when it’s not perfect.

 

There is ZERO quench pad on the E31, E88’s, N42, N47.  The P-79, P-90 and MN-47 all have quench pads.

 

The E31, E88, N42 and N47 are considered “Open” Combustion Chambers; Where the P-79, P-90 and MN-47 are considered “Closed” combustion chambers.  
 

“Open” combustion chambers have little to no quench pads.  
 

The reality is, none of the Z heads have great “quench.”  So don’t worry about it.  
 

Now that’s not to say BPE Heads, Rebello’s….  Can’t weld up any of these heads and create perfect quench.  It’ll just cost you money.  
 

 

 

 

 

 

[NewZed]

Also hilarious when somebody joins a forum for the sole purpose of criticizing another person's post.  Even funnier when they don't offer any sources or even a clue about who they are.  Just another voice in the wind.  Hear my opinion.

[DuffyMahoney]

On 1/10/2018 at 7:47 PM, Nismospek said:

Found a nifty calculator. Decided to convert everything to 25 inches which is what I believe Rebello uses. 

 

 

100 lift  58 cfm

200 lift  117 cfm

300 lift  158 cfm

350 lift  178 cfm

400 lift  189 cfm

450 lift  192 cfm

500 lift  200 cfm

550 lift  205 cfm

600 lift  213 cfm

650 lift  219 cfm

 

 

 

Mine actually flowed the best at .500 lift.  235.  Interesting that his flows higher as lift goes up.

[Tony D]

On 3/3/2022 at 1:26 AM, DuffyMahoney said:

Mine actually flowed the best at .500 lift.  235.  Interesting that his flows higher as lift goes up.

Not really, until the valve head is away from the seat more than a given ratio to it's diameter, it represents a flow impediment. On a ported head capable of flowing more, the further away that valve head needs to be to not impeded the inward rush of airflow. Since the valves are relatively large, compared to a DOHC Valve and do not tilt inward away from the cylinder walls like a Pent-Roof DOHC again... it represents a "shrouding" of the valve.

This is why people cut the heads combustion chamber in the area of the valves... it 'unshrouds' the valve at low lifts and represents a considerable amount of flow increase (ESPECIALLY on Turbocharged/Supercharged builds) given the assymetric nature of the cam profiles used on Nissans and their time spent 'just off seat'.

If he's got large ports, it only stands to reason that higher lift gives more flow. If the porting is conservative, you will hit a wall and not flow more regardless. Even at that, you can still use a higher lift cam as it will spend more time "under the curve" at the peak flow number with no restriction at all than if you used a cam that only lifted to the max your head was capable of flowing.