Cylinder head troughs by spark plug

[RLJ]

Does anybody know the purpose of the troughs cast in the head by the spark plug in the combustion chamber. See them in most Datsun L series heads. 
The head I’m working on now has them on cylinder 2 and 3. The one in this photo has them on cylinder 1 and 4. 
On heads like in the photo, the trough exposes the edge of the seat insert in the trough leaving a sharp edge. Would think it could create a hot spot. 
 

 

[Stoffregen Motorsports]

Well, it is what it is, so just smooth them out and call it done.

 

FWIW, you should remove all sharp edges in the combustion chamber, just as a matter of course.

[datzenmike]

It's been discussed but no answer.

 

Here's more...

 

 

What's the purpose of the troughs or channels in the front two intake manifold runners?????

 

Why do Datsuns have such dim dash lights..... and then have a dimmer switch??????

[paradime]

It's good advice to clean them a bit, but unless you're building a super high compression engine and trying to prevent knocking, I say don't even mess with it. There are known ignition and harmonic issues with the L series. Those cylinders are opposite in the 4 stroke firing order, so it likely has something to do with that. Err on the side of caution, beause rounding them off too much could adversely effects what they're designed to do.  My $0.2 anyway.

[datzenmike]

I'm still wondering what they are designed to do.

[paradime]

Me too. I'll get right on it.

 

 

 

 

Edited November 6, 2023 by paradime

[paradime]

4 hours ago, datzenmike said:

I'm still wondering what they are designed to do.

 

With no harmonic balancer on the crank, and a completely analog ignition system with no way to adjust timing for individual cylinders, maybe it changes combustion just enough to smooth things out? Grasping here trying to prove my theory on crank resonance harmonics aka "excitation" BTW, and I found this wack ass Indian engineering paper on Excitation Force Identification on the Basis of Discrete Spectrum Correction.  https://www.hindawi.com/journals/mpe/2015/175257/

 

Although I'm a self described research sadomasochist, this stuff is not in my wheelhouse. BUT, I'm pretty sure it's saying to be discrete whit your spectrum correction on those funky trough edges. I'd give this the font treatment but it's Sunday, I've had a double gin martini, and now I'm too lazy. 🥴

[Stoffregen Motorsports]

12 hours ago, paradime said:

 

 

Although I'm a self described research sadomasochist, this stuff is not in my wheelhouse. 

 

I'd give this the font treatment but it's Sunday, I've had a double gin martini, and now I'm too lazy. 🥴

You and I would make a great team. I loathe research. I shoot from the hip and I rely largely on passion and evoked responses.

 

I also get lazy after my second or third Manhattan.

[paradime]

15 minutes ago, Stoffregen Motorsports said:

You and I would make a great team. I loathe research. I shoot from the hip and I rely largely on passion and evoked responses.

 

I also get lazy after my second or third Manhattan.

 

Psychologists would define this behavior as a form of OCD, Letterman would call it a Stupid Human Trick, and Mike the pot guy would call it a PITA. Thanks to your "second or third Manhattan", you see value in it because drunk minds think alike. Yet another one of my dingbat theories, but I'm sure I could find a scientific basis for it. LOL'n

[datzenmike]

13 hours ago, paradime said:

 had a double gin martini, and now I'm too lazy. 🥴

 

1 hour ago, Stoffregen Motorsports said:

 

 

I also get lazy after my second or third Manhattan.

 

I never blame my laziness on liquor.

[iceman510]

I never blame my liquor on laziness.

[paradime]

I blame everything on my self. It's just easier to drink more that way.

[datzenmike]

I skipped self blame and went directly to self loathing. It's quicker that way.

[paradime]

This quickly slid into complete F'ery even before the second page had a chance, as do most unanswerable thread topics. While we offered no definitive answer, I think we've done very good work here. We can clock out early gentlemen, it's Miller time! 

[datzenmike]

16 minutes ago, paradime said:

This quickly slid into complete F'ery even before the second page had a chance, as do most unanswerable thread topics. While we offered no definitive answer, I think we've done very good work here. We can clock out early gentlemen, it's 4:20 time

 

[Stoffregen Motorsports]

20 hours ago, datzenmike said:

 

 

20 hours ago, paradime said:

This quickly slid into complete F'ery even before the second page had a chance, as do most unanswerable thread topics. While we offered no definitive answer, I think we've done very good work here. We can clock out early gentlemen, it's Miller time! 

I agree wholeheartedly. Eventually the question will be answered, but only after we take it all the way to the bottom and back. You have to hit rock bottom.

[banzai510(hainz)]

Beautiful  Head!!!!!!!!!!!!!!!!

[datzenmike]

If it weren't for the F'ery  there would only be one post and this topic would be buried 10 pages under soon to be with the three other post on this that went unanswered. It's still not answered but at least it's exposed and I had fun.

[Datsunscott]

My guess is the spark plug area opens up the mixture area around the plug for more reliable ignition.

 

The troughs in the intake likely route any liquid gas droplets to the best side of the intake to hopefully prevent wetting/fouling the plug,

probably for starting issues - and possibly reintroduce the fuel into the airstream at the best point for breaking up droplets?

That side of the port probably flows more air.

 

What do you think?

[Stoffregen Motorsports]

On 1/8/2024 at 10:10 PM, Datsunscott said:

My guess is the spark plug area opens up the mixture area around the plug for more reliable ignition.

 

The troughs in the intake likely route any liquid gas droplets to the best side of the intake to hopefully prevent wetting/fouling the plug,

probably for starting issues - and possibly reintroduce the fuel into the airstream at the best point for breaking up droplets?

That side of the port probably flows more air.

 

What do you think?

That's what I've always thought, about the troughs. They were to channel liquid fuel.

[datzenmike]

On 1/8/2024 at 10:10 PM, Datsunscott said:

My guess is the spark plug area opens up the mixture area around the plug for more reliable ignition.

 

The troughs in the intake likely route any liquid gas droplets to the best side of the intake to hopefully prevent wetting/fouling the plug,

probably for starting issues - and possibly reintroduce the fuel into the airstream at the best point for breaking up droplets?

That side of the port probably flows more air.

 

What do you think?

 

 

 

The #1 and #3 and the #2 and #4 chambers look like identical pairs to me so why don't they all have this????????????????

 

 

 

But the intake ports in the head don't continue the 'troughs' so it dead ends at the head.

Why would the front runners flow more air than the rear, and why would the front have more droplets

 

 

Not all have this. Below the bottom L16 intake does not. Maybe just the later L20B. I'll bet 100 internet points that the '75-'77 co-joined intakes without the water warmed/cooled runners do not have these troughs.