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turbogrill

Vavle size vs Intake port size vs Runner size

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Hi,

I am trying to understand how the whole induction system works on a NA engine. 
Plenty of contradicting information on forums.

 

These are some diameter measurements on the Datsun L28 EFI induction system:

 Intake valve: 1.74"
 Intake port: ~1.5"    
 intake runners: 1.258" (on the head side, not TB side)

 

A few interesting things going on here:

 

 1. The runners cross section area is only 53% of the valve cross section area. (1.74^2 vs 1.258^2).
How come the intake runners are so much smaller than the intake valve? I would think this would cause issues.
If I would decide I would have everything be 1.74"

 

2. The intake port of the cylinder head is larger than the runner. (~1.5 vs 1.258)
I have read the reason is that this will help with a anti-reversion. Not sure I understand why.
Is this only interesting for low RPMs? So for higher RPMs a port matched runner would be better?

 

3. There is a slight taper on the runners. They are slightly larger at the TB side than on the head side.
Is this also only interesting for low RPMs?

 

4. Hard to answer but would it be pointless to put in a hotter cam and port the head if the intake runners are so small?
(The Datsun community are having a hard time agree on this, as many oppions as there are Datsuns)

 

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50 minutes ago, turbogrill said:

 1. The runners cross section area is only 53% of the valve cross section area. (1.74^2 vs 1.258^2).
How come the intake runners are so much smaller than the intake valve? I would think this would cause issues.
If I would decide I would have everything be 1.74"

For this one anyway (and definitely not a complete or researched answer), when the valve opens it doesn't just disappear, it's still sorta in the way. Air has to flow through the opening, then turn to flow around the valve disc and into the chamber. There's also the issue of the valve stem taking up some of that area (but not much). So in short, even though the valve opening is much larger in area than the intake runners, it doesn't flow a much larger amount of air.

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If the heads have zero "pot work" or a "stock" valve job it doesn't really matter. Port the heads as best you can. Not sure how the water jackets run in those heads, just be careful. The cam is going to make a difference. Typically the more port work you do...the more the heads will flow the more cam you can use.  It  is all about getting the good air in and the bad air out. Yeah I know I didn't answer your question.

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7 hours ago, enginerd said:

For this one anyway (and definitely not a complete or researched answer), when the valve opens it doesn't just disappear, it's still sorta in the way. Air has to flow through the opening, then turn to flow around the valve disc and into the chamber. There's also the issue of the valve stem taking up some of that area (but not much). So in short, even though the valve opening is much larger in area than the intake runners, it doesn't flow a much larger amount of air.

 

If you did want your valves to disappear then you need valves like this: http://www.coatesengine.com/csrv-system.html  Just like a rotary engine it is relatively limitless in RPM as it is not trying to completely reverse the direction of travel of things like pistons and valves multiple times per complete cycle.

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1 hour ago, Ron_e said:

 

If you did want your valves to disappear then you need valves like this: http://www.coatesengine.com/csrv-system.html  Just like a rotary engine it is relatively limitless in RPM as it is not trying to completely reverse the direction of travel of things like pistons and valves multiple times per complete cycle.

Um, wow. I would put a lot of that article under creative writing rather than reference material. I know you were only pointing out an alternative to poppet valves, but thanks for the entertaining read, Ron!

 

To expand with more "info" from another site:

"The real magic of CSRV lies in the numbers; horsepower and torque to name a few. A stock 302ci 5.0L Ford small-block was chosen as a test engine to demonstrate the awesome characteristics of CSRV. The original, stock engine was dynoed at 260 hp and 249 lb-ft of torque. After the CSRV heads were installed, and with no other changes to the short block, the same engine churned out 475 hp and 454 lb-ft of torque! This is due to the reduction in frictional losses and improved airflow. Furthermore, the lack of valvetrain limitations allowed the engine to spin to 14,750 rpm."

 

I would very much like to see the bottom end of that "stock" 302! :rolleyes:

 

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31 minutes ago, mender said:

...allowed the engine to spin to 14,750 rpm."

Image result for mother of god meme

 

 

I think I know what the Premium Dudes are upgrading next:    camshaft or valve train, non-OE: 50 pts per engine     

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12 hours ago, turbogrill said:

Hi,

I am trying to understand how the whole induction system works on a NA engine. 
Plenty of contradicting information on forums.

 

These are some diameter measurements on the Datsun L28 EFI induction system:

 Intake valve: 1.74"
 Intake port: ~1.5"    
 intake runners: 1.258" (on the head side, not TB side)

 

A few interesting things going on here:

 

 1. The runners cross section area is only 53% of the valve cross section area. (1.74^2 vs 1.258^2).
How come the intake runners are so much smaller than the intake valve? I would think this would cause issues.
If I would decide I would have everything be 1.74"

 

2. The intake port of the cylinder head is larger than the runner. (~1.5 vs 1.258)
I have read the reason is that this will help with a anti-reversion. Not sure I understand why.
Is this only interesting for low RPMs? So for higher RPMs a port matched runner would be better?

 

3. There is a slight taper on the runners. They are slightly larger at the TB side than on the head side.
Is this also only interesting for low RPMs?

 

4. Hard to answer but would it be pointless to put in a hotter cam and port the head if the intake runners are so small?
(The Datsun community are having a hard time agree on this, as many oppions as there are Datsuns)

 

Read this article by The Vizard of engines first:

http://www.superchevy.com/how-to/engines-drivetrain/sucp-0902-chevy-engine-port-variations-measuring/

 

Then this one with some nice pictures:

http://atlanticz.ca/zclub/techtips/headporting/index.htm

 

First, the quick answers:

1. Ditch the stock intake and go directly to a trio of 42 or 45 Webers. Big change for only 100 pts.

2. Match port the Weber intake and the intake ports.

3.Taper is good but not essential; don't sweat it.

4. More cam and porting = more hp even if the intake is small. Many racing series are based on little carbs and/or intake restrictors and the racers find a way. Compression helps a bunch.

 

Longer answers:

1. Port vs valve head size: usually the target is about 80% port diameter vs valve head size in the bowl area just below the valve seat. Bigger than that and the charge has to slow down to get into the port. Better to have it accelerate slightly instead; see #3.

2. Yes, a small step helps bias the flow in the right direction and is much better than having the opposite. Typical production practice is to have the intake runner slightly smaller than the head runner to allow for core shift during the casting process. Anti-reversion can be important with large cams but not much of an issue for what we do. Port matching is the way to go.

3. Taper tends to accelerate the charge slightly as it approaches the seat area, which in turn helps get the air around the turn and past the valve head into the chamber. The exact amount of taper can be a bit of a moving target depending on engine configuration and parts combo but just keep it in mind when you blend the port matching into the port.

4. Every engine has some impediment to flow. The trick is to open things up as much as you reasonably can then match the rest of the package. That will give you the most area under the curve. Keep your goals in mind throughout the process and you'll have a better shot at making decent power while keeping your efficiency up.

 

P.S. Like I said, compression helps just about everything. :)

Edited by mender
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I take no responsibility in bringing this to anyone's attention if they were not aware of it before.  Specifically if they were to find some way swap out each spherical valve with a tiny turbo utilizing only hand tools at their disposal... :lol::angry::lol:

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With out a flow bench you kind of in the dark. There is a lot of good info out there now that will show you the right way to do head work and porting.

I ran a flow bench and dyno for over 10 years so I got a good feel what works and what not to do.

i would look here for all your needs

https://www.goodson.com/

  • for the beginner  would do a 5 angle valve job 
  • match the ports and intake
  • clean up the ports with out taking metal out
  • up the spring rate or shim them a bit
  • use the best valve seal you can find

Bob Mann

www.DRVOLKS.com

bobtec@comcast.net

drvolkslogo.jpgtdtuninglogo.jpg

 

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