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1/22/2021 5:50 PM  #1


Engineering theory question

Historically, there are a lot of articles written about exhaust headers and how they pair up cylinders for efficiency.

What would be the ideal pairing on the intake side?
With 15426378 or 13726548?
I’m not an engineer., that’s why Im asking.

I’m thinking that the intake would look like a bundle of snakes.

 

1/22/2021 7:01 PM  #2


Re: Engineering theory question

Can you say........."single plane" as apposed to dual plane.
Single plane is just open and each cylinder sucks vapor when it needs it.
Tunnel ram is a single plane with a big-old 'bread-box' plenum underneath. That way there is a "box/plenum" full of gas vapor just waiting to be sucked by each hungry cylinder.
6s6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

1/22/2021 7:19 PM  #3


Re: Engineering theory question

God, I hope winter in UP goes away soon...


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

1/22/2021 8:02 PM  #4


Re: Engineering theory question

MS wrote:

God, I hope winter in UP goes away soon...

They be loooong winters up dare MS....sit back and unjoy da show...

 

1/23/2021 6:44 AM  #5


Re: Engineering theory question

It doesn't really matter.  The best intake is an individual runner system with a carb or throttle body on each runner because it best equalizes flow.  Such systems are expensive and very hard to tune.  Multi carb setups are in theory better than a single carb, but those are also hard to tune, and practically a single 4V on a proper manifold for the application will perform best.  Here's why:

Intakes and exhausts are quite different.  The idea behind pairing exhaust ports has to do with the pulse created in the pipe as the exhaust valve opens.  The exhaust operates under pressure, whereas the intake operates under vacuum.  When the exhaust valve opens pressure is expelled.  When the intake valve opens a vacuum is created that sucks the air and/or fuel into the cylinder. 

The idea with pairing exhaust ports is to equalize those pulses so they move at a consistent rate down and out of the exhaust system.  This creates the least amount of backpressure, because the pulses are timed to ensure that a pulse isn't created right behind another pulse, creating a bottleneck and resultant backpressure that prevents the second cylinder from fully evacuating.  Done properly there is a scavenging effect created that actually helps pull the exhaust into the pipe when the valve opens. 

On the intake side, by contrast, the air and/or fuel is always going to be sucked into the cylinder.  There is no pulse; nothing to conflict with another cylinder's supply of air.  So intake designs are instead tuned for the engine's intended operating RPM.  A short runner tends to be best for higher RPM operation, while a long runner builds low end torque.  Packaging constraints have led to long runner intakes looking crazy (think about the Max Wedge Chryslers that had the carbs over the valve covers). 

The other criteria for an intake is the plenum.  Typically as runners get shorter the plenum volume goes up.  The plenum is the reservoir for air and/or fuel.  At higher RPM it needs to be bigger, and less is needed at lower RPM.  Think about the effects of adding a carb spacer.  Basically you are just adjusting plenum volume.  This tends to improve HP on the top end, but may trade a little low end torque.  This is why in magazine dyno tests they often add a carb spacer that would never fit under the hood of a real car in the interest of chasing that peak number, which is all they care about.  In reality that spacer may cost low end torque that you'd rather have on the street than 10HP at 6,500RPM. 

Lastly, the reason I keep saying air and/or fuel is that EFI manifolds with port injection are dry whereas carbed or throttle body injection manifolds are wet.  You have to be careful comparing the two because dry flow and wet flow provide a different set of design criteria. 

In summation, intakes are designed based on runner length and plenum volume.  There's no benefit to pairing specific cylinders.  All of the designs like the Max Wedge, Cross Fire, etc are done in the interest of having a very long runner, and look crazy because of that, not any effort to pair specific cylinders.  Port EFI manifolds changed the way long runner intake are designed because without having to worry about the fuel falling out of suspension, from the mixture slamming into the walls of a convoluted runner, engineers were able to twist the runners around to get very long runners (A TPI Chevy has 18" long runners).  This is one reason the EFI engines make so much low end torque. 

 

1/23/2021 9:19 AM  #6


Re: Engineering theory question

TKO, what state do you live in?


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

1/23/2021 2:07 PM  #7


Re: Engineering theory question

MS wrote:

TKO, what state do you live in?

Confusion mostly.

 

1/23/2021 2:45 PM  #8


Re: Engineering theory question

This is my concept of what the intake would look like.


After my sketch, I noticed something very similar to the 5.8L truck intake.




Apparently some engineer thought this was a good design for the trucks.
Wouldn’t it have been cheaper to make it like the Mustang intake?

MS...you can blame Daze with his EFI 351W...and 9 months of winter.

     Thread Starter
 

1/23/2021 2:51 PM  #9


Re: Engineering theory question

I will take the blame  The truck upper is a dual plenum setup so each throttle body is feeding 4 cylinders.  There is however a dime sized hole cast between the two chambers, just past the throttle body mounting flange.  I can not see any way that the truck upper could be used on enything except a newr truck.  In fact the older bronco guys can't even use them as they won't clear the hoods.


If it isn't broken...modify it anyway! http://www.DazeCars.com https://galaxieforum.boardhost.com
 

1/23/2021 4:07 PM  #10


Re: Engineering theory question

I’ll share it with ya Daze.😁.

If you look at a carb dual plane intake, it is setup the same way.


     Thread Starter
 

1/23/2021 5:55 PM  #11


Re: Engineering theory question




Here ya go!!!!  Great minds do think alike!!
  Guess this would be a real torque monster with runners this long.
6s6
I just can't hep myself!

Last edited by 6sally6 (1/23/2021 6:00 PM)


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

1/23/2021 6:03 PM  #12


Re: Engineering theory question



should work great with this exhaust set-up!


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

1/23/2021 7:09 PM  #13


Re: Engineering theory question

6sally6 wrote:




Here ya go!!!!  Great minds do think alike!!
  Guess this would be a real torque monster with runners this long.
6s6
I just can't hep myself!

Naahh!!
He just did that so he could get the big stuff up high enough so he could see the road.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

1/24/2021 8:34 AM  #14


Re: Engineering theory question

What you are seeing in the carb intake is the desire for equal length/flow runners.  You are misinterpreting this to mean that there was some benefit to the arrangement of the runners based on the firing order of the engine.  Here's hole one in that theory:  That intake can be used on any SBF, with any cam, and therefore any firing order. 

Here's hole two: your reasoning as to why the runners are arranged the way they are is inherently flawed.  Your theory assumes that it must be due to the way the cylinders fire.  In actuality its so the runners are closer to equal length given the packaging constraints of a single 4V carb having to feed all of them.  The runners are designed to be equal length to equalize torque across cylinders, and also so that no cylinder has a longer more convoluted runner than another (within reason).  This is purely to keep the fuel from falling out of suspension as it moves through the runner.  Fuel only burns effectively when atomized.  Liquid fuel doesn't burn very well.  Therefore the arrangement you see is so the fuel reaches the cylinders in an equal length flow path with the fuel as atomized as possible. 

Then you're really muddying the waters comparing a truck intake to a carb intake.  The truck intake is not concerned about the fuel falling out of suspension because it does not see fuel.  So the question is, why does the truck intake have a dual plenum/dual throttle body arrangement that seems to be based on the firing order?  Its not what you think.  The truck intake was designed with the longest runners possible, while still being constrained by packing concerns.  The runner length precluded the possibility of a single large plenum.  Trucks are all about torque.  A long runner/small plenum combo is exactly what you want for torque, which is why the truck intakes have longer runners and smaller plenums that the car intakes.  The trucks were designed to rev out to 5,000RPM, whereas the Mustang had a fuel cut at 6,250RPM.  The Mustang was also considerably lighter, so they could trade a little low end for top end without it feeling soggy down low.  So it would have been cheaper to slap the Mustang intake on the truck, but they still had to sell trucks, and a truck with weak low end torque doesn't sell.  Different design criteria, and thus different intakes. 

The throttle body was changed to a dual setup because a single large throttle body produces inherently worse throttle response due to the surface area of the blade and how much area is exposed as the blade opens.  Its much harder to calibrate the fueling based on TPS input when the blade is huge.  Keep in mind that the trucks did not have an MAF; they were speed/density systems.  They could not measure the actual air mass entering the engine.  Properly calibrating for a big TB is hard even on an MAF engine, which is why tuners advise people to only run as much TB as they actually need.  Slapping a 75mm TB on an engine that's stock is a quick way to kill throttle response.

So fast forward and what you'll see in terms of intake innovation is that engineers decided that if they designed a variable runner length system they could have the best of both worlds.  Some engines came out with two sets of runners and could switch between long and short.  Others used valves to change the volume able to pass through the runners.  Its like VTEC for an intake.  Get the best of both worlds

Then that fell out of favor as manufacturers started to monkey with cam timing in a running engine.  Once they could change the intake air available with cam timing they basically abandoned the variable length runner systems.  Modern intakes have a single large plenum with either short straight or medium length curled runners.  Low speed torque can be achieved with cam timing, so midrange and top end power has been the primary design goal with these intakes. 

One thing I always go back to when I think I've figured out something the factory engineers didn't was something Smokey Yunick said in his book.  Basically, every time he thought he had some great new idea no one had ever thought of he would start to research it and most of the time discover that there was already a patent for it dating back 30 years, or he'd experiment with it for months only to find no tangible benefit.  Be careful of confirmation bias (looking at things only from the perspective of them proving your theory) and false correlation (drawing conclusions based on information that is coincidental instead of causal). 

 

1/24/2021 2:04 PM  #15


Re: Engineering theory question

Good info  TKO...............although I do nod off at times!!!  J/K
    (you add a lot to this board)
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

1/24/2021 3:07 PM  #16


Re: Engineering theory question

California emissions 94-97 trucks (4.9, 5.0, 5.8, and 7.5) had MAF.

Federal emissions trucks were speed density.

Last edited by Nos681 (1/24/2021 3:09 PM)

     Thread Starter
 

1/25/2021 5:55 AM  #17


Re: Engineering theory question

Nos681 wrote:

California emissions 94-97 trucks (4.9, 5.0, 5.8, and 7.5) had MAF.

Federal emissions trucks were speed density.

Yes, and you can add MAF to any of the trucks fairly easily, but the fact remains the intakes were designed for a speed/density application.  Even 1st gen Lightnings were speed/density. 
 

 

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