Making an intake runner thinks it's longer?

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427dart
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Making an intake runner thinks it's longer?

Post by 427dart » Thu Mar 08, 2018 10:00 am

Let's say you have a tunnel ram type intake manifold that has runners shorter than you want for a particular RPM/ HP range.
Say for example the runner is 6 inches in length and results in power range from 5000-7500 RPM.
Would adding a divider about .090 in thickness and 4 inches in length centered in the runner speed the airflow up thus moving the power range down
to 3500-6500?
Just one of those "what if" ideas!

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Re: Making an intake runner thinks it's longer?

Post by 67RS502 » Thu Mar 08, 2018 1:15 pm

In a tunnel ram you could fill the plenum by extending the runners in to it.
This would kill some plenum volume and give you the runner length desired
and move the powerband down.
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Re: Making an intake runner thinks it's longer?

Post by groberts101 » Thu Mar 08, 2018 1:20 pm

Could work as a bandaid but generally you want the mass up high in the induction to gain more speed as it eventually approaches the valve seat. This softens the returning signals towards the carb and creates a sort of funnel effect of mass into the cylinder.

What I myself would look towards is.. fill the lower portion of the manifolds runner exits to gradually close up the CSA about 3-4" up towards the plenum entries. If the engine is very well fed and doesn't need all of that excess surplus flow capability then you can turn your attention towards port velocity to improve some of the lower rpm ranges power and response. Better to be a little too small than way too big. The other benefit that could be capitalized on is the entry angles and specific location of the manifolds port exit location. This could mean the ports exit is puttied to locate that now smaller port location to say.. the top right corner(exaggerated for concept of course) of the heads entry port to reduce slamming into the PR pinches bulge. basically move the fastest moving mass away from the pinch intrusion. Having the manifolds port exit up high/higher head entry also allows those now higher floor speeds to start navigating over the SSR from a higher starting point. Double apex that allows flow to stay off that "ski jump" and bend where it needs to based on mass flow rates.

The other beneficial result would be the natural anti-reversion characteristics created from such a port mismatch. This also has the effect of making the cylinder think that the manifold runner is longer than it actually is when the signals get bounced and buffered away from the carbs booster even more. The smaller cross section also does this to a degree in that reverse flow fights a faster moving river to make it back upstream. Also consider what a smaller primary pipe size does on the exhaust ports pressure differentials. As Calvin Elston said many times over the years.. it "shuts the back door" to help reduce charge contamination. This would be shutting the front door to help reduce reversion and trick the cylinder into thinking the port is longer than it actually is.

Could also sharpen up radii for the transitions to each runner entry which gives the initial charges movement into each runner a "better snap" to mimic a longer runners inherent dynamic response benefits. Works best with dry EFI intakes but also allows some tuning on carb'd intake tract as well.

PS. you don't know how hard I had to try not to quickly post.. "just put a 55° seat on it and open up the throat!". Glad I didn't do that though. :mrgreen:

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Re: Making an intake runner thinks it's longer?

Post by Newold1 » Thu Mar 08, 2018 4:21 pm

I like a lot of groberts 101 ideas. X2

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 4:40 pm

You can try out all your theories on a simple p pipe like a organ pipe.. Instead of trying to make a intake "think" it is longer or shorter ehy not make the pipe be longer or shorter as needed, on the fly... Make the intake runner adjustable length.

Now you have real adjustable resonant tuning of the induction system.

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 4:44 pm

In real terms it is easier and more practical to make a long pipe act (or be effectively) shorter then try to make a short pipe act longer.

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Re: Making an intake runner thinks it's longer?

Post by groberts101 » Thu Mar 08, 2018 4:52 pm

sure.. but the induction has to still be low enough to not fly off the engine at over 100mph. :lol:

all I was getting at is to adjust the runner speeds and pressures within the existing manifold to make the CYLINDER think that the manifold gained some length. You can't add 12" of runner length, no.. but you can maybe tune things to make the motor respond like it gained another 1". That along with the previous posters plenum fill which does actually gain some length will make the motor see even greater runner lengths. Some of this stuff often cancels out other gains found elsewhere though, so it's all about the test and tune to flush out positive results in the end.

Any other idea's revolving around "what's actually possible with his current parts?"

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 6:23 pm

It is really hard to make something be different using the same parts... You need to think outside the box.

If you want intake runners that can be both longer and shorter
as needed and also have short carb height too,

Make the runners flexable.. Now bend hte runner outward in the middle... result longer runner path, same carb height.

Make the runner of a new material that can be streched and bent too.

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 6:29 pm

If you want a short tunnel ram manifold with common open plenum to be more responsive at lower rpms add a slidable plenum divider plate or collapsable plenum divider.

Divided plenum at low rpm,, open plenum at high rpm

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 6:33 pm

Make a new 2x4 carb plenum top for the maniifold with a sliding internal plenum divider.

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Thu Mar 08, 2018 6:59 pm

a trumpet a trombone a clairenet or flute aee all examples of adjustable length tunable dresonant ducts ( tunaple pipe)

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Re: Making an intake runner thinks it's longer?

Post by 427dart » Thu Mar 08, 2018 7:41 pm

F-BIRD'88 wrote:
Thu Mar 08, 2018 6:29 pm
If you want a short tunnel ram manifold with common open plenum to be more responsive at lower rpms add a slidable plenum divider plate or collapsable plenum divider.

Divided plenum at low rpm,, open plenum at high rpm
I actually made a slidable plenum divider for a single plane intake years ago for my Mopar 340 project!
The divider would move from halfway down to fully divided by way of a choke cable which was routed down thru the air cleaner stud hole on the Holley carb.
You could hear and feel the idle smooth out a bit when you raised the divider slide up. The throttle response was much improved also.
If I recall this was on my W-2 headed 340 using the Holley single plane intake which was one of only 2 intakes that were available for the w-2 heads during the early 80's.
Later on I found a Edlebrock LD-340 high rise dual plane intake that was cast for the new W-2 heads.
Edelbrock made only a dozen of these W-2 intakes which were available to some NASCAR teams for testing and I got that one from Petty Racing.
It worked very well on the street! I should have kept that manifold when I sold my 1969 Dodge Dart GTS with that engine.

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Re: Making an intake runner thinks it's longer?

Post by BOOT » Thu Mar 08, 2018 8:13 pm

groberts101 wrote:
Thu Mar 08, 2018 1:20 pm
Could also sharpen up radii for the transitions to each runner entry which gives the initial charges movement into each runner a "better snap" to mimic a longer runners inherent dynamic response benefits. Works best with dry EFI intakes but also allows some tuning on carb'd intake tract as well.

I'm interested in more detail of this for a small engine efi intake I am gonna do.

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Re: Making an intake runner thinks it's longer?

Post by F-BIRD'88 » Fri Mar 09, 2018 1:01 pm

A dual plane intake acts as if its longer than its runners are.

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Re: Making an intake runner thinks it's longer?

Post by Belgian1979 » Fri Mar 09, 2018 4:09 pm

427dart wrote:
Thu Mar 08, 2018 10:00 am
Let's say you have a tunnel ram type intake manifold that has runners shorter than you want for a particular RPM/ HP range.
Say for example the runner is 6 inches in length and results in power range from 5000-7500 RPM.
Would adding a divider about .090 in thickness and 4 inches in length centered in the runner speed the airflow up thus moving the power range down
to 3500-6500?
Just one of those "what if" ideas!
My toughts :
Not sure if I understand it correctly, but I don't see why adding a divider 'in' the runner would do anything in terms of added intake tract length. I could see some effects taking place in directing airflow or smoothing airflow maybe.

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