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How to decide runner taper?

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Re: How to decide runner taper?

Postby swampbuggy » Sun Jan 08, 2017 7:37 pm

Newold 1---------Please expand a little on what you mean by THINK END BELL in your above comments, thanks Mark.
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Re: How to decide runner taper?

Postby nhrastocker » Sun Jan 08, 2017 8:05 pm

F-BIRD'88 wrote:Be aware that a NHRA IHRA Superstock motor is VERY HIGH RPM.
They launch at a higher rpm than 6500 rpm. :^o Thats why the short(er) runner works.

Just saying. ... But beauti looking intakes.


There is not a single big block Super Stock that launches at 6500 rpm or higher. [-X [-X
One of my closest friends launches his record holding SS/GT Chevy Cobalt with a Chevy 350 between 3600~3800 RPM's.
Another friend of mine with a record holding 383 Barracuda in Super Stock class, launches between 3200~3600 RPM's.
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Re: How to decide runner taper?

Postby MrBo » Sun Jan 08, 2017 9:34 pm

nhrastocker wrote:
F-BIRD'88 wrote:Be aware that a NHRA IHRA Superstock motor is VERY HIGH RPM.
They launch at a higher rpm than 6500 rpm. :^o Thats why the short(er) runner works.

Just saying. ... But beauti looking intakes.


There is not a single big block Super Stock that launches at 6500 rpm or higher. [-X [-X
One of my closest friends launches his record holding SS/GT Chevy Cobalt with a Chevy 350 between 3600~3800 RPM's.
Another friend of mine with a record holding 383 Barracuda in Super Stock class, launches between 3200~3600 RPM's.

If you take it down to brass tacks, you can’t “launch” a car with a 7000 RPM converter at 3500 RPM.
You can only “cut the light” from the RPM chip. After the time required for you to roll through the beams to start the clocks (12”?), the converter should be near stall if the engine is making good beans.
"I promise you Sheriff, I won't throw one more rock... Didn't say nothin' 'bout no brick!" --Ernest T Bass
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Re: How to decide runner taper?

Postby nhrastocker » Sun Jan 08, 2017 10:31 pm

MrBo wrote:
nhrastocker wrote:
F-BIRD'88 wrote:Be aware that a NHRA IHRA Superstock motor is VERY HIGH RPM.
They launch at a higher rpm than 6500 rpm. :^o Thats why the short(er) runner works.

Just saying. ... But beauti looking intakes.


There is not a single big block Super Stock that launches at 6500 rpm or higher. [-X [-X
One of my closest friends launches his record holding SS/GT Chevy Cobalt with a Chevy 350 between 3600~3800 RPM's.
Another friend of mine with a record holding 383 Barracuda in Super Stock class, launches between 3200~3600 RPM's.

If you take it down to brass tacks, you can’t “launch” a car with a 7000 RPM converter at 3500 RPM.
You can only “cut the light” from the RPM chip. After the time required for you to roll through the beams to start the clocks (12”?), the converter should be near stall if the engine is making good beans.


Unless you run a Competition Eliminator style engine with a small CID in Super Stock Modified, you will not find a normal Super Stock or Super Stock GT running a 7000 RPM torque converter.
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Re: How to decide runner taper?

Postby F-BIRD'88 » Mon Jan 09, 2017 1:06 am

You mean he stages up against the trans brake at 3800rpm, Then releases the stage rpm limit chip and trans brake and launches at the flash stall speed. Usually 6500rpm+.
The engine rpm never drops below that rpm during the 1/4 mile.
I have S/S championship winning racing friends here too. I know how they run.
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Re: How to decide runner taper?

Postby Newold1 » Mon Jan 09, 2017 9:17 am

When I mentioned an end bell like shape on a tapered runner in a plenum, this was what I was referring to.
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Re: How to decide runner taper?

Postby Stan Weiss » Mon Jan 09, 2017 10:36 am

Erland Cox wrote:I use 90% of the valve curtain area at full lift for the area in the runner just before the radius to the plenum.
Make the radius 1/2" to 5/8" not greater.
You can change the tuned length with the radius.

Erland


Hi Erland,
I have asked this question before in these kinds of thread and always got differing answers. Do you select the plenum end size of the runner and the taper falls where it may, or do you set the taper and the plenum end size of the runner falls where it may?

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Re: How to decide runner taper?

Postby Erland Cox » Mon Jan 09, 2017 10:50 am

I calculate the port area with Pipemax to 260 fps at the CSA and try to get as little strangulation as possible from the pushrod.
So where the runner starts in size sepends on the type of head, Either a taper from the min CSA or from the push rod choke.
This is on a carbureted plenum type manifold.
On IR manifolds with Webers the area gets much bigger with a 46mm valve with 14,5mm lift and a 55 mm opening in the carb before the bell.
That is 106,5 % of the curtain area in the carb.
But a plenum manifold probably needs a stronger signal I guess.
I do not use a set angle, the taper is a byproduct of port lengths and areas and they are related to the camshaft.

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Re: How to decide runner taper?

Postby blownzoom440 » Mon Jan 09, 2017 3:22 pm

I looked at using my BDS blower intake on my 440 as a n/a but I think at lower rpm the fuel will fall out in the big plenum with runner length about 10" total with the head.I would agree with the 2/3* taper just going off what I may have read around here.
Note:That Modman intake is very much like my BDS that makes me think it will work.
"69"satellite,3900lbs,8-71,edel victor heads,I/C,446cu.in W/gas 1250 carbs
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Re: How to decide runner taper?

Postby JRL » Mon Jan 09, 2017 7:07 pm

Newold1 wrote:When I mentioned an end bell like shape on a tapered runner in a plenum, this was what I was referring to.


makes sense, reminds me of Jean-Michel Le Cléach's theories on acoustic horn designs.
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Re: How to decide runner taper?

Postby swampbuggy » Mon Jan 09, 2017 11:25 pm

Thanks Newold 1 for the answer, Mark .
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Re: How to decide runner taper?

Postby rebelrouser » Tue Jan 10, 2017 12:49 am

I race nostalgia super stock with a 64 dodge, 512 wedge engine. We have to run two carbs and keep them under a stock hood and factory available scoop. For a long time I ran a 63 max wedge intake. The motor has max wedge port Edelbrock victor Jr heads. With the cross ram it ran low 10's in a 3200 lb car. Car was kind of stuck at that ET for a few years. I could not afford to buy an indy cross ram, so I decided to build a manifold. Our rules say no sheet metal intakes, but we are allowed to modify the top of a production cast manifold. I started with a Edelbrock victor intake with max wedge ports and welded a box on the manifold and took and end mill and started hogging out the center. I then put it on a flow bench and started using cardboard and clay to make modifications. then used aluminum plate and a spool gun to build the inside of the manifold. Some of the guys in the group kind of scoffed at the idea how it would work. With no other modification but a few jet changes and the manifold the car went from a 10.20 et to a 9.75 at 140mph. I read a lot about plenum volume and runner taper before building the intake. I basically used the rate of taper built into the existing manifold runners and a plenum as big as I could make it. The runner finished at about 4 inches long in the manifold, which should be too short, but it worked. I run the engine about 6500 rpm so I don't have to wind it up to make it run. I also have to say the engine idles smoother and is much more drivable, it has a .712 lift cam with 275 duration and a 108 centerline. Last year I changed cams and went to a little more duration and got it to go a 9.64 I would post a picture but could not get it to work. If someone wants to see the manifold explain how to post to the forum and I will be glad to.
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Re: How to decide runner taper?

Postby F-BIRD'88 » Tue Jan 10, 2017 1:18 pm

If the picture is raw from your digital camera you want to process it a bit to make it more internet/forum friendly. Then post it.
Download and use Irfanview to do that. Its free.

Convert the camera picture to a JPG file format and resize it (make it smaller) 640x480 is plenty big
320x 240 is very forum friendly.
Resave in JPG format and increase the compression rate a bit to make the pic file size smaller
That makes it display faster on the forum page.
Your raw camera digital pics are way too big and the wrong format for posting.
http://www.irfanview.com

You can also correct the colour and brightness and sharpness of the pic using this free pic program. Often raw digital camera pics are too dark (poor lighting, poor exposure settings)

when while writing your post on the page scroll down the web page and find the Options upload attachment live link.
Click it and find the location on your computer where you saved the picture you want to post.

You can create a convenient easy to find working folder on your computer C drive
that starts w A eg: AAABIN that will always appear at the top of the folder list.
makes it easy fast to find when attaching stuff to emails or forum posts.
As long as the pic is not huge and is a JPG you can attach it directly to your posts from your computer.
other options are to upload your pics to a web picture archive host user acount like http://www.Photobucket.com offers.
and then add a link to that pic in the text of your posts.
It will show up as a live link.
Like this:
http://www.Irfanview.com
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Re: How to decide runner taper?

Postby F-BIRD'88 » Tue Jan 10, 2017 1:44 pm

I have also considered converting-MacGyver ing good single 4bbl single plane racing intake manifolds for multi carbs 2x4 3x2 etc with a added plenum box/carb adapter.
Very interested in what you did to yours.
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Re: How to decide runner taper?

Postby rebelrouser » Wed Jan 11, 2017 10:56 pm

000_0237.jpg
000_0237.jpg


Here are a couple pictures that I could find when I was building the intake. I first bolted to an old engine to hold it ridged, then welded a box and floor on the intake. Used an end mill in a Bridgeport and hogged out the center of the intake to make a plenum. I then set it up on the flow bench and used cardboard and modeling clay to get the flow as equal as I could to each cylinder. I also added some material to make the plenum turbulent. And welded material on each runner and made a bell type radius. I have never seen one up close but Dart makes a single 4 manifold for a BBC called the box ram that looks a lot like the manifold I built. http://www.jegs.com/i/Dart/301/43145000 ... wAod0-YBwQ
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