BBC Manifold Runner Parameters

Post by **SchmidtMotorWorks** » Thu Jun 02, 2005 2:15 pm

Yes i have thought about tall narrow shap but I see that the trend in tunnel rams is to make round opeings. Does anyone know the advantages or disadvantages of the round vs tall narrow openings?

todd8541 · Post by **todd8541** » Thu Jun 02, 2005 2:27 pm

I can't give you exact numbers but this is what I remember from fluids class and some tinkering. From a straight on shot the full circle is the most efficient shape for flow. But when the flow is coming at an angle (at entrance) it can be anything really. Mostly depends on the a variety of things. I have found that the correct shape is determined thru testing. I havent done any testing on a prostock intake but I am sure the reason the round is working for them is the distance from the carb to the intake runner is sufficient enough to allow it to react like a straight shot.

Todd

cboggs · Post by **cboggs** » Thu Jun 02, 2005 3:59 pm

Yes I think Todd is right on, .. with the sheet metal maifolds
the plenum is big enough and the shape allows for a round opening, ..
in a single for cast manifold you don't have the room, .. so
tall entries is the way to get the proper cross sections.

Have a look at some current manifold, .. like a Dart or Brodix, ..
then perhaps some one can post a pick of a good ported one, ..
I don't have one in the shop righ now to post.

Curtis

jdeleon · Post by **jdeleon** » Thu Jun 02, 2005 10:53 pm

CBoggs,
On the photo you posted of a comp sheetmetal intake.. I noticed the bolts on the side and bottom of the plenum. Could someone shed a little light on what might be stuffed in there.

Great thread!

Schmidt,
Really nice cad work.. i think you've got a great idea, port spacing for the thousands of brodix and darts out in service right now would be a nice market.

cboggs · Post by **cboggs** » Fri Jun 03, 2005 1:45 am

jdeleon wrote:CBoggs,
On the photo you posted of a comp sheetmetal intake.. I noticed the bolts on the side and bottom of the plenum. Could someone shed a little light on what might be stuffed in there.

it's discussed in the thread that contains that photo, ..
viewtopic.php?t=1164

Varius forms of "stuffers" are used in the plenum to effect volume
and sometimes entry radius.

Curtis

Post by **SchmidtMotorWorks** » Fri Jun 03, 2005 2:02 am

Here are some guesses.

I have made a few sets of cutomer designed plates that are bolted into the inside of some older profiler manifolds that had short runners. It extended the runners and filled the plenum some. I also made some plenum spacers for the same guy.

I had a Honda Interceptor (back when they were cool (86?)) and it had these rubber tubes extending the carb into a v plenum. They were held down by a plate that had screws on the outside if I remember correctly.

I saw some manifolds at Honda HPD that had trumpets bolted to the inside.

Post by **SchmidtMotorWorks** » Sat Jun 04, 2005 2:02 pm

OK here is the next version, 0.5" radius divided runners, bigger plenum, etc.

This is a positive of the inside of the manifold.

What do you think?

cboggs · Post by **cboggs** » Sat Jun 04, 2005 4:01 pm

Don't think that'll work, ..

here's photo from Larry's web site of a plenum, . Larry I hope
you don't mind.

See how the pairs of runners meet under each veturi of the carb, ..

perhaps try taking your original design and shift the runner where they
meet the plenum so they are side by side instead of on top of each other?

Curtis

Post by **SchmidtMotorWorks** » Sat Jun 04, 2005 4:45 pm

I was thinking of how I would make this manifold if I wasn't building it from flat pieces.

or this one

What I see in the modified aftermaket manifolds are efforts to make longer runners by crowding them into the plenum. I am thinking that the existing manifolds are the way they are because of manufacturing costs and racers are just making the best they can out of what they have to work with. A casting like you see from Brodix can be made in green sand for about $100, one like my tunnel ram or the new one I just posted would cost about $300 to cast in dry sand. I know for certain the way the runners are angled on all single plane manifolds that I have seen is so that the cope side of the pattern can mold the entire top side of the manifold.

Even if a manifold like the one I just posted made 50hp, I doubt that brodix or Dart etc. would make it becuase it would cost 2-3X what the current manifolds cost to tool and cast and as far as I know, none of them even use 3D solids CAD to design thier manifolds or tooling and making a manifold like this would be a nightmare without CAD CAM.

Post by **SchmidtMotorWorks** » Sat Jun 04, 2005 5:16 pm

See how the pairs of runners meet under each veturi of the carb, ..

perhaps try taking your original design and shift the runner where they
meet the plenum so they are side by side instead of on top of each other?

I am not convinced that those dividers guide fuel distribution for a couple of reasons:

1. When you look straight down on them they are off center from the venturis and appear that they would bias flow toward one cylinder much more than the other.

2. The firing order influence is similar on cylinders 1&2 and 7&8 yet the manifolds seem to be indifferent to this characteristic. My conclusion is that there really isn't that much science there.

On friday I was at a foundry that makes prototype cast manifolds for small block engines (probably NASCAR) directly for OEM (about 15K each). On those manifolds the plenums were long and narrow. The end runners were about 3 inches to the (front and back) away from the carb. Since they were making at least 8 of them that I saw, I guess this design has some merit (at a $115,000 bill).

67RS502 · Post by **67RS502** » Mon Jun 06, 2005 10:59 am

The old "inside" looked good, the outside runners were point straight at the plenum.
On the new "inside" it looks like you moved the inside runner out (front & rear) and moved the
outside runners move so. Can you move both sets of runners "in" (front to rear) so the outside set
have a straighter show from the plenum. I think you tried to make it too much like a tunnel ram,
and it should still be like a singleplane - tall, with a straighter shot from the plenum to the outside
runners, with as large a radius at the runner dividers as possible.

Post by **SchmidtMotorWorks** » Mon Jun 06, 2005 12:44 pm

Can you move both sets of runners "in" (front to rear) so the outside set
have a straighter show from the plenum. I

Yes, I am thinking the same thing. I am working on a next model with that in mind. Thanks.

Harbinger · Post by **Harbinger** » Fri Jun 10, 2005 7:22 pm

The manifold LOOKS good. The modeling is impressive.

I'm curious about functionality. What are you using for CFD to make sure you can get the most out of this design the first time around?

Thanks.

Post by **SchmidtMotorWorks** » Fri Jun 10, 2005 8:37 pm

I have access to Fluent CFD, COSMOS and the legacy stuff from SDRC.

I doubt that any of those basic software will show reveal any suprises unless you get into modeling the pulses with something like riccardo and I have heard the Fluent has something for that now too. Unfortunatly ricardo is way beyond what an aftermarket or hobby person can afford in money or the time to learn it, plus I don't have the pressure/timing data to input. Those type of analysis projects must have teams of people collecting data.

I would like to work with someone that did IC stuff to aleast get their perspective.

One of my coworkers used to work at a company that did analysis software that included CFD. He told me that when you get to IC stuff that success is considered coming within 25% of what you find in the real world.

I tried to model a surfing wave one time in CFD, I think I was at 150 hours before it looked anything like a real wave.

shawn · Post by **shawn** » Fri Jun 10, 2005 8:38 pm

wouldn't it be nice to have one of those stereo lithography machines to spit one out and test with?
shawn