Advanced Engineering Tech - Intake manifold runner length.

So I will be building a manifold for my 383, I know I want a plenum volume of around 210 in3. Its been awhile since ive done the math and I cant figure out what length runner to use, Im not looking to make top end power so the runner will be longer, I would like to make power from 1500-6700 rpm range. every time I do the math I come up with an 11" runner what am I doing wrong? what should it be?

this might i mean might just help

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=471

Ill check it out, I was starting ti wonder if I would ever get a reply.

You want a taper in the sidewalls

Tapering the runners increases top end, that's not what I'm looking for.

Tapering the runners increases top end, that's not what I'm looking for.


I suggest that you get professional help to do your intake manifold. Much of what you have posted is questionable.

FWIW, some of the references in this thread are not all that good either.

If you want to make power 1500-6700 there are some OEM and aftermarket choices, especially for cathedral port heads, that work quite well. Why are you tyring to reinvent the "wheel"?

Good luck whichever route you take.


Jon

I would just like to make one for a lsx motor, this is not my first sheet metal manifold, its just been awhile. The last one I made was for a turbo application on a 4 cylinder. Im not trying to reinvent the wheel just want to do it for fun. plus I don't think it will cost me anything with the materials I have laying around, I might need some more injector bungs machined but I might have enough.

I would just like to make one for a lsx motor, this is not my first sheet metal manifold, its just been awhile. The last one I made was for a turbo application on a 4 cylinder. Im not trying to reinvent the wheel just want to do it for fun. plus I don't think it will cost me anything with the materials I have laying around, I might need some more injector bungs machined but I might have enough.

Sorry I ragged on you. I thought you wanted to make power rather than just have some fun fabricating.


Jon

Sorry I ragged on you. I thought you wanted to make power rather than just have some fun fabricating.


Jon

There can be a hell of a lot of satisfaction in achieving both.

I just love welding aluminum! and manifolds are fun and always look cool when your done. It doesn't matter if you do a stainless turbo manifold or an aluminium intake manifold, when you show it to others and they know you did it your car will always be Bad ass! :devil: I know its not a manifold, or a lsx car but here are some of the latest things Ive been fabing up on my track car. http://i391.photobucket.com/albums/oo355/TeamTruax/IC3.jpg http://i391.photobucket.com/albums/oo355/TeamTruax/IC1.jpg http://i391.photobucket.com/albums/oo355/TeamTruax/IC2.jpg my newer inter cooler/oil cooler set up.

There can be a hell of a lot of satisfaction in achieving both.


Absolutely! However the design has to be correct to make the power. That's where most folks fail.

To corrupt Gusteau's book title: "Anyone Can Weld"

FWIW: 10 bonus points if you know where that ^^^ came from.


Jon

So I will be building a manifold for my 383, I know I want a plenum volume of around 210 in3. Its been awhile since ive done the math and I cant figure out what length runner to use, Im not looking to make top end power so the runner will be longer, I would like to make power from 1500-6700 rpm range. every time I do the math I come up with an 11" runner what am I doing wrong? what should it be?

11" is gonna be towards the upper RPM. It all depends on which pulse you are trying to catch. A longer runner will grab a stronger pulse, which also makes the manifold work in a narrower RPM range. Also remember when calculating runner legnth the measurement is from the valveseat to the plenum in the center of the runner. So 11" may be slightly long if you want it to lay down at 6700 RPMs. Someone correct me if im wrong. Its been awhile since ive messed with the intake math.

11" is gonna be towards the upper RPM. It all depends on which pulse you are trying to catch. A longer runner will grab a stronger pulse, which also makes the manifold work in a narrower RPM range. Also remember when calculating runner legnth the measurement is from the valveseat to the plenum in the center of the runner. So 11" may be slightly long if you want it to lay down at 6700 RPMs. Someone correct me if im wrong. Its been awhile since ive messed with the intake math.


With a headport C/L length about 5.4 inches, plus an 11.0 inch intake manifold runner I get peaks at 7400, 5500, 4300, 3500.

If the intake runner is about 12.7 in. long I get peaks at 6700, 5000, 3900, 3100.

If you drop the intake runner to 8.0 in, you drop another harmonic. I get peaks at 6700, 5200, 4200.


Jon

Now I get more useful info, Im looking for the calculation. I cant find my text book on it right now its buried in the garage somewhere. Are you saying the head port C/L is 5.4 or are you just saying if it is 5.4?

Now I get more useful info, Im looking for the calculation. I cant find my text book on it right now its buried in the garage somewhere. Are you saying the head port C/L is 5.4 or are you just saying if it is 5.4?


You should measure your heads and decide what intake centerline length you want to use. Cathedral port LS heads have a considerable length difference from the long side to the short side. Some folks take the average as the C/L length.

Jon

Ok this is one of the reasons why I want to make a manifold. If you buy one it will be standardized for the 347ci with stock heads I would assume, and not account for any changes in ci or head manufacturer.

Absolutely! However the design has to be correct to make the power. That's where most folks fail.

To corrupt Gusteau's book title: "Anyone Can Weld"

FWIW: 10 bonus points if you know where that ^^^ came from.


Jon

I don't know where that came from, but I'm guessing it applies handily to my shitty welding "skills".

Ok this is one of the reasons why I want to make a manifold. If you buy one it will be standardized for the 347ci with stock heads I would assume, and not account for any changes in ci or head manufacturer.


See post #6:

I suggest that you get professional help to do your intake manifold. Much of what you have posted is questionable.

Jon

With a headport C/L length about 5.4 inches, plus an 11.0 inch intake manifold runner I get peaks at 7400, 5500, 4300, 3500.

If the intake runner is about 12.7 in. long I get peaks at 6700, 5000, 3900, 3100.

If you drop the intake runner to 8.0 in, you drop another harmonic. I get peaks at 6700, 5200, 4200.


Jon

Would you mind going over how you arrived at those numbers?

My understanding is that you'd need the cam's intake duration to put a specific RPM and runner length together.
I don't recall cam specs being mentioned...

Would you mind going over how you arrived at those numbers?

My understanding is that you'd need the cam's intake duration to put a specific RPM and runner length together.
I don't recall cam specs being mentioned...

Cam specs come last, not first. Well, that's not always what you hear, is it?

FWIW,"Anyone can weld" was not a reference to the quality of anyone's welding. It just means that anyone can learn to weld, but not everyone takes the time and study to understand how engines work and how to successfully design systems for them.

Making a beautiful looking intake manifold which has the wrong dimensions for making power is a lot like polishing a turd. It may look good, but in the end it's still a turd.


Jon

not everyone takes the time and study to understand how engines work and how to successfully design systems for them.

Making a beautiful looking intake manifold which has the wrong dimensions for making power is a lot like polishing a turd. It may look good, but in the end it's still a turd.


Jon[/QUOTE]

So true, or they do and then they dont use it all the time and forget.

while i agree that an intake needs to be designed by "professionals" to be correct for the application,most "professionally" built sheetmetal intakes have nothing to do with being correct for the engine-but more to do with what looks good and fits under the hood.

A very basic formula is:

L = 72C/N, +/- 3 inches

Where L = intake tract length, N = RPM of max ram effect, and C = speed of sound. This formula is accurate though if and only if speed of sound in the runner is 1166 ft/sec.

As for the valve events, the intake and exhaust tuning formulas are based off that in relation to camshaft degrees. That's where the cam comes in.. last, as Jon said. The exhaust side (header primary diameter and length) is imo just as important as what you want to do on the intake side. There are formulas to calculate that too. But, you only get the first formula, :)

Side note: Jon, do you happen to have "Hot Rod Magazine" July and August 1964 issues laying around? I'd pay to have Gordon Blair's article Xerox'd and mailed to me.

A very basic formula is:

L = 72C/N, +/- 3 inches

Where L = intake tract length, N = RPM of max ram effect, and C = speed of sound. This formula is accurate though if and only if speed of sound in the runner is 1166 ft/sec.

As for the valve events, the intake and exhaust tuning formulas are based off that in relation to camshaft degrees. That's where the cam comes in.. last, as Jon said. The exhaust side (header primary diameter and length) is imo just as important as what you want to do on the intake side. There are formulas to calculate that too. But, you only get the first formula, :)

Side note: Jon, do you happen to have "Hot Rod Magazine" July and August 1964 issues laying around? I'd pay to have Gordon Blair's article Xerox'd and mailed to me.


1964? Damn, I had just turned 21 and got my first GTO. Prof. Blair is a little older than I but he was still a youngster back then.

Perhaps you meant 2004?

You can get most of his info in here:

http://www.amazon.com/Design-Simulation-Stroke-Engines-R-186/dp/0768004403/sr=1-2/qid=1164855875/ref=sr_1_2/002-4919722-9619246?ie=UTF8&s=books

FWIW this in in the sticky Books 101 in this forum. Too bad people don't study it.


Jon

After a physics degree and John Dixon's "Tires, Suspension and Handling", I'm no stranger to heavy reading or doing my own research. When the time comes I'll be getting some of those books. I think I already have Scientific Design of Exhaust and Intake Systems on the shelf... just haven't built the first headers or manifold yet.

I am continually amazed at how unwilling people are to explain advanced topics in a forum called "advanced engineering tech". I moderate tech forums elsewhere on the internet and I get *tired* of answering the simple questions. It makes my day when someone wants to dig down into the deep magic and really understand something.

Oh well...

A very basic formula is:

L = 72C/N, +/- 3 inches

Where L = intake tract length, N = RPM of max ram effect, and C = speed of sound. This formula is accurate though if and only if speed of sound in the runner is 1166 ft/sec.


Thanks.

While this is a nice formula, I'm looking for the *derivation* of this and similar math (*math*, not arithmetic; there aren't any numbers in math). I guess it just isn't on the internet anywhere.

I am continually amazed at how unwilling people are to explain advanced topics in a forum called "advanced engineering tech". I moderate tech forums elsewhere on the internet and I get *tired* of answering the simple questions. It makes my day when someone wants to dig down into the deep magic and really understand something.

Oh well...

I am continually amazed at the peple who want to be spoon fed the answers without expending any effort to try to understand what it is all about. That's why I don't give out the math. It is available and if one studies the "why" and gets an understanding then the formulae are useful.

A few years ago I tried explaining things in detail on this forum, but most of it fell on deaf ears and the typical response was, "So what is the answer I need. I don't have time to figure it out." I decided to stop explaining (give the man a fish) and rather suggest avenues where they could find the information for themselves (teach a man to fish). Those that "learn to fish" are better for it and those who just want to be given a fish....well I don't care to oblige.

There are times when you can lead someone toward understanding, but they just don't get it. Either their mind is already made up (often on an erroneous notion) or they don't have the ability to understand. Either way it is frustrating to deal with such people.

"There are some people who, if they don't already know, you can't tell 'em."....Yogi Berra

God love you, Yogi!

A few other folks I know also stopped explaining stuff they learned the hard way to those who are too lazy to work for the information.


Jon

Thats what I was looking for thanks!

A few years ago I tried explaining things in detail on this forum, but most of it fell on deaf ears and the typical response was, "So what is the answer I need. I don't have time to figure it out."

Pearls and swine. The average Joe wants the cookbook answer and actually gets frustrated when you try to help him understand why it works. Strange.

My take is that the average Joe can buy a cookbook and find the good enough answer more easily than even the apt pupil can sift through hundreds of pages and hundreds of dollars (the advanced engine analysis books in the recommended reading thread total over $800) of advanced reading, do all the derivations, etc.

I realized a long time ago that I can't fix all the ignorance on the internet. These days I usually just toss out a casual question to get someone to doubt his fundamental assumption. If the light bulb comes on, great. If not, oh well.

http://xkcd.com/386/

I am continually amazed at the peple who want to be spoon fed the answers without expending any effort to try to understand what it is all about. That's why I don't give out the math. It is available and if one studies the "why" and gets an understanding then the formulae are useful.

A few years ago I tried explaining things in detail on this forum, but most of it fell on deaf ears and the typical response was, "So what is the answer I need. I don't have time to figure it out." I decided to stop explaining (give the man a fish) and rather suggest avenues where they could find the information for themselves (teach a man to fish). Those that "learn to fish" are better for it and those who just want to be given a fish....well I don't care to oblige.

There are times when you can lead someone toward understanding, but they just don't get it. Either their mind is already made up (often on an erroneous notion) or they don't have the ability to understand. Either way it is frustrating to deal with such people.

"There are some people who, if they don't already know, you can't tell 'em."....Yogi Berra

God love you, Yogi!

A few other folks I know also stopped explaining stuff they learned the hard way to those who are too lazy to work for the information.


Jon

So true, Jon. No reason to continually :bang: