Wilde Racing

iTrader: (26)

First off, a few notes.
I do know there are a few threads about this topic on this site, but I havn't seen a thread were any real world results have been posted....
Also, I already know, I am not smart enough for this crap!!!

I've been working on a custom sheet metal intake for my truck. Well, I have the flanges made and I'm about to start fabing the runners. I've done quite a bit of on-line research on this site as well as others. But I have a few questions and ideas that I'd like to get feed back on...

First a little more of what I want from this sheet metal intake. The most important thing to me is equal flow/air distribution to all cylinders. I also want peak torque in the 5,000rpm range. Drivability is a huge concern for me. I want the intake to perform well at a vacuum but not be too restrictive at full rpm and boost. Basically I want the best of all worlds...

I've started figuring the intake runner length for my desired RPM of 5000 to taking advantage of helmholtz theory, but I don't know if I'm calculating this right...

Some stock truck intake data. Info from "HPBooks"
Plenum volume is 244.09 CID
Runner volume is 31.305 CID
Runner length is 10.35 inches
Now I know the stock runner width at the head gasket is 1", the volume is 31.305 and the length is 10.35, so the runner height "should" be 3.025 right? I figured the diameter (not that there is such a thing for square tubing) would be 1.9268. So using this formula,
L = ((EVCD × 0.25 × V × 2) ÷ (rpm × RV)) - ½D
Where: EVCD = Effective Valve Closed Duration RV = Reflective Value V = Pressure Wave Speed D = Runner Diameter
Formula with values
22.156= ((544 x 0.25 x 1275 x 2) ÷ (5000 x 3)) -.9634
22.156 is WAY too long, and even if I use the fourth or fifth pressure wave the runners still WAY too long.. Is there something I'm missing? The stock LQ4 cam duration is 196 correct? I know there are other formulas out there. Is this the best one to use?

I also want to divide the cylinders up in to two separate plenums. For the helmholtz theory to work effectively I couldn't just make a left bank plenum and a right bank plenum. I would need cylinders 1, 4, 6, and 7, and 2, 3, 5, and 8. This brings up another problem. How would you get equal flow and velocity to each cylinder when the runners would have to have different bends and lengths?

O.K this post is getting a bit long, I'll add more later if needed.....

Other related threads on LS1tech
https://ls1tech.com/forums/showthrea...ight=helmholtz
https://ls1tech.com/forums/showthrea...ight=helmholtz

Thanks for reading, if of course you made it this far......

1989GTA

"Runner length is 10.35 inches". Does that include the runner length inside the head? If not you need to include it. At 5000 rpm to pick up the 3rd harmonic wave your total runner length will probably be at least in the high teens length wise. That number may not be to far off.
Be sure to include the head for total runner length.

Old SStroker

I agree with 1989GTA that total length must include the head.

The source I use suggests the following for a 5000rpm peak:

24.25 in. with an additonal peak ~3700 rpm

18.00 in. with additional peaks @6700 (hp?) and 3900

14.00 in. with additional peaks @6400 and 4000

11.30 in. with an additiional peak @ 6200

A stock LS1/6 has a total length ~14.5 in. which tunes about 48-4900 and 6200. Not a bad idea to copy, IMO.

I would NOT suggest dividing up the cylinders as you propose.

Unless you have a lot of vertical height above the engine, you will need to bend the runners. You might look at the C5R and C6R LeMans Vette engines built by Katech which had rather low rpm peaks for induction ideas. No sense completely reinventing the wheel.

If you have never fabricated a sheet metal intake prepare yourself for significant distortion from welding.

Bottom line, IMO, is that the cost/benefit/hassle to build a sheet metal intake with runner lengths similar to stock or available aftermarket isn't worth the possible gains. I did not see your engne size and projected hp peak rpm, but unless the displacement is very large and you are looking for hp in the 8s or 9s NA, I'd look as what is already available.

As was mentioned in your referenced thread, just call Keith Wilson or perhaps Carl Folze and pony up the cash. Wilson has some new "combination" manifolds which consist of multiple CNC pieces welded together for runners and a curved sheet metal cover for the plenum. They look to be more economical to produce than his fully CNC, "minimum number of parts" manifolds. They can also get the runner lengths you need with the curved, multipiece runners.

My $.02

Wilde Racing

iTrader: (26)

I understand that the head needs to be accounted for. And it is not in the figures I posted above.

Can I ask how you got this info?

Which pressure waves are the ls1 intakes using? My info states they have a 10.35 inch runner without the head. There is no way the center of the intake valve is four inches in the head... What am I missing?

Is there a specific reason why not to divide the cylinders up?

I have a bit of room with the intake as it is going in a 2000 Silverado.
And you are right. The size of my engine and my hp goals do not need a custom intake. I have seen many people push far beyond my goals with stock stuff. But I want equality. Something I know a truck manifold could not give me....

Thank you both for your input so far.

1 FMF

iTrader: (1)

it's sat. morning and my brain is off so i haven't really *understood* your formulas above to be able to say if they are correct or what they might be missing.

buy the book how to build hp volume 2, carb's and intake manifolds, by dave vizard.
It has a decent amount of technical info, including formulas, and even has the word helmholtz in the text. I think of it more as acoustical ramming= where you tune the intake port length so the pressure wave peaks at the intake valve. this is the first time i've heard it referred to as helmholtz.

http://www.amazon.com/How-Build-Hors...7732291&sr=8-1


it was 2 years or more since i last read the book, but i'm pretty sure the helmholtz/acoustical ramming method is the least significant of all tuning methods. It's the last thing you try for to get that little bit extra, and it only has an affect in very narrow rpm ranges so this tuning method is really only geared to oval track engines where they run 6000-8000 rpm all the time. You had stated driveability is a major concern but you want peak torque in the 5000 rpm range, these 2 things contradict themselves especially on a truck engine i would think but i don't know what your goals are.

The biggest aspects of intake design is port cross sectional area and that affects performance over the entire rpm range. I would be most concerned with this first, before even considering runner length.

from my book for your initial question,

L = [ [(720 - ECD) * 0.25 * V * 2] / [rpm * RV] ] - (0.5 * D)

RV = reflected value
D = diameter of inlet pipe in inches
V = speed of sound but for intake air temperature, and would also be different if in a carb'd application where it's an air/fuel mixture
ECD = effective cam duration

and there's a blurb stating the reflection wave doesn't happen exactly at the end of the runner but about half it's diameter out from the end.

Old SStroker

No, it's very close to 5.0 inches from the manifold flange.

My numbers were based on work published by Prof. G.P. Blair. His stuff is quite good, but his software is pricey.

I wouldn't get all worked up over your "equal flow" thing. There are more productive places to spend your money. A great port and valve job on production heads comes to mind, as well as a valvetrain very specific to your application. Both of those things are available, but not here.

Jon

Wilde Racing

iTrader: (26)

Wow, I would have never guess the intake valve was so far in the head. I was planning on measuring it, but I wanted my runner length info first.

As far as cross section goes, I did not plan on changing it much. I still have the stock 317 heads, and the intake valve is the restrictor. Am I right in this line of thinking? I want the cross section to be as small as possible and still do the job...

I'm hung up on the equal flow because our truck intakes are far from flowing equally. Number 7 gets more airflow than any other cylinder, so you are limited to number seven for timing. Maybe the car style intakes do not lean out as bad as the truck intakes once boost is applied?..

Believe me, I already know the time involved in a project like this. I've already spent countless hours on just the flanges, which still need about 8 hours more work. But it is winter here, I need an intake, and I can weld. So why not? Even if my goals don't exactly deem a custom intake necessary. Plus the pride that comes with making your own parts is far greater than opening the hood and seeing a vic jr intake or someone else’s work, of course only if your intake works.....

Old SStroker

Whatever floats your boat, Wilde.

The engine doesn't give a crap what the intake manifold length is. It only cares what the toal intake length is.

You need to get help from a professional if your goal is to make more power and torque. Your ideas are, well, interesting, but not necessarily correct. If making it yourself is your goal, and screw the power and torque which you might got or not get, you are on the right track.

The ego is a dangerous thing.

Wilde Racing

iTrader: (26)

I was kind of hoping to talk to a professional here. I have a hard time calling people to ask questions about a service they charge for. I know I hate it, and I doubt "they" would appreciate it when there is nothing to gain from it other than the shear amusement of talking to me for hours....

I still would like to know why you think dividing the cylinders is a bad idea?

EGO IS a dangerous thing, but luckily my head is pretty big so I should be able to handle it.... I'm not saying I have to build it myself. If I had the money to pay someone else I would, but I don't and I kind of like a challenge...

Old SStroker

Part of this you answered in your first post:

If you want to divide up the cylinders, do it by bank. There are some good examples from Ferrari and even Chrysler, I believe. I'm not so sure you should base all of your design on Helmholtz theory from the HP book. If a front mounted throttle body doesn't enthuse you, mount one on top like a carb.

IMO, with one correctly sized plenum and similar runners with the correct entry bellmouth, you will get equal flow to the cylinders. Average velocity is basically flow divided by area so it will be the similar if the ports are similar. I would be more concerned with mass flow, the correct intake tract length and taper and the correct valve events. Oh yeah, at the top of my list would be the best port I could afford that fits the design goals I had for the engine. That is actually more difficult to find than a good manifold builder.

FWIW, you keep asking for advice, but I sense what you are after is agreement with your ideas. You may not get that here nor from paid "experts". I'm not an expert, but I have been involved in manifold design and build similar to what you are trying to do. My advice here is free...and worth at least as much as you are paying for it.

Jon

pantera_efi

iTrader: (1)

Hi ALL, I have created intake manifolds the allow for MORE air to flow into the manifold using a Helmholtz design.

This thread SHOULD be read AND remembered.

Lance