Sheet metal intake building

[sanger351]

I just came across this site.  http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466

Do not forget to go to page 2.  What do you guys think about the info?
Thankyou for all the info so far and keep it coming.

[Blue]

I just came across this site.  http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466

Do not forget to go to page 2.  What do you guys think about the info?
Thankyou for all the info so far and keep it coming.

These rules are very good for engines around 10,000 RPM.  For lower RPM, we have to go back to the formulas and experimental evidence in Taylor and Heywood's books (what, you don't have them?!?!?).

Big rules for intakes:
1. Runner length and diameter should be based on the tables in Taylor.
2. Velocity stacks are critical.
3. Position the runners in the plenum by at least 1/2 the diameter of the runner.
4. Minimum plenum volume should be 1X engine displacement, 2X is better, more doesn't matter.

Hope this helps.

[ddahlgren]

Blue I beg to differ with you on plenum size that bigger does not matter. Everything matters and have had first hand experience with engines with to much plenum and they were very evil running things.

The guys in the article for the b-18 stuff are almost dead wrong on many things as well especially the stuff about the itb setup not resonating.. the use of sound waves is easy to understand but has little to do with intake tuning. I have designed this stuff for a living for over 30 years and have a small clue of what works..LOL..
Dave

[John Burk]

"have had first hand experience with engines with to much plenum and they were very evil running things."

Dave was this a wet plenum with fuel separation problems? What size plenum/displacement ratio do you like?

John Burk

[ddahlgren]

Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave

[Blue]

Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave

My comments reflected two givens that I should have stated:
1. Dry manifold with sequential port EFI where the fuel doesn't hit any wall before the intake valve.  To stay sequential the injectors need to be at <30% duty cycle.  Not to many people do this and it really whacks the idle control unless it's a dual injector per cylinder setup.
2. Throttle response doesn't matter.  For aircraft and LSR, this is a good idea.  For almost any other form of racing or street driving, it's a bad one! <LOL>

LSR is one of the few forms of racing that lends itself to optimizing for continuous power at a narrow RPM range and letting the rest of the power band fall where it may.  Of course, we have to get up to speed and fewer gears are simpler, stronger and lighter.  The only un-compromised vehicle I can think of with regard to throttle response is aircraft.  On a point design, resonance makes a huge difference that hurts the performance at any lower throttle or RPM setting.

Other than plenum volume, my experience shows the other 3 points are valid even needing good throttle response.  Trade offs are everywhere.

[panic]

Mr. Delaney's article (Integra site) completely confuses:
1. individual throttle bodies without a common plenum (ref: Weber IR, etc.)
2. individual port runners ending in a common plenum with a single throttle body (Edelbrock JG manifold as shown)
3. individual throttle bodies with or without a plenum fed from a Helmholtz resonator box

A sheet metal manifold is (generally) a "tunnel ram" design with tuned length port runners ending inside a sized plenum (plenum = storage device). If multiple throttle bodies/carbs are used, their air-horns may also end in a Helmholtz box (box = tuning device).
An important distinction: Helmholtz boxes are always dry, plenums are either dry (TB) or wet (carb) depending on the mixer - not on the manifold design.
Tunnel ram plenum volume is critical to power and response. If the volume is too low, peak demand cannot be satisfied by the flow rate of the throttle bodies (the obvious conclusion: if the TB flow rate is high enough, you don't need a plenum except as a connecting passage). If the volume too high in carburated apps, velocity and vacuum at the venturi drops and fuel drop-out occurs, fuel curve will be weird, poor response etc. In injected apps this is (obviously) not a problem but high volume may still cause other problems such as bad TB sensor readings.

The statement "ITB's do NOT use ram theory to get that extra kick at peak torque because they usually in race form do not have a plenum" is of course incorrect since it premises all ram theory on the "spring" and elasticity of air in a box.
What is given as "David Vizard's rule" for runner length is, in fact his rule for the intake pipe length of a Helmholtz box - not a runner at all.

[dieselgeek]

Too large a plenum will lag a driver request for more or less power a small one will lead think capacitor low pass filter sort of thing.. If you do some simple math and see what the plenum sees for demand per degree of crankshaft rotation it becomes obvious. It equally depends if the air metering device is before or after the plenum. After the plenum the plenum is invisible before and it is an active component.
Dave

My comments reflected two givens that I should have stated:
1. Dry manifold with sequential port EFI where the fuel doesn't hit any wall before the intake valve.  To stay sequential the injectors need to be at <30% duty cycle.  Not to many people do this and it really whacks the idle control unless it's a dual injector per cylinder setup.
2. Throttle response doesn't matter.  For aircraft and LSR, this is a good idea.  For almost any other form of racing or street driving, it's a bad one! <LOL>

LSR is one of the few forms of racing that lends itself to optimizing for continuous power at a narrow RPM range and letting the rest of the power band fall where it may.  Of course, we have to get up to speed and fewer gears are simpler, stronger and lighter.  The only un-compromised vehicle I can think of with regard to throttle response is aircraft.  On a point design, resonance makes a huge difference that hurts the performance at any lower throttle or RPM setting.

Other than plenum volume, my experience shows the other 3 points are valid even needing good throttle response.  Trade offs are everywhere.

not to question obvious authority, but my observation at bonneville is that the "peajy" power plants have the hardest time getting to their max speed, because of an on/off nature to their powerband.    It is (might be was) my opinion that having a nicely-variable, drivable powerband is not only a good idea, but almost necessary, for a driver to be able to ease up to their top speed...

Correct me where I am wrong!  thanks!

-scott

[sanger351]

What is a peajy engine??
This will be an EFI manifold and I would like the discusion to continue.  What are the thoughts on injector placement?  If I put the injector up the runner or in the bell vs in the head pointed at the valve, how will this affect injector timing? 
One thing to consider is that this is a purpose built engine operating between 4000-8500 rpm with a manual transmission.  Idle quality and lower rpm driveability are not a priority like many of the manifolds used for street use. 

Thank you everyone for the help so far, I am learning alot and I respect everyones input and experiances.

[Stainless1]

What is a peajy engine??

Thank you everyone for the help so far, I am learning alot and I respect everyones input and experiances.

Peaky with a typo, they are close together, the k and j

[dieselgeek]

oops, yes:  "peajy" = "peaky" typing way too fast. 

[rebelce]

For some of us, those who run Harley's or the vintage GMC/Chevy's with siamese intake ports, the problem of manifold tuning becomes even harder.  Are there any programs out there that simulate these designs?  I've had limited success with different length stacks on a Chevy 6 but would like to do a little research before logging up too much dyno ($) time. I absolutely hate the concept of  "It can't be done".

[4-barrel Mike]

Vintage Four Fords!

Exhaust Intake Exhaust Exhaust Intake Exhaust

Most intakes designed in the 30's.

I'm leaning towards a 4-barrel Holley mounted sideways.

Mike

[jimmy six]

Mike, worked for me. JD

[John Burk]

Nobody has mentioned how intake runner tuning actually works . A negative pulse starts when the intake cycle starts and turns into a positive pulse when it bounces off the upper opening . For most engines the runner length would be way too long but it works to let the pulse bounce up and down the runner multiple times and get to the valve as it's closing . When waves bounce back from the open end they change sign and maintain the sign when they bounce off a closed end . Acoustically an open valve is like a closed end so on the odd cycles (1st , 3rd) it comes down as positive pressure and negative pressure on even cycles . On 3rd cycle intake tuning the 1st and 2nd cycles happen during the intake stroke and cancel . The timing of the 3rd cycle is important which I think should be at bottom center.

It's basic math , 6000 rpm is .01 sec/ rev and 180 deg is .005 sec . At 1100 ft/sec x .005 sec is 5.5 ft  divided by 6 (3 up and 3 down) is a runner of .92 ft or 11" . Air speed adds about 10% to the round trip time the 6000 rpm length is actually 9.9".

At 2/3 and 4/3 of tuned rpm the negative pulse arrives at bottom center so it's important to pick a runner length that avoids these .

Exhaust tuning works the same but sound travels faster in hot air so the lengths are longer .

John