I am working on my intake manifold for my engine. But working with the pulses that generate when the intake valve closes that bounce off and travel back down the lenght of the runner then come back that shove more air into the cylinders when the valve is opened once again, is confusing me.

I have the H23 IM and am considering buying the Blacktrax IAB delete spacers. Maybe even several of them to bring down the RPMs where the pulses will be generated to help cylinder filling. This is on a f22b2 low revving engine so this is why i am doing this, i want low and mid range on my engine as it isnt a B series higher revving beast lol.

I measured once sloppily so may be off by a bit but im just asking a general question. When figuring the runner length do i measure from the valve to the runner opening at the plenum? OR from the valve to the back wall of the plenum. Im not sure because it makes sense to me the sonic pulse would be hitting that back wall of the plenum then coming back into the runner, but im not sure if it will just reach the end of the runner where it opens into the plenum and be bounced back at that point due do difference in the air movement or maybe even pressure... Might be dumb yes but it made sense to me and i am just trying to figure it out...

thanks

 

The waves bounce off the back of the valve, if that helps.

As for where it ends, not sure. I'm interested in that too. I'm thinking it's right where the splitter is, on the floor of the runner.

 

jeez

just build a couple and test them

its the only way to know if what you made truly works best

 

Some of us don't have access to dyno time as cheap as you do, Randy.

 

who says my dyno time is "cheap" haha

if hes building a manifold im assuming hes gonna go to the dyno at some point

so bring a couple of them to test

i have found calculations and theory to not hold true most of the time

how will you ever know something works better if you dont have anything to compare it to?

 

i definately dont want to sound rude in any way

thats just an aweful lot of calculating not to mention typing that post lol

if you are better w/ a calculator than you are w/ fabrication than keep up the good work

however if fabrication isnt a problem for you, then testing things in real life is ALWAYS the way to go

 

I have the same mind-set as you, just lack the tools/money/hook-ups you have.

And I don't think the OP is actually building a manifold, just modifying a stock one.

Come next year though, I will have the answer to what the OP really wants to know. I'm gonna test various H23 IM plenum/runner setups on a buddies 11:1 f22a build.

 

its fine, and i probly wont see dyno time, atleast not anytime soon. what i have done to my car is very very mild ha, i doubt i really have gained much, but hey im having fun and learning. Im not really better at either ha, just trying to figure things out. Im just brainstorming how i can get more "low and mid range". a high end screamer is nice, but as far as street (and abiding to speedlimits , i think mid range torque is the way to go..

 

You can do it on the cheap without dyno access.

Drop VTEC to 3500, or something low but not too low that you have oil pressure issues.

Each time you add a spacer, look at your 2-D WOT fuel map. Your BSFC will be highest at peak torque. Based on the shape of your fuel curve, you can determine where the resonances are occuring, and see as they increase versus engine speed or decrease.

Coming from someone who spent 2 years designing intake setups for restricted FSAE engines, there is no 'equation' or 'calculator' that can accurately predict wave resonances. There are way too many variables involved.

And to answer your first question, effective runner length is defined as the backside of the intake valve to the apex of the velocity stack, or for end of 'pipe'. While the waves do bounce off the back of the plenum wall, they also bounce off the mass of air inside the plenum.

 

very informative, thank you. I just dont have software/ the wideband sensor. So i really have no way seeing my fuel map... and i do not have vtec ha.

 

I think you are trying to run a marathon before learning to jog.

You need to get your tuning setup in place before you can realize the potentials of any bolt-ons. Sure you can make a few extra HP here and there from boltons, but you really need some sort of tuning solution before going too far from what the stock ECU can support.

Having no VTEC makes the analysis of the fuel curve even easier!

Hope that helps some.

 

Good to know, i was actualy under the assumption that getting a socketed ECU and gettin it tuned would be a waste with JUST bolt ons... but thats good to know ha, I was gonna hold off untill i got a new cam, some headwork/ valvetrain goodies

 

Sure, at that point the level of modification (cams, headwork, etc) is much beyond what the factory fuel and ignition map can support.

For reference, I made 186whp with my stock ITR + JDM 4-1 header + exhaust, after tuning I made 194whp, peak numbers increased a little, but it was the midrange gains of 10-15hp and 8-12tq that made the biggest difference from the tune.

I am certain you will gain more from a tune than from any amount of intake spacers.

My $0.02

 

wow, ha well ill look into that most definitly, i wouldnt have thought that a tune at that level of upgrades would yeild anything significant. Thank you

 

1. Decide on what RPM you want the IM to provide extra power to. 60 divided by that number will tell you how many seconds it takes the motor to make one revolution at that RPM (a).

2. Figure out how long your intake valves are open at that rpm. This is accomplished by first finding out how many degrees of crankshaft rotation your intake camshaft opens its valves for (b). Since the valves open once every two revolutions of the crank, you subtract (b) from 720 (720 degrees in two revolutions). This will give you the number of degrees of crankshaft rotation between when the valve closes and when it opens again (c). Next, divide (c) by 360. This will convert degrees into revolutions and you end up with (d). Finally, multiply the number of crankshaft revolutions between intake valve closing and opening (d) by the number of seconds the motor needs to make one revolution at your chosen RPM (a). This equation will tell you how many seconds pass between when the intake valve closes and when it opens again (e).

3. Since the shockwave reflected off of the intake valves travels at the speed of sound, you multiply (e) by 1125 [roughly the speed of sound in fps at sea level; this number can be altered if the motor will be run mostly at a different altitude] to get the number of feet the shockwave will travel during the time the intake valves are closed at your chosen RPM (f).

4. Since the shockwave must travel back and forth along the manifold runners to get back to the valves, you divide (f) by two to get the optimum length of the intake runners for maximum power at the chosen RPM.

The number will likely be way to big for intake runner length on an automobile. However, the benefit of the shockwave can be exploited to some degree with shorter runners as well. If we divide (f) by four instead of two, we get the length that the intake runners would need to be for the shockwave to bounce off of the closed valves, bounce off the back of the manifold, bounce off of the valves a second time, bounce off of the manifold back a second time and get back to the valves at the same time they open again. Number of feet (f) can be divided by any even number to accomplish a similar hp boost at different runner lengths. Each time the shockwave is reflected, it loses some of it's force and hp benefit. The reflections also make small changes in the time the shockwave takes to travel but that's usually not considered since we aren't aiming for that specific of an RPM. The shape of the intake runner and reflecting surface inside the back of the manifold can have a strong effect on how efficiently the shockwave is utilized.

 

Is this the same as "Ram Induction" ?http://www.chrysler300club.com/uniq/.../ramtheory.htm