Disclaimer: I may not have any idea what I'm talking about...I am just interested in a little technical discussion. And I want to get some stuff out of my head.


What makes hp? Well from what I gather, the amount of oxygen to burn when the spark plug ignites is what creates hp...essentially, or at least there is some sort of direct correlation there.

So we can assume the the total amount of flow into the engine is proportional to the total amount of HP we create. Now the equation for Mass Flow Rate = Pressure x Area x Velocity. So think about that....if you increase Velocity just 10%, that has the same effect on your engine as if you were to add say 22lbs of boost instead of 20lbs of boost.

As far as I can tell, no current intake manifold is optimized to promote velocity. If fact, I guess we just decided that the people doing headwork are the ones who need to worry about that? I have no proof, but just by looking at current manifold design ( for hondas) They would be designed more for increasing the Area part of the equation. Looks to me like air would enter the throttle body, then just hit a wall of turbulence, because it has no idea where to go. Velocity would be fucked. Now some companies may have realized this and that is why they put velocity stacks in their manifolds, which do help. (we'll talk about them later)

So why isn't there a manifold that promotes equal length and velocity? The only thing I can think of is that people may think that it would require runners that are too long. Long runners = bad for making power right? I disagree...well I do agree in a sense, because I can see where they would be bad in the current manifold design, because there would be a huge pressure drop which would drop the Mfp (mass flow rate) Now some people who want more torque will get a manifold with a little bit longer, thinner runners. Why does this make more torque? I have no idea, but what if it's because the air in the runner has more time to get rid of it's turbulence, thus increasing it's velocity. Increased velocity = better atomized fuel, which equates to the same amount of air in the cylinder but a better more efficient burn which = more torque.

So why isn't there an intake manifold that is designed similiar to our equal length turbo manifolds, with well thought out collectors...divided housings, and are designed to promote flow, not area? If it was 50% better in maintaining velocity, that would be like upping the boost from your 20 to a 50% better 30lbs.

 

i think they are trying to optimize velocity to all cylinders equally. Its easy to think velocity could be easily enhanced if you forget about the (intake) valves being closed for most of the cycle.

disclaimer: just my opiinion i have done only a little research on IM theorys

 

Well if you had a cam with higher duration, I think that is why they make more torque also, because the valves are open longer which gives a chance for the air to start flowing again which gets rid of the turbulence and the velocity picks back up. Like in Corey from Slowmotion's car. His cams have a crazy high duration I think, which allows the velocity to increase (or at least revert to full flow) which in my theory creates more torque.

With his high duration cams, a lot of people would have to worry about reversion of exhaust gasses back into the intake manifold, but if there is a free flowing exhaust side, you are golden.

 

Look up resonance and you may answer a lot of your questions about short vs. long and why it matters for low end vs high end. Velocity is very important look at Full-race's design on their IM.

 

Full-Race's design is the same basic design, that I would think would be more conductive to turbulence than velocity.

 

My STR intake manifold picked up A LOT of power from 4500 to 7500 on a stock LS turbo setup. The STR intake manifold had built in velocity stacks tho I’m sure that helped.


Velocity helps a lot on NA setups because think of your motor as an Air Pump. Idea of the game to get the combustibles in & out as quickly as possible. The more air out, the more aloud to come back in and this is when you need velocity to speed the oxy. into the cylinders as quick as possible before combustion takes place. The more Oxy/fuel you get into the chamber the more heat/power your engine can produce. The more you get out, the more non-combustibles you'll clear from the cylinders to make room for more/new fresh combustibles during the next cycle.

So I’m sure it'll help greatly with N/A setups because the engine has to scavenge its combustibles into the chambers/cylinders on its own. A pressurized F/I setup mainly needs the less restrictive exhaust side to benefit because with a pressurized head side can cause a slight restriction into a major one. You have 3(+)X's the non-combustibles to clear from the chambers. That’s why the larger your exhaust with boost the better and the more boost you run the greater the benefits from freeing up back pressure. With the intake side instead of so much velocity characteristics, mainly a well directed and high volume flow path would be best with the runners in a tapered effect to a port matched chamber. This will aloud easy flow of the combustibles, but will cause a pressure drop as the combustibles enter the chamber making a "chill" effect cooling the chamber down. When you have an open flow that moves threw a metered smaller area, then back into an open space you get a pressure drop and a temperature drop. But this is all just my theory.. and my $.02



Modified by JDMs1eeper at 2:24 PM 7/30/2006