My new bottom end is almost put together and I have to decide on a fuel injection system soon. Would the Holley Stealth Ram make a significant difference opposed to something such as a Multi-Port System or a Replacement TBI system

Runner length obviously helps with N/A engines, but would they do anything for an engine with forced induction???



Nick

 

Nick, one thing I learned while going through the numerous physics classes in college is that a fluid (also air) acts the same under pressure. It is just more dense and it turn has more mass. Therefor, to an extent runner length will still effect performance. However, it is not as critical on a force-fed motor. Still flow and intake velocities matter.

If engineermike pops in, he will most likely be able to give you some examples to work with.

Wingnut

 

Most people will say that it doesn't matter since the supercharger is forcing the air in, so you don't need ram-tuning.

I, however, disagree.

I believe that ram tuning is at least as important with a supercharger.


NA ram tuning: momentum of air in the intake runner continues to fill the cylinder even though the piston has stopped at BDC or is rising on compression. Let's assume a very well tuned intake runner matched to a proper intake lobe builds 3 psi pressure at BDC.

SC: You attempt to put 15 psi pressure into the cylinder, but it doesn't all get there due to restrictions in the port and valve. You may end up with 10 psi in the cylinder at BDC.


So, why not use ram tuning + supercharging to get 13 psi?

Supercharging does NOT render ram tuning ineffective. In fact, the opposite may be true.

Momentum of the air in the inlet port is what causes ram tuning, as described above.

Momentum = mass X velocity

Example:
Longer runner = more mass
Smaller runner = more velocity (but more restriction and less mass consequently)

Supercharging increases the density of the air in the runner. Higher density means more mass in the same runner and, thus, more momentum. Also, since the motor flows more air when supercharged, the velocity in the runner will be higher.

So, all things being equal, a supercharged motor has the capability of accomplishing more ram tuning than NA due to the higher density and velocity of the air in the runner. However, with a supercharger, you are trying to get 2 X more air through the same restrictive intake valve, so you still can't get it all in the cylinder.


That being said, stay away from TBI due to limitations of the injectors and poor fuel distribution.

The single plane and stealth ram intakes appear to have nearly the same runner lengths, but the stealth ram has the advantage of high runner entry angle, so I'd go that direction.

Mike

 

I had a couple of questions along the same lines....

How much does plenum volume effect a forced induction engine in the real world

i.e. comparing the large plenum of the stealth ram to the smaller plenum of a single plane intake.(vic jr)

 

Engineermike..... you are the man. Your answer is real convicing and logical. However, I have asked this questions to many people and have gotten both answers.

The people that mostly say that runner length does not matter, usually say something along the lines of "Since the gas/fuel mixture is being constantly forced in, runner length does not matter."

I would love to see some dyno numbers comparing the two.

Nick