FFIM design questions

[starscream5000]

Actually , you don't need velocity stacks, you need a smooth transition into the intake runners like Ron's, those aren't velocity stacks as they are flush with the bottom and don't protrude up and create turbulence during boost like a velocity stack would.

Ron's setup is the best compromise so far that I've seen.

 

[SuperRunner]

who said velocity stacks MUST protrude into the manifold?

Def:

A velocity stack is a trumpet shaped device which is added on to the air entry of an engines fuel system, carburetor or fuel injection.

It does not say it HAS to prodrude. A velocity stack is just another name for a radius port, or venturi.

 

[starscream5000]

A "stack" would be raised up, no?

 

[SuperRunner]

OMG, SEMANTICS!!!!!

How about we just call it Raised Velocity Stack, or Flush Velocity Stack. Either way you look at it, they are velocity stacks.

 

[starscream5000]

That works, thanks for the clarification

A flush Velocity stack would be ideal.

 

[IJ.]

I don't think there's anyone that makes an FFIM that doesn't radius the entry SR.

 

[SuperRunner]

Haha, I have seen many home built stuff that hasn't.

Also, the difference between a 2" radius and a 3" is HUGE!!! And machined vs hand beveled.

 

[IJ.]

ewwww

 

[wesbeech]

About how high would the idle have to be? I wouldn't mind as long as it's 2000rpm or lower

Inever had a icv on my car when i ran stock ecu i just had to set my idle at about 900 to a 1000 and never had a problme

 

[jdub]

you still need velocity stacks, just don't have them protrude into the manifold, keep them flush.

Back to my original statement:

USE VELOCITY STACKS, or you will hurt your performance dramatically.

And yes, two intake valves are FULLY open, but they are for the same cylinder, same runner.

Yes, but use of that term (velocity stack) brings to mind images of the horn shaped tubes on top of big block Chevy's

And to be crystal clear...two cylinders at a time are on the intake stroke on a 7M at the same time. That make two runners active and 4 intake valves open at the same time feeding air from any plenum attached...stock or FFIM.

 

[SuperRunner]

Yes, but use of that term (velocity stack) brings to mind images of the horn shaped tubes on top of big block Chevy's

And to be crystal clear...two cylinders at a time are on the intake stroke on a 7M at the same time. That make two runners active and 4 intake valves open at the same time feeding air from any plenum attached...stock or FFIM.

Well, now we ALL know that a velocity stack doesn't have to be protruding, but has a specific function.

And I will state again, I said one cylinder at MAXIMUM FLOW. I stated that specifically so not be misquoted.

 

[jdub]

SR - I know what you said, but that is difference between theory and what is actually happening in the flow from the plenum to the head.

And it is also why I went into what is happening (flow and velocity wise) in the piping from the turbo, to the IC, to the TB, to the plenum. That too is theory, but is a starting point for determining what you need to do. It is a system and what happens in one area affects performance of the rest. That needs to be considered when designing a major component like a FFIM.

I'm not disagreeing that the plenum connection to the runners need a radius, but it is also only one piece of the puzzle. Volume and runner length also have a big impact.

 

[SuperRunner]

agreed.

 

[turbodriz]

Should we be concerned about bottom end torque on an already torque happy motor? Should'nt we be more concerned about overall max flow on a motor that can always stand to use a little more topend? Just curious guys

 

[SuperRunner]

Should we be concerned about bottom end torque on an already torque happy motor? Should'nt we be more concerned about overall max flow on a motor that can always stand to use a little more topend? Just curious guys

It is all about preference. If you want a lower revving street car that builds boost by 2500RPM and maxes out at 6,000 RPM, then longer stacks would be better. If you want to build an all out drag car, and don't care about low end, short is better.

 

[IJ.]

Or you can use the physical dimensions to juggle the torque delivery around, I've used 3.0L Plenums to 6.3L and runners from Stock length to 40mm long in the 5 FFIM's I've made

 

[TurboStreetCar]

You made a 6.3 Liter Intake manifold?! wholly shit!

IJ in your opinion and experiance, what length runners and size plenum work the best in compromise between low end torque and high end flow for good top end?

 

[IJ.]

Chunks: Too many variabes to give an answer sorry.

 

[starscream5000]

Bear in mind here people, Ian's car is used for a daily driver/toy. His power output on the bottom end was overwhelming the car's ability to hold traction (and he does have a full aftermarket suspension, tire setup already), thus the need for a larger plenum to "soften the hit" as he would put it (along with DBW assisted traction control :biglaugh. That, and the fact that he is running a wet manifold (propane as the main fuel) makes a difference in what you should choose in your own application.

 

[Justin727]

His car must be ready for action if it has a "WET" manifold all the time!!!