FFIM design questions

[supra_kid101]

Ok i'm building my own ffim and i have a few question.
1. Do I need the cold start injector?
2. Do I need the ISC and if I don't how does it idle correctly?
3. If I keep the ISC is there any way it needs to be plumbed or just a flange? What about the check valve and rubber thing?

 

[jdub]

1) Depends...do you live in a cold climate? The worst case is a longer start on cold days. I live in Phoenix and eliminated the CSI.
2) If you are running the stock ECU vs a stand alone EMS, keep it. You can get away without it on a stand alone, but idle will not be as nice and will have to be set above a higher rpm than stock.
3) You can use other ISC valves from other sources with a stand alone...the Ford ISCV comes to mind. These can be plumbed using threaded fittings vs the supra flange...you'll have to research what works, but it will require some sort of check valve to prevent a boost leak. Mine have a stock supra manifold flange welded to the bottom of the FFIM...it retains the check valve.

 

[supra_kid101]

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

 

[jdub]

You're looking at 800-900 rpm...if you retain the AC, it will need to be 1000-1100 rpm. Like I said, this is with a stand alone, not a stock ECU...if you keep the stock ECU, life is much easier if you keep the ISCV. Don't cut corners on this one

 

[SuperRunner]

Velocity stacks
Velocity stacks
Velocity stacks

And let me say it again.....
Velocity stacks.

In my own testing, if you do not have velocity stacks with a custom manifold, you will lose performance. Also, find someone with a flowbench and flow the thing.

 

[dbsupra90]

if you run a map based system on the stock ecu (vpc, maftpro, map ecu, etc) you dont have to route the isc back into the intake. you can make an aluminum box w/ the stock flange to mount the isc. run a hose to the intake manifold to the box. since you ar running map based, you can run a small breather filter on the box for air inlet. that make sense?

or you could just weld the stock flange to the intake manifold. but, again since it is map based you can just run a filter on the inlet of the isc.

jdub is right, without the isc you will have to crack open the throttle body some to let air into the motor. and obviously this will raise idle rpm. my car idles about 800-900rpm, just like he said. idle quality is smooth, just higher.

here is a video- http://www.youtube.com/watch?v=gOfq1CzMHWU

 

[supra_kid101]

Could I use an older throttle body with the idle screw? From what i've read the ISC just brings in metered air. Wouldn't the idle screw do the same thing? I can make the FFIM easily enough but I don't have the machines to make a replica of the ISC housing like on the stock manifold.

 

[jdub]

Velocity stacks
Velocity stacks
Velocity stacks

And let me say it again.....
Velocity stacks.

In my own testing, if you do not have velocity stacks with a custom manifold, you will lose performance. Also, find someone with a flowbench and flow the thing.

Not so sure about using velocity stacks inside a FFIM under boost...everything I've seen (from IJ and Seth's experience) leads me to believe velocity stacks will disrupt air flow under positive pressure. Velocity stacks will give you better bottom end flow off boost though.

The biggest effect is plenum volume and runner length. Short runners are not good for low end...long runners are. Smaller plenum volume makes a high output turbo hit hard, larger volume will soften it up.

Bench testing for flow is expensive and it will need to be done for specific plenum volume, runner length and turbo pressure to get valid results. Goals for the motor will determine which is best for the application.

Could I use an older throttle body with the idle screw? From what i've read the ISC just brings in metered air. Wouldn't the idle screw do the same thing? I can make the FFIM easily enough but I don't have the machines to make a replica of the ISC housing like on the stock manifold.

If you're going to a FFIM, you want it for better flow and a more direct path from the IC. Using a stock TB kinda defeats the whole idea IMO

Like db said, if you go to speed density, you don't have to worry about a metered air source...this is a better option IMO.

All you have to do is get a donor stock upper intake manifold and cut the ISCV flange out of it. Clean it up a bit and weld.

 

[dbsupra90]

Could I use an older throttle body with the idle screw? From what i've read the ISC just brings in metered air. Wouldn't the idle screw do the same thing? I can make the FFIM easily enough but I don't have the machines to make a replica of the ISC housing like on the stock manifold.

our throttlebodies are shut at idle. thats why the isc is needed. the idle screw on the older ones are not going to work on their own. you dont have to use a toyota isc. you could use a ford or nissan for that matter. but if you did want to use a stock isc, you could just cut the flange off the stock manifold.

 

[SuperRunner]

Not so sure about using velocity stacks inside a FFIM under boost...everything I've seen (from IJ and Seth's experience) leads me to believe velocity stacks will disrupt air flow under positive pressure. Velocity stacks will give you better bottom end flow off boost though.

Positive pressure? It is ALWAYS under positive pressure, unless a backfire. Air acts the same under boost as it does under vacuum. Under boost just is a higher depression. I certain cross section area(CSA) will have a determined coeffiecient discharge(CD). By having a velocity stack, or just a nice radius port, will increased the CD of the same CSA, effectivly making the intake runner seem like it is larger.

Bench testing for flow is expensive and it will need to be done for specific plenum volume, runner length and turbo pressure to get valid results. Goals for the motor will determine which is best for the application.

I actually have my own flow bench, and from that I have tested velocity stacks, and I gained 20cfm over the sock manifold at 28" of water. Without the velocity stacks, I lost 20cfm over the stock manifold. So the velocity stack in turn increased 40cfm than just the runner alone, which was about 20% more air making it to the head. Yes it was only at 28" of water, but at 553" of water, or 20psi, the CD remains the same, only static air pressure changes.

Some people flow at 10" some at 25" some at 28" and some at much greater pressures. There is a calculation you can use to convert your flow numbers to each depression. Air moves from a great pressure to a lesser pressure. Some people believe that to test forced induction on a flow bench, you must BLOW through the port. That is incorrect. By sucking through you are creating higher pressures on the outside of the port than on the inside, which in effect is the exact same thing that goes on in forced induction. The only thing that will change at different depressions is turbulence. You may find out there are certain anomalies that happen at different pressures that didn't exist before. This is really the only reason why you would even test at higher pressures. In Theory, the different pressures would still be linear in comparison.

 

[quake]

^^ this may be but it is still an improvement over a stock plenum, and for most it will suffice. This has been proven via dyno numbers before and after. The stacks may improve performance but the cost must equal the improvement. If not most would rather use the extra money to purchace another upgrade that will provide more power.

 

[SuperRunner]

but not using them, or at least a nice radius will hurt performance. A straight edge port will decrease airflow, that is just basic fluid dynamics. I would recommend that the radius starts out at about 2 1/2". I would like to see a plenum with a sharp edge runner out perform a stock manifold. The stock manifold has somewhat of a radius port built in, which is why it would flow 20cfm per runner more than with just the lower runners attached.

This is also why you can really never get the true numbers of a port an polish of a valve job, without the intake runner and manifold attached, they impact airflow greatly.

 

[Doward]

Positive pressure? It is ALWAYS under positive pressure, unless a backfire. Air acts the same under boost as it does under vacuum. Under boost just is a higher depression. I certain cross section area(CSA) will have a determined coeffiecient discharge(CD). By having a velocity stack, or just a nice radius port, will increased the CD of the same CSA, effectivly making the intake runner seem like it is larger.



I actually have my own flow bench, and from that I have tested velocity stacks, and I gained 20cfm over the sock manifold at 28" of water. Without the velocity stacks, I lost 20cfm over the stock manifold. So the velocity stack in turn increased 40cfm than just the runner alone, which was about 20% more air making it to the head. Yes it was only at 28" of water, but at 553" of water, or 20psi, the CD remains the same, only static air pressure changes.

Some people flow at 10" some at 25" some at 28" and some at much greater pressures. There is a calculation you can use to convert your flow numbers to each depression. Air moves from a great pressure to a lesser pressure. Some people believe that to test forced induction on a flow bench, you must BLOW through the port. That is incorrect. By sucking through you are creating higher pressures on the outside of the port than on the inside, which in effect is the exact same thing that goes on in forced induction. The only thing that will change at different depressions is turbulence. You may find out there are certain anomalies that happen at different pressures that didn't exist before. This is really the only reason why you would even test at higher pressures. In Theory, the different pressures would still be linear in comparison.

Just to point out a couple of things:

1) Pulling air (sucking) into the combustion chamber is not the same as pressurizing the intake tract. It is called 'forced' induction for a reason.

2) The density of air changes with the pressure of the air. (aka 1 atm vs 2 atm)

 

[SuperRunner]

Just to point out a couple of things:

1) Pulling air (sucking) into the combustion chamber is not the same as pressurizing the intake tract. It is called 'forced' induction for a reason.

2) The density of air changes with the pressure of the air. (aka 1 atm vs 2 atm)

Actually that is a common misconception. Here is a quote I found. I can get you the source of that quote if you want.


"Superchargers(Forced Induction) only increase the air density in the runners but not really how much they flow in CFM or the velocity they flow at. The ports act much the same under boost and the engine will still lose breathing effeciency whether blown or not after a certain rpm plus you will start clogging up the exhaust port as well with the supercharger. It's like the people that think you have a lot more velocity when you are running boost! You don't. People measure it. It's just denser."

 

[jdub]

I'd like to see the source for that quote

This part I have a problem with:

It's like the people that think you have a lot more velocity when you are running boost! You don't. People measure it. It's just denser."

Corky Bell (CarTech's founder) has wrote numerous articles on forced induction and talks about critical velocity in IC piping. The higher the boost, the higher the velocity of air flow through the pipe...on a turbocharger, the amount of air flowed is determined by the CFM it's capable of producing. At a point (critical velocity...300 ft/sec iirc) air flowing in a pipe changes from laminar flow to turbulent flow effectively limiting the amount of air you can push through the pipe. This results in a pressure drop and can be changed with an increase in pipe diameter. By the time the air hits the plenum, most of the restrictions in the turbo system are past...the combined diameters of the 6 runners is larger than the IC piping and does not produce a restriction to flow. The point of all this, is if a FFIM can handle the flow the turbo is capable of producing and the piping is capable of delivering, it really doesn't matter if the FFIM can flow better or nor...you will get no gain from the FFIM due to the restrictions (piping, IC, TB) present in the rest of the system.

I agree that the runners where they meet the plenum need to have a radius...plus, the runners themselves need to be as smooth as possible and match the intake ports on the head. Any effort to reduce the amount of turbulence as the air charge transitions to the head is a good thing. I'm not convinced on the need for velocity stacks though. Ditto for determining flow rate by sucking on the runners vs pressuring the plenum.

 

[SuperRunner]

I agree that the runners where they meet the plenum need to have a radius...plus, the runners themselves need to be as smooth as possible and match the intake ports on the head. Any effort to reduce the amount of turbulence as the air charge transitions to the head is a good thing. I'm not convinced on the need for velocity stacks though.

Hmm, I can't find where I got that quote, I had used it before, but it was awhile ago.

Agreed, the radius is the most important due to the CD of the orifice, so the velocity stack is use more for off boost because as stated, your runner will be longer than without, which will increase the VE off boost.

Now as for the air charge, think of it this way:

Why does air move, basic fundementals here. Air moves from a high pressure to a low pressure. A pressure differential is just that, a difference in pressure. It does not matter how the difference in pressure is formed or on what side of the port it is formed on. When dealing with pressure there is no such thing as " pulling" or "pushing". There is only a difference in pressure. When using forced induction, you are just creating a larger differential.

Also, if what you were saying were true that the restrictions are all BEFORE the intake manifold, then why even bother to port and polish? You would get ZERO gain on boost. So lets just stop wasting our money on porting, because that is not where are restrictions are, according to what you say Cortney Bell says.

 

[jdub]

Also, if what you were saying were true that the restrictions are all BEFORE the intake manifold, then why even bother to port and polish? You would get ZERO gain on boost. So lets just stop wasting our money on porting, because that is not where are restrictions are, according to what you say Cortney Bell says.

LOL...restrictions as in the TB (butterfly), bends in the pipe, the IC itself, and if you're not thinking, changes in IC pipe diameter. It was pretty obvious what I was getting at...the FFIM is not the restriction. And, it's obvious that reducing turbulent flow is the point of smoothing out the path to the head (as I said). But nice try at twisting around what I was saying

In post #8, I said velocity stacks will help bottom end power (off boost). I just don't see the benefit under boost (air flow being pushed along the plenum vs pulled into the cylinders) due to the turbulent flow caused by the stack protruding into the plenum. I could be wrong, but have yet to see anything to convince me otherwise.

I understand that from a theoretical view, that the CFM values through a pipe (a runner is a pipe) would be the same for a pull vs a push. However, the velocity and density do change under pressure. I do know (for a fact) that once velocity increases to critical, the flow rate drops off due to the turbulent flow. Plus, density will affect the actual O2 available for combustion and the dynamic compression experienced inside the cylinder. IMO, any bench test should take velocity into consideration at minimum to be valid.

 

[SuperRunner]

To explain more about what Cortney says, there is more to it than that. The intake and TB just gets the air to the plenum. After that it is the runners job to get it to the head. And since only 1 runner at a time is actually drawing in air at full capacity, the intake system is WAY more than capable of flowing the air. Not all 6 are sucking in at the same time. So when you look at it that way, the runner intake becomes the next restriction. Using a radius port will help increase the pressure difference, since the CD of the orifice is increased.

You should try this on a flow bench with a head attached. Again, forced induction doesn't matter, you just inceased the pressure differential. I test at 28", but that can be calculated to whatever depression I want. If my runner flows 250cfm@28", then it flows 1105cfm@550"(20psi)

 

[SuperRunner]

LOL...restrictions as in the TB (butterfly), bends in the pipe, the IC itself, and if you're not thinking, changes in IC pipe diameter. It was pretty obvious what I was getting at...the FFIM is not the restriction. And, it's obvious that reducing turbulent flow is the point of smoothing out the path to the head (as I said). But nice try at twisting around what I was saying

This would ONLY be true if all 6 runners were taking in air at the same time.

But yes, you are correct on the velocity stacks, they won't help under boost it is the RADIUS PORT, which is really what I was getting at. You usually don't see a good radius port unless you have velocity stacks. Velocity stacks will also help build boost quicker since they will increase VE off boost. Now with that in mind, how long are the velocity stacks? If the stacks are only 2" long, that isn't going to make much difference. In fact in my design, the stacks are soo short, I had to bump up my idle to 1,000 RPM in order to maintain a smooth idle.

Here is a picture of my stacks. I was more going for the raidus port than the actual lengthend runner. As you can see they are really short.

 

[jdub]

Nice
How about building up material around the stack in the plenum to cut down on turbulence? The way you have the runner protruding into the plenum would have the effect of a longer runner and improve bottom end power. The raidus port is far more important on an FFIM though...you want a smooth transition.

This would ONLY be true if all 6 runners were taking in air at the same time.

Well...that is true, but there are 2 runners taking in air at the same time on a 7M.

So, you're saying velocity (due to pressure) does not have an effect on flow?