I just had a thought.

After installing my plenum spacer, it amazed me how much power I picked up. It really transformed my engine into something different. All because of a design flaw.
According to explanation, it is because it equalizes airflow to the front two cylinders (#5 and 6). This makes good sense to me.

With this being the case it means that the VQ in z form has a flawed design. With this being the case isnt putting FI on a motor with a flawed plenum design a recipe for disaster???

Think about it: Even without forced induction, if cylinders 5 and 6 are not getting as much air as the others, it means the combustion in these cylinders is not as powerful thereby throwing off the harmony of the engine.
It might not sound like much. but at higher RPMs. little problems like this are amplified exponentially.

I am not an engineer. This is just speculation, but If those with experience chime in, maybe we can come to a conclusion.

Some info that might help....
#1 Any FI engine failures WITH an aftermarket plenum??

#2 Has anyone done a dyno test with an FI engine. (FI with and without plenum?) I dunno maybe a pressurized intake charge negates our poorly shaped plenums airflow flaws

Any thoughts?

 

Performance Motorsports ran a 8.33 on the stock plenum, there is no problem with it.

 

Ummm thats not what i meant. It obviously works. Most FI peeps have a stock plenum.

The question was if people are more likely to blow an FI engine with a stock plenum than a Crawford, Kinetix(for those that do boost with it) or one with a plenum spacer.

I know Shariff (GQ) has a Crawford on his beast. i'd like to hear his thoughts!

 

I don't think the air starvation has anything to do with blown motors. 90% of F/I is tuning, so if the equipment is right, and your motor blows, it is the tuning. Say if you had an APS TT kit, but used an E-Manage instead of the Unichip, if the motor blew, you could safely assume it was tuning (as long as the rwhp was correct) (I don't say Unichip because a dealer isn't going to push your car until near breaking point). Now, assuming tuning was great, and the equipment was fine, it was scattered ignition timing.

If it happened on autocross or road course it would be safe to assume oil starvation if the rod bearings had spun, if not, it was scattered ignition timing.

So IMO, the only reason these motors are blowing are due to: scattered ignition timing, extremely poor tuning, and oil starvation on autocross or road courses (it would most likely happen on two or more abrupt swerves or a really abrupt/tight turn). Now, that's assuming you go with a kit such as Turbonetics or Power Enterprise.

So like I said, air starvation to #1 and #2 cylinders shouldn't be an issue.

Sharif is switching to a different plenum, and he's going to test stock vs. new plenum vs. Crawford to prove that this new plenum is worthy.

Heck, if the HKS F-Con V-Pro has indiviual fuel injector control you can just adjust the fuel to the #1 and #2 cylinders and the air starvation doesn't matter because you have matched the air/fuel ratio better. phunk, does the V-Pro allow this?

 

when i finish my car i plan on getting the AAM plenum spacer, which is supposed to do pretty much the same as the other plenums...

Im going to go over there to get it tuned... I'll see what they can do reguarding a dyno without thier spacer and then one with thier spacer... Im not sure what kind of information you guys want from it... Let me know.. Ill write it down and bring it to AAM and see what research they can do from my car since it will be FI... it will also be builtup at high boost... so we can see if it really makes a difference on high end apps.

 

There have been people who have popped motors with aftermarket plenums. I'd have to do some "searches" to name specific people, but I there have been a few.

I don't think the stock plenum helps, but I'm more inclined to think the crank angle sensor wire is more often at fault than the plenum. Just my gut feeling.

 

I know there have been some damaged motors, even with aftermarket plenums, but like Nis and McDuck mentioned, the blown motors have more to do with tuning, high boost, crank angle sensor issues, weak internals and a host of other variables.

In my opinion, the benefits of the plenum with F/I are related to the increased plenum volume, which usually results in more power across the board in F/I applications. I am not 100% convinced that certain cylinders run leaner with F/I and stock plenum.

Let me tell you my reasoning for this. In the F/I world, the plenum is presurized under boost. In other words, there is more air in that plenum than the engine can consume at any given moment in time. The air is going to travel through the path of least resistance, and completely presurize the plenum and runners. The valves open in series and phases, and they are never all open or all closed at the same time, so there is plenty of reserve air floating around in the runners, and plenum , due to that fact it is pressurized.

Some companies have done flow bench testing to demonstate the air starvation issue at the front cylinders. But the flowbench flows air through the plenum, and into an open head without any valves in it. In this scenario, its very likely there will be uneven distribution of air. But the same cannot be said when you have an engine in motion, with valve train operating normally, and the entire intake track is pressurized.

So I think there are definate power benefits...especially in the F/I world, but the air distribution theory is debatable.

 

great point!!!

 

So what's a better opion for a TT setup, the Crawford plenum or the new Kinetix IM ?

I'm sure both are good but does one have an advantage over the other ?


Tasso-

 

Think about what you're saying. If 1&2 get less air, they will run rich, not lean. Those would be the last two cylinders to suffer detonation due to the same fuel going to all 6 but those to getting less air.

 

Does not appear much real data has been made avail to answer the question intelligently. Looking at the Dyno results from Sungnam (sp.) where the New IM was tested against the Kinetix V4 no appreciable gains are evident.. Low to mid tq. gain is slight..Also remembering the effort to get to the V4 version from the earlier versions sort of suggests waiting until enough have been installed and proven.

Now if astetics is the criteria the new IM win's.

 

the cylinders closest to the tb, in this case 5 & 6, will generally run richer, and the cylinders farthest away will run leanest. with the inlet velocity almost at the speed of sound, the incoming air has a very difficult time turning into those first 2 cylinders. a larger plenum helps a little simply by slowing the air down after the tb to allow it to turn better. individual cylinder trim inconsistency is exacerbated by fi not alleviated. whereas in na, any airflow differences are only at atmospheric pressure, in fi your boost is a multiplication factor. the difference in mass airflow between 2 cylinders would be the cfm times the boost pressure.

 

Royce you lost me on that. If the plenum is pressurized at 10psi, there is more than sufficient volume of air inside the plenum to fill every space inside the plenum, so the air should havent to fight to find its way to an open valve. I am not an engineer, so I am learning about this too...just trying to understand exactly what happens inside that plenum when its pressurized.

 

No, the plenum alone is not at fault with FI on this motor. If you run the a/f to the limits where the back to cylinders go lean, that is more the tuner's fault because they where travling on the threshold in the first place.

 

the air isn't stagnant in the plenum just because it's pressurized. the intake charge has so much velocity going into the intake manifold that all it's momentum will carry it to the back of the plenum. race engineers try to make the turn easier into the cylinders closest to the tb by tapering the cross sectional area of the plenum, angle of the tb, and the total volume of the plenum. cylinder trim's not too big a deal on a street car, you can just tune for it anyway.

 

royce -- do you know empircally whether the inlet flow is subsonic or supersonic?

i'd imagine that due to the composition of the plenum that it is subsonic (massive increase of cross sectional area coming out of the intake leads to a slowdown & increase of turbulent flow == higher burn efficiency), but as i've found, the more i dig into the VQ, the weirder the **** gets

thanks!

 

yeah it's subsonic, the slower you make the flow at the plenum better.