Secondary restriction thing AGAIN???
Secondary restriction thing AGAIN???
Well I finally got the 3.0 up and running right.
Turns out the miss I had was from a broken injector, replaced those and now its running like a champ.
Now here are some questions I've got.
It still dont have respectable low-end torque, I currently got the secondaries (What is the propper term for these) turned wide open.
I noticed people running gutted secondaries and understand they underwent a tune to run these?
I called around and Diablosport dont offer a tune for my box-code so they don't offer a tune for my Contour.
So in theory, if they're wide open now, if I get my second set, and gut them I wouldn't be losing any power, but it'd be at the same stage I'm at but w/ higher flow?
So Should I gut them and put gutted secondaries on?
I was wondering how you guys got your intake plenums polished? What methods do you use, is there a step-by-step?
Also was wondering if I would notice a difference in a cat-back exhaust system, or if its worth the money to go headers/performance cat/duels?
If so, what is the best setup you guys found so far?
Thanks guys in advance
-Jared
So in theory, if they're wide open now, if I get my second set, and gut them I wouldn't be losing any power, but it'd be at the same stage I'm at but w/ higher flow?
So Should I gut them and put gutted secondaries on?
Here is the misconception that most people have.
First lets ask a couple of key questions.
1.)What is the purpose of the secondary IMRC control?
2.) Where is the most flow needed in the engine rpm range?
3.) What happens when I pin them?
4.) What happens when I remove them?
First understand that the engine's air flow is dependent upon the displacement and the rpm range that it operates in.
For example, at 2000 rpm your 3L engine at normal vol. efficiency and full throttle can only move about 100cfm of air, though the real amount is surely less because of the cam design at this point.
AT 4500 rpm the engine can move around 235cfm, and at 6000rpm you are breaking 310 cfm. This is just based on assumed 100% vol efficiency, there are only a few times in the rpm range where that happens due to cam timing matched with intake manifold design, and in some cases it may exceed 100% in the optimum design ranges.
So we know we aren't going to be blowing much past 300cfm anyway on the best tuned engine and logically that isn't going to happen until well past 5000 rpm.
The dual runner system is designed to provide low restriction airflow to the rpms 4000 and above.
Below that rpm on a Naturally aspirated car the engine just cannot handle more airflow than only one intake runner can provide. It just cannot and mathematically you can indirectly prove it like with these airflow calculations
If you engine runs darn good at 5000 rpm then two runners must be supplying a decent amount of air for that flow rate.
IF you cut the rpm in half to 2500 then your airflow requirements cut in half as well. So you need half the runner size to supply it. I don't even want to try to discuss the superchargine effect that decreasing the runner size can provide at some rpm as well as the tuning length of the manifold reinforcing pressure waves. But suffice it to say that a slightly restrictive intake can impove the velocity of the air and to a point the faster air flowing with more momentum will fill the cylinder more than if you left it open to the air. The airflow in the primary runner while closing off the secondary runner achieves this goal around 3000 rpm but as it becomes restrictive the second runner opens up and air velocity begins to drop again. However the engine is accelerating rapidly so the velocity climbs again and by 5000 rpm the engine is happily singing along.
So when does this contraption become a restriction? How about when the airflow requirement of the engine exceeds the flow capacity of the two runners? When is that? Seems to me that on well tuned cars it with otherwise low restriction intakes it is about 7000 rpm but I cannot prove that as the cams, although still good at this rpm are now becoming less efficient on the other side of their tuned optimum rpm (5000).
So if you KNOW you will spend a lot of time reving 7000k and above, you may want to increase the flow capacity. I would say that all you really have to do is do what the SHOShop did back in the day and that is rebore the secondary IMRC runner in the lower intake out 2mm and add a new machined throttle plate to replace the older IMRC plates to fit. Then port out your secondary intake runner as well as perhaps. All this to gain maybe a bit more torque at 7K rpm. At least this way allows you to keep the IRMC system to keep low end torque boosted.
There are some who say that removing them on a 3L is no loss in torque. Ahh, but that is when comparing the new 3L with no secondaries to a 2.5L WITH secondaries. Of course the torque from another .5L is going to offset their removal. But what about a 3L with good porting of the secondary runner that retains them? Should be no loss in either realm of operation and you would have a boost in low-end by keeping them. Also, you can't get forced induction by removing them. Thats a nice way of saying making a bigger hole won't push more air in for you.
The Final Verdict:
In your case the secondaries are still there, so no high rpm gain potential through removing them, and that assumes the rest of your setup can rev to 7K and above to actually use it....for most NOT.
Then down low where you have more than enough airflow you are running into low intake airflow velocity issues by having them pinned. You produce less torque because the air is so slow.
So return them to operation and compare how it feels.
Remember that if you need more airflow at higher rpm then you can always make the existing system BIGGER to accomodate it without removing the benefits it had for the low end.
