Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance remove secondary intake runners?

Originally posted by DemonSVT:

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Your thinking is definitely on the right track & the flow theory is sound. However you are a bit flawed your basis.

The stock manifold setup was designed for a 170HP engine and the fact it would be primarily mated to a slushbox. Also the UIM was a compromise to fit under the stock hood. (It was EH'd for moderate flow improvement and port uniformity for the SVT)

Now about the IMRC. The rpm range of "just the short runners" drops drastically as you improve the efficiency of the engine and attached parts. (i.e. mods) The more modified the engine is beyond the stock 170HP slushbox range the lower the maximum rpm range of the short runners will be. There comes a point where the rpm range of the short runners is below even cruising range. Albeit, like you said, not on the stock engine or one close to stock. This rule of flow dynamics is part of the reason why an SVT has a 400-600rpm lower IMRC point even though the engine has a higher powerband due to the cam change. At a lower RPM point it needs more air then "just the short runners" can supply. That's even considering the bit of flow improvement the EH process added to the short runners.

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Did you know that I'd pop up on this???

I am in agreement except on the sticking point where you imply that the plates have to be removed for performance.
No, not really.
For naturally aspirated performance it is very important to keep the runners operational.
If you increase the airflow requirements for that engine then you need to enlarge your runners accordingly.
Removing them is only a viable option if you are having problems with your system.
Flutter, or coding problems that cause unnecessary opening and closing are important. When my secondaries weren't clean I had issues with the IMRC not being able to open them and it really sucked.

However, after I removed them and properly enlarged and modified them when I went to 3.0 liters of displacement I never had a problem. In fact, they complemented the 3L so well that I would never remove them naturally aspirated! I had them pinned open for testing purposes back when I was having a lot of driveability issuse and it really sucks away the low rpm torque, EVEN with a 3L. For me it turned out to be bad plug wires that were really hurting me.
On top of that, I opened my IMRC box and cleaned it up checked connections, etc. I still use my original in the stock location and it works great! No more sticking secondaries. Less manifold cleanings. Etc.

Wow, should I actually give away my secret for success??
I've explained to you in detail what I have done and you have seen the torque curves from the dyno graphs. You know as well as I do that the torque curve is going to tell you the most about whether your secondaries are helping or hurting. You can't argue that my torque curve wasn't as flat as a table top with very slight, almost non-existent torque drop where the secondaries open.