I read the K cycles fasters, meaning it reacts faster then the J?

would the k help to smooth out the spikes we get?

The forge 007 valves are my pick.. they eliminated my spikes.
The 75 valve will help your turbos deliver quicker and respond quicker.

the wastegate is what controls the boost the turbo makes and the n75 controls the wastgate by pulsing between pressure and atmosphere.... i assume the k would help smooth out the spike cause it reacts faster..... meaning it opens faster when the computer tells it to... letting the wastegate open sooner so you dont get as big a spike...

710n has 0 to do with any of this... at least in my car....

How they react to the boost.. quick..snap like or in a smooth progression is part of the boost spike equation.

If you increase your boost to a stock valve.. it SNAPS open too fast and allows a spike of air pressure into the system. Because the air spiked in.. there is less pressure behind it so you keep cycling up and down. If you regulate this with an upgraded valve.. like a Forge or other (stronger sping, no rubber diafragm) then the increase air..power...boost is controlled better and eliminates..or minimizes the spikes.

boost spikes are directly related to how fast or slow the wastegate opens...

thats why people put in manual boost controlers in line with the n75 or elimante the n75 valve all together....

the bypass valve only opens when you close the throttle body, an create a vacum in the manifold...

why did my spikes stop when I put in the Forge 007 BPVs? While the K75/n75 will effect the wastegate and its cycling,(output) its the BPVs that effect the use of that pressure (input)
The whole system works together. In effect..we are both right.

boost spiking.

Under boost the BPV is changing its position (A) to allow the flow of air. When you close the throttle the valve closes and its position (B) changes again. When boost is requested the transition from (A) to (B) has a great deal to do with the flow of the boosted pressure. If the change from (A) to (B) is quick and constant and it holds its position then you have a continued level of boost. If the change oscilates then you have spiking and fluttering and inconsistent levels of boost.

Most of the S4 forum uses the 710N and has no problems with "fluttering" or spiking from the BPV's. They work fine.

The transition between open and closed on the BPV's is very quick. Boost spikes are a function of software and N75 lag time...not BPV's.

But they also relate to the 710 valves. And I'm not exagerating the mechanics.. its a simple open and close situation. If it cant hold open or occilates open then your boost is being diverted when its needed. Its actually simple mechanics. But, we will have to agree to dissagree on this..

The problem with your statement is the "if". The 710N's have no problems operating correctly. There is no boost fluctuation or leaking.

Stock valves use a rubber diaphragm. As the age or in the case of added boost (chip/DiPP) they don't hold up.. under pressure. Spikes in your boost result becaus the engin is calling for boost and not getting what it expects and then calling for more. It finally gets it at a high point and then reduces the call..these are the spikes. Changing to a better Diverter..one that doesn't use a rubber diaphram will eliminate these spikes. Changing to one that is adjustable..like a forge (if chipped) will also smooth out the power delivery..not just eliminate the spikes.

The 710N's are designed for use on the Audi TT which produces the same boost levels as a chipped S4. I routinely test mine and I've never had a problem. I also run more boost than 99% of the S4 forum. It's quite rare to have a 710N unit fail.

To clarify, I'm not arguing with you. I have no problems keeping this to a civil discussion.<ul><li><a href="http://www.s4biturbo.com/art-dvtests.shtml">To boot, the response time of the 710N is quicker than the Forge.</a></li></ul>

They do fail at times. I have personal experience with it as well as experiences of others.

But my story shold work.

With APR.. my acceleration was wonderful and delivery was a sudden rush. after a few months I noticed a spitting of the boost at times. I also found that at a continued hard drive with 4-5000 rpm shifts, the car would overboost (VAG Verified) and go into fail safe mode for a minute of so.

I investigated on the boards, and spoke to some heavy mod mechanics and the general consensus was to change from my stock 710B to the 710N or if $$ prevailed go to the forge adjustables.

I went the cheaper way to the 710N valves and they worked but still with a rush, but then after a month or so the same pattern started to arrise.. spitting delivery of the boost and under extreme conditions into fail safe at 4-5000 rpm shifts (3rd-4th).

This time I went with the forge valves and used spring # 2. The above conditons NEVER reappeard and the delivery of power was so stock like smooth.. but at a slighlty lower level of...hmmm..strength? than the 710N gave.

SO... one day I made the change in the spring to the lighter Green spings in the forge valves. And The strenght of power was back.. it was a great ride with the lower setting. BUT.. One day after waterfest at a light...with another car...

lets just say the fail safe mode came back right before I heard a certain lady scream.

My son has a heavy modded GTI.. and we would watch his boost gauge climb up..spike.. and taper down..like a roller coaster. He too switched to another billet style valve and this eliminated the probelem.