Exeleration problem and dump valve question

Draco · Post by **Draco** » Thu Jan 04, 2007 8:08 am

It has happened a few times here and there, when I gun the car and change gears it feels like there is a fast delay before the car starts pulling again, I change a gear then as soon as I changed and hit the petrol it has a delay then it comes in, it's not lag because the delay is to fast for lag, it's like half a second then starts pulling.

Dump valve, where should the dump valve open, on higher revs or as low as possible, I have been told that it should almost suck open on idle which means it should open sooner on lower revs, the same guy later told me after driving with me that my valve opens to soon....WTF!!!!!

Dislex666 · Post by **Dislex666** » Thu Jan 04, 2007 9:30 am

i assume you have a DV... is it adjustable?

Also - That 'delay' you check between changing gears and WOT is actually what turbo lag is all about.

the time it takes from 0 rpm to 3500rpm for full boost is called spoolup - not lag.

I have it in my car too.

If you find that the car jerks a bit on very slight throttle at cruising speed then that's the DV opening too soon.

Also the 'where' a DV opens has got to do with the amount of boost/vac it experiences. Ie. my DV will only open if the boost the i create is more than 2 psi (because i run a MAP sensor it's safe for me to do so, cuz on MAFS this will cause the jerking that i spoke about)

The Calibrator · Post by **The Calibrator** » Thu Jan 04, 2007 9:32 am

Thats lag.
Every turbo car I have driven has it to some degree. The only way to eliminate it completely is with a antilag system. This however is not very kind to turbos.

Sokar · Post by **Sokar** » Thu Jan 04, 2007 10:15 am

Hi Guys,

Not treading on any toes here, but I'm sure Derek knows what Lag is, he's saying this happens every now and again, its a problem, not the norm. From what I'm reading he's saying the following:

Normal: Boost -> Change gear -> Lag -> Boost
Problem: Boost -> Change gear -> "Delay" -> Lag -> Boost

Correct me if I'm wrong though...

Question, is the valve venting as a recirc or to atmosphere?

Draco · Post by **Draco** » Thu Jan 04, 2007 10:17 am

Thanks for the input, but....this happens now and then, it doesn't happen everytime I do this, most times gearchange is normal, as I said, my car is normal for a while then just sometimes it starts this, then it goes away, lag is there or it isn't, it doesn't appear when it feels it is time now.

Draco · Post by **Draco** » Thu Jan 04, 2007 10:27 am

Sokar...it seems you understand me better, this happens on very high revs 5500 too 6000 revs, previosly or shal I say normally on this revs this happens....boost>gearchange>boost(because of high revs falls to about 5000), now and then boost>gearchange> delay(bit of a nose dive)>boost.

On low revs...Boost -> Change gear -> Lag -> Boost

Sokar I think atmosphere, I am not sure I understand what the difs between atmosphere and recirc(what does recirc mean?)

Dislex666 · Post by **Dislex666** » Thu Jan 04, 2007 10:36 am

ahaaa!

i like sokar's explanation...

Mmmmm, i used to have that too on my car. But never bothered me much, it almost felt like sometimes it got too much juice after a gear change and then it was like 'too rich' till i lifted my foot off and depressed it again *shrug* prolly a nissan thing - cuz my sentra was also a bit oppie koffie w.r.t consistent performance

Sokar · Post by **Sokar** » Thu Jan 04, 2007 11:20 am

A recirc BOV will drop the "dumped" air back into the intake, just after the MAF, an atmosphere BOV will drop the air our of the intake totally into the wild blue yonder.

Option 1 is better for stockish as it lengthens the life of the turbo, but doesnt work too good on high boost applications.

Option 2 is bad for the stock system as the MAF has metered the air you've dumped so the car runs rich for a second, that might be the delay, do you get a crackle or backfire when changing?

You'll need to try find a connection the between times the car does this, is it on a hot day, or a cold day, were you sitting in traffic etc etc, it might even be something that happens all the time, but its worsens due to some factors.

Rezlo · Post by **Rezlo** » Sun Jan 07, 2007 3:58 pm

Sounds like a torn/jamming stock recirc valve or a sticking atmospheric one.

With a good adjustable bov you can run atmospheric low or high boost, low or high power, though the lag time will be slightly higher due to the motor going rich for a split second between shifts.