I've noticed that in 3rd gear, while I get 10-lbs of boost at WOT, if I drop and hold the throttle to 6000 RPMS, and then nail it, I only get 5-lbs of boost and then about 3-seconds later 10-lbs. of boost.

Is this normal ?

If not, what could be the problem ?

BTW: vaccuum is good at (-)18, and I replaced all lines with VITON.

Thanks,
Neil

 

once above 4500 rpm the car stays non-sequential until you drop down to 3000 rpm again so it lags a little... maybe I'm wrong

 

This is true, once you pass the sequential point (4,500RPM), the turbos will not respond as well after you release the pressured air. This is due to the fact that they are still in sequential mode until you let the rpms drop below ~3,000RPM.

M104-AMG, do you boost 10-8-10 in all gears? (even after you do a WOT run in multiple gears)

 

check yoru charge control solenoid and vacuuuuum chamber

 

I will boost 10-8-10, if I start at about 3000 RPM, in all gears.

Here's how I normally drive autox:

Hit first and second hard at 10-8-10.

Back off the throttle while in second, and modulate around 6000 RPM through the corners; then WOT out. Here is where I have poor boost, more like 5-6 lbs then 2-3 seconds later, I'm up to 10lbs, but too late for that section, so back to modulating the throttle around 6000 RPM.

I just replaced BOTH the charge control solenoid and the turbo control solenoid. Both solenoids were tested with 12VDC and a pressure test to 15-lbs so there should be not sticktion.

I also just tested both vacuum chambers, and each hold 15-lbs of pressure and vaccuum.

New Viton hoses done in January 2005.

Maybe this is just normal for a stock non-sequential ?

neil

 

It's obvious that no one here goes to the track anymore...sigh.

If you are hitting the throttle at 6k rpm, there is NO lag. Period. Even on a stock car. On the track, I am in non-sequential mode the entire session and there is never any lag. Anywhere, anytime. Even with the stock cat.

There is something wrong with his control system.

 

u test the actual charge control valve too? they fail, not too common though. how are you controlling boost? could be a throtle issue.

 

Since I only had it at Roebling Road raceway two-times last year before the new engine, I've been struggling with the control system, and that's even with my mechanic helping.

I vaguely remember how it used to be, and I am glad you said there should be "NO LAG PERIOD".

Time to do it by the book and very methodical. . . .

When you say control system, what specifically do you mean ?

BTW: would a clogged cat cause this problem, or running too rich with the M2 Stage III ECU?

Neil

 

uh... yeah a clogged cat causes severe lag. and its bad for you engine, ESPECIALLLY with a too rich ECU. back preassure and all.

 

When you replaced all your hoses, did you ensure that you didn't mix up the charge relief valve with the air bypass valve (stock BOV)?

 

I'm just wondering why he started another thread on the same subject?

 

From what I have read and experienced, there has always been a slight delay in boost (<1second) when one goes past 4,500RPM in one gaer, then lets off the gas (maintaining RPMS above 3,000 the entire time), then gets back on the boost. Are you willing to present data that negates this? I am not trying to contradict what you are saying, but I just want to clarify your statement with some proof.

 

Once you cross the transition with 8+ psi of boost, the turbos are locked in non-sequential until you drop below a certain rpm. The default rpm for this is 3000 rpm in the PFC. That may also be the rpm it occurs with the stock ecu. No one's disputing that and in fact, I have posted that many times.

So yes, if you go up to 5k rpm boosting and then let it drop back down to 3500 rpm, there will be some lag (much less if you are full non-sequential and open exhaust) when you nail the throttle. However, at 6k rpm, there is no lag, at least not in MY experience. Certainly not to the extent that M104-AMG was describing. If your car works that way, there's something wrong with your control system.

M104-AMG was even stating this occured in 2nd gear! I don't know about you but if I nail the throttle anywhere above 3000 rpm in 2nd, it's immediate and hard acceleration.

I have runs several dozen track sessions, all effectively in non-sequential (due to the behavior noted above). I have never noticed any lag except for when I wasn't driving properly (or in a few cases, due to the track condition) and was below 4k rpm -- with a stock cat. Then again I am not MASHING the throttle on the track, but SMOOTHLY going WOT, which may hide the "lag" a small amount.

 

The turbo control system is the solenoids, vacuum lines, and actuators/valves.

The biggest source of slow/laggy boost is the solenoids - Dave Disney developed a little test that shows solenoids which are sticking under backpressure. Next time you're in there, take them out and bench test them with a Mityvac according to his test.

Another 'slow' control component can be the CCA. I found that disassembling the butterfly and linkage and cleaning/regreasing it keeps it moving nice and snappy.

Dave

 

Yep, I replaced the slow/laggy solenoids and pressure tested via the Dave Disney procedure.

I'll have to re-examine and play with the butterly and linkeages, but they "look" clean and feel snappy.

Yes, I am MASHING throttle not slowly going to WOT, since this is in AutoX.

So far:

I have tested chamber "B" of the charge control actuator (http://www.autosportracetech.com/RX-...leshooting.htm) and it was not holding pressure or vaccuum. This was replaced with a tested one.

I also found the vaccuum lines to the charge control relief valve and the double-throttle control actuator were slightly pinched. These we re-routed with new VITON lines.

Although the check-valve for the vaccuum chamber tested good (vaccuum & pressure upto 25 psi on both sides), I replaced it with a new VITON one from Dave Clark.

Test drive feels better, and better response as well.

We shall see . . .

:-) neil