I recently went to have a built bottom end LS engine tuned on the dyno. The same turbo setup was used before on a stock ls but never pushed past 14 psi.

All went well until pushing past 18 psi and I'm curious if it may be because of the current wastegate spring. It sounded like the boost was fluctuating but unfortunately I don't have a log of the run, only a video. Relatively new tuner, had time constraints.

I'm using a 35 mm Tial wastegate with the large red spring and a greddy profec spec b electronic boost controller. According to Tial the spring is rated for 11.6 psi.
FYI, Here's a link regarding Tial's spring ratings:

http://www.dsmtuners.com/forums/freq...ion-table.html


Here's a link of the dyno run. At 18 seconds in, you can hear it fluctuate with volume way up. That was the last run:

 

My vote would be the spring.

 

Am I missing something here? How are you producing more PSI than the spring is rated for?

 

 

cheapest and easiest ways to trouble shoot it in order:

1 check for boost leaks and exhaust leaks

2 replace wastegate spring

2 replace profect with a MBC

3 time to look at the turbo as being the culprit

 

might be a boost controller setting

 

My thoughts as well.

 

are you running oem valve springs? the first time i tuned i had crower all motor springs i forgot the spring rate but they weren't 85lbs and when we started raising the boost it wasn't making any power and the injectors (1000cc) were at almost full duty cycle so we did a leak down and boost leak test and everything checked out... i changed the head setup a month later with supertech 85lb springs and there wasn't a single issue making power

Check the most obvious problems first though like everyone else said wg spring, boost controller/boost solenoid, vacuum leaks...etc

 

what settings are you running on the boost controller?

 

The problem still persists.

So far I have (listed in chronological order)

1) Checked for boost leaks
2) Tried running a different vacuum line to map sensor.
3) Installed an additional spring to the Tial 35mm wastegate. To allow more boost.
4) Tried disconnecting the electronic boost controller and using a cheap manual boost controller. Oddly I didn't build boost past 8 psi with the manual boost controller.
5) Bought a Demon and started using Neptune RTP for use and to analyze the problem.

I have a few video runs of the ebc set for roughly 20 psi or higher. Again, around 16 to 17 psi, the car either acts like it hits boost cut or will jerk randomly (cut in and out). The majority of the time when this happens, Neptune will crash.

I'm running a 3 bar zeetronics map sensor. Also the turbo manifold is an older Revhard log style manifold.

Here's a few quick videos...I tried to incorporate sound on the first. The latter two show datalogging when it happens:

 

I finally got a decent log with neptune. I have it saved but I'm not sure how to post it...

When I replicate this problem the map sensor reads increasing pressure or boost to 17 psi or so as it should but when the boost fluctuates or when engine starts to cut out or stall at WOT the map reading goes into vacuum (negative pressure) with the throttle pedal depressed 100%.

If anything the map should read at least 0 boost or no vacuum with the pedal at WOT.

I'm wondering if the map sensor is failing above the 17 psi threshold. It's a 3 bar map sensor, however maybe it's defective. Ordered another new 3 bar map yesterday. Hopefully that will cure the problem.

 

Hope you got a good GM 3 bar or a Hondata one.

 

UPDATE: I ordered the Omni 3 bar map and it fixed the problem. I'd like to see 20 psi+ out of this setup however I believe the Revhard log manifold is holding me back.

 

No. the Revhard wasn't causing that problem at all or "holding you back" in this case. the setting in the neptune was probably set to see a specific voltage reading from a different map sensor, than the OEM you had on there before, in which it creates a fuel cut at a certain PSI reading.

In addition, the GM 3BAR gives a different voltage signal reading than an Omni. More than likely your Neptune setup was defaulted to the Omni voltage reading and not the GM traditional 3 Bar. It wasn't defective, it was just not set correctly with the Neptune. Hondata has the same options.

It also seems from the first video that the limiter on the Profec b was not adjusted for the right percentage for its boost cut. Its a soft boost cut, depending upon the percentage that you used to limit.. (For example, if the Limiter on the Profec is set to 5%, there's a second area about one dial turn over that helps you select at WHAT PSI its supposed to limit. So say you have a 10% boost cut at 15psi. that means that when the car reaches 15psi or even spikes to that amount of boost pressure, it will boost cut the amount of pressure down by 10% or 13.5psi softly.

If you try to key in the Neptune to the map sensor AND try to act as a boost cut in conjunction with the profec B. you're going to have some issues as to which will take over first. The answer is the Profec B, since its directly connected to the top of the TiAL wastegate.

Make sure you're going though the Profec B instruction manual before trying to increase boost pressure on the next dyno session. Just tune with the neptune like normal, and set the boost limiter on the Profec B a bit higher than you want target boost to be. So for example, if you want 20psi on this setup, then set the Boost limiter on the Profec B to be 21psi with a 10%-15% cut. That way you won't spike.

IN case you don't have one, or bought the unit used, here's the instruction manual in English.. It gives some guidance as to how to set things. It's actually MUCH easier than people first think. but unlike a T.V. or stereo, you can't just "play" to see how to set things. these instructions do work.

Good luck..