I recently had an experience that demonstrated how the right dyno used correctly can be a powerful tool that is good for more than a hp number.

My daily driver is a 2.5l MK5 VW Jetta with an aftermarket turbo kit and a reflashed stock ecu. Considering it is just my daily and the roads have been icy I wasn't too concerned with what sort of power it was making until my friend asked me. I found myself up at Xenocron Tuning recently and decided to answer the question.

Xenocron Tuning not only has a great dyno cell they also have a Mainline Dyno that in addtition to being awd capable offers a number of datalogging options. Besides the the normal boost and afr logging there are a number of additional temperature and pressure inputs as well as the ability to log OBD2 data directly from the factory ecu. The dyno will also communicate with a number of Aftermarket ecus and log parameters from them.

I loaded my car up on the dyno and planned on only making a couple quick pulls as the stock ecu isn't adjustable beyond the reflash. I hooked up the dyno's map sensor to the intake and put the wideband in the tailpipe and also connected the OBD2 cable from the dyno to the car. The cool thing about the OBD2 logging is you just need to connect to the ecu and it automatically logs all the available parameters so you don't have to decide beforehand what you want to see. The dyno logs the available channels - including ignition timing, rpm, engine load, throttle position, etc. and you can cycle through the data later.

I made my first pull and started looking at the dyno chart. I noticed right away that boost was tapering off in the higher rpms. I began to wonder if it was a boost leak or something going on with the wastegate. I decided to do a quick boost leak test and found no apparent leaks. The wastegate was getting its signal straight off the compressor housing as is common in order to keep the line as short and fast acting as possible. I decided to hook up a second map sensor signal to the dyno and log pressure in the compressor housing/wastegate signal line. I made another pull and looked at the data. Boost in the intake manifold fell off the same as the first run but the map signal from the compressor housing was dead flat. Obviously there was a significant pressure drop from the intercooler and piping at higher rpm. Down low the intake manifold pressure equaled the compressor outlet pressure but at higher rpm there was 2+ psi difference. I found a vacuum line coming from the intake manifold that I could repurpose for the wastegate and hooked that up and blocked the line coming off the compressor housing. I did another pull and sure enough boost in the intake manifold stayed flat. With no additional peak boost the car picked up 25 hp just from changing the wastegate reference line.



Oddly though as you can see power rolled off up top where it was flat before. I started looking at the OBD2 data and saw that right where power was dropping the ecu was closing the drive by wire throttle body due to either a maxed maf sensor or some sort of load calculation in the stock ecu. Like many modern ecus VWs are tuned based on a number of torque tables and limits vs straight rpm vs engine load. I also saw that in the midrange the ecu would vary timing to keep tq to a certain level even if engine load / maf readings varied.

Granted there are programs that will log OBD2 data that I could have used they require either a laptop or an android device and additional hardware and none of them will lay over the dyno chart with the click of a button. Also this data is now stored on the dyno computer for future reference and not on a separate device. I could have dug up a second boost gauge and logged compressor outlet pressure manually as well but that would have meant finding a gauge, running a line, figuring a way to mount it temporarily where I could read it and then comparing to the gauge that is installed in the car. Instead with a little extra time setting up the dyno I got a bunch of data and some answers to questions I didn't even know I had.

I went in with the expectation of just getting a power number and ended up picking up 25 hp with no real tuning and no additional peak boost. I also learned that there was no point in turning the boost up any higher as the stock maf was hitting its limits at higher rpm at the current boost levels.

Since this was a quick unplanned test I only grabbed the one quick photo of the peak gains but I can get any charts/graphs anyone wants to see. I just thought this was a cool example of focusing more than power numbers and using the dyno as a tool. Fire away with any questions you might have,

 

Neat. Makes alot of sense to have the boost source from the intake manifold if you have a lot of piping / restriction.

 

I'd like to hear more about the quick boost leak test,
how it was done?

 

If you do a search there are a bunch of how tos all over the net but basically I made a tester out of a rubber coupler, a pvc cap, and a valve stem for a tire. I took the filter off the inlet pipe to the turbo and used the tester and an air compressor to fill the system with air. Then I sprayed soapy water over all the connections to look for a leak. Ideally you would cap off both ends of the system and see how long it stayed pressurized but this was a quicky like I said.

 

That's great and all, but contrary to popular belief most waste gates aren't designed to see engine vacuum. Do people do it and get away with it? Sure do. Is it a risk I am willing to take? Hell NO!!! Read up about your specific wast gate diaphragm design before you leave it. Also, this is what boost controllers are for (to a point) but it also comes down to the entire setup haha...

 

Tial calls for Prethrottle body as you've said.



Mine has always been off the intake manifold

 

Good point and that's why I originally had the source coming from the compressor housing. Since its a quality gate though I am not too worried about the diaphragm seeing vacuum. Boost control was stable as well which is the other concern as there can be some odd behavior inside an intake manifold. I agree it's not ideal but neither is losing 2 psi up top.

I welcome any comments or discussion. Hopefully we can spark some good conversation.

 

This ! Transition from boost to vacuum back and forth does a real number on diaphragms.