Just for kicks - 67mm vtgs and e85 plotted out. The alphas seem to have slightly better spool than the 67VTGs, interesting. I shouldn't have used 2nd gear for spool, look how crazy boost/load get then smooth out in 3/4 gears. Todd's still tweaking this map but close to final.

2nd gear spool up:


3rd gear continuation:


And 4th Gear:

 

Nice data Chk -- thanks for sharing. Boost holds up throughout the range. That's awesome. Car must feel really good.

 

Yeah its very smooth feeling on acceleration. The tq dropping off up in the RPM range on the VTGs is where the alphas you've got are going to fly. You won't see the load/tq dropping like that, and thus just zoom zoom :-)

 

Coooool graphs! If you get a chance Dave please overlay the load graph of your old modded vtgs with the alpha graph. It may bring me to tears, but it would definitely be interesting.

I must say that the power bandwidth of the modded vtgs is amazing to me, I wouldn't give it up for more power higher up the rpms. I'm just curious about the 3-4k rpm response for the alphas.

 

Here you go Asher.

 

If I understand this correctly, the alphas spool earlier than modded vtgs, is that right??? I realize your boost is "only" at 1.3 but even then I thought the alphas would have way more hp/tq (and load) than the vtgs, no?

 

That does appear to be the case, at least for my situation. I'll test at 1.5 bar and see where things land. As Chk pointed out, this is maf vs map comparo. Are you running mafless? If so can you check to see if your values are the same with maf?

 

Awesome build. Protomotive do some great work.

 

I'm currently running mafless but when I sent you the datalog file I think I was using the maf. I'll log both ways and report back.

 

That would be great. Thanks Asher.

 

Question please: Is this observation of "earlier spool" based on generally accepted observations of VTG vs. Alpha, or is it based on the dyno-type curves that Dave posted?

I don't believe you could tell turbo spooling speed from Dave's dyno curves, no? These curves may appear to indicate speed of spooling, but I don't think so as there is no time element in either axis.

Spooling speed comparison I think would require a graph of RPM vs. Time on x axis, not these dyno curves, and would require that WOT to be applied at exact same RPM.

 

Based on these curves, boost is clearly being generated earlier than VTGs. But once the VTGs kick in, the slope is steeper due to physical design attributes between the two different turbos.

 

Dave, what I meant is, yes the curves show that A3076 boost starts at 2500 rpm, and VTG at 3200 rpm, but to answer whether "spool up" is faster in one or the other, you need to know the time elapse between WOT and peak boost. And *time* element is not graphed in these curves, it tells you boost vs. RPM, not boost vs. time.

In other words, in Durametric data, we need to look at time that WOT starts, use this as 0 on x axis (time axis), and graph against boost on y axis (boost axis). I've actually looked at my data already, to compare spool of GIAC vs. stock, but was just too lazy to graph that yet.

Also, another question for the graph, unrelated to above: in the 2 runs of Alpha vs. VTG, did WOT start at identical engine speed (2000 rpm or whatever) in each run? The Alpha seems to rise so much earlier, could it be that you apply throttle at a lower rpm? Your comparison seems to show exact opposite of what's expected of VTG, earlier RPM rise, no?
Thanks for sharing the data; I am learning a lot.

 

Can, These are good points and questions. I believe these are WOT data but will check starting point, etc...when I have some time and get back to you. Dave

 

Observation and question. Leaving 'Load' component aside, the obvious difference in the comparison chart, appears to be the boost threshold speed(rpm). The alphas speed is much lower, but the VTGs time from boost threshold speed to maximum boost is faster. Is it the VTG variable design that causes this late boost? If the ECU controls boost via the vanes, can't it be programed to boost earlier?

Thoughts?