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Well, I had nothing going on today, so I ended up doing some fairly extensive testing trying to get my turbo to spool better. I tested the a/f between 10:1 and 16:1, and the ignition timing +-10 degrees, mostly in 3rd and 4th gear.

My conclusion... none of this stuff really even matters! The turbo is pretty much going to spool when it wants to spool. I'm not saying tuning doesn't help, but the benefits appear to be very small and hardly even worth the effort, plus there are some tradeoffs. For these tests, I was changing the fueling and timing between 0-16 psi only, and after that I have my a/f set to go back to 11.8:1. I found that slightly more hp and torque are made around 12.5:1 as expected (5-15 hp from 1500-5000 rpm). Not very noticeable on the street, but probably worthwhile. I found that 14.7:1 was about optimal for helping the turbo spool faster (100-200 rpm). I found that an a/f of more than about 15:1 started to make the car feel a little dead and under 11:1 make it start choking on the fuel a little, as expected.

Timing didn't seem to do much at all. Retarding it a lot made the car start feeling extremely dead and only helped the spooling a tiny bit. Advancing it didn't seem to do much either, except the car felt a little better.

So, there are tradeoffs with both fueling and timing. Less fuel and less timing help the turbo spool at an earlier rpm, but the car is slightly more sluggish and makes less hp and torque up to that point. It looks like the advantages of each sort of negate the other. I would say, if you're tuning for the dyno, tune your spool-up area to about 14.7:1 and keep the timing somewhat low. If you're tuning for the street, it's better to tune more toward 12.5:1 so the car feels a little more lively.

If anyone else has done their own tests please share your conclusions!

Paul
T72 Supra
 
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Discussion Starter #2
By the way, I also did a little testing on my Blitz DSBC boost controller. I tried several different gain (aka response) settings and compared the logged data. Normally I always set the gain at 100% because it spools the fastest, but after looking at the data it makes sense to set it much lower, around 25, to help maintain traction. Although max boost was achieved 200-300 rpm later, the transition as it reaches max boost is much much smoother. At 100%, it comes to a sharp point and levels off instantly. At 25%, it has a very nice curve at the top. Much more than 25% didn't have nearly as nice of a curve at the top and much under 25% was a little too laggy. So if you have a boost controller with some sort of wastegate response or gain setting, be sure to use it when you're having trouble getting traction! works great!
 

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Shawn Davis
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What did your knock log look like during all this testing. I imagine 15:1 felt flat because you were detonating and timing was pulled...
 
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Discussion Starter #4 (Edited)
I didn't notice any increased knock noise in the log, although I wasn't paying real close attention to it. You think running that lean could cause detonations even for such a short time period? I didn't think it would, but you might be right. Maybe I'll take a closer look at it later. I guess it wouldn't be a bad idea to richen it up a little sooner..
 
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