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I brought my IS to Street Rods and Classics in Boca Raton, FL. They're one of the few local shops with their own dyno. I brought my Miata there when I first put the turbo in. They're nice people and they have pretty reasonable dyno rates.<P>

I had previously installed my SRT Intake, but had removed it prior to an autocross event. Installation and removal after the initial setup is fairly easy (since the ECU harness is already soldered in). I swapped out the stock intake for the SRT unit in about ten minutes, if that. (And yes, I disconnected the battery during the procedure.)<P>

The biggest challenge was getting decent, repeatable runs with the automatic transmission. You can't keep it in any one gear and accelerate full throttle without it kicking down a gear. This made it impossible to do fourth gear runs or any gear other than first. First gear is undesirable because at such low gearing, the run from 2k to redline happens so fast that the computer can't get enough samples for an accurate reading. The reason fourth gear is preferred is because it results in a 1:1 driveline ratio which creates the least amount of crank-to-wheels power loss. While it is possible to modify the IS to stick in a gear for purposes of a dyno run, it involves the cutting of wires in the ECU and not many people are keen on the procedure.<P>

In the end, we managed to develop a technique for consistent 3rd gear runs. This results in two things that may make the dyno graphs look disappointing. First, the peak power output is less than what you would see on fourth gear runs. Second, due to the downshifting of the automatic, the car had to be eased into full throttle, so the low end range of the rpms are not well represented. However, the goal here was to see the difference in power made by the SRT Intake and that shows cleary enough.<P>

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Now, if want to play with the math. Here's the way I worked out the peak power gains:<P>

<B>Stock, 3 runs:</B> (HP/Torque)<BR>
162.5/162.0<BR>
163.6/164.0<BR>
165.2/161.9<BR>
<BR>
AVG: 163.8/162.6<BR>
<BR>
<B>SRT HFI, 2 runs:</B><BR>
172.2/172.4<BR>
174.7/171.2<BR>
<BR>
AVG: 173.5/171.8<BR>
<BR>
<B>Peak Power Difference:</B><BR>
AVG/AVG - +9.7/+9.2<BR>
MAX/MIN - +12.2/+10.5<BR>
MIN/MAX - +7.0/+7.2<BR>
AVGofMM - +9.6/+8.9<BR>
<BR>
So, the end result? I'll call it a 10hp and 10ftlb increase. That's something I can live with!<P>

<I>NOTE: Remember, all quoted power numbers are "at the wheels" (RWHP). Manufacturer's stated power ratings are "at the crank" and will be higher by a certain amount, typically 20%. Fourth gear runs of the IS on the dyno should result in a peak power of around 170hp, so you can see how the 3rd gear runs affected peak numbers. But again, since all the runs are similarly affected, the proof is in the difference. Also, different cars on different dyno in different climates will yield different results. The purpose of any dyno tuning session should be to measure quantitive differences in power output due to modifications performed. Anything else is just a number without qualitive reference.</I>
 

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