I'm considering getting my hands on a brand new PDI 170% just so I can test it out on my platform... the last time I worked with one, it was putting out close to 430fps. Although I don't want to buy one just to test since I know I'll have a hell of a time trying to sell it.

The materials between the 170% and 150% must be different, hence the different lengths.

Ok, so im getting confused with all this.
Im stock right now...SR16, but I have a set of systema super torque up gears comming, systema reinforced piston, systema steel bushing, and systema piston head...All these were spares a friend of mine has, so Im not picking and choosing.

I don't wanna blow my mechbox, so whats the most powerful spring I install and stay safe...while getting as many FPS as possible....

If you want to play with the guys at the LZ and PQAC, you'll have to limit your fps to 400. Use a PDI 150% max. I'm using it with a TN barrel and it'll be very close to 400fps or slightly over.

my only concern is that my finds wont allow for a reinforced mechbox for awhile yet....so keeping FPS high, without blowing the mechbox

That's the gamble we all take when it comes to the Version2 mechboxes my friend. Especially if we play in the winter with an upgraded spring. A M120S will for sure crack your mechbox in the winter. I've crack a Progear and a Systema one already.

I'll go with a Top Power 150%, PDI 140% or a M100 spring to be safer. I hear Top Power springs are better for the mechboxes but I gave mine to Vondnik before I could use it.

ANd he loves it over any other spring he ever installed in any guns... Now the only catch is finding more of them damn it...

You might want to consider KM/Head 1950 springs... they're short and "feel soft" like Top Power springs as well. They don't hold their initial velocity too well, but once settled in, they're damn consistent. In my tests, they were more consistent than Top Power springs.

That's why I have a couple of them on the way... :)

The PDI 150% in my MP5 shoots roughly around 340fps. I know, I chronied a number of shots. Doubt a tightbore would knock the fps that much (as said above). And Apoc has a PDI 170% spring in his SR-16, and it's only sitting around 360-370fps. Will be up a bit more soon, as I'm installing a bearing spring guide this weekend.

I'll vouch on the length difference between the PDI 150 and 170 springs. Couldn't figure out why the 170 was shorter. I'll just say that the 170 is easier to compress and hold to get the mechbox back together.

That's incredibly low... 340fps with a PDI 150% and 360-370fps with a 170%??

Can I ask what chronograph you are using? And is it optical or radar? Optical chronies are much more accurate and radar's usually have difficulty picking up BBs or give results that are too low or too high.

The length differences between the PDI 150 and 170 can be attributed to different materials used. A softer steel is used for the 150, but a greater length must be attributed to get it to perform where PDI wants it to perform. That material is used because there is no ecconomical grade of steel between what's used in the 150 and the 170.

With my MP5 I used an M120 spring and was shooting around 440-450fps with some shots as low as 403. My mp5 is since retired and am looking at getting a good spring for 390 fps.

PDI 150 should do you well.

my g3 with pdi 140% spring installed shoots at about 385fps

What's your spring guide, piston head and inner barrel?

origional piston head with 4 small holes. origional barrel
hurricane bearing spring guide

the nut on the original piston head compresses the spring more - putting more preload on it, and giving it a higher output. Its height is almost double that of the bearings on the piston head I used for testing the springs in my spring chart.

As well, the chart is not here to tell you exactly what velocity you will get exactly with what springs. It's there so that you can compare springs against other springs as well as to give you a *general* idea of what velocity to expect with a particular spring.

The Airsoft manufacturing process is not consistent enough to allow another P90 upgraded with the exact same parts I used to output exactly the same velocity. The chances of that happening are pretty slim, given all the variables.