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Old 05-23-2018, 10:53 PM   #50
Jordan Silveira
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Join Date: Feb 2016
Drives: 2016 Subaru Series.HyperBlue #631
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Originally Posted by nikitopo View Post
Thanks for your reply. Yes the throttle body and pulley modifications were quite controversial discussions here. A reason I focused on these mods was because it is not legal to remove the cats in Germany. So, I had a reason to search for alternatives and experiment a bit more.

The usual critique for the tb is that the stock unit is big enough and it can handle even FI applications, but the same can be said about a 2.75" or 3" exhaust. Such exhaust sizes are too big for a NA application, but even in this case there is evidence that can give a few more gains. Personally, I believe that the sweet spot for a tb is the 67-68mm size which is +2-3mm from stock. You can go even bigger, but then you're losing the tapering entrance which is also important. Toda Racing provides a 67mm unit and recently I found another vendor with the same spec. There was also some measuring from an independent shop and the gains were calculated to 225bhp from 215bhp on a car with header and exhaust. In my car I think that the gains are less, because my header is a bit better (+'17 oem) but still catted. I don't have before and after figures, but the car reads currently in virtual dyno unusually high (~189whp based on my car's weight) and the application is know to be accurate. I have one more measurement before the flywheel installation in a local dyno shop and it was also reading high (~185whp). The average of the stock cars are reading here around 160-165whp. Here is the link of the other tb vendor: https://de.part-box.com/at-power-67m...0049-504424280

About the pulley kit, I don't have much to say. I provided recently a link with formulas that provided just for the crankshaft pulley a 15kg gain in 1st gear and a 7kg gain in 2nd gear. If you add the rest of the pulleys and you under-drive a bit the alternator you are getting certainly even more. The real weight difference of the factory and an aftermarket pulley is usually 2kg, but this is before the gearing so this gain is multiplied in a low gear pull (1st, 2nd or 3rd gear). There was a similar discussion in the German forum which I find quite mature. One racing driver provides an overview of a pulley and a flywheel combination and how hard the car pulls even on slick tires and another engine designer mentions exactly the same reason of the additional weight and the extra rubber of the factory unit. That it is mainly for NVH purposes and the longevity of the belt and the external peripherals (i.e. alternator and A/C unit). You can check the discussion in Google translator:
https://translate.google.gr/translat...469b&edit-text=
Well @nikitopo you certainly won't get any argument from me. I have seen throttle body modifications made on many other cars including my 4th gen Ludes make a difference. As for pulleys I've always been perplexed on how people are so apt to change driveshafts for the sake of "freeing" up power through less wasted movement by converting to a 1 piece driveshaft. Yet, when it comes to new pulleys weighing less and ultimately "freeing" up some so called "restrictions" (as little as they may be in the case of pulleys) the forum is so quick to negate and dismiss it. Anyways, it is what it is and the beauty of public opinion is that is is just that, opinion. I believe we should all pursue our own desires insofar as it doesn't directly affect anyone else and in the case of pulleys, throttle body, STI Brembo conversion or otherwise, the same applies.
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Last edited by Jordan Silveira; 05-24-2018 at 02:22 AM.
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