Just recently Ive been getting bad gas mileage. Normally i would get 350 miles on one tank of gas, and now Im getting 250 miles on one tank of gas. The only things I did recently was add a 55mm throttle body, OBX intake manifold, and Royal Purple Oil. The hoses check out fine. Any help would be great.

thanks.

Im not completely sure but, the intake mani. and the TB would lower your mpg. Check your sparkplugs, fuel filter, VC and sparkplug gaskets. I know Im getting around 15mpg since I changed my fuel filter, but thats because one of the copper gaskets wouldn't fit and I used plumbers tape to try to seal it. I need to redo it i suppose. Either that or my "Low Fuel"(which has just recently started working) light has gone berserk along with my fuel gauge (which has never worked).

hows the O2 sensor. I bet that obx manifold does more to hurt intake vel and VE then help. Also, with that tb, if you press on it the same amount as the old one, it will allow more air in...

Well the throttle body is only a 55mm, not much bigger than the stock one. And I have a SAFC 2 leaned all the through the range at 23% and still bad gas mileage.

Did this change show up right after the mods or did you go a couple weeks/months before seeing the reduction in economy? Personally, I would ditch the intake manifold and SAFC. On a fully built engine, you might see close to 10whp, but if your only mods are bolt-ons like that, the SAFC is a waste of money and the intake manifold, like Chamuko said, is hurting you.

Think about it like this: You engine can only pull in so much air per cycle. You only need an intake manifold when the stocker becomes a restriction - such as with a turbosystem pushing a lot of boost. When you install a larger intake manifold like that, it's like the difference between you trying to drink a Coke with a regular straw or with a garden hose. Which has the Coke flowing the fastest when it gets to your mouth?

The best intake mods for a naturally aspirated 2GNT are:
-eBay or DIY short ram intake w/ K&N filter
-55-57mm bored TB
-gasket matched intake manifold with the injector humps machined

That's really it. I wouldn't consider anything more. To go larger would sacrifice bottom end for throttle response. To spend more would be foolish.

Most likely a bad o2 sensor or your injectors could use a good cleaning.

This bad gas mileage came right after the intake manifold and throttle body installation

You can go back to the stock mani and see if that makes any difference. It's the cheapest idea...

TB would not change mileage. I'll be posting up some stats that show that sometime in the future