Yellowsierra

iTrader: (7)

I thought I had some boost bleed off some were and it turns out I do. I called whipple up and they said if I was running that much boost(10 psi) with the stock tb it probley is building up vac. behind the tb at wot. This in turn holds the bypass open a little bit which causes boost to leak out. I tested mine by first cuttin the vac line between the bypass and the back of the supercharger then hooking the vac. gauge to this with a t valve. At wot it showed 3 p.s.i of vac. I guess I will be buying a bigger tb which isn't bad it just gives me a reason to buy one. I think I mit end up getting the FAST 90mm tb it looks pretty sweat.

James B.

iTrader: (1)

That makes sense. I realized there was a lot to gain by freeing up the intake as much as possible after reading how much success others were having modifying their inlet castings for more flow on 5.7L Vortecs. On these inlets there is huge obstructing relief cast into it to clear the brake booster. Obviously an afterthought. After cutting out that obstruction and welding in a patch I picked up half a pound of boost from just that mod alone.
When you install the new throttle body you might have issues with the transmission shift schedule. The bigger TB causes more air to get in with less throttle. The shift schedule will be changed to give you a little more line pressure vs TP in the lower region. Speed vs TP for the shiftpoints might need to be moved down a little bit since there will be less throttle resolution to work with. The bigger Throttle Bodies on an NA motor don't exhibit this as much as they do with a Whipple. The effect is hard to explain, you'll probably just have to deal with it if it comes up. I just wanted to give you a heads up.