View Full Version : 99 7.4 vortec throttle body 78mm
04-22-2012, 09:10 AM
I purchased a throttle body on E-bay than was machined to 78mm instead of 72mm. When I went to install it I noticed that the breather passages were blocked on the one I just received. I contacted the seller and he said the crank case breather doesn't run through the throttle body. It sure looks like it does to me. The breather comes from the valve cover and through the intake and through the throttle body. He said he has sold 1000s of these and never had a problem. My question is what will happen if I block the breather he says isn't there? Thanks for any help
04-22-2012, 10:17 AM
If you block it off the pcv will pull vacuum on the crankcase and eventually suck seals in like oil pan and valve cover gaskets. You can run the tube into the intake so filtered air is allowed into the vent. Is your engine basically stock? Reason I ask is the stock throttle body is in no way a restriction and a quick check with a tech2 scanner will show map sensor reading zero vacuum at wot. The bigger tb will make you think it helped because it will take less throttle as far as percentage open while driving. But peak hp and torque will show no gains, maybe even a loss if the oversize tb does not match the intake.
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