vacuum question
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
vacuum question So I'm moving along with my build, and I just installed my Fast 102 onto the motor. Not wanting to fight with it in the car and be doubly sure, I decided to do a vacuum test on the manifold and see if it would hold vacuum.
Issue I'm running into is... it's not. I triple checked that the vacuum and brake booster lines are fully capped off, I'm pulling vacuum from the Evap port and hte pcv is blocked off as well. I've got the fresh air port on the tb plugged, and a rubber glove over the inlet, so it should be sealed. The pushrods aren't installed so I don't have an open valve somewhere.
I'm assuming this isn't normal. Anyone have any advice? Not really sure 100% where to start looking.
Issue I'm running into is... it's not. I triple checked that the vacuum and brake booster lines are fully capped off, I'm pulling vacuum from the Evap port and hte pcv is blocked off as well. I've got the fresh air port on the tb plugged, and a rubber glove over the inlet, so it should be sealed. The pushrods aren't installed so I don't have an open valve somewhere.
I'm assuming this isn't normal. Anyone have any advice? Not really sure 100% where to start looking.
If you're being very thorough which it seems you are it's probably not the intake it's probably the valves. If you can pressurize the cylinders pressurize each one and listen for air to come through the intake and while you're doing it listen for it to come out of the exhaust, just to get an idea about the exhaust valves as well. I've never had a problem with a FAST leaking air that I've installed and I'm a thorough person as well. I didn't vacuum check them, I just ran em and didn't have any issues with idle or fuel trims etc.
Have the heads been milled? If so is the intake contacting the heads flush?
The smoke machine would be nice so you can see where it's leaking and you can also use the flow gauge on the smoke machine to gauge the size of the leak.
It could also be the intake perimeter gasket, the shell gasket. Check to make sure the bolts are snug, doesn't require a lot of torque it's all plastic so snug plus a tiny amount is enough.
Have the heads been milled? If so is the intake contacting the heads flush?
The smoke machine would be nice so you can see where it's leaking and you can also use the flow gauge on the smoke machine to gauge the size of the leak.
It could also be the intake perimeter gasket, the shell gasket. Check to make sure the bolts are snug, doesn't require a lot of torque it's all plastic so snug plus a tiny amount is enough.
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
So this is interesting...
For ***** and giggles, I ended up taking the mityvac off the intake and using my lungs instead. To my surprise, I got vacuum. I could see the rubber glove on the throttle body mouth getting sucked inwards (and eventually I ran out of air to suck in lol)
My guess is that since the mityvac is so small it just doesn't have the ability to pull enough air out of the intake to actually register on the gauge, whereas my lungs can pull a ton of air by comparison.
Regardless, I've got vacuum so I'm happy lol.
For ***** and giggles, I ended up taking the mityvac off the intake and using my lungs instead. To my surprise, I got vacuum. I could see the rubber glove on the throttle body mouth getting sucked inwards (and eventually I ran out of air to suck in lol)
My guess is that since the mityvac is so small it just doesn't have the ability to pull enough air out of the intake to actually register on the gauge, whereas my lungs can pull a ton of air by comparison.
Regardless, I've got vacuum so I'm happy lol.
So this is interesting...
For ***** and giggles, I ended up taking the mityvac off the intake and using my lungs instead. To my surprise, I got vacuum. I could see the rubber glove on the throttle body mouth getting sucked inwards (and eventually I ran out of air to suck in lol)
My guess is that since the mityvac is so small it just doesn't have the ability to pull enough air out of the intake to actually register on the gauge, whereas my lungs can pull a ton of air by comparison.
Regardless, I've got vacuum so I'm happy lol.
For ***** and giggles, I ended up taking the mityvac off the intake and using my lungs instead. To my surprise, I got vacuum. I could see the rubber glove on the throttle body mouth getting sucked inwards (and eventually I ran out of air to suck in lol)
My guess is that since the mityvac is so small it just doesn't have the ability to pull enough air out of the intake to actually register on the gauge, whereas my lungs can pull a ton of air by comparison.
Regardless, I've got vacuum so I'm happy lol.
Thread Starter
Joined: Jun 2014
Posts: 1,241
Likes: 47
From: Noblesville, IN
I ended up just pinching off the hose with a clamp, let it sit for about 20 minutes or so and came back to it. Glove was still tightly sucked to the throttle blade and gave a reassuring "psssssh" when I released the clamp. I'm calling it good.
