Can I increase vacuum?
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Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
Can I increase vacuum? NPP wont close fully
So I just had the hooker blackheart axle back system installed on my C6Z06. The car does have a larger camshaft and I'm only getting about 10in of vacuum at idle. The valves on the exhaust wont fully close unless you raise the idle and create more vacuum. I had sporadic issues with the factory system not closing fully unless you gave it gas. So when I'm driving the valves will stay closed, but as soon as I get to a stop, they crack open a little bit. I really dont think theres any way to increase vacuum, but I thought it might be a shot in the dark that someone had an idea. Would a check valve placed somewhere on the line going to the mufflers help?
Last edited by Maligator; Dec 16, 2023 at 03:14 PM.
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So I just had the hooker blackheart axle back system installed on my C6Z06. The car does have a larger camshaft and I'm only getting about 10in of vacuum at idle. The valves on the exhaust wont fully close unless you raise the idle and create more vacuum. I had sporadic issues with the factory system not closing fully unless you gave it gas. So when I'm driving the valves will stay closed, but as soon as I get to a stop, they crack open a little bit. I really dont think theres any way to increase vacuum, but I thought it might be a shot in the dark that someone had an idea. Would a check valve placed somewhere on the line going to the mufflers help?
There are also several electric versions which work even better but I'd try this one first.
https://www.summitracing.com/parts/cca-5200
Thread Starter
Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
I run this one which helps hold the car at the starting line after doing my burnout. Without it, I would have trouble keeping the car from creeping forward.
There are also several electric versions which work even better but I'd try this one first.
https://www.summitracing.com/parts/cca-5200
There are also several electric versions which work even better but I'd try this one first.
https://www.summitracing.com/parts/cca-5200
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I mounted that one just above the steering rack on the driver side, right by the #3 and #5 cylinders.
When I had the electric one I screwed it to the inner wheel well on the passenger side.
Car's currently in storage otherwise I'd post a picture.
When I had the electric one I screwed it to the inner wheel well on the passenger side.
Car's currently in storage otherwise I'd post a picture.
Thread Starter
Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
Curious, how large is it? Its hard to tell by the picture Summit has. And how does it hook up? I just see the one fitting/port at the top. Thanks for your help
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Drifting
Joined: Oct 2017
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From: Los Angeles, ca
I’d check for a leak as well. Get a vacuum reading at a few places including. the engine and the valves. Disconnect the valve vacuum source at the engine and test for vacuum again and see if it’s any different.
Le Mans Master
Joined: Dec 2004
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From: West coast CA
A check valve should keep your muffler's exhaust valves shut, but how are they supposed to open?
It seems like you'd need a pressure relief valve plumbed around the check valve to release vacuum to the manifold at high load.
Perhaps you could adjust the actuator linkages to keep the valves closed with less vacuum.
It seems like you'd need a pressure relief valve plumbed around the check valve to release vacuum to the manifold at high load.
Perhaps you could adjust the actuator linkages to keep the valves closed with less vacuum.
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Thread Starter
Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
I wonder if adding a second OEM style vacuum reservoir would do the trick
Le Mans Master
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Thread Starter
Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
its .660 lift 243/251 114LSA thats just me reading off the cam card, im no cam expert, but its a little rowdy. But I agree, I feel like 10in seems low. I'm going to mess around with it today with my mightyvac and make sure theres no leaks. But I just had my mamo msd installed and my guy smoke tested the vacuum side of everything for leaks before it left his shop.
Le Mans Master
Joined: Dec 2005
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From: Southeast TX
its .660 lift 243/251 114LSA thats just me reading off the cam card, im no cam expert, but its a little rowdy. But I agree, I feel like 10in seems low. I'm going to mess around with it today with my mightyvac and make sure theres no leaks. But I just had my mamo msd installed and my guy smoke tested the vacuum side of everything for leaks before it left his shop.
Race Director
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I have a 17° overlap cam in my LS7. I have no problem with vacuum. I have about the same exhaust duration as OP, but 10° less on the intake. However, my cam is on a 112° LSA, and less lift. Not apples to apples, FWIW......
Thread Starter
Melting Slicks
Joined: Aug 2011
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From: Frankfort,IL
turns out, its not a vacuum volume issue, theres a leak (I think). I dont know if my mightvac hose wasn't seated correctly or what, when I checked it at the intake manifold. I got 14-15in of vacuum all the way back to the solenoid. With the solenoid open, which would close the valves, I had the same reading. Once I put a "T" in-between the solenoid and the line running to the valves, I watched the vacuum drop to 8in and just stay there. When I applied vacuum from the mightvac to the hose going to the exhaust valves, I couldn't even get 5in of vacuum. How a car with this low miles would have a broken plastic vacuum line is beyond me. Anyway, instead of buying the stock OEM plastic lines, I could just use rubber hose right? Its not like its touching the exhaust, its just running up the bumper to the solenoid.
Thread Starter
Melting Slicks
Joined: Aug 2011
Posts: 2,097
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From: Frankfort,IL