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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #1 ·
My cowl induction is not working properly and I’m looking for help. I’ve read all the threads and this is what’s going on with mine. Freshly installed GM zz454 crate with mild hydraulic roller cam (469hp). When the car is off the hood flapper goes up and when I crank the car it immediately goes down. The problem is when I accelerate driving WOT, it will not come up. I have no check valve. I have a T on the back of the intake manifold; one line goes to my brake booster and one goes directly to the vacuum pod. There are no kinks. The test I have done is to put a adjustable valve in the vacuum line to the pod and this is where it gets tricky. With the car idling and hood flapper closed I turn the valve off where there is no flow in the vacuum line to the pod and the pod will not open the flapper. So do I have a bad pod? It just doesn’t make sense. How can this be?
TIA
 

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sounds like it could be a problem with the pod or maybe not enough manifold vacuum drop. Without the check valve it should open and close real quick. I ran mine without the check valve and it would open and close really fast with the zz502 but I wanted the outside flap to stay open longer. I got the repro check valve (the one with the gold/black color) and i wasn't really happy with it. I got a yellow/black delay valve for cars from the 80's and it stays open longer (about 2-3 minutes) and closes real slow. The green/black one stays open for like 4-5 minutes and that was too long. I know you mentioned that you don't have any kinks in the line but another spot the line gets smashed is if you have the cowl screens that are under the wipers. I have those on mine and the middle one was hitting the pod when I closed the hood so I cut out some of the screens and now it works fine.

Wood Gas Wire Electric blue Recreation
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #3 ·
sounds like it could be a problem with the pod or maybe not enough manifold vacuum drop. Without the check valve it should open and close real quick. I ran mine without the check valve and it would open and close really fast with the zz502 but I wanted the outside flap to stay open longer. I got the repro check valve (the one with the gold/black color) and i wasn't really happy with it. I got a yellow/black delay valve for cars from the 80's and it stays open longer (about 2-3 minutes) and closes real slow. The green/black one stays open for like 4-5 minutes and that was too long. I know you mentioned that you don't have any kinks in the line but another spot the line gets smashed is if you have the cowl screens that are under the wipers. I have those on mine and the middle one was hitting the pod when I closed the hood so I cut out some of the screens and now it works fine.

View attachment 726505
Thanks for replying. I do have the screens under the pod and I already filed them down where it was hitting with the hood closed but I will just take it out and see if it helps.
Thank you, Billy
 

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When you close the valve the diaphragm side is holding a vacuum and keeping the door closed. Pull off the hose and release the vacuum and it should open.
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #5 ·
When you close the valve the diaphragm side is holding a vacuum and keeping the door closed. Pull off the hose and release the vacuum and it should open.
Okay I did that and you are right. Then I just cracked open the valve after resetting it like you suggested and it still doesn’t respond. So I will try this next: my mechanic friend said to put a “tee” in the line with the valve on it, basically having an open vacuum when the tee is cracked open. This will allow the pod vacuum to escape as we were talking about at the beginning of this conversation. I have this set up and will try it today and let you know. Thank you for your help-Billy
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #6 ·
Sorry for the delay but the cheap plastic tee cracked open seems to be working and not affecting engine performance. So unless I find a better way this is how I will be riding. Thank you for all the help.
 

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No other vacuum using item should be Teed into the vacuum booster line, it is a dedicated vacuum hose!!
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #8 ·
No other vacuum using item should be Teed into the vacuum booster line, it is a dedicated vacuum hose!!
Understood, but I couldn’t get the cowl induction to work otherwise. Any suggestions other than what’s listed previously? TIA
 

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I think you have a bad cowl pod. Maybe a weak spring. The door moves freely correct? There are holes in the metal base of the pod, are those clean? I'm pretty sure you are running off manifold vacuum, so that's not the issue.

Without the pod installed mine acts like it's on bearings. Mine flaps like a girl on crack. Might be because my cam has so little vacuum.

I wonder if that pod has some sort of induced vacuum leak inside of it. I highly doubt it because I can't see the General inducing an engineered vacuum leak in the pod.

I want to check my pod with a mityvac but I loaned mine to my neighbor and the cluck ran it over. I'll want to pull a vacuum on it and see if it holds. If vacuum bleeds off, then there is an engineered leak in the pod. I think my dad has a mityvac and I'll see him tomorrow. Stay tuned for results or an excuse. 🤪
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #11 ·
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Wow those instructions and pictures were great thank you very much. Where did you get those or what book are those in? I bought the three assembly manuals but mine are not nearly as good.
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
Cowl Induction Assembly/Installation Instructions Check out the pictures and instructions in this link and good luck!
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #12 ·
I think you have a bad cowl pod. Maybe a weak spring. The door moves freely correct? There are holes in the metal base of the pod, are those clean? I'm pretty sure you are running off manifold vacuum, so that's not the issue.

Without the pod installed mine acts like it's on bearings. Mine flaps like a girl on crack. Might be because my cam has so little vacuum.

I wonder if that pod has some sort of induced vacuum leak inside of it. I highly doubt it because I can't see the General inducing an engineered vacuum leak in the pod.

I want to check my pod with a mityvac but I loaned mine to my neighbor and the cluck ran it over. I'll want to pull a vacuum on it and see if it holds. If vacuum bleeds off, then there is an engineered leak in the pod. I think my dad has a mityvac and I'll see him tomorrow. Stay tuned for results or an excuse. 🤪
Door moves very freely when not hooked to pod and small holes in base pod are clean.
 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #13 ·
I think you have a bad cowl pod. Maybe a weak spring. The door moves freely correct? There are holes in the metal base of the pod, are those clean? I'm pretty sure you are running off manifold vacuum, so that's not the issue.

Without the pod installed mine acts like it's on bearings. Mine flaps like a girl on crack. Might be because my cam has so little vacuum.

I wonder if that pod has some sort of induced vacuum leak inside of it. I highly doubt it because I can't see the General inducing an engineered vacuum leak in the pod.

I want to check my pod with a mityvac but I loaned mine to my neighbor and the cluck ran it over. I'll want to pull a vacuum on it and see if it holds. If vacuum bleeds off, then there is an engineered leak in the pod. I think my dad has a mityvac and I'll see him tomorrow. Stay tuned for results or an excuse. 🤪
I think you have a bad cowl pod. Maybe a weak spring. The door moves freely correct? There are holes in the metal base of the pod, are those clean? I'm pretty sure you are running off manifold vacuum, so that's not the issue.

Without the pod installed mine acts like it's on bearings. Mine flaps like a girl on crack. Might be because my cam has so little vacuum.

I wonder if that pod has some sort of induced vacuum leak inside of it. I highly doubt it because I can't see the General inducing an engineered vacuum leak in the pod.

I want to check my pod with a mityvac but I loaned mine to my neighbor and the cluck ran it over. I'll want to pull a vacuum on it and see if it holds. If vacuum bleeds off, then there is an engineered leak in the pod. I think my dad has a mityvac and I'll see him tomorrow. Stay tuned for results or an excuse. 🤪
I think you have a bad cowl pod. Maybe a weak spring. The door moves freely correct? There are holes in the metal base of the pod, are those clean? I'm pretty sure you are running off manifold vacuum, so that's not the issue.

Without the pod installed mine acts like it's on bearings. Mine flaps like a girl on crack. Might be because my cam has so little vacuum.

I wonder if that pod has some sort of induced vacuum leak inside of it. I highly doubt it because I can't see the General inducing an engineered vacuum leak in the pod.

I want to check my pod with a mityvac but I loaned mine to my neighbor and the cluck ran it over. I'll want to pull a vacuum on it and see if it holds. If vacuum bleeds off, then there is an engineered leak in the pod. I think my dad has a mityvac and I'll see him tomorrow. Stay tuned for results or an excuse. 🤪
I’m waiting anxiously……
Wow those instructions and pictures were great thank you very much. Where did you get those or what book are those in? I bought the three assembly manuals but mine are not nearly as good.
 

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OK...So I pulled a vacuum on the cowl door and the door begins to close at 3 inHG and is fully closed by 4-5 inHG. The pod holds a vacuum, there is no engineered vacuum leak in the pod. This is without the restrictor inline.

My pod is original, so 52 years old.

You might try another vacuum source or replace the vacuum line. Make sure you are using vacuum line because if it pinches shut it may hold vacuum.

Pull the air cleanerlid and check to make sure your throttle plates are opening completely when someone floors the gas pedal.

Last, try a new pod.


 

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70 Chevelle SS, L41, 454 GM 469hp crate, TKX 5 speed, 3:42
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Discussion Starter · #15 ·
OK...So I pulled a vacuum on the cowl door and the door begins to close at 3 inHG and is fully closed by 4-5 inHG. The pod holds a vacuum, there is no engineered vacuum leak in the pod. This is without the restrictor inline.

My pod is original, so 52 years old.

You might try another vacuum source or replace the vacuum line. Make sure you are using vacuum line because if it pinches shut it may hold vacuum.

Pull the air cleanerlid and check to make sure your throttle plates are opening completely when someone floors the gas pedal.

Last, try a new pod.

Thank you for your response.
I guess I really should hook up a vacuum gauge so I can read it whilst driving. Then I could start to replace the parts you mention starting with the cheapest which would be the vacuum line, then the pod. I wish mine was even close to being as responsive as the one in your video. What baffles me is how the flapper raises right up when engine turned off and it goes right down when cranked. So why doesn’t she pop up under acceleration?…….


Door moves very freely when not hooked to pod and small holes in base pod are clean.
 

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You are still holding a vacuum in that line. When you floor the throttle your engine vacuum should drop to near 0 and the cowl opens. Look down the carb with a flashlight and floor the throttle. You may not be getting full throttle.
 

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It would not be a bad idea to hook up a vacuum gauge to your vacuum source and drive the car around. That'll give you an idea what's actually happening. If you're not dropping down to about 5HG at Full Throttle and you know you will have an issue with the cowl opening.
 
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