Vacuum low on a 327 - Team Camaro Tech
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post #1 of 12 (permalink) Old Jul 16th, 09, 07:43 PM Thread Starter
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Vacuum low on a 327

My friend's 67 Camaro with a 327 has very low vacuum. This car has a close to stock, if not stock cam. Its a 327 with a 4bbl Edelbrock carb, an Offenhauser manifold, with 1 3/4" headers to a dual exhaust and a TH350 trans.
The car is very doggish. He thinks its an intake airflow problem and I think its his mufflers that are causing too much obstruction. No idea what the brand is. They are very quiet and when you accelerate, it seems to me, it just feels like its not able to get rid of the exhaust fast enough.
I agree that the intake air flow needs to be worked but I think the bigger issue is exhaust.

I put a vacuum gauge on it and its under 5!!
This is not a big radical cam, its a very smooth idle.
I checked everywhere for vacuum leaks and I replaced a few cracked and dry vacuum lines but that didn't help the idle vacuum.

I'm pretty sure the we don't have a vacuum leak.
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post #2 of 12 (permalink) Old Jul 16th, 09, 07:52 PM
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Re: Vacuum low on a 327

check the timing and see where its at
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post #3 of 12 (permalink) Old Jul 16th, 09, 08:56 PM
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Re: Vacuum low on a 327

also i think 1 3/4 headers are to big for a basically stock 327, i only have 1 5/8 headers on my 327.
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post #4 of 12 (permalink) Old Jul 16th, 09, 09:04 PM Thread Starter
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Re: Vacuum low on a 327

Where should the timing be? About 8 or so?
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post #5 of 12 (permalink) Old Jul 16th, 09, 09:14 PM
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Re: Vacuum low on a 327

alot of people have told me to turn the distributor for highest vacuum, then back off just a little, i have mine set at 18 initial, with vacuum plugged, but i have fairly big cam in my motor, what are the cam specs?
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post #6 of 12 (permalink) Old Jul 16th, 09, 09:38 PM
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Re: Vacuum low on a 327

The 1-3/4 headers wouldn't be the problem, that would take a little away from the exhaust theory unless it has cats that are really clogged or the muffler is as well.
If it's stock it's probably just a tired old motor that needs to be rebuilt, couple of burned valves, rings worn... cam is probably around 114lsa if it is "near stock" and should be pulling much higher vacuum.

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post #7 of 12 (permalink) Old Jul 16th, 09, 10:02 PM Thread Starter
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Re: Vacuum low on a 327

Quote:
Originally Posted by ace's68 View Post
The 1-3/4 headers wouldn't be the problem, that would take a little away from the exhaust theory unless it has cats that are really clogged or the muffler is as well.
If it's stock it's probably just a tired old motor that needs to be rebuilt, couple of burned valves, rings worn... cam is probably around 114lsa if it is "near stock" and should be pulling much higher vacuum.

The motor is fairly new. Probly 5k miles on it.
I agree, the cam, I don't know the specs has no lump to it at all. Its mild if not stock. The previous owner had a GM shop build this motor and he tried to build it to the cars numbers.
The heads are the double humps but I haven't gotten the numbers from them yet so not sure what the double humps mean. I hear a lot of people tell me what they think they mean but the answers are all different from person to person.
I've heard they are a high performance head but still not sure what the double humps really mean.
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post #8 of 12 (permalink) Old Jul 17th, 09, 04:20 AM
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Re: Vacuum low on a 327

Could be the restrictive mufflers. Uncork the headers and see if vacuum goes up. If restrictive exhaust, watch vacuum gauge and rev engine up, then vacuum gauge will slowly climb to zero, or close to it.
As said, advance the timing and check vacuum.

Compression check shows? Anything over 120 PSI would mean the camshaft is in time with the crankshaft - retarded cam, lower vacuum. If stock camshaft, set #1 intake rocker for 0.050" lash, and rotate crank and I think valve starts to open, when lash is gone, at something like 7° BTDC? Its still measureable using the timing tab and h/bal mark.

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post #9 of 12 (permalink) Old Jul 17th, 09, 09:13 AM
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Re: Vacuum low on a 327

Where are you measuring the vacuum? Make sure it is on a manifold vacuum source, not ported.

My 327/4 barrel pulls 19-20 inches at idle, this one should be close to that if relatively stock and in good shape.

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post #10 of 12 (permalink) Old Jul 17th, 09, 09:50 AM Thread Starter
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Re: Vacuum low on a 327

Quote:
Originally Posted by Melrose RS View Post
Where are you measuring the vacuum? Make sure it is on a manifold vacuum source, not ported.

My 327/4 barrel pulls 19-20 inches at idle, this one should be close to that if relatively stock and in good shape.

I'm measuring manifold vacuum.
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post #11 of 12 (permalink) Old Jul 17th, 09, 09:51 AM Thread Starter
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Re: Vacuum low on a 327

Quote:
Originally Posted by Everett#2390 View Post
Could be the restrictive mufflers. Uncork the headers and see if vacuum goes up. If restrictive exhaust, watch vacuum gauge and rev engine up, then vacuum gauge will slowly climb to zero, or close to it.
As said, advance the timing and check vacuum.

Compression check shows? Anything over 120 PSI would mean the camshaft is in time with the crankshaft - retarded cam, lower vacuum. If stock camshaft, set #1 intake rocker for 0.050" lash, and rotate crank and I think valve starts to open, when lash is gone, at something like 7 BTDC? Its still measureable using the timing tab and h/bal mark.

Been wanting to uncork it and do just that. If for just letting it idle and not revving it too much.
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post #12 of 12 (permalink) Old Jul 17th, 09, 11:33 AM
 
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Re: Vacuum low on a 327

It could be a flat cam too, who knows.
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