Thread: Low engine vacuum but no vacuum leaks.

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Originally Posted by techinspector1

On page 1, post 13, I outlined two procedures to help you determine the problem(s). Apparently you ignored them, because I have not seen any results. All of us are grabbing at straws trying to help you, but if you're not going to follow our suggestions, then you're probably not going to find the problem and that's OK because I'll still sleep well tonight regardless. I didn't start this post to be snotty, but damnit, I'm not getting any input and I'm beginning to think I'm wasting my time trying to help. Now get your sheets together or I'm outa here and I suspect the rest of the gang will be too.

I have seen all the suggestions given here, and I said I appreciate it. I'm just hoping to gather more suggestions as I am currently out of town therefore haven't been able to work on the car till I arrive next weekend.

Originally Posted by techinspector1

Now get your sheets together or I'm outa here and I suspect the rest of the gang will be too.

Originally Posted by NTFDAY

Turn out the lights, the partys over............................

/\ /\ What they say!!!

if it's anything like some of my ordeals you'll end up setting on a chair by it wondering how you remembered to breath. i have spent weeks chasing some of the simplest things . good luck with it .

Originally Posted by 34_40

In addition to what every one else has offered.
Don't hesitate to open the exhaust at the manifolds and re-do a vacuum test. It's not seen much anymore but exhaust pipe sometimes had a interior pipe that would swell and kink closing off the pipe. This would effectively choke the motor airflow/vacuum. Like I said, you don't see this anymore but it should be easy (relatively speaking) to open the headers/manifolds and double check the vacuum.

Could you please specify what you mean by opening the exhaust at the manifold ? Do you mean to remove the exhaust manifold to check for obstruction? Thanks

He means disconnect the exhaust pipe where it connects to the manifold. This would remove any back pressure generated by the exhaust.

Yes, open the connector/ connection at the manifold and re-do your vacuum readings, see if it improves

The problem could be a loose timing chain. That was very common on those small block Chevys, when the nylon falls off of the camshaft sprocket.

Originally Posted by DennyW

Yes, I mentioned that in my post. #6. No replies though...He is out of town I guess.

Whoops, I read through it and missed that.

Sorry for the late update,lost my user name and password and just got it back.
I'm still having the low vacuum issue. But I believe the issue is due to a rad cam. The person who I bought the car from said he thought the car had a big cam but he was the 2nd owner of the car so he was't really sure. But at least I was able to figure out why the car was running like crap...and it was due to a bad HEI ignition module. I replaced the module and the car is running much better, but still at about 10'' of vacuum at idle.

I see this is an old post but I am dealing with that now on a new cam install. Valves hanging open is what the internet say. I'm going thru the valves again using a different method. I'll let you know how it goes.

Originally Posted by selmorides

I see this is an old post but I am dealing with that now on a new cam install. Valves hanging open is what the internet say. I'm going thru the valves again using a different method. I'll let you know how it goes.

I doubt the valves are hanging open. I suspect the problem is that you have installed a race cam when what the motor wanted was a street cam.

Here is the proper procedure for adjusting valves on a SBC and BBC.....
http://www.crankshaftcoalition.com/w...stment_SBC/BBC
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Probably the same issue as me..too big a cam for a pretty stock engine. Big cam= low vacuum. Most vacuum I get is about 10''. I had to install a vacuum canister to help with the brakes but that made no noticeable difference.

Originally Posted by 47Fordcoupe

Probably the same issue as me..too big a cam for a pretty stock engine. Big cam= low vacuum. Most vacuum I get is about 10''. I had to install a vacuum canister to help with the brakes but that made no noticeable difference.

It's a common problem in the hobby. Nobody understands that the cam is NOT a free-standing part, that it relies on every other part of the motor and drivetrain to operate as a team toward a desired end.

When my youngest son was growing up, racing go karts and motorcycles, I was teaching him about ****THE COMBINATION****. It is not one part or only a couple of parts that make a winner.....it is ALL THE PARTS working in combination with each other that makes a winner.

His buddies who used to come around to the garage and ask me about a cam for their ride used to call me "Mr. No-Cam" because of the mild grinds that I would recommend for their motors. Then I would have to explain the awful truth to them, that their motor was somewhere between 7.75:1 and 9.00:1 static compression ratio, a range that will not support a cam that idles with a "rump-rump". Some got it and some didn't, just like my audiences on Club Hot Rod and other sites.

This may come as a surprise to some of you, but you can make a WAY quicker ride by changing the torque converter and rear gear than you can by changing the camshaft. A 3000 stall 10" converter (yep, still streetable), together with a rearend gear change to 3.73/4.11, will make you think you did an engine swap.
https://www.youtube.com/watch?v=njL2x-msbZQ
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