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How much vaccuum shoudl the 30-30cam pull?

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69z28boy

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Discussion starter · #1 ·
In a 302, all stock and in perfect running condition.
how much Vaccuum should the 30-30 make in a 302?

and how much would you expect it to make in a 327?

I've used this cam 3 times in a 302 but my Corvette has the 327-365 motor in it and I've lashed it at 30-30 but it seems more responsive that the 302s, which i would attribute to 25 cubic inches.
It pulls about 14-15 inches of vaccuum at about 800 rpm at idle and sounds great. nice and lopey.

starts to pull at about 2500 but reallly comes on at about 4000 but starts hitting a peak at 5500-6000 but I only got a 600 CFM holley on it.


What do you guys think?

Timing is at 38.

I'm trying to find out if in fact I do have the 30-30 cam without pulling the bitch apart. LOL

I am gonna try to measure lobe lift tonight.

But I want to know for sure.
 
Discussion starter · #4 ·
Yeah,

I thought 7-9 was a little low myself.

Most people agree that 12-15 inches at idle is what is required to run vaccuum brakes.

My 327-365 sounds like a 30-30 but pulls 14-15 inches of vaccuum.

I believe I was getting 10-12 in my DZ302s with the 30-30 cam but I don't remember anymore.

If the 302s pulled 12 or so, wouldn't it make sense for a 237 with the same cam to pull a few inches more?

There has to be someone on this forum with a stock DZ302 that can check a quick vaccuum reading at idle/

Thanks

Aaron
 
#6 ·
Yeah, the extra cubes should get a little more vacuum. What is your compression ratio? A engine with more compression will create more vacuum than another engine with less compression.

My 412ci motor, with about 12.5:1 CR, gets about 12" at 850RPM with a big 302* cam.

Mark, how do your power brakes work? I want to get power brakes, but I don't know if a make enough vacuum.
 
Discussion starter · #8 ·
well, I've got a 327 with 11.5 to 1 compression, and I'm in Detroit area so we are at sealevel.

So I'm trying to determine if i've really got a 30-30 cam in it. It sounds like one and pulls like one above 4000 but starts to fall off at about 5500 but that could be fuel starvation or point float as well.

i've only got a 600 vac sec carb on it. It idles like a 30-30 but makes 14 inches of vaccuum at about 750rpm.

Whatcha think?
 
#10 ·
Matt, with 12" of idle vac you'll be fine with power brakes. When I had the single plane intake on my 388, it pulled 10.5-11" vac and my power brakes still worked. They was a little stiffer than with a stock motor, but still worked just fine.
 
#12 ·
69z28boy,

Would you please consider that the Great Lakes waters have to fall at least the distance they do when going over the Niagara falls and that the St. Lawrence Seaway goes down hill to boot so Detroit should be right at 600 feet.

pdq67
 
Discussion starter · #13 ·
Yeah sure, but wouldn't that lower my vaccuum readings?

I'm trying to determine if my 327 has the 30-30 cam in it. It sounds like one, runs like one, but pulls 15inches at idle, and about 20 inces at 2000.

I was hoping to check the lobe lift, but my dial indicator doesn't have enough range to account for the .323 lift of the 30-30 cam.

I figured if 15inches was totally out of the question, then that wouldn't answer it for me, so i could go ahead and get one to install, but I dont' wanna buy a 30-30 cam untill I know for sure that my car has somethng else in it.

Aside from the Vaccuum, the other tell tale sign is that if falls flat at about 5500. pulls like a mother untill there and then runs out of steem. I wondered if the 600cfm holley doesn't have enough CFM to get it to pull to 6500 or 7000 but according to the formulas, it should be enough.

Any other thoughts?
Thanks

Aaron
 
#14 ·
I have 8-9 inches of vacume at 950 rpm. I used to try to adjust the idle mixture to get it higher, I finally gave up and decided that that's where the vacume was supposed to be.
 
Discussion starter · #17 ·
So, figuring that the 302 idles with about 8-10 or so Vaccuum,

would an 11 to 1 327 pull about 14-15 at idle with the same cam?

I guess I just have to go and measure the lobes to see what I'm dealing with.

Although i suppose that you could have any number of cams with .323 lobe lift, although if it wasn't the 30-30, that would be one hell of a coincidence.
 
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69z28boy
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