I have a question about engine vac.

[larry33kc]

I have read somewhere that you should have about 17"'s of vac. at idle. My car is around 10"'s at idle. I have sprayed a whole can of carb cleaner, and no luck finding a vac. leak.

My question is, does the size of cam affect how much vac. you can pull? I have a 224/224 cam I think, the preveous owner wasn't sure, and the builder dosn't remember what the put in it. The most I know is, it is a Comp Cams special grind roller cam.

What do I look for if this is not enough of vac.

 

[HellOnWheels]

I have the same cam and 10" +/- is what mine idles at.

 

[GNRick]

I always thought a vacuum leak is determined by blm numbers. BLM over 128 means you have a leak. Not sure if the cam influences this number, though.

 

[1984 t-type]

Big cams don't make a lot of vacuum, had one in my big block chevy and had to buy a vacuum reservoir to help out with the brakes

 

[TurboDave]

I always thought a vacuum leak is determined by blm numbers. BLM over 128 means you have a leak. Not sure if the cam influences this number, though.

Not at all true. Just because BLM's are over 128 does not mean a vacuum leak. Could be any one of a number of things, even the weather has affects.

Now, if the BLM's peg at the high end, then yes, it's likely a vacuum leak or pre turbo exhaust leak.

 

[GNRick]

Not at all true. Just because BLM's are over 128 does not mean a vacuum leak. Could be any one of a number of things, even the weather has affects.

Now, if the BLM's peg at the high end, then yes, it's likely a vacuum leak or pre turbo exhaust leak.

Dave- could you elaborate? What else causes high blm's?

 

[TurboDave]

Dave- could you elaborate? What else causes high blm's?

See my post above: Two most common causes are, Vacuum leaks, or pre turbo exhaust leaks. Much less common causes: a bad O2 sensor could be suspect, possibly also bad MAF.

 

[neilb]

A N/A engine should have 18-20" hg vacuum at idle, and with a turbo and a larger cam, lower vacuum readings are normal.

 

[larry33kc]

Well I have BS3 with no Maf. I don't know what my BLM's are because I can't get my laptop talk to it. I was just seeing if it is normal.

 

[Pronto]

Gee, with all those KB bolt ons you should have at least 600hp (according to his catalogs).

 

[TurboDave]

Well I have BS3 with no Maf. I don't know what my BLM's are because I can't get my laptop talk to it. I was just seeing if it is normal.

Since you're running BS3 you're not going to have any BLM's to look at.

 

[larry33kc]

Yea that car in the sig. is gone. I have a new one. It is a stock block stroker crank, ported GN1-R heads, GN1 intake, GN1 throttle body & doghouse, RJC girdle, PTE 76 dual BB turbo, 3 1/2 DP.

 

[Pronto]

Ah, that makes the 224/224 cam more worth it.:wink: Time to update your sig then...