what should an Ls1's Vacuum be?
 

I realize vacuum may change with mods so here are mine... 1998 m6 transam - I have an LS6 intake and 224/224 568 568 114 lsa cam ported tb and some cat backs, tuned by Frost (mail order since i'm not done building it) so downstream 02's are deleted...

I put the gauge on it and it's pulling 17 hg steady off the pcv valve, it does increase to 20ish but only when i hold the throttle down at about 2-3k from the engine bay (guessing). My gauge tells me 17 is the bottom end of acceptable but i thought i read somewhere a while back that 22-23 for an LS1 at idle was about right. I can't find it again! Anyone know?


Car doesn't have any symptoms other than feeling sluggish (I can't turn over 275's tires in 1st at a rolling stomp from 2500 rpms! but i do have stock m6 rear) The mods have been on the car about 3-4 k miles and It has always had the "sluggish problem".

Oh and I did do comp beehives and hardened pushrods when I swapped my cam.

I don't know what ls1's should be but for a motor with a bigger cam 17 is pretty good.

The built 327 I had in my nova(sold it for my 6.0l) only had 7psi at 900rpm's

You need a better tune...mail order tunes arent really all that great. That cam isnt all that big...it should cause a slight vaccuum decrease, but not that much. I think a better tune would definitely help out. If not, i know with my old car being a heads/cam car with a TREX V2, the LS6 intake and ported stock TB were a huge restriction and I had terrible vaccuum...then I swapped for a Fast 90/90 and all the extra air helped out alot. Vaccuum issues were gone. So, maybe look at an intake restriction, maybe get a better TB or intake if you can afford it...I know they arent cheap...mine was used at the time.

^ TB and intake should not cause that sluggishness at all..if your car is mechanically healthy i would say it is the tune. you might want to check if its running rich or lean? is it missfiring or just slow to rev?

Not misfiring that I can tell, though I was wondering that when I was doing the vacuum yesterday. Hard to tell with a lopey idle. My exaust doesn't smell rich and I'm not getting any codes for a knock or misfire. Engine seems completely smooth above 1200 rpms like it should.

As far as checking for running rich, my rear o2's are off, so I guess you mean by plugging a sensor into the rear o2 spot? I don't have a tool for that any suggestions or tricks to test? I guess I could pull all the plugs and compare. I changed them when I did my cam so I suppose they could tell a tale, hate that rear passenger plug tho!

They will if the car is struggling to breath enough air to run on...let alone breathing enough to feed the vaccuum needs.

with a 224 cam? i dont see how the stock TP and intake would cause sluggish ride due to improper flow...he is saying that he cant get the wheels loose in first...that is pretty much lower than stock..OP you could hook a live tuner and check af ratio maybe? not a tuning expert but some could chime in..you could also check the plugs too but generally you could tell if you're running too rich..at least black smoke will be there..

Yah no smoke at all. No backfiring, nothing. I don't have a live reader for the rear O2 hole, can anyone tell me what that is actually formally called so I can try and borrow / buy one.

Thanks.

So does anyone know what the vacuum actually should be?

I see idle kPa about 50ish with a little more LSA, which
would be 15 inHg or so. I think you're pretty much normal.
If you played with timing and fueling / air mass fidelity you
might find a little more vacuum (the best indicator of what
the motor likes, in my book).

Thanks JimmyBlue