Low engine vacuum at idle after engine rebuild

**jbrltoliver** · 06-02-2013

Good morning. I would like to get some input on my Vacuum at idle. I have just completed a Top Swap w/full rebuild and installed a ZZP VS cam, LS7 lifters, Stock length ZZP OR push Rods and LS6 Valve springs. I have sent the piston and connecting rods from my L26 to get reconditioned and put on new rings. So fare i have driven almost 40 miles on the motor and my Engine Vacuum at idle is 13.5 to 14.5 at idle and dances between 13 and 14 constantly. DOes not stay steady. the heads are off a L32 and were rebuilt and cleaned at the machine shop.

COuld i have not timed it properly? If i didnt then i am a absolute retard because it is very simple. Do i probably have a valve hanging open? do i have low compression? Or maybe my Rings are not properly seated yet.

Any suggestions!!!!

Thanks!

**L36 Killer** · 06-02-2013

Not sure about SC engines, but my vaccuum at idle usually dances between 15-16.

**sco77** · 06-02-2013

A cam will result in less vacuum.

**dsmuts** · 06-02-2013

You probably have a vacuum leak somewhere

**Jevik** · 06-02-2013

I've got 17.1 vacuum at idle on my l67. Definitely check the lines

**Fivefingerdeathpunch** · 06-02-2013

A VS cam is so small that it will hardly effect engine vacuum at idle.

A stock car should be around -19 to -20 vacuum at idle, the VS cam should make it around the same -19 ish.

**jbrltoliver** · 06-02-2013

Thanks for the input guys. I know have 140 miles on the engine since the rebuild. This morning i started it up and vacuum was between 16.5 to 17 in park at idle. When i put it in gear it drops to 15.5. it still goes up and down by 1 HG" vacuum. I check it with my vacuum gauge in my a pillar and also use a hand vacuum and they read the same. I guess the rings are seating, but should it be more. Before i did the topswap and cam i had around 22"HG at idle on a stock L26 set up. I will email zzp tomorrow and see if this is normal.

**dsmuts** · 06-02-2013

With a cam your vacuum is supposed to go down like that. Mine is around 16-17 with an s1x.

**CTKGP09** · 06-02-2013

i would check the lines, i replaced ALL the shotty stock plastic ones with rubber when i kept finding hairline cracks in the plastic. now i get -19 to -20 at idle with an S1X

**dbextreme** · 06-02-2013

Higher lift cam results in less vacuum.

Stock cam .413/.408 IIRC
VS cam .512/.508
XP cam .520/.536

Stock Vacuum is around ~20 - 21 (whatever units) My XP shows 14.5 - 15 (whatever units) I'd assume you should be around 16-17 with your VS cam. With my top swap I redid all the vacuum lines with new hoses and T's.

**jbrltoliver** · 06-03-2013

Originally Posted by CTKGP09

i would check the lines, i replaced ALL the shotty stock plastic ones with rubber when i kept finding hairline cracks in the plastic. now i get -19 to -20 at idle with an S1X

Where did you get new boots and hoses from? I have been looking all over to find replacements and cannot find any besides the salvage yard.

**CTKGP09** · 06-03-2013

bought new Ts and a few feet of rubber vacuum hose from autozone, i have a genV and N* setup so most of it is custom anyways

**jbrltoliver** · 06-03-2013

Originally Posted by CTKGP09

bought new Ts and a few feet of rubber vacuum hose from autozone, i have a genV and N* setup so most of it is custom anyways

Oh okay so the hose side does not really matter just as long as it fits snug then?? I thought i would have an issue if i did not put the stock size hoses on. for the Map and B

**jbrltoliver** · 06-03-2013

qUOTE{Sounds good.
Yes, the vacuum sounds right. The stock cam was probably 20 HG but it sucks so yeah 17ish is about right.

Thank you for your business,}

Turbo Tim
ZZPerformance.com
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I Also reached out to Turbo Tim at ZZP and he explained above that 17ish for vacuum at idle is normal with the VS Cam.

**Jevik** · 06-03-2013

Is there a way to tell if one has a stock cam or aftermarket cam?

My idle is set to 950 when warm, 1150 while cold, and vacuum is at 17.1, which is telling me that I either have a vacuum leak, or a VS cam....

Sorry to threadjack..

**dbextreme** · 06-03-2013

Just get 4-5 feet of 1/4 up, it's cheap and can be used for other applications.. The Map sensor is the largest nipple IIRC so ask the parts store to pull one off the shelf and use it as a reference for your largest hose.. O'Reily's let me walk behind the counter and see what all they had. The nipple under the supercharger is larger diameter then the fuel pressure regulator.. Map sensor has a larger niple. Like I said I got several feet of each size and bought one of the assortment packs of T's, straight pieces, and reducers... Laid it out, cut to fit, taadaa... And if you do it, I'd have a T coming off your map sensor and plug one end. this allows your to add a boost gauge later down the road if you want to.

Also I flipped my map sensor over so it sits upside down now, just made it easier to plug it in and hook vacuum to it. Easier then reaching under it..

**mkyota1** · 06-04-2013

Originally Posted by Jevik

Is there a way to tell if one has a stock cam or aftermarket cam?

My idle is set to 950 when warm, 1150 while cold, and vacuum is at 17.1, which is telling me that I either have a vacuum leak, or a VS cam....

Sorry to threadjack..

With the higher idle the vacuum will read lower.