Vacuum at idle with big cams 272 280

[marcmsj]

What kind of vacuum are you guys seeing with your cams?

With my 280's, i'm only seeing about 4 inches and that seems way too low for me. We checked for vacuum leaks but couldn't find any but I'm pretty sure we're missing something.

So what vacuum are you guys seeing just so I can get a base line.

 

[JMiller]

I've got 272s and my guage reads between 15 and 17 for about 500-750rpms. I'm not sure if the vaccum should go up or down with bigger cams but i think 4 is to low for any type of cam.

 

[marcmsj]

Vacuum should go down with bigger cams, but I'm pretty sure it's not supposed to be as low as what I'm seeing. I'm having a very hard time getting it to idle at all. Even idleing at 1000rpm, I have just about no vacuum, something must be up.

 

[No_Skillz]

BLTed?

 

[Epic904]

Check the cam timing and the ignition timing and make sure all the hoses on the intake manifold are tight. My 272 idle around 17 to 22 depending on the rpms.

 

[need2boostpsi]

I got 12-14 inches of vacuum, with HKS 272's, when i first installed them the car ran like crap and idled at 900 with about 8 inches of vacuum, checked ignition timing and i was about 10* off, set it back to 5* BTDC and idles great!

 

[1992awdlaser]

15" of vacuum with my fp2's at 1000rpm idle. 4" of vacuum is WAY too low. You should be seeing 15"-12" of vacuum.

Do what epic904 suggested and then report back.

 

[marcmsj]

Base timing and cam timing are where they're supposed to be. All hoses are tight and clamped. It's a brand new motor but we did put a few miles on it already. Think it just needs more time for the rings to seat?

 

[Epic904]

I rebuilt my motor and still pulled around 17 at idle. The only thing I can think of is that you have a vacuum leak somewere that you can't find. Did you break in the cams and valve springs by revving it at or around 2500 for a few minutes then varying it? What kind of vaccum/boost guage are you using as it might not be reading right either. I mean does it run real rough at idle because it should barely be running with that kind of vacuum.

 

[marcmsj]

It's an autometer mechanical gauge, It's been in the car for a while and never had any problems with it, it always read correctly. Everything has been broken in. And yes at 4 inches it's idleing very rough, almost stalling out and actually stalling at times. I'll double check for vacuum leaks and report back.

 

[ekanddsm]

Verify compression,
If you have low compression it will do that too.

Low compression may be caused by cam timing as well, Guessing on a dsm costs alot of money.

Do a leak down test, make sure your not bleeding it out to somewhere else.

 

[MitEclipse2G]

do compression test. check all the lines make sure u not getting leak.

 

[Lonnie gandee]

If its that low, I'd be checking for a "blown" out gasket... The car has to pull like crap!!

Did you by chance replace the intake mani gasket? You didnt use a paper one did you??

 

[Lonnie gandee]

Vacuum should go down with bigger cams, but I'm pretty sure it's not supposed to be as low as what I'm seeing. I'm having a very hard time getting it to idle at all. Even idleing at 1000rpm, I have just about no vacuum, something must be up.

You gotta have a big leak.

 

[1992awdlaser]

Make sure the biss screw is set correctly also. That and ignition timing are the first things I look at. Did you ground the timing when you checked it? Are you sure your crank pulley isn't starting to seperate?

 

[marcmsj]

Timing was ground and correct but I'll double check it. Crank pulley is good, brand new fluidamper harmonic balancer, everything on the motor is new.

 

[illeffekt vr-4]

I'm at 13 with BC272's at 850rpm idle.

 

[ekanddsm]

Motor is new doesnt mean that it is perfect. Do a compression check.

Dont overlook it, if it cant suck it in, it cant compress it, then it wont boost it.

 

[Dsmx17]

since no one else is running the same cams I thought i would post, I also have the bc 280's with their springs/retainers I pull around 9 inches of vac at idle. seems normal on the bigger bc cams, a buddy of mine runs them on his colt and has around the same.

 

[Burnett03]

9-11 here on 272 cams at 5,280ft above sea level at 950rpm.

 

[Anarchology]

I will be kicking over my Talon within the next couple days, and this was actually a concern of my own when it came to vac pressure and larger cams on DSM's. I am used to the cammed, push rod, V8's that see good drops in vacuum pressure, but was wondering about DSM's.

I have a set of BC 272 cams sitting on my head that is ready to fire over, and I will post back within the next day or two when I see the vacuum pressure on my gauge.

 

[gob4sho89]

My 272 idle around 17 to 22 depending on the rpms, and my good friend has the same cams as you and he sees 15-18... I used to have theat problem, mine was a leak in the hose running from the intake manifold to my boost gauge. It leaked under vac, but when I boosted her the hose would straighten out... good luck

 

[1992awdlaser]

My autometer gauge is about 7" off from actual vacuum. I know what actual vacuum is because of my map sensor.

 

[marcmsj]

My car is still at the shop, so I haven't had a chance to look at it. I might try to stop by after work and doubling checking everything. Thanks for all the responses.

 

[doesitonall4rs]

used to get 15-20 on stock cams, now i get 5-10 with BC 272/272s