New cams low vacuum

[rstchris]

I knew to expect lower vacuum with 272/264 cams but from what I read most people have about 14-15 inches. Mine has 6-7 inches at 750rpm. That seems a little low being that earlier today it held 16 inches at 750 with stock cams. I did have .007 taken off the head and do not have adj. cam gears so do I need to degree these?

 

[olmytsi]

Either a vacuum leak or most likely (hopefully not) your timing is a little off.

 

[Bender]

That vacuum seems about right undegreed.

 

[daren_p]

264/272 is not a very "aggressive" setup, I would expect more vacuum then that. My first thought would be timing if off a tooth somewhere, I'd verify that first.

 

[rstchris]

I triple checked the valve timing and reset ignition timing. It runs perfect over 1500rpm. Valve timing is right on except for a hair from the head shave. Most see more than 16in stock so I'm not sure if this is normal or not. I don't have any leaks on the IM as of a couple weeks ago but the issue is from stock to 272.

 

[toofast82]

I recently installed a set of 264/272 cams myself. My current vacuum is about 12-14 at 850 rpm. With the stock cams it was about 20. Although when I let off the gas with the new cams the needle still goes to about 22.
I would say check for vacuum leaks as well as check the tune. I had to add quite a bit of fuel on the low side to get them to idle right.

 

[rstchris]

It's running in closed loop so it's 14.7 Does it want more fuel at idle? I think it may be a degree thing cause even at a 1500rpm free rev it only gets 9".

 

[toofast82]

It's running in closed loop so it's 14.7 Does it want more fuel at idle? I think it may be a degree thing cause even at a 1500rpm free rev it only gets 9".

If closed loop has already compensated the a/fs to 14.7, then I would definitely look into vacuum leaks or possibly being a tooth off on timing.
What does the vacuum go down to after you rev it?
Have you tried a slightly higher idle speed like 850-950?

 

[rstchris]

Decel from a free rev will see 10-12. The timing is NOT off a tooth. Higher idle takes it to 6-7" but thats still crazy low.

 

[toofast82]

Yeah, thats definitely lower than it should be from my experience. For starters, i've had 4dsms and they all would be ~19-22in/vac at idle with stock cams.
What are you tuning with? Like I said, when I first installed the cams with no changes, it was very lean at low throttle/idle

 

[rstchris]

I'm tuning with Openport2.0/Ecutune. I have not made any changes to fuel trims for the cams yet but my WB says 14.7 I'll check for leaks again tomorow. My vacuum was the same before and after the head gasket job so on second thought it may be a different problem.

 

[toofast82]

I'm tuning with Openport2.0/Ecutune. I have not made any changes to fuel trims for the cams yet but my WB says 14.7 I'll check for leaks again tomorow. My vacuum was the same before and after the head gasket job so on second thought it may be a different problem.

Good, just wanted to make sure you had some sort of fuel control. If you're showing 14.7, which is good of course, i'm curious why your vacuum is so low? You said you were sure the timing was in line.
Dare I ask if you've done any compression/leakdown tests on the engine since the head/cams install?

 

[rstchris]

I did a leakdown before the headgasket and compression check after the head job. It was good. Maybe elevation?

 

[jjrock5]

I knew to expect lower vacuum with 272/264 cams but from what I read most people have about 14-15 inches. Mine has 6-7 inches at 750rpm. That seems a little low being that earlier today it held 16 inches at 750 with stock cams. I did have .007 taken off the head and do not have adj. cam gears so do I need to degree theese?

As in 272 INTAKE and 264 EXHAUST? I had these in my GST and my idle was like 11-12, pretty low to me. Never found a leak, these were Delta reground cams. And the 'typical' setup is the other way around. I was happy with my buy but I wish Delta had recommended me the typical setup.

 

[rstchris]

Mine are 272I/264E aswell. My elevation is 3400ft.

 

[nikkeebabee]

bump your idle up to 950 or 1k and get some vac back. You wont get 19-20 with cams...

 

[jjrock5]

^ Agreed

 

[toofast82]

Mine are 272I/264E aswell. My elevation is 3400ft.

Your elevation may have something to do with it but i'm not sure how much. I would bump your idle up as said to at least 850rpm and try and see what the vacuum is at.
What made you decide to go with the 272I/264E and not the other way around?

 

[rstchris]

Cause thats what I could get for a little $$. I did a compression check and boost leak test and it's good. I got the idle up to 8-850ish and saw 8" of vac. so I guess I can put up with it til I get some gears and degree them.

 

[91-gsx]

What brand of camshafts are you using?

For the other people who have degreed their cams, did you notice a bump in vacuum after you degreed your cams? How much of a bump?
Thanks for the help

 

[Turbo Talon DL]

Have you tried adding any fuel in the idle-RPM range? I bet your fuel trims are maxed lean according to the ecu. I think its either a vacuum leak, not enough timing, or not enough fuel. You should pull at least 10" @ 800-950 RPM. Stock idle is too slow and idles rough. I degreed mine a few years back to about 2* advance on both cams. Noticed almost no difference with them straight up.

 

[Maglin]

You have to much valve overlap if your definitely sure it's not off a tooth. I would get some adjustable gears and actually degree in your cams properly. Then see what your idle vac. is which I bet will still be pretty low. Then try advancing the exhaust cam just a tad like 2* and recheck. It will go up some. Then retard the intake 2*. If your vac. is up to around 12-14" you might want to make a run to see how it runs. The higher your idle vacuum the better your cruise fuel economy will be along with bottom end power. With your current situation I bet your EGT's are just insainly high as well as your fuel consumption.

Also when you degree in your cams check to see how far you can go before your valves start to hit the pistons and then stay at least 4* away from their when you are adjusting your cams. Granted your cams are not so large that you should ever adjust them to the point where the valves would hit the pistons. It wouldn't be making good power at all.