GrannySShifting

iTrader: (10)

Given that overlap is the same, does an early opening/closing help or hurt idle characteristics in your opinion

PREDATOR-Z

Yes, because it changes the valve events, (times at which they open, close).

GrannySShifting

iTrader: (10)

Ok, but which does which? In your opinion. late closing i beleive woudl be most beneficial... but

itchygomey98

iTrader: (2)

I installed a pretty healthy cam in a 302 (yea I know, a Ford motor) straight up first - power really started coming on at about 3000 rpms.
I advanced the cam 4 degrees - power came on ealier - at about 2600 rpms
Straight up, it bucked if you were in 5th at 55. I had to run it in 4th to stay in the power band. Advanced, it would run in 5th at highway speeds without whiplash. I would think that an LS1 would respond the same. By advancing the cam, I would think that it would make power earlier.

GrannySShifting

iTrader: (10)

yes advancing cam usually does move torque curve forward in a way. Most interested in what it does for driveability

Ferocity02

iTrader: (60)

I dont think it will create any driveablitiy problems, as long as you dont advance or retard too much. My cam has 4 degrees advanced ground in, it peaks a 5800 rpm w/o any driveability problems.

nuzee

iTrader: (2)

In the past, when I over-cammed a low compression motor, I used 4 degrees advance to help get rid of a soggy low end. It helps, but was not enough of a band-aid to really correct the problem. All the cam-advance does is close the intake valve sooner to make more cylinder pressure. Over the years I've found that advancing the initial ignition timing to combat low cylinder pressure is an easier solution that can net similar results. Again it is just another band-aid solution. The correct way is to get the combo right so you don't need to use band-aids.

Anyway, to answer your question, yes, advancing the cam can help improve lopey idles. But the farther over-cammed the motor is, the less the cam-advance will help.

FASTONE

Thats a good question GrannySShifting,but wouldn"t you be more interested in degreeing it for all around perfomance?Which cam are you thinking about?Advancing the cam (closing the intake sooner)will help the idle and boost low end but at the cost of top end power.

GrannySShifting

iTrader: (10)

I know it wil make more cylinder presure but Ive never actually done any testing of vacuum at idle same cam with differnt installed centerlines etc. Driveability is not an issue, have 242 XER lobes cam on 110 LSA driving all over here just fine in automatic car, just wondering if anyone actually knows the effect installed centerline would have on idle characteristics, torque curve is obvious what that will do. More so looking at a small dur tight lobe cam for a customer, and trying to tame it down as much as possible, without the weak suck torque curve of a 220/220 cam on a 114

I dont think about any off the shelf cams FASTONE.. thats boring

itchygomey98

iTrader: (2)

I have never checked vacuum before and after. On the one that comes to mind, either way I installed it I needed a vacuum resevoir to have brakes. Anyone ever do vacuum test straight up and then advanced?

nuzee

iTrader: (2)

I can vaguely remember getting almost 2 psi from a 4 degree advance on a SBC. But I can't remember if that reading was taken before or after I adjusted the tune. Bumping up the idle speed can do the same thing to the vacuum.

DAPSUPRSLO

iTrader: (14)

It can also hurt driveability while advancing a cam as you are opeining the exhaust valve sooner to reducing some low speed torque and opeining yourself up to more reversion posibilities. This will really be the case with a traditional split with a high lsa and a big exhaust duration. Heads can be modified to counteract the reversion problem though.

GrannySShifting

iTrader: (10)

Or just run more compresion

Ragtop 99

iTrader: (7)

Jeff:
In the cam thread, there was some discussion of centering the overlap on TDC. If the cam has its overlap centered on TDC and then you advance it, I think the jist of the thread was that idle quality might decrease slightly. I know I tried to center my overlap on TDC for my new cam.

GrannySShifting

iTrader: (10)

ack, theres no real way to check that except for two dial indictors, adj timing chain, playing with prod length etc

Ive heard of that usefor power.. but not idle quality

GTS346

iTrader: (1)

Throw it in straight up and dial it.

You'll loose some low down (vs advanced)n and top end (vs retarded) but its average will be better.

DAPSUPRSLO

iTrader: (14)

Why would you loose average power by advancing or retarding a cam?

kossuth

iTrader: (12)

If you retard a cam it will act sluggish and doggish down low because the intake valve will be open too long but the topend will be much stronger. On the LT4 the cam had about 2 degrees retard ground into the cam I believe and that motor made power much higher up in the powerband than a LT1 did, (could actually cause PTV issues also). Just the inverse occurs with an advanced camshaft but you still could have PTV issues going that way too. Basically like somebody said advancing and retarding a cam is just a bandaid. Get the cam grind right don't mess the timing around.

Ragtop 99

iTrader: (7)

You can check the valve events from the cam card and go from there. Many cams with advance do not have the overalp centered on TDC. For example, a 228/228 114 XE-R cam has zero overalp at .05. If you grind it on a 114 ICL, the IVO and EVC both occur at TDC. The overlap is centered. If you grind the cam on a 110 ICL, the IVO and EVC both occur 4* before TDC.

I think overlap is more of a factor, but this something to consider.

GrannySShifting

iTrader: (10)

OKay guys just to clarify.. were not talking advance/retard in terms of power production anywhere. im very well aware of what that does and its causes... its the relationship on idle that Im really thinking about

Yeah joel on a singel pattern cam with symmetrical lobes you cna do that, but I dont ever run the same lobe on intake adn exhaust