opinions, can retarding/advancing a cam change idle/driveability characteristics
#4
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.
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.
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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.
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.
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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.
#9
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
I dont think about any off the shelf cams FASTONE.. thats boring
#10
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?
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Originally Posted by itchygomey98
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?
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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.
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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.
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.
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Originally Posted by GTS346
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.
You'll loose some low down (vs advanced)n and top end (vs retarded) but its average will be better.
Why would you loose average power by advancing or retarding a cam?
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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.
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Originally Posted by GrannySShifting
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
Ive heard of that usefor power.. but not idle quality
I think overlap is more of a factor, but this something to consider.
#20
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
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