All I have been hearing lately about lobe seperation is totally different than what I'm use to dealing with with roundy round cars. Every one on this board is pretty confident that a tighter lsa makes power peaks higher in the rpm band. With circle cars the tighter lsa = lower peaks. Not saying the ls1/6 guys are wrong but is it the runner lenght that changes the equation?? I just want some hard core evidence from testing that states facts behind this lsa question. Thanks

 

Here we go again! These discussions always turn into a "food fight"! LOL!

There was a recent article in Car Craft that compared dyno #'s w/ three different cams, same lift & duration specs, but different LSA's. The three LSA's were 106, 110, & 114. The 106 LSA cam had peak HP at 5900 RPM's, about 300 RPM higher than the 110 or the 114 (they were almost the same). However, this was with an SBC mule, not an LS1.

The consensus seems to be that a tighter LSA narrows the powerband, increases the peak HP, and moves it higher in RPMs. It may also increase mid-range torque, at the expense of low-end torque. Idle quality and tip-in response suffer. This is not a problem w/ a racing engine, but a big problem on the street.

IMHO, there isn't really that much powerband difference when comparing an LSA difference of a couple of degrees, say between a 112 and a 114 LSA. The difference is only going to be a few HP.

The closest to a "roundy-round" LS1 cam is the SCCA showroom stock cam, which is lift-limited by rule.

 

I'm no expert my any means, however I will comment on this as I understand it.

NineBall posted a dyno graph comparing B1 and T1 cams. Exactly the same cams except B1 (114 LSA) and T1 (112 LSA). The T1 make power a little sooner in the mid-range rpms. The B1 cam on a few hundreds rpm later. Both graphs looked very similar. The peaks were essentially the same. The T1 had a tad more area under the curve in the lower rpm. Both cars ran evenly matched when racing because both lauched at about the same rpm which was at place in the powerband where both cams made the same power. In the upper range they were ~equal.

Lower LSA pulls the power band lower in the rpm range and may tend to bump the peak numbers up a little all other things being equal. Lower LSA tend to idle worse

Higher LSA flattens the power band but often will result in a little less power in the lower rpms range compared to a similar lower LSA cam. The peaks can tend to be a little lower with a higher LSA cam. The higher LSA will often have the effect of pushing the peaks up a little. Higher LSA idle better.

Duration, advance/retard, heads, exhaust etc will have an effect on the power band too. The ICA (Intake or installed intake I can't remember)Centerline Angle - very often confused with the LSA.

I think the following is true:

LSA - advance = ICA

112 LSA cam - 2 degrees advance = 110 ICA
112 LSA cam - 4 degrees advance = 108 ICA
113 LSA cam - 2 degrees advance = 111 ICA
113 LSA cam - 4 degrees advance = 109 ICA
114 LSA cam - 4 degrees advance = 110 ICA
114 LSA cam - 6 degrees advance = 108 ICA

LSA + retard = ICA

112 LSA cam + 2 degrees retard = 114 ICA
112 LSA cam + 4 degrees retard = 116 ICA
113 LSA cam + 2 degrees retard = 113 ICA
113 LSA cam + 4 degrees retard = 117 ICA
114 LSA cam + 4 degrees retard = 118 ICA
114 LSA cam + 6 degrees retard = 120 ICA

So as I think of it slightly changing the LSA is sort like advancing/retarding a cam. So the ICA you end up at is what really determines the way the powerband reacts. Higher ICA tend to push power band up and flatter and lower ICA tend to pull power band lower and peaker. This doesn't always mean 1 or 2 degrees is going to make a major difference but 4 degrees usually will show a difference all other things being equal.

Maybe one else like NineBall, PSJ, the Colonel, on a sponsor in the know can chine in and actually explain how this works.

<small>[ November 29, 2002, 09:20 AM: Message edited by: 99 Black Bird T/A ]</small>

 

I remember the T1/B1 comparison too.

What I would like to know is whether the advance in the cams was the same. Following on Patrick G's theory, if both had equal advance that would have shifted the T1 down, not because of the LSA, but due to 2 degrees sooner ABDC valve timing.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Ragtop 99:
<strong>I remember the T1/B1 comparison too.

What I would like to know is whether the advance in the cams was the same. Following on Patrick G's theory, if both had equal advance that would have shifted the T1 down, not because of the LSA, but due to 2 degrees sooner ABDC valve timing.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That's a good question!

I thought MTI always had 4 degrees ground in for their cams.

 

It is not lsa that brings the cam on sooner but the common 4 degrees advance associated with lsa. 4 degrees advance on a 110lsa cam closes the intake valve 4 degrees earlier then 4 degrees advance on a 114lsa cam. Closing the intake valve earlier helps low end power while sacrificing top end and vica versa for closing it later.