finalymodded

why can't you just take something like a tr224 and put it on a 117.5 or so lsa and have a good idling car that still has power advantages? I just don't understand. Is there a site that really explains this or even a book maybe a textbook? anything, I have searched and all info is not all inclusive, all info says well...... it depends on alot of things. So does anyone really know what all these 'things' are? I just need some direction I guess. I am in school now for physics and chemistry, and if i had time i'd go o school to learn why but, I can't until I finish this part of school. Only one more semester in Physics fo a B.S. and 2 semesters in Chem for a B.S., so i know i have the capacity to learn it just need direction.

<img border="0" alt="[gruffy cottonball]" title="" src="graemlins/gr_gruffy.gif" />

DriveATransAm

itll put your powerband way high. the larger your lsa is, the farther your powerband moves up. so with a cam like that you wouldnt be seeing peak power till after 7K <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

LOnSLO

iTrader: (15)

Exactly. The stock duration is somewhere around 198 degrees for a stock cam. Couple that with a 117 LSA, and you have good power down low, while the high LSA will extend that power band up to about 5800 or so, at the same time giving excellent idle and fuel economy. Putting a 224 cam on a 117 LSA will give a great idle, but give up low rpm torque, and extend the power band way too high to be usable.

finalymodded

Ok, so how do you get a higher lsa bigger than stock cam back down into a useable rpm range?

LOnSLO

iTrader: (15)

1) Lower the total duration
2) Increase intake advance degrees

DriveATransAm

3) use a power adder in addition <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

HITMANSS

Beg to differ, but most of this is just dead wrong.

A wider LSA does not raise the power peak; if anything it will lower it. What it does do is widen and smooth out the power band. Power will come on earlier (below 2K RPMs), and extend a bit farther past the peak HP RPM.

The narrower LSA cam will idle rougher because of the increase in valve overlap. But that same overlap also helps scavenge & fill the cylinders, resulting in increased power throughout the mid-range, all the way up to peak HP, after which it will fall off slightly more quickly.

These differences are very subtle. I have seen several dyno charts comparing the B1 & T1 cams --- they have identical specs except for the LSA. They dyno at almost exactly the same HP & TQ.

Most of the wide LSA cams are OEM designs that have a large split duration --- much more exhaust duration than intake. This combo gives a good idle, but also a smooth, wide powerband throughout the mid-range, at the expense of peak power.

IMHO, combining a wide LSA with a straight-pattern grind such as a 224/224 would not be that productive. If the intent is to improve idle quality, a 115 or 116 LSA should be sufficient. The idle quality for a 224/224 114 cam is already pretty good, especially w/ tuning.

DriveATransAm

so would a cam with more exhaust duration have better street characteristics than a cam with more intake duration?

in case like this, which would idle better: 230/227 or a 230/234, both on a 112 lsa

Dean98TA

In my thinking, the LSA is not actually a metric in and of itself that you try to manipulate to acheive a certain power level. The LSA is the result of the combination of when the valves open and the duration of how long the valves stay open.

If you think about it, the more duration you give the valves being open, the less available LSA will be available because there is a limit to how soon you can open the intake valve, and there is a limit to how late you can open the exhaust valve, before you start actually making less power.

You can't just say, grind in 117 degrees into the cam's LSA and expect it to work. With smaller cams you can, but by their nature, they are limited in how much power they can make due to their shorter durations.

About the only way I know to make a big cam idle like stock is to give your cylinders more cubic inches. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

HITMANSS

Dean, I'm having a real hard time following your logic. Instead of arguing w/ you, let's go back to the original question.

You can find a very cogent explanation of valve timing events and their effect on performance at the Comp Cams website --- just click on "Timing Tutorial".

Widening the LSA has the effect of reducing valve overlap --- that's the number of degrees that the intake and exhaust valves are open at the same time. If you look at the camshaft itself, you can see that the lobes are placed close together on one side of the shaft. The lower the LSA, the closer the lobes are together.

A 224/224 117.5 LSA cam might idle better and have better street manners than a 224/224 112 LSA, because it has so much less overlap. But, it might not be so much better to justify the power loss. It's a tradeoff.

Dean98TA

I think it is helps in understanding just what is changing when you say "widening the LSA". The camshaft lobes represent what the valves are doing, so if you think about it in terms of the valves, it helps understand where the most power is being made.

All cam timing is relative to the piston, therefore you can change the LSA two ways, either by closing the exhaust sooner or by opening the intake later. Either way can make a difference in how much power is made, especially when you factor in the duration the intake and exhaust.

In the relatively small range of camshaft sizes for the LS1, you can say that generally, the LSA shifts the power up higher in the RPM range, but that is not necessarily true in the broader sense. I've seen an example of a cam with a lower LSA make power higher in the RPM band than another cam with a higher LSA, both on the same motor (it was an LT1, but that shouldn't matter).

I'm skeptical that the 224/224 117 LSA cam would run well at all simply because to acheive that LSA with those durations means you coulb be probably either opening the intake too late, or opening the exhaust too soon, or a combination of both. You simply cannot change the LSA while keeping the durations the same, withoug changing the overall valve event timing, possibly enough to cause the cam to make less power overall, not simply where the power is made.

It just sounded like the original poster wanted to understand more about LSA than it merely describing how close the two bumps on the bumpstick are.

finalymodded

When saying a tr224 @ 117 lsa, I was using it as a generic term because it (tr224) has become almost a household name on this web site. It could be any cam. The referal to the comp cam site and what area to look for info was exactly what i was wanting thank you. The other information in this post has been very helpful also and I appreciate the posts if you know of any other sites/books/information stocks, please post them. Again thank you for the information.

<img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

DriveATransAm

i suppose the term moving the powerband up wasnt the right way to say it. it sounds like it just increases the whole powerband, which in effect makes it higher than it is impratical to use though.

HITMANSS

To answer your question, I think the reverse split cam would idle better --- because of its lower total duration & overlap.

Street manners involves more than idle, though. Both cams have a lot of duration, which puts the powerband high, but weakens the bottom end. The split duration can may do better in the mid-range, where the exhaust pulse helps fill the cylinder.

HITMANSS

Dean, it's obvious that you don't really understand what LSA is, and how it relates to valve timing events. I suggest you do some more reading.

bone, there are some other sites that might be helpful to you --- one is: http://www.howstuffworks.com/engine.htm It has a nice working diagram of how the cam, valves, and pistons interact.

DriveATransAm - widening the LSA doesn't move the powerband up OR increase it. What it does is to broaden it slightly, so that you have better off-idle response, and power falls off less quickly after peak HP. Peak HP and TQ may drop a little.

Tightening the LSA has the opposite effect. There is more valve overlap, so idle quality and off-idle response is worse. Peak HP and TQ are slightly higher, but will fall off more quickly after peak. Peak HP may occur at a slightly higher RPM. A recent dyno study in a major magazine showed compared an SBC w/ 106, 110, and 114 cams. The 110 and 114 cams peaked at the same RPM, while the 106 peaked 300 RPMs higher.

In general, engines that breathe extremely well (such as LS1's, especially w/ ported heads) do not respond as well to tighter LSA's --- they don't need as much help to scavenge & fill the cylinders. That's why you don't see many LS1 guys running LSA's much under 112.

Dean98TA

Whatever, Hitman. You wanna come off as the "expert" here, I suppose.

Obviously, you know how to parrot what you've read on these boards, however, you still haven't provided any real info that shows you understand what's going on. Posting a link to Comp Cam's website is the only enlightening info you've given. All you have to do is examine the cam profile pic on Comp Cams' website to see what I'm talking about. I believe you know the url.

If you look at the picture, you see that Lobe Sep Angle is the difference in degrees between the two lobe peaks. Duration, ramp rates, and intake centerline all determine where the respective peaks occur with respect to piston timing. But what is the cam for in the first place? To dictate the timing of the valve events. So far, you've only succeeded in giving the trivial information of what lobe sep angle is.

If you have two cams with identical durations, but with different LSA, what exactly have you changed? Well, if you don't change the intake centerline (i.e. intake timing), you are changing the exhaust valve timing, otherwise you are changing the intake timing or maybe even both. Agreed? If you don't see that, then it's clear it is you that doesn't understand what LSA is.

Now it should be clear that you can change the LSA in one of several ways, each of which distinctly affects how much power is made. Do you think that degreeing your cam with an adjustable timing gear is just a cool sounding mod to have? No, people do it to change the valve event timing in the quest to make more power.

Your posts make it sound like you are trying to make a blanket generality that changing the lobe sep angle is a very simple concept and that it will always causes a certain effect, when I've seen real live cases where that is not true. It may seem that way with LS1 motors because of there relative small size differences of LS1 cams, plus the fact that each cam manufacturer probably has a preferred way of grinding their LS1 cams (for example, most seem to grind in 4 degrees of advance). But you do know that cam makers will grind a cam to any spec for you though, right?

I don't claim to be an expert, and I realize this is an LS1-centric board (I'm giving you an out), but it sounds really silly when you try to come off as a cam "expert" and use only LS1-specific cases to back your supposed knowledge and claim that changing the LSA always causes a certain effect, without even knowing how the LSA was changed.

<small>[ January 28, 2003, 01:55 PM: Message edited by: Dean98TA ]</small>

HITMANSS

Dean, I can readily see why you don't claim to be an expert. You seem to have a basic understanding of some concepts, but you're off base on some others. I'm not going to try to educate you, or argue with you. Believe what you want to believe. When you buy your own cam, you can get it in any flavor you want. If you decide to order your custom grind cam from Comp Cams or from anyone else, please share with them your theories about all the different ways you can change LSA --- I'm sure they'll be fascinated.

My knowledge of cams is based on over 30 years of building hi-po GM V8 engines. In addition to my LS1, I have two other stroker/blower motors in my garage, and 6 or 7 different cams sitting on my shelves.

My opinions are worth exactly what you pay for them --- they're just opinions, but they're based on real world experience. Save the flames, you're just wasting your time & energy.

Dean98TA

Gee whiz. For someone with "over 30 years of building hi-po GM V8 engines", one would think you'd have a bit more helpful information to share, instead of just parroting what is found in any one of these cam threads. You're also amazingly quick to claim how wrong others are without even pointing out which part was in error.

I guess there will always be those that just have to try and prove their manhood on the internet by just claiming others are wrong outright, without even pointing out the error or providing the correction. I guess it's easier to keep up the illusion of how smart you are if you don't really have to provide any facts to back up your statements.

<small>[ January 29, 2003, 10:41 AM: Message edited by: Dean98TA ]</small>

TJF

bone camaro: Listen to HITMANSS - he's 100% correct. Take a look at Crane and Isky's wesites as they also have very good tutorials on cam design and function.

ChrisB

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HITMANSS:
<strong> A wider LSA does not raise the power peak; if anything it will lower it. What it does do is widen and smooth out the power band. Power will come on earlier (below 2K RPMs), and extend a bit farther past the peak HP RPM. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong>


I think this is a semantics disagreement - a wider lsa, everything else equal, will typically raise the RPM at which your horsepower peak occurs (a function of broadening out the torque curve) - but whether it increases or decreases the actual hp value is a function of the rest of the setup. - It just depends if you mean RPM @ or actual value when you say "raise the power peak" - it can be interpreted both ways.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">In my thinking, the LSA is not actually a metric in and of itself that you try to manipulate to achieve a certain power level. The LSA is the result of the combination of when the valves open and the duration of how long the valves stay open.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

Exactly, and I agree with Dean 100% in this - the lsa in and of itself means nothing really - it is only through it's effect on the valve events that it has any meaningful effect on the engine. This isn't a matter of semantics though, because other things besides the LSA can effect the valve timing (advance/retard, lobe selection, etc.)
LSA is a useful factor to look at in and of itself - but it doesn't tell you anything really unless everything else is equal - once you start changing lobes, advance, etc. it doesn't tell you nearly as much.


</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Dean, it's obvious that you don't really understand what LSA is, and how it relates to valve timing events. I suggest you do some more reading.
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

Deans explanation was pretty good, and is about what I would have typed. What you are missing here is that there are different ways of looking at this (different levels of abstraction).
The LSA is a *function* of the events, as Dean mentioned - but the reason you can't only look at LSA is that the events aren't solely a function of LSA - and the events themselves are what effect the car (overlap, cylinder pressure, etc.)

The website tutorials, etc. give you a certain level of abstraction, and in general situations, esp. where the lobes are the same/similar, will hold true. But it is still an abstraction, making certain assumptions, assumptions which are very easily rendered invalid. (the main assumption being lobes/advance are equivalent).

This isn't to say abstraction is bad - if you could look at everything without abstraction you would be more than qualified to be engineering your own camshafts. But you can just as easily over-abstract, and loose validity on your conclusions because of incorrect assumptions.

Anyway, not much really left to say here - everything Dean has posted is correct and true. Everything HITMANSS posted is perfectly true given that lobes and advance are identical - (between the two compared camshafts) the more you change those parameters, the less accurate the generalization.


Chris Bennight