Raben

iTrader: (5)

I'm still learning as I go on these things and curious about the LSA on cams. Don't quite understand it.

I'm wanting to go with a TR227/224 cam but unsure if I should use 112 or 114lsa. Any suggestions on what that means and what I probably should go for on a street/strip car?

It's an A4 with all bolt ons except headers & LS6 intake. Already been tuned with LS1 edit and surely after installing a cam will need to be retuned


Thanks for any info.

J-Rod

https://ls1tech.com/forums/generation-iii-internal-engine/101100-camshaft-discussion-part-ii.html

bryan c

LSA is an acronym for lobe separation angle. It is the angle between the intake and exhaust lobe centerlines. A lower LSA (lobes closer together) increases valve overlap. Overlap is when the intake and exhaust valves are open at the same time. The effect of inreased overlap (up to a point) is better scavenging of the cylinder at lower engine speeds. This scavenging effect increases the velocity of the gasses through cylinder, thereby increasing power/torque. This effect decreases at higher engine speeds. So in general, for a street car, this is a good thing.

bodhi

Overlap and Compression- A very common idea, although for the most part incorrect, is that overlap bleeds off compression. Overlap, by itself, does not bleed off compression. Overlap is the angle between the exhaust closing and intake opening and is used to tune the exhaust's ability draw in additional intake charge as well as tuning idle vacuum and controlling power band width. Cylinder pressure is generated during the compression cycle, after the intake valve has closed and before the exhaust opens. Within practical limits, an early intake closing and late exhaust opening will maintain the highest cylinder pressure. By narrowing the Lobe Seperation Angle 'LSA' for a given lobe duration, the overlap increases, but the cylinder pressure can be increased as well. Thus cylinder pressure/compression can actually increase in this scenario, by the earlier intake closing and later exhaust opening. By increasing duration for a given LSA, the overlap will increase, the intake closing will be delayed, and the exhaust opening will occur earlier. This will decrease cylinder pressure, but the decrease/bleed-off of compression is not due to the overlap, it is due to the intake closing and exhaust opening events.

http://www.wighat.com/fcr3/confusion.htm

Raben

iTrader: (5)

Thanks for the needed info, that's great!!!

Cal

iTrader: (1)

Going from a 114 to a 112 LSA is supposed to lower the rpm at which the engine reaches peak power by 200 rpm on the average. That is usually a good thing, since the longer the cam duration is, the higher it peaks at. So the smaller LSA's benefit a street driven car, BUT if you must pass emissions testing, it makes it harder because you get a rougher idle with the smaller LSAs.

Colonel

I think one thing that is commonly overlooked is that with a wider LSA, the power drops off slower after the HP peak. This has more significance than whatever small difference in peak HP or peak HP RPM there may be between a narrow and a wide LSA.

Take two cams that are identical with exception to the LSA. One is a 110 and one is a 116. The two will make somewhat similar peak HP numbers. The 110's peak will likely come a little lower than the 116. Maybe ~300-400 RPM. The 110 will make less power at the extreme lowend of the RPM scale where it's overlap really mucks things up. It will make a good bit more power throughout the midrange before the HP peak. It's power will ramp up much quicker to the HP peak after a slow start on the bottom end. Midrange power will be EXCELLENT...this is where the narrow LSA cam shines. After the HP peak, things really start to calm down in a hurry for the 110. The power drops off fast making shift points not much higher than the HP peak. This is where the 116 shines. After the HP peak (which, as I stated before, will be about the same value as was seen with the 110 but at a little higher RPM), the 116 just wants to keep on going and going and going :Energizer Bunny:. The peak plane of this curve looks like a tabletop by comparison to the 110. It's a slow dropoff. Optimum shift points will be WELL after the HP peak.

And, we all know about the idle characteristics of both. 110 = RUMBLE RUMBLE SHAKE SHAKE...oops the car died out again! And 116 = "Hey, is that thing stock?"

Cal

iTrader: (1)

I agree, I personally like the wider LSAs for that flat powerband. I did some Land Speed racing this year, and my 114 lsa cam really worked out well to maintain traction on the slippery surface of the salt, as well as extend the the rpm range of my engine. You don't want a peaky powerband on the salt.

Raben

iTrader: (5)

Hmmm so passing emissions (they don't do the sniff test, however visual test for cat converters and computer testing for codes) I wouldn't want to go any lower than saw, 112? Or would that even be too much.

But the base of LSA is RPM range the Peak HP with hit? Just want to be sure I'm understanding this right. Say for example 110lsa reaches peak hp at 4800rpms and then a 114lsa may hit peak hp around 5200rpms??

And a 116 would sound almost stock? no rumbling or anything but still have the performance so to speak?

I'm debating if I want something to sound somewhat rumbly loud or not. I've heard some wav files from this site with people running TR224/224 with lsa of 14 and it rumbled some but sounded really good.

With that cam setup, the A4 shouldn't stall out or anything right? And pretty much run smoothly?

Colonel

Passing emissions may be tough with a 112. It has alot to do with other factors though. Your duration has alot to do with it too because really what we're looking for when shooting for an emission friendly cam is less overlap. Overlap is simply the time spent when the intake and exhaust valves are both open and this is a result of duration, both on the intake and exhaust, and LSA. In other words, a 215/215 110 would be alot cleaner than a 230/230 116.

As I described in my last post, the RPM at which the peak HP will hit is only influenced a small amount by changes in LSA. It's not as much as you might think. I'd say 150 RPM per 2 degrees would be a good rule of thumb. What's influenced MORE is how quickly the power builds on the way up to the peak and how quickly it falls off after the peak. If you want to seriously change the peak HP RPM (and number) then the intake duration (and exhaust duration to a lesser degree) will have the most influence in that regard.

A 116 LSA MIGHT sound almost stock depending on many factors including the CI of the engine, duration, lobe ramp rates, the entire exhaust system, idle speed, compression ratio, and other factors that I may not be aware of. The 116 LSA cam that I have (Stealth II from MTI) sounds stock in my car but not stock in others. Go figure.

A 224/224 with a 114 shouldn't be very hard to tune to prevent stalling and it will have a moderate idle. Not stock but not aggressive.

Cal

iTrader: (1)

I have a 224/224 114 and I believe this is one of the best street cams out there. It does have a choppy idle/lope to it, but how severe it is depends a great deal on tuning. If you raise the idle speed to 950 and add 4 degrees of idle tuning like I did, it will sound very mellow (esp. through a quiet exhaust) but still not quite stock. Before I tuned it and put a better muffler on there, it sounded pretty wild. So anything in between is also possible depending on your setup. BTW, it has never stalled even once with this cam, but I have a M6.

jrp

iTrader: (16)

nothing wrong with a 110.5lsa


copy past the url into your windows media browser.

http://www.imagestation.com/picture/...8/facac7a3.mpg

. for what its worth though im gonna swap it out for a 224 on the 112 to pass emissions easier.

Bearcat Steve

Colonel - best desciption I have ever rtead regarding LSA. Thanks!!!

Sport Side

iTrader: (6)

oh yeah? jrp?

jrp

iTrader: (16)

my new cam has 65.5* overlap now, wonder how thats gonna do w/ emissions

Sport Side

iTrader: (6)

But, what does a wider lobe seperation do to valve events?

You pick, the valve events for the application. If you go with a wider lobe seperation just for the benefit of holding peak power... then, you've changed the whole characteristics of the camshaft..

how do you guys see it?

Ed Curtis

Cripe...

I thought it only had 13*...

Ed

Dragaholic

iTrader: (180)

So if the T-Rex is tight (110 LSA), then how come it makes so much power and puts good times at the track? How come people are getting the best results shifting 200-300 rpms above the hp peak? From what Ive read, a cam with a numerically lower LSA, the hp will drop faster after it peaks. If thats true, then why arent people shifting right at or just a tad after peak power?