Actually, you can have the advance ground into the cam; you don't have to have adjustable timing chain. I've got my eyes on an F13-112+4.

 

Someone mentioned it earlier, and I would like to correct my post. LSA does nothing to determine where peak power occurs. The IVC point does that. 2 identical cam IVCs and different LSAs will peak at the same RPM, all other things being equal (exhauts, heads etc.). Retarding or advancing a cam, after it is ground, will alter the peak power point. A tighter LSA usually yields higher peak power than a wider LSA, with the power coming on earlier but falling away quicker past peak.

 

I wouldn't stick closely to that part of your answer, especially the bold part. You might want to
dive into the advanced tech forum and read a post called, "The Truth About LSA"

 

that is the way I understand it. Maybe a picture of a dyno with the same cam by different LSA would be good to show this

 

Buy both cams, put each in your car, dyno them, findout the answer you self, keep the one you like and sell the other. End of the story, bala bang bala boom!!!
















I figure its about time for some simple minded answers since everyone else's answers are so complictated.

 

Okay, after reading through this, all of you people who have put forth conjectures about if this and if that are missing the simple question... he isn't asking about a T-Rex on a 110 vs a 224/224 on a 114, he is asking about the same cam, one on a 112, the other ground on a 114.

When an F13 on a 112+0 is installed in a 346 with all the supporting mods it will make more torque and peak earlier than an F13 on a 114+0. Well, how the hell do I know that?

Valve events.

The IVC at 49 ABDC on a 114 and at 47 on a 112. More importantly, the IVO at 1 BTDC on the 114 and 3 on the 112, meaning that the same lobe at 230 rated duration at .050" lift holds the valve open for 48 degrees of the cam cycle vs 44, meaning not only will the 114 make more peak power due to the later closing point, but it will make more average power due to the valve being held open longer.

Another thing to consider is that the dynamic compression ratio will be higher on the 112, meaning more cylinder pressure and torque. Though, it should be noted that the difference would be minimal.

As for a T-Rex peaking really late on a 110, that's because it is very big for a 346. More duration pushes the RPM peak up higher, and you bring it back down with a tight or numerically smaller LSA. With a 110+0 LSA, the T-Rex closes at 51 ABDC, but it opens at 11 BTDC. It has a narrow powerband. Which cam would be faster? That depends on how fast the engine goes through it's operating range, and thus the T-Rex would be faster because of its violent on/off nature due to the big duration and tight LSA. An F13 on a 114+0 peaks nearly as high with a much broader power band. It may not have the same intensity in its powerband, but it would be smooth on the street.

 

I think I should jump in to really stir it up with my rotary engine experience, hahaha bare with me here. From my understanding a LSA number directly translate to over lap timing. The amount of over lap will effect where the optimium volumetric effeciency of the ports. ie on a normally aspirated rotary where believe it or not max torque is about 150-160 lb. but the amount of over lap from the intake and exhaust ports greatly effect where the peak happens and how it drops off. So with more overlap it means peakier power and where the motor is happy does not last very long and drop off sharply, but also is moved up in the rpm range. Less over lap means the motor seems to be happy every where with a softer and flatter curve, however the rpm range is lower. Which is more powerful? well that is hard to say becuase one hits hard but for shorter amount of time and the other hits for longer but with a softer punch. But I think most prefer more overlap and higher rpm because on a normally aspirated motor the only way is to spin higher rpm. I could be totally wrong but with a valveless motor overlap literally builds the character of the motor.

 

No, it's not a direct relation. You'll have to peek back in this thread, or some
of the basic cam threads to understand the difference between lobe seperation
and valve overlap.

Overlap can contribute to this, but is not solely responsible.

In a 'nutshell', that's the general rule. The curve rolling off may have more to
do with runner volume, engine rotating limitations, etc. than valve timing.
Sometimes people will stick in large cams that are tuned for high RPM motors
(4000-7000 RPM), but their engine is built and tuned for 2000-5500 RPM.

 

Good explanation, but I thought it was bass-ackards of what you said. I've heard from several folks that a narrow LSA puts all the power in a small range... totally fine for racing and nothing else. And that a wider LSA won't make as much peak power, but will make better average power, as in a flatter curve on the dyno sheet.

 

Guys,

There is no direct relation to overlap by choosing a cam with a certian LSA.

You should dive into the Advanced TEch forum and read a thread called, "The truth about LSA".

I can show you two cams with identical LSA numbers, but with totally different
overlap regions.

 

This is what Crane has to say about it.


What is Camshaft Lobe Separation and how does it affect the engine?


Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes.


This separation determines where peak torque will occur within the engine's power range. Tight lobe separations (such as 106°) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 112°) allow the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.

 

I also have an A4 and I just ordered the Futral F13 230/232 .595/.585 114 LSA with Manley dual springs, titanium retainers, and FMS hardened pushrods. Should be a nice setup.

 

Thank you JakeFusion for bringing valve events into this!

Here's a graphical depiction of two 'identical' (there's some minor differences) set-ups, 112vs114LSA

112 torque peaks earlier and *will* peak much higher given the same drivetrain configuration

114 peaks later, if you can even call it a peak! The thing's flat!

Of course, as duration increases, the valve events change and so does the need for LSA

 

Unless this comparison is on the same car...(which because of the huge differences it obviously isnt)....its not even a remotely valid comparison.

 

2* less duration on the exh lobe and 114 vs 112 LSA

Otherwise a very similar set-up.

The 112 also has a heavy drivetrain, but I didn't put it up there to compare how much power it makes but to compare where it makes power.

 

If you can't make up your mind, do what I did. I ordered a 113 LSA.

 

get a 113 and be DONE

 

i think this thread will never end bc every one has there opinions and thoughts and nothing will every change there thoughts.

 

And it is very apparent that noone really knows what they are talking about.

Gotta love the internet.

It has been an intertaining thread however.

Perry

 

i saw an experiment of two tr 224 cams the only diffrencess was in the lobe one of them

114lsa and the other one is 112lsa i saw both dyno cheet and its make the same peak power but the diffrence was in the torque

the 114 make less torque than 112

and the112 reach its peak torque earlier than 114 .

and the 112 makes sound rough at ideling than 114