marc_w

I had my nose in an old (1990?) 'how to build horsepower' book last night.

My original understanding was that a smaller LSA, on the same spec cam, would bump the peak power DOWN in rpm's, and give a rougher idle.

A wider LSA would move the peak horsepower UP in rpm's, and smooth out the idle.

--

In this book, it says that a wider LSA will give a broader powerband, while providing a smoother idle. (Okay, that goes with what I thought.)

A smaller LSA will make the cam 'peaky'. It will create more horsepower, but in a smaller rpm range. It will also be more inefficient at lower rpm's, and hence a rougher idle. The idea being that less LSA provides more overlap. More time for scavenging to do it's thing... which is bad at low rpm's, but great when it's in it's 'zone'. (Okay, when I let this sink in, it somewhat goes with my original thoughts - just a little different)

--

SO! To clear things up for me, Say I'm looking for lowend power in a custon ground cam, starting with off-the-shelf specs:

Does a smaller LSA actually help?

Would it actually be wiser to go UP in LSA?

Is LSA just a secondary spec, where I should concentrate more on duration?

Does lift play a role in this at all?


_THANKS_

BigTex

iTrader: (16)

Duration will be the biggest factor in your RPM power band, as wel as the lobe profile. LSA will determine more how long the power band lasts and how peaky it is. A small LSA will create a shorter powerband with a higher peak, while the larger will extent the total power with a little less peak HP.

If you want a combo of both low end and good upper end, you'll want to choose a more aggressive lobe that opens and shuts the valve quickly. That will keep the low end and allow you to run more .050 duration without sacrificing the low end. Comp cams XE High rpm cams are a good example. Lift is higher, durations are larger, but the open and close time of the valve is about the same as a smaller cam that has less aggressive lobes.

Your LSA will do alot to determine how friendly your cam is, how much lope, your idle rpms needed, etc. Look at duration for the overall power, but LSA for how the cam acts. You could get away with a little more duration with a larger LSA on stock tuning.

marc_w

Thank you sir!

Things are starting to weave together in my head. I'm sure I'll pop a few more questions by the end of the day.

Hit Man X

Don't forget an LSA of 110* for example will drop idle vac a lot making the computer freak out some times (not sure about the LS1 motors and such, but the Ford EEC-IV goes nuts) and the brakes aren't as good as the vac is low.

The 112* will have some chop-chop at idle and the 114* will sound closer to stock.

Just some stuff I have noticed too...

marc_w

Good point HitMan... My boat needs all the anchor it can get...

How much of a difference would 2* of LSA make?

Ex, a mild 114*LSA cam is topping out at 6200rpm. Theoretically, in the perfect world, where would the 112* drop off?

BigTex

iTrader: (16)

Oh man, this is where things get interesting.

Its my opinion that a wider LSA will have the powerband starting lower in the rpms, while a smaller LSA will move it higher, all things being equal. Thats opposite of what you said in your opening statement. If the cam is ground the same on a 112 and a 114, the 112 would have an ICL (intake center line) 2 degrees more advanced than the 114 cam. The ICL is critical in determining where the powerband is. So to make the 114 and 112 cams have the same ICL, the 114 cam would need 2 degrees of advance ground in. So to compare apples to apples, a 112 cam with +4 degrees advance ground in would need to be matched with a 114 cam with +6 degrees ground in. Advancing the cam will bring the rpm of peak power down some and boost low end, at the cost of peak HP. I think thats why lots of guys say the 112 cam makes more low end power, because inherently, it has a 2 degree lower ICL than a 114 cam with the same amount of advance. Does this make sense to anyone, or can someone prove me wrong?

To answer your question, a 112 LSA cam will probably drop off just a bit earlier than the 114, but the peak will be just a bit later than the 114. Remember its more peaky, so it peaks later yet ends sooner.

marc_w

This *is* interesting. Like I said, bells and whistles are starting to go off in my head. Gotta go digest this one for a bit.

BigTex

iTrader: (16)

I've had to reread my post a couple of times to convince myself, I think.....