Does the LSA of a cam have anything to do with the amount of lope you will get at idle? I.E.- the more LSA, the louder the lope and harder to idle?

 

yes
lower the number (like 110 = alot of lope) versus 115 = alot less lope

 

More overlap means a rougher idle.

Lower LSA = More Overlap
Higher LSA = Less Overlap

More duration also increases overlap.

 

Overlap is what gives you the lope.

A 236/236 116LSA cam will lope much harder than a 214/214 108LSA cam. Overlap is the amount of time the exhaust valve and intake valve are open at the same time. It's purely a matter of intake and exhaust duration. LSA is the displacement angle between intake and exhaust centerline.

 

As stated above by Blackhawk "More overlap equals a rougher idle"
Lower LSA = More overlap
Higher LSQ = Less overlap

Patrick. In the referred post you said a cam on a 116lsa will lope much harder than a cam on a 108lsa.

116 > 108 ...so would not the 108 idle rougher?

I am new to this but i have been trying to understand and research this for many many months and its almost as if the entire community is split 50/50 on which is correct. Can anybody give me a definate answer?

My understanding is for example 2 cams. Typical 224/224 114lsa and a 224/224 112lsa

The 114 will idle smoother yet the power band will be wider meaning it will peak at lets say 6500rpm. Whereas the 112 will ldle rougher yet peak earlier than the 114 lets say 6200rpm. I am correct on this?

 

^
For your TR224 cam comparo, you are correct.

Now, take a TSP 231/237 112. This cam lopes pretty hard.
Take a Futral F13 230/232 112. Lopes less.

MTI T1 221/221 112 Choppy little cam
MTI C1 222/222 112 Less choppy.

Goes beyond lsa alone.

 

Because valve overlap is what causes the lope and:

Correct.

 

Let me chime in for Patrick, since I would like to ask him a question.

The 214/214 108 hits .050 1 deg before tdc on the exhaust and 1 deg after on the intake. There is -2 (minus two) degrees of overlap at .050, and probably 45-50 deg at .006.

The 236/236 116 hits .050 2 deg after tdc on the exhaust and 2 deg before tdc on the intake. 4 deg of overlap at .050 and probably 50-60 deg at .006.

Note that is the real opening and closing, not the .050 level, that determines overlap. So a more aggressive cam can have a longer duration at .050 and a shorter duration off the seat. For example my 248/256 solid lifter cam has the about the same seat time as a 226/234 XE-R.

Another example: The Comp Xtreme Energy Street Roller would allow a 236/242 with the same seat time as an XER 224/224 or LSK 227/227. Someone else might know what the emissions implications are.

Patrick, what do you think of a 259/263 108 cam? How is the idle and low speed drivablity?

 

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Thanks guy I see what you are leading to but I think i still have a lot to learn as far as the valve events go and how to determine the degrees before and after TDC...

 

Interesting. That cam looks similar to a hydraulic cam with LSK lobes I've been working on for a hot street 346 LS1:

0.006 0.050 0.200
Intake Duration - ID 289 239 164 2130 LSK .649 lift
Exhaust Duration - ED 293 243 168 2131 LSK .653 lift
Lobe Center Angle - LCA 108 108 108
Intake Centerline - ICL 107 107 107

Intake Valve opens - IVO 37.5 12.5 -25 BTDC (- indicates ATDC)
Intake Valve closes - IVC 71.5 46.5 9 ABDC
Exhaust Valve Opens - EVO 75.5 50.5 13 BBDC
Exhaust Valve Closes - EVC 37.5 12.5 -25 ATDC (- indicates BTDC)
Exhaust Centerline - ECL 109 109 109
Overlap 75 25 -50 degrees

This cam is similar to what might be used to achieve Engine Masters powerband numbers (max power from 3500-6500). I think this cam will have excellent mid-range because of the IVC occuring where the tuned runner length of the LS1 intake seems to like. Go too far past 46 degrees ABDC (at .050) on a 346 and you start asking for a power peak past the ideal rpm level dictated by the intake manifold runner length. The idle will be OK with speed density tuning, but the overlap would make low-speed operation much harder to tune with a MAF.

You didn't say whether your cam was for a 346 or a 400+ motor, but if it's a solid roller grind (as I suspect), then it would be very similar to my LSK cam, but with a lot more area under the curve. Sounds juicy.

 

I got a Comp Cam 224/228 112LSA, sounds great and lopes pretty good! Stick with the Lower LSA For Sure!

 

I`m going with a 244 248 620ish on a 114 with my new 408. My ET heads are really going to flow well with this cam. I wanted to be very streetable, and sound good!

 

Actually, its a cam being discussed for a 454 in another thread. LSK. Harrop 55mm individual TBs. ET 265 heads. Beast96Z.

What idles are reasonable for the street. The cam you spec'd above has 73 deg of overlap. However, a 259/263 LSK (notice how LSK replaces XE-R) would have 95 deg of overlap (309 and 313 @ .006). What is the reasonable street limit.

Now that you mention it, how do you get the runner diameter and length for the intake. For LS1, LS6, LS2, LS7, LS4. FAST, and Harrop? I believe the LS1 is a 10" long, 2" diameter runner.

Similarly, for the head, port diameter and length. Actually, length and volume would be enough.

Thanks,

David

 

While on the subject,


Would a thunder racing 224/224 .563/.563 112 LSA lope pretty good?

I love the graph they show on their site with all it's torque being made at 2k rpm.

 

If your sole goal is a rumpa-rumpa idle. Not an emissions cam. More performance than stock but well under the specs for a performance cam.

 

the hot cam lopes really good