What is the maximum overlap at .006 or .050 that I can run and not hear any lope/chop ? I understand a higher idle rpm can reduce lope but to help me understand better lets assume stock-like idle of 800 rpm.
Thanx in advance for any replies.

 

So many variables. Cubes, compression, exhaust design. Etc. my old combo of 10.85:1 five seven had neg twelve @ .050" and was stock smooth at 850. More inches and more compression could probably sneak about negative six or eight but may need the idle speed in the 875-925 range to kill ALL stumble

 

Not really an answer for that, like AR said, there are too many variables including what you think "0 lope" sounds like. I would think even the lobe could make a difference.

 

I'll try to narrow the variables by describing my combo. 5.7L , 850 rpm idle, 1 7/8 primaries 28" long into 3" collectors into 4" Flowmaster Y into a large straight thru muffler. It's not very loud.
For compression, I'm shooting for around 8.5 DCR. Does more compression tame lope or make it more pronounced ?
To me, "0 lope" would sound like a steady burble with no hunting for idle. I would guess lope would be determined by overlap @ 0.006 so XE-R lobes (49) would be smoother than HUC lobes (55) of the same .050 duration.
Would you say less lope = more throttle response ?

 

You're somewhat on the right thought in that having the most @ .050 per degree of advertised will help minimize overlap, however it also gets hard on the lifter, push rods, valve springs, as well as increase the shear noise volume which emanates from the rockers.
Compression ratio (static) does increase sound intensity and the manifold vacuum which not only helps smooth the idle but sharpens the throttle response . Maximizing cranking compression or DCR within fuel limitations is what Mamo always describes as explosive...that butterflies in the tummy feeling you get from the power band seemingly there no matter the rpms....LOL

 

Whether or not it is detectable will also depend on whos ear is listening. I can tell you that the 222/224 112+2 cam that i had in my Skylark when I first built it was perceptable to me, but it did not lope or chop. It kind of reminded me of the old small block chevy 151 cam (yes, I am old LOL). I think the low 220s cams on a wider lobe center like 114 make great power everywhere and I find them to be very stealthy. I bet a 220/220 on 114+4 might fit the bill. If you need even stealthier than that, something around 208 @ .050 would be very smooth, but give up some good power to the cam above.

 

I'm glad you asked about this squalor...I'm going to start my forged 6.0 "stealth sleeper" build and would like to have the optimum performance with a stealthy idle...

 

222/224 112 +2 has VE's of 1/41/46/-2 for -1 overlap in a 364ci , what was your SCR ?
It's not that I want to be stealthy as much as I want throttle response. If -2 overlap makes enough manifold vacuum that I have fast throttle response off idle then maybe 0 overlap would give the same throttle response at 1200 rpm and +2 overlap would give snappy throttle response at 1800 rpm.
PREDATOR_Z once said that every degree of positive overlap is worth 2 hp (rough estimate). I'm more into driving fast on twisty roads than I am drag racing. I'm willing to give up peak horsepower to gain fast, predictable throttle response.

 

Good Read guys i appreciate where this is going , Stealth is the key

 

The first cam i installed had -1 overlap at 050 on XER lobes, and the idle was noticeable. Then I went to a +2 at 050 on XER lobes, and the idle was even more noticeable. Now I'm at +7.5. On this last one, I also increased compression to 11.5. Each time, throttle response improved. Point is, for throttle response, compression is more important than overlap - at least in these overlap and compression ranges on my engine.

Another theory I've sort of seen kicked around is that it's the 006 to 006 overlap that makes for choppiness. I think I've come to the conclusion that isn't true, that the 050 number is more critical to idle chop. The comparison I'll make to illustrate is the Comp XER273 vs a stock LS1 cam.

At 006, the stock cam has 47.5 degrees of overlap vs 48 for the comp. At 050, the stocker is -34.5, and the comp is -1. So, for almost the exact same 006 event, the behavior is completely different. Since I once ran a comp XER 273, I can tell you first hand, it does not idle like stock.

I propose that the "lift area" of the overlap event will ultimately determine the propensity for lope and surge. So, increasing the ramp rate at the same 006 overlap duration OR increasing the 006 duration at the same 050 duration would increase lope if that theory is correct. Another way to look at it is to increase the rocker ratio from 1.7 to 1.85. The 006 events are the same, but the valve opens and closes faster, so I would expect the idle to lope more.

Remember, idle chop is really just a vacuum leak at the valves, so it's about how much of a leak you create. Wider cracks leak faster than narrower cracks.

But, I've also found that there is a ton that can be done in the tune to affect it as well. If you define "lope" as hunting for idle speed, then mine doesn't lope. If you define it as the "choppy" or "popping" sound you get with each cylinder pulse, then mine lopes and it's awesome. Tuner did a hell of a job with injector timings, spark timings, etc, and really tamed the cam, and once the coolant crosses 140 degrees, it idles smooth. I think there is a whole lot more to be said, but I want to be careful not to hijack the thread.

 

We ran a 220r on a 115° in a LS1 f-body back in the day that was very hard to tell that it had a cam in it sound wise. More compression will pronounce the sound even more. If you want dead quiet I would shoot for no less than -12° of overlap in that set up. Though like stated, proper tuning can hide quite a bit.

Lonnie

 

What size combustion chambers?

 

So I had this wonderful response all typed up, with overlap equations and all sorts of neat poop, but when I went to submit it, I fat-fingered it real bad and hit the previous thread link instead... So I guess this reply will have to suffice.

Anyways, superchevy magazine did a ls3 cam comparison where they established a manifold pressure measurement on "driveability". Their definition of streetable was a 950rpm idle, or lower, no lope/shake or searching at idle, no surging or bucking at low speed or partial throttle. And there empirical testing concluded that 35-45kpa manifold pressure is your typical production car with a factory cam. 50kpa is still streetable. And anything above 70kpa manifold pressure has noticeable shake at idle, stumbles upon coming to a stop, typical "big cam" poor driveability issues.

Something to consider is that all the factory cams, with the ASA cam being the only exception, have negative overlap @ .050", and all the factory cams have zero lope, smooth idle, etc...

The superchevy article said there is a direct correlation between increasing overlap and increasing manifold pressure. And they used manifold pressure as the meter for measuring driveability.

I would think it's safe to say that negative overlap @ .050" will make for a "stealth" and streetable cam. And any positive overlap @ .050" starts to become a trade-off of how it behaves down low, versus the gains at the top, and that's all dependant on the driver's personal tolerance levels for what is considered "streetable".

 

Adding into this.

The tune can play a lot into "lope". You can smooth out a big cam by adding fuel, timing, and a bit more idle speed.

Conversely you can make a small cam sound nasty by doing exactly the opposite.

 

Squalor, I'm going to make a rather unorthodox suggestion, but the number of times I've read your posts and your goals, I'm becoming more and more convinced this might be the route for you to go. I think you should at least consider doing almost a "heads only" build.

And I mean a badass set of heads like the Mamo220's, TFS220's, or AFR215's. Couple them with a rather mild cam, say the cammotion stage 4 drop in for 5.7L - 220/224-116+3 with events -3, 43, 51, -7. Has -10 degrees overlap. Fast92/92. Run a .041"head gasket, have the heads milled to 62cc's.

Assuming stock bottom end, that all puts you at 11.15 SCR, 8.53 DCR. Should run fine on 91 octane (93 would be better). The throttle would be nice and snappy, lobes are relatively mild, so your valvetrain will be nice and stable, port velocities from the heads will improve cylinder fill, even without the cam to support it.

That would give you a very broad torque curve, smooth application of power, tame idle, and nice, snappy throttle response, no gas smell, and will probably embarrass a lot of over-cammed, stock-headed cars on the street.

 

So for the people searching for "stealth" cam specs, and in the future find this thread, a cam with -12 overlap@ .050 would be almost sure to work. If the stars are aligned just right a cam with -8 might work.

I have read that the .006 events influence overlap to some degree but the biggest influence is the EVO. I read that intake flow is minimal @ .006 and really starts @ .050 so when you say, " I think I've come to the conclusion that isn't true, that the 050 number is more critical to idle chop", that makes sense.
There are no MMS 220's in my future and the only after market casting I could consider would be redtan's AFR 205's. I've been saving since last Christmas and only have $1300 , it's hard to put money back on a security guards wages.
When I first started studying cams, I thought I wanted a El Toro (230XFI/230XE-R 111 +2) but my latest "Cam of the Week" is a 223/230 112.5 +1. If I'm going to lope at 2* I might as well lope at 8* . A cam with -12* overlap sounds like a old man cam. I may be 57 but your never too old to have a happy childhood.

 

Here is another good thread that touches on that topic
https://ls1tech.com/forums/generatio...manifolds.html

Post #2

-10 to about -5 (@ .050")

 

There are plenty of old threads on stealth cams. I agree though if you want a stealth cam, you pair it with the right cam and a good set of heads for maximum effect. Since a stealth cam will typically be a small cam I'd recommend maximizing power under the curve with a smaller CC head with good velocity.

 

Thunder Racing had the "CheatR Cam" that had a stockish idle. Specs were 219/230 on a 117. Depending on your exhaust setup and exhaust flow on the heads you get, you could go ~221/228 118 and should be pretty close to sounding stock and still have snappy throttle response, especially if you can get to 11.5 - 11.8:1. Overlap is -11.5 and IVC is 45.5 (using 0.050 numbers) which I think would be in the high 8's DCR. On 93 octane it should be safe if tuned well.

Jason