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Build it right the first time
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Discussion Starter #1
what numbers in the specs of a cam will tell you if it has a lopey idle or not and if so how much?
 

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Some Punk Kid
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786 Posts
Your looking for valve overlap. Look for a high dur / low LSA. I would say the lope might start at 220+ degree dur and 110- LSA. But that would be a little lope. If you want to shake your teeth out keep it around 108 or less on a high lift cam. Is it going to be in a race car or a daily driver?
 

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Build it right the first time
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227 Posts
Discussion Starter #3
its goin in a daily driver for the moment but within a year it'll be a street maching its a 388 stroker smallblock chevy, i have a comp cams 280H in it right now but i dont like it no low end and it doesnt lope liek i want it too, main power is only after 3500 rpm.....which i might add is a ****load of power but its too high for me access where idrive i want low end but i want power all the way to 6400 rpm 6000 minimum and a lopey idle :p
 

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Member# 3287
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2,625 Posts
You want both worlds, low end power and a rough idle. But, one excludes the other. You seem determined to have that rough idle which means, as stated, you need high duration which drives the power curve up.
 

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Chasing dreams with a ball bat
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545 Posts
You might be able to do a custom ground cam, keep the duration low (like 220/225), but narrow the LSA to 106 or 104 to create the overlap and then install it 4 deg. adv. to pick up a little more bottom end. If you have a PC dyno program you could try it and see.
 

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Crane 3/4 cams...........Energizer 3/4 Race Hydraulic Flat Tappet Camshaft & Lifter Kit
Lift: .470''/.470''
Duration: 282°/282°
RPM Range: 2400-6200
ROUGH IDLE, MODERATE PERFORMANCE USAGE, GOOD MID-RANGE TO UPPER RPM HP, 3000-3400 CRUISE RPM, 9.5 TO 11.0 COMPRESSION RATIO ADVISED.

Grind Number: 282 H06
Operating Range: 2400-6200 RPM
Duration Advertised: 282° Intake / 282° Exhaust
Duration @ .050'' Lift: 226° Intake / 226° Exhaust
Valve Lift w/1.5 Rockers: .470'' Intake / .470'' Exhaust
Lobe Separation Angle: 106°
Max Lift Angle: 101° ATDC Intake / 111° BTDC Exhaust
Open/Close @.050'' Cam Lift: Intake - 12° BTDC (opens) / 34° ABDC (closes)
Exhaust - 44° BBDC (opens) / 2° ATDC (closes)

I have this cam in a 355 and it sounds quite healthy, but has more low end power than you would think.......
 

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Banned
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1,533 Posts
Comp XE 262, 268 good low rpm power with nice lope and good driveability. I will never understand why people want to sacrifice low end torque on a street motor for a lopey idle. Tune your exhaust instead if you must have a lopey idle. Stand next to a new Vette and tell me you don't like the exhaust sound but it idles smooth as a baby's butt! :cool:
 

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155 Posts
In my experience, especially with big displacement motors, a variable pump lifter, Rhoads specifically, can give you the best of both worlds, a rumpity-rump idle with major power when you make it spin.
 

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Administrator
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18,400 Posts
This "lopey" business is driving me Loopey....................pick a cam for how it performs, not what it sounds like. Jeeeeeeeeeeeessssus-H-Key-rist..........
 

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Hates: Liver. Loves: Diesel
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5,659 Posts
^^^ +1 !!

Look through Comp's custom lobe catalog. Choose a duration and LSA for you target use of the vehicle, period. If you want it to be a touch lopey sounding, use a roller with a really fast exhaust opening ramp and then use good quality headers. The fast ramps will put a more forceful exhaust pulse in the exhaust giving it a slight tick-it sound. Not the lopey idle you want, but a nice sound anyway. I learned this from a Lunati grinder who is retired. He hangs around some of the Oldsmobile forums you might be able to find him for more tech on it.

If you choose a cam for how it sounds, you are almost guaranteed to be disappointed in its performance.
 

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Hates: Liver. Loves: Diesel
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5,659 Posts
True, but those thumpers START at 283 advertised, 227 degrees @50. That is strictly 2500-stall and light car territory in my book. He said he currently has a 280 advertised cam and that's too much for him.

If you could maybe get them to do a 212/222 on that same 107 LSA you might retain some lope but bring your torque peak out of the rafters.
 

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I haven't ran it yet, but I'm using a Lunati VooDoo 262 cam with 1.6 rockers and a 105 LSA in my 388 in hopes of exatly what you are searching for. I'm running it in a 87 TA with stock tire height so low end isn't a huge ordeal, but I want a streetable cam with a nice sound. I've ran bigger rand smaller camms and they all have their place, but I think this time around this cam will be perfect. Also according to DesktopDyno (which is really just a good SWAG) my peak torque should be around 3500 with peak hp at about 5500. 475/450. With a good dual plane, headders, a good carb, good heads, roller rockers and gapless rings I say that should be pretty possible.
 

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You got a leaky spark tube...
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Correct me if I'm wrong but I believe engine size will have an effect on how a cam sounds would it not? I don't know where I got this or even if it's right but somewhere along the line I've come across this. Would a Comp 280H sound rougher in a 283 than in a 400? Also, I know big cams tend to have more of an effect on vacuum on smaller engines than on the bigger ones.
 

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Poncho, you must be old school like me. Nothing makes my hair stand on end than somebody saying they are shopping a cam by how it sounds rather than how it performs.
 

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cool rockin daddy said:
Poncho, you must be old school like me. Nothing makes my hair stand on end than somebody saying they are shopping a cam by how it sounds rather than how it performs.

No, I'm just old.........Cars dont go to school.
 
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