cam lope [Archive] - Chevelle Tech

: cam lope


427stingray
Mar 30th, 07, 7:31 AM
What causes a cam to have the loping sound. If I were looking for a cam that sounded like that, which of the cam specs would I look at to get that sound.

Aaron
Mar 30th, 07, 7:34 AM
Overlap. Duration and lsa have alot to do with this.

Augustboy2009
Mar 30th, 07, 9:10 AM
yep, If you want to understand cam stuff better take a look at The Comp Cams website. On their site, they have an "articles" section. Once your in the articles section you can read an abundance of info on how a cam works and all of its characteristics such as duration, LSA, overlap, seat timing, lift, area under the curve, etc. I would think duration has a lot to do with the "lope lope" of a cam. Most general performance street cams are usually ground on a 110lsa.

kirkwoodken
Mar 30th, 07, 10:53 AM
"Cam Lope" is caused more by uneven cyl/cyl fuel distribution than the cam grind. If you were to put an 097 cam in 2 barrel 283, it would lope like crazy; in a fuel injected car, it idled smooth. What lope really means is that your engine could run better if you had a better intake manifold. When I hear an engine that lopes, I hear an engine that needs tuning.

moonbeam1999
Mar 30th, 07, 11:09 AM
FYI, if you are looking for the sound more than performance, Comp Cams has their new Thumpr line of cams designed specifically for that purpose. Generally speaking it is true that lope does not equal power or performance. You can have a lopey cam thats a dog in a given combo, and a smoother cam that kicks a$$ in a given combo.

dreis454
Mar 30th, 07, 11:28 AM
"Cam Lope" is caused more by uneven cyl/cyl fuel distribution than the cam grind. When I hear an engine that lopes, I hear an engine that needs tuning.

so your SB with a 250@ .050 cam has NO lope? & all pro drag cars need tuning?:confused:

sorry kirk, gotta call BS on that

jbird
Mar 30th, 07, 11:34 AM
so your SB with a 250@ .050 cam has NO lope? & all pro drag cars need tuning?:confused:

sorry kirk, gotta call BS on that

I agree. Could you explain that a little further? In certain specific situations this may be true, but not as a blanket statement. JMHO.

stealth71
Mar 30th, 07, 1:45 PM
One more for the EFI and lope = needs tuning. Not true at all.

Go to the LSX world, they are mostly EFI and still lope like a SOB w/ a big cam. Some are putting down 430rwhp SAE cam only from a 346.

BillyGman
Mar 30th, 07, 2:10 PM
I agree with the general consensus. What about fuel injected dragsters that run like crap until the engines are taken up to 3,000 RPM? It's the big camshafts that do that. Long duration camshafts are made and intended for not only more power, but for higher RPM operation. They move the throttle response and the available power further up the RPM scale than shorter duration camshafts do.

So with that extra power delivered by the longer duration cam, there is a trade-off. Because idle and low RPM operation in general is compromised. it's a sacrifice that's made for increased high RPM power. The longer duration cams cause rougher idle characteristics, but Lobe separation angle (LSA) is more specifically the cause. The tighter LSA cams (such as 108, and 110 LSA) will tend to cause choppier idle quality, but they will also cause the power band to be a little narrower. So the power will begin later and end sooner within the RPM scale with the tighter LSA's. However, that narrower power band will also come on stronger and will be more intense than with wider LSA cams.

540Hotrod
Mar 30th, 07, 4:27 PM
You can also pick up a lot of sound by using a cam with an early opening exhaust valve. You lose a little low end TQ because you let cylinder pressure out early...but it will help the *thump* part without going crazy with overlap and it's poor manners.

Plus compression always helps sound..the more the better!!

JIM

-SS454-
Mar 30th, 07, 4:34 PM
Its worth agreeing with kirkwoodken in the fact that EFI in most cases will mellow out a lope a bit, as it can constantly fine tune the fuel mapping and ignition at idle and change in an instant with the dab of throttle. BUT, i do not agree at all that lope is more to do with that, than the cam. The cam certainly makes the lope.

Its also worth noting that lope is amplified when your talking big cam, and little engine. A 236/244@.050 on a 110 will be pretty mild in a 400 SBC, but that same cam in a 283 will be rough.

kacp-o
Mar 30th, 07, 4:44 PM
Slightly OT, but exhaust configuration has a bit to do with it, as well, correct? Straight duals will sound more lopey than duals with a crossover due to the pressure equalization with a crossover.

GRN69CHV
Mar 30th, 07, 5:15 PM
Early timing events both produce that sound. A well advanced cam will produce that rolling lopey sound from the early intake valve opening. Early exhaust opening produces a very distinct sound due to exhaust valve opening at peak cylinder pressures.

BillyGman
Mar 30th, 07, 7:48 PM
You can also pick up a lot of sound by using a cam with an early opening exhaust valve. You lose a little low end TQ because you let cylinder pressure out early...but it will help the *thump* part without going crazy with overlap and it's poor manners.

Plus compression always helps sound..the more the better!!

JIMDitto, absolutely!

Johnny O
Mar 30th, 07, 8:46 PM
You can also pick up a lot of sound by using a cam with an early opening exhaust valve. You lose a little low end TQ because you let cylinder pressure out early...but it will help the *thump* part without going crazy with overlap and it's poor manners.

Plus compression always helps sound..the more the better!!

JIM

OK, so if one cam has ex. open at 64.5* BBDC, and another opens at 67* BBDC,
the lower one, 64.5, is the earlier opening??

pdq67
Mar 30th, 07, 9:19 PM
Please go to Isky's site and get into Ed's old notes on this b/c it will help a bunch, imho!!

And think about his 5-cycle cam theory too!!

pdq67

BillyGman
Mar 30th, 07, 10:13 PM
OK, so if one cam has ex. open at 64.5* BBDC, and another opens at 67* BBDC,
the lower one, 64.5, is the earlier opening??Nope. The earlier opening is the higher number BBDC because 67 is further away from Bottom Dead center ("BBDC" means Before Bottom Dead Center) than 64 degrees BBDC is.

kirkwoodken
Mar 31st, 07, 12:48 AM
so your SB with a 250@ .050 cam has NO lope? & all pro drag cars need tuning?:confused:

sorry kirk, gotta call BS on that

That is correct: my 255* cammed engine has no lope. You can tell by the volume of the exhaust noise that the exhaust is opening earlier than a stock cam, but it idles smoothly at 1100 RPM. I'm sure you will say that is high idle speed, but the Rochester requires an idle speed that high to get enough signal vacuum because of the two air meters. I will stick with my original comment about the early Corvettes with 097 cams. The injected cars idled very smooth compared to similar carburated engine of that era. What you hear in a ProMod is more related to the blower/injector setup. A continuous flow injector, such as the Hilborn on a blower, is made to run properly at only one speed; WOT. In that mode, it doesn't lope. Also, a blown fueler is not in the same catagory as a street car. This question was primarily about a streeter with a lope, not a 10,000 RPM engine with a lope. I picked my example to point out that the exact same cam in the exact same engine could idle much differently because of two different induction/exhaust systems and because it is something I have first hand experience with. I put the old 097 in numerous engines, some loped, some didn't. I'm only trying to point that just because a particular cam lopes in one engine, it may not lope in another. Lope CAN be caused by poor mixture distribution. I don't think that should be the goal of someone that is looking for performance.

You can run much wilder cams with street FI and not have them sound wild. Of course, extra duration emphesizes the mixture upset caused by neighboring cylinder exhaust pulsing, and long headers will reduce the lope caused by that.

So I would say, if you want a lope, get a cam with a lot of duration and close LDA, put an antique 2 barrel manifold on it and stay with stock exhaust manifolds.

daveseitz
Mar 31st, 07, 8:30 AM
I started playing with a Dyno program and cam specs. Some of what I did learn was that big was not always better. Though I'm not near the level of understanding as most on this board, I can say this.
Look at what the TQ and HP #s desired are.
Some made great HP and no TQ.
Do you want the show sound or go power.

I showed a coworker his engine specs with the cam he runs in his dirt car. I also showed him the same combo with a smaller cam making 30 less HP. That cam made 60ftlbs more of TQ at same RPM. It also pulled more TQ from 2000-6000 then the bigger cam.
Combo was a 355 10:1 comp, 650cfm2bbl carb, dual plane intake, stock manifolds, set by his class rules.
Now he is rethinking the big HP #s his engine builder shoots for. The program was close to his actual dyno of last year as well.

540Hotrod
Mar 31st, 07, 1:57 PM
Racing is whole 'nuther deal. In most cases...no one cares what it makes at 2000 rpm. That's just off idle and ought to be pulling into a parking place. I can't imagine a roundy round car spending much time under 4000 rpm. I'd really look into to the actual range he works in. For sure overal TQ range is very important for a circle track or drag car...just gotta be sure you are looking at correct range. Peak HP chasing can make for a slow car,......but the folks who win usually do just that and spin it a little higher.

JIM

senior
Apr 1st, 07, 10:38 AM
Well obviously by raising the idle RPM you can smooth out any but the most radical cam!

There is something to the statment... "but it idles smoothly at 1100 RPM. I'm sure you will say that is high idle speed, but the Rochester requires an idle speed that high to get enough signal vacuum because of the two air meters."

but if the motor idles smooth at 1100 it's the cam change that caused it to need that much rpm to idle smooth! Even with an FI set-up I'll bet if you slowed your idle a pronounced lope will develop with that cam :yes:

Where's Harold when you need him :p

BillyGman
Apr 1st, 07, 10:58 AM
Well obviously by raising the idle RPM you can smooth out any but the most radical cam!

There is something to the statment... "but it idles smoothly at 1100 RPM. I'm sure you will say that is high idle speed, but the Rochester requires an idle speed that high to get enough signal vacuum because of the two air meters."

but if the motor idles smooth at 1100 it's the cam change that caused it to need that much rpm to idle smooth! Even with an FI set-up I'll bet if you slowed your idle a pronounced lope will develop with that cam :yes:

Where's Harold when you need him :pI agree.... I had a SBC 350 with a cam duration of 244@.050 and an LSA of 110, and it idled rough at anything below 900 RPM, but once I brought it up to 1,000 RPM, it smoothed right out even with a Holley 4150 carb. So there's no magic there.

So with a 255 duration cam in a SB engine, I bet your idle would be rough and choppy at 750-800 RPM no matter what carb you had in there. I think that the only way that wouldn't be the case is if maybe you had a very wide LSA on the cam ( you didn't mention what the LSA spec is on that cam of yours).

charbilly2001
Apr 1st, 07, 2:31 PM
OK, so if one cam has ex. open at 64.5* BBDC, and another opens at 67* BBDC,
the lower one, 64.5, is the earlier opening??

Other way around

crazychevelle
Apr 5th, 07, 9:06 PM
Here is a chart that one of my teachers taught me in college not too long ago about how to remember the basics on the camshaft. I didn't write and degrees in but it gives you an idea. Im sure almost all of you guys know this but ill post it up for us newbies :)

http://memimage.cardomain.net/member_images/4/web/436000-436999/436436_22_full.jpg