What Causes a Lopey Idle?

[@94racing88]

It’s actually the long duration that causes more overlap that’s what gives you the chop chop

[@SealofPerfection]

Correct, the LSA has nothing to do with it. And LSA has nothing to do with how much overlap it has, either.

[@user-yo3sz8xe2s]

​@@SealofPerfectionLsa has everything to do with overlap

[@SealofPerfection]

@@user-yo3sz8xe2s Not the way it works. Duration is what give you the overlap. LSA is irrelevant. You can have 10 cams for the same motor with all different LSA's, and all can have the same overlap. Duration is what does it.

[@mattphillippi5591]

@@SealofPerfection right so the placement of the lobes apart from each other in degrees has nothing to do with how their bases overlap. No both lsa and duration give you overlap. Also wouldn't the right valve event timing be the most important thing a cam needs to do? Isnt that directly related to lsa? You could then say for a given application I need X amount of overlap and as a result duration is given to you.

[@SealofPerfection]

@@mattphillippi5591 Go watch Powell Machine's video about this one. He's a cam grinder and explains it all. LSA has nothing to do with how much overlap you have, and overlap is what makes a cam chop. You can have the same overlap with any LSA. Watch his video

[@jimgagne3801]

Hard to live with on the street...... I could live with it.. ;)

[@TakeAGuessWhatsNext]

Not the gas prices though. But then again that's what we build them for.

[@loadb5985]

It is worth noting that LSA is relative to the cam profile and motor. Overlap is the true source of lope. The desired overlap is application dependent, there is a balance between form and function.

[@claiborneeastjr4129]

I haven't heard the term "overlap" used lately. Seems like it was used more often years ago.

[@martywilsonwilsonenginesho7940]

It's OVERLAP that you hear.......get it right please.

[@taquitopicante5863]

Well explained.

[@SealofPerfection]

Yet wrong

[@taquitopicante5863]

@@SealofPerfection Yeah, I thought about it later and I think it's just the opposite. A wide lobe separation gives you that choppy idle.

[@SealofPerfection]

@@taquitopicante5863 Not what I meant. LSA has nothing to do with the chop. Overlap is what causes that. LSA doesn't come into play. You can have wide or narrow LSA and still have the same overlap, and both cams will idle the same.

[@Faolan161]

​@@taquitopicante5863 I ran a 204/214, 114 lsa cam with a lope, a 214/224, 112 cam with a smooth idle... Then a 200/212, 108 lsa cam with a smooth idle. Lsa doesn't determine idle quality, it's a combination of factors.

[@mattphillippi5591]

It's the overlap that causes that. "Tight" or "loose" lsa does not mean more or less overlap, the duration dictates that. An engine that is seen as a lower performing engine ie a stock low compression engine will actually require a tighter lsa to maximize torque, sometimes as low as 103° but most ending up around 106-108° vs a high performance high compression engine which may actually require 116-120 lsa to maximize torque. The overlap is what causes the chop.

[@shadowopsairman1583]

Depends on where you need the power band, in racing it's needed in the higher rpm range (wot), lower for street, i got a cam to increase torque in the lower range for hauling payloads

[@mattphillippi5591]

@@shadowopsairman1583 yes. So you either chose the cam based on duration or based on lsa/overlap. Both theories seem to work however the standard for years has been off duration and seems to me more willy nilly than David vizards theory which seemingly can better predict the right cam for a given engine the first time.

[@paulbzzz7636]

Is that why the race shop is named Lopers?

[@jasonkaiser5150]

There pushing exhaust gas back up the runner at low rpms.

[@user-yo3sz8xe2s]

That lope in the exhaust is from duration mostly.

[@mattphillippi5591]

Actually that's overlap

[@masjuggalo]

So basically how the ghost cams work? You just face the cams differently to tighten up the LSA and make it choppy

[@Faolan161]

Ignition timing and a/f ratio have an impact as well.

[@john-davidcairns1615]

Think you need to watch David vizard video on lsa and duration

[@apollorobb]

Watch Powell Machine Daniel Explains this and gets it right .

[@blueridgemountainprepper2166]

Nice to see somebody else besides me understands

[@Faolan161]

Nice to see that someone besides you has the same incorrect thought process? Lsa doesn't determine idle quality.

[@Faolan161]

Not true. It's a combination of port size, cam, compression ratio, exhaust flow, and ignition timing. I've run a custom 212/219, 108 lsa with smooth idle, and a 204/214, 114 cam with a lope. Large cams always have a lope regardless of lsa. Why is this thought becoming mainstream? Second time today, and it's simply false.

[@demarques1911]

Don't forget the aggressive durations

[@383mazda]

So, is it really a tight LSA, or an early intake valve opening? I'm other words, will a low duration cam on a tight LSA still sound like a bigger duration can with the same LSA?

[@justlookingaround]

Holy shit, local boys from speedway. Any connection with speed way salvage??

[@louielouie777]

WRONG WRONG WRONG

[@gordonsillars]

Stupidest explanation ever!! The overlap causes some “reversion”, exhaust gases blowing back up through the slightly open intake valves into the intake manifold. This causes an uneven fuel/air mix, and THAT’S what causes the chop. As the engine revs up the speed of the air coming in overcomes the reversion and the engine smooths out. The more the overlap, the higher the engine has to rev to smooth out.

[@DoNotResuscitateAgain]

When your intake valves and exhaust valves are both slightly open for a brief moment at the same time. So what you're saying is... Tap some sparkplugs into the tail pipes!! Set the asphalt a blaze?!! 🤘🏻😈🤘🏻

[@MoreBollocks-ui2zs]

You're describing valve overlap.

[@jasonkaiser5150]

That's not how that works. When the rev limiter shuts the spark to the plugs the engine is still pushing fuel through the engine. Since the fuel is not burning in the cylinder the mixture is pushed out the tail pipe. You can ignite the unburnt fuel with a spark plug in the tail pipe. Lsa has nothing to do with it.

[@jimthomas1989]

​@@jasonkaiser5150, Never had a Rev limit er Built small block Chevy engines to scream to the moon , My little 327 screams to 11,000rpm before the valves start to float , then the 11 inch heavy-duty clutch is released and power goes to a M-21 Muncie 4 speed trans and then to a posi rear end , pulls both front tires off the ground in a 66 Chevelle Super Sport that weighs 3200lb , What's a Rev Limiter 😂

[@DoNotResuscitateAgain]

@@jasonkaiser5150 before your time i reckon.

[@DoNotResuscitateAgain]

@@MoreBollocks-ui2zs Ya so was he... But without calling it overlap. did yall watch this video? 🤣