LS1Silverado05

iTrader: (41)

Ok guys, be easy on the "not so advanced" guy here...just thinking in terms of cam profiles...what is the more effective way to take air into the motor. It would seem to me that a little longer duration at a smaller lift would net the same amount of air into the motor as a smaller duration at a higher lift...by all means if this is wrong, help me understand why. That said, is one better than the other?...That is to say, would you be better off with more lift, or duration for a given ammount of air on a NA motor?..I am sure the answer will revolve around the manners that the motor would exhibit....just trying to get some foundation of understanding to work from. How does one determine the "sweet spot of lift/duration"? Thanks fellas!

capn smokey

iTrader: (1)

As engine speed increases the valves need to stay open longer therefore duration is the key as long as the accompanying lift is sufficient. Lift and duration have to paired according to your needs, if youre motor is to spin high rpms and youre heads flow well then duration should be the focus. If the motor is to run at low rpms then increased lift with low duration will produce more power. Air velocity is the key to producing power and duration is what makes that possible(i.e. the quicker you can move air through your motor at a given rpm the more power it will make for that rpm). Sorry if it sounds like jibberish, just trying to put it in as simple of terms as possible.

LS1Silverado05

iTrader: (41)

Is there a point in lift where the lift becomes large enough to stall the velocity? It would seem that once optimal lift and duration have been found, going larger on lift would actually slow the velocity. Now the million dollar question is, how in gods name does a guy determine what his motor wants?...Do even you advanced guys rely on cam tech lines, or do you do alot of math with known head flow rates etc... I just want to make the very best educated cam selection I can.

Old SStroker

Good observations. I'm not sure "stall the velocity" is the correct term, but there may be a lift when flow gets "choked" or just stops being useful. The engine designer might limit lift to that point. Of course that may cause problems getting enough "area under the valve lift curve" to feed the engine. If it were easy to do it well, everyone would be doing it. Come to think of it, almost everyone is trying.

Different engine guys use different methods. Very few use cam tech lines, I'd guess. Many use the "design-build-test" method to close in on a good cam for the application. This can be very costly and/or time consuming, especially if the first guess is way off.

If you are looking for a cam for your application, don't choose the valve events yourself. Rather look at what works based on other's experience, and see if there are a few "cam guys" responsible for the best results. Filtering out the BS will then be your biggest challenge.

edcmat-l1

iTrader: (10)

http://www.compcams.com/Community/Ar...ID=-2026144213
This should be made into a sticky.
Read it. When you think you got it, read it again.
Several key points answering your exact question.
First, run as much lift as possible within the valvetrain and engines limitations. Within reason. If your springs are rated at .600 lift, you dont necessarily want to run .598.
Then, choose the duration and LSA based on several key factors including driving usage, tuneability, etc.

LS1Silverado05

iTrader: (41)

Thanks for the link.

z28hustle

that link is pretty informative...

12secSS

iTrader: (30)

I like seeing the lift match the flow characteristics of the head in question, then decide on what rpms the engine needs to turn for the best "under the curve" power band to decide on the duration (or vice versa). Speaking only with respect to lift vs duration obviously.

Also you need to consider what your heads (or should I say intake tract) can flow. You do not want to pair up a .650"+ lift cam with a head that goes turbulant at anything past .610" lift.

PowerShift408

iTrader: (44)

I've always wondered why Gen 3 cams were big on lift, lower on duration as compared to say, a Gen 1 cam, which has very little lift even compared to our smaller cams, but waayy more duration.

LS1Silverado05

iTrader: (41)

Speaking in terms of what a LS6 Intake + stock head flows, or a mildly ported head flows...what lift should be considered max before things get turbulent on such a mild setup?

Old SStroker

Don't you see that being done regularly? Engines dislike stuff like that and usually tell you so by not making power. Keep thinking the way you are. You may need to change your screenname to 11secSS.

SScam68

iTrader: (20)

At what level of engine are you talking about. What I mean is, are you refering to a professional competitive field/customer? Or are you referring to the average Joe?

I run under some unique, at least compared to most, circumstances. That being really thin air. I know a custom grind is the way to go, but how many iterations is it going to take a real pro achieve my goals?

LS1Silverado05

iTrader: (41)

I see alot of reverse split cams...what is the main advantage to this type of cam profile? Anf furthermore, what applications to they specifically help to shine?..Thanks for all the info guys..

Old SStroker

It could be literally hundreds or thousands of iterations....on a very good simulator program with input data that accurately models your engine. This can be done for any level of engine design. The more one-off the engine is, the longer it takes to accurately model the base engine. ECA (Engine Cycle Analysis) programs show trends and allow a proficient user to narrow in on optimum valve events before cutting the first cam. They are not always home runs, but I've seen a lot of triples.

From what I've seen, some guys get very close this way...some don't. It sure beats "we've always used this cam in a SBC so it's gotta work in an LS engine" thinking. Different engines and different atmospheric conditions ask for very different valve events. Look at the newer LS rectangular port engine OEM cams. The timing looks strange to many...but apparently not to the engine.

DrkPhx

iTrader: (15)

David Vizard wrote a real good article about cams that was specific to the LS1 a couple of years ago in GMHTP.

Ari G

iTrader: (25)

They got more Velocity and better flow

zz4camaro1980

Quote:
Originally Posted by 12secSS
I like seeing the lift match the flow characteristics of the head in question, then decide on what rpms the engine needs to turn for the best "under the curve" power band to decide on the duration (or vice versa). Speaking only with respect to lift vs duration obviously.

Also you need to consider what your heads (or should I say intake tract) can flow. You do not want to pair up a .650"+ lift cam with a head that goes turbulant at anything past .610" lift.

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Isnt the flow always turbulant at any lift? I didnt think the flow was laminar at any point.

Old SStroker

Perhaps turbulent wasn't exactly the correct word, but it paints a picture. Let's say on the flow bench the flow increases steadily with increasing valve lift with a smooth sound until the ~.600 point where the flow virtually stops increasing and the sound in the port changes indication the air is not "happy". You might describe this as "chaotic" flow. If it's chaotic on the steady-state flow bench, picture what it is in a cycling engine.

I interpreted 12secSS's post to mean this. If you lift the valve into this chaotic flow regime, there is a good chance the engine won't like it. It does present a challenge to getting more air in. "Fixing the port" is not always possible.

Jon

zz4camaro1980

that makes sense, thanks for the explanation!

N4cer

iTrader: (11)

I believe the Gen III cams are bigger, but we speak of Gen III cams in terms of duration at .050", where Gen I guys use advertised duration as their guide.