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duration @ .050"/ .200"

General engine tech -- Drag Racing to Circle Track

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dan miller

duration @ .050"/ .200"

Post by dan miller »

Could someone please ‘splain what can be discerned by comparing two cams with the same duration @ .050", but different @ .200"?

For instance, consider a cam, 236 @ .050", 150 @ .200", .340" lift, 108 lsa, as compared to a similar cam, but 152 @ .200".

Does a degree @ .200" make more or less difference than a degree @ .050"? I’d guess more. If so, how much? Does 2 degrees @ .050 have about the same impact as 1 degree @ .200"?

Thanks, Danny
trmnatr

Re: duration @ .050"/ .200"

Post by trmnatr »

dan miller wrote:Could someone please ‘splain what can be discerned by comparing two cams with the same duration @ .050", but different @ .200"?

For instance, consider a cam, 236 @ .050", 150 @ .200", .340" lift, 108 lsa, as compared to a similar cam, but 152 @ .200".

Does a degree @ .200" make more or less difference than a degree @ .050"? I’d guess more. If so, how much? Does 2 degrees @ .050 have about the same impact as 1 degree @ .200"?

Thanks, Danny
This is IMO, Im not a cam grinder

The bigger number @.200" will have more area up top than the first cam but the first cam will usually be easier on parts but is not always true.

I have one grind that is FAST off the seat but slows down for high rpm stability and higher rocker ratios but then again I have another one that has more @ .020" and .200" but they open at the same rate just cam 2 closing side is much longer.

Camshaft 1 (makes great torque and works good with higher rocker ratios and high rpm)
307/313 @.020"
278/284 @.050"
198/204 @.200"
.452"/.452" lobe lift
.678"/.678" with sbc 1.5's

Camshaft 2 (makes great torque with 1.5's and will rpm well & can be used with high rocker ratios but takes more pushrod & spring with lighter valves than camshaft 1)
312/320 @.0175"
308/316 @.020"
200/206 @.200"
.4467"/.4467" lobe lift
.670"/.670" lift with sbc 1.5's

Just my opinion
BlitzA64
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Re: duration @ .050"/ .200"

Post by BlitzA64 »

I would ask the same question as the original post. I have two cams with 261 @.050 with 3* difference @.200
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Re: duration @ .050"/ .200"

Post by pastry_chef »

BlitzA64 wrote: Wed Oct 21, 2020 8:53 pm I would ask the same question as the original post. I have two cams with 261 @.050 with 3* difference @.200
Please post all the specs you have for both cams and details about your intended engine / application.
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Re: duration @ .050"/ .200"

Post by Stan Weiss »

BlitzA64 wrote: Wed Oct 21, 2020 8:53 pm I would ask the same question as the original post. I have two cams with 261 @.050 with 3* difference @.200
With the same or different max lobe lift?

Stan
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http://www.magneticlynx.com/carfor/carfor.htm
Do you use engine simulation software that uses cylinder head flow files?
We have a package of more than 3100 DFW/FLW Files
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Re: duration @ .050"/ .200"

Post by Geoff2 »

Another 10 yr old thread?
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Re: duration @ .050"/ .200"

Post by BlitzA64 »

Could someone please ‘splain what can be discerned by comparing two cams with the same duration @ .050", but different @ .200"?

For instance, consider a cam, 236 @ .050", 150 @ .200", .340" lift, 108 lsa, as compared to a similar cam, but 152 @ .200".

Does a degree @ .200" make more or less difference than a degree @ .050"? I’d guess more. If so, how much? Does 2 degrees @ .050 have about the same impact as 1 degree @ .200"?
This was the question I was looking for the answer to for while searching so yes I brought the post back to see if someone had an answer. The question seems pretty straight forward to me but I guess gets lost in the translation.

Sorry I wasted the few seconds it took to read an old post that I found using the search option everyone bitches about others not using and thanks
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Re: duration @ .050"/ .200"

Post by frnkeore »

I too, am interested in this and would like to know more about it.

More .200 duration, usually means more lobe lift and faster ramps. To take advantage of it, you would normally go to larger lifters, larger than the the usual .842 profiles.

How much more spring pressure does it take to increase .200 duration? Would there be a "rule of thumb" amount say, in percentage?

Thinking of it logically, I would think you would get higher hp, with longer .200 duration and higher lift and a wider torque band with less overlap, maybe at the expense of less valve train life?

Are there any dyno comparisons, using the same .050 duration with greater .200 duration.
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Re: duration @ .050"/ .200"

Post by pastry_chef »

A bit like asking how high is high, it depends.

I'm known for being a deep searcher. :)

Some great comments here: viewtopic.php?t=12012

Mike Jones stated -

"Since the .200" number changes with the design, and is not only a product of the required duration, but the required lift, it can't be calculated without all the info on the engine and the cam you are running now."

"Too much lift at any one point, and the pressure differential gets too low. Not enough lift, and it gets too high."
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Re: duration @ .050"/ .200"

Post by digger »

pastry_chef wrote: Thu Oct 22, 2020 8:29 pm A bit like asking how high is high, it depends.

I'm known for being a deep searcher. :)

Some great comments here: viewtopic.php?t=12012

Mike Jones stated -

"Since the .200" number changes with the design, and is not only a product of the required duration, but the required lift, it can't be calculated without all the info on the engine and the cam you are running now."

"Too much lift at any one point, and the pressure differential gets too low. Not enough lift, and it gets too high."

Doubt in practice you’d get a top end power loss with too much intake lift if duration seat / 0.050 doesn’t change appreciably might be diminished returns and eating itself alive
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Re: duration @ .050"/ .200"

Post by gmrocket »

Not sure lift has to be more if the .200” is greater

Plenty of cheater cams have bigger .200” numbers with less lift than those with smaller .200” specs and more lift
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Re: duration @ .050"/ .200"

Post by frnkeore »

gmrocket wrote: Thu Oct 22, 2020 11:04 pm Not sure lift has to be more if the .200” is greater

Plenty of cheater cams have bigger .200” numbers with less lift than those with smaller .200” specs and more lift
This is what Howards and Comp list for the .875 lobe for .050 @ 260.
-----------Ave .050 .200 Lobe 1.5 - 1.6
Howards - 288 260 177 0.400 .599 .639

Comp cam 286 260 176 0.385 .578 .616
So, the lift isn't set in stone but, in general, with the exception of lift rules, the higher .875 lifter rate will in general have a higher lift than the high lift .842 lifter cams.

The opening side of the lobe, doesn't mean as much to me my only concern, is the closing rate. Do the cam makers slow the closing rate, with the .875 and larger diameter lifter lobes?
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Re: duration @ .050"/ .200"

Post by frnkeore »

I would be interested in what Cam King thinks about how the .200 duration, effects engine performance and if what I suggested, might have any relevance:
Thinking of it logically, I would think you would get higher hp, with longer .200 duration and higher lift and a wider torque band with less overlap, maybe at the expense of less valve train life?
This is a cam that I'm having Howards make for me, using 1" mushroom lifters, in a SBF, with 280 cfm heads and four 4412's on the Holley 300-275 TR. The intake lobe is for a 1" lifter and the Exhaust lobe is a .904 lobe.
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Re: duration @ .050"/ .200"

Post by learner1 »

Frnkeore..

The quote you posted from Mike "Too much lift at any one point, and the pressure differential gets too low. Not enough lift, and it gets too high."

This is why designing the opening and closing profiles based on the rod ratio is so important. The flow bench isn't the only tool that gets used incorrectly..the dyno does as well. It's not always about how much power but how fast the engine revs and recovers from a shift. Just because there's no power increase doesn't mean the engine won't perform better.
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Re: duration @ .050"/ .200"

Post by ClassAct »

frnkeore wrote: Sat Oct 24, 2020 5:17 pm I would be interested in what Cam King thinks about how the .200 duration, effects engine performance and if what I suggested, might have any relevance:
Thinking of it logically, I would think you would get higher hp, with longer .200 duration and higher lift and a wider torque band with less overlap, maybe at the expense of less valve train life?
This is a cam that I'm having Howards make for me, using 1" mushroom lifters, in a SBF, with 280 cfm heads and four 4412's on the Holley 300-275 TR. The intake lobe is for a 1" lifter and the Exhaust lobe is a .904 lobe.

Where did you get the mushroom lifters???
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