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  #31 (permalink)  
Old 04-04-2018, 12:37 PM
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So, getting back to the OP, the better performing cam would have the advertised and the .050 duration specs closer together. Example: 240 @.050, and 292 advertised is better than 240 @.050 and 312 advertised.

Of course, you also have to calculate lift into this equation because if two lobes have the same duration, but one has .500 lift and the other is .600 lift, the one with .600 lift would have a quicker rate.

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  #32 (permalink)  
Old 04-04-2018, 01:50 PM
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Quote:
Originally Posted by Greg T View Post
So, getting back to the OP, the better performing cam would have the advertised and the .050 duration specs closer together. Example: 240 @.050, and 292 advertised is better than 240 @.050 and 312 advertised.

Of course, you also have to calculate lift into this equation because if two lobes have the same duration, but one has .500 lift and the other is .600 lift, the one with .600 lift would have a quicker rate.
Thanks for the response, this is kind of what I was driving at with the question..

Really what I'm wondering is about powebans vs drivability.

If, say, there is a cam with 195 degrees at 0.050 and 270 adv.

And a cam with 215 degrees at 0.050 and 290 adv.

Then a better one with 250 at 0.050 and 270 adv. Will the better cam have the poweband of the bigger of the two with the drivability of the smaller two?

Not sure I'm making sense, but not sure what to expect from a better cam with more duration at 0.050 but the same advertised duration.
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  #33 (permalink)  
Old 04-04-2018, 03:01 PM
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That's right where funny marketing comes from. fudging the numbers can make things look like a different cam but they use the same lobe. They like to "adjust" where the numbers start measuring from to make things look different.

For example:
234/[email protected] 298/302 advertised .488/.510 lift the Edelbrock RPM cam.
234/[email protected] 292/300 .488/.510...from Summit Racing

Same cam.....

This cam is an old grind that has been copied tons of times. You see it everywhere from all different kinds of brand names and even some white box stuff. It's all the same cam with the measuring points adjusted.




Advertised numbers are usually from .006 but can be anywhere as there not an industry standard there.
That is why the .050 number comes into play as it's the accepted industry standard.

You won't be able to reliably calculate the numbers from .050 to advertised directly because you don't know where the advertised starts from. As a very very general rule of thumb, if all advertised duration figures come from .006 tappet rise(they don't) than the one with more lift from the same duration will make more power.

Like I said earlier. Open it faster, hold it open longer, close it faster will net the best power. Assuming you can control it with the spring.
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  #34 (permalink)  
Old 04-04-2018, 03:14 PM
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Thanks for the explanation. I understand fully what you are saying.

My question is more in regard to drivability , rather than power.

I'm not trying to compare cams with just a few degrees difference in advertised, but rather 10 degrees or more, but with the same or similar duration at 0.050.

Said another way: what happens if I add 10 or 15 degrees duration at 0.050 without adding any advertised duration?

What happens to the powerband? What happens with regard to drivability?

Understanding that these cams have more lift and will create more power based on the higher lift, but in the bigger picture, where does the meat of the torque curve go?

Does it stay the same because the advertised duration stayed the same? Or does it shift up because the duration at 0.050 increased?
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  #35 (permalink)  
Old 04-04-2018, 03:27 PM
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Well, that's a multi faceted question.
Take and look at this visual aid and thing about where the measurements are being taken from and visually think about how the shape of the lobe changes with duration and lift.

Generally speaking, increasing duration moves the cam working range up in RPM while lift lets in more air/fuel for the same amount of duration.

There is a point where the cam shape is so pointy, the lifter crashes into the side of the lobe and destroys it. So to make that work, you increase the duration to makes the ramp more gentle.

The one I've drawn on shows you about where the .050 numbers are calculated.

Watch this dude...


The area between the arrows and where the picture indictates the valve starts to open is the no mans land. marketing likes to play in the area to change the numbers so the cam seen different but hold the same shape.
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  #36 (permalink)  
Old 04-04-2018, 03:58 PM
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I agree with last several guys comments. But your question about driveability is a tough one because it has nothing, or very little, to do with max power.

My answer to your question about the best driveability comes down to determining the operating range that you want to run in. If you want a range of 1200-3000 for maximum driveability, then you need to pick a small cam. When you get into small cams, trying to find enough lift to still run decent at higher rpms turns problematic. The situation that Greg and Johnson describe is that a faster lobe ramp rate will increase performance is correct, but it takes longevity out of the cam. A cam with 50-60 more degrees of total duration than .050" is much easier on the valve train.

There has to be give and take depending on what your expectations for the cam are. Also the ICL and LSA play a large role in maximizing the performance at lower rpm's.
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  #37 (permalink)  
Old 04-04-2018, 09:22 PM
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Quote:
Originally Posted by 64nailhead View Post
I agree with last several guys comments. But your question about driveability is a tough one because it has nothing, or very little, to do with max power.

My answer to your question about the best driveability comes down to determining the operating range that you want to run in. If you want a range of 1200-3000 for maximum driveability, then you need to pick a small cam. When you get into small cams, trying to find enough lift to still run decent at higher rpms turns problematic. The situation that Greg and Johnson describe is that a faster lobe ramp rate will increase performance is correct, but it takes longevity out of the cam. A cam with 50-60 more degrees of total duration than .050" is much easier on the valve train.

There has to be give and take depending on what your expectations for the cam are. Also the ICL and LSA play a large role in maximizing the performance at lower rpm's.

Exactly. And to add to that, the term "driveability" is might subjective. The term is difficult to use when describing a cam alone. For instance, a long duration cam with a tight LSA equals large overlap. Add this to an automatic and 3.08:1 rear gear and you have driveability issues. BUT, install a 3k RPM converter and a set of 4.56:1 gears and that cam will be fine. I think the term/characteristic you're looking to define is valve overlap. Changing duration, or LSA affects the overlap which will pretty much dictate your driveability. Even tho you use LESS duration, if you tighten the LSA you will increase the overlap. In that case, you can decrease the driveability even with less duration. This is why I like using David Vizards cam method. You pick your overlap for the intended use, then use his calculations, working off the ratio between valve size and bore to determine your duration.
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  #38 (permalink)  
Old 04-04-2018, 09:48 PM
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lots of "random bits" of information here in the last few posts,,,
Lets do a comparison with real stats just to truly confuse you
2 engines to compare
NEW LS-7 small block Corvette engine 505 hp (not to be confused with LS-7 rat)
Direct comparison to my street engine in my 81 Vette sbc displacing 434 cubes,,,same enough in size

427 small cam hydraulic roller guessing specs
214 ish @ .050
1.7 or 1.8 shaft rockers netting .590" lift
more than 120 Lobe Separation Angle

nets smooth idle power from just above idle
peak power 6300 rpm
505 hp
Max torque around 4800 rpm


My Cam Solid roller 256 @ .050
.670/640 lift
Peak horse power @ 6500 rpm
peak torque around 4800 rpm
rougher idle
power from 1800 rpm same redline

My car idles at 1050 rpm the new style LS-427 small block idles just over 900 rpm

The new style engine runs down the highway without complaint at 1400 rpm
My old style sbc will run down the highway at 2000 rpm just fine

The LS has fuel injection, far superior to my 950 Holley
The new engine has a superior intake manifold with long runners
The new engine has superior flowing heads with bigger valves

because the LS has a tiny cam it produces a lot less power but way easier to drive

you decide how much power and how much inconvenience is tolerable

BIG NOTE:I have around 32 more duration but my peak power is only 200 rpm higher

theres a lot more to an engine than the cam
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  #39 (permalink)  
Old 04-04-2018, 09:57 PM
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GREG: 4.56 gears in my car would be totally useless on the street. May as well drive on marbles. I can be in 5th gear my 60 mph (Ive done 50) and it drives just fine. I will make a driving video with my car soon. Maybe a little traction testing also,,,

I wen from 2.73 gears to 3.50 gears for saving the clutch and most hair pin corners you slow to about 30 mph. I can come out of a hairpin using 1st gear if I can get enough traction. Also 3.50 gears give me a theoretical top speed close to 200 mph. Some place I will not likely ever venture
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