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Help with Cam selection (again)

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Greyhounds_AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 2:56pm
Yes, there's a nice chart available courtesy of David Vizard:


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 3:10pm
Originally posted by Greyhounds_AMX Greyhounds_AMX wrote:

I disabled the static compression ratio limits on the spreadsheet and then it came up with just 4 off the shelf cams. Three really, as the Elgin and Summit are the same cam.

I couldn't get a very clear screen shot, so here's a link. I had it plot the smallest and largest just for fun.

https://lh4.googleusercontent.com/axs8EuRyZpoMEjfWkP_CVbDa4dQrOrUGvv0O2LIY-4O73ITwvdZL4nt_uU8=w2400

The revised Bullet cam came in at 8.25 DCR so it didn't make the cut.

….and the Howard's 223-.480 on 114 that I suggested and asked your opinion of earlier is identical to the Crower that you just posted.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken_Parkman Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 3:24pm
Be careful using dynamic compression ratio calculations, as cranking compression really tells you nothing about operating cylinder pressure and detonation resistance. Far more to it than that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXrated Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 3:32pm
Originally posted by Greyhounds_AMX Greyhounds_AMX wrote:

Yes, there's a nice chart available courtesy of David Vizard:



Ok, think I understand. 8:1 or less is the target for 93 octane and to ensure against detonation, right?  Based on that, the 3 cams in your spreadsheet should run with pump gas, correct?  

Looks like the Summit cam is targeting an RPM band of 2200-5500, the Crower is 1800-4500.  Can't find any specs on the Erson E710018 but I would guess it is going to be close to the Crower.

Sorry--I forgot to respond to your earlier question about what fuel I was going to run.  93 pump gas would be nice, but I am not opposed to running an additive or blending with E85 if it helped open my cam spec options.  

Thanks.

[EDIT]

Sorry--I think I was looking at the Summit 8601 cam specs.  The 8600 has an RPM range of 1,500-5,000.


Edited by AMXrated - Oct/12/2018 at 12:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXrated Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 3:33pm
Originally posted by Ken_Parkman Ken_Parkman wrote:

Be careful using dynamic compression ratio calculations, as cranking compression really tells you nothing about operating cylinder pressure and detonation resistance. Far more to it than that.

Whoops--guess I should have waited for Ken's response before asking my last question about DCR and detonation...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXrated Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 3:57pm
Noticed Crowers also has a 45243 cam that is a little more aggressive than the 45246.

Duration: 228/234
Lift: .512/.525
LSA: 112
RPM Range: 1800-4500, Redline @ 5K.

The 112 LSA would make for a rougher idle.  Wonder what the effect on DCR would be?

Greyhound, do you have that cam in your library?  Maybe your spreadsheet already eliminated it.

Thanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXrated Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2018 at 4:30pm
This is interesting--I filled out Crower's online cam rec form yesterday and they just replied recommending the 45243 Cam which I just posted info on.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2018 at 11:31am
Originally posted by AMXrated AMXrated wrote:

Noticed Crowers also has a 45243 cam that is a little more aggressive than the 45246.
Duration: 228/234
Lift: .512/.525
LSA: 112
RPM Range: 1800-4500, Redline @ 5K.
The 112 LSA would make for a rougher idle.  Wonder what the effect on DCR would be?
Greyhound, do you have that cam in your library?  Maybe your spreadsheet already eliminated it.
Thanks.

I've got pretty much every off the shelf catalog cam available for AMC V8's loaded in to the spreadsheet. There's only about 135 of them, so it's really not too much data. I've also loaded in a few interesting custom cams that folks have used.

The spreadsheet calculates something called Overlap Factor, which is probably the most accurate indicator of idle quality for a given cam in a given combination. It accounts for bore size, valve size, the flow capacity of the valves in the reverse direction, etc. So the spreadsheet sorts the cams in order of increasing Overlap Factor.

I extended the DCR limit to 8.3 and set the Overlap Factor range from 1.8 to 2.5, and that gives a pretty interesting group of cams to look at. I've got it comparing the 2nd Bullet custom cam with the Crower 85243.


Here's some key points that I noticed:
1) Flow Capacity: The Crower has about 4% less intake flow capacity because it's not a 904 lobe profile and runs a little less intake duration.
2) Overlap Factor: It's so close between the two cams that they should have the same idle.
3) DCR: The Crower has a lower DCR, which may allow you to run lower octane fuel.
4) EVO: The EVO for both cams is the same, and as the Overlap Factor is also essentially the same these two cams should have extremely similar power bands.
5) Intake H.I.: The Intake Hydraulic Intensity is higher (lower number) on the Bullet cam at 51, and actually in the more aggressive range as you would see on a VooDoo or Comp cam lobe. The slightly lower Hydraulic Intensity of 59 on the Crower will have lower valvetrain noise and lower risk of wear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Greyhounds_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2018 at 11:37am

Another thing that may help you is that for your application you can ignore the cam lift numbers. Any cam you use will be between 0.450 and 0.600 lift, and the flow rate of your heads peaks at about 0.450, so anything above that doesn't significantly increase flow. 

Certain relationships between duration and lift are required though in order to prevent mechanical problems, so lift will increase along with duration. There are exceptions (like dwell nose cams), but they aren't reliable or quiet enough for street use.

For example, here's a comparison of the flow you will get when using the lowly Edelbrock 2132 cam versus a much higher lift Engle, assuming your typical ported iron AMC dogleg heads. The peak flow rates are the same, only the increased duration adds to the flow area (the graph on the right). The increased peak lift doesn't really matter.



If we compare the same two cams again but with ported Edelbrock heads, you can see that the improved peak flow rates of the heads complement the increased lift of the Engle cam.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote AMXrated Quote  Post ReplyReply Direct Link To This Post Posted: Oct/12/2018 at 12:00pm
"only about 135 of them...really not too much data" Ha!

Thanks again for running the numbers for me.  Still very impressed with the spreadsheet--I work in business analytics so I know a good one when I see it.

I am really liking the specs on the Crower 45243.  Based on everyone's thoughts/recommendations it seems to hit the high points.  And, given the estimated DCR, it at least gets me closer to possibly using pump gas if everything else works in relation.  

Kind of wanted a cam that took advantage of the .904 lifter diameters, but based on the link that Phat69AMX sent, it looks like it has the greatest effect on gross lift and rate of lift if the cam is designed around that.

Are there any issues running narrower lobes on the .904 lifters?

Thanks again.
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