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Help with Cam selection (again) |
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Greyhounds_AMX 
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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 Posted: Oct/11/2018 at 1:56pm |
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Yes, there's a nice chart available courtesy of David Vizard:
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1968 AMX 390 w/T5
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Sonic Silver
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Joined: Nov/23/2011 Location: East Tennessee Status: Offline Points: 7949 |
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Posted: Oct/11/2018 at 2:10pm |
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Ken_Parkman
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Joined: Jun/04/2009 Location: Ontario Status: Offline Points: 1813 |
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Posted: Oct/11/2018 at 2:24pm |
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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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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/11/2018 at 2:32pm |
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/11/2018 at 11:50pm |
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You can have my Hurst shifter when you pry it from my cold dead hand.
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/11/2018 at 2:33pm |
Whoops--guess I should have waited for Ken's response before asking my last question about DCR and detonation...
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You can have my Hurst shifter when you pry it from my cold dead hand.
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/11/2018 at 2:57pm |
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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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You can have my Hurst shifter when you pry it from my cold dead hand.
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AMXrated
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Posted: Oct/11/2018 at 3:30pm |
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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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You can have my Hurst shifter when you pry it from my cold dead hand.
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Greyhounds_AMX
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Posted: Oct/12/2018 at 10:31am |
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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1968 AMX 390 w/T5
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Greyhounds_AMX
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Joined: Nov/14/2009 Location: Kansas City Status: Offline Points: 1268 |
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Posted: Oct/12/2018 at 10:37am |
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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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1968 AMX 390 w/T5
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AMXrated
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Joined: Jul/26/2015 Location: Indiana Status: Offline Points: 290 |
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Posted: Oct/12/2018 at 11:00am |
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"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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You can have my Hurst shifter when you pry it from my cold dead hand.
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Greyhounds_AMX wrote:
