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Camshaft Lobe Width? |
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Trader 
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6881 |
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 Topic: Camshaft Lobe Width?Posted: Mar/01/2019 at 4:22pm |
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Actually priced the custom grind today and as it would not come as part of a cam/lifter kit it's $140 more. A little much so started looking at off the shelf with new found knowledge and the Lunati 10100276 would be very close with the ICL at 104.
More lift does not necessarily make more power. Timing events make the power. Decision time I guess. Thanks for everyone's input.
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Shawn_Watson
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Joined: Dec/05/2018 Location: Carlsbad, NM Status: Offline Points: 117 |
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Posted: Mar/01/2019 at 11:05am |
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Interesting. If I were doing a 9.5:1 401 with stock heads and exhaust manifolds, I'd probably default to Howard's .903 lobes for something like 271/271 at .006, 224/224 at .050 on a 107 +5 without looking at calculators. The lift ends up being .552 so that probably wouldn't work without changing the rockers, though.
I wonder if running numbers like you are would make me see something worth changing. I'm pretty sure it wouldn't be considered a "sleeper" cam
 Edited by Shawn_Watson - Mar/01/2019 at 11:07am |
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Trader
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Posted: Mar/01/2019 at 8:33am |
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This is a combination of several tools:
1) a calculation in crank torque moments by degrees based on input of stroke, bore, rod length. This is based on 100% efficiency but does give the highest torque angle as a start point. 2) based on this angle, using Greyhounds posted information on cam aggressiveness for bridge rockers, calculate the duration required. Also using his insight to calculate the best point to open the exhaust valve - thanks Greyhound. 3) based on the duration and the aggressiveness come up with the @0.050" 4) Calculate the dynamic torque with an online calculator and tweek for near 8.0:1 DCR 5) Plug everything back into the crank torque to get kw pressure. 6) Plug that into an engine HP conversion and get some numbers that you would never know true unless you put it on a dyno after the build. Easy!!! After all this I got thinking yet again and changing my exhaust duration to 268 and 221@0.050 to reduce overlap and move the opening to 19 ATDC, close 69 BBDC, Lift reduction to 0.476" ups the DCR just a hair but delivers 5 HP more (says 8 HP but I still don't believe it). Any less duration seems counter productive unless I change the LSA which in turn reduces overall HP for street application RPM's. Any more duration seems counter productive as it opens the exhaust early and you loose HP also.
Edited by Trader - Mar/01/2019 at 9:19am |
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Shawn_Watson
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Posted: Mar/01/2019 at 7:42am |
What are you using for this? Shawn
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Trader
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Posted: Feb/28/2019 at 9:16pm |
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Yes, there are a few calculators that use 0.006" vs 0.009" on the lift point.
Anyhow, I was talking today with several cam manufacturers and my heads a spinning. Doing my own math for my 401 and bridge rockers: 273 duration intake and exhaust, KISS. 111 LSA, 107 ILC Intake open 29 BTDC, close 63 ABDC Exhaust open 71 BBDC, close 21 ATDC 224 @0.050 0.485" to 0.493" lift Have not looked for this cam yet but the math put 7.9:1 DCR with everything else and 83% of usable power stroke which turns out to be quite good. This in turn math wise looks like 460 HP @ 4500 RPM but I believe the math is being way too optimistic. Different formulas, VE, heat loss,valve size, put this at 412 ftlbs torque - fairly flat on the power band and 420 HP at 4700 RPM. Need to go back to math class!!! Head hurts - good night,
Edited by Trader - Feb/28/2019 at 10:03pm |
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Sonic Silver
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Posted: Feb/28/2019 at 8:30pm |
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Trader
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Posted: Feb/28/2019 at 7:44pm |
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No everyone is doing the math right. I just was trying to get the most DCR out of a Howard's cam without looking at the exhaust event.
Turns out that peak torque on a 401 happens at 24 degrees ATDC between 1200 and 5500 RPM (very flat actually) and diminishing returns happen rapidly after 42 degrees BBDC. Opening at 80.5 degrees BBDC would be a 10% power loss. The difference between 80 degrees BBDC and 70 degrees BBDC is 6% power at the crankshaft. Actually doing the math is quite interesting that between 80 degrees BBDC and BDC there is only 20% left of total power available. Stroke length makes a huge difference on were power is delivered. I'll look at other cams, but really want the correct lobe width.
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Sonic Silver
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Posted: Feb/28/2019 at 6:58pm |
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I'm getting 80.5 BBDC EVO with 8 degrees advance also. What are we doing wrong? My way of figuring events may be wrong? I take the duration of 277 and divide by 2 to get 138.5, then I add the lobe separation angle of 114. 138.5 + 114 = 252.5, then I subtract 8 degrees advance 252.5 - 8 = 244.5. I subtract 180 degrees from 244.5 to get 64.5 degrees for the intake closing figure (244.5 - 180 = 64.5.)
That gives an intake opening of 32.5 BTDC.(32.5 + 64.5 + 180 = 277 intake duration). The 8 degree advance gives an EVO of 16 degrees greater than 64.5, which is 80.5. Now 180 + 80.5(exhaust open) + 16.5 (exhaust close) = 277 exhaust duration. Hard to explain. |
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Greyhounds_AMX
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Posted: Feb/28/2019 at 5:20pm |
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Almost every current tech cam uses asymmetric lobes, with the opening ramp steeper and the closing ramp gentler. So when you calculate intake events for example you can't just divide the lobe duration in half on either side of the ICL. The opening side will be a little shorter (reducing the IVO), and the closing side will be a little longer (increasing the IVC point). It's useful to look at the EVO compared to other similar cams. For the cam you're looking at installed 4 degrees advanced at I'm coming up with an EVO of 83. For comparison purposes, here's some commonly used cams and their Exhaust Valve Opening point, all calculated using the same method: Isky 270-HL, EVO=70 Comp 268H, EVO=70 Comp 270H, EVO=70 Comp 280H, EVO =76 Comp XE268H, EVO=76 Edelbrock 2132, EVO=75 VooDoo 10100702, EVO=76 VooDoo 10100703, EVO=78 Crane H-272, EVO=80 The Howards cam you are looking at would open the exhaust earlier than all of these cams. I've had experience with the Crane H-272 (EVO=80) in a similar 401 with late model dogleg heads, Machine intake, free flows, Holley 750. It had virtually no valvetrain noise, but the exhaust was much louder than comparable 390/401 cars, and the throttle response was soggier than we expected. The idle was smooth with no lope, but was more "puff" than "pop". Also the car ran hotter than expected, which makes a little
sense if you think about the cylinder pressure energy not being converted to
work, but instead being dumped out through the exhaust port and soaking the
head with heat. Remember John Elle and his love of the Isky 270HL (with EVO of
70)? He was in Arizona heat and never had overheating issues - just something
to think about. Here's a comparison of the Howards cam advanced 4 degrees (in Blue) versus the same cam but on 110 LCA and 106 ICL (in Yellow). The intake lobes ends up in the same exact position (so you can't even see the Blue intake curve as it's covered by the Yellow).
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1968 AMX 390 w/T5
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wheelz
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Posted: Feb/27/2019 at 8:09pm |
not enitrely true. Howard's offers lifters in .903 and 904 diameters so be sure to order .904 I use Howard's lifters in all my engines especially the EDM on mechanical cams but do not like the profiles of their cams. I have Schneider grind my cams which is an old school shop but very accurate and proven profiles
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Trader wrote: