Lobe separation and lobe ramp speed
#2872765
01/11/21 06:16 PM
01/11/21 06:16 PM
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Joined: Apr 2009
Posts: 447 NJ
JCCuda
OP
mopar
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OP
mopar
Joined: Apr 2009
Posts: 447
NJ
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I'm replacing my solid roller cam in my 508. 4.250 stroke 4.360 bore, compression ratio 12.11 Edelbrock RPM heads Intakes flow 308 CFM, M1 4500 flange, 950/4150 Ultra XP., 2" pirimary tube TTI headers, 727 with 8" PTC converter flashes 56-5800RPM, 4.56 gear, 14 x 32 tire, weight with me in the car is 3378 lbs. 71 Cuda Race only. I spoke to 3 cam manufacturers. All 3 recommended similar cams.
#1 310/318 adv. 279/287@.050 .713 lift at the valve with my current rocker 1.67 ratio 109 lobe separation 31* between advertised duration and @.050 #2 314/316 adv. 278/287@.050 .708 lift at the valve with my current rocker 1.67 ratio 106 lobe separation 36* between advertised duration and @.050 #3 308/315 adv. 308/275@.050 .733 lift at the valve with my current rocker 1.67 ratio 108 lobe separation 33* between advertised duration and @.050 My current cam is 306/273@ .050 .694 lift at the valve with my current rocker 1.67 ratio 108 lobe separation 33* between advertised duration and @.050
With the current cam the 508 made 645 HP @ 6000 RPM and 643 Tq. at 4900 RPM and went as fast as 10.03/132 through the exhaust. My question's are what would be recommended for the Lobe Separation based on the small cylinder head, the weight of the car and the converter stall and any other variable that I may not be thinking about? My second question is how does the ramp speed affect the way the cam act's. I think the slower ramp is a little easier on springs etc.. Is there a good reason HP/tq. wise to want the faster ramp speed? This is a footbrake bracket car. Thanks
Last edited by JCCuda; 01/13/21 12:52 PM.
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Re: Lobe separation and lobe ramp speed
[Re: JCCuda]
#2872794
01/11/21 07:02 PM
01/11/21 07:02 PM
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Joined: Jan 2003
Posts: 6,150 Melbourne , Australia
LA360
master
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master
Joined: Jan 2003
Posts: 6,150
Melbourne , Australia
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Basing any comparisons off advertised duration can be misleading. There isn't really a standard, so some cam companies can define it differently. This information should be stated somewhere in the camshafts information.
Most when camparing camshaft profiles will look at the duration @0.200" and 0.050", along with the lobe lift. Generally speaking, the faster you can get the intake valve open, the more power you'll make, provided you can control its motion.
As for lobe separation, I would imagine it would need to be on the tighter side, but I'll leave that for someone whom is more knowledgable on your style of engine.
Alan Jones
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Re: Lobe separation and lobe ramp speed
[Re: JCCuda]
#2872796
01/11/21 07:06 PM
01/11/21 07:06 PM
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Joined: Aug 2003
Posts: 43,307 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,307
Bend,OR USA
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I wouldn't use any of those cams suggested on your motor Way more duration @ .050 than I would like, are any of those companies Bullett or Ultra Dyne? I have built and raced a street car with similar parts with less compression and more rocker arm ratio and net lift at the valves, that cam was 260 @ .050 with .420 lobe lift on the intakes and 266 @ .050 with .409 lobe lift on the exhaust lobes ground on a 108 LSA installed at 1.06 ILC with Harland Sharp 1.65 ratio roller rockers that had between .695 and .720 net lift at the retainers with checking springs, that cam flat work very well I did end up using the Crower solid roller lifters with the .820 wheels in them after breaking two Mopar Brand solid roller lifter wheels in half that had the smaller .750 diameter roller wheels in them Your car may be as fast or faster than my old pump gas Duster that weighed 3450 Lbs. with me in it, best of 10.09 at 127+ MPH through the complete exhaust system with the air cleaner on with the Eddy CNC ported RPM heads Me thinks they are recommending a BB Chevy type cam for you instead of one for your motor with your heads IHTHs
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Lobe separation and lobe ramp speed
[Re: JCCuda]
#2872955
01/12/21 01:25 AM
01/12/21 01:25 AM
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Joined: Nov 2015
Posts: 884 Missouri
jwb123
super stock
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super stock
Joined: Nov 2015
Posts: 884
Missouri
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Just to give a few ideas. With the duration cams given, you need to spin the engine pretty fast, so I am not sure the cylinder head flow will support the kinds of engine RPM the cams are ground for. and the 2 inch headers would seem a little small for that size engine. I am a big proponent of using engine software to design my engine combinations, taking time to put good exact numbers into the programs, before talking to the cam companies, and then putting their recommendations through the program as well, a few bucks on computer software is a lot cheaper than several cams and the cost to replace them. I really liked the camshaft recommended by Mike Jones " cam king", it was a little smaller on duration than most cams the other companies wanted me to use, and it gave me the best ET and MPH the car ever had. 540 with two AFB, NSS car 3200 lbs I went 6.03 @ 114mph in the 1/8, ran a string of 9.70's in high humidity and 90 degree heat this summer in the 1/4 as well.
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Re: Lobe separation and lobe ramp speed
[Re: jwb123]
#2873061
01/12/21 10:28 AM
01/12/21 10:28 AM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,514
So. Burlington, Vt.
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It’s a 508 with std port Ede heads and a std port intake.
It’s not going to peak at a very high rpm no matter how big the cam is.
The main hurdle with those heads is coming up with enough installed height to fit a spring big enough to allow a cam that’s fast enough/big enough to make much of a difference than what’s posted, or the current cam. The other issue is with the “big springs”, the integrity of the fairly small rocker stands would be a concern for me.
My guess is, there wouldn’t be too much difference in power from different cams with similar lift and duration, if they are all designed to operate with what is a “typical” spring used on those heads.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Lobe separation and lobe ramp speed
[Re: fast68plymouth]
#2873469
01/12/21 11:53 PM
01/12/21 11:53 PM
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Joined: Jan 2003
Posts: 5,486 SoCal
Brian Hafliger
master
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master
Joined: Jan 2003
Posts: 5,486
SoCal
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It’s a 508 with std port Ede heads and a std port intake.
It’s not going to peak at a very high rpm no matter how big the cam is.
The main hurdle with those heads is coming up with enough installed height to fit a spring big enough to allow a cam that’s fast enough/big enough to make much of a difference than what’s posted, or the current cam. The other issue is with the “big springs”, the integrity of the fairly small rocker stands would be a concern for me.
My guess is, there wouldn’t be too much difference in power from different cams with similar lift and duration, if they are all designed to operate with what is a “typical” spring used on those heads.
Yep, best power is changing the heads! Cam change won't net much if anything.
Brian Hafliger
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Re: Lobe separation and lobe ramp speed
[Re: Brian Hafliger]
#2873567
01/13/21 09:51 AM
01/13/21 09:51 AM
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Joined: Jan 2003
Posts: 10,020 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,020
Frostbitefalls MN (Rocky&Bullw...
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It’s a 508 with std port Ede heads and a std port intake.
It’s not going to peak at a very high rpm no matter how big the cam is.
The main hurdle with those heads is coming up with enough installed height to fit a spring big enough to allow a cam that’s fast enough/big enough to make much of a difference than what’s posted, or the current cam. The other issue is with the “big springs”, the integrity of the fairly small rocker stands would be a concern for me.
My guess is, there wouldn’t be too much difference in power from different cams with similar lift and duration, if they are all designed to operate with what is a “typical” spring used on those heads.
Yep, best power is changing the heads! Cam change won't net much if anything. This raises the question, will the block live with a substantial power increase? If you definately are going after more power with an rb(i assume) shortblock, i would be tempted to try a tunnelram, e85 or methanol, mechanical injection and maybe wrap all three into one package. I ran a mechanical fuel injection and used a carb with no boosters or fuel in it for a throttle body. Worked great. Picked up .25 et and 3 to 4 mph over a gas dominater. Going this way should be easier on the shortblock than bigger heads. Most of the gain will be torque in the same rpm range. If you have interest in this route pm me and i can help you avoid the pitfalls.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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