Author Topic: Cam selection basics  (Read 6063 times)

Offline Chryco Psycho

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Cam selection basics
« on: May 12, 2002 - 12:46:53 am »
I keep getting asked the same ?s so I will try to explain the basic principals of cam design & selection. The cam is basically the heart of the engine and controls the power. It is also 1 of the least understood parts of the engine.
There are 4 parameters in the design of cams - duration, lift , overlap, & centerline.
1] duration - this is the most important aspect of the cam as it determines what rpm the cam works at , this is the # of degrees that the valve stays open measured in crankshaft rotation. When selecting a cam this is the first thing to consider determine what you use the engine for & be honest or you will be disappointed with the performance !!
This works as a guide & the numbers are approx as centerline, porting, roller cams etc. will vary the results a bit.
Advertised @.050 RPM
240 - 250* 200 - 210* idle - 4500
250 - 260* 210 - 220* idle - 5000
260 - 270* 220 - 230* 1300 - 5400
270 - 280* 230 - 240* 1500 - 5700
280 - 290* 240 - 250* 2200 - 6000
290 - 300* 250 - 260* 2700 - 6200
300 - 310* 260 - 270* 3000 - 6500
310 - 320* 270 - 280* 3500 - 7000+
The peak Hp will be reached approx 500 rpm before the max rpm & the peak torque will be reached approx 1500 rpm before max rpm, the other secret to making power is to match all the other components such as intakes, headers ,head work converters to work at the same rpm so the whole package works together, you will be disappointed if you match an intake rated for 4500 rpm max with a cam that starts working at 3500 rpm!!
2] lift - this is how far the valve is lifted from the seat, lift does not affect the rpm the engine works at but the more the better at a given duration , Mopar cams use a wider lifter so the valve can lift faster than other makes. UltraDyne , Hughes & Mopar all have cams designed to take advantage of the wider lifters Also the Mopar heads stop flowing more air or the valve becomes invisible to the air flow around .550 lift without port work.
3] overlap - this is the amount of degrees both of the valves are open at the same time & this is done to use the velocity of the exiting exhaust to help pull in the new air/ fuel mix this effect works better with higher rpm which is why the overlap increases with bigger cams, but the increase also hurts idle quailty & causes the lope when the engine is running. Larger headers will also hurt this effect by decreasing the velocity & resulting vacuum.
4] centerline - this is the least understood aspect of cam design & to over simplify the higher the # of degrees the longer & flatter the power band becomes [eg 115*] & the lower the # the shorter & more peaked the power band becomes [eg 106*] for example a 115 cam may give you 300 hp from 3500 - 5500 rpm with a peak of 375 hp where a 106* cam would give you 275 hp from 3500 -5500 rpm & a peak of 395 hp [these figures are arbitrarily made up] I prefer the long flat power band , it works well with the long mopar rods & gives pull everywhere but if you have ideal gearing & 5 speeds in the trans to decrease the rpm drop between shifts the car should run faster with a lower centerline cam.
Generally choosing a smaller cam will hurt you less than choosing a cam that is bigger than you need.

If you have more ??s , ask!!



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Offline Chryco Psycho

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Re: Cam selection basics
« Reply #1 on: October 02, 2012 - 09:32:06 am »
The main reason I stick with Lunati is Harold , he was the one of the first to take advantage of the wider Mopar lifter & increase the ramp speed accordingly although I am sure Mopar engineers understood the advantages in the 50s when they designed the V8 engines . Harold started UltraDyne & I could see the advantage of using UltraDyne cams years ago , but UltraDyne went out of business & I printed their online catalog before it was removed from the internet . Hes was hired by Lunati at the time he closed his own business , Ulradyne . Since then many have copied him with Mopar specific grinds having more lift at the same duration . Most Comp Cams designs for Mopar are copied from the small block Chev, you can find the exact same grind in both the Mopar & small block sections although they are starting to change , the SBC has a very short rod ratio & needs a totally different cam than the Mopar , it is just lazy to copy the SBC design for Mopar . Harold has created a whole new series of cams for Lunati for all makes of engines which is sold as VooDoo as well most of the UntraDyne profiles can be found in the Lunati catalog still . There is a section around pg 185 with various lobe profiles in Hyd & Solid lobes specifically for the 904 lifter Mopars & AMC

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Offline ChallengerHK

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Re: Cam selection basics
« Reply #2 on: October 02, 2012 - 03:06:36 pm »
Good info, Neil. Thanks.


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Offline MEK-Dangerfield

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Re: Cam selection basics
« Reply #3 on: October 02, 2012 - 04:09:40 pm »
Man, you dug up a 10 year old thread. I think we have a new record here.   :swaying:

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Offline jdavis2169

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Re: Cam selection basics
« Reply #4 on: October 02, 2012 - 05:10:23 pm »
Thanks for digging up the post and all the info. I was trying to figure out how to pick a can and you just showed me the way. :cheers:

Offline Chryco Psycho

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Re: Cam selection basics
« Reply #5 on: October 02, 2012 - 07:10:28 pm »
 I cannot believe it was 10 years ago that I wrote that  :eek2:     Where did that decade go  :clueless:
The info has always been here LOL
« Last Edit: October 02, 2012 - 07:15:16 pm by Chryco Psycho »

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Offline Aussie Challenger

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Re: Cam selection basics
« Reply #6 on: October 12, 2012 - 08:30:04 pm »
Info like this is critical to the novice and these answers are what is behind the questions that get asked all the time. Maybe it should be put up there as a sticky so it can be found more easily.   :2thumbs:
Dave

Offline 1BADFISH

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Re: Cam selection basics
« Reply #7 on: October 12, 2012 - 09:29:11 pm »
Hey Neil, speaking of Lunati what is the number and guy I ask to speak with so I can order my cam. I been meaning to do that for 2 years lol. I think I have the grind info, but will touch base with you again before I order.   :2thumbs:

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Offline Chryco Psycho

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Re: Cam selection basics
« Reply #8 on: October 14, 2012 - 12:58:55 am »
Steve Slavik or Jeff in tech .
 It was so long ago I have no clue what we picked to fix your engine !

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Offline Tonker1

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Re: Cam selection basics
« Reply #9 on: October 21, 2012 - 05:33:42 am »
Awesome write ups on the cam, enough detail to be use full and make sense! Also thanks for pointing out the major difference between Voodoo and Comp Cams, I've been wondering about that for a while.

Offline Chryco Psycho

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Re: Cam selection basics
« Reply #10 on: December 04, 2012 - 08:48:58 pm »
Further to this is the Chev is a short rod engine with a 1.45 rod ratio
Mopar is typically in the 1.7 - 1.8 range  with much longer rods  .
 This changes a number of things , @ both TDC & BTC the piston moves much slower & actually stops for a longer period of time this does 2 things it allows more time for complete burn of the fuel & moves away slower allowing more time for the pressure to work on the piston which results in increased torque & decreased fuel consumption ! If you have driven an older GM pick up you are lucky to get 9 MPG while a 440 can get into the teens & sometimes into the 20s , the best I have done so far is 24 mpg in a 440 Challenger on the highway & 512 " strokers pushing high teens on the highway even with dynoed stupid power .
 The downside to long rod engines is the intake , the piston moves away slower so the engine tends to pull less hard on incoming air flow . Ever notice that the 440 Port is only slightly larger than the Chev small block while the 454 , 455 , 460 even the 351 boss have Huge intake ports ? The trick is velocity  , by using a smaller port the air speed in the port is higher so the air flow is kept moving even when the valve is closed building pressure behind the valve & creating a mild supercharging effect . conversely the short rod engines pull air better so having a bigger port with more air available makes sense .
 Back to the cam choice do you really think a cam designed for a short rod engine is ideal in a long rod engine ?

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Offline Super Blue 72

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Re: Cam selection basics
« Reply #11 on: December 04, 2012 - 10:54:17 pm »
Great info! Thanks, Neil!  :thumbsup:
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Offline mrbill426

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Re: Cam selection basics
« Reply #12 on: February 17, 2013 - 11:10:47 pm »
Yes thanks, very well explained  :wave:
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Offline blown motor

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Re: Cam selection basics
« Reply #13 on: February 20, 2013 - 10:26:29 pm »
I'm fairly new here and I'm not a motorhead. All of your articles in the Archives section are facsinating. Thanks CP
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Offline TinCuda

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Re: Cam selection basics
« Reply #14 on: February 20, 2013 - 11:03:42 pm »
 :popcorn:  Nice


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