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#41
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ta man's post can relate to the subject of cam intensity here:
http://www.4secondsflat.com/Cam_Design.html Also related take note of what Harold Brookshire points out in his post number 6 here: https://www.chevelles.com/forums/13-...y-formula.html Also noted in this thread and important to keep in mind is the seat to seat or advertised specs can vary with different cam companies, already mentioned is .004" and .006". Then there is the ramp design as described here from Lunati and touched upon by Harold above.... SYMMETRICAL: is a term that refers to the "profiles" of the opening and closing ramps of a camshaft lobe. All "early technology" camshafts were ground on a symmetrical design, meaning both sides are exactly the same. That is to say the profile of the closing ramp is a "mirror image" of the opening ramp ASYMMETRICAL: refers to a camshaft lobe profile where the opening and closing ramps are not exactly the same. The reason some camshafts are this way is to try to achieve an opening ramp profile that has a high velocity and a closing ramp profile that has a slower velocity. In this way the valve can be set down more "gently" than the rate at which it was first opened. And important is to evaluate the duration at 0.200" tappet lift. That can open up a bucket of worms.... http://460ford.catsboard.com/t25901-...ation-200-lift I know Lee Atkinson who posts here and designs cams often compares the difference between the seat duration and the .200" duration. .
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
#42
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#43
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All good info.
I read and re-read David Vizard theory on camshaft selection. Good stuff to ponder. Wanted to test the waters here because you guys live in the real world. Theory doesn’t always translate into a street engine and chasing 8 hp isn’t that big a deal for me when one is at around 500 hp level. I do understand everything written here so don’t feel like you wasted any time here. I appreciate. And honestly with this virus I have more time on my hands to give myself a bigger headache. Lol |
#44
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There are differences between the big intake tracks like what you would see on a BBC or a Ram air V and a typical Pontiac head. The engine with big cross sectional ports like less seat timing and to keep velocity’s higher, usually use a little narrower LSA too. An E head Pontiac has a pretty small cross section on the intake to some other heads. Personally I don’t think Vizards BBC cam theory and Pontiac engine theory play all that well together.
The other guys mentioned the .2 specs and lift’s effect on the engine. If the engine has enough head flow and velocity the bigger .2 specs with the same seat and .050 timings can actually make the engine more docile. Extra lift can drop the power peak rpm and raise the average power some from filling the cylinders more. When you add good head flow to these bigger cams most people would be amazed how they do on the street. Doesn’t really sound like there are reasons to push the limits to much for your planned combo. Last edited by Jay S; 03-21-2020 at 01:38 PM. Reason: Edit |
#45
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#46
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I have confidence his theories and target math will work for most any platform.
With his Torque Master program comparing to "Pontiac" norms it is obvious most street Pontiac's are low on induction flow and valve lift for target displacement and RPM. It would be cool if one day TM can be used for valve timing for a Pontiac V8, the program has platform specific calibration. http://speed-talk.com/forum/viewtopic.php?f=1&t=46038 On page 4 an LSA comment from Len Caverly, a Pontiac builder with his own dyno and has competed in Engine Masters. Quote:
95% of those reading this here (street forum) would be thrilled with 11 something performance. For this a car that weighs 3700 ish pounds running a decent 455 engine, LSA does not "need" to be optimal. Hell, run 116 if you want. Last edited by pastry_chef; 03-21-2020 at 02:30 PM. |
#47
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Vizard is a big proponent of valve lift and points out a typical 2-valve ported cylinder head responds to valve lift without a sacrifice of idle and low speed qualities. So is Tilden Technologies:
"Once the four timing parameters are established, the cam should be designed for maximum lift." https://www.tildentechnologies.com/C...rformance.html Bottom line, the engine wants all the lift it can and thrives on it so run as much as mechanically achievable or unless prohibitive because of cost limitations. That said, this from Lee Atkinson in a related post from another Pontiac website. And note his comments related to valve lift and note his use of custom cams rather that a shelf cam with a ginchy name.... Topic: What are the defining factors to choosing the right cam? * Flow characteristics of the heads, to determine lift - It is silly to use a .450" lift on heads that flow well past .600". It is also silly, IMHO, to use high lift cams with heads (such as stock D-ports) that gain virtually no flow past .400" lift. * Performance goals of the owner - what RPM range do you need most power? People often chase some arbitrary "horsepower" number, and end up sacrificing a lot of lower RPM torque in order to gain a little of upper RPM HP. To me, the camshaft is the conductor of the performance. It should be selected LAST, and be designed to make the other parts work in harmony. There is no Magic-Cam that works best for everything. I've had about 100 cams custom ground over the last few years, and have only used a duplicate of a previous grind maybe 3 or 4 times. .
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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE Last edited by Steve C.; 03-21-2020 at 03:08 PM. |
#48
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"Doesn’t really sound like there are reasons to push the limits to much for your planned combo."
Agree, and for the most part much of this information from me is conversation around the coffee table. And pastry_chef's comment regarding using the wide lobe separation... if he does he can avoid stinky hair .
__________________
'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
#49
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#50
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But one thing that I got from Vizard was that tighter lobes gave you more overlap and that allowed more fuel into the cylinder starting at very low lift and up. Scavenging. |
#51
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#52
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“Lobe separation angles,” he continues, “are influenced by the camshaft grind. If a street car has smaller lift and duration numbers, they might run 112 or 114. Widening their separation angle helps increase upper rpm power output. Alternatively, if you are running a bigger camshaft to gain maximum top-end power, cam makers often suggest reducing the lobe separation angle to recover power lost in the lower rev range.”
https://www.enginelabs.com/engine-te...-relationship/ Offered for general interest only, some might suggest what you read on the internet regarding lobe separation does not apply to a Pontiac ! I've run a few combinations with a 108-110 lobe separation... never a complaint from the wife .
__________________
'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
#53
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Last edited by pastry_chef; 03-21-2020 at 04:19 PM. |
#54
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I didn't think so.
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#55
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I'm using a similar combination to start of string. But with 10.4:1 using Dave's KRE 85cc heads although with a 140 seat. Also using Dave's Old Faithful. My car is used as a streetable performer and I am very happy with the combination. Used a custom Bullet previous and although fun, the Old Faithful simply pulls better across the rpm range. Using a 10" Jim Hand Special behind a tired TH 400, for now :>).
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#56
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#57
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Sure do. Ground in 2010. 4/7 swap. Dur at .05 is 224 226. Gross lift .551 and .555. Dur at .006 is 284 277. Separation 112 for degreeing to 109. Grind No. PO 284/277-12HR. Part No. 507000. Designed by a member of this forum, but at the "other one" at the time. The cam was meant for crazy fun and low-end torque. Might have lost some higher rpm HP but gained below 4500. Used with Performer intake. Since then I swapped over to the RPM intake and other changes, which is why I changed to the Old Faithful. I don't have dyno numbers.
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#58
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144 @ .200 wasn't going to compete against the 160 @ .200 of the OF.
Intake HR284/367 284 224 144 .3670 .000 CRA Exhaust HR277/370 277 226 151 .3700 .000 CTA |
#59
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That's for sure, and seat of the pants agrees too. But, my goals (and other parts) were very different at the time and the Bullet was a hoot. And a lesson to me that "small" grinds can be awesome if designed accordingly.
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#60
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Follows right along with Cliff Ruggles general adage of not running under 230 degrees intake duration in a 455 based combo.
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__________________
'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 ) Old information here: http://www.hotrod.com/articles/0712p...tiac-trans-am/ Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine) 5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension https://www.youtube.com/watch?v=qDoJnIP3HgE |
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