Eric's cam challenge
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No. That's not what I was speaking about. The industry standard for the given in the formula for calculating duration @ .050" is .750. Mopar performance used .850 for that given instead of .750. I used to know the formula off the top of my head, but I don't anymore. It's in the MP engine manual, which I am too lazy to go dig out.
Correct! Thank you.
junkyardhero
Well-Known Member
ah... i figured since we was on topic of this cam challenge and LS uses roller cam my lizard brain thought roller and then just ran off on that tangent.
per usual, kindly disregard my nonsense babbling!
It's ok. I've gotten used to it. LOL
You took it in the intent I meant it. Obviously, some got butthurt over it. lol
Interesting. I haven't heard of this. Wonder why they didn't just measure the @ .050" specs? Unless this comes from a time back before it was common to do so. Maybe this was used as a way to compare data from old catalogs or something?
It seems odd to provide a formula to calculate the @ .050" specs and then state "do not use". Unless all cams were ground with the same profile from seat to @ .050" ...
Nevermind, looking at it from todays perspective the whole idea seems short sighted but I kind of get why they may have done this.
RAMM
Well-Known Member
RAMM
Well-Known Member
Just a few thoughts..........
1. I never really look at this part of FABO (Racers Forum) but I am really surprised to see this topic. This is pretty cool that Eric's content even though its LS based has reached this far.
2. I often watch Eric's YT content and when he released the first video about his intent to do this cam challenge, I actually texted him basically in real time that I'd like to have a cam ground and enter. He moved so fast on this and being in Chinada, it wouldve taken at least 4 weeks for the grind to reach me and then another week for me to have it checked locally and probably another to ship it to him. I realized I would have never made the deadline.
3. Point 3 is neither here nor there because I would have not spec'd what performed best. In fact I would have came very very close to the intake duration and LSA, but never would have given as much exhaust split...and never mind the actual lobe design..I doubt my cam design would have been in the top ten.
4. Eric is a beast for taking on this task AND editing and uploading quality content. I still cant figure it out..LOL.
5. I imagine CamMotion's phone is ringing off the hook...
J.Rob
1. I never really look at this part of FABO (Racers Forum) but I am really surprised to see this topic. This is pretty cool that Eric's content even though its LS based has reached this far.
2. I often watch Eric's YT content and when he released the first video about his intent to do this cam challenge, I actually texted him basically in real time that I'd like to have a cam ground and enter. He moved so fast on this and being in Chinada, it wouldve taken at least 4 weeks for the grind to reach me and then another week for me to have it checked locally and probably another to ship it to him. I realized I would have never made the deadline.
3. Point 3 is neither here nor there because I would have not spec'd what performed best. In fact I would have came very very close to the intake duration and LSA, but never would have given as much exhaust split...and never mind the actual lobe design..I doubt my cam design would have been in the top ten.
4. Eric is a beast for taking on this task AND editing and uploading quality content. I still cant figure it out..LOL.
5. I imagine CamMotion's phone is ringing off the hook...
J.Rob
TT5.9mag
Two atmospheres are better than one
Great post.
Hopefully you can enter if he has another challenge which he’s talking about doing on a few different engine platforms.
I think the need for so much more exhaust threw a lot of the contestants off, one of the guy's felt it was cause of the smaller headers, I have no idea if he was right, think it was Brian Salter.
Newbomb Turk
Well-Known Member
I don't know why, but did notice all the top hp engine had at least 250 exhaust or more.
I'm trying to figure out how that would work ? Guessing along with flow, csa and velocity also wouldn't be factored.
If say you took a 340 with 318 heads vs X heads vs Trick Flows and ran the same/similar cams and cr with appropriate intake and exhaust systems. Could see making similar hp per cfm but the hp and rpm be vastly different from one another. Not saying your wrong just not getting how head flow (cfm/csa/velocity) don't play a major role in cam choice?
Newbomb Turk
Well-Known Member
The math some assumptions. It assumes the guy doing the math understands how to build an engine.
Surprisingly the math asks for rod to stroke ratio but not head flow. Think on that for a bit.
It also weighs more on stroke than bore size.
RPM matters, so the guy doing the math has to be honest about where he wants peak torque and power.
Did you happen to buy and read Billy Godbold’s book? He covers it in there. You just have to read between the lines.
And you have to read it all. If you don’t it might not make sense.
I mean I read it the first time and was almost half way through it and I thought how will this book ever teach how to pick a cam.
The answer is it won’t. It can’t. But what it can do is teach you what to consider when choosing events. It took me until 2/3rds of the way through before it started to dawn on me.
I’ve read the book five times already and parts of it many more times and I’m still gaining from it.
Plus the Taylor books, Obert, Larew and several others I refer to on a fairly regular basis.
As I’ve said before, looking at flow (and I suppose port size and even header construction) like it’s the end of the discussion then you are missing it.
One of the books I reference almost daily is written for engine builders. Actually most of them are. Some are engineering books. Those hurt my head and require reading many times across many years. And I still learn from them.
Think it through. It will come to you. Just visualize what’s happening right before the exhaust valve opens.
On the other side of it, visualize what’s happening right before the exhaust valve closes.
So basically it does in around about way, so if you pick the right parts (including head flow/csa/velocity) to make peak hp and torque at x & y rpm's with z cid the formula would help pick the right cam events as long you used the right top end.
This book ?
Newbomb Turk
Well-Known Member
They didn't start printing that in the catalogs until the late '80's when the duration @.050" became a "thing", up until the mid/late '80's the average guy didn't know about or hear it referenced often, or care. Mopar had settled on a basic lift rate by then, & that conversion was a pretty close hit on the actual measured duration, but......
If Your PurpleShaft is rated 280°@.015"Adv., but Your Comp Hi Energy is 280°@.006"Adv., they didn't want You correlating the cams because of either similar Adv. or @.050" ratings...they definitely will not perform or idle the same. Hence, they wanted You to follow the racer science formulas to select the right PurpleShaft for the job.
I have a Crane master catalog around here somewhere from like 1973 and it has .050 duration for every cam listed.
That's not what I stated, I stated the "average guy" wasn't talking picking cams based on the @.050" numbers, they were picking them based on the general advertised durations. Magazine articles started bumping up the awareness that for example, not all 292° cams are the same, the average Joe started actually looking at/for them.....the DC/MP catalogs or racing manuals NEVER published @.050" specs, putting the .850 conversion in there was the response to what I stated, which is 100% fact.
Using adv duration for comparison is pretty useless, because the tappet lift at which it is measured varies between cam companies & even for the same brand. Bullet use 0.0045" & 0.006", depending on the lobe series.
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