Just wondering which cam profile has a more aggressive ramp angle, the low cam or high cam. Of course the high cam has the higher lift bump, but which cam accelerates the valve quicker?

_SHig

Higher lift = higher accel
lower duration = higher accel imho

Just wondering which cam profile has a more aggressive ramp angle, the low cam or high cam. Of course the high cam has the higher lift bump, but which cam accelerates the valve quicker?

_SHig
S,

the difference in lift and the relatively "normal" shape of both the high and the low cam lobes indicates that the high lobes do have the more aggressive ramp.

Cool, thanks for the input hpro! So if the engine is safe at 8500 on the high cams, then 8500 on the low cams is cake.

_SHig

S,

the difference in lift and the relatively "normal" shape of both the high and the low cam lobes indicates that the high lobes do have the more aggressive ramp.

wrong

It's a function of the duration vs the lift.

Cool, thanks for the input hpro! So if the engine is safe at 8500 on the high cams, then 8500 on the low cams is cake.

_SHig

i think that would be extraordinarily bad

Please explain. I keep getting "that'd be fine" or "that'd be bad", but I'd love to understand WHY?

Are you saying that the low cam ramp is more aggressive?

Or are you saying that dropping off the high cam is the "bad" part?

What if I revved on low cam only to 8500 (on mod springs of course - hence the "IF" the engine is safe at 8500 etc etc...).

Thanks!

_SHig

Please explain. I keep getting "that'd be fine" or "that'd be bad", but I'd love to understand WHY?

Are you saying that the low cam ramp is more aggressive?

Or are you saying that dropping off the high cam is the "bad" part?

What if I revved on low cam only to 8500 (on mod springs of course - hence the "IF" the engine is safe at 8500 etc etc...).

Thanks!

_SHig

I have no idea what the specs are on the cams, so I'm just talking in general here. If you have two cams with identical lifts but one with a shorter duration, the one with the shorter duration will have to accelerate faster to reach that same lift since it has less time to do so.

I have no idea what the specs are on the cams, so I'm just talking in general here. If you have two cams with identical lifts but one with a shorter duration, the one with the shorter duration will have to accelerate faster to reach that same lift since it has less time to do so.

Of course this is correct, however the VE cams' low lobe has less lift AND duration. Also, even though the high cam may have a longer duration, there's more of a "coast" where there's little lifting or lowering going on.

So, the question stands...

_SHig

http://www.audietech.com/

campro plus

buy that and youll have all the answers you need

I'll check my Paypal balance immediately! <lol>

Groan. It just ain't that simple, boys and girls. There are LOTS of pieces to the puzzle. GIVEN THE SAME RAMP START in degrees (go look up the techie terms), the higher lift REQUIRES BY DEFINITION a steeper ramp. If the design engineer figures he/she can start earlier (greater total duration), then the ramp angle decreases. GIVEN THE SAME TOTAL DURATION, the low cams have a less aggressive ramp than the upper cams. YOU'D BE NUTS to leave the low cams "on" to redline; you might not even get there under load. What would be the point? The high cam is DESIGNED for the high revs and HP. The low cam is DESIGNED for low speed TORQUE. The spring isn't the problem on the way UP, it's in following the ramp ON THE WAY DOWN to get closed so it doesn't float. "Float" is just after the top of the lobe. Suggest you go search the 'net for cam stuff - try a bunch of keywords - and get the basics. I'm not chewing on you for being a newbie. If you've got some marbles upstairs, go play student and get yourself educated on cam technology. THEN you'll be able to ask pertinent questions and, if you're REALLY good, they'll get answered by maybe the 5-10 folk here (I'm not one of 'em)
Jer

I'll check my Paypal balance immediately! <lol>

Scott,

I would not be doing that if I were you... unless you are looking for a mid 3-zero balance in your Paypal.

http://www.audietech.com/

campro plus

buy that and youll have all the answers you need

Now Bigtom, seriously,

no matter what the motives, guy asks a simple (or even "simplified") question and the pointer is towards a US$ 3K+ solution?

Groan. It just ain't that simple, boys and girls. There are LOTS of pieces to the puzzle.
...
I'm not chewing on you for being a newbie. If you've got some marbles upstairs, go play student and get yourself educated on cam technology. THEN you'll be able to ask pertinent questions and, if you're REALLY good, they'll get answered by maybe the 5-10 folk here (I'm not one of 'em)
Jer

But this is exactly what you are doing here Jer! And worse, Scott is hardly a newbie.

As for the puzzle pieces, most anyone does know about them. Any time camshaft design is the topic of a thread anywhere, the thread runs upwards of 300 posts. The unoffcial Web-record was by the LS1 forum where 3 cam-design specific threads totaled more than 3000 posts before purged of useless posts.

STILL, Scott posted a very very specific question.

(I cannot delve into his motives or why in particular he did ask this question, this may be the topic of another thread).

Question was:

On N1 cams, does the large lobe has the steepest ramp angle or is it the small lobe that has the steepest ramp angle?

I did answer making my best estimation:

The large lobes have the steepest ramp angle. I am 99% sure for this on the exhaust cam and somewhat less-sure for the intake cam.

i think that would be extraordinarily bad

Chris, seriously, care to expand on it? You do now have extensive experience in this matter....

Heh... Looky what I started! :^)

The reason I asked the simple question was this: IF I didn't get a rev limiter (which I have ordered so now it's strictly hypothetical and moot except for a fun excercise) I was wondering if by using the 8969 window to drop from high cam to the low power-inefficient-breathing low cam at let's say 8500 (using N1s and springs), would it be bad? Exactly as Jerry mentioned, it wouldn't make power, and I was actually HOPING that it wouldn't be possible to maintain that RPM due to flow restriction. If the low cams stress springs and valves less than the high cams I'd guess that the answer is NO. However I keep getting differing _OPINIONS_ so I was hoping for a definitive answer.

I guess maybe now based on discussion I should clarify that I don't need to know which cam has the highest ramp angle, but which has the highest likelyhood of float.

_SHig

It has nothing to do with ramp angles. The real reason why it's not good is it stresses the valve train to have such a small cam spinning at such a high rpm.The valve spring has to open and close to fast because of such small lift and duration. When you have big cam on 8k it takes valves longer to open and close making it easer on the valvetrain.You might break the spring, retainer, valve guides or valves revving small cams @8-9k.It damages everything.. I don’t want to get to technical because alot of people won’t know what I am talking about.

It has nothing to do with ramp angles. The real reason why it's not good is it stresses the valve train to have such a small cam spinning at such a high rpm.The valve spring has to open and close to fast because of such small lift and duration. When you have big cam on 8k it takes valves longer to open and close making it easer on the valvetrain.You might break the spring, retainer, valve guides or valves revving small cams @8-9k.It damages everything.. I don’t want to get to technical because alot of people won’t know what I am talking about.


Don't pull punches, share your knowledge. I don't give a crap about "a lot of people". I have an BS in ME, so do your worst, hurt my brain. I dare you. Numbers make it better.

Here's a pic of N1s.

http://i160.photobucket.com/albums/t177/shigspeed/VE%20Swap/DSCF6975.jpg

Hmm... So your contention is that it has "nothing to do with ramp angles". Really? Explain what you mean by "The valve spring has to open and close to fast".

Maybe I'm using the wrong terms. I understand that under most if not all situations, you will NOT run into problems on the up slope. Based on the above pic, it seems like the big cams up and down slope are definitely steeper than the small bump's.

Now, though the big cam's slopes are steeper, there is a visibly more gentle transition from up to peak and from peak to down, so this helps keep the rocker in contact with the cam by minimizing acceleration, right?

Okay, now small bumps. The down slope transition from peak does by eye seem a tad less gradual than the high cam, but not hugely so. I'd love to see a linear graph of the two overlapped.

I guess the only thing left in the equation here that I can currently think of is spring compressive force. At high lift, you're going to have a higher force available to keep the rocker smooshed against the lobe. On the low cam, since the force is lower due to less deflection, if the retreating acceleration is identical to the high cam, you'll still be more likely to float becuase of this difference. Now, I do know that there's preload on the spring so even though it's a linear increase in force vs deflection, there is an offset value. With this in mind, and assuming the heights of the max lift is approx 30% higher than the low cam so we can assume that the max seating force (rocker to cam) is somewhere less than 30% lower on the low cam peak vs on the high cam peak. This could become significant, right?

So I pose another question: What is your GUESS as to what the rev limit on low cams only (N1 + springs) would be? The limit would be the point at which you get valve float, right?

Bring it!

_SHig