FASTONE

DenzSS, I do totally agree that to many guys buy too big a cam and too big of HEADS TOO!! Neither = MORE HP!!

MUSTANGEATER

iTrader: (10)

LOL!


I really wish the LS1 world had more Custom Engine guys, I can only name a few... Most people I've encountered just tell you go with off the shelf stuff or a similar deritative that they call custom. It's still a wonder to me how Renegade Mustangs run 8's in a 3000 lbs car with a Single Power Adder, heads that flow nowhere near a ported ls1 and 302 Cubes.

Bink

on with the show....

DenzSS

How about 40-odd years of development. Similar to the SBC...1955 baby. A lot of years to perfect it and new technology is still creeping in. There are still people out there racing on 40 year old cam designs. That is why you see one or two guys at the top and everyone else trading places in the lower ranks. The top guys are doing something right that the rest are missing.


We just now getting out of the niche market. More pros are getting into it and we'll start to see some real innovation soon.

FASTONE

OK I get it one cylinder at a time ,I still don't see 280 cfm?

DenzSS

Too large or small for you?

mshiznitzh

280 sounds about right to me, but I am lost in what you are looking for. Without know the flow rate of the heads I don't see us coming up with a cam. These flow numbers should not be peak flow but a flow that is like how you came up with the flow rate to fill the chamber. What I mean is I think how you came up to 280 is by saying that at t(0) (right pass tdc and the piston going down) the vaccum was at it's max and at the last t(before the piston hit bdc) vaccum had came to it's limt.

I think this is how you came up with the number am I right?

I think with ported heads the duration of the cam should need to be smaller than not ported head. Of couse this is saying everything is equal in ramp rates, lift, lsa between the two cams and that we where able to get to these 280 cfm (avg) with unported heads.


Hell I have been studying all night and maybe talking out my *** so I am going to bed now. I will check back in tomorrow.

PREDATOR-Z

Super interesting! I have to admit that I do not posses the engineering capabilities of quite a few poeple here. However after some 30 odd years of SBC and about 3 into the LS1 world of street/track/racing, I've been bashed a few times for sticking to my belief that high duration cams are not really necessary (somewhat unwaranted); and that big doesn't mean quicker or faster.
One thing I firmly believe is that parts do not work alone and the trick is to fine tune a bunch of them together in "perfect" harmony.
Here is where I agree with Colonel " Get in the ballpark, test, modify, test, modify, and it keeps going on and on and on"
Did I mention "money is a factor too, LOL "

Cstraub

iTrader: (1)

Denzss is starting out the way a professional engine builder does when designing his winning recipe. . . he has selected the maximum rpm that the bullet will see during competition, now he figures the neccecsary CFM it will take to make power. Armed with this information and by following steps you can build a "system matched" bullet. Selecting parts because "he posted this", or "my buddy the carpenter says it will work" is like making pot luck stew. . .yeah you may get lucky, but it may me $hit!!

Looks like this post has brought in some new views, Welcome Tahoe.

Chris
Stef's Performance

dazman

if cams are getting too big for the 346 motor then "how" is nascar making 750 hp with a 355? they have to have huge cams and HOGGED out heads for it to make that power, and i bet they couldnt imagine a cam that is TOO big ( compared to our aftermarket cams) because they already prolly have their pistons wedged all to hell now how it is. hell, nascar is restricted with carb limitations. think about what they could do if they were to get the full go ahead for max power.

by the way, i think ive learned more in this thread then in any other

mike

critter

iTrader: (9)

279 CFM to fill a cylinder that is 0.025 cu ft 3400 times a minute??? And you need calculus??? OK, I have to see the formula. I will PM. The only way this makes any sense is if you are looking at instantaneous CFM during the time the valve is open.

jimmyblue

iTrader: (11)

If the head flow numbers are for continuous then
you would need to "chop" that with an effective
valve-open duty cycle - balling up the periphery and
the instantaneous lift and the air column inertia
and all that happy jazz. Figure the valve effective
at something like 15-20% I reckon, what with the
time consumed by ramps. 224/720 duration at the
low-lift base is 31%, the integrated lobe profile is
smaller than that (area-under-the-curve) and high
speed effects, column inertia / resonance, etc.
would make it a pretty intractable analysis.

Cstraub

iTrader: (1)

Dazman,
The cup engines are in the 830HP range with a flat tappet. Camshafts are in the 240 range to 260 range depending on track. They spend more money on a bore and hone job then most here do on a set of heads and cam.

Chris

Ed Curtis

Then there's the cost of the coatings on the cylinder walls...

... huh? Did I say that? Nevermind...

Ed

DenzSS

Ok. Here's another thing to add to the cylinder fill discussion since people are getting a little confused about throwing a camshaft on top of this, opening and closing valves, etc.

Using stock configuration I gave at the beginning of this thread, the maximum piston velocity is 112fps (feet per second).

When the valve is popped off the seat as it begins to open, the air/fuel charge is moving at roughly 1100fps as it begins to equalize the pressure between the cylinder and the outside world.

We have a piston moving at 1/10 the speed of the incoming air/fuel charge. Comparatively we have a large amount of time to fill the cylinder.

Does that make any sense?

mshiznitzh

But that 1100fps is an instantaneous velocity that is dropping off fast. (At a slope much quicker than the piston is getting to it's max.) You think you could post up the postion function you used to get the piston velocity and air? A graph overlay could help out alot.


Or am I way off?

Bink

When the valve is popped off the seat as it begins to open, the air/fuel charge is moving at roughly 1100fps as it begins to equalize the pressure between the cylinder and the outside world.



Where did 1100 fps come from???

DenzSS

It doesn't move at exactly 1100fps, just a raw estimate but it works for this discussion. When equalizing pressure, air travels initially at roughly the speed of sound (Mach 1 or roughly 1100fps). It does drop off from there, but it is still traveling a whole lot faster than the piston. In the configuration we're using for this conversation the piston never exceeds around 112fps ( or Mach .1).

Does that help give you a little perspective on the relative velocities?

Bink

Does that help give you a little perspective on the relative velocities?


Big help, thank you.

2002Z06yellow

nice discussion going on here.. i am keeping up .. getting the general idea...but i have a noob question... how can you tell that an enigine is over cammed?