So, after rebuilding my engine and installing everything, i put the head on, bolted it down, and started doing the usual BS, needed to get my car running.

Well, that got me thinking about cams and cams profiles, valves and valve sizes... and on and on it goes.

I've noticed several times that the profiles for our cars require a different setup for exhaust and intake. ie the profile is different for each one. Why is that? i know that our exhaust valves are smaller than our intake valves and that exhaust gases are slightly different in form because of their "heated" nature. I also know about the gas laws and how gas has different "fluidit" and so forth. I'm wondering cause if the exhaust valve is already smaller, then shouldn't that take care of the gas temp difference already, right, and theres should be no need for a differnt cam profile? So why should the exhaust cam be different too? Does the exhaust gas really exit that much faster? My brain tells me its something to do with port sizes.


Basically, i'm lookin for a shakedown/crash course in cams for our cars. I've wondered for a while why they make such things as stage one N/A cams or the turbo grinds, when evertime i read something on them, someone says to just skip to a stag 2 N/A cam or equivilent. I know N/A cams are more aggresive because of what an N/A motor is trying to accomplish but why do shops make those other cam sets if they don't provide any significant gain?

Power is basically made through improving and engines efficiency at consuming/effecting and air fuel mixture, so what the heck is wrong with our engine to require an N/A cam...or are the manufactures the dumb ones? just wondering.

All postitions, theories, hypothesis, and ideas welcome.



I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

do a search for 'cam discussion'

I would post the link for you, but it wont load for me for whatever reason. I am sure you know how to use the search function, so I wont tell you all that crap. It was a discussion/comparison from a few years ago of just about every set of camshafts for the 420a motor.

Hope that gives you a little info.

-MIKE-

Stroked 2.2L

Thank you. Much appreciated.

EDit:

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=32&topic_id=91
I found one that matched nicely in the search but when i got to it it said moved to the above link. Well that link no workie.

I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

You really are a confused individual. 90% of what you posted is wrong on so many planes of existance. Quit trying to impress everyone with bullshit you dont understand. It only draws attention to the basics you dont know and are asking.

There is no rule of thumb that every single motor needs a different cam profile than the other motor. Now if you were asking why each cylinder has a different profile then the answer is quite clear when you remove the head and see the pistons at a different positions and we know they fire at different times. If the profile was the same then it would be hard to get the engien to run when all valves open at the same time. As for duration and valve lift, they are all the same. Quit reading the Camshaft section of better homes and gardens.

Exhaust valve is smaller for a few reasons. 1. its easier to push air out of a chamber than it is to vacuum it in. Lack of room in the combustion chamber. 3. Cam timing, larger exhaust valve requires the valve to close sooner to avoid hitting the piston. Makes scavanging effect more difficult. As for why the aftermarket larger valves work, that is becuase engineering dept design things to maximize production cost. And of course there are about a dozen other reasons.

Call up crower and have a detailed discussion with them and post thier response to you here!

I think you need to go re-read some magazine. Now that you clarify, you are even more clueless than i thought. I feel like I am talking to a 10 year old. Ask Teklein of DJtrickee they can spell it out for you

oK...I just want some info on the cams. Thats all. Not a bunch of junk. I searched and didn't find my answers.
I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

Its common sense why the exhaust cam has a different profile. You dont need a Forum to teach you the basic engine theory. If your an expert in gas flow then you already know.

Intake cams are used during the intake cycle of the clyinder. if they open too early, you will not have proper engine vacuum and you will get reverse flow. If they open too late and you will get insufficient flow.

Exhaust you want to open at just the right time and you want it to remain open to allow the exhuust pulse to create vacuum in the intake.

Each cam has a different purpose and must operate of diffent guidelines. As I stated once before intake air is harder to draw in than exhast is to push out.


Pick up any book on basic engine theory and you will find this info. Its even in my High School Automechanics book. Yes I still have that from 15 years ago.

Its just like the gases in a bomb. They are superheated and want to expand rapidly. That's the combustion part. The exhaust part is much the same from what i understand. right? I also know that velocity and volume are both important factors. Too big you lose velocity, too small you lose maxiumum volume. That's why you have the smaller valve (but mbetter preportioned valve for the state of the gases)

My question is: if you already have the smaller valve why is (and i hope i get it right this time) the lift and duration different? Why can't the lift and durtation be the exact same as the intake valve? That's the part i can't figure out.

Understand that i know it has to open at a differnt time as the intake so that the intake is closed when it opens so the exhaust goes out through the headers and not up into the intake.

I guess when i said profile it was the wrong term.

I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

wiki home page:http://www.2gnt.com/index.php?d=bullettdsm

OH, i will will give him points! As much as the system will let me. It is a mouthful and will take me a day or two to proccess but its exactlty what i was looking for.

I'm sry you did have to repeat. But the best teachers can do it a million times and never miss a beat. It does get old and i'm sorry. I'm tryin to learn this stuff so i can help make contributions. I've been reading the turbo manifold theory stuff like crazy. I love things like that. It fascinates me to the enth degree.

ps. can we make sure this info is right were someone else will need it in the future?

I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

No, i do not want what i posted anywhere but here in this post for the reason that I dont want to hear anyone read and misunderstand it like I am sure someone will then go run thier mouth about this or that.

Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

wiki home page:http://www.2gnt.com/index.php?d=bullettdsm

Ok, that's fine. Your info, your deciscion. Thanks. Do you care, after i get all this tucked away, i ask another question? Its pertaining to the design of an intake manifold, displacment and flow rate.

I love my car...
I love Horsepower...
I love reliability...
So why do i own a DSM again?

very nice job Terry

"Tutto fa brodo."

Todd Scungio
98 RS
15.173 @ 90.70 MPH

And also a 2011 Ralliart

I think Terry should right the book on 2GNT's. If he put all his knowledge in there, I dont think there would be anymore questions.

- Ryan