hello dont know if i am in the right place for this question , i got a cam the specs are 230/244 @ .50 and 290/307 adv. duration, 112 ls with 4 degrees advance. what is the 4 degrees advance and how do u work that? any help would be very much apprciated!

 

theey have books for that, lol. I gots one but you gotta know what the parts of the engine are and some other stuff before you get into it. I was just reading some of it tonight. It's kinda hard to explain. basically your cam for the intake lobe center is 4 degrees more than your lobe seperation angle and your exhaust lobe center is 4 degrees less than your lobe seperation angle, I think that's how it goes anyway. lol, I can't even remember all I read.

 

I believe the 4 degrees advance refers to the fact that most aftermarket cam manufacturers grind thier street /strip cams with 4 degrees BTDC of advance already in them. It would be the same as taking a cam installed with 0 degrees advance and advancing it 4 degrees using the 4 degree BTDC keyway in a roller chain, though thier are a couple of otherways to do this. It helps thier cams retain more bottom end performance. All the events and specs remain the same they just occur 4 degrees before TDC. Hope that helps.

 

Don't try advancing it yourself because it'll probably either lose power, make the idle rough, or make it less able to pass smog. Cam timing is for people that know how timing works in the first place. I am learning how it all works right now and maybe when I am done I can post some simplified tutorials on how it all works and so you can actually pick something better than just some random timing that you think will give you more power.

 

Metaldrgn has it right, sorta.

Since the LSA of that cam is 112*, installing it "straight up" would be at 112* Intake Centerline.

Since the LSA is 112*, and the Intake Centerline (aka IC) is advanced 4*, then the IC is 108*.

Basically it's how many degrees of camshaft rotation the intake valve is at max lift AFTER TDC of the #1 piston.

The way to find out the Exhaust Centerline (aka EC) is to take the LSA X 2, then subtract the IC.

Since the cam is advanced 4*, the LSA is 112* and the IC is 108*, the Exhaust will be at max lift at 116* BEFORE TDC.
(112* x 2 = 224 - 108* = 116*)

The IC will always be ATDC, and the EC will always be BTDC.

So, for example, let's say you advance your cam ANOTHER 4* (for a total of 8*) by using a keyway on the crankshaft sprocket. Now the IC is 104* ADTC (LSA f 112* - Degrees advanced 8*), and the EC is 120* BTDC ( (LSA x 2) - IC).

This normally increases low RPM torque, and sacrifices upper RPM HP. It doesn't "make the idle rough, or make it less able to pass smog." I can't say for sure that it won't effect smog, but I've never heard of that. The only thing that will certainly effect that IS the LSA, and that can only be changed by re-grinding the cam.

A good rule of thumb from David Vizard...
If you advance the cam and see a remarkable improvement in LOW-MID RPM torque, then you've selected a cam that's too aggressive for the engine combo. If you retard the cam and see a remarkable improvement in UPPER RPM HP, then you've selected a cam that's too conservative.

For a street motor, it's usually better to be more conservative. The loss in power is less than if you "over cammed" the engine. Trust me.

But Metaldrgn is right about not messing with it. That's always the safe bet. Unless you have access to a dyno to do tests.

 

hey thanks aj and the rest of u for ur help im just not gonna mess with that anytime soon im trying to get the car started but cant cuz of ignition problems wont get online with the dfi gotta go spend some money dang!

 

Well you are almost right there too, but alittle off. The "straight up" term comes from the averge of the LCA's (lobe centerline angle rather than seperation angle as I previously posted wrong for someone else) of the intake and exhaust (I will double check tomorrow or the day after because I am working alot of hours this week and book is in my car). To find the LCA you have to find out at what degree the cam opens and closes plus 180 divided by 2 for the exhaust and intake strokes and then add them and divide by 2 for the average. Then you minus the LCA from the average to find the advance or retard (where positive numbers are advanced).

intake LCA - average = advance/retard timing
average - exhaust LCA = advance/retard timing

There is a lot more to cam timing than you could think of. It even gets as complex as to show you the importance of exhaust backpressure flow for higher performance and overlap timing for your situation. Like I said I am starting to get into it, but I am reading about an LT1 rebuild for my car before I really get into that book. I plan to put one in my camaro, redo ALL the wiring, make sure the smog system works, and change some other misc parts like electric window rollers, fuel pump, and get a LS differential with 28-spline nitride hardened (I think that's what they do to make it like 35% stronger) axles.

 

I only repeated what I read in David Vizard's book about valvetrains.

I guess he must be wrong then.

You can't dispute something based on "from what I remember, but I'm not sure if it's 100% right."

I've done the math numerous times with various cams to make sure I FULLY understood what he was saying.

We're not talking about LSA (or LCA... tomato, tamato, potato, patato), we're talking about IC (intake centerline). The intake centerline is where the intake valve max lift is in relation to the #1 piston ATDC, expressed in degrees of camshaft rotation.

What you're talking about is correct on how to find the LCA (or LSA ), but we're talking about the intake centerline (i.e. "advancing" the cam).

To find the LCA (what you're talking about), we need the timing figures of when the intake just begins to open (either .006" of lift or .050"), when is just closes, when the exhaust valve just begins to open, when it just closes, etc. etc.

You had it right, but you're thinking of a different thing.

Cool?

 

No, because that's the book I got lol

I read it wrong the first time. It's a good book, have you read it all yet? I'm still towards the beginning. did you get the book for the heads yet? I am thinking about buying it, but is it worth it?

The IC is the LCA of the intake stroke and the LSA is the seperation in degrees from the intake to exhaust. When I reread the first part I noticed that he didn't say anything about LSA when calculating timing. That quote you did from his book is good, but incomplete. It doesn't show how to get the LCA. It was just part of a previous answer. There is another example and i'll put it on after work if you don't first. Plus you can calculate the exhaust advance/retard too ya know. He does that too.


ALSO, like I said, it was what I had remembered from that book and I would double check when I have time. Maybe instead of going back and forth at each other, we can help each other to fully understand this. I see we both have some learning to do. I am going to bring a notepad with me today so I can draw out the figures to make it better understandable becuase I'm still alittle confused and I believe that unless you have years of experience in cam timing and the dyno tests to show it that anyone else who read it is too.

 

Yes I have the head book and yes it's worth it.

In my first post I never said anything at all about how to calculate LCA. I showed how to calculate the Intake and Exhaust centerline.

The LCA and the IC are NOT describing the same thing. LSA and LCA are.

They're two different ways of expressing how many degrees the lobes are split. Some people call it the Lobe Seperation Angle, and some call it the Lobe Centerline Angle.

The only reason I told daxfas26 how to figure out the Exhaust Centerline angle is because YOU started explaining it to him. I was just showing the right way, even though it wasn't necessary for you to mention it at all.

All he asked is
The first part of my answer told him

The rest was just trying to explain what you started to, but you couldn't remember.

I'm not trying to step on toes either. I'm just trying to explain the answer to his question, not confuse him with info he isn't asking about. :sillylol:

 

I'm sorry, I see what you are saying now. He doesn't make that clear when I was reading it so I think I got confused seeing how I've just started the book. In the beginning, from the illustration(figure 2.2 I believe), it looks like he is saything that the LCA is the Centerline. He mentions the CCA or crankshaft centerline angle which is the same as the LSA, but didn't say that the LCA had anything to do with it and I think there are some typos that make it seem like the LCA is the centerline. I finally finished my LT1 rebuild book so I can move onto that one. I've also got his book on building a gen I motor for power on a budget and haven't read that all the way either and I think it mentioned something about LSA and that's what confused me.