LS1IMPULSE

iTrader: (42)

I had another thread in here about installing a cam and after a discussion with another member I had a few questions that went un-answered. I had orginally asked about how to install the cam (dot-to-dot, advanced or retarded) and I was answered with this:

That answered my question but gave me a few more on how the cam works (which I figured no-one would answer in that thread about how to install a cam) so I made this one. Anyways here is what I posted back and am still wondering about:

LS1IMPULSE

iTrader: (42)

B-U-M-P...Still No Answers ?

Xtnct00WS6

iTrader: (8)

He's referring to valve events.

To answer one of the questions, to the best of my knowledge there is no difference between advancing the cam with an adjustable timing chain and having the advance ground in. Some people actually end up changing the advance/retard with the adjustable timing chain if the cam is ground with too much/too little advance. It's possible to order a cam with a +2 but end up getting a +3.5. In that case you can compinsate for this with the adjustable timing chain.

I'd bet most of the time when you see people saying "matching VE's" they're talking about to their application. Example...There isn't much point in buying a cam with 645 lift on the intake if your cylinder heads run out of breathe at around 600 lift. It would probaby work fine, but it's not an optimized setup. To fully take advantage of the high lift LSK lobes, you should *in my opinion* have high flowing cylinder heads.

LS1IMPULSE

iTrader: (42)

I'm reffering to VE's in terms on Valve Events caused by the cam not SD and MAF systems.

Im not looking for advice on a cam either I'm just trying to learn how the valve events effect effect the way the car will perform...For example, I saw Patrick G looking over a cam the other day and he said the overlap was exhaust biased, which I cant remeber what that caused in terms of the way the power was distributed but this is the type of thing I am tying to figure out...how all the different valve events effect everything.

LS1IMPULSE

iTrader: (42)

Thanks for the answer I wasn't to sure about that

Xtnct00WS6

iTrader: (8)

If you want to know if a cam is intake/exhaust biased you can take a cam like this for example: 230/236

236-230= 6
6/4=1.5 (result / 4 = number of degrees biased)

So this would be 1.5 degrees intake biased since it's the smaller of the two numbers. Someone please correct me if I'm wrong. It's pretty close to my equation above. I'm not sure what happens when you advance or retard the cam though. Maybe someone will chime in with that answer.

LS1IMPULSE

iTrader: (42)

I can't remember if I am right but I beleive Patrick said the biases can be determined from IVO - EVC

So for a 230/236 .598/.598 112 +2

IVO - 7 BTDC
IVC - 43 ABDC
EVO - 50 BBDC
EVC 2 ATDC
9 Degrees overlap

So if I am rigth this cam would have a 5 degree intake bias (im guessing intake since the most overlap is BTDC)

But what about the world of other VE, how do THEY effect how the car drives.

Patrick G

iTrader: (14)

First off, those valve events are wrong for a 230/236 112LSA +2 cam. They're actually this:
IVO: 5 BTDC
IVC: 45 ABDC
EVO: 52 BBDC
EVC: 4 ATDC
This cam has its overlap biased 1/2 degree to the exhaust side of TDC.

Here's a better illustration. Same cam, but different advances:
230/236 112LSA +4
IVO: 7 BTDC
IVC: 43 ABDC
EVO: 54 BBDC
EVC: 2 ATDC
This cam has its overlap biased 2.5 degrees to the exhaust side of TDC. This means it will be strong down low, but run out of breath faster after its power peak.

230/236 112LSA +0
IVO: 3 BTDC
IVC: 47 ABDC
EVO: 50 BBDC
EVC: 6 ATDC
This cam has its overlap biased 1.5 degrees to the intake side of TDC. This means it will pull harder and longer after its power peak.

LS1IMPULSE

iTrader: (42)

So it looks like IVO - EVC /2 will give you your bias with a negative number being the intake and a positive the exhaust? Do you know of any write-ups that will explain how all the other VE affect the cars perfromance?

And what about this question from the original post:
And what would it be better to add duration or lift since they both pretty much effect how long the valve is open what would be the difference in 232 duration .600 lift -and- 228 duration .630 lift (or whatever would allow the valve to stay open just as long as the first scenario)

also which calculator are you using to get VE's? The one I have must be wrong.

thank you for posting!

brad8266

iTrader: (23)

Wrong. He is referring to overlap bias.

Xtnct00WS6

iTrader: (8)

I'm pretty sure it's correct in terms of a rule of thumb to see if a cam is intake or exhaust biased. If it's not correct, do you know what it is?

brad8266

iTrader: (23)

You were talking about the cams duration split being more exhaust biased. What everyone else in this thread is talking about is the valve overlaps bias, whether it is intake or exhaust biased in relation to piston TDC. The overlap bias does have an affect a few things such as peak power rpm and low end torque. Overlap bias can be controlled to a point by changing the ICl.

Ragtop 99

iTrader: (7)

Your formula is wrong because it does not account for advance/retard. Overlap bias is based upon VE's: Bias = (EVC-IVO)/2

hammertime

iTrader: (1)

There are different schools of thought on how to select a cam for such a scenario. Conventional wisdom says that you want a cam that maxes out at the same point that flow maxes out. While that seems to make sense, it depends on the head. If your heads become turbulent or fall sharply after the peak, then that would work best. On the other hand, some heads just stall, or gain very little above .600 lift. In these cases, a more aggressive lift curve and higher overall lift allow the curtain area (area that is exposed to flow air) greater dwell time at a higher flowing potential. Time at the max lift where air has stalled, but is still flowing quality air allows greater filling than lower lift profiles.

Another way to compare cams is duration at .200 lift. .006 and .050 are industry yardsticks that allow general comparison of the profiles, but .200 lift figures can vary greatly between cams that on the surface appear similar. Two cams that have similar seat and .050 durations and similar LSA and ICL should also operate in much the same way. More agressive lobes have more duration at .200 and offer the potential to flow more air. Generally to keep valve acceleration under control, higher lift is also necessary.

The DCR calculator in my signature will also give VE's. Also, read up on the cam guide link there.

LS1IMPULSE

iTrader: (42)

thanks for the new calculator, but I this this link for the cams is a little more informative http://www.compcams.com/Community/A...?ID=-2026144213 but ive only made it to like page 5 so far.

Xtnct00WS6

iTrader: (8)

That link doesn't work.
Try this: http://www.compcams.com/Community/Ar...ID=-2026144213

LS1IMPULSE

iTrader: (42)

ls1tech is changing the address im putting in so copy paste these two parts togather in the url bar:

http://www.compcams.com/Community/Articles

/Details.asp?ID=-2026144213

hammertime

iTrader: (1)

I've seen that article before, and posted it in the Advanced Tech Forum.
Cam Design Theory from David Vizard
After reading it, I more or less applied its theory to a cam I had been looking into, and seemed to fit rather well. See that thread to see what tech's better contributors had to say.

LS1IMPULSE

iTrader: (42)

thats were i found it

eLTwerker

Why is overlap bias divided by two?