R_Andersen

I'm currently building a NA 383 for a 93 M6 Camaro and I'm trying to make a choice in cams. I live in NY and have to be able to pass emissions (roller test). I've decided on either the XE 224/230 or the 230/236 but I am unsure whether to go with the low or high lift version? I will be running a special "emissions tune" when it's time to test. I'm curious what effect the extra lift of the high lift version would have on emissions? For example, these are two of the cams I'm considering, both with a 112LSA:

Comp Cams 224XH Camshaft 224/230 duration @ .050", .567"/.584" lift with 1.5 rockers, .605"/.622" lift with 1.6 rockers.

Comp Cams 224XL Camshaft 224/230 duration @ .050", .503"/.510" lift with 1.5 rockers, .536"/.544" lift with 1.6 rockers.

Any thoughts on the effects of increased lift with respect to emissions would be appreciated.

Thanks,
Rob

Mindgame

Lift doesn't effect emissions.
Just talking cams...... overlap is the most critical variable.

-Mindgame

R_Andersen

Ok, thanks. I was hoping that was the case. On a side note, does anyone know the total duration of these two particular cams? I'm wondering how many degrees of total overlap they would have on a 112LSA?

-Rob

Wild1

You can call Comp Cams and ask. However, it is hit and miss whom you talk to. I've had some good and bad tech line help from them... mostly bad.

Mindgame

You only need look at the intake valve opening (IVO) event and exhaust valve closing event (EVC).
I looked up the cam on Comp's site (#07-503-8). The spec chart showed (112* LSA) an IVO of 30* and an EVC of 24* for a total of 54* of overlap seat to seat.
Both cams have the same seat to seat overlap, the one with more lift is going to have a greater area under the curve... it's gonna accelerate the lifter faster, but the events are going to be the same.

-Mindgame

arnie

Couldn't a change in the total lift at the valve affect the operating range of the cam, similar to the effects of a change in duration?

Wild1

Without getting complex, lift and duration have different attributes. Typically (and this is very general as there are many variables to the equation) duration will affect when the powerband of the cam really comes on. Over 280 for the street can be considered excessive. People have gone to 290 Advertised Duration but that will give you a Very Noticeable Idle... lol. Lift will generally affect the power as a whole. Steep ramp angles will provide more area under the curve.

If you really want good info, get one of David Vizards books on Camshafts. It is really good and I recommend it if you love technical information.

arnie

Maybe you misunderstood me. What I'm really implying, is cams with more lift (same cam othrwise) will move the power band up the rev scale, not unlike the affect of more duration. This realized on a dyno by a performance group. Are others in agreement with this?

Mindgame

Lift and duration are only different depending on where you look.
2 cams... same duration, cam "A" has .580 lift and "B" has .550 lift. Seat to seat they have the same duration but at .050" lobe lift, cam "A" has more effective duration. Plot the point on cam A's curve and compare it to cam "B" and you'll see that cam "B's" duration is effectively "smaller". So lift does effect duration in a comparison situation.... same duration, same lsa, etc.

-Mindgame

Mindgame

Got yours in right before mine arnie but yeah, I'm pretty much in agreement with that, although I'd say that you generally get more average power more so than peak in this situation.

edit: I know that some years back, the profiles weren't near what they are now. Those engine made good power... they just weren't as 'thick" on power as the new cam profiles. We're talking cams that were say 250* @ .050 with some .580" lift. They're getting that lift now with 224* lobes.

-Mindgame

arnie

Hey MG, ya I understand you and agree. APPARENTLY, that is what is causing the move of the powerband. In the particular case we (over the phone) discussed, it involved an 224/230 EE comp cam, comparing their mild lift version to their extreme lift version. (3192/4 to the 3314/5) Ironically, the same cams in question above. Wasn't sure if others were aware of this affect, or even agreed with it. This is how these cams could have an effect on the outcome of emissions testing. So, in my own little way, this is saying that I respectfully disagree with your initial post above.

BTW MG, in regards to your PM ?....... ...really, no big deal.

Mindgame

That's an interesting point arnie.
Would the cam with more area under the curve be 'dirtier' than the other?
I don't rightfully know...... but it is interesting to ponder. Another question worth thinking on....... would the cam with more area under the curve have better EGR characteristics?

It'd be interesting to see where GM went on their LS1 to LS6 cam change and what effect that had. Might answer a few of those questions.... of course they did that with a compression bump. Same with the LT1 to LT4... no EGR.

Interesting.

-Mindgame

Wild1

The amount of lift has no effect on the duration of the valve opening. The time and degree that it opens and closes remains unchanged.

I agreeas stated earlier, the area under the curve is affected with lift and ramp angles. The area could also be affected with roller rocker ratios.

As far as affecting emissions, overlap affects emissions. You are not increasing or decreasing overlap with lift. Valves will continue to open and close at the same time with duration constant regardless of lift.

Yes, I've seen the dyno runs with 1.5s and 1.6s Roller Rockers on four tests swapping them around between tests...
IN 1.5 / EX 1.5
IN 1.5 / EX 1.6
IN 1.6 / EX 1.5
IN 1.6 / EX 1.6
The last test did increase HP by 18 and raised the RPM Pk by 250. This has a lot to do with the intake system and exhaust system set ups and can vary greatly. So, that would prove the point that higher lift can raise the RPM peak to a certain extent.

But affecting lift will not affect duration.

I think we are all in agreement here, just explaining it differently.

Mindgame

Thinking beyond Car Craft magazine here....

Overlap is more than just where the seat timing is. Arnie's point is valid when you look at overlap in the context he's putting forth. Not overlap based on degrees but overlap based on lift area!
The Xtreme 3100 series lobe has a steeper ramp, therefore it has more "overlap" with an intake valve lobe lift of .050 than a cam with a less aggressive profile.
So we're not just talking the basic seat to seat overlap here but overlap in inch-degree. Big difference.

edit: The LS1 vs LS6 cam specs for instance.

LS6 .525/.525 204/211 116* lsa
LS1 .500/.500 198/208 115.5* lsa

No overlap for either of those cams at .050 but at .005 the LS6 has 45* to the LS1's 49*. Looks like the LS1 cam has more overlap until you look at the overlap based on the lift area. .52 inch-degrees for the LS6 and .42 inch-degrees for the LS1.
The more aggressive lobe has more overlap.... not as obvious looking at overlap based on degrees but the math tells a different story.

-Mindgame

Wild1

In terms of degrees of duration overlap, nothing will change. I see your point about "overlap under the curve" which would increase/decrease relative to lift. I am man enough not to be egotistical. I do not appreciate that car craft comment.