I'm in the middle of a build. I have a SuperRam, TFS 23* big spring heads (.6 lift), and the rest is still on paper.

Comp makes a nice cam grind, the XR269HR. Its specs are as follows:

Dur. @ .05: 218/224
Lift: .495/.503
Lift w/ 1.6: .528/.536
LSA: 112

I can get this same cam ground on a 114 LSA. Comp does custom grinds. I was planning on Pro-Magnum 1.6 RRs.

How does camshaft duration, lift, and lobe separation angle affect vehicle emissions. All emissions controls will be intact on my new engine. I currently have to pass IM240 dyno testing. Everyone with cam/sniffer experience please shed some light! TIA


------------------
-Jason M. 1991 Camaro Z28

 

Well, before your question can be answered please tells us the CID of the planned engine. That cam is almost at the emission limit for, say a 355.

As for how Duration, Lift and LSA effect emissions it is a combination of other factors as well. The LSA affects how much of the intake (unburned fuel) is bled in the exhaust (to help clean the cylinder), but it also affects how much vacuum you can produce (very important with computer controlled engines). The narrower the LSA angle, the "cleaner" the chamber for the new mix. But you exhaust is also now contaminated (from IM240 stand point). Lift doesn't affect it as much as the others (but is similar to duration), so I'll skip this. Duration, much like LSA can allow to much fuel (and air) in to the chambers at lowers speeds (2500 and 3500 rpms for IM240 test). This can also give poor reading on the test probe (too rich). But that cam (based on the CID your engine is) could pass smog. Maybe not legally, but the sniffer won't catch it (assuming you tune the engine properly). All this is based on my personal experience, others can have other inputs varing from mine.

------------------
George P. Lara
1984 Z28
2001 SS #0391
SCCA, SCFB, SC3GFB

[This message has been edited by MRZ28HO (edited August 05, 2001).]

 

George,

Thanks for the reply. It's a 350. I'm using a new shortblock so its standard bore.

The engine will be in stock tune, and I'll keep reprogramming PROM's until I get 128/128.

------------------
-Jason M. 1991 Camaro Z28

 

anyone?

------------------
-Jason M. 1991 Camaro Z28

 

I have a 218/218 @.05, .503/.503 lift, 110 LSA, and I passed the on the dyno in CA. I think you will pass too.

------------------
1989 IROC-Z 5.7L
NOS 5151 150HP kit
ProBuilt 700R4, PI Vigilante 2800 stall lockup
Baer Brakes 12" Sport System

 

Is there a certain rule of thumb to duration as to whether or not you will melt down a cat. My project is going with a 388 with 234/234 duration @.050 (292 adv) on a 114 LSA and I need a cat to pass inspection (No emmisions) and I don't want to ruin it or I'll try to find something that looks like a cat to put in there (hollow) but the cat thats on there is v6 (2 1/4 in or something like that) so I can't use it. I have no smog pump either.

 

Jason,

Another option is the XR-276HR-14 .510"/.510", 220°/230°, 114° LSA, +4° advanced grind. This cam is designed for the LT1 family engines at stock displacement. Ask some of the LT1 guys how they pass the dyno sniffer with this cam.

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

Put it this way, if the cam says rough idle, you can hang up getting it to go closed loop. If you can't go closed loop, the motor will not have the right A/F ratio to prevent from hurting the cat. And 234 at .050 is pretty stout. It will not idle smooth at less than 900 rpm i bet. The fact that it is a single pattern, will increase reversion even more (makeing the idle even rougher). You might be able to pull it off with a 114 lsa but I don't think so. I would cut out about 5 degrees of intake duration at least.


[This message has been edited by jcb999 (edited August 06, 2001).]

 

I kinda figured. It claims 'fair' idle. I can't go smaller though because my compression is too high (11:1) and I want to run pump gas. (The power won't hurt either )

Thanks.

 

Heres what LPE wrote me in an email regarding their 219 cam.

The camshaft is emissions legal in CA with the proper programming and stock fully ported heads, but it is impossible to say with aftermarket heads. It should pass, but I cannot say for sure. If I can help you with anything else, let me know. Thanks.

Michael Wittkopf -- LPE

------------------
-Jason M. 1991 Camaro Z28