Ok you guys I got another question about emissions and a cam. My first question is about the cam. OK with a cam that has a duration @.05 of about 224 in/ 230 ex, max lift .51 for both in/ex, 1.6 complete roller rockers. Ok now lets say you have two of these cams and the only difference was the lsa, one was 112 and the other was 114; o yah and the motor is computer controlled. What will be the ending results of the motor due to these two different cams? And the other question is, how will these two cams effect emissions; will one pass emissions easier then the other? If you guys know please let me know.

Thanks.

 

LSA is lobe seperation angle, think of it as overlap basically, higher LSA=less overlap.

So, with more LSA, less overlap, the car will idle smoother, and have a flatter torque band, and be better for emissions

Lower LSA (going down to 106 to make the point), will give a rumpy idle, peakier powerband, and worse emissions. '60s cars had low LSA's, new FI cars have high LSA's for driveability and fuel emissions.

Go for the higher LSA for your computer controlled car IMHO.

 

Thanks!!! That was a really good answer I will go for the higher lsa!! Im guessing that I will not loss that much power by going with the higher lsa, or am i wrong? But thanks again.

 

I could scan the article from Vizard himself about this, but I know a few other members know this, so they could chime in.

The 112-114 LSA is such a small difference it's almost negligable anyway.
I'd say that a broad torque curve compared to a peakier torque curve is actually more desirable on the street. Plus, even if you "lose" a couple HP on the max of the curve, but gain it elsewhere, the engine will probably still move the car down 1/4 mile at the same time.

 

Well thats good news then!! Im going to have to decide wich one i want to go for!! Thanks

 

The factory roller cam in 88 had an LSA of 117! It idles real well and pulls from just off idle.

 

wow i did not know that it was the high!!!

 

Yep, pretty wide LSA on the factory sticks. TPI likes wide LSA. So do emmissions, reducing the valve overlap helps you at the engine speeds where they actually do the tests. If you live in a state that has stiff smog test requirements, I'd recommend you go with a big LSA cam. It will also help the streetability, particularly if you get caught in traffic.

 

I've seen it posted here and read it in other places also. It has something to do with the relationship between the EGR and LSA, and it boils down to the wider LSA cams are more compatible with EGR.
Which might explain the wide LSA of the factory cams.
Supposedly the longer overlap period of tighter LSA cams can create an EGR effect that can compensate for the lack of an EGR valve itself in a tailpipe test.
I'm no smog pro, but whatever gasses that are reduced by the EGR system, are also reduced when using a cam with more overlap, in some cases.
Hopefully someone more knowlegable than I am will chime in on this.

 

quick coment about what you just said. I am planing on using the mini ram and i dont know if you have read any of the other threads that I started but I asked about creating a fake egr because the mini ram doesnt have one and I have visual inspections in my state, new mexico. Anyways my point with all this is that since I will not be using the egr should i just go with the larger lsa? I know what you guys were saying about the hole thing about it being more drivable but if i went with the cam with the:

114 lsa has the duration @.05 is 220 in / 230 ex; lift .51in / .51 ex

112 lsa has the duration @.05 is 224 in / 230 ex; lift .503in / .51 ex

These are the differences. Do you think that going with the the cam with the lsa of 114 would be ok for my set up look at my signature for parts.

 

It's not the lobe separation that makes the difference as far as EFI-friendly or whatnot. It's the valve overlap that is consequent of the LSA (as well as duration).

More overlap, being when both valves are open, allows a little bit of exhaust to get pulled into the combustion chamber, having the EGR effect - in a nutshell.

Keeping in mind you have to tune everything once you get it installed, I would go with the smaller cam (more lobe separation, less duration), pending the rest of the setup. Another thing, you have 72cc chambers. More overlap bleeds off cylinder pressure at low RPM's.

 

Here is a link to a very informative article by David Vizard. This will answer all of your questions.

http://www.hotrod.com/techarticles/18218/index.html

 

Now to me this sound like a set back, could you please give me a little more information about this. I was under the impression that I would want more pressure at low and higher rpm's. Thanks for you input.

 

You want less overlap the less your compression ratio. This will effectively increase cylinder pressure because the intake air is not going out the exhaust valve.

 

Any lobe seperation that is reasonable will work. Put it this way, if your motor runs clean, for the most part it is tuned good. It doesn't matter if you are making 150hp or 612hp. If it's tuned good then it's emissions will be good. Use some of the emissions parts like the cats. High flow aftermarket of course.

 

One of the trillion dumb things he said. I don't think there will be a another pres. like him again in our lifetime. At least I hope.

Just wondered if you liked him.

 

Well I read the article and let me tell you there is a lot of information there!! I think I am going to have to read that a couple more times to completly understand everything in there. I mean there are so many variables to concider, and I think I am a little bit more confused after reading that artical But from what I was understanding I am thinking that I will probably go for the lsa of 112. And is 110 too small of an lsa for emissions, ideal, vaccum, and a computer controled motor? Well thanks again for all your help you guys!!

 

More LSA and smaller overlap = better emissions, idle quality, and vacuum.

 

You don't want to know what i think. Conspiracy....