So what is it that makes the emissions worse with large cams.

I have a dinky XE262-14 now, 218/224, .5/.5 w/ 1.6 Rockers, 114ēLSA. Comp says 1500-5500, -7deg overlap @.05, 38deg @adv



My HSR wants more RPM.

I want to pass emissions. I have all emissions except the EGR.

Is it the duration, is it the overlap, separation?


I am looking at the XE 274: 230/236, 110LSA, .52/.52lift w/ 1.6 Rockers. 13Deg overlap @ .05, 60Deg @adv.
1800-6000rpm.

Maybe the XE284, but it seems that may make it tough. And I'm not sure my bottom will rev high enough to take advantage of it. Fresh rebuild, bearings, stock rods checked and honed, hyper pistons, Cast Crank, 2bolt 10:1CR. 240/246, 110LSA, .54/.54 lift w/ 1.6 Rockers, 2300-6500 23deg overlap @ .05, 70deg @ adv.


So what is it that makes it harder to pass?!

 

Most likely it is the tune, secondary is the LDA. Ratty cams with lots of overlap tend to self-EGR (which is good) while at the same time dump some of the intake charge right out the exhaust (which is bad). Raising the idle speed and leaning out the mixture helps a lot. Trax has a thread about his quest in passing emissions, quite interesting.

RBob.

edit: here is the thread:

https://www.thirdgen.org/techbb2/sho...on%2A+AND+lean

 

oddly enough MAF's are pretty easy to tune for emisions. However tweking of the o2 sensor parameters might be needed.

 

I am glad to hear someone else say this. I keep bringing up the O2 terms and . . . and . . . nothing. . . folks act like they don't exist. Can make significant changes in how an engine runs with these.

RBob.

 

i have played with the 02 limits to no avail lol.............least no major changes that i could see and i didnt spend hrs and days on it either....

Rbob , can u explain the relation of the 02 limits and settings in the 730 $8d mask? And what effect each has....what i have found is that u can slightly change the idle ie.. richer or leaner. but nothing else i have surmised as of yet....



Also could u do a primer post or 2 on how to find code lines and operations? like a editing for dummies beginner series?
have PP@ software and tunercat editor but still clueless. Need to get time to sit down and call bruce as well

thanks as always
Jeremy

 

So the consensus with MAF and large cams and Emissions, is that you can run a large cam on a 110, aslong as you raise the idle and lean out the idle.....?

What about the O2 values really, I've read in places that tight LSA cams can throw the o2 readings off.

What tweaking is meant? Are we talking about raising or lowering what it thinks is ideal a/f? $6E code?

 

Im curious about this as well. Bruce told me to try and experiment with the rich/lean 02 settings at idle to see if i could further tame my cam and idle down some more.... I dont know if my results were misleading or i improperly understood the tables or at that point in time my tune was out of whack enuff for it to not make a difference when i was trying to experiment..
thanks and later
Jeremy

 

You can run any combo..
It's the results thou that are what matters.
While a monster cam can live well in a 406 and MAF, that same cam in a 305 would be alot harder to tame. There are lots of minor tweaks to getting things really correct.

As you increas overlap, at lower RPM, the side effect is that you increase the self EGR'ing of the engine. So at low speeds you have to add more timing and fuel to get the motor happy.

From a performance point of view, it's really really hard to out do a MAP system. Having only 50ish fuel points, and the limited RPM range that the MAF codes do, you can at times have to make sacrifices to get things even close. I've spent alot of time trying to get a MAF based system to run as well as a MAP and just haven't gotten it even close in drivibility between the two. WOT isn't a big deal, to me, if your only interested in drag racing then you can go just as fast with a properly done MAF.