2 Questions actually:

1. Would a B18C1 w/ 84mm or 84.5mm bore, 12CR, and ITR/Spoon/Skunk-stage1/Jun2 cams pass smog? If not, what about 81.25mm bore, JDM ITR pistons (~11.5CR), and same cams pass smog??

2. How much of a TQ increase should I expect when going from 81.25mm @ 11.5CR to 84mm(1.93L) or 84.5mm(1.95L) @ 12CR?

Thanks.

 

ttt

 

I might be off about this, but don't passing smog test depend more on weither or not you are running a "legal" catalytic converter instead of what the displacement of the engine is? If your engine is tuned properly you should be all right.

I have no idea about how much torque you would gain with 84mm pistons, all I know is that you would need to resleeve the block to install them.

 

Thanks JPP. A couple of ppl have told me that raising the CR will fail smog. I'm not entirely sure why or even if it's true. Someone else told me that increasing displacement changes the hydrocarbon (or something) specs they have in the computer for that motor so upping displacement fails smog also. Anyone?

 

theres so many ways to get past smog, dont let the sniffers stop you from doing what you want to your car!

 

Well if your increase compression substantially then yes you will fail smog big time. This is assuming that the only change is the compression itself. The reason why is that with higher compression comes higher cylinder temps thus more NOx is produced. NOx production tends to begin at 2500 deg.F but goes up dramatically at hotter temps. The specs for passs/ fail are pretty much in stone. The inspecting technician will not, cannot change the specs according to your displacement. BTW, telling the technician that you increased/changed the displacement will get you a fail everytime. Some things to think about. When calculating compression you have to think about what your final numbers will be. Static vs. dynamic. I'm not sure how to calculate it but what i'm getting at is this. You can have a high comp. motor but add high lift cams to the mix and some comp. is bled off. So dynamic compression will be lower overall. Cam gears are pretty much an automatic fail also. Assuming the tech can see them. Also since our motors have no egr, they rely on vavle overlap to recirculate exhaust gas. Having adjustable cam gears gives the end user the possiblity of dialing out overlap and thus eliminate the NOx reduction benefits. Still with me?

I'd think twice about your future mods if you want to remain emissions legal. Peace.

 

Thanks Vago!! Great info! I guess now the question specifically pertains to this setup:

- 81.25mm bore w/ JDM ITR pistons ~11.5:1 static CR (stock is 10.1:1)...I don't know how to calculate dynamic CR
- small cams like ITR/Spoon/Skunk2-1

Pass or no pass sniffer for this specific setup? Thanks.

 

I'm a little confused about the reply here. Maybe you can straighten me out...

if you have a more efficient burn from raising the compression, how does that worsen emissions? I mean the whole premise to lean burn technology is to reduce emissions.

If you completely burn your fuel from better thermodynamic efficiency how does that generate more NOx?

I thought a gas' temperature goes up as cylinder pressure goes up? PV =nRT.

Increase cylinder pressure by increasing CR and you increase temperature...did I miss something? How does NOx increase temperature in the cylinder again?

I guess if you move the top ring higher there will be less fuel trapping in the upper part of the cylinder walls in the combustion chamber. Fuel trapping from lower top ring locations leads to incomplete burning of fuel which in turn increases emissions.

Most of these aftermarket pistons with high CR have higher top rings locations do they not?

An increased bore results in a further distance for the spark flame to travel and so I guess that may reduce complete burn....but I don't see how increasing CR can hurt your emissions....

 

Hey MD, how's it going? Well let me get to your questions.
If your talking about HC and Co, then yes higher compression will not (in most cases) worsen emissions. Here in cali we also test for NOx. Think of it as a see-saw if you will. Things you do to reduce HC/CO emissions end up making NOx levels higher. And things you do to reduce NOx are usually bad for HC/CO levels.

Temp. and pressure go hand and hand. If pressure increases so does the temperature. So given a sample motor, if you increase its compression you will also increase the cylinder temperature. Think of it this way. The mixture is being compressed more and so the resulting "spark" is more violent thus creating more heat.

As far as NOx goes, it does not increase the cyl. temp, its more like the other way around. The higher the cylinder temp the more NOx is produced. Smog reduction is the goal here and NOx is the big contributor to photochemical smog.

So yes you can build/tune to make a car run extremely "clean" but more than likely its NOx levels will be thru the roof.

Peace.

 

if done right ! you shouldnt have a problem . jun did a b16a and made it all motor monster by increasing everything from stroking the engine to 1.8 to running bigger cams and also using their program on obd 1 and they pass smog like nothing, clean !

 

I see. the EGR people like to recirculate things and drop that NOx level but that pretty much kills performance.

I'm glad you cleared up that statement about NOx increasing cylinder temp that you stated before. I guess I must have misread it.

So in CA, if you pass on hydrocarbons and carbon monoxide but fail on NOx, do you fail altogether?

 

Yeah. Sad but true. It doesn't really matter which part you fail in. Your done.

EGR kills performance but then again it gives you better gas mileage. Sorry just looking for something positive to say. peace.


[Modified by vagoITR, 11:17 PM 3/28/2002]

 

Thanks again Vago! Someone also posted in another post that they passed w/ Toda B's by zeroing out the cam gears and leaning out the fuel. I assume I would be able to do that also to take the cams out of the equation for smog. But would going from 81mm 10.1CR to 81.25mm 11.5CR fail me for the Nox test??? Thanks very much!