Kamaro

Hi,

My car did not pass emissions test, it has to be less than 1200 ppm of HC, right now its 3750 ppm. the car is a 2007 Z06 with stock short block and modified high end, it has a little chopey idle (camshaft uknown, bought the short block that way), all pistons have very good compressions, passed the leak down test. The car has a LT headers and no cats.

What are the things that I can do to lower the HC? more/less timing? more/less idle speed? engine temp?

G Atsma

High HC means unburned gas; Lean it out, and possibly add cats to the exhaust.

clinebarger

I don't see you passing any emissions (Probe Analyzer) testing without Catalytic Converters, If you lean it out to reduce HC..... NOX will go up.

MontecarloDrag

iTrader: (3)

Camshafts give false lean readings, unburned gas will show as high HC so you need to adjust fueling a little to the lean side.
Catalytic converters make passing a lot easier, I see it difficult to pass without them with a cammed engine. Not impossible but even if there is no visual inspection you need to adjust it to where most HC are burned without raising NOX levels (lean mixture).
Some people use ethanol mixed with the gas to help pass, it burns cleaner and leans mixture. Worth a try

ChopperDoc

I know you said you don't know what cam you have, but it sounds like End of Injector Timing (EOIT) should be adjusted due to overlap.

Try rolling your EOIT back to when the exhaust valve closes. You are spraying raw fuel into your open exhaust valve. Roll the injectors back 10* at a time until the smell dies down. Do this by adding to the normal injector value 1 decimal at a time. Sure would be great if you knew your valve events though. If anything, delay it to about 370* (6.32 ish on the normal table) so at least your piston is moving down when the injector fires. A lot of guys also report a few extra ft/lbs in the mid range by getting this right.

You don't have to lean it out, but you can do that too. Won't hurt, unless it starts running like crap.

GEN III PCM uses 8 reference periods. Formula for calculating EOIT:

Boundary + normal * 90 - 784 = EOIT.

360 is TDC between valve events. 300.5* is stock on most GEN III cars... As in fuel hits the back of the closed intake valve.

GEN IV is in degrees. There are calculators out there for that. I have one, but it won't let me post it. If you have a GEN IV I can email it to you.

ChopperDoc

Also, add some CATs, or 50% alcohol to your fuel tank... But you didn't hear that from me

clinebarger

Yeah...Maybe, With 1200 PPM being the limit. Which in no way reflects any emissions test I'm aware of? 1982-1995 Federal Emissions vehicles have a max of 220 PPM allowed. 2007 standard is probably 2/3 of that?

ChopperDoc

You can also temporarily move to another state, reside a month or two (long enough to get a bill), register your car there and then zero f**ks will be given from then on. I haven't had cats for something like 10 years, and my cam overlap is 20* at .050". What emissions? lol. It also helps being military.

Kamaro

Where I live they don't check for NOX, they only check HC and CO.

Kamaro

Thanks a lot guys for all the valuable tips. I will get the idle leaner (they only check the emission @ idle). I have a few gallons of VP M5 methanol fuel, would that help burning cleaner??

Darth_V8r

iTrader: (4)

Funny story how my S10 passed emissions once. The exhaust pipe had a side exit on it, and the elbow was rusted out. When the guy stuck the probe in, it was exposed to fresh air. Boomshackalacka!

ChopperDoc

Lmao... free cutouts? That's hilarious.

MontecarloDrag

iTrader: (3)

Raise the idle RPM, it will also help cleaning exhaust gas, less cam chop less raw fuel to exhaust.
Find the correct RPM, AFR and timing advance where the engine is happier (highest vacuum).

rpturbo

iTrader: (47)

I agree with this! Also several others as well, but this will probably have the biggest affect IMO.