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**dieselgeek** · January 19, 2009, 08:18 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

PAGING DR. GREENJUNK!

**squirrel** · January 20, 2009, 07:26 AM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

I really haven't messed with late models at all....so if you can find info from guys who have, I'd suggest you listen to them! but from what I've seen, if you change the cam to get more top end power, you're likely to increase HC at lower rpm significantly. Right now the cats are able to keep HC to about half of the limit, but it's possible you could get into trouble if you go too high on duration. The one you listed may work, it may not, it's hard to say! I assume the dyno test runs the vehicle thru a varying RPM/load test? if so, maybe the higher rpm loaded part of the test will offset the crappy low rpm situation.

NOx is funny....it's caused by high combustion temps...and might be a bit hard to predict what will happen. Experience with that dyno test on similar engines is probably going to be most helpful, so that leaves me out!

Interesting how well cats and closed loop operation can keep CO down to almost nothing. Typical numbers for older hot rods that are adjusted so they're driveable are in the 2% to 5% range

**DanStokes** · January 20, 2009, 10:08 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions lega

See my PM. Also, I'll give you some general guidelines. More duration and/or more lift - in other words, more area under the curve - yields more HC and usually more CO. Increased overlap yields LOWER NOx (acts like internal EGR) but tends to increase HC and CO. CO2 is not currently regulated but translates directly to MPG - more CO2, lower MPG.

What's probably going on with your cats is that they likely don't have enough O2 to work with. HC (unburned fuel) shows up in the cat and needs air to convert in the cat to the desirable gasses. There are several ways to make that happen including adding an air pump, but I'll give you the method my friend Norm Brandes uses (he's all over the shop tips section in last month's HRM). Pick up 2 gulp valves - 2 of the units from a Vaccupan will work nicely. Plumb the inlet end into the air cleaner so you don't suck crappy air into your cats - electrical conduit works pretty well for the tubing, with rubber connections.. Plumb the downstream side into your collectors - they are a low pressure area under most vehicle operation. Put the gulp valves into the lines so that if the collector goes to positive pressure no exhaust will enter the air cleaner. Now fire that mother up. The cats should have plenty of air to keep everything happy, and no moving parts. Wish I was cleaver enough to have invented this, but it's a great system.

I'm still working with bad eyes (see "Whining" in General) so I hope you can make this out OK

Dan

**TheSilverBuick** · January 21, 2009, 11:52 AM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

Ok, Dan's got a pretty decent handle on this I think. I'll probably re-read it later to add more but here is my impression on the first pass through.

From just reading the change in the two tests, not looking at the modifications this is what I see happening.

Your NOx went up, causes are from increased combustion chamber temperatures. That would be from 1) Increased Compression Ratio. 2) Advanced timing 3) Lean burn

Your HC went up, causes from incomplete combustion. That would be from 1) Excess cam overlap 2) Running too rich 3) Too late timing

CO went up a notch, cause is not enough O2 in the exhaust, either means the airpump can't keep up with the extra fuel the engine now burns or the engine is running richer than originally designed.

CO2 no change.

O2 got cut in half (it key!) more of the oxygen is being burned than introduced by the system. This is where I think you can make the most improvement.

Pretty much to remain emission legal you have to off set the tail pipe gasses for the changes. I listed each emission and what basically effects it, so you try and use one of the other factors to offset (always a comprimise). The thing to do though is try and force all the effects on to CO2 as that one is measured but not regulated(yet :-\), and CO2 will go up with every improvement.

Like Dan mentioned, you need to get more O2 directly into the exhaust system. If your car does not currently have air tubes going into the catalytic converters you can upgrade to them. Find an after market cat and install an electric air pump (fairly easy to find at junkyards). Parts stores have these blue tubes (I think the application is for an Astro van) that are for connecting the air pump lines to the catalytic converter. If you do have those tube in your cats already you might be exceeding their air flow, so either you need a bigger air pump, install a second one (one per bank) or as Dan mentioned a vac-pan (I have no experience with those).

The Tune on the fuel and timing will effect the HC and NOx the most, you can always run a "smog" tune and a "power" tune (unless they've gotten good enough for a good combination). Pay special attention to the balance between too rich (<HC's) and too lean (<NOx) for tune. And timing for NOx.

That's all I can think of for now.

**SpiderGearsMan** · January 21, 2009, 02:58 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

egr valves can be a problem on f body lt1

**TheSilverBuick** · January 21, 2009, 03:11 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

Originally posted by SpiderGearsMan

egr valves can be a problem on f body lt1

x2, I was assuming all parts in good working order. EGR issues usually result in raised NOx.

**DanStokes** · January 21, 2009, 05:17 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions lega

EGR is there to lower combustion temp and therefore lower NOx. It also has some positive effect on fuel economy. Based on that I figured his was OK, but definitely worth a check.

TSB gives a great summary.

Dan

**TheSilverBuick** · January 21, 2009, 05:47 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions lega

Originally posted by DanStokes

EGR is there to lower combustion temp and therefore lower NOx. It also has some positive effect on fuel economy. Based on that I figured his was OK, but definitely worth a check.

TSB gives a great summary.

Dan

Thanks Dan. This is just from personal research trying to get my Skylark smogged every two years in CA with the 231 V-6 and how I planned on legally shoe horning in the 455. Seemed every two years a different value was over the limit and I had to figure out how to correct it or off set it for an engine issue.

**SpiderGearsMan** · January 21, 2009, 06:21 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

2 things get you high nox - egr and cam timing

**Freiburger** · January 23, 2009, 05:20 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

Here's a fantastic thread on the subject:

Chevy Impala SS Forum

http://www.impalassforum.com/vBulletin/showthread.php?t=75422

A forum community dedicated to Chevy Impala SS owners and enthusiasts. Come join the discussion about performance, modifications, troubleshooting, maintenance, and more!

**58yeoman** · January 23, 2009, 05:22 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions lega

beat me to it DF!

**tcbnj** · January 25, 2009, 06:30 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

Thanks to all replies, Special thanks to 58 Yeoman and DF for the link to impalassforum.com. It was very informative for an LT1 owner. It?s amazing that the thread as been alive since Sept 2000.

A few follow up questions:

1) What impact, if any, do heads have on emissions, this was never discussed on the impalass forum?

2) Danstokes, please confirm if the Vaccupan tubing device has to be plumbed downstream of the O2 sensors. It would seem to me that the tubes should be downstream to prevent interference with the sensor?s readings.

3) A local shop who specializes in NJ emission compliance noted that often aftermarket hi flow cats loose their effectiveness as they don?t have as much precious medal as factory cats; comments?

**DanStokes** · January 25, 2009, 10:13 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions lega

Tell you as much as I know -
1. The O2 sensors need to be in the same relative location as they were from the factory. If they were designed to read post-cat, then they were reading after the auxiliary air was added to the system and should be located there. If they were reading engine-out, then they need to be upstream of the air input. Some cars have both engine-out and post cat sensors. So just look at the original system and replicate it.

2. On cat loading - these are sold and have been verified as replacement parts. Therefore, the folks doing the verification (usually the state of California) is comfortable that they are equivalent to OEM - even if they have a bigger inlet and outlet. A common misconception is that the noble metal loading in a cat gets "used up" over time. It lasts virtually forever (I've seen EPA run testing on cars with 150K miles and the original cats are working perfectly). Cats die because the coating gets contaminated - essentially covered up by a third substance (like tetraethyl lead). The activity of the cat is controlled by the amount of loading - that is, how much of the substrate is covered with noble metal (usually platinum and rhodium, sometimes others). The more of the good stuff, the more active - this happens at the time of manufacture.

Hope that helps
Dan

**greenjunk** · January 27, 2009, 03:33 PM

Re: Request for Junkie advice for LT1 upgrades while remaining NJ emissions legal

Sorry I didn't catch this earlier, It appears as though I was Honeymooning in Hawaii... I hope you understand... ;D

Anyways, enough gloating. I can tell you plenty of combinations that will make great power. The deal is, how much power do you want, how much driveablility do you want. How much work are you willing to do when it comes time for emissions testing. Are you willing to remove or add exhaust pieces, superchargers, what does NJ's requirement for stock appearance under the hood. AFR is not the best head you can get, neither is the comp cam. remember its easy to swap computers on these, and you can put a computer in that will run like crap, but pass emissions, there are no ready codes in OBD1, as far as I remember, or they come ready very quickly. There are many ways around the emmissions.

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