I am thinking very seriously about removing my Vortech supercharger and having a 427 Darton MID based engine with AFR 225s (when available) built for my C5. One of the things that I am concerned with is the ability to pass a tailpipe/roller emissions test.

Has anyone out there been through this? Is it possible to cam a big engine so that it produces good power and still runs clean?

 

It gets harder to pass emissions w/ larger cubes and/or larger bore. Your cam choice will probably be the largest factor though.

 

I would say probably not as emissions are tested in parts/per million. A 427 is going to pull more air and fuel IN than the 346 just by the fact that it is bigger (even if you had a really little cam) so you will automatically have more exhaust and thus more parts/per million of emissions coming out the tail pipe.

To give you an example of how much air you will increase, I have a 388 with a 246/253 109 (really inefficient at idle) and am in the process of tuning it. My first thought was "well this engine will be so inefficient that I will need to lean it WAY out (cut the VE table) at idle." I went in and cut the 55%, 65%, and 85% that everyone said to do and when I put a wide band on the car it was 22:1 air/fuel (LEAN!!!!!!!!!) . So I said "well let me go in and just see what the STOCK VE table would do at idle." 12:1 air/fuel . While the engine is still VERY inefficient at idle (does not like closed loop), just by it being 42CI larger it needs as much air and fuel to run as a stock 346 would. The trick with a larger CI engine wasn't to lean out at idle, but to richen everywhere else to make up for all the air this big PUMP moves.

So there you go.....big CI = LOTS of air/fuel no matter what which = emissions (good thing we do OBD2 here in AZ )

 

True there are a lot of factors, but as the bore gets larger, there is more crevice volume (between piston and wall and rings) for HC to hide, so that becomes somthing that's harder to control.

 

I do emissions repairs at my shop in Ohio. The thing that will be the problem is a big cam (cubes really have nothing to do with it). If the cam has much of a lope that is unburned fuel which will peg the hydrocarbons. My 418 passed (barely) with a 214/224 cam (I had the converters on for the test too).

 

Thanks for the replies. The issues that you guys raise are exactly what I was thinking about when I posted my question. I am thinking that I would have to put such a tiny cam in it to pass emissions that it would hardly be worth it. I guess that maybe I need to reevaluate my current setup, build a forged 346, and stuff a bunch of boost into it.

 

if emissions is a concern, forged with lots of boost will get the job done

 

why not just switch the cam to a smaller lobe when you go in for emissions, then swithch it back when your'e done.

 

Do you think that a 402 with a stock fbody cam and converters would pass? I really do mind swapping the stock cam out for it true cam after the test.

 

There was a member awhile back, from Cali I think, that ran a 427 with a TR224 cam. He said it idled smoother than stock, passed emmissions and dynoed like 450/450. Nice sleeper.

 

I had problems passing in NY with a stock 346 CI and a small 220/220, 561/561 cam and cats and an LS1-Edit tune...

I had to dump 18 bottles of dry gas (sold as alcohal-based injector cleaner) in a 1/4 tank of gas - which barely worked...

Westchester county in NY state significantly decreased the allowed hydrocarbons AFTER my car had been manufactured, in essence, imposing a more strict emmissions standard retroactive to older cars.... Consequently, this change blows for any modified car in Weschester NY! ..and we don't even have a polution problem like L.A., Commiefornia!

Most states are moving towards a ECM test which is an electronic computer check to see if any codes have been thrown, however.... this eliminates the sniffer tests for newer OBDII cars...

people tell me that a code test will be much easier to pass ...so don't rule out the big cubed motor...

You should post this question under the PCM tuning section for better hits....

 

Here it is:

https://ls1tech.com/forums/showthrea...hlight=427+C5R

With the new goodies out nowaday like the 90mm intakes and tb, I bet you could get close to 500rwhp with a tiny cam in it.